Home – Home – Jornals – Journal of Structural Chemistry 2014 number 2

Results of the study of structural and electronic properties of the 8-ZGNR/h-BN(001) heterostructure by the pseudopotential method using plane waves within density functional theory are presented. Within one approximation the features of the spin state at the Fermi level are studied along with the role of the edge and substrate effects in the opening of the energy gap in the 8-ZGNR/h-BN(001) heterostructure in both ferromagnetic and antiferromagnetic orderings. The effect of a substrate made of hexagonal boron nitride was found for the first time. It consists in the opening of the energy gap in the p electron spectrum of the 8-ZGNR/h-BN(001) heterostructure for the ferromagnetic spin ordering. It is shown that the gap was 30 meV. Contributions of the edge effects of the graphene nanoribbon and the substrate to the energy gap formation are differentiated for the first time. It is found that in the 8-ZGNR/h-BN(001) heterostructure the dominant role in the opening of the energy gap at the Fermi level is played by the edge effects. However, when the nanoribbon width decreases, e.g., to six dimmers the substrate role in the gap opening increases and amounts to 45%. Local magnetic moments of carbon atoms are estimated. It is shown that small magnetic moments are induced on boron and nitrogen atoms at the interface.

The spatial and electronic structures of trimethoxyaluminum complexes with neutral molecules are calculated by the MP2/6-31(2d,p) method using the PC GAMESS-Firefly program package. The main characteristics of aluminum bonds in these molecules are determined by AIM and NBO methods. It is shown that these bonds can be characterized as the bonds between the atoms with closed shells.

The results of non-empirical quantum chemical calculations of geometric parameters, total energies, partial atomic charges, dipole moments, energies of frontier molecular orbitals obtained within second order Möller-Plesset perturbation theory in the MP2/6-31G(d,p) approximation are presented for a homologous series of N-alkyl pyridinium cations containing from 1 to 16 carbon atoms in the hydrocarbon radical. Differences are found in the electronic structure of lower and higher homologues.

Decomposition of 2-fluoro-2,3-dihydrophosphinine (1), 2-chloro-2,3-dihydrophosphinine (3), 2-bromo-2,3-dihydrophosphinine (5) to phosphinine was investigated using Molecular orbital and density functional theory. Study on the B3LYP/6-311+G** level of theory revealed that the required energy for the decomposition of compounds 1, 3 and 5 to phosphinine is 30.56, 28.23 and 24.03 kcal×mol^–1, respectively. HF/6-311+G**//B3LYP/6-311+G** calculated barrier height for the decomposition of compound 1, 3 and 5 to phosphinine is 57.56, 37.26 and 30.77 kcal×mol^–1, respectively. Also, MP2/6-311+G**//B3LYP/6-311+G** results indicated that the barrier height for the decomposition of compound 1, 3 and 5 to phosphinine is 46.59, 47.28 and 42.57 kcal×mol^–1, respectively. Natural bond orbital (NBO) population analysis and nuclear independent chemical shift (NICS) results showed that, reactants are non-aromatic but products of elimination reaction are aromatic, C-H and C-X bonds are broken and H-X bond is appear.

The use of the previously proposed parameter U proportional to the vibrational component of intramolecular energies, which can be considered as a kind of molecular topological characteristics, enables the estimation of gas chromatographic retention indices of isomeric unsaturated compounds. The latter include both isomers differing in the position of С=С double bonds in the carbon skeleton of the molecules and isomers with different configurations of these bonds (E and Z).

An X-ray absorption spectroscopy study of the electronic structure of unsubstituted and hexadecafluoro-substituted copper phthalocyanines is performed. L absorption spectra of the copper atom and K absorption spectra of carbon, nitrogen, and fluorine atoms of unsubstituted and hexadecafluorosubstituted copper phthalocyanine are examined. A comparison of the absorption spectra in one binding energy scale enabled the estimation of contributions of AOs of all atoms of the considered compounds to lower unoccupied molecular orbitals and to determine the sequence of levels, their energies, and the occurrence of the interaction between certain atoms.

The important feature of the present work is that the crystal data are obtained first time for the directly synthesized complex [Cu(D,L-but)₂] from pure zero valent metal and butyric acid in water. Further investigation involves the comparison of structural parameters from the XRD data of the title complex [Cu(D,L-but)₂] in solid state with the theoretically optimized structure in the gaseous state and its simulated spectra (vibrational and electronic) are generated. The results show that the structural parameters determined by computational studies and crystal structure studies are in good agreement. In the computational calculations, the geometric optimization is carried out using the MM3 method and electronic spectra are calculated using ZINDO, a semi-empirical quantum mechanical method of Scigress explorer 7.7. The theoretical calculations of HOMO-LUMO energies have revealed that the charge transfer interactions occur within the complex. The crystal data for the [Cu(D,L-but)₂] complex are: space group P2₁/c; a = 11.096(5) Å, b = 5.062(4) Å, c = 9.475(3) Å; β = 92.4°; ρ_calcd = 1.673 g/cm³; Z = 2.

Molecular orbital calculations at the DFT-B3LYP/aug-cc-pVDZ level are performed for the possible tautomers of 1-nitroso-1,2,4-triazol-5-one-2-oxide. We have examined the substitution effects of carbonyl, N-oxide, and nitroso groups by comparing the calculated geometries, relative energies, and electrostatic potentials of model molecules. The optimized structures, vibrational frequencies, and thermodynamic values for triazolone-N-oxides are obtained in the ground state. The results show that 1H, 4H tautomers are most stable. Detonation velocity and detonation pressure are evaluated by the Kamlet-Jacob equations based on the predicted density and the calculated heat of explosion. The explosive properties of the designed compounds seem to be promising compared with those of 1,3,5-trinitroperhydro-1,3,5-triazine (D 8.75 km/s, P 34.70 GPa), octahydro-1,3,5,7-tetrnitro-1,3,5,7-tetrazocine (D 9.10 km/s, P 39.3 GPa), and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (D 9.20 km/s, P 42.0 GPa).

Self-diffusion coefficients of different classes of polar solvents are measured by the proton spin echo method in the temperature range of 288-318 K. In the same temperature range viscosities and dielectric relaxation times of the liquids under study are measured or taken from the literature and the activation energies of self-diffusion processes, viscous flow, and dielectric relaxation are calculated. The results obtained are compared with the literature data on structural relaxation times in the studied solvents and the conclusion is drawn about the role of the spatial hydrogen bond network in the mobility of molecules forming this network.

Kirkwood-Buff integrals are calculated from the thermodynamic data for binary mixtures of water with methanol, ethanol, 1-propanol, and 2-propanol at a temperature of 298.15 K in the pressure range from atmospheric to 100 MPa. The values of local compositions Δn_ij are calculated which characterize the excess (or deficit) of molecules i around the central molecule j. It is found that the pressure affects destructively the homoassociation in all mixtures studied. In a series MeOH < EtOH < 2-PrOH < 1-PrOH an excess of molecules around the similar type molecules increases in the local environment and the pressure effect on the local composition is enhanced.

Data on the relationship between the molecules involved in various heteroassociates (HAs) and «free» molecules in the HF-Et₂CO binary liquid system (BLS) are obtained by two independent methods: experimental and computational. The first method is applicable in the 0:1-6:1 molar range provided that the IR spectrum of the solvent molecule contains a band whose frequency and intensity can be measured when this molecule passes from the «free state» to the composition of all Has present in BLS. The second method is based on taking into account the material balance between the «free» molecules and molecules involved in various HAs of the solvent and HF. This method requires the knowledge of stoichiometric ratios of molecules in HAs and concentrations at which they appear in the solution. It is shown that in HF-Et₂CO BLS, starting from the molar fraction of HF of ~0.25, the majority of molecules is involved in the composition of the complexes, and at the molar fraction of HF of ~0.50-0.92 already 90-100% of molecules of the solution form HAs.

Thermodynamic characteristics of mixtures of aprotic amides with water and organic solvents with hydrogen bond networks are calculated. Within a model approach the specific and non-specific components of the total energy of the intermolecular interaction are determined, based on which the corresponding contributions to the enthalpies of component mixing are calculated. It is found that negative enthalpies of mixing in the mixtures under study are due to non-specific interactions rather than heterocomponent specific ones. It is shown that the difference in the structural-thermodynamic characteristics of aqueous and nonaqueous mixtures of aprotic amides is mainly caused by packing features of solutions and the behavior of hydrogen bond networks of water and organic solvents.

By single crystal X-ray diffraction the crystal structure of the complex salt [Co(NH₃)₅Cl]₂(W₁₀O₃₂)×4H₂O is determined and the IR spectrum is interpreted. The crystal chemical analysis of the structure of complex cations and decatungstate anions and their packing in the structure is performed.

The molecular and crystal structure of binuclear boron difluoride acetylacetonate, in which two boron chelate moieties are linked by a disulfide group, is determined. It is found that in the crystalline state, the chelate moieties are non-equivalent. The differences identified stem from the fact that molecules crystallize in pairs: two chelate ring (one from each molecule of the pair) are linked with each other by the stacking interaction. The other chelate rings of the pair do not participate in intermolecular interactions.

Novel mixed salts of the paratungstate anion Na₂(NH₄)₈[H₂W₁₂O₄₂]×12H₂O (1) and Na_7.5K_2.5[H₂W₁₂O₄₂]×22.2H₂O (2) are obtained by slow concentration of tungstate solutions and characterized by single crystal X-ray diffraction.

The crystal structure of two modifications of [PdEn(NO₂)₂] is determined by single crystal X-ray diffraction. The geometric characteristics of the complexes and the motifs of their mutual arrangement in the structures are compared. The thermal properties in different gaseous atmospheres are studied.

By single crystal X-ray diffraction the structures of [CuEn₂][Pt(NO₂)₄] and [PdEn₂][Pt(NO₂)₄] are determined. In the structures, the main structural moieties are identified. It is shown that the structure of [PdEn₂][Pt(NO₂)₄] can be considered as quasi-one-dimensional: in the Y axis direction, the stacks of alternating complex cations and anions locate.

In treatment of trans-[Ru(NO)(NH₃)₄(OH)]Cl₂ with concentrated sulfuric acid on heating trans-[Ru(NO)(NH₃)₄(SO₄)](HSO₄)×H₂O (I) is obtained with a yield close to quantitative. In the interaction of the saturated solution of I with a saturated NaNO₃ solution a trans -[Ru(NO)(NH₃)₄(SO₄)]NO₃×H₂O (II) precipitate forms whose structure is determined by single crystal XRD: space group Р2₁2₁2₁, a = 6.8406(3) Å, b = 12.6581(5) Å, c = 13.3291(5) Å. A monodentately coordinated sulfate ion is in the trans-position to the nitroso group. Compound II is characterized by IR spectroscopy, powder XRD, and diffuse reflectance spectroscopy. The process of its thermolysis is studied; by differential scanning calorimetry the thermal effect of the dehydration reaction occurring on heating to 120°C (ΔH = 58.9 ± 1.5 kJ/mol) is estimated. The final product of the thermolysis of II is a mixture of Ru and RuO₂.

It is found that diffraction patterns of complexes I–V of the composition [Ln(Phen)(C₄H₈NCS₂)₃] (Ln = Sm, Eu, Tb, Dy, and Tm respectively) are similar. Single crystals of [Dy(Phen)(C₄H₈NCS₂)₃]·3CH₂Cl₂ (VI) obtained are. According to the X-ray crystallographic data, in the structure of VI the unit cell contains two crystallographically independent molecules of the [Dy(Phen)(C₄H₈NCS₂)₃] complex and six CH₂Cl₂ molecules. The N₂S₆ coordination polyhedron of the Dy atom is a distorted square antiprism. In the range of 2–300 K the magnetic properties of complexes I–V are studied. It is found that complex III passes to the magnetically ordered state; the spontaneous magnetization at 2 K is 24 600 G·cm³/mol. At 300 K compounds I–IV exhibit photoluminescence in the visible spectral range. It is found that the photoluminescence intensity of complex I is several times higher than the photoluminescence intensity of complexes II–IV.

The crystal structure of the bimolecular crystal of CL–20 with new promising highly energetic compound 7Н– tris–1,2,5–oxadiazolo[3,4–b:3',4'–d:3»,4»–f] azepine is obtained and studied.

A reaction of [MoO₂(acac)₂] (where acac = acetylacetonate) with two hydrazone ligands in methanol yields two mononuclear molybdenum(VI) oxo complexes with the general formula [MoO₂L(CH₃OH)], where L = L¹=(4-nitrophenoxy)acetic acid [1-(5-chloro-2-hydroxyphenyl)methylidene]hydrazide (H ₂L¹) and L = L²=4-dimethylaminobenzoic acid [1-(2-hydroxy-3-methoxyphenyl)methylidene]hydrazide (H₂L²). The crystal and molecular structures of the complexes are determined by the single crystal X-ray diffraction method. All of the investigated compounds are further characterized by the elemental analysis, FT-IR spectra, and thermogravimetric analyses. Single crystal X-ray structural studies indicate that hydrazone ligands coordinate to MoO₂ cores through enolate oxygen, phenolate oxygen, and azomethine nitrogen atoms. The Mo atoms in both complexes are in octahedral coordination.

YYCl₃×6H₂O reacts with 1,10-phenanthroline (phen) to yield a complex of 1:2 yttrium:ligand stoichiometry. The yttrium(III) complex is characterized by the elemental analysis, UV-Vis, IR as well as the X-ray diffraction analysis. The crystal of [Y(phen)₂Cl(H₂O)₃]Cl₂×H₂O obtained from a methanol solution crystallizes in the triclinic system, space group P₂, Z = 2, a = 10.3236(4) Å, b = 10.4566(4) Å, c = 12.5270(5) Å, α = 97.354(2)°, β = 108.740(2)°, γ = 93.458(2)°, R_int = 0.046. The Y(III) ion is eight-coordinated by four nitrogen, three oxygen atoms and one chlorine atom.

Two complexes of gallium(III) with adduct ion pair compounds containing pyridine-2,6-dicarboxylic acid and two different Lewis bases are synthesized. The chemical formulae are (dmpH)[Ga(pydc)₂]×2H₂O, (1) and (bpyH₂)_1/2(pydcH₂)_1/2[Ga(pydc)₂]×4H₂O, (2) where pydc, dmp, and bpy are pyridine-2,6-dicarboxylate, 2,9-dimethyl-1,10-phenanthroline, and 4,4'-bipyridine respectively. The two crystal structures illustrate that the Ga^III ion is six-coordinated by two pyridine-2,6-dicarboxylates. Hydrogen bonds as well as other noncovalent interactions such as ion-pairing, C-O⋯π, C-H⋯π, and π⋯π stacking play an important role in the formation of supramolecular systems. Particular attention is given to the molecular geometries and NMR properties of the complexes from the computational point of view. The electronic properties of the complexes are analysed using the parameters derived from the atoms in molecules (AIM) and natural bond orbital (NBO) methodologies at the B3LYP/6-311++G(2d,2p) computational level.

The enthalpies of dissolution of imino acid L–proline in aqueous solutions of methanol, 2–propanol, ethylene glycol, glycerin, and urea are measured by the calorimetric method at 313.15 K. Enthalpic parameters of the interaction of L–proline with nonaqueous components are calculated and compared with the data at 298.15 K. It is found that the sign of the heat capacity parameter of the pair and ternary interactions depends on whether the nonaqueous solvent component is a destroyer or stabilizer of the water structure. Partial molar heat capacities of proline in mixed solvents are obtained by the integral dissolution heat method. Temperature changes in the reduced enthalpy and entropy of the proline solution are determined at an increase in the temperature from 298 K to 313 K. It is shown that there is entropy-enthalpy compensation at temperature changes in the characteristics during dissolution.

The reaction of Cs₄[Re₆Te₈(CN)₆]×2H₂O with Cu(en)₂Cl₂ in water affords crystals of a cluster complex [{Cu(H₂O)(en)₂}{Cu(en)₂}Re₆Te₈(CN)₆]×3H₂O. The structure of the compound is determined by single crystal X-ray diffraction (a = 10.8082(4) Å, b = 16.5404(6) Å, c = 24.6480(7) Å, β = 92.696(1)°, V = 4401.5(3) ų, Z = 4, space group P2₁/n, R₁ = 0.0331, wR₂ (all data) = 0.0652). In the complex, cluster [Re₆Te₈(CN)₆]^4–anions are linked by Cu²⁺ cations into zigzag chains through cyanide bridges. The coordination environment of the copper cations is complemented by ethylenediamine molecules. Each of the cluster anions is additionally coordinated by a terminal fragment {Cu(H₂O)(en)₂}.

Relativistic time-dependent density functional (TDDFT) calculations including spin-orbit interactions via the zero order regular approximation (ZORA) and solvent effects are carried out on the [Re_6–xOs_xSe₈Cl₆]^{(4–x )–} (x = 0–3) cluster. These calculations indicate that the lowest energy electronic transitions of the MMCT and LMCT type are similar to those observed in strongly luminescent 24–electron hexanuclear rhenium chalcogenide clusters [Re₆Se₈Cl₆]^4–. Thus our calculations predict that [Re_6–xOs_xSe₈Cl₆]^(4–x)– (x = 0–3) clusters could be luminescent.

By the AgClO₄ interaction with 1allyl-5-(2-Pyridyl)-1H-tetrazolee (1 aPyt) in a methanol solution, an [Ag₂(1 aPyt)₂](ClO₄)₂ π-complex is obtained, which is studied using single crystal X-ray diffraction.

By single crystal X-ray diffraction the crystal and molecular structure of 1-(3-ammoniopropyl)silatrane chloride (I) is determined. One of three cations in the asymmetric unit of the crystal of I differs from the other two by the length of the coordination N ® Si bond. The opposite electronic effects in two geometrically similar cations are transferred inductively through a three-carbon chain.

A new hybrid material [BiF4BrBzTPP]₂[Co(NCS)₄] (1) (BiF4BrBzTPP⁺ = 2,6-bisfluoro-4-bromobenzyltriphenylphosphinium, NCS^– = isothiocyanate) is synthesized and characterized by elemental analyses, IR, UV spectra, ESI–MS, molar conductivity, single crystal X-ray diffraction and magnetic susceptibility measurements. Compound 1 crystallizes in the monoclinic space group C2/ c with a = 15.272(2) Å, b = 24.779(3) Å, c = 14.482(2) Å, β = 101.037(2), V = 5378.9(12) ų, Z = 4. The compound comprises two cations and one anion which exhibits a distorted tetrahedral coordination geometry. The short F⋯F, C⋯Br and N⋯Br interactions and C–H⋯S hydrogen bonds consolidate the stacking of the molecules. Magnetic susceptibility measurements in the temperature range 2–300 K show that 1 exhibits weak antiferromagnetic coupling behavior.

A new μ_1,1–OMe–bridged dimeric iron(III) complex, [Fe₂L ₂(μ_1,1–OMe)₂(NCS)₂], where L is the deprotonated form of 2-[(2-ethylaminoethylimino)methyl]-5-methoxyphenol, has been prepared and structural characterized by elemental analysis, IR spectrum, and single crystal X-ray crystallography. The complex crystallizes in the monoclinic space group P2₁/c, with unit cell dimensions a = 10.156(1) Å, b = 11.972(1) Å, c = 14.256(2) Å, β = 102.643(3)°, V = 1691.3(3) ų, Z = 2, R₁ = 0.0394, and wR₂ = 0.0922. Each Fe atom in the complex is in an octahedral coordination. The Fe⋯Fe distance is 3.102(1) Å. The thermal stability of the complex was studied.

The 1-(diphenylmethylene)-2-(thiazolo[4,5-b]pyridin-2-yl)hydrazine compound (IV) is synthesized based on 3-amion-2-chloropyridine precursor and characterized by single crystal X-ray diffraction. The structural analysis reveals that compound IV belongs to the monoclinic system, space group P2₁/c, a = 11.869(5) Å, b = 13.155(6) Å, c = 10.970(5) Å, β = 102.431(5)°, V = 1672.6(12) ų, Z = 4. In the crystal structure, the molecular species are linked by intermolecular N-H…N hydrogen bonds into one-dimensional chains.