![Schematic potential energy curves [CASSCF/NBO(a,a*)2/631G*] for dissociation of B-O-B-O and O-B-B-O to 2B-O fragments, showing the avoided crossing barrier associated with reorganization of Lewis structure in the B-O-B-O case.](https://www.researchgate.net/profile/Frank-Weinhold-2/publication/234974264/figure/fig2/AS:654411370082306@1533035237799/Schematic-potential-energy-curves-CASSCF-NBOa-a2-631G-for-dissociation-of-B-O-B-O_Q320.jpg)
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Boron oxides: Ab initio studies with natural bond orbital analysis
Abstract and Figures
We employ ab initio theory and natural bond orbital (NBO) analysis to describe the structure, energetics, vibrational properties, and bonding in small boron oxides, BmOn, supplementing recent studies on isovalent aluminum oxide clusters, Al2On, in order to extend the overview of bonding tendencies in group IIIA metal oxides. The comparison of analogous boron and aluminum species reveals many surprising differences, such as the V‐shaped (M=B) vs linear (M=Al) geometry of M2O3, the altered tendency toward cyclic structures (higher for M2O2 with M=Al, for M3O3 with M=B), and the diminished role of electron correlation in the boron congeners. Correlation effects are examined by a recently introduced selective, localized multiconfigurational approach. Differences in bonding patterns are traced to basic hybridization and electronegativity shifts (reduced ionic character of B–O vs Al–O bond). Detailed comparisons with recent experimental BmOn data (including isotopomer ir shifts) provide additional support for theoretical assignments in corresponding aluminum species, where significant disagreements between theory and experiment persist.
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... The infrared absorption spectra of BBRTIL, 2-amino-1-butanol, and solid B 2 O 3 have been investigated in the region 400-4000 cm −1 . The structure of the B 2 O 3 molecule, which is used as a boron precursor in ionic liquids, has been the subject of debate for many years and is now accepted to have a V-shaped pattern (it is a triangular planar molecule with boron-oxygen double bonds with symmetry of C2ν symmetry) [29,30] in the most stable plane. Structural effects are of great importance in spectral studies. ...
... In Table 1, the physical properties of BBRTIL and other components are given. The structure of the B 2 O 3 compounds is a V-shaped pattern (it is a triangular planar molecule with boron-oxygen double bonds with symmetry of C2ν) [29,30] in the most stable plane. As seen in Table 1, in the structure of B 2 O 3 , which is one of the components of BBRTIL, all boron atoms are equivalent, and only three equal oxygen atoms are coordinated to two boron atoms [16,29,30,35]. ...
... The structure of the B 2 O 3 compounds is a V-shaped pattern (it is a triangular planar molecule with boron-oxygen double bonds with symmetry of C2ν) [29,30] in the most stable plane. As seen in Table 1, in the structure of B 2 O 3 , which is one of the components of BBRTIL, all boron atoms are equivalent, and only three equal oxygen atoms are coordinated to two boron atoms [16,29,30,35]. Another component, 2-amino-1-butanol, is coordinated with hydroxide, amine, and methyl groups in its structure. ...
In the present work, a new boron-based room-temperature ionic liquid (BBRTIL) is reported. An ionic liquid based on the boron cation was synthesized by an easy metathesis procedure yielding clean products. The composition, thermal behavior, physical, and electrochemical properties of the BBRTIL were identified by nuclear magnetic resonance spectra (NMR), Fourier transform infrared (FTIR) thermogravimetric analysis (TGA), linear sweep voltammetry (LSV), and cyclic voltam-metry (CV), respectively. NMR and FTIR have confirmed the structure formation of 0.3-0.4-mm-sized B 2 O 3-based BBRTIL. Furthermore, the correlation between the electrochemical stability and the identified electrolyte equilibrium species was investigated via voltammetry. This procedure, in the future, could be an original alternative to the deposition of elemental boron through easy, one-step synthesis from high-temperature molten salt electrolysis.
... 4,7,8,10,12,14,16,18,20,22,26) have been also reported [103][104][105]. A large number of studies have been done on B2O suboxide [103,[106][107][108][109][110][111]. It was reported [103] that B2O with a graphite-like structure can be obtained as a result of the boron interaction with B2O3 at pressures to 7.5 GPa and temperatures to 2100 K. B2O diamond phase was observed during oxidation of BP with CrO3 at 4 GPa and 1500 K [106,107]. ...
... According to the literature data [103,[106][107][108][109][110], In this chapter we will present a description of our XRD measurements of β-B2O3 under high pressure in order to refine its EoS. It will be followed by the phonon studies of β-B2O3 at ambient and under high pressures. ...
This thesis deals with the study of the boron chalcogenides under extreme conditions. After a short review of boron and boron compounds under extreme conditions (Chapter I), the experimental part (Chapter II) provides a brief description of the high-pressure devices used in this PhD work. The employed analytical techniques are described as well as the main principles of the performed ab initio theoretical calculations. The following part is devoted to our experimental and theoretical studies of β-B2O3 and r-BS. Chapter III presents the results of in situ high pressure XRD and phonon measurements (Raman and IR) of β-B2O3 at room temperature. The experimental data were considered and completed with results of ab initio calculations. Based on the total obtained dataset the complete description of β-B2O3 structure change and phonon behavior under compression at room temperature are detailled. Chapter IV contains the results of in situ high pressure XRD and vibrational spectroscopy studies on r-BS at room temperature. In combination with results of theoretical calculations the structure and phonon nature of r-BS in a wide pressure range at ambient temperature are described. Also, the formation of a new metastable high-pressure phase of BS is described and its probable structure and EoS are discussed. The last part (Chapter V) concerns the primary in situ XRD HP-HT studies in B-Se system. Based on the results of XRD and Raman measurements of the recovered samples, a new compound was synthesized. This compound was found to be metastable at ambient conditions. Its probable chemical composition and structure are discussed.
... Among B-rich compounds, boron suboxides (B x O, x>1) have a great attention in the industrial areas due to their promising and outstanding properties such as high hardness, low density, high tensile strength, semiconductivity, high chemical stability and large bulk moduli. B 2 O phase has a special place as an "unsymmetrical" analogue of carbon [18][19][20][21]. Even though the high temperature/pressure syntheses of B 2 O in both graphite-like [18,20] and diamond-like [20] was discussed, the later studies propounded that these phases of B 2 O were not stable [22,23]. ...
... No symmetric BB vibrations were found for all studied neutral molecules except in the region 1700 cm À1 <m< 1800 cm À1 ( Table 1) that agree with a previous estimation [28]. Higher frequency for a BB containing molecule was detected for B 2 O 2 (OBBO) at 2060 cm À1 , but it must be interpreted rather as an in-phase O@B stretch than a BB vibration [29][30][31]. ...
Coordination of a B2 fragment by two σ-donor ligands could leads to complexes with a formal triple B≡B bond L→B≡B←L. Formation of L-B σ-bond leads to excess electrons around the B2 central fragment. A subsequent direct π-charge transfer from B≡B moiety to the ligands L is a necessary condition for incorporation of BB fragment to the conjugated LBBL system. Quantum-chemical calculations (DFT, CCD and CAS) show that the stabilization of a linear L-BB-L structure is possible but is accompanied by lowering of the B-B bond order. The ammonia-boryne structure H3N→BB←NH3, which is studied as a model system, shows a perfect triple BB fragment relative to other LBBL adducts. The comparison of the conjugation between the B2 fragment and two types of σ-donor ligands, with or without π-back-donation, provides an indication of the character of BB multiple bond. Three studied boryne molecules are calculated to have a high barrier for dissociation XXBBXX→XX+BBXX, yet a high reactivity of these compounds is indicated by the low-lying excited states of borynes (ΔES0-S1<1.5 eV). The largest gap ΔES0-S1~2.6 eV is calculated for the room temperature stable bis-NHC-boryne.
... Therefore, it is not possible in principle to derive an analytical expression concerning this correlation by means of a rigorous analytical mathematical treatment. Also, it is well known [69,70] that the electronic correlation included in NBOs is smaller than in canonical delocalized MOs. In this section we calculate explicitly the correlation content and the unpaired electrons of both bonding and antibonding NBOs; we are looking to find a numerical law concerning the unpaired electron populations with respect to the one-electron ones. ...
Adopting the 2nd order Density Matrix level, the usual Natural Bond Orbital (NBO) populations are explored accordingly: they are split into paired and unpaired (defined as ''the simultaneous occurrence of an electron and a hole of opposite spins in an orbital ") populations. The Coulomb correlations and the unpaired electron populations are calculated explicitly, revealing new and unexplored features for NBO sets. It is shown that the 'natural' origin of these sets implies that the intra-pair correlations, and hence the unpaired electrons, are minimal in NBOs. The unpaired electron populations in valence NBOs provide a criterion for the quantal/classical, and hence for the active/inert behavior of bonds and molecules; this is tested in several well known prototypical systems. The interaction of two unpaired electrons between bonding and antibonding NBOs of two different bonds gives rise to a Heitler-London structure between the two bond regions; its weight (probability), and the included Coulomb and Fermi correlations are calculated in the basis of a spin-dependent formalism of generalized Density Matrices.
... Therefore, it is not possible in principle to derive an analytical expression concerning this correlation by means of a rigorous analytical mathematical treatment. Also, it is well known [69,70] that the electronic correlation included in NBOs is smaller than in canonical delocalized MOs. In this section we calculate explicitly the correlation content and the unpaired electrons of both bonding and antibonding NBOs; we are looking to find a numerical law concerning the unpaired electron populations with respect to the one-electron ones. ...
Some elements of the mathematical logic and the contributions of key characters involved in development of Natural Bond Orbital (NBO) concepts, as well as their numerical implementation in successive NBO program versions, are recounted in retrospective historical fashion.
Boron oxide clusters are electron‐deficient species with novel structures and bonding, in which the emergence of rhombic and boroxol rings is of interest. We report on computational prediction of the global‐minimum structures for two boron oxide clusters: B4O5 and B4O5−. These structures differ distinctly, as established through global machine searches and electronic structure calculations at B3LYP and single‐point CCSD(T) levels. While B4O5 neutral cluster has a rhombic B2O2 core, the B4O5− anion features a boroxol B3O3 ring. One electron completely changes the potential landscapes. Bonding analyses show that the 4π electron‐counting is crucial for a rhombic BO cluster, in contrast to π sextet for a boroxol ring, which underlies the competition between rhombic and boroxol rings in B4O5/B4O5− clusters. A possible pathway for rhombic‐to‐hexagonal transformation is proposed based on intrinsic reaction coordinate calculations. Anion B4O5− cluster, a new member of the inorganic benzene family, is among the smallest BO species with a free‐standing boroxol ring, governed collectively by composition and electron‐counting. The global minimum of B4O5− cluster features a six‐membered boroxol ring, being stabilized by 6π aromaticity. Its neutral counterpart is governed by the four‐center four‐electron “o‐bond” with 4π electrons. The process causes an important structural rearrangement and leads to a rhombic neutral structure instead. One electron overturns the potential landscapes.
Recent joint experimental and theoretical investigations show that seashell-like C2 B28 is the smallest neutral borospherene reported to date, while seashell-like Cs B29-(1-) as a minor isomer competes with its quasi-planar counterparts in B29- cluster beams. Extensive global minimum searches and first-principles theory calculations performed in this work indicate that, with two valence electrons detached from B29-, the B29+ monocation favors a seashell-like Cs B29+ (1+) much different from Cs B29-(1-) in geometry which is overwhelmingly the global minimum of the system with three B7 heptagonal holes in the front, on the back, and at the bottom, respectively, unveiling an interesting charge-induced structural transition from Cs B29- (1-) to Cs B29+(1+). Detailed bonding analyses show that, with one less σ bond than B29-(1-), Cs B29+(1+) also possesses nine delocalized π-bonds over its σ-skeleton on the cage surface with a σ+π double delocalization bonding pattern and follows the 2(n+1)2 electron counting rule for 3D spherical aromaticity (n=2). B29+(1+) is therefore the smallest borospherene monocation reported to date which is π-isovalent with the smallest neutral borospherene C2 B28. The IR, Raman, and UV-vis spectra of B29+(1+) are computationally simulated to facilitate its spectroscopic characterizations.
A density functional theory investigation on the geometries, electronic structures, and electron detachment energies of BS -, BS 2-, B(BS) 3- and B(BS) 3- has been performed in this work. The linear ground-state structures of BS - (C ∞v, 1Σ +) and BS 2- (D ∞h, 1Σ g+) prove to be similar to the previously reported BO - and BO 2- with systematically lower electron detachment energies. Small boron sulfide clusters are found to favor the formation of -B=S groups which function basically as σ-radicals and dominate the ground-state structures of the systems. The perfect linear B(BS) 2- (D ∞h, 3Σ g) and beautiful equilateral triangle B(BS) 3- (D 3h, 2A 1") turn out to be analogous to the well-known C 2v BH 2 and D 3h BH 3, respectively. The electron affinities of BS, BS 2, B(BS) 2 and B(BS) 3 are predicted to be 2.3, 3.69, 3.00 and 3.45 eV, respectively. The electron detachment energies calculated for BS -, BS 2-, B(BS) 2-, and B(BS) 3- may facilitate future photoelectron spectroscopy measurements to characterize the geometrical and electronic structures of these anions.
The CASSCF method was applied to compute the potential energy curves for the lowest 2.4Σ+, 2.4Π and 2.4Δ states of BO, and the lowest 2Σ+, 2Π and 2Σ− states of LiO. The curves were obtained for internuclear distances ranging from 2 to 25 au using a medium-sized basis set of CGTOs. The results were compared with previous accurate ab initio calculations and available experimental data. The changes in the wavefunction structure along the potential curves were discussed.
Ab initio gradient calculations of the geometry and vibrational force field of B2O3 have been carried out at the double zeta plus polarization level of the RHF method, with the value obtained for the inversion barrier being checked with the MC—SCF technique. B2O3 is a planar molecule of C2V symmetry with equilibrium BO and BO bond lengths of 1.33 and 1.20 Å, respectively. The central angle of 136° is extremely flexible, with an inversion barrier of only 2.4 kcal mol−1 at the linear geometry. The OBO group is bent by 2°. The complete quadratic force field has been determined along with the most important cubic constants, and the vibrational spectrum has been predicted. The main features of the structure obtained in a recent electron diffraction study are confirmed, but the vibrational force field resulting from the analysis of that work appears to be seriously flawed. The expected vibrational frequencies and the intensifies of the infrared transitions are also computed and compared with the limited experimental data presently available.
The He i photoelectron spectrum of B2O2 is presented. A comparison of abinitio molecular orbital calculations and the observed spectrum provides the most conclusive evidence to date that the geometrical structure is D∞h O–B–B–O. Even though the experiment is conducted at 1200 °C, vibrational structure is evident in the first two bands. A complex Franck–Condon fitting is used to infer the geometrical changes occurring when the various ionic states are formed. The results are in fairly good agreement with ΔSCF calculations. The orbital ordering in B2O2, πg,πu,σg,σu differs from that in the isoelectronic molecule C2N2.
Boron atoms from Nd:YAG laser ablation of the solid have been codeposited with Ar/O2 samples on a 11±1 K salt window. The product infrared spectrum was dominated by three strong 11B isotopic bands at 1299.3, 1282.8, and 1274.6 cm−1 with 10B counterparts at 1347.6, 1330.7, and 1322.2 cm−1. Oxygen isotopic substitution (16O18O and 18O2 ) confirms the assignment of these strong bands to ν3 of linear BO2. Renner–Teller coupling is evident in the ν2 bending motion. A sharp medium intensity band at 1854.7 has appropriate isotopic ratios for BO, which exhibits a 1862.1 cm−1 gas phase fundamental. A sharp 1931.0 cm−1 band shows isotopic ratios appropriate for another linear BO2 species; correlation with spectra of BO−2 in alkali halide lattices confirms this assignment. A weak 1898.9 cm−1 band grows on annealing and shows isotopic ratios for a BO stretching mode and isotopic splittings for two equivalent B and O atoms, which confirms assignment to B2O2. A weak 2062 cm−1 band grows markedly on annealing and shows isotope shifts appropriate for a terminal–BO group interacting with another oxygen atom; the 2062 cm−1 band is assigned to B2O3 in agreement with earlier work. A strong 1512.3 cm−1 band appeared on annealing; its proximity to the O2 fundamental at 1552 cm−1 and pure oxygen isotopic shift suggest that this absorption is due to a B atom–O2 complex.
A new class of gas-phase boron oxides has been produced by particle-induced desorption from vitreous boron trioxide. Six distinct homologous series of boron oxide cations were identified by fast atom bombardment mass spectrometry and studied by collision-induced dissociation. Common structural features within each series were confirmed by the identification of common collision-induced fragments. Two important series are described by the general formulas (B/sub 2n+1/O/sub 3n+1/)/sup +/ (n = 0.6) and (B/sub 2n+2/O/sub 3n+3/)/sup center dot +/ (n = 0-4). Ions of the first series show the highest relative abundance in the desorption spectrum of boron trioxide and are the most abundant ionic fragments in the collision spectra of nearly all boron oxide cations. The most important of these is (BâOâ)/sup +/, which is proposed to exist as (O/double bond/B/emdash/O/emdash/B/emdash/O/emdash/B/double bond/)/sup +/ and is stabilized by extensive resonance and electron sharing. Gas-phase boron oxide cations are proposed to exist with boron limited to two- or three-coordination with oxygen. The ions are thus built upon integral BOâ triangles, and branches are terminated with -B/double bond/O units.
A source configuration that lies intermediate to a low-pressure effusing molecular beam and a high-pressure flow device is used to generate boron cluster molecules in a highly oxidizing environment. Using this source operating in an NOâ oxidative environment, the authors generate a chemiluminescent emission spectrum, which they attribute to the asymmetric BBO molecule. The observed spectrum is characterized by a strong ..delta nu.. = ..delta nu.. = 40 cm/sup /minus/1/ sequence grouping and a weaker ..delta nu.. = + 1 sequence (..delta nu.. = 40 cm/sup /minus/1/), 440 cm/sup /minus/1/ to higher energy. A second sequence with ..delta nu.. /approximately/ 142 cm/sup /minus/1/ is also observed. Combining the 440-cm/sup /minus/1/ upper-state frequency with the 142-cm/sup /minus/1/ sequence structure implies a lower-state frequency of /approximately/ 582 cm/sup /minus/1/ for the B-B stretch, consistent with ab initio calculation.
Boron atoms from YAG laser ablation of the solid have been reacted with water vapor and the products condensed with excess argon at 12 K. Reagent isotopic substitution (H2O, (H2O)-O-18, D2O, B-10, B-11) and variation of water and boron concentrations have led to identification of the major products as HBO and BO. Further reaction with excess boron atoms gave the new symmetrical BOB molecule; isotopic data verify the stoichiometry and predict a nearly linear molecule. No evidence was found for the insertion product HBOH. The calculated activation energy for the insertion reaction (12 kcal/mol) requires hot boron atoms and reaction above the surface of the matrix, which precludes relaxation of the energized (HBOH)* product by the matrix and leads to the BO and HBO decomposition products.
Ab initio molecular orbital theory at the HF/6-31G* level has been used to investigate the structures of Lewis acid/base adducts of boron hydrides with argon and a variety of substrates that may be encountered in the mechanism for the oxidation of diborane. By use of fourth-order Moller-Plesset theory, i.e., MP4SDTQ, correlation effects are calculated at the HF/6-31G* geometries. Borane was found to form stable adducts with dioxygen, hydroxyl radical, O(3P) atom, and H-B = O. Structures of isomeric forms of HBO, H2BO, H3BO, H3BO2, H5B2OH, H4B2(OH)2, H5B2O, H5B2O2, H4B2O, and cyclic (HBO)3 were investigated. Evidence is presented for Lewis acid/base adducts with BH2 radical and some oxygenated boranes. The number and stability of these adducts suggest that the mechanism of the oxidation of diborane is much more complicated than that of ethane where adduct formation can be neglected.
The following conclusions may be listed. 1. The octet rule is found to be equivalent to the condition that the number of unshared electrons in a valence-bond structure be as small as possible, or, when this number is zero, to the condition that the number of three-centered bonds be as large as possible. 2. For a molecule that is not electron-deficient, the number of pairs of electrons in two-centered bonds is (4N + n) - (1/2)V. This expression incorporates (a) the assumption of atomic orbitals and of their overlap to form two- and three-centered bonds (four-and other multicentered bonds are unlikely among s-p hybrid orbitals, on steric grounds), (b) the Pauli exclusion principle (subscripts ≤ 2), (c) the efficacy of the periodic classification of the elements (i.e., the neglect of all inner-shell electrons in the computation of V), (d) the neglect of all atomic orbitals with two or more nodes (i.e., the neglect of 3d orbitals in the computation of Σ for first-row elements), (e) the cardinal tenet of quantum mechanics that the energy be minimized, and (f) recognition of the fact that item (e) implies that the number of unshared electrons should be as small as possible. It may be added that expression 11 incorporates Zachariasen's rules (318). 3. A molecule is electron-deficient if the number of valence electrons V is less than 4N + 2 if N is even or 4N + 4 if N is odd, or if V < Σ. 4. The number of three-centered bonds per heavy atom in the hydride of an element for which Ut = 0 is equal to 4 less the group number of the element. 5. A covalent molecule that contains a total of twelve or twenty electrons cannot satisfy the octet rule. This review consists of two interwoven parts. One part, which may be considered independently of the other part, consists of a collection of selected experimental data on bond angles, bond lengths, inductive constants, dipole moments, force constants, ionization potentials, and heats of addition. The other part, which is more provisional, is an attempt to review in nonmathematical terms a self-consistent interpretation of these data. It is concluded that between the customary complexities of descriptive chemistry and the mathematical complexities of pure quantum chemistry there lies, rooted in the other two and complementary to them, a domain of pragmatic chemical theory that encompasses two familiar concepts, valence-bond structures and orbital hybridization, which separately from their inception and recently in union have proven useful in understanding and establishing correlations among molecular properties.