Home – Home – Jornals – Journal of Structural Chemistry 2011 number 4

Within the theory of coupled clusters, it is proposed to use the orbital basis set of ethylene molecules in the π electron calculations of the polarizabilities and hyperpolarizabilities of conjugated systems. Test calculations show high accuracy of the method in comparison with the full configuration interaction method.

A comparative ab initio quantum chemical study of methanol interaction with potassium and rubidium hydroxides surrounded by DMSO molecules is performed. The reaction profiles of the formation of a nucleophilic particle in the direct interaction of methanol with an undissociated molecule of alkali metal hydroxide are considered. The levels of the description of the reacting system by different cluster continuum models are compared.

An ab initio quantum chemical study of the reaction profiles of the nucleophile particle formation in the interaction of methanol, methanthiol, and acetoxime with an undissociated molecule of alkali metal hydroxide is performed for the gas phase and also with the explicit inclusion of a dimethyl sulfoxide molecule into the calculation and with allowance made for solvation effects within the continuum model.

The vibration-rotation energy level spacings of homo- and heteronuclear rare gas dimers are calculated for some more common analytical intermolecular potential energy functions in
a unified way by employing the discrete variable representation (DVR) method.

In this paper, a first-principles study on the stability, electronic and magnetic properties of MRh₁₂ (M = Rh, Fe, Co and Ni) clusters is performed. By optimizing the geometrical structure, we find that MRh₁₂ clusters change from a perfect icosahedron to a distorted structure and have an obvious bond length contraction as compared with the corresponding bulk phase; FeRh₁₂, CoRh₁₂, and NiRh₁₂ clusters are more energetically stable than the RhRh₁₂ cluster. The effect of the impurity M on the density of states, valence band width, HOMO and LUMO for MRh₁₂ clusters is not significant, but when the central Rh atom is substituted with M, the magnetic moment of MRh₁₂ reduces dramatically. The Mulliken population analysis indicates that there are more charge transfers from other orbitals to Rh4d and M3d orbitals, and the spd hybrid effect in d orbitals of MRh₁₂ clusters is stronger than that in the RhRh₁₂ cluster. this situation means that the unpaired d electrons have more chance to be paired, and the magnetic moments of MRh₁₂ clusters can be reduced reasonably.

The nature of [HB≡CH]^-, [H₂B=CH₂]^-, and boratabenzene interactions with alkaline and alkaline earth metals are studied by ab initio calculations. The interaction energies are calculated at the B3LYP/6-311++G(d,p) level. The calculations suggest that the cation size and charge are two influential factors that affect the nature of the interaction. AIM and NBO analyses of the complexes indicate that the variation of densities and the extent of charge transfers upon complexation correlate well with the obtained interaction energies.

A combined gas electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pVTZ, B3LYP/cc-pVTZ, midix (Cl), and MP2/cc-pVTZ) study of the structure of a 2-NO₂-C₆H₄-SO₂Cl molecule is performed. It is found experimentally that at a temperature of 345(5) K the gas phase contains two conformers of the C₁ symmetry. Conformer I with a nearly perpendicular arrangement of the S-Cl bond with respect to the benzene ring plane (the C(NO₂)-C-S-Cl torsion angle is 84(3)°) is contained predominantly (69(12)%). In conformer II, the S-Cl bond is located near the benzene ring plane (the C(NO₂)-C-S-Cl angle is 172(3)°). The following experimental internuclear distances (Å) are obtained for conformer I: r_h1(C-H) = 1.064(15), r_h1(C-C)_av = 1.397(3), r_h1(C-S) = 1.761(6), r_h1(S-O)_av = 1.426(4), r_h1(S-Cl) = 2.043(5), r_h1(N-O)_av = 1.222(4), r_h1(C-N) = 1.485(16). In both conformers, the NO₂ group is turned by more than 30° relative to the benzene ring plane.

Rare-earth chromium borates RCr₃(BO₃)₄, where R = La-Er, obtained as a result of spontaneous solution-melt crystallization and belonging to two polytypic modifications (R32 (D) and С2/с (C) space groups) are studied by infrared spectroscopy with the factor group analysis of vibrations. Borates with R = La-Nd are shown to crystallize in the monoclinic С2/с space group. Borates with R = Sm-Er in the 1:1 ratio of batch and solvent form rhombohedral (R32 space group) and monoclinic (С2/с space group) phases at the 2.3:1 ratio, except EuCr₃(BO₃)₄ and GdCr₃(BO₃)₄ that have the rhombohedral structure under all crystallization conditions. Both rhombohedral and monoclinic polytypes may contain oppositely ordered layers. Y-, Tm-, Yb-, Lu-chromium borates are not formed.

Based on the corrected phase diagrams proper growth conditions for Li₂Zn₂(MoO₄)₃ crystals are selected. Large crystals (up to 100 mm), both impurity-free and activated by transition metal ions (Cu, Cr), are grown by the low-gradient Czochralski method. By the EPR method the charge state and structural position of copper and chromium ions are determined. The performed studies of luminescent properties show that for impurity-free crystals luminescence with λ = 388 nm with a two-exponential luminescence decay with τ₁ = 2 ns and τ₂ = 6 ns is observed at room temperature. At 77 K for both impurity-free crystals and those activated with transition metal ions luminescence with λ = 560 nm and the luminescence lifetime τ = 100 ns is observed, the intensity of luminescence with λ = 560 nm depending on the nature and concentration of transition metal ions. Cation vacancies responsible for the charge compensation of impurity transition metal ions are assumed to be also responsible for low-temperature luminescence.

Trichlorfon or O,O-dimethyl-(2,2,2-trichloro-1-hydroxyethyl) phosphonate is an organophosphorus insecticide with cholinesterase inhibitor activity that has been widely used in protection of field and fruit crops. Trichlorfon rearranges to other more toxic organophosphate insecticides (such as dichlorvos at pH 6-8) in aqueous media. Trichlorfon is a thermally labile compound that cannot be easily determined by gas chromatography coupled with mass spectrometry (GC-MS) and has no functional group for sensitive detection by high performance liquid chromatography (HPLC). In this study, ³¹P dynamic nuclear magnetic resonance is used to elucidate the stability of trichlorfon and derivatives. These spectrums are compared with the theoretical studies with the Gaussian software to determine the stability and identify the structure. Two derivatives are identified by this method.

The extractability of palladium nitro complexes with the charge state of sulfur and oxygen atoms in thiacalix[4]arenas in the cone and 1,3-alternate conformations are compared. The results of X-ray photoelectron and X-ray emission studies indicate the presence of considerable electron density on the bridging sulfur atoms, which is due to the contribution of the sulfur 3p AO to the upper occupied MOs of molecules. A series of changes in the electron density on sulfur atoms in the order calixarene thioethers > thiacalixarenes > dialkylsulfides ((С₁₀Н₂₁)₂S) > (C₆H₅)₂S not completely coincide with changes in their extrability, which can be caused by different nature and stoichiometry of the formed palladium complexes.

The properties of an expansion of the statistical sum of a simple liquid with respect to the potential in thermodynamic perturbation theory are analyzed. The coefficients of this expansion are determined by the unperturbed potential, depend on temperature and density, and can be calculated by means of mathematical modeling. It is shown here that the derivatives of these coefficients with respect to temperature and density are expressed through the higher expansion coefficient (these relations are usually called a hierarchy of equations). These coefficients determine the expansion of the Helmholtz free energy and RDF with respect to the perturbation potential. The thermodynamic characteristics of the system (entropy, internal energy, pressure) are expressed through both the differential relations for the Helmholtz free energy and the integral expressions containing RDF. It is found that the hierarchy of equations obtained in this work makes these different methods equivalent. This is important for the application of thermodynamic perturbation theory because it becomes unnecessary to model any other equilibrium properties of the system apart from the expansion coefficients.

The relations for the calculation of the partial molar volumes of NaCl, NaBPh₄, and Ph₄AsCl in an aqueous urea solution are obtained. The salt characteristics are divided into ionic components. Different methods of the division are discussed. It is shown that the hydration numbers of Na⁺ and Cl⁻ ions decrease with increasing urea concentration; therewith, the dehydration of Cl⁻ ion occurs relatively faster.

The results of the investigation of the chemical constitution and structure of (HfO₂)_x(Sc₂O₃)_1-x thin films are reported. The films are obtained by chemical vapor deposition (CVD) from hafnium 2,2,6,6-tetramethyl-3,5-heptandionate (Hf(thd)₄) and scandium 2,2,6,6-tetramethyl-3,5-heptandionate (Sc(thd)₃) coordination compounds. It is demonstrated by powder X-ray diffraction and infrared spectroscopy that depending on the scandium content in the films the structure is changed from monoclinic to cubic. Voltage-capacity dependences of test Al/(HfO₂)_x(Sc₂O₃)_1-x/Si structures are used to calculate the dielectric constant of the films. For the films with the cubic structure it is found that k = 21, while for the films with the monoclinic structure k = 9.

(C₈H₁₁N)₂·Zn(OAc)₂ (1a), (C₈H₁₁N)₂·Cu(OAc)₂ (1b), and (C₈H₁₁N)₂·CuCl₂ (1c) complexes are synthesized by a simple one-pot method. The crystal structures of 1a, 1b, and 1c are determined by X-ray crystallography. The complexes are also characterized by NMR, IR, MS, and elemental analysis and used as the catalysts applied to the Henry reaction; moderate to high yields are obtained at room temperature.

Two new hydrazone compounds C₁₄H₁₀I₂N₂O₃·CH₃OH (1) and C₁₉H₁₆N₂O₃·2CH₃OH (2) are synthesized by the condensation reactions of the equimolar quantities of 4-hydroxybenzohydrazide with 3,5-diiodo-2-hydroxybenzaldehyde and 2-methoxynaphth-1-yl-methylene respectively in methanol solutions. Compound 1 consists of a hydrazone molecule and a methanol molecule of crystallization, and compound 2 consists of a hydrazone molecule and two methanol molecules of crystallization. Both compounds are characterized by elemental analysis, IR spectra, and single crystal X-ray diffraction. As expected, each hydrazone molecule adopts an E configuration about the C=N double bond. In the crystal structures of both compounds, the hydrazone and methanol molecules are linked through intermolecular N-H⋯O and O-H⋯O hydrogen bonds, forming layers along the bc direction.

A version of a computer nanoscope is proposed for single crystals with the known atomic structure for a detailed analysis of surface coordination bonds forming on nanosized nuclei due to the intermolecular interaction. Different stages of the study of rhombic and monoclinic sulfur (from the atomic/molecular structure on the first stage to the model packing growth polyhedra on the final stage) are analyzed. The calculation results of the coordination numerical sequences revealed in the computer experiment when the coordination spheres are filled with S₈ molecules with the formation of rather large molecular clusters with a size of about 10 nm or more are presented.

The possibility to modify the carbon fiber surface by refractory hafnium compounds via chemical vapor deposition of volatile metal-organic complexes is studied. Thermodynamic modeling is applied to calculate the CVD diagram of the Hf-C-O-F-H system within a 25-1200°C temperature range, 10^-1-10 Torr pressure range, and 0-2000 hydrogen/precursor vapor ratio. It is demonstrated that the deposition should be carried out at the maximum hydrogen flow and the minimum total pressure in the system. SEM and AFM techniques are used to examine the morphology and topography of the coatings on the fibers. Continuous coatings that are uniform in length and diameter of monofilaments and are tightly bound to them are obtained.

In the approximation of molecular mechanics and РМ3 quantum chemical methods, a conformational analysis of the side chain of five representatives of steroid phytohormones is performed: synthetic (22S,23S)-(epi- and homobrassinolides) and natural (two stereoisomers of (22R,23R)-24-epibrassinolide and (22R,23R)-28-homobrassinolide). It is shown that the 22R,23R-diol structure in the steroid side chain enhances its flexibility as compared to the 22S,23S-configuration. This leads to a high possibility of the occurrence of two conformers of natural brassinosteroids in the solution. In one of these conformers, hydroxyl can form an intermolecular hydrogen bond instead of forming an intramolecular hydrogen bond within the diol system of the side chain, which is important for hormone-receptor interactions.

The work is devoted to a microscopic analysis of the reactive capacity of chitin. An algorithm for modeling the deacetylation reaction in a monomeric unit of chitin is described. The reaction coordinate and the potential energy surface topography are determined taking into account the electron-vibrational interaction and low-symmetry perturbations within Jahn-Teller theory. Based on this algorithm, the topological modeling of the deacetylation process is performed for the first time and a mechanism of the biological activity of chitosan is proposed.

A new CuL₂ (HL = α-hydroxyacetophenone) complex is synthesized and investigated by elemental analysis, IR, UV-Vis, and X-ray diffraction. The complex crystallizes in the orthorhombic space group Pbca, a = 14.595(3), b = 12.517(3), c = 15.474(3) Å, V = 2826.88(1) ų, Z = 4. The title complex has a square-planar geometry around the central Cu²⁺ ion. Two molecules form a dimer via a weak Cu1…O3 interaction, and the neighboring dimers of molecules are connected into a 2D structure through two very weak C-H¡O interactions. The title complexes has high activity of killing pine wood nematodes.

Layered ternary carbides and nitrides of d and p elements exhibit a unique combination of properties characteristic of both metals and ceramics. This determines their high technological potential as materials for high-temperature ceramics, protective coatings, sensors, electrical contacts and also attracts attention to a detailed investigation of the nature of their properties. Along with remarkable achievements in the synthesis, studies of functional characteristics, and solutions of materials science problems, great progress in the description and prediction of fundamental physicochemical properties has recently been achieved with the use of first principle (ab initio) methods. By the example of titanium silicon carbide Ti₃SiC₂ (a prototype of the МАХ phase family) the possibilities of current ab initio methods are considered for the analysis and prediction of structural, cohesive, mechanical properties, non-stoichiometry and doping effects, the description of electronic characteristics and features of the chemical bonding in nanolaminates. The data on the quantum chemical studies of the Ti₃SiC₂ surface states as well as its hypothetical nanotubular forms are discussed.

A topological method of quantum chemistry (AIM) is used to study the contact area of a triangular bridging group {СS₃} in 12-nuclear cluster fragments of {Re₁₂CS₁₇}. It is shown that in the region under consideration the intramolecular interaction is characterized by a ring critical point (rcp), and its parameters depend on the oxidation state and explain the unusual structural changes in cluster complexes in redox transformations: [Re₁₂CS₁₇(CN)₆]^8- ↔ [Re₁₂CS₁₇(CN)₆]^6-.

A new compound C₁₇H₂₀FN₃O·CuBr·H₂O is synthesized in the crystal form, where C₁₇H₁₈FN₃O₃ (CfH, ciprofloxacin) is 4-oxo-7-(1-piperazinyl)-6-fluoro-1-cyclopropyl-1,4-dihydroquinoline-3-carboxylic acid. Crystallographic data of ciprofloxacinium tetrabromocuprate(II) monohydrate, C₁₇H₂₂Br₄CuFN₃O₄: a = 8.214(1) Å, b = 10.781(2) Å, с = 13.703(2) Å, α = 85.144(2)°, β = 79.119(2)°, γ = 84.018(2)°, V =
1182.5(4) ų, space group, Z = 2. Supramolecular architecture of the crystal differs from that established for C₁₇H₂₀FN₃O·CuCl·H₂O by the absence of π-π interactions of the aromatic rings of CfH ions and also the structural motifs formed by intermolecular hydrogen bonds.

A single crystal X-ray diffraction study is carried out for [Pd(P(i-Pr)₃)₂(acac)]BF₄, T = 150(2) K. Crystal dat a: a = 10.2935(4) Е, b = 11.3591(5) Е, c = 13.8728(6) Е, ± = 89.154(2)°, І = 68.448(1)°, і = 85.032(1)°, P-1 space group, V = 1502.75(11) Е³, Z = 2, d_x = 1.354 g/cm³.

A single crystal of [Pd(NH₃)₄]₃[Ir(NO₂)₆]₂·H₂O double complex salt is studied by X-ray diffraction. Crystallographic characteristics are as follows: a = 21.0335(5) Å, b = 8.0592(2) Å, c = 21.3452(5) Å, β = 91.254(1)°, V = 3617.43(15) ų, P2₁/с space group, Z = 4, d_x = 2.714 g/cm³. Single-layer pseudo-hexagonal packing of complex anions is determined along the [-1 0 1] direction in the structure. Complex cations and crystallization water molecules are located between the mentioned layers.

We have previously found that ethazole and sulfadimethoxine (sulfanilamide representatives) do not coordinate to Mg(II), Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) metals, and they are outer-sphere anions in the complex compounds of these metals. This work presents the results of the structural study of yet another sulfanilamide representative: the [Ni(A)₂(OH₂)₂] compound containing sulfapyridazine. Here A is the sulfapyridazine anion (C₁₁H₁₁N₄O₃S is 6-(p-aminobenzenesulfamido)-3-methoxypyridazine) coordinated by nitrogen atoms (N(1) and N(2)), thus functioning as a bidentate cyclic ligand. The symmetry and unit cell parameters are as follows: monoclinic, C2/c space group, а = 20.116(3) Å, b = 8.221(2) Å, c = 16.923(4) Å, β = 75.19(5)°, V = 2705.6(7) ų, T = 293 K, and Z = 4. The final value of R = 0.048 was obtained for 1930 independent reflections with I > 2σ(I). The structure consists of complex molecules.

Ir(acac-O,O)₂(acac-C³)(pyridine), 1 is synthesized, and its crystal structure is determined by single crystal X-ray diffraction. In the complex, the central Ir(III) atom displays a distorted octahedral geometry wherein the equatorial positions are occupied by four oxygen atoms of two acetylacetone ligands, and the apical positions are coordinated by a carbon atom of one acetylacetone ligand and a nitrogen atom of pyridine.

The crystal and molecular structure of a 1-(1- silatranylmethyl)-3,5-dimethylpyrazole complex with zinc dichloride (I) is determined by XRD. The coordination polyhedron of the zinc atom is a tetrahedron formed by two covalent Zn-Cl bonds and coordination Zn ← N and Zn ← O bonds. Compound I is the first example of how an endocyclic oxygen atom of the silatranyl fragment participates in the coordination of the metal atom with the formation of a six-membered heterocycle.

The crystal structure of 5-methyl-N-phenyl-1,3,4-thiadiazole-2-amine (I) is determined. The molecule of compound I is non-planar; the mean square plane of its phenyl cycle is located at an angle of 22.8°with respect to the planar thiadiazole fragment. The studied compound forms infinite chains in the crystal due to the translation along a, in which the molecules are bound by N-H…N and C-H…N bonds. Along with the van der Waals interaction, there is also a X-H…Cg (π ring) interaction between the chains in the crystal.

The reaction of 3,4-dimethoxybenzaldehyde with 4-chloroaniline (1:1 molar ration) leads to the formation of a new Schiff base (E)-4-chloro-N-(3,4-dimethoxybenzylidene)aniline (1) that is successfully obtained and characterized by elemental analyses, FT-IR and ¹H NMR spectroscopy, and single crystal X-ray diffraction. The strong absorption band at 1620 cm^-1 in the FT-IR spectrum and a singlet signal at 8.32 ppm in the ¹H NMR spectrum of 1 clearly proves the presence of the C=N (azomethine) group. Single crystal X-ray analyses reveal that the title compound adopts an E configuration with respect to the C=N bond.