Home – Home – Jornals – 2010 number 2

A full potential FLAPW-GGA method is used to study for the first time the electronic structure of cubic tungsten subnitride W₂N, and its equilibrium lattice parameter, density, energy of cohesion, coefficients of low temperature heat capacity and Pauli paramagnetic susceptibility are calculated. It is discussed in comparison to the similar values of hexagonal and cubic tungsten mononitrides WN.

The character of alkaline (M⁺= Li, Na, K) and alkaline earth metal ions (M²⁺= Be, Mg, Ca) interactions with disilyne and acetylene has been studied by using high-level ab initio computations. The interaction energies were calculated at MP2/6-311++G(2d,2p) level. These calculations show that the size and charge of cation are two significant factors that affect the character of interaction. AIM and NBO analyses of Mⁿ⁺…X₂Y₂ interactions specify that the variation of densities and the extent of charge transfers upon complexation correlate well with the obtained interaction energies.

By the example of combined calculation methods (CCMs) corresponding to calculations in MP4/6-311+G(fd,p)//MP2/6-31G(d,p) and MP4/aug-cc-pvTZ//МР2/cc-pvDZ approximations the factors affecting their accuracy are considered. By total energy calculations made for a number of compounds it is shown that the accuracy of CCMs reduces when valence double- and triple-split basis sets are applied together, and also when different methods are used to allow for electron correlation. The use of empirical corrections taking into account the character of the electron distribution in a molecule allows an enhancement of the accuracy of CCMs. The mentioned factors taken into account enable us to obtain CCM, for which the mean absolute deviation of calculation data is 1.0 kJ/mol and the largest maximum deviation is 8.0 kJ/mol in the total energy calculation in the MP4/6-311+G(f,d,p) approximation.

The vaporization enthalpies of mono- and dicarbonic acids with different structures are calculated under normal conditions using the modified Randič method and the energies of hydrogen bonds. The results demonstrate good agreement between the experimental and calculated data.

Gas electron diffraction at a temperature T of 641(5) K is used to study the structure of an N,N′-ethylene-bis(salicylaldiminato) zinc(II) molecule, ZnO₂N₂C₁₆H₁₄, further Zn(salen). The structure of a gaseous Zn(salen) complex has C₂ symmetry and is characterized by a substantial turn of two chelating fragments of the ligand with respect to each other, and also by a big difference in the length of coordination bonds: r_h1(Zn-O)=1.902(7) Å and r_h1(Zn-N)= 2.027(7) Å. Results of the DFT/B3LYP calculation with 6-31G* and CEP,TZV basis sets of the molecule structure well agree with the experimental data. The electronic structure of Ni(salen), Cu(salen), Zn(salen), and Zn(acacen) molecules is considered.

Nonempirical methods are used to calculate the geometric parameters, the frequencies of normal vibrations, and thermochemical characteristics of ions existing in saturated vapors over sodium bromide and iodide: Na₂X⁺, and (X = Br, I). According to the calculations, Na₂X⁺ and triatomic ions have a linear equilibrium configuration of D_∞h symmetry. Pentaatomic ions can exist in the form of three isomers: linear with D_∞h symmetry, planar cyclic with С_2v symmetry, and bipyramidal with D_3h symmetry. At a temperature of ~1000 K, and pentaatomic ions are shown to be present in vapor mainly in the form of linear isomers. The energies and enthalpies of ion molecular reactions with the participation of the above ions are calculated, and the formation enthalpies of the ions are determined, Δ_fH°(0 K): 293±2 kJ/mol (Na₂Br⁺), 354±2 kJ/mol (Na₂I⁺), -536±2 kJ/mol -458±2 kJ/mol 24±5 kJ/mol 143±5 kJ/mol -810±5 kJ/mol and -675±5 kJ/mol

In the microwave spectrum of a 5-methyl-1,3-dioxane sample, the rotational transitions of а and с types with 4 ≤ J ≤ 11 for five isotopomers of a molecule with ¹³С and ¹⁸О isotopes in different sites are identified in a frequency range of 18 GHz to 42 GHz. The spectroscopic constants of isotopomers are found. The substituted r_s and effective r_о structural parameters of 5-methyl-1,3-dioxane are determined. By the B3PW91/aug-cc-pVDZ density functional method the equilibrium structure of the molecule is calculated. The results of quantum chemical calculations are compared to the experimental data.

The UV induced photopolymerization of Langmuir-Blodgett films of lead salt of 2-docosynoic acid (CH₃(CH₂)₁₈C≡CCOOH) is studied using IR and Raman spectroscopy. It is found that the films are a highly ordered system with trans-configuration of alkyl chains and a bridged complex generated between the carboxyl group and the lead ion. Based on a change in the absorption band intensity in the IR spectra corresponding to the triple bond vibration, the degree of polymerization depending on the irradiation time is determined. In the Raman spectra, a peak at ~1635 cm^-1 appears during polymerization, which corresponds to the C=C double bond. The formation of conjugated double bonds in these systems is observed for the first time. During polymerization, methylene chains of molecules retain trans-configuration; the structural ordering of molecules in the film is observed.

The synthesis of alkyl 2-chloro-3-formylacrylates 1 from alkyl pyruvates was carried out using Vilsmeier reaction. The reaction is highly stereoselective and leads to a 95:5 mixture of Z and E stereoisomers. Both stereoisomers were characterized by ¹H and ¹³C NMR. In CDCl₃ solution, the NMR data, particularly the NOEDIFF experiments, show that the major species formed is the Z stereoisomer. Heating compound 1 in THF at reflux afforded the cyclic product 2 in 90 % yield. The interpretation of the experimental data were further supported by DFT/B3LYP calculations.

Based on the density functional quantum chemical calculations, the electronic structure of binuclear manganese decacarbonyl Mn₂(CO)₁₀ is analyzed. The calculation results are used to interpret the CKα, OK_α, MnL_α, and X-ray fluorescence spectra of Mn₂(CO)₁₀. The theoretical fluorescence spectra constructed using these calculations are in good agreement with the experiment

The paper analyzes the physical implications of the result obtained in the work [1] that a random variable - the number of the nearest neighbors M_λ in a fluid consisting of N hard spheres in the Gibbs canonical ensemble - can be expressed as a sum of N independent and similarly distributed random variables. The mean value of a functional of this random variable determines the free Helmholtz energy of a fluid with the SW interaction potential (hard sphere plus square well). The paper shows that the said property of the random variable M_λ allows one to average this functional using the general methods of the probability theory (the Cramer theorem or the method of large deviations) without expanding it in a perturbation theory series. All the mathematical variables introduced in the proof of the Cramer theorem have a simple physical meaning and are determined by the thermodynamic characteristics of the SW fluid. The conditions of the Cramer theorem are shown to hold in the entire region of the fluid existence except the critical point area.

A method to construct model radial distribution functions (RDFs) fr om the already known structural data is described. The method includes the procedures to calculate termination ripples that always appear on the experimental RDF because of the bounds of the integration lim its in the Fourier transformation of the X-ray scattering curve. The introduction of this procedure increases the accuracy of the comparative RDF method used to elucidate the phase composition of nanodispersed materials and to determine the features of the local structure of the phases as compared to their well crystallized analogues. Cerium dioxide samples with different dispersion exemplify the applicability of this method to determine the features of the local structure.

Two approaches to the description of changes in the bond length in molecules and crystals with changing coordination number of atoms are studied. They are based on a difference or ratio of interatomic distances when the structure is changed. The second approach is shown to yield more accurate results. The change in the interatomic distances in polar compounds has the same character as the change in the ionic radii when coordination numbers are varied.

A new fluorine-containing tetradentate ligand 1,2-bis(5,5,5-trifluoro-4-oxopent-2-en-2-amino)benzene and its complexes with Ni(II), Pd(II) and Cu(II) are characterized by single crystal X-ray diffraction. It is found that the enaminoketone fragments of the ligand are identical in bond lengths and angles; they are almost planar, and make the angles of 51.3° to the plane of the benzene ring. The structures of Ni(II), Pd(II), and Cu(II) complexes are similar and have a saddle-shape configuration. The metal ions have square planar coordination and are located almost in the center of the N₂O₂ square. The average M-N bond lengths are longer than M-О ones by 0.014 Å and 0.034 Å for the Ni(II) and Cu(II) complexes respectively, while in the Pd(II) complex, M-О is longer than M-N by 0.029 Å. The average chelate angles N-M-O in the complexes are: N-Ni-O 95.12°; N-Pd-O 95.68°; N-Cu-O 93.88°.

A neutral complex of palladium(II) with 2,9-dimethyl-1,10-phenanthroline [Pd(2,9-Me₂-phen)Cl₂] (goldish orange colored) is examined by single crystal X-ray diffraction. The crystals of [Pd(2,9-Me₂-phen)Cl₂] are monoclinic and belong to the space group P2₁/n (a = 11.8670(7) Å, b = 7.8195(5) Å, c = 14.2418(9) Å, β = 92.5450(10)°, Z = 4, V = 1320.25 ų, R = 0.0289). The complex [Pd(2,9-Me₂-phen)Cl₂] exhibits a strong distortion of the usual square-planar geometry with a deviation of the central Pd²⁺ ion and two chloride acido-ligands from the plane of coordinated 2,9-dimethyl-1,10-phenanthroline. The lengths of two Pd-N bonds are slightly different and are 2.058 Å and 2.067 Å, the lengths of the Pd-Cl bonds are equal and are 2.285 Å. 2,9-Me₂-phen itself also suffers some distortion of the planar geometry resulting in the boat conformation of the molecule. The crystal structure of the [Pd(2,9-Me₂-phen)Cl₂] complex is characterized by the presence of π-π stacked dimers arranged in infinite tilted stacks.

The reaction of lacunary arsenitotungstate [AsW₉O₃₃]^9- with [M₃S₄(H₂O)₉]⁴⁺ in aqueous solution leads to the formation of the complex [{Mo₃S₄(H₂O)₅}(H₂AsW₉O₃₃)₂]^10-. X-ray crystal structure analysis of its cesium salt of the composition Cs_5.6K_4.4[{Mo₃S₄(H₂O)₅}(H₂AsW₉O₃₃)₂]·19.15H₂O (1) is reported. Similarly, the reaction of [AsW₉O₃₃]^9- with [W₃S₄(H₂O)₉]⁴⁺ and NaAsO₂ yields [{W₃S₄(H₂O)₅}(H₂AsW₉O₃₃)(HAsW₉O₃₃AsOH)]^9-. For K_6.35(NH₄)_2.65[{W₃S₄(H₂O)₅}(H₂AsW₉O₃₃)(HAsW₉O₃₃AsOH)]·23.7H₂O (2) the crystal structure is determined. In both compounds, the {M₃S₄}⁴⁺ cluster cores coordinate one polyoxometalate ion, which functions as a bridging ligand between two metal atoms, and one bidentate polyoxometalate. The other five coordination sites at the cluster core are occupied by water molecules. The complex anions form dimeric associates held together by hydrogen bonds and S…S contacts.

A method of transfer with an inert carrier gas is used to obtain temperature dependences of pressure vapors. The thermodynamic functions of sublimation processes are calculated for seven molecular crystals that belong to the group of non-steroidal anti-inflammatory drugs: diclofenac, niflumic, flufenamic, tolfenamic, mefenamic, N-phenylanthranilic acids, and diphenylamine. Differential scanning calorimetry is applied to study the melting processes of the selected substances. Single crystal X-ray structural literature data are analyzed, and they are compared with the obtained thermodynamic and thermophysical parameters of sublimation and melting processes. A correlation between the values of the enthalpy of sublimation and the melting temperature under standard conditions is found. The effect of different substituents on the crystal lattice energy of this class of compounds is studied.

The examples of computer experiments on the propagation of wave motion in molecular nanostructures are presented. Some patterns of energy transfer and dissipation inside the molecular structures are discussed.

Simulation of diffraction patterns, radial distribution function analysis, and electron microscopy are applied to study the features of the structure of nanosized pseudoboehmite obtained by the sol-gel method. It is found to consist of plate-like particles with a thickness of one lattice constant in the [010] direction. Such a structure of the pseudoboehmite particles results in the absence of the 020 diffraction peak in the diffraction pattern.

The crystal structures of catechol (o-dihydroxybenzene) and its 2:1 complex with dimethylsulfoxide are determined at T = 150 K. Crystal dat a: C₁₄H₁₈O₅S, M = 298.37, triclinic, space group unit cell parameters: a = 7.7285(13) Е, b = 9.9924(17) Е, c = 10.3188(18) Е, ± = 89.963(4)°, І = 89.968(4)°, і = 69.076(5)°, V = 744.3(2) Е³, Z = 2, D_x = 1.331 g/cm³, R1 = 0.048; C₆H₆O₂, М = 110.11, monoclinic, space group P2₁/n, a = 9.8206(6) Е, b = 5.5903(3) Е, c = 10.4439(6) Е, І = 114.952(2)°; V = 519.85(5) Е³, Z = 4, D_x= 1.407 g/cm³, R1 = 0.0289. In the 2:1 complex the molecules are joined in a supramolecular ensemble by D-H…A hydrogen bonds (D = O, C; A = O, А); in catechol they are bonded only by O-H…O. The state diagram of the catechol-dimethylsulfoxide system is examined by DTA.

The nature and theoretical models of spin crossover equilibrium between high-spin and low-spin forms of transition metal complexes are reviewed. Spin crossover compounds are promising materials for information storage and display devices. In the solid state spin crossover is accompanied by several phenomena related to phase transitions. A critical analysis of theoretical models proposed for the explanation of these phenomena is given. The paper mainly focuses on two models that provide for adequate descriptions of the majority of experimental data, viz. the model of the Ising-like Hamiltonian and the molecular statistical model. Descriptions of spin crossover yielded by these two models are formally similar but not identical and they are based on fundamentally different concepts of molecular interactions and ordering, the latter being the origin of the two-step spin crossover. The Ising-like Hamiltonian model approaches spin crossover fr om the point of view of properties of lattices wh ereas the molecular statistical model explains this phenomenon starting from molecules. The latter approach provides for the elucidation of the molecular nature of cooperative phenomena observed in spin crossover which is important for developing the synthetic strategy of promising spin crossover compounds.

Anharmonic effects are shown to be obtained immediately in the statement of a quantum problem as a general electronic vibrational problem in the matrix formulation and without the use of a traditional anharmonic potential. The methods to form the matrix and to calculate all matrix elements are presented.

The RHF, B3LYP, and PBE0/6-311G** quantum chemical methods are used to determine the point symmetry group and the equilibrium structure of bicyclo[2.2.0]hex-1(4)-ene (I, D_2h), its two stable dimers (tricyclo[4.2.2.2^2,5]dodeca-1.5-diene (II, D_2h) and 2,5-dimethylenetricyclo[4.2.2.0^1,6]decane (III, C₂)), and pentacyclo [4.2.2.2^2,5]dodecane (IV, D₂) that is a hypothetical intermediate in the dimerization reaction of the molecules of I. The relation of total energies is obtained with regard to zero-point vibrations: E(III) < E(II) ? E(IV) ? 2E(I).

The phase of the composition CaBaLaCu₂FeO_7.5 is synthesized from the previously obtained CaCuO₂, La₂Cu₂O₅, and BaFeO₂ double oxides enriched up to 14.7% in ⁵⁷Fe. The phase has the orthorhombic crystal system with the unit cell parameters as follows: a = 0.3882(3) nm, b = 0.3911(3) nm, c = 1.1823(8) nm. Based on the Mössbauer spectra analysis, the conclusion is drawn that iron atoms occupy only Cu(1) sites in the lattice, while more than 90% of them are in the Fe⁴⁺ valence state (80% of these atoms have the tetragonal pyramidal coordination).

New supramolecular adducts of cucurbit[6]uril with triangular cluster chloroaquacomplexes of Mo and W with mixed sulfido-selenido bridging ligands, {[W₃S₃Se(H₂O)₇Cl₂]₂(C₃₆H₃₆N₂₄O₁₂)}Cl₂·15H₂O (1), {[W₃S_1.5Se_2.5Cl_1.5(H₂O)_7.5]₂(C₃₆H₃₆N₂₄O₁₂)}Cl₅·18.5H₂O (2), and {[Mo₃SSe₃(H₂O)_7.5Cl_1.5]₂×(C₃₆H₃₆N₂₄O₁₂)}Cl₅·11H₂O (3) are obtained treating the mixture of products in Mo-S-Se-Br and W-S-Se-Br systems, isolated, and structurally characterized. In all compounds, the supramolecular structure is based on hydrogen bonded associates of cucurbit[6]uril molecule with two cluster cations.

In the crystal of K₄[Zn(Citrate)₂], two citrate anions coordinate Zn(II) cation with octahedral geometry in the [Zn(Citrate)₂]^4- complex anion, and the charge is balanced by four potassium ions. Crystal dat a: monoclinic, P2₁/c, a = 8.502(2) Е, b = 13.210(3) Е, c = 8.942(2) Е, І == 113.132(4)°, V = 923.5(4) Е³, Z = 2, R = 0.0229.

Two new zinc(II) complexes have been synthesized and studied by single crystal X-ray diffraction method: [Zn(L1)Cl₂]·2DMF (1) and [Zn(L2)Cl₂]·DMF (2) (L1 = 3,3′-bis(2-benzimidazolyl)-2,2′-dipyridine, L2 = 3,3′-bis[2-bis(2-ethylbenzimidazolyl)]-2,2′-dipyridine). Compound 1 is monoclinic, C2/c, a = 23.142(3), b = 11.845(1), c = 14.735(3) Å; compound 2 is orthorhombic, C222₁, a = 12.140(7), b = 16.283(9), c = 16.51(1) Å. In both compounds, Zn(II) cations are coordinated by two chlorine atoms and two benzimidazole nitrogen atoms in a slightly distorted tetrahedron fashion. Structural features responsible for fluorescent properties of the complexes are discussed.

2-(2-p-Tolyloxyethoxy)ethylchloroacetate is synthesized and its single crystal X-ray diffraction analysis is performed.

The synthesis of methyl-10,14,19,19-tetramethyl-4-oxo-20-oxahexacyclo[15.3.1.1^6.18.0^6.15.0^9.140^17.21] docosane-10-carboxylate III is performed and its molecular structure is determined. Compound III С₂₇H₄₀O₄ crystallizes in the monoclinic system with the cell parameters as follows: а = 12.8081(11) Å, b = 7.0384(6) Å, c = 12.8904(12) Å, β = 105.828(2)°, P2₁ space group, Z = 2, d = 1.273 mg/m³.

The crystals of 2-(6-chloro-4-(p-tolylamino)pyrido[3,2-d]pyrimidin-1-ium-1-yl)acetate (zwitterionic form) oxonium bromide, C₁₆H₁₃ClN₄O₂·Br^-·H₃O⁺ (I) were prepared and studied by single-crystal X-ray diffraction method. The compound crystallizes in the triclinic space group P-1 with a = 8.3121(8), b = 9.3885(8), c = 13.2903(12) Å, α = 106.788(2), β = 95.204(3), γ = 110.871(2)°, V = 905.81(14) ų, Z = 2; final R = 0.053, wR2 = 0.150. It is interesting that methylene C in the BrCH₂COOH molecule binds to the N1 of the pyrimidine ring. In the crystal studied, two neighboring organic molecules are connected by hydrogen bonds through carboxylate oxygen, oxonium and bromide ions to form a dimer.