No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Ab Initio Study of the Structural, Energetic, Bonding, and IR Spectroscopic Properties of Complexes with Dihydrogen Bonds
Abstract
The results of an ab initio study of complexes with X−H···H−M dihydrogen bonds are presented. The proton donors include HCCH and its derivatives HCCF, HCCCl, and HCCCN; HCN and its derivatives HCNLi+ and HCNNa+; CNH, and H2O, and the proton acceptor is LiH. For comparison, selected complexes with NaH as the proton acceptor have also been investigated. The structures, binding energies and harmonic vibrational frequencies of all complexes were obtained at the MP2/aug‘-cc-pVTZ level of theory. The most stable complexes with C−H groups as proton donors are the cationic complexes NaNCH+:HLi and LiNCH+:HLi. These complexes exhibit very short H····H distances and are prototypical of dihydrogen-bonded complexes that may dissociate by eliminating H2. The calculated binding energies correlate with the H···H distance, the elongation of the C−H donor bond, the amount of charge transfer into the H····H bonding region, and the charge density at the H···H bond critical point. As in conventional hydrogen-bonded complexes, the elongation of the proton donor C−H group correlates with the strength of the interaction, and with the red shift of the C−H stretching frequency. Although changes in the Li−H bond length do not follow a simple pattern, the Li−H stretching frequency is blue-shifted in the complexes.
... There are many studies of series of gas phase dihydrogen-bonded systems which can be found in literature (see for example [5,115,120,123,154,155,172,176,218,221,224] as the most recent studies). One of the MH molecules mostly used is LiH, where the hydrogen atom has clear hydride behaviour, holding a charge about -0.8 au. ...
... In order to study the behaviour these dimers present in gas phase, they have been compared to MH · · · HCN and MH · · · HCCH, which are known to have a minima with all real harmonic vibrational frequencies. [4,5,218] The other series of dihydrogen-bonded systems studied in this section are those with M = Be and B with the same halogens defined before. ...
... All these dimers can be classified as conventional hydrogen bonds as it was shown before in the framework of the atoms in molecules theory. [5] The fact that the electronegativity of X = CN, CCH) is very low compared to (X = F, Cl, Br), causes these complexes to be thermodynamically less stable, with weaker interaction energies, larger dihydrogen bond lengths and lower values of intermolecular formation of vibrational frequencies. ...
... The hydrogen bond is probably the best known example and consists, as briefly mentioned in the above definitions, of a proton shared between two electronegative atoms, often denoted symbolically as dÀ X-H d1 Á Á Á dÀ Y. [22][23][24][25][26][27] A variant of the hydrogen bond, ubiquitous in organometallic chemistry, is the dihydrogen bond. [8][9][10][11][28][29][30][31][32][33][34][35][36][37][38][39][40] This special type of hydrogen bond involves not one, but two, hydrogen atoms. One of this pair of hydrogen atoms is positively charged, formally the proton of the hydrogen bond, and the second is a hydridic hydrogen atom, which gains its negative charge from a metal atom, and which acts as the proton acceptor. ...
... One of this pair of hydrogen atoms is positively charged, formally the proton of the hydrogen bond, and the second is a hydridic hydrogen atom, which gains its negative charge from a metal atom, and which acts as the proton acceptor. [8][9][10][11][28][29][30][31][32][33][34][35][36][37][38][39][40] Thus, and recapping the definitions advanced earlier, the dihydrogen bond can be thought of, classically, as a primarily electrostatic interaction and could be denoted as dÀ X-H d1 Á Á Á dÀ H-M d1 . ...
The field of crystal engineering concerns the design and synthesis of molecular crystals with desired properties. This requires an in-depth understanding of the intermolecular interactions within crystal structures. This new book brings together the latest information and theories about intermolecular bonding, providing an introductory text for graduates.
The book is divided into three parts. The first part covers the nature, physical meaning and methods for identification and analysis of intermolecular bonds. The second part explains the different types of bond known to occur in molecular crystals, with each chapter written by a specialist in that specific bond type. The final part discusses the cooperativity effects of different bond types present in one solid.
This comprehensive textbook will provide a valuable resource for all students and researchers in the field of crystallography, materials science and supramolecular chemistry.
... Interaction energies of DHBs are generally between 1 and 7 kcal/mol, and because of their similarity to HBs, they are often treated as a subclass of HBs [16]. It has been suggested that DHBs are predominantly of electrostatic nature [16][17][18][19], accompanied in stronger DHBs with a substantial covalent contribution [16,[20][21][22]; although, this has not been quantified so far. DHBs can influence molecular properties in the gas phase, in solution and in the solid state, yielding broad potential utilities in catalysis and materials sciences. ...
In this work, we analyzed five groups of different dihydrogen bonding interactions and hydrogen clusters with an H3+ kernel utilizing the local vibrational mode theory, developed by our group, complemented with the Quantum Theory of Atoms–in–Molecules analysis to assess the strength and nature of the dihydrogen bonds in these systems. We could show that the intrinsic strength of the dihydrogen bonds investigated is primarily related to the protonic bond as opposed to the hydridic bond; thus, this should be the region of focus when designing dihydrogen bonded complexes with a particular strength. We could also show that the popular discussion of the blue/red shifts of dihydrogen bonding based on the normal mode frequencies is hampered from mode–mode coupling and that a blue/red shift discussion based on local mode frequencies is more meaningful. Based on the bond analysis of the H3+(H2)n systems, we conclude that the bond strength in these crystal–like structures makes them interesting for potential hydrogen storage applications.
... As any other hydrogen bond, a major source of stability in the dihydrogen bonds is electrostatic including for example dominant dipole-monopole and dipoledipole contributions. The dihydrogen bond is the subject of considerable current theoretical [3,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] and chemical informatics [41] interest and has been fully characterised based on the topological properties of the electron density [26]. ...
This chapter reviews some of the recent work about hydrogen-hydrogen bonding (an essentially non-electrostatic closed-shell interaction) and contrasts it with dihydrogen bonding (a predominantly electrostatic closed-shell interaction). These two modes are shown to represent the two extremes of a continuum of closed-shell interactions between pairs of hydrogen atoms in molecules.
In this work, dihydrogen bond between five-membered heterocyclic compounds (furan, thiophene, pyrrole, arsole, borole, phosphole, and silole) and alkali metal hydride HM (M = Li, Na, and K) were carried out by density functional theory and ab-initio calculations. A two pure (PBE, M06L) and four hybrids (B3LYP, B3P86, B3PW91, wB97XD) DFT functional and MP2 method with 6–311 + + G** basis set were used for five membered heterocyclic dihydrogen bond interactions. Molecular geometries, puckering parameters, energies, and natural bond orbital analysis of all the complexes were calculated by various DFT functionals and MP2 method. For all the complexes, smallest H∙∙∙H bond distance is observed for thiophene∙∙∙HK which has significant interaction energy (∆EC), while largest H∙∙∙H distance with smallest ∆EC is observed for pyrrole∙∙∙HLi complex. Among all the functionals, M06L predicted the smallest dihydrogen bond distances for all the complexes, while largest dihydrogen bond distance was observed by B3LYP functional. The infrared vibrational frequency analysis for all the complexes has revealed propensities in red and blue shift for the C–H and M–H bonds, respectively. Natural bond orbital and quantum theory of atom in molecules analyses were performed to examine the nature of interaction along with the molecular electrostatic potential which further confirm the existence of dihydrogen bonding.
Owing to the fact that σ stacking is as important as π stacking in determining the structural motifs of aliphatic saturated cyclic hydrocarbons, in this work, we have provided the first unambiguous spectroscopic evidence for the existence of σ stacking interaction in cyclohexane dimers at low temperatures. Molecular beam experiments performed using effusive nozzle and supersonic jet sources on cyclohexane in N2 matrix generated cyclohexane dimers stabilized through σ stacking and the dimers were characterized by infrared spectroscopy. The ab initio computations carried out on cyclohexane dimers identified eclipsed (face-to-face), parallel displaced and T-shaped structures, which are predominantly stabilized by σ stacking interactions. While Natural Bond Orbital analysis substantiated a significant amount of σ→σ* interactions involved in the stabilization, the Atoms in Molecules analysis indicated that the stacking is induced by a plausible ‘dihydrogen bonding’ interaction. Energy Decomposition analysis disclosed that a large measure of dispersion interactions effectively contributes for the overall stability of cyclohexane dimers.
A theoretical study on the intermolecular dihydrogen bonding (DHB) of ground state B3N3H6···HM (Li, Na, and K) complexes were investigated by B3LYP and MP2 methods with 6-311++G** basis set. Thermodynamic parameters (entropy, enthalpy, heat capacity and Gibbs free energy) of the complexes were calculated at different temperatures in the gas phase. The vibrational analysis of N–H···H–M DHB bond formation reveals that the calculated N–H and M–H stretching frequencies undergo red and blue shifts, respectively. The calculated interaction energies correlate well with the geometrical parameters wherein the shortest H···H intermolecular distance is obtained for B3N3H6···HK complex. The chemical shift of ¹H, ¹¹B and ¹⁵N NMR predict large variation for B3N3H6···HK complex which has large protonic hydrogen than the hydridic hydrogen. Furthermore, natural bond orbital and quantum theory of atoms in molecule analyses were carried out to explore the non-covalent interaction along with the molecular electrostatic potential to predict the reactive sites of electrophilic and nucleophilic attack.
Graphic abstract
Open image in new window
In the present work, ab initio calculations are performed to investigate the geometry, interaction energy and bonding properties of binary complexes formed between metal-hydrides HMX (M = Be, Mg, Zn and X = H, F, CH3) and a series of π-acidic heteroaromatic rings. In all the resulting complexes, the heteroaromatic ring acts as a Lewis acid (electron acceptor), while the H atom of the HMX molecule acts as a Lewis base (electron donor). The nature of this interaction, called ‘hydride-π’ interaction, is explored in terms of molecular electrostatic potential, non-covalent interaction, quantum theory of atoms in molecules and natural bond orbital analyses. The results show that the interaction energies of these hydride-π interactions are between −1.24 and −2.72 kcal/mol. Furthermore, mutual influence between the hydride-π and halogen- or pnicogen-bonding interactions is studied in complexes in which these interactions coexist. For a given π-acidic ring, the formation of the pnicogen-bonding induces a larger enhancing effect on the strength of hydride-π bond than the halogen-bonding.
Dimers of borazine were studied using matrix isolation infrared spectroscopy and ab initio quantum chemical calculations. Computations were performed at the MP2 and M06-2X levels of theory using 6-311++G(d,p) and aug-cc-pVDZ basis sets for the various homodimers. At both levels of theory, an aligned stacked structure was found to be the global minimum, which was nearly isoenergetic to a parallel displaced structure. A T-shaped structure, where the N-H of one borazine pointed towards the N of the second borazine, was found to be a local minimum. In addition to these structures, a dihydrogen bonded structure, where the hydrogen attached to the nitrogen of borazine interacted with the hydrogen attached to the boron atom of another borazine, was also indicated. Experimentally, we observed the T-shaped dimer and the dihydrogen bonded dimer. This is one of the rare examples of an experimental evidence for a dihydrogen bond, in a system other than in a metal hydride. These results for the borazine dimer were clearly different from the benzene dimer where the parallel displaced structure was found to be the global minimum followed by the T-shaped structure at MP2/aug-cc-pVDZ level of theory. AIM, EDA and NBO analysis were carried out for all the structures to explore the nature of interactions.
The cooperativity effects are investigated in the possible linear dihydrogen-bonded ternary complexes, F-H⋯X-H⋯H-M and X-H⋯H-M⋯F-H, and non-dihydrogen-bonded quaternary systems, F-H⋯X⁻⋯H-H⋯M⁺ and X⁻⋯H-H⋯M⁺⋯F-H (X=F, Cl, Br; M=Li, Na, K) using the DFT-B3LYP/6-311++G(3df,2p) and MP2(full)/6-311++G(3df,2p) methods. The result shows that for the dihydrogen-bonded complex, remarkable cooperativity effect is found and the cooperativity effect of the H⋯H bond on the H⋯X or M⋯F interaction is more pronounced than that of the H⋯X or M⋯F contact on the H⋯H interaction. The complexation energy and cooperativity effect in F-H⋯X-H⋯H-M are larger than those of the corresponding X-H⋯H-M⋯F-H system. Thus, the F-H⋯X-H⋯H-M complex is preferentially formed and F-H prefers to be attached to the X end. For the non-dihydrogen-bonded quaternary system, due to the stronger complexation energy and cooperativity effect of Cl⁻⋯H-H⋯Li⁺⋯F-H or F-H⋯Br⁻⋯H-H⋯K⁺ as compared to those of F-H⋯Cl⁻⋯H-H⋯Li⁺ or Br⁻⋯H-H⋯K⁺⋯F-H, F-H prefers to be attached to Li⁺ or Br⁻. Cooperativity effect is analyzed using the charges on hydrogen in the H⋯H moiety, surface electrostatic potentials and atoms in molecules analysis.
The dihydrogen bond-an interaction between a transition-metal or main-group hydride (M-H) and a protic hydrogen moiety (H-X)-is arguably the most intriguing type of hydrogen bond. It was discovered in the mid-1990s and has been intensively explored since then. Herein, we collate up-to-date experimental and computational studies of the structural, energetic, and spectroscopic parameters and natures of dihydrogen-bonded complexes of the form M-H···H-X, as such species are now known for a wide variety of hydrido compounds. Being a weak interaction, dihydrogen bonding entails the lengthening of the participating bonds as well as their polarization (repolarization) as a result of electron density redistribution. Thus, the formation of a dihydrogen bond allows for the activation of both the MH and XH bonds in one step, facilitating proton transfer and preparing these bonds for further transformations. The implications of dihydrogen bonding in different stoichiometric and catalytic reactions, such as hydrogen exchange, alcoholysis and aminolysis, hydrogen evolution, hydrogenation, and dehydrogenation, are discussed.
A quantum chemical study of the H2 activation at fluorides of coinage metals, MF (M = Cu, Ag and Au), and its splitting was performed. The following reaction path was analyzed: FM•••H2 → FH•••HM → HM•••FH, where both the molecular complexes and the corresponding transition states have been characterized at the CCSD(T)/aug-cc-pVQZ//MP2/aug-cc-pVQZ level of theory. Further single-point CASSCF/CASPT2 calculations, including spin-orbit coupling effects, were also performed to analyze the role of non-dynamical correlation. The scalar relativistic effects are included via aug-cc-pVQZ-PP basis sets used for the metals. The dihydrogen-bonded copper (FH•••HCu) and silver (FH•••HAg) complexes are observed as a result of the H2 cleavage, while the corresponding FH•••HAu gold complex is not found but the HAu•••HF arrangement is observed, instead. The energetic and geometrical parameters of the complexes have been analyzed and both the Quantum Theory of Atoms in Molecules approach and the Natural Bond Orbitals method were additionally applied to analyze the intermolecular interactions.
Five fully optimized structures of complexes between aza-calix[6]arene host monomers (Ma∼Me) and complexes (a∼e) have been obtained at the B3LYP/6-31G(d) level. Natural bond orbital (NBO) analysis was performed to reveal the origin of the interaction. The intermolecular interaction energy was evaluated with basis set superposition error correction (BSSE) and zero point energy correction (ZPEC). The B3LYP/6-31G(d) calculations on the five complexes have shown that the greatest interaction (-13.98 kJ/mol) is found in the complex between HMX and hexa-a2a-calk[3]-p-tri-arene[3]-2-amido-l,3,5-tri-azine. The results have indicated that intermolecular interaction energies of aza-calix[6]arenes with substituted group are stronger than those without substituted group, and those with amido are greater than with nitryl. Thus, hexa-azacalix[3]-p-tri-arene[3]-2-amido-1,3,5-tri-azine is rather equal to eliminate HMX from explosive waste water.
Four optimized structures of azacalix [6] arene host monomers (Ma-Md) and their complexes (a-d) with HMX were obtained at B3LYP/6-31G (d) level. Natural bond orbital (NBO) analysis was performed to reveal the origin of the interaction between hosts and objects. The intermolecular interaction energy was evaluated with basis set superposition error correction (BSSE) and zero point energy correction (ZPEC). The B3LYP/6-31G (d) calculations on the four complexes show that the largest interaction energy is -13.98 kJ·mol-1 in the complex composed of HMX and hexaazacalix [3]-p-triarene [3]-2-amido-1, 3, 5-triazine. Results show that intermolecular interaction energies of azacalix [6] arenes with substituted groups are stronger than that without substituted groups, and intermolecular interaction energies of azacalix [6] arenes with amido groups are stronger than that with nitryl groups.
Two types of the hydrogen bond are described and compared here; the A– H···H–B dihydrogen bond and theA–H···σ interaction. In a case of the dihydrogen bond the H···H contact between the hydrogen atoms characterized by the opposite charges is observed; i.e. between the protonic (A)H and hydridic (B)H hydrogens. For the A–H···σ hydrogen bond the A–H proton donating bond interacts with the σ-electrons of the molecular hydrogen. These interactions are topologically different since for DHB the bond path linking the attractors of H-atoms with the corresponding bond critical point is observed. For the A–H···σ interaction the bond path between the (A)H-atom attractor and the bond critical point of the H–H bond of the molecular hydrogen is observed. Both types of the hydrogen bond are characterized by the significant σ → σ* orbital-orbital interaction, σBH → σAH* in a case of DHB and σHH →σAH* for A–H···σ. There are also evidences that A–H···H–B and A–H···σ may be classified as the hydrogen bonds. The examples of complexes characterized by the mentioned above types of the hydrogen bond are analyzed in this chapter, the theoretical as well as experimental examples are presented.
The reaction of the N-thiophosphorylated thiourea (HOCH2 )(Me)2 CNHC(S)NHP(S)(OiPr)2 (HL), deprotonated by the thiophosphorylamide group, with NiCl2 leads to green needles of the pseudotetrahedral complex [Ni(L-1,5-S,S')2 ]⋅0.5 (n-C6 H14 ) or pale green blocks of the trans square-planar complex trans-[Ni(L-1,5-S,S')2 ]. The former complex is stabilized by homopolar dihydrogen CH⋅⋅⋅HC interactions formed by n-hexane solvent molecules with the [Ni(L-1,5-S,S')2 ] unit. Furthermore, the dispersion-dominated CH⋅⋅⋅ HC interactions are, together with other noncovalent interactions (CH⋅⋅⋅N, CH⋅⋅⋅Ni, CH⋅⋅⋅S), responsible for pseudotetrahedral coordination around the Ni(II) center in [Ni(L-1,5-S,S')2 ]⋅0.5 (n-C6 H14 ).
The C-H center dot center dot center dot H dihydrogen-bonded complexes of methane, ethylene, acetylene, and their derivatives with magnesium hydride were systematically investigated at MP2/aug-cc-PVTZ level. The results confirm that the strength of dihydrogen bonding increases in the following order of proton donors: C(sp(3)) H<C(sp(2)) H<C(sp)-H and chlorine substituents enhance the C-H center dot center dot center dot H interaction. In the majority of the complexes with a cyclic structure, the Mg-H proton-accepting bond is more sensitive to the surroundings than C-H proton-donating bond. The nature of the electrostatic interaction in these C-H center dot center dot center dot H dihydrogen bonds was also unveiled by means of the atoms in molecules(AIM) analysis. The natural bond orbital(NBO) analysis suggests that the charge transfer in the cyclic complexes is characteristic of dual-channel. The direction of the net charge transfer in the cyclic complexes is contrary to that previously found in dihydrogen bonded systems.
The DFT-B3LYP/6-311++G(3df,2p) and MP2(full)/6-311++G(3df,2p) calculations were carried out on the binary complex formed by HM (M=Li, Na, K) and XH (X=F, Cl, Br) or C6H6, as well as the ternary system XH⋯HM⋯C6H6. The cooperativity effect between the dihydrogen-bonding and HM⋯π interactions was investigated. The result shows that the H⋯H and HM⋯π interactions are strengthened in the ternary complex in comparison with those in the corresponding binary system. The cooperativity effect of the dihydrogen bond on the HM⋯π interaction is more pronounced than that of the HM⋯π interaction on the H⋯H interaction for the ternary system with HNa or HK, while it is contrary in the ternary complex with HLi. Furthermore, the moderate cooperativity effects between the H⋯H and HM⋯π interactions exist in the ternary complexes with FH, while the remarkable cooperativity effects are present in those with the partially covalent ClH⋯HM or BrH⋯HM dihydrogen-bonding interaction. Cooperativity effects follow the order of XH⋯HNa⋯C6H6>XH⋯HLi⋯C6H6>XH⋯HK⋯C6H6 and ClH⋯HM⋯C6H6>BrH⋯HM⋯C6H6>FH⋯HM⋯C6H6. Cooperativity effect was analyzed using the surface electrostatic potentials, electron density shifts and AIM (Atoms in Molecules) methods as well as charges of the hydrogen atoms in H⋯H moiety. Although the same optimized geometry is obtained, the cooperativity energy obtained considering that it comes either from "X-⋯H2⋯M+⋯C6H6" or "XH⋯HM⋯C6H6" is different.
The interaction between various proton donors (indole, CF3CH2OH, (CF3)(2)CHOH, (CF3)(3)COH) and (NNC)PtH hydrido complex (NNC-H = 6-(1,1'-dimethylbenzyl)-2,2'-bipyridine) was investigated through low-temperature IR and NMR spectroscopy in combination with density functional theory calculations at the M06 level of theory. The experiment shows formation of very weak hydrogen bonded complexes (Delta H-HB degrees, ca. -1.0 kcal mol(-1)), which undergo subsequent proton transfer surprisingly easy. Computational analysis of the hydrogen bonded complexes geometry, electronic parameters (obtained by NBO and AIM analysis), and orbital interaction energies shows that all the complexes are better described as bonded to the metal atom. At that in case of weak alcohols (CH3OH, TFE) there is also the additional interaction with the hydride ligand. These computational results allow explaining the observed experimental trends and give the first example of hydrogen bonding to a metal atom in the presence of hydride ligand.
Complexes F2XO∙∙∙HCN (X = C and Si) have been studied by quantum chemical calculations at the MP2/aug-cc-pVTZ level to investigate the competition between π-hole interaction and hydrogen bond. F2XO has a dual role of a Lewis acid and base with the π-hole on the X atom and the O atom to participate in the π-hole interaction and hydrogen bond with HCN, respectively. Both types of interactions become stronger for X = Si, and the π-hole interaction is much stronger than the hydrogen bond, particularly, the π-hole interaction in F2SiO∙∙∙NCH complex shows a binding energy of -119.8 kJ mol(-1). The C-H∙∙∙O hydrogen bond is dominated by the electrostatic interaction, and this conclusion holds for the π-hole interaction in F2CO∙∙∙NCH complex, but the electrostatic and polarization contributions are similar in F2SiO∙∙∙NCH complex.
The nature of HMH center dot center dot center dot HB NH and HMH center dot center dot center dot HN BH (M=Be, Mg and Ca) interactions were studied with ab initio calculations. The interaction energies were calculated at MP2/6-311++G(2d,2p) level. The calculations suggest that the size of cation and the interaction mode of HB NH are two influential factors that affect the nature of interaction. AIM and NBO analyses of complexes indicate that the variation of densities and the extent of charge transfers upon complexation correlate well with the obtained interaction energies. The character of interactions has been compared with the HMH center dot center dot center dot HC CH complexes.
The hydrogen bond interaction in [AH 3-H 3O]
+ rad radical cations for A = C, Si, Ge, Sn and Pb is
studied at the CCSD(T)/6-311G++(3df,2pd)//MP2/6-31G++(d,p) level of
theory. Two unusual hydrogen bond structures are found to be stable: the
single-electron (SEHB) and the proton-hydride (PHHB) ones. The latter
structures have been found to easily evolve to a [AH 2H
2O] + rad -H 2 complex, from which H
2 can be eliminated.
The cooperativity between pnicogen bond and dihydrogen bond interactions in HMH center dot center dot center dot HCN center dot center dot center dot PH2X (M = Be, Mg, Zn; X = H, F, Cl) complexes is studied by ab initio calculations. To understand the properties of the systems better, the corresponding dyads are also investigated. The cooperative effects are analyzed in terms of geometric, energetic and electron charge density properties of the complexes. The estimated values of cooperative energy E-coop are all negative with much larger E-coop in absolute value for the systems including PH2F. It is seen that the electrostatic interaction is a dominant factor in enhancing both types of interactions. The electron density at the P center dot center dot center dot N and H center dot center dot center dot H bond critical points can be regarded as a good descriptor of the degree of cooperative effects.
An ab initio computational study of the properties of the
dihydrogen-bonded complexes of H 2 - nX nAlH ( n =
0-2; X = F, Cl) with the rare gas (Rg) compounds HArF and HKrF was
carried out at the MP2(full)/6-311++G(2d,2p) level of theory. For all
the studied complexes, we found a low zero-point corrected binding
energies. Large red shifts of the H-Rg vibrational stretching frequency
in both complexes were predicted. Electrostatic interactions between the
individual monomers are also predicted.
An ab initio computational study of the properties of 10 dihydrogen-bonded complexes of H,MH (M = Be, Al, Ga, Si, Ge) with the rare gas derivatives HArF and HKrF has been carried out at the MP2(full)/6-311++G(2d,2p) level of theory. Red shifts of H-Rg and Rg-F along with blue shifts of M-H vibrational stretching frequency were predicted. Variations of the 'H chemical shielding of the HRgF molecules versus the H center dot center dot center dot H distance of the complexes were also studied. (c) 2005 Elsevier B.V. All rights reserved.
New kinds of sodium bonding complexes XH ··· NaH (X = HBe, LiBe, NaBe, HMg, LiMg, and NaMg) have been predicted and characterized in the present paper. For each XH ··· NaH complex, the hydride-sodium bond is formed between the negatively charged H atom of XH and the positively charged Na atom of NaH. Due to the formation of the complexes, both the X–H and the Na–H bonds are elongated, and the Na–H stretching vibrational frequency is redshifted. The interaction energies in the XH ··· NaH complexes at the MP2/6-311++G(3df, 3pd) level increased in the order: HBeH ··· NaH (−4.50 kcal/mol) Document Type: Research Article DOI: http://dx.doi.org/10.1080/00268976.2012.695807 Affiliations: State Key Laboratory of Theoretical and Computational Chemistry,Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People's Republic of China Publication date: December 1, 2012 More about this publication? Editorial Board Information for Authors Subscribe to this Title ingentaconnect is not responsible for the content or availability of external websites $(document).ready(function() { var shortdescription = $(".originaldescription").text().replace(/\\&/g, '&').replace(/\\, '<').replace(/\\>/g, '>').replace(/\\t/g, ' ').replace(/\\n/g, ''); if (shortdescription.length > 350){ shortdescription = "" + shortdescription.substring(0,250) + "... more"; } $(".descriptionitem").prepend(shortdescription); $(".shortdescription a").click(function() { $(".shortdescription").hide(); $(".originaldescription").slideDown(); return false; }); }); Related content In this: publication By this: publisher In this Subject: Nuclear Physics By this author: Wang, Shu-Jian ; Li, Ying ; Wu, Di ; Li, Zhi-Ru GA_googleFillSlot("Horizontal_banner_bottom");
In this communication a systematic computational survey is done on some rigid
hydrocarbon skeletons and their chlorinated derivatives in order to seek for
the so-called ultrashort "non-bonded" hydrogen-hydrogen contacts. It is
demonstrated that upon a proper choice of the main hydrocarbons backbone and
adding some bulky chlorine atoms instead of the original hydrogen atoms in
parts of the employed hydrocarbons, the resulting strain triggers structural
changes that yields ultrashort hydrogen-hydrogen contacts with distances as
small as 1.38 Angstrom. Such ultrashort contacts is clearly less than the world
record of a ultrashort non-bonded hydrogen-hydrogen contact, 1.56 Angstrom,
very recently realized experimentally by Pascal and coworkers in
in,in-bis(hydrosilane) [J. Am. Chem. Soc. 135, 13235 (2013)]. Accordingly, it
is demonstrated that various backbones, e.g. half-cage pentacyclododecanes and
tetracyclododecanes, after proper structural modifications, are capable to
reveal ultrashort non-bonded hydrogen-hydrogen contacts. Thus the observation
of ultrashort hydrogen-hydrogen contact is not an exclusive phenomenon in
computational design though not easily materialized in real world synthesis.
The resulting computed structures as well as the developed methodology for
structure design open the door for constructing a proper set of molecules for
future studies on the nature of the so-called non-bonded hydrogen-hydrogen
interactions that is now an active and controversial area of research.
The weak dihydrogen-bonded interactions are found between HBBH (1Δg) and HM (M = Li, Na, K, BeH, MgH or CaH) using MP2 and CCSD(T) methods with 6-311++G(3df,2p) and aug-cc-pVTZ basis sets. The binding energies follow the order of HBBH⋯HK > HBBH⋯HNa > HBBH⋯HLi > HBBH⋯HCaH > HBBH⋯HMgH > HBBH⋯HBeH. The interactions in HBBH⋯HM are weaker than those in HCCH⋯HM. The calculated binding energies correlate with the H⋯H distance, the elongation of the BH bond and the charge density at the H⋯H bond critical point. The analyses of the natural bond orbital (NBO), atoms in molecules (AIM) and electron density shifts reveal the nature of the dihydrogen-bonded interaction. In these interactions, many of the lost densities from HM or the hydridic hydrogen of HM are shifted toward the BH bond or the H atom of the BH moiety. The polarization of the BB double-bond plays a role in the formation of the dihydrogen-bonded interaction. Thus, the concept of dihydrogen bond is extended to MHδ−⋯+δHBBH system where the BH group can be as the proton donor.
As a follow-up to our study on the interaction between HB=BH and HM, in this paper, the substituent effect on the dihydrogen-bonded interaction between HNa and RB=BH (R = -F, -Cl, -H, -NC, -CN or CO) is investigated using the MP2(full) and CCSD(T) methods with the 6-311++C(3df,2p) and aug-cc-pVTZ basis sets. The binding energies follow the order of NCB=BH center dot center dot center dot HNa > CNB=BH center dot center dot center dot HNa > HB=BH center dot center dot center dot HNa > ClB=BH center dot center dot center dot HNa > FB=BH center dot center dot center dot HNa, and correlate with the H center dot center dot center dot H distance, the decrease of the H-Na bond length and the charge density at the H center dot center dot center dot H bond critical point except for OCB=BH center dot center dot center dot HNa. The analyses of the natural bond orbital (NBO) and atoms in molecules (AIM) show that, the substituent -CN or -NC increases the positive charge in the B1 atom by means of the pi-pi conjugative effect, leading to an increase of the acidity of the H3 atom and the strengthened dihydrogen-bonded interaction in comparison with HB=BH center dot center dot center dot HNa. However, the substituent effect of -F or -Cl on the dihydrogen-bonded interaction is not obvious. The analyses of reaction path of the H(2) elimination, NBO and AIM confirm that the loss of H2 might occur from the neutral dihydrogen-bonded complex OC-B=B-H center dot center dot center dot HNa.
A theoretical study of the inverse hydrogen bonds complexes formed by the XeH2 molecule and hydride and fluoride derivatives of Li, Be, Na and Mg has been carried out by means of DFT (B3LYP/DGDZVP) and ab initio [MP2/DGDZVP and MP2/LJ18/6-311++G(2d,2p)] calculations. The complexes obtained present interaction energies up to −81 kJ/mol. The analysis of the electron density shows electron transfer from the XeH2 to the electron acceptor molecules. The calculated absolute chemical shieldings show the high sensitivity of the xenon atom upon complexation.
The regulating function of methyl group on the strength of dihydrogen bond was investigated in HBeH-HCCH and HMgH-HCCH complexes at the MP2/6-311++G(3df,2p) level. The bond lengths, infrared spectra, interaction energies, and charge transfers were analyzed. The presence of methyl group in the proton acceptor enhances the strength of dihydrogen bond, whereas its presence in the proton donor weakens the strength of dihydrogen bond. The charge analyses indicate that the methyl group in the proton donor and acceptor is electron-donating, thus the methyl group in the proton donor plays a negative role, whereas in the proton acceptor it plays a positive role in the formation of dihydrogen bond.
In this work, a systematic theoretical investigation on a series of dimeric complexes formed between MH2 and HX has been carried out by employing correlated ab initio methods. It was shown that besides dihydrogen bonds, there also exists novel noncovalent X⋯H interactions between the two molecules, which have similar characteristics to traditional halogen bonds. Upon complexation, the HX bonds tend to elongate in all cases, concomitant with red-shifts of the HX stretching frequencies. X⋯H interaction energies, calculated at the MP2/aug-cc-pvtz level, range from −2.11 to −11.78 kJ/mol; the interactions are much weaker than corresponding dihydrogen bonds. The major stabilization source of dihydrogen and halogen bonds arises from the electrostatic force, while charge-transfer force plays a minor role in the formation of the complexes. AIM analyses further confirm the presence of X⋯H interactions in the systems, and the electron density at bond critical points correlates fairly well with the interaction energy.
Ab initio and density functional studies of the properties of 11 linear dihydrogen-bonded complexes pairing XeH2 with different proton donor molecules was undertaken at the MP2/6-311++G(2d,2p)/LJ18, MP2/DGDZVP, and B3LYP/DGDZVP computational levels. Red shifts of H–X along with blue shifts of Xe–H vibrational stretching frequencies were predicted. A linear correlation was established between interaction energies versus dipole moment enhancements of neutral complexes (R2=0.99). It is shown that there are linear correlations between absolute chemical shielding of 129Xe and 1H versus the charge on these atoms in XeH2 studied complexes (R2=0.99 and 0.96, respectively).
In our continuing effort to identify NMR spin−spin coupling constants as fingerprints for hydrogen bond type and use these to obtain structural information, EOM-CCSD calculations have been performed to determine one-bond (1dJH-H) and three-bond (3dJX-M) spin−spin coupling constants across X−H···H−M dihydrogen bonds for complexes with 13C−1H, 15N−1H, and 17O−1H proton-donor groups and proton-acceptor metal hydrides 7Li−1H and 23Na−1H. Unlike two-bond spin−spin coupling constants across N−H−N, N−H−O, O−H−O, and Cl−H−N hydrogen bonds that are determined solely by the Fermi-contact term, 1dJH-H receives nonnegligible contributions from the paramagnetic spin−orbit and diamagnetic spin−orbit terms. However, these terms tend to cancel, so that the curve for the distance dependence of 1dJH-H is determined by the distance dependence of the Fermi-contact term. The value of 1dJH-H is dependent on the nature of the proton donor and proton acceptor, and the relative orientation of the bonded pair. Hence, it would be difficult to extract structural information from experimentally measured coupling constants unless EOM-CCSD calculations were performed on a model complex that closely resembles the experimental complex. 3dJC-Li values for the equilibrium structures of seven linear complexes stabilized by C−H···H−Li bonds are dependent on C−Li distances, and are also sensitive to structural changes which remove any one of these four atoms from the dihydrogen bond. 3dJO-M for the complexes HOH:HLi and HOH:HNa exhibit unusual behavior as a function of the O−M distance, increasing with increasing distance through a change of sign, reaching a maximum, and then subsequently decreasing.
Interaction of the salt (Ph3PNPPh3)BH3CN with the various OH and NH proton donors in low polar media was studied by variable temperature (200–290K) IR spectroscopy and theoretically by DFT calculations. The formation of two types of complexes containing non-classical dihydrogen bond to the hydride hydrogen (DHB) and classical hydrogen bond (HB) to nitrogen lone pair was shown in solution. The 1:1 complexes of both types (XH⋯H and XH⋯N) coexist in the presence of equimolar amount of proton donor. The addition of excess XH-acid leads to the increase of the classical HB content and appearance of the 1:2 complexes, where two basic sites work simultaneously. The structure, spectral characteristics, energy and electron redistribution were studied by DFT (B3LYP) method. The comparison DHB parameters of [BH3CN]− with those of the unsubstituted analogue [BH4]− allowed analyzing the electronic effects of the CN group on the basic properties of boron hydride moiety. The electronic influence of the BH3 group on CN−⋯HX hydrogen bond was also established by comparison with the corresponding classical HB to the CN− anion.
The hydrogen bond interaction in [AH3–H3O]+ radical cations for A = C, Si, Ge, Sn and Pb is studied at the CCSD(T)/6-311G++(3df,2pd)//MP2/6-31G++(d,p) level of theory. Two unusual hydrogen bond structures are found to be stable: the single-electron (SEHB) and the proton-hydride (PHHB) ones. The latter structures have been found to easily evolve to a [AH2H2O]+–H2 complex, from which H2 can be eliminated.
The lithium bond between HMgH and LiNH2 has been predicted and characterized with quantum chemical calculations at the MP2/6-311++G(d,p) level. Upon formation of the lithium bond, both the MgH and LiN bonds are stretched. The LiN bond undergoes a red shift, whereas the MgH bond exhibits a blue shift. The lithium-bonded complex is controlled mainly by electrostatic and polarization interactions. The binding energy of HMgH with LiNH2 is computed to be 12.47 kcal/mol. The binding of the two molecules is enhanced by the substitution with the methyl group in the Li acceptor, whereas it is weakened by the replacement with whether the electron-withdrawing group such as F, Cl, CN, NC, or the electron-donating group (OH and HN2). A negative cooperativity is present in the ternary system of 2LiNH2 and HMgH. The polarization interaction plays an important role in the negative cooperativity. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Reaction of NC<sub>5</sub>H<sub>4</sub>-2-NH<sub>2</sub> with the [6-Ph- nido -6-CB<sub>9</sub>H<sub>11</sub>]<sup>-</sup> anion ( 1 ) in the presence of hydrated FeCl<sub>3</sub> gives [6-Ph-9-(NC<sub>5</sub>H<sub>4</sub>-2-NH<sub>2</sub>)- arachno -6-CB<sub>9</sub>H<sub>12</sub>] ( 4 ) and thence [1-Ph-2-(NC<sub>5</sub>H<sub>4</sub>-2-NH<sub>2</sub>)- closo -1-CB<sub>9</sub>H<sub>8</sub>] ( 5 ), in which the pyridine substituent is on a boron atom α to the cluster carbon atom. This behaviour contrasts to the reactions of organyl-substituted pyridines NC<sub>5</sub>H<sub>4</sub>R to yield neutral 9-pyridine arachno species [6-Ph-9-(NC<sub>5</sub>H<sub>4</sub>R)- arachno -6-CB<sub>9</sub>H<sub>12</sub>] and thence neutral 6-pyridine closo species [1-Ph-6-(NC<sub>5</sub>H<sub>4</sub>R)- closo -1-CB<sub>9</sub>H<sub>8</sub>], in which the pyridine substituent is on a boron atom β to the cluster carbon atom. The chlorinated analogue [1-Ph-2-(NC<sub>5</sub>H<sub>4</sub>-2-NH<sub>2</sub>)-4-Cl- closo -1-CB<sub>9</sub>H<sub>7</sub>] ( 7 ) is also identified as a minor by-product from the reaction system. Reaction of anion 1 with NC<sub>5</sub>H<sub>4</sub>-4-NH<sub>2</sub> does not proceed further than [6-Ph-9-(NC<sub>5</sub>H<sub>4</sub>-4-NH<sub>2</sub>)- arachno -6-CB<sub>9</sub>H<sub>12</sub>] ( 8 ). The 2-NH<sub>2</sub> compounds 4 , 5 and 7 exhibit intramolecular BH-HN dihydrogen bonding, whereas the 4-NH<sub>2</sub> compound 8 exhibits an intermolecular BH-HN dihydrogen-bonded network that involves inversion-related pairs of dihydrogen-bonded chains.
The crystal structures of the tetraphenylborates of the dabcoH+, guanidinium (MeCN solvate), and biguanidinium cations are shown to contain a variety of C-H···H-C dihydrogen (DB) bonds of nominally zero polarity, as well as a variety of N-H···N, C-H···N, N-H···Ph, and C-H···Ph hydrogen (HB) bonds. These intermolecular bonds have been characterized topologically after multipole refinement of the structures. The coexistence of the DBs and HBs in each of the structures makes it possible to establish their relative strength hierarchy. It also illustrates the importance of the DBs in satisfying the tendency of these structures to maximize the total intermolecular bonding engagement. To compare the above DBs with other DBs, the results of an extensive set of MP2/6-31G(d,p) calculations (supplied by I. Alkorta) were analyzed for reference correlations between the bond-critical parameters. Thus, for an X-H···H-Y bond, the difference Δε(H)m between the Mulliken charges on the H atoms in the uncomplexed X-H and H-Y components correlates quite well with the X-H···H-Y parameters and can be used for predicting the topological strength of an X-H···H-Y bond. The use of the difference Δε(H)cin the bond does not appear to change the correlation significantly; closer correlations are observed when the amount of charge transferred on formation of the H···H bond is used instead of Δε(H)m or Δε(H)c. Bonding interactions are obtained even between like or symmetry-related H atoms as a consequence of induced-dipole interactions, which accounts for the existence of the above intermolecular C-H···H-C bonds with d(H···H) = 2.182.57 Å, electron density at the bond-critical point of ~0.050.08 e/Å3, and a rough estimate of the H···H binding energy of ~1-5 kcal/mol. Examination of the bond-critical parameters of X-H···H-Y bonds also suggests a criterion of stability of these bonds with respect to the transition from non-shared (closed-shell) X-H···H-Y interaction to covalent (shared-shell) X···H-H···Y interaction. This transition appears to be discontinuous.Key words: bond-critical parameters, bond topology, dihydrogen bonds, hydrogen bonds, organoammonium tetraphenylborates.
The effects of high pressures (up to 40 kbar) on the dihydrogen-bonded BH3NH3 molecular crystal were
investigated using Raman spectroscopy in diamond and moissanite anvil cells. The stretching mode frequencies
of the NH3 proton donor groups exhibited moderate red shifts with increasing pressures, as found in many
conventional hydrogen-bonded systems of weak to medium strength. The stretching modes corresponding to
the BH3 proton acceptor group, on the other hand, showed large blue shifts with increasing pressure, which,
however, are not related to the changes in the N-HâââH-B interactions. The BH3NH3 crystals undergo a
pressure-induced disorder-order phase transition around 8 kbar, which is facilitated by the presence of
dihydrogen bonds.
The binding energies, geometries, 7 Li magnetic shielding, and electric field gradient ten-sors of hydrogenated lithium clusters, LinHm (m ≤ n ≤ 4), were studied via density functional theory approach. We optimized the structures using B3LYP functional and 6-311++G (2d,2p) basis set. The calculated binding energies of lithium hydride clus-ters indicate that hydrogenation energy of LinHm clusters decreases as the number of hydrogen atoms within the cluster increases. Our calculations also showed that for n = 4 clusters, the three-dimensional structure is more stable than the planar one. The study of the trends in the 7 Li magnetic shielding isotropy, σ iso , and anisotropies, ∆σ, values are explained in terms of the interplay between the electronic and geometrical effects. The variations in the 7 Li nuclear quadrupole coupling constants, χ, and their associated asymmetry parameters, η Q , for different isomers of the lithium hydride clusters and the influence of hydrogenation on the EFG tensors are also discussed. For n = 4, we obtained a noticeable difference in the χ value from the planar to the three-dimensional structures. The atoms in molecules (AIM) analysis at the Li–H bond critical point reveals remark-ably different topographical properties of the charge density and associated Laplacian fields for the planar and three-dimensional lithium hydride clusters.
We report here an investigation into the correlation between dihydrogen bond energies, three-centre bond indices and group indices in some dihydrogen-bonded dimers. This kind of bond is generated by interaction between proton-donator and proton-acceptor groups, XHσ+…H′σ − M, where X is a more electronegative atom and M a less electronegative atom than hydrogen. The different electronegativities of the X atoms, as well the M atoms, would affect the correlations between Hσ+…H′σ − distances and bond energies of these systems. In this work it will be shown that three-centre bond indices and group indices exhibit a better correlation with bond energies when compared to Hσ+…H′σ − distances for this kind of system.
An ab initio computational study of the properties of four linear dihydrogen-bonded complexes formed between the recently discovered argon-containing compound HArF and the XBeH (X=H, F, Cl and Br) molecules was undertaken at the MP2(full)/6-31++G(d,p) level of theory. The calculated complexation energy at G2MP2 level show that stability of complexes decreases as HBeH⋯HArF > BrBeH⋯HArF > ClBeH⋯HArF > FBeH⋯HArF. Atom in molecule (AIM) analysis is used to discuss effect of substitution on the H⋯H bond length.
Ab initio studies of complexes HCCH···H2, FCCH···H2, HCCH···HLi, FCCH···HLi, HCCH···HBeH, FCCH···HBeH, HCCH···HBeF, and FCCH···HBeF with H···H intermolecular binding contacts were carried out up to the MP2/6-311++G(3df,3pd)/MP2/aug-cc-pVQZ level of theory. Binding energies extrapolated to the complete basis set (CBS) limit indicate that the results obtained at the MP2/6-311++G(3df,3pd) level of theory are almost saturated. An analysis of the geometrical and energetic parameters was performed, indicating that the more strongly bonded complexes could be classified as X−H+δ···-δH−Y dihydrogen bonds, whereas the weaker ones may belong to the X−H···σ category. In the first case, the electrostatic and exchange contributions are the most important energetic terms, whereas in the second case, the correlation term also makes a sizable contribution to the overall dimer stability. The atoms in molecules (AIM) theory was also applied to explain the nature of all of the complexes. A complete analysis of the different parameters of the complexes shows that the stronger complexes may be classified as H bonded and that the weaker complexes my be classified as van der Waals complexes. However, there is no evident borderline between them, which indicates the ambiguous nature of dihydrogen-bonded complexes or the arbitrary character of the definitions used to categorize the molecular complexes.
The dihydrogen-bonded complexes of methane and its fluoro and chloro derivatives with lithium hydride are analyzed using ab initio methods as well as the Bader theory. All calculations were performed using Pople's basis sets (6-311++G(d,p), 6-311++G(2df,2pd), and 6-311++G(3df,3pd)) and the Dunning bases (aug-cc-pVDZ and aug-cc-pVTZ) within the MP2 method. The results of the calculations show that the binding energy for the analyzed complexes increases with the increase of the number of fluoro or chloro substituents, up to 7 kcal/mol. In the same order there is an increase of the electrostatic energy term, showing that for the CF3H···HLi complex the dihydrogen bond interaction is similar in nature as for the water dimer where a conventional O−H···O hydrogen bond exists, while for the CCl3H···HLi dimer the exchange energy term outweighs the electrostatic energy. Hence, the other attractive energy terms are important. A topological analysis based on the Bader theory supports the results of the ab initio calculations since the electron densities at the H···H bond critical points and the other topological parameters are similar to those calculated for moderate conventional hydrogen bonds.
The crystal and molecular structure of pyrrole-2-carboxylic acid (PCA) determined by single-crystal X-ray diffraction is presented. Intermolecular H-bonds for this structure are analyzed. The DFT calculations at the B3LYP/6-311++G(d,p) level of theory and ab initio calculations at the MP2/6-311++G(d,p) level are performed for dimers of pyrrole-2-carboxylic acid and for similar model species. The X-ray data and calculations show that the pyrrole moiety within pyrrole-2-carboxylic acid influences the π-electron delocalization and hence the strength of the hydrogen bonds. The geometrical and energetic features of H-bonds of PCA dimers and of model complexes are analyzed. Additionally, the Bader theory is applied, and the characteristics of the bond critical points and ring critical points confirm the influence of the pyrrole moiety on the strength of H-bond interactions.
The crystal and molecular structures of [4-((E)-but-1-enyl)-2,6-dimethoxyphenyl]pyridine-3-carboxylate (BDMP) and [4-((E)-pent-1-enyl)-2,6-dimethoxyphenyl]pyridine-3-carboxylate (PDMP) are investigated by low-temperature X-ray diffraction measurements. The geometries of these molecules indicate that intramolecular dihydrogen bonds may exist for these structures. The use of the Bader theory supports this statement. To analyze the nature of such interactions, model calculations on styrene and its derivatives have been performed at B3LYP/6-311++G** level of theory.
The present work reports the results of the MP2/6-31+G(d,p) study of the interaction between CH4 and (H2O)2 and H5O2+, including the optimized geometries of the stable structures, their harmonic vibrational frequencies, total energies with the two- and three-body contributions, and natural charges. Three stable structures exist on the potential energy surface of the CH4·(H2O)2 complex formed via a CH···O hydrogen bond. Under its formation, the corresponding CH bond undergoes a small contraction, resulting in a blue shift of the corresponding ν(CH) vibration. One of the structures, resembling a cyclic trimer with relatively short distances between two hydrogen atoms of CH4 and the terminal hydrogen atom of (H2O)2, is characterized by the largest total and the largest two-body interaction energies. This suggests the existence of a weak attractive interaction between the three hydrogen atoms. To shed light on the nature of such an interaction between three hydrogen atoms, we study the complex between CH4 and H5O2+ and demonstrate that its formation originates from a substantially stronger interaction between three hydrogen atoms and induces a marked asymmetry of the central (O···H···O) hydrogen bond of the cation. The distances between two hydrogen atoms of CH4 and one of the terminal hydrogen atoms of H5O2+ are very short (1.87 Å), implying that these three hydrogen atoms interact with each other due to a relatively strong ionic multi-dihydrogen bonding.
Theoretical calculations up to MP2/6–31G** with BSSE correction are carried out on a series of A–HH–B dihydrogen bonds (A = B, Li, Be; B = N, C).
Hydrogen bonds (HBs) are the most important ‘weak’ interactions encountered in solid, liquid and gas phases. The HB can be defined as an attractive interaction between two molecular moieties in which at least one of them contains a hydrogen atom that plays a fundamental role. Classical HBs correspond to those formed by two heteroatoms, A and B, with a hydrogen atom bonded to one of them and located approximately in between (A–H···B). Recently, knowledge of the number of functional groups which act as hydrogen bond donors or acceptors has increased considerably and most of these new groups are discussed.
In the past, basis sets for use in correlated molecular calculations have largely been taken from single configuration calculations. Recently, Almlöf, Taylor, and co‐workers have found that basis sets of natural orbitals derived from correlated atomic calculations (ANOs) provide an excellent description of molecular correlation effects. We report here a careful study of correlation effects in the oxygen atom, establishing that compact sets of primitive Gaussian functions effectively and efficiently describe correlation effects if the exponents of the functions are optimized in atomic correlated calculations, although the primitive (sp) functions for describing correlation effects can be taken from atomic Hartree–Fock calculations if the appropriate primitive set is used. Test calculations on oxygen‐containing molecules indicate that these primitive basis sets describe molecular correlation effects as well as the ANO sets of Almlöf and Taylor. Guided by the calculations on oxygen, basis sets for use in correlated atomic and molecular calculations were developed for all of the first row atoms from boron through neon and for hydrogen. As in the oxygen atom calculations, it was found that the incremental energy lowerings due to the addition of correlating functions fall into distinct groups. This leads to the concept of correlation consistent basis sets, i.e., sets which include all functions in a given group as well as all functions in any higher groups. Correlation consistent sets are given for all of the atoms considered. The most accurate sets determined in this way, [5s4p3d2f1g], consistently yield 99% of the correlation energy obtained with the corresponding ANO sets, even though the latter contains 50% more primitive functions and twice as many primitive polarization functions. It is estimated that this set yields 94%–97% of the total (HF+1+2) correlation energy for the atoms neon through boron.
Correlation consistent and augmented correlation consistent basis sets have been determined for the second row atoms aluminum through argon. The methodology, originally developed for the first row atoms [T. H. Dunning, Jr., J. Chem. Phys. 90, (1989)] is first applied to sulfur. The exponents for the polarization functions (dfgh) are systematically optimized for a correlated wave function (HF + 1 + 2). The (sp) correlation functions are taken from the appropriate HF primitive sets; it is shown that these functions differ little from the optimum functions. Basis sets of double zeta [4s3p1d], triple zeta [5s4p2d1f], and quadruple zeta [6s5p3d2f1g] quality are defined. Each of these sets is then augmented with diffuse functions to better describe electron affinities and other molecular properties: s and p functions were obtained by optimization for the anion HF energy, while an additional polarization function for each symmetry present in the standard set was optimized for the anion HF + 1 + 2 energy. The results for sulfur are then used to assist in determining double zeta, triple zeta, and quadruple zeta basis sets for the remainder of the second row of the p block.
Cited By (since 1996): 6085, Export Date: 25 August 2011, Source: Scopus
Ab initio calculations at the MP2/6-31+G(d,p) level of theory have been carried out to determine the equilibrium structures and vibrational spectra of three series of complexes involving the hydrogen halides HF, HCl, and HBr, and a set of 4-substituted pyridines. The hydrogen bonds in these complexes span the range of hydrogen bonding possibilities, including traditional Y-H...N, proton-shared Y...H...N, and ionic Y-...H+-N hydrogen bonds. The type of hydrogen bond in a complex is related to the proton affinity of the substituted pyridine and the nature of the hydrogen halide. Plots of normalized distance and force constant changes versus the proton affinity of the substituted pyridines exhibit breaks which correlate with the three types of hydrogen bond. The infrared spectra of all complexes exhibit very intense bands associated with motion of the hydrogen-bonded proton along the Y-N axis. The shift to lower frequency of this band in complexes with traditional hydrogen bonds increases as the proton affinity of the substituted pyridine increases. A shift of greater than 40% relative to the free HY frequency is a spectroscopic signal of the presence of a proton-shared hydrogen bond.
DFT
calculations (B3PW91) predicted structures for hydrogen-bonded complexes of type Ir(H)(L)(bq–G)(PH3)2q+
(bq–H = benzo[h]quinoline-10-yl, L = empty site, FH or OH2; G = H or NH2, q
= 1; L = F−, G = NH2, q
= 0), which are either too unstable
for X-ray crystallography study, or for which the crystal structure does not allow H atom positions reliably
to be located. The work shows how the two-point binding site provided by the bq–NH2
complex is ideal for HF but
not for H2O binding, thus stabilizing the former to the extent that it can be observed by NMR at low temperature.
Fluxionality in the aqua complex is fully interpreted by location of the appropriate TS. One such TS is strongly
stabilized by hydrogen bonding leading to rapid exchange of NH2 positions
even at −80 °C. An improved ligand is
suggested for stabilizing an HF complex.
The calculation of accurate electron affinities (EAs) of atomic or molecular species is one of the most challenging tasks in quantum chemistry. We describe a reliable procedure for calculating the electron affinity of an atom and present results for hydrogen, boron, carbon, oxygen, and fluorine (hydrogen is included for completeness). This procedure involves the use of the recently proposed correlation-consistent basis sets augmented with functions to describe the more diffuse character of the atomic anion coupled with a straightforward, uniform expansion of the reference space for multireference singles and doubles configuration-interaction (MRSD-CI) calculations. Comparison with previous results and with corresponding full CI calculations are given. The most accurate EAs obtained from the MRSD-CI calculations are (with experimental values in parentheses) hydrogen 0.740 eV (0.754), boron 0.258 (0.277), carbon 1.245 (1.263), oxygen 1.384 (1.461), and fluorine 3.337 (3.401). The EAs obtained from the MR-SDCI calculations differ by less than 0.03 eV from those predicted by the full CI calculations.
The OH group of the iminol complex [IrH2L′(PPh3)2]SbF6·2H2O where L′ is the iminol tautomer of quinolin-8-acetamide, takes part in an O–H H–Ir hydrogen bond.
The monohydrate of xenon dihydride has been studied (XeH
2
) using
ab initio molecular orbital theory. The XeH
2
–H
2
O complex was found to involve an unconventional dihydrogen bond. The computational BSSE-corrected interaction energies at the MP2/6-311+ + G(2d,2p) and CCSD(T)/6- 311+ + G(2d,2p)//MP2/6-311+ + G(2d,2p) levels are –10.6 and –9.0 kJ mol
−1
, respectively. The vibrational properties of the molecular subunits upon complexation are found to undergo large perturbations.
A dynamic equilibrium between the dihydride trans-RuH2(dppm)2 (1) and the hydrido dihydrogen complex [(dppm)2HRu(H2)]+(OR)- in the presence of phenol or hexafluoroisopropyl alcohol has been established by 1H NMR, and the thermodynamics of the reaction (namely ΔH = 17 ± 3 kcal·mol-1 and ΔS = 75.8 eu in the case of phenol addition) could be determined.
We present in this paper an electronic structure and quantum nuclear dynamics study of a modeled version of trans-[Os(H···H)Cl(dppe)2]+, an elongated dihydrogen complex classified as being between the fast and slow H2 spinning limits and whose J(H,D) coupling constant increases on increasing temperature. We have found that the librational potential energy barrier for the motion of the H2 unit is quite low, in agreement with the spinning regime of the H2 unit reported from experiment. Additionally, while the electronic structure study does not manage to describe the experimentally reported geometry obtained through neutron diffraction experiments, the quantum nuclear motion study reproduces the experimental findings very satisfactorily. Finally it is seen that only when the librational motion of the H2 unit is taken into account in an explicit way in the quantum nuclear motion calculations the temperature dependence of the J(H,D) 1H NMR coupling constant is also correctly accounted for.
Intermolecular hydrogen bonding of acidic alcohols (PhOH, (CF3)2CHOH (HFIP), (CF3)3CHOH (PFTB)) to the hydride ligand of WH(CO)2(NO)L2 (L = PMe3 (1), PEt3 (2), P(OiPr)3 (3), PPh3 (4)) has been observed and characterized by IR and NMR spectroscopy in hexane, toluene-d8, and CD2Cl2 solutions. The H-bonding is an equilibrium process with medium −ΔH° of 4.1−6.9 kcal/mol; the enthalpy increases on going from 4 to 1, i.e., the strongest bonding is found for the smallest and the most basic L = PMe3. The value of −ΔH° depends on the pKa of the proton donors, increasing as the acidity does (PhOH < HFIP < PFTB). The IR and NMR data suggest C2v symmetry around tungsten in the ROH···HW(CO)2(NO)L2 adduct, with the H···H distance of 1.77 Å (L = PMe3) estimated from the hydride T1min relaxation time. The relevance of the hydrogen bonding to the mechanism of protonation of metal hydrides is suggested.
Intermolecular interactions between HR (R = F, OH, H2O+) and the hydride and NO ligands of Mo(H)-(CO)(2)(L)(2)(L') (where cis-ligand L = PH3, NH3; trans-ligand L' = NO, Cl, H) and the W(H)(CO)(2)(NO)(PH3)(2) complex have been studied using HF/3-21G and DFT (B3LYP, BLYP, B3PW91) methods. The structure of the complexes depends upon the nature of the trans-ligand and the proton donor ability of HR. H ... H bonding exists in the case of poor and moderate proton donors HR and the strong pi-acceptor trans-ligand. A strong sigma-donor cis-ligand strengthens the H ... H bonding. The change from poor proton donor to strongly acidic HR leads to a eta(2)-H-2 structure. The dihydride structure is formed with replacement of a pi-acceptor trans-ligand by a sigma-donor as a result of greater nucleophilicity of the metal atom. Energy decomposition analysis shows that the H ... H bond consists of a large electrostatic component, with a small but significant contribution from both charge transfer and polarization, distinct from the pattern of the conventional H-bond wherein polarization makes a more minor contribution. Whereas HF/3-21G predicts a preference for a H ... O interaction, the DFT approaches favor H ... H. B3PW91 results are in the best agreement with available experimental data.
The preparation, NMR and X-ray diffraction studies of a series of azolylboron hydrides derived from pyrrole, indole, and carbazole coordinated with tetrahydrofuran, pyridine, and imidazole are reported. The azolyl substituents are very electroattractive leading to an acidic boron atom which strongly coordinates with the Lewis bases. The stabilization of the BH2groups against disproportionation could be explained in terms of the interactions found between the acidic hydrogen atoms of the heterocycles (CHδ+ acceptor) and the hydrides (BHδ– donors).
It is shown that the total charge density is a valid source to confirm hydrogen bonding without invoking a reference charge density. A set of criteria are proposed based on the theory of ''atoms in molecules'' to establish hydrogen bonding, even for multiple interactions involving C-H ... O hydrogen bonds. These criteria are applied to several van der Waals complexes. Finally a bifurcated intramolecular C-H ... O hydrogen bond is predicted in the anti-AIDS drug AZT, which may highlight a crucial feature of the biological activity of a whole class of anti-AIDS drugs.
The referred elongated dihydrogen compounds cannot be described by simply interpolating dihydrogen and dihydrido models. According to the results reported here, it is more appropriate to describe them as complexes containing two hydrogen atoms moving freely in a wide region of the coordination sphere of the metal.
Diagrammatic many-body perturbation theory (MBPT) has been applied to
the correlation energy of NaH, AlH, and HCl, within a basis of 47
Slater-type functions located on both centers in the molecule. By
summing all second and third order two-body diagrams plus a selection of
higher order diagrams via a denominator shift, about 80% of the total
correlation energy could be obtained in each case. The individual pair
correlation contributions are analyzed and grouped into the shell
structure of these molecules, showing that the principal deficiency lies
in the inadequacy of the basis sets to describe the inner-shell
correlation to extremely high accuracy. Using experimental values for
the correlation energy of the Ne-like inner cores of these molecules,
together with the calculated MBPT valence shell values, gives an
improved estimate of the total correlation energy that is within ~5% of
the experimental result for each of the three molecules.
High levels of ab initio molecular orbital theory were used to study the structures and binding energies of water trimers. These calculations included HF/6‐311++G(2df,2p) geometry optimizations for the 17 structures considered. Harmonic vibrational energies were obtained at the HF/6–311++G(2d,2p) level. The HF potential energy surface present three minima whose geometries were refined at the MP2/6–311+G(d,p) level. The global minimum corresponds to an asymmetric cyclic structure which presents significant cooperative effects with respect to the Cs dimer. To properly describe these nonpairwise effects, ZPE (zero point energy) and correlation corrections must be taken into account. They are reflected in a stiffer intermolecular potential, shorter O–O distances, longer donor O–H bond lengths, larger energies per hydrogen bond (HB), and greater shifts of the donor O–H bond stretching frequencies than the Cs dimer. Contrarily, the other two local minima present HBs which are weaker than those of the dimer. These nonpairwise effects upon trimerization are mirrored in the topological characteristics of the electronic charge distributions of these clusters and there is a good linear relationship between the energies per HB and the charge density at the HB critical point. The binding energies for the three minima were evaluated at the MP4SDQ/6–31+G(2d,2p) level using the MP2 optimized geometries. For the remaining structures considered they were obtained at the MP2/6–311++G(2d,2p) level using the corresponding HF optimized geometries. We have also shown that nonpairwise effects can be qualitatively explained in terms of acid‐base arguments.
A new ruthenium hydride complex of the aminocyclopentadienyl ligand (Cp-N)RuH(PPh3)2 (Cp-N = C5H4CH2CH2NMe2, 1) has been prepared and characterized by X-ray diffraction. Protonation of 1 with excess HPF6 leads to the dicationic derivative [(Cp-NH)RuH2(PPh3)2](PF6)2 (2), in which both the metal and the amino substituent have been protonated. Addition of 1 equiv of HBF4·Et2O to 1 leads to the complex [(Cp-N)Ru(PPh3)2](BF4) (3), containing a chelating amino cyclopentadienyl ligand after elimination of H2. However, using (HNEt3)(BPh4) or (HPBu3)(BPh4) as protonating agent, it is possible to form [(Cp-NH)RuH(PPh3)2](BPh4) (4), which was isolated as yellow crystals of 4·H2O upon addition of undistilled methanol and characterized by X-ray crystallographic analysis. A fluxional process exchanging the ammonium proton and the hydride without changing the thermodynamic state of the system could be established by 1H NMR, and activation energies of 11 kcal·mol-1 were calculated for 4·H2O and the product resulting from in situ addition of [HNEt3][BPh4] to 1, whereas an activation energy of 10.1 kcal·mol-1 was found for the product resulting from in situ addition of [HPBu3][BPh4] to 1. A density functional study (B3PW91) was carried out, and the dihydrogen bond in the model system for 4 was calculated to be 1.545 Å, in excellent agreement with T1 measurements (1.52 Å). The proposed mechanism for the fluxional process does not involve a proton transfer within the dihydrogen bond.
The reduction of water to H2 by the tris(pyrazol-1-yl)borate complex [Pd(CH2CH2CH2CH2){(pz)3BH-N,N‘}]- with concomitant formation of the palladium(IV) complex Pd(CH2CH2CH2CH2)(OH){(pz)3BH-N,N‘,N‘‘} has been studied theoretically at the MP2//SCF level using [PdMe2{(H2CNNH)3BH}]- as a model for the pallada(II)cyclopentane reagent. The calculations suggest that the uncoordinated pyrazole group has a major role as an intramolecular nucleophile in delivering 2H+ (per mole of H2 formed) to the palladium center, with an eventual role as a coordinated group in the palladium(IV) product. Thus, initial protonation leads to formation of a N-protonated palladium(II) species Pd(CH2CH2CH2CH2){(pz)2(pzH)BH-N,N‘} containing a “Pd···H−N” interaction, followed by hydroxide coordination and hydrido ligand formation to give a palladium(IV) species trans-[Pd(CH2CH2CH2CH2)(H)(OH){(pz)3BH−N,N‘}]-, a second protonation to form trans-Pd(CH2CH2CH2CH2)(H)(OH){(pz)2(pzH)BH−N,N‘} prepared for a dihydrogen bond interaction “Pd−H···H−N”, and finally by elimination of H2 and coordination of the pyrazole group to form Pd(CH2CH2CH2CH2)(OH){(pz)3BH-N,N‘,N‘‘}.
High-level ab initio calculations have been performed on dihydrogen-bonded complexes with hydrogen fluoride (HF) as a proton-donating molecule and simple molecules as proton-acceptors (CH4, SiH4, BeH2, MgH2, LiH, and NaH). MP4(SDQ)/6-311++G** and QCISD(T)/6-311++G** results show that H-bond energies for such systems are significant. For example, the H-bond energy is −11.9 kcal/mol for the LiH···HF complex at the QCISD(T)/6-311++G** level of theory; the basis set superposition error (BSSE) was included, and the geometry of the complex was optimized at the QCISD/6-311++G** level. The relationships between the geometrical parameters of these complexes are in good agreement with those obtained from the bond valence model. The BSSE is taken into account in all levels of calculations. A comparison of the results of the calculations shows that the MP2/6-311++G** level of theory is sufficient for a description of dihydrogen-bonded complexes. Additionally, Bader's theory is included in the analysis of the investigated systems.
The existence of intramolecular dihydrogen bonding in the main group elements is investigated at the ab initio level of theory. The AHn−XHm complexes (with A = Li/B/Al and X= F/O/N/Cl/S/P) in general do not show intramolecular dihydrogen bond (DHB) in their equilibrium structures; however, it is observed in the transition state for the dehydrogenation reaction AHn−XHm → AHn-1−XHm-1 + H2. The barriers to these reactions have been calculated and are found to be least for the complexes having DHB in the equilibrium structure or having eclipsed geometry favorable for DHB formation. The topological analysis of electron density distribution provides crucial information on the existence of DHB as well as on the extent of the dehydrogenation reaction. The above features indicate that the motivation for the formation of intramolecular DHB is likely to facilitate the dehydrogenation reaction from complexes similar to AHn−XHm.
The occurrence of dihydrogen bonds in the complexes and dimers of complexes involving the main group elements is systematically investigated. The complexes of LiH, BH3, and AlH3 with HF, H2O, and NH3 as well as dimers of these complexes are studied using ab initio calculations at the MP2 level. The complexes having H···H bonding are observed; however, in most of the cases they are not minima on their PES. The [H2OLiH]2 has a compact C2h structure with a large dimerization energy where the H···H bond exhibits features of a hydrogen bridge. The H···H bond energy in [BH3HF]2, [BH3H2O]2, and [AlH3H2O]2 is analogous to the conventional moderate or weak hydrogen bond. The bonding features of these complexes and their dimers are analyzed using electron density topography. The structures of dimers are rationalized using molecular electrostatic potential maps. The decomposition analysis of interaction energies of dimers reveals the predominance of electrostatic contribution followed by charge transfer and polarization.
A new type of hydrogen bond, called a dihydrogen bond, has recently been introduced. In this bond a hydrogen is donated to another (hydridic) hydrogen. We apply a set of criteria developed in the context of the theory of “atoms in molecules” that were previously successfully used to study conventional hydrogen bonds. This method enables one to characterize the dihydrogen bond on the basis of the electron density only. We investigated a dimer structure of BH3NH3 at the ab initio level which contains two dihydrogen bonds that differ in strength. The combination of a theoretical density with our hydrogen-bonding criteria turns out to be a valuable new and independent source of information complementary to techniques such as NMR, IR, and structural crystallography.
During the past decade dramatic progress has been made in calculating the binding energies of molecules. This is the result of two advances reported in 1989: an accurate method for solving the electronic Schrödinger equation that is applicable to a broad range of moleculesthe CCSD(T) methodand families of basis sets that systematically converge to the complete basis set limitthe correlation consistent basis sets. The former provides unprecedented accuracy for the prediction of a broad range of molecular properties, including molecular binding energies. The latter provides a means to systematically approach the complete basis set limit, i.e., the exact solutions of approximations to the Schrödinger equation. These two advances combined with a thorough analysis of the errors involved in electronic structure calculations lead to clear guidelines for ab initio calculations of binding energies, ranging from the strong bonds derived from chemical interactions to the extremely weak binding due to dispersion interactions. This analysis has also led to surprises, e.g., it has shown that the Møller−Plesset perturbation theory is unsuitable for calculation of bond energies to chemical accuracy, i.e., with errors of less that 1 kcal/mol. This applies whether one is interested in absolute bond energies or relative bond energies. Although the analysis presented here is focused on the calculation of molecular binding energies, this same approach can be readily extended to other molecular properties.
This report explores the potential of the unconventional hydrogen bonds between the hydridic hydrogens in X−BH3- (X = H, CN) and traditional OH or NH proton donors (dihydrogen bonds) to serve as preorganizing interactions for the topochemical assembly of covalent materials. Evidence for such topochemical control in the reaction B−H···H−X → B−X + H2 was obtained in studies of the solid-state structures and reactivities of N-[2-(6-aminopyridyl)]acetamidine (NAPA) cyanoborohydride and triethanolamine (TEA) complexes of NaBH4 and NaCNBH3. The X-ray crystal structures of all three new compounds studied exhibit multiple dihydrogen bonds which are significant in defining the packing of the molecules in the solid state. Moreover, this new type of interaction is a powerful tool for crystal engineering; as planned, NAPA H3BCN crystallized in the desired (NAPA H3BCN)2 closed loop coordination. Solid-state decomposition of NaBH4·TEA is topochemical, leading to a trialkoxyborohydride, which is not achievable in solution or melt. In addition to close H−H contacts, the relative acidity/basicity of the proton−hydride pairs make a significant contribution to the solid-state reactivity of dihydrogen-bonded systems, as demonstrated by the contrasting reactivities of the NaBH4·TEA and NaCNBH3·TEA complexes.
A reversible protonation of transition metal hydrides by weak proton donors has been found by NMR spectroscopy. The reactants are mixed at room temperature, but the protonation is induced only at low temperature by an increase of the dielectric constant of a suitably chosen solvent. Under these conditions the decomposition via dihydrogen release is avoided. Thus, the unstable complex [Cp*RuH4(PCy3)](+) was obtained in CDF3/CDF2Cl by protonation of Cp*RuH3(PCy3) with fluorinated alcohols.
in CD2Cl2 yielded, in a straightforward manner, the dicationic η2-dihydrogen complex [tpmRu(PPh3)2(H2)](BF4)2, which, as expected, is more acidic than its monocationic Tp [Tp = hydrotris(pyrazolyl)borate] analog [TpRu(PPh3)2(H2)]BF4 (pKa: 2.8 vs. 7.6). The complex [tpmRu(PPh3)2(H2)](BF4)2 is unstable towards H2 loss at ambient temperature. However, acidification of [tpmRu(PPh3)2H]BF4 with excess aqueous HBF4 or aqueous triflic acid in [D8]THF gave very interesting results. Variable-temperature 1H- and 31P-NMR studies revealed that the aqueous acid did not fully protonate the metal hydride to form the dihydrogen complex, but a hydrogen-bonded species was obtained. The feature of this species is that the strength of its Ru–H···H–(H2O)m interaction decreases with temperature; this phenomenon is unusual because other complexes containing dihydrogen bonds show enhanced M–H···H–X interaction as the temperature is lowered. Decrease of the dihydrogen-bond strength with temperature in the present case can be attributed to the decline of acidity that results from the formation of larger H+(H2O)n (n > m) clusters at lower temperatures; steric hindrance of these large clusters also contribute to the weakening of the dihydrogen bonding interactions. At higher temperatures, facile H/H exchange occurs in Ru–H···H–(H2O)m via the intermediacy of a “hydrogen-bonded dihydrogen complex” Ru–(H2)···(H2O)m. To investigate the effect of the H+(H2O)m cluster size on the strength of the dihydrogen bonding in [tpmRu(PPh3)2H]+, molecular orbital calculations at the B3LYP level have been performed on model systems, [tpmRu(PH3)2H]+ + H+(H2O) and [tpmRu(PH3)2H]+ + H+(H2O)2. The results provide further support to the notion that the formation of larger H+(H2O)n clusters weakens the Ru–H····H(H2O)n dihydrogen bonding interaction.
Many-body (diagrammatic) perturbation theory (MBPT), coupled-pair many-electron theory (CPMET), and configuration interaction (CI) are investigated with particular emphasis on the importance of quadruple excitations in correlation theories. These different methods are used to obtain single, double, and quadruple excitation contributions to the correlation energy for a series of molecules including CO2, HCN, N2, CO, BH3, and NH3. It is demonstrated that the sum of double and quadruple excitation diagrams through fourth-order perturbation theory is usually quite close to the CPMET result for these molecules at equilibrium geometries. The superior reliability of the CPMET model as a function of internuclear separation is illustrated by studying the 1∑ potential curve of Be2. This molecule violates the assumption common to nondegenerate perturbation theory that only a single reference function is important and this causes improper behavior of the potential curve as a function of R. This is resolved once the quadruple excitation terms are fully included by CPMET.
An approximate fourth-order expression for the electron correlation energy in the Møller–Plesset perturbation scheme is proposed. It takes into account all the contributions to the fourthorder energy neglecting only those of the triple-substituted determinants. It is size consistent and correct to fourth order for an assembly of isolated two-electron systems. Illustrative calculations are reported for a series of small molecules.
The XeH2–H2O complex has been studied using DFT theory employing various standard basis sets. The complex was found to involve an unconventional dihydrogen bond, i.e. both complex subunits interact via hydrogens (Xe–H⋯H–O). The DFT calculations predict an interaction energy of moderate strength (ca. −10 kJ mol−1) and large perturbations of the vibrational spectrum of the complex is noted. Electron localization function analysis has been employed to study the bonding properties of the XeH2–H2O complex, and the interaction between XeH2 and H2O was found to be mainly of electrostatic origin.
A new kind of hydrogen bonding is proposed. It is a π-electron delocalization-assisted intramolecular dihydrogen bond. This bond is similar to the resonance-assisted hydrogen bonding investigated extensively by Gilli and co-workers (J. Am. Chem. Soc. 111 (1989) 1023). HF and MP2 calculations with 6-311++G(d,p), 6-311++G(2d,2p) and 6-311++G(3d,3p) basis sets have been performed in this study on boron molecules for which intramolecular dihydrogen bonds exist. The atoms-in-molecules theory of Bader is also applied to study these systems.
The interactions of the IrH⋯HX type (X=O, N) were studied theoretically in models of the neutral complex [Ir(H)3(PPh3)(C5H4NHR] and the two cationic derivatives cis-[IrH(OH)(PMe)4][PF6] and [IrH2(CO)(PPh3)2(pzHN)][BF4]. The geometries were optimized using both RHF and MP2 calculations and an analysis of the charge density was carried out with the atom in molecules (AIM) procedure. The conclusion was that a hydrogen bond between the hydride and the protonic hydrogen is found only in the neutral complex. In the cationic species, the counterion is determining in order to get a good agreement between the optimized and the X-ray determined structures, and the short H⋯H distance is a consequence. The only hydrogen bonds appear to be formed between hydrogen atoms and fluorine atoms of the anion.
To investigate the hydrogen transfer within a crystal by means of the crystal field, the effect of an external electric field over three different proton equilibrium systems has been studied with ab initio methods. The equilibria chosen were: (1) from neutral molecules dihydrogen bonded to cation/H2/anion complexes, (2) from neutral/H2/neutral complexes to charged molecules dihydrogen bonded and (3) from neutral and charged molecules dihydrogen bonded to charged/H2/neutral complexes. The electric field was applied along the molecular axis increasing from 0.00557 to 0.03342 au. At the theoretical level, it has been found that by applying an external field the transfer of H atoms between two heavy atoms is possible. Thus, a coordinated hydrogen molecule became a dihydrogen bond in the case of Li+⋯HH⋯F−. Oppositely, a dihydrogen bonded complex became two molecules coordinated to molecular hydrogen in the case of the H3N+H⋯HBH3− system.
The structure, energetics and dynamics of the dihydrogen bonding were discussed. The dihydrogen bonding to the main group hydrides and transition metal hydrides were elaborated. The self-assembly of extended dihydrogen-bonded systems and the reactivity and selectivity control by dihydrogen bonding in solution were also studied.
- S Berski
- J Lundell
- Z Latajka
- E S Shubina
- N V Belkova
- A N Krylov
and Berski, S.; Lundell, J.; Latajka, Z. J. Mol. Struct. 2000, 552, 223.
(7) Shubina, E. S.; Belkova, N. V.; Krylov, A. N.; Vorontsov, E. V.;
(32) Rozas, I.; Alkorta, I.; Elguero
- G S Denisov
- L M Epstein
- S Sabo-Etienne
- B Chaudret
- A Milet
- A Dedieu
- A A M Canty
- J I Tolosa
- A J Lledós
- Am
- Chem
Denisov, G. S.; Epstein, L. M.; Sabo-Etienne, S.; Chaudret, B. Inorg. Chem.
1999, 38, 2550.
(32) Rozas, I.; Alkorta, I.; Elguero, J. Chem. Phys. Lett. 1997, 275, 423.
(33) Milet, A.; Dedieu, A.; Canty, A. Organometallics 1997, 16, 5331.
(34) Barea, G.; Esteruelas, M. A.; A., L.; López, A. M.; Tolosa, J. I.
Inorg. Chem. 1998, 37, 5033.
(35) Gelabert, R.; Moreno, M.; Lluch, J. M.; Lledós, A. J. Am. Chem.
(8) Padilla-Martínez, I. I.; Rosalez-Hoz
- Soc
Soc. 1996, 118, 1105.
(8) Padilla-Martínez, I. I.; Rosalez-Hoz, M. J.; Tlahuext, H.;
- S J Grabowski
- S Grabowski
J. Phys. Chem. A 1999, 103, 9330.
(4) Grabowski, S. J. J. Phys. Chem. A 2000, 104, 5551.
(5) Grabowski, S. J. Chem. Phys. Lett. 2000, 327, 203.
(6) Lundell, J.; Petterson, M. Phys. Chem. Chem. Phys. 1999, 1, 1691
- Soc Orlova
- G Scheiner
- S Calhorda
- M J Lopes
Soc. 1998, 120, 8168.
(36) Orlova, G.; Scheiner, S. J. Phys. Chem. A 1998, 102, 260 and 4813.
(37) Calhorda, M. J.; Lopes, P. E. M. J. Organomet. Chem. 2000, 609,
53.
Alkorta, I.; Elguero, J.; Foces-Foces
- I Alkorta
- I Rozas
- Elguero
Alkorta, I.; Rozas, I.; Elguero, J. Chem. Soc. ReV. 1998, 27, 163.
Alkorta, I.; Elguero, J.; Foces-Foces, C. Chem. Commun. 1996, 1633.
- S Grabowski
Grabowski, S. J. Chem. Phys. Lett. 2000, 327, 203.
- J Lundell
- M Petterson
Lundell, J.; Petterson, M. Phys. Chem. Chem. Phys. 1999, 1, 1691
- S Berski
- J Lundell
- Latajka
and Berski, S.; Lundell, J.; Latajka, Z. J. Mol. Struct. 2000, 552, 223.
- I I Padilla-Martínez
- M J Rosalez-Hoz
- H Tlahuext
- C Camacho-Camacho
- A Ariza-Castolo
- R Contreras
Padilla-Martínez, I. I.; Rosalez-Hoz, M. J.; Tlahuext, H.; Camacho-Camacho, C.; Ariza-Castolo, A.; Contreras, R. Chem. Ber. 1996, 129, 441.
- R Custelcean
- J E Jackson
Custelcean, R.; Jackson, J. E. Chem. ReV. 2001, 101, 1963.
- R J Bartlett
- D M Silver
Bartlett, R. J.; Silver, D. M. J. Chem. Phys. 1975, 62, 3258.