[show abstract][hide abstract] ABSTRACT: In the title co-crystal, 2C6H5NO·C4H4O4, two crystallographically different hydrogen-bonded trimers are formed, one in which the components occupy general positions, and one generated by an inversion centre. This results in the uncommon situation of Z = 3 for a triclinic crystal. In the formula units, mol-ecules are linked by O-H⋯N hydrogen bonds.
[show abstract][hide abstract] ABSTRACT: Co-crystallization of 4-nitrophenol (I) with five aminopyridines (4-aminopyridine 1, 3,4-diaminopyridine 2, 2,3-diaminopyridine 3, 3-aminopyridine 4, 2-amino-6-methylpyridine 5) and 2,4-diaminopyrimidine 6 resulted in six adducts with the ratio of components 2:1 in five and 1:1 in one final compounds. Single crystals were grown by slow evaporation technique using ethanol as a solvent. Five adducts with 1–5 crystallize in acentric P21 and Pna21 space groups, and one, 2(I)·6 – in centrosymmetric P21/c space group. Compounds 2(I)·1, 2(I)·2, 2(I)·3 are isomorphous, and demonstrate similar H-bonding patterns despite the differences in aminopyridine molecules. Compound 2(I)·5 is isomorphous to two previously reported compounds. Adducts 2(I)·1, 2(I)·2, 2(I)·3, 2(I)·5, 2(I)·6 represent organic salts composed of pyridinium/pyrimidinium cation, 4-nitrophenolate anion, and 4-nitrophenol neutral molecule. The H-bonded 4-nitrophenol–4-nitrophenolate anionic dimers were found in all compounds with 2:1 molar ratio. In adduct I·4 both molecules are in neutral form. The IR spectral data support crystallographic conclusions on salts formation. Plane wave pseudopotential density functional theory calculations were used to predict hyperpolarizability tensor components. Our calculations suggest 2(I)·3 as the best candidate for nonlinear optical materials (14 times more active than urea).
[show abstract][hide abstract] ABSTRACT: In the title salt, C5H8N3 (+)·C3H3O4 (-), the 3,4-di-amino-pyridinium cation is almost planar, with an r.m.s. deviation of 0.02 Å. The conformation of the hydrogen malonate anion is stabilized by an intra-molecular O-H⋯O hydrogen bond, which generates an S(6) ring. In the crystal, N-H⋯O hydrogen bonds link cations and anions into layers parallel to the ab plane.
[show abstract][hide abstract] ABSTRACT: The product of exfoliation and restacking of MoS2 in acidic conditions is studied in detail using X-ray powder diffraction, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The temperature dependence of powder patterns reveals that the heating of exfoliated-restacked MoS2 is a way to a new nanostructured MoS2-based layered material that remains nanosized even upon heating to 850 °C. Previously this material has been described as 2H-MoS2, but according to the X-ray diffraction (XRD) data, its structure cannot be correctly described by any of the ?usual? MoS2 polytypes. A model of the structure of the material describing its XRD patterns and thermal behavior is discussed in detail.
The Journal of Physical Chemistry C. 04/2013; 117(16):8509-8515.
[show abstract][hide abstract] ABSTRACT: The title natural compound, isolated from var. King Alfred crystallizes as a hemihydrate, CHNO·0.5HO, with four crystallographically independent dioxolophenanthridinone mol-ecules and two crystallographically independent solvent water mol-ecules in the asymmetric unit. All four crystallographically independent dioxolophenanthridinone mol-ecules are geometrically very similar and differ only in the orientations of the three hy-droxy groups at the terminal cyclo-hexene rings. The five-membered dioxolane ring has a planar conformation (the r.m.s. deviations are 0.010, 0.019, 0.025 and 0.004 Å, for the four crystallographically independent molecules), and the six-membered dihydro-pyridone and cyclo-hexene rings adopt sofa conformations in each mol-ecule. The flattened structure of each dioxolophenanthridinone mol-ecule is supported by a strong intra-molecular O-H⋯O hydrogen bond. The N atom has a slightly pyramidalized configuration. In the crystal, the dioxolophenanthridinone mol-ecules form layers parallel to (101) with O-H⋯O and N-H⋯O hydrogen bonds linking the dioxolophenanthridinone mol-ecules both within and between the layers and the water mol-ecules, forming a three-dimensional framework. The absolute configurations of the chiral centers are 2, 3, 4 and 4a.
[show abstract][hide abstract] ABSTRACT: In the title mol-ecule, CHN, intra-cyclic angles cover the range 117.15 (10)-124.03 (11)°. The N atoms of the amino groups have trigonal-pyramidal configurations deviating slightly from the pyridine plane by 0.106 (2) and -0.042 (2) Å. In the crystal, the pyridine N atom serves as an acceptor of an N-H⋯N hydrogen bond which links two mol-ecules into a centrosymmetric dimer. Inter-molecular N-H⋯N hydrogen bonds between the amino groups further consolidate the crystal packing, forming a three-dimensional network.
[show abstract][hide abstract] ABSTRACT: In the title mol-ecule, CHN, the endocyclic angles are in the range 118.43 (9)-122.65 (10)°. The mol-ecular skeleton is planar (r.m.s. deviation = 0.007 Å). One of the two amino H atoms is involved in an N-H⋯N hydrogen bond, forming an inversion dimer, while the other amino H atom participates in N-H⋯π inter-actions between the dimers, forming layers parallel to (100).
[show abstract][hide abstract] ABSTRACT: Three thermochromic phases (α, green; β, red; γ, yellow) and six polymorphic modifications (α(1), monoclinic, P2(1)/n, Z = 2; β(1), monoclinic, P2(1)/c, Z = 4; β(2), triclinic, P1̅, Z = 4; β(3), monoclinic, P2(1)/n, Z = 4; γ(1) and γ(2), tetragonal, P4(2)/n, Z = 4) have been found and structurally characterized for copper(II) diiminate Cu[CF(3)-C(NH)-CF═C(NH)-CF(3)](2) (1). The α phase is stable under normal conditions, whereas the high-temperature β and γ phases are metastable at room temperature and transform slowly into the more stable α phase over several days or even weeks. X-ray diffraction study revealed that the title molecules adopt different conformations in the α, β, and γ phases, namely, staircase-like, twisted, and planar, respectively. The investigation of the α, β, and γ phases by differential scanning calorimetry showed that the three endothermic peaks in the range 283, 360, and 438 K are present on their thermograms upon heating/cooling. The two peaks at 283 and 360 K correspond to the solid-solid phase transitions, and the high-temperature peak at 438 K belongs to the melting process of 1. The temperature and thermal effect of all the observed transitions depend on the prehistory of the crystalline sample obtained. A reversible thermochromic single-crystal-to-single-crystal α(1)⇌β(1) phase transition occurring within a temperature interval of 353-358 K can be directly observed using a CCD video camera of the X-ray diffractometer. A series of other solid-solid α(1)→γ(1), β(2)→γ(1), β(3)→γ(1), and γ(1)⇌γ(2) phase transitions can be triggered in 1 by temperature. It has been suggested that, under equilibrium conditions, the α(1)→γ(1) and β(2)→γ(1) phase transitions should proceed stepwise through the α(1)→β(1)→β(2)→β(3)→γ(1) and β(2)→β(3)→γ(1) stages, respectively. The mechanism of the phase transitions is discussed on the basis of experimental and theoretical data.
[show abstract][hide abstract] ABSTRACT: A variant structural skeleton of epipodophyllotoxin was synthesized and found to rival the natural cyclolignan in antiproliferative and microtubule destabilizing properties. This discovery leads to a new structural class of tubulin targeting agents.
Chemical Communications 09/2012; 48(84):10416-8. · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: 4H-Pyrano-[2,3-b]naphthoquinone is a structural motif commonly found in natural products manifesting anticancer activities. As part of a program aimed at structural simplification of bioactive natural products utilizing multicomponent synthetic processes, we developed a compound library based on this heterocyclic scaffold. We found that several library members displayed low micromolar antiproliferative activity and induced apoptosis in human cancer cells. Selected compounds showed promising activity against cancer cell lines resistant to proapoptotic stimuli, demonstrating their potential in treating cancers with dismal prognoses.
[show abstract][hide abstract] ABSTRACT: A series of 1,8-naphthalenedicarboximide derivatives containing substituents of different steric and electronic nature were
studied by X-ray diffraction analysis.Ab initio quantumchemical calculations in the HF/3–21G approximation demonstrated the high conformational flexibility of the imide
tetrahydro ring in the molecules of these compounds. The electronic nature of the substituents has no effect on the geometry
and conformational flexibility of naphthalenedicarboximides due to weak conjugation between the imide and naphthalene fragments
in the molecules. However, the steric effects of the bulky substituents noticeably affect the equilibrium geometry of the
imide ring by increasing its conformational flexibility.
Russian Chemical Bulletin 04/2012; 49(1):70-76. · 0.42 Impact Factor
[show abstract][hide abstract] ABSTRACT: The annular tautomeric equilibrium of two 4-cyano-3(5)-aminopyrazoles having hydrogen atom or methyl group in position 5(3) was studied by X-ray crystallography for the solid compounds and by DFT B3LYP/6-31G** and CBS-QB3 calculations for the free molecules. The 3-amino tautomer was found to be the more favorable form for the free molecules and the sole form in the solid state.
Journal of Molecular Structure 04/2012; 1014:63–69. · 1.40 Impact Factor
[show abstract][hide abstract] ABSTRACT: The results of the single crystal X-ray diffraction analysis of 2,5-diphenylphosphacymantrene (η5-C4H2Ph2P)Mn(CO)3 (1) and experimental charge density distribution study of [(η4-C4H2Ph2P(O)H)Mn(СO)3]−[NH2Et2]+ (2) are discussed. The resultant density was analyzed using the quantum theory of atoms in molecules (QTAIM). Here, we focused on the analysis of the interaction between the metal atom and the π-ligand depending on the mutual orientation of the Mn(CO)3 moiety and the heterocyclic fragment (cis and trans conformers). The electronic structures of cis and trans conformers of both the complexes 1 and 2 have also been studied by ab initio density functional theory calculations, showing rather a good agreement with the experiment. Redistribution of the electron density in the vicinity of the metal atom upon the reorientation of the carbonyl groups causes the changes in the geometric and electronic characteristics of the heterocycle. The most significant changes occur in the molecular topology, in particular, in the connectivity of the metal atom with the π-ligand.
Journal of Molecular Structure 04/2012; 1014:81–91. · 1.40 Impact Factor
[show abstract][hide abstract] ABSTRACT: The structures of tricarbonyl(formylcyclopentadienyl)manganese(I), [Mn(C(6)H(5)O)(CO)(3)], (I), and tricarbonyl(formylcyclopentadienyl)rhenium(I), [Re(C(6)H(5)O)(CO)(3)], (II), were determined at 100 K. Compounds (I) and (II) both possess a carbonyl group in a trans position relative to the substituted C atom of the cyclopentadienyl ring, while the other two carbonyl groups are in almost eclipsed positions relative to their attached C atoms. Analysis of the intermolecular contacts reveals that the molecules in both compounds form stacks due to short attractive π(CO)...π(CO) and π(CO)...π interactions, along the crystallographic c axis for (I) and along the  direction for (II). Symmetry-related stacks are bound to each other by weak intermolecular C-H...O hydrogen bonds, leading to the formation of the three-dimensional network.
[show abstract][hide abstract] ABSTRACT: Stereoregular cyclolinear organosiloxane copolymers containing vinyl groups with diorganosiloxane spacers as well as cyclohexasiloxane fragments were synthesised. Comb-shaped liquid crystalline (LC) cyclolinear polymethylsiloxanes with mesogenic side groups were prepared by hydrosilylation of stereoregular cyclolinear organosiloxane copolymers with (4′-cyanobiphenyl-4-yl)-11-(1,1,3,3-tetramethyldisiloxyl)undecanoate in the presence of the Karstedt catalyst. The chemical structure of the copolymers synthesised was confirmed by proton and silicon nuclear magnetic resonance spectroscopies and infrared spectroscopy. Their phase behaviour was characterised by differential scanning calorimetry, X-ray analysis and optical polarising microscopy. It was shown that the appearance of the LC state, the temperature range of its existence and polymesomorphism are determined by the molecular mass of the copolymer and by the content of the mesogenic groups. The introduction of three mesogenic groups per monomer unit results in polymesomorphic transitions. The tacticity of the backbone influences the interchain distances in the comb-shaped LC cyclolinear methylsiloxane copolymers. Studying the Langmuir films of the stereoregular LC methylsiloxane copolymers revealed that different types of molecular arrangements could be observed depending on the number of mesogenic groups attached. LC copolymers having three mesogens per monomer unit demonstrate a two-stage monolayer collapse.
[show abstract][hide abstract] ABSTRACT: The review generalizes the results of structural studies of crystals of organic and organometallic compounds by modern quantum chemical calculations within the framework of the density functional theory reported in the last decade. Features of the software for such calculations are discussed. Examples of the use of quantum chemical calculations for the studies of the electronic structure, spectroscopic and other physicochemical properties of molecular crystals are presented. The bibliography includes 223 references.
Russian Chemical Reviews 01/2012; 81(2):105-129. · 2.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: Six new derivatives of the previously reported chromophore 2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (OH1) with potential application in electrooptics were synthesized and their crystal structures characterized using a single crystal X-ray technique. The presented chromophores have a D–π–A structure with a phenol donor, ring locked polyene conjugated bridge and dicyanomethylydene acceptor. In order to potentially alleviate problems with the quality of melt grown films of OH1, the melting point was tuned through the introduction of alkoxy groups of various lengths and onto various positions on the chromophore core as well as through the modification of the bridge structure. We show that the melting point of these materials can be significantly decreased with the increased number of carbon atoms in alkoxy group. However, the molecular arrangement was found to be highly sensitive to the addition of substituents, and regardless of the size and position of the alkoxy groups, all presented chromophores formed centrosymmetric structures. The distinctions in crystal packing are explained by the mutual arrangement of donor (OH) and H-acceptor (OAlk, C(CN)2) groups in the molecules. Static first order hyperpolarizabilities along with molecular geometry in isolated state were calculated using DFT.
Journal of Molecular Structure 12/2011; · 1.40 Impact Factor
[show abstract][hide abstract] ABSTRACT: The conformational effects in bicyclo[3.3.1]nonanes, while thoroughly studied, have not yet received the full theoretical explanation. R. F. W. Bader's quantum theory of atoms in molecules presents unique opportunities for studying the stereoelectronic interactions (SEI) and weak intramolecular bonding leading to these effects. Here, we report the study of 3,7-dithia-1,5-diazabicyclo[3.3.1]nonane by means of the topological analysis of the calculated (MP2(full)/6-311++G**) and experimental (X-ray derived) charge density to reveal the origins of the so-called "hockey sticks" effect observed in similar compounds. A new explanation of the relative stability of bicyclo[3.3.1]nonane conformers based on the analysis of the QTAIM atomic energies is given. The H···H and S···S interactions in bicyclo[3.3.1]nonane and its dithia derivatives are shown to be significant factors contributing to the differences in the relative stability of the conformers.
The Journal of Physical Chemistry A 09/2011; 115(45):12738-45. · 2.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: Experimental and calculated electron density functions ρ(r) of the title compound in the crystal were obtained. These were compared with ρ(r) for an isolated dimer. Application of the `Atoms in Molecules' theory allowed the visualization of the electron lone pair (Lp) of tin(II) and the calculation of some bond energies and all atomic charges. The stereochemical activity of the Lp was demonstrated and its volume was estimated to be approximately 10 Å(3). The energies of N→Sn and Sn-O bonds were found to be 13-18 and 25-52 kJ mol(-1). According to the experimental, AM05-PW and PBE0/6-311G(d,p) calculation data, µ(2)-2-(dimethylamino)ethoxoate accepts 0.68, 0.45 and 0.40 e from the Sn atom. Using the example of µ(2)-2-(dimethylamino)ethoxoates and complexes of bis(n-butyl)tin(IV) it was demonstrated that the more screened the Sn atom, the better the catalytic activity of its complex in polyurethane synthesis.