Home – Home – Jornals – Journal of Structural Chemistry 2014 number 6

The structure of the effective one–electron Hamiltonian R in the Hartree–Fock equation RΦ_i = ε_iΦ_i is discussed in many works. The most general definitions of R satisfying all necessary conditions imposed by the variational principle for the energy in open shell systems are derived by Dyadyusha and Kuprievich and by Hirao and Nakasutji. In this work it is shown that these definitions cannot be concordant with additional variational conditions imposed by Koopmans' theorem. A more general form of R is proposed which provides a combination of the variational conditions imposed on the Hartree–Fock orbitals by the variational principle and Koopmans' theorem.

Electron localization functions (ELFs) are calculated at the hydrogen bond critical points for a number of molecules having the intramolecular hydrogen bond C–H∙∙∙X (X = N, O). It is shown that the values of the core and valence electrons bifurcation index (CVBI) are positive in all cases. This enables the characterization of the studied hydrogen bonds as weak interactions of mainly electrostatic nature. For stronger intramolecular hydrogen bonds N–H⋯О with a significant contribution of covalence to the bonding, the bifurcation index is negative. A relationship between the parameters calculated within the theory of the electron localization function (ELF) and the quantum theory “Atoms in Molecules” (QTAIM) is observed. In the ¹Н NMR spectra, the resonance shift of the bridging hydrogen atom, induced by a hydrogen bond is much smaller for the hydrogen bonds having a positive bifurcation index than that for the hydrogen bonds with the negative bifurcation index, and the interatomic H∙∙∙X distance is much longer in the former case. In the IR spectra the positive bifurcation index corresponds to a blue shift of the stretching vibration of the covalent bond of the hydrogen donor due to the hydrogen bonding and the negative bifurcation index corresponds to the red shift of this band.

Model structures of low, high, and very high density amorphous ices are obtained by the molecular dynamics and conjugate gradient methods. By means of the lattice dynamics method the vibrational properties of the obtained structures of amorphous ices are calculated. The delocalization of collective vibrations in amorphous ices is shown. The distribution of the number of molecules over the potential energies and amplitudes is derived. The directions of vector projections of the instantaneous displacement of molecules reveal the similarity of low-frequency collective vibrations to optical vibrations in crystals. Model cells of amorphous ices are considered as the crystal unit cells having periodical boundary conditions. Based on this assumption, the dispersion curves of amorphous ices are constructed, which also indicate the crystal-like collective vibrations.

This paper reports a predictive model for the rate constant of the bimolecular nucleophilic substitution involving the azide moiety. It predicts reaction rate constants in different solvents, including organic mixtures, and with different organic and inorganic azides as reactants. The optimal descriptors describing solvent effects and a cation type in the azide salt were suggested. A reasonably good predictive performance of the model in cross-validation has been demonstrated. The model was applied to predict the rates of the reactions between sodium azide with two conformers of calixarenes as well as 3-bromopropyl phenyl ester. For sterically non-hindered molecules, a good agreement between predicted and experimental reaction rates was observed. On the other hand, the model poorly reproduces the results for sterically hindered molecules.

It is shown that in a model chain of exchange clusters magneto-structural transitions are very sensitive to the variation of initial exchange integrals of the model. The cases of three-spin chains (a model of polymer chains of exchange clusters of the family of compounds of “breathing crystal” with the “head-head” motif) and two-spin chains (a model of these chains with the “head-tail” motif) are studied theoretically. A change in the exchange integrals under the effect of external pressure can substantially modify the thermal dependence of the magneto-structural and magneto-resonance properties of “breathing crystals”, which calls for the experimental studies in this aspect. The dependence of these properties on external pressure in “breathing crystals” is expected to have a more complex and diverse form than the ordinary high-temperature shift in the traditional spin-crossover compounds based on iron complexes. Some competing physical factors able to cause such a diversity are described qualitatively. Model calculations show that apart from the temperature shift, the application of external pressure to the “breathing crystals” can result in a change in the low-temperature limit of the effective magnetic moment in the exchange clusters of these compounds.

X–ray photoemission and absorption spectra of TiS₃ are studied. The temperature dependence of the magnetic susceptibility is measured and the electron density of states is calculated. Titanium ions in different oxidation states are found to coexist.

X–ray emission spectra of oxygen OK_α and X–ray photoelectron O1 s spectra are obtained for stable nitroxyl radicals: 3–imidazoline derivatives and their diamagnetic derivatives. It is shown that the highest occupied molecular orbitals in the nitroxyl radicals mainly consist of oxygen and nitrogen 2p atomic orbitals of the nitroxyl group. Distinctions in the X–ray emission spectra of oxygen of the compounds studied can be due to the presence of the unpaired electron in the radicals.

X–ray photoelectron spectroscopy and quantum chemistry are applied to study tris–dibenzoylmethanates of rare-earth elements (Sc, Y, and La). New information on the electronic structure of the complexes is obtained: the geometric and electronic structures of the compounds are calculated, the nature of the chemical bond of these compounds is established, the bands in X–ray photoelectron spectra of the valence and sub-valence regions are identified. The XPS and DFT studies of Sc, Y, and La tris–dibenzoylmethanates and Li(Dbm) и F₂B(Dbm) monochelate complexes made it possible to find the regularities of changes in the electronic structures depending on the complexing agent and also the effect of С₆Н₅ substitution for СН₃ groups in the ligands.

Ligands with Schiff bases are obtained in the condensation of propylenediamine (pda) or 2,2–dimethylpropylenediamine (dmpda) with acetylacetone (Hacac) in the 1:2 molar ratio. The ligands are characterized by the elemental analysis methods, T_melt = 90–92 °C for pda(Hacac)₂ (pda(acac)₂ is N,N'-propylene-bis(acetylacetoniminato) (2–)), T_melt = 84–86 °C for dmpda(Hacac)₂ (dmpda(acac)₂ is N,N'–2,2–dimethylpropylene-bis(acetylacetoniminato) (2–)). The tautomerism of the ligands is established by the single crystal X-ray diffraction (XRD) analysis, IR spectroscopy, and ¹H, ¹³C NMR spectrometry. The synthesized complexes [Cu(pda(acac) ₂)] (1), T_melt = 121–122 °C and [Cu(dmpda(acac)₂)] (2), T _melt = 156–158 °C are studied by the XRD method. In both complexes, copper atoms have a planar square geometry, and the chelate bond lengths and angles are: Cu–O ≈ Cu–N 1.903(2)–1.942(3) Å, ∠ O–Cu-N = 94.44(12)–94.99(12)° for 1 and Cu–O ≈ Cu-N 1.909(1)–1.943(2) Å, ∠ O–Cu–N = 94.63(6)° for 2. By the thermogravimetric method it is found that both complexes can be passed practically quantitatively into the gas phase.

Structures of β–diketonate cobalt(II) chelates with 1,3–diaminopropane (pda) are determined by single crystal X–ray diffraction (XRD) at temperatures of 100 K and 293 K respectively: Co(pda)(hfac)₂ and Co(pda)(tmhd)₂ (hfac is 1,1,1,5,5,5–hexafluoro–pentane–2,4–dionato(–), tmhd is 2,2,6,6–tetramethyl–heptane–3,5–dionato(–)). Crystallographic data for Co(pda)(hfac)₂ (C₁₃F₁₂H₁₂O₄N₂Co) are: a = 8.427(3) Å, b = 10.625(3) Å, c = 11.369(3) Å, α = 111.751(7)°, β = 97.968(7)°, γ = 93.070(7)°, space group P–1, V = 930.2(5) ų, Z = 2, d_x = 1.954 g/cm³, R = 0.0241; for Co(pda)(tmhd)₂ (C₂₅H₄₈N₂O₄Co): a = 9.459(1) Å, b = 11.856(1) Å, c = 14.186(1) Å, α = 71.607(2)°, β = 71.314(2)°, γ = 88.179(2)°, space group P–1, V = 1425.7(2) ų, Z = 2, d_x = 1.137 g/cm³, R = 0.0265. In both cases, there are only van der Waals interactions between the molecules. Thermodynamic values of the melting processes are found by differential scanning calorimetry (DSC). Experiments on the chemical vapor deposition of cobalt-containing films are performed with the use of Co(pda)(hfac)₂ as a precursor.

The crystal structures of complex zirconium fluorides (C₂H₅N₄)₂Zr₂F₁₀×H₂O and (H₃O)₃(NEt₄)₂Zr₄F₂₁×3H₂O synthesized for the first time are determined. The formation of new structure types of polymeric chain complex anions is found in them. Two crystallographically independent zigzag-like polymeric chains _∞(ZrF₅)^– composed of pentagonal bipyramidal polyhedra of Zr atoms sharing F–F edges form a polymeric chain complex anion in the (C₂H₅N₄)₂Zr₂F₁₀×H₂O structure. The polymeric chain complex anion in the (H₃O)₃(NEt₄)₂Zr₄F₂₁×3H₂O structure is formed of tetranuclear –Zr(1)F₇–Zr(2)F₈–Zr(3)F₈–Zr(4)F₇– moieties in which Zr(2)F₈ and Zr(3)F₈ polyhedra are linked by a common thiangular face and Zr(1)F₇ and Zr(4)F₇ polyhedra are bonded to Zr(2)F₈ and Zr(3)F₈ polyhedra by common edges. In the polymeric chain of the complex [Zr₄F₂₁]^5– anion the tetranuclear fragments share edges. The structural fragments of the compounds are combined in three-dimensional units by a branched system of N–H⋯O, N–H⋯F, and O–H⋯F hydrogen bonds.

The crystal structure of the boron(III) complex [BF₂L] synthesized for the first time, where L^– is the 3,3',5,5'–tetramethyl–4–ethyl–4'–iododipyrrolylmethene–2,2' monoanion (iodo–BODIPY, monoclinic crystals: a = 12.0329(6) Å, b = 15.9657(8) Å, c = 8.5080(4) Å, β = 103.753(1)°, V = 1587.64(13) ų, Z = 4 ( Z' = 1), space group P2₁/c) is determined. In the structure, two pyrrol rings and the central six-membered ring containing a boron atom are in one plane, perpendicular to which a plane formed by a group of F–B–F atoms is located. The crystal packing is formed by van der Waals interactions. In the electron absorption spectra of iodo-BODIPY solutions in nonpolar solvents, unlike polar ones, a red shift up to 3–8 nm of the maximum of the first intense band is observed, for which the lge value reaches ~4.71. Along with intense chromophoric properties, the synthesized iodo-BODIPY complex is a sufficiently strong fluorophore and can be used as a fluorescent marker.

The dynamics of liquid argon (~49 000 atoms in a cubic periodic cell) near the triple point is simulated. Two–particle correlation functions describing the simultaneous diffusive displacement of a pair of particles are calculated. Time dependence of the mean scalar product of the displacement vectors of two particles reaches a plateau. Previously, we detected such a behavior of this function for liquid water.

By heating a solution of LiOH and 1,1'–cyclohexanediacetic acid (H₂chda) coordination polymer [Li₂(chda)] (1) having a layered nature is obtained and characterized.

Two new copper (II) complexes [Cu(2–Pic)₂(4–NPA) ₂] (1) and [Cu(2–Pic)₂]×2H₂O (2), where 2–Pic is 2–picolinic acid and 4–NPA is 4–nitrophenylamine, are synthesized hydrothermally and their crystal structures are determined and analyzed. Complex 1 is crystallized in the monoclinic system space group P2₁/c and complex 2 is in the triclinic system space group P–1. Single crystal X–ray analysis reveals that the coordination environments around the Cu atoms of two complexes are four-coordinated and six-coordinated respectively. Complex 1 forms a 2D layer of a supermolecular structure through hydrogen bonds, and complex 2 is a 1D stair-stepping polymer chain and two water molecules linked by a hydrogen bond intersperse among the chains.

A novel phenolato, azido, and acetato co-bridged trinuclear zinc(II) complex [Zn₃L₂(m₂–CH₃COO)₂(m_1,1–N₃)(N₃)], where L is the deprotonated form of 4–chloro–2–[(2–diethylaminoethylimino)methyl]phenol, is prepared and characterized by elemental analysis, infrared spectrum, and single crystal X–ray determination. The complex crystallizes in the triclinic space group P1, with unit cell dimensions a = 12.7196(5) Å, b = 13.6597(6) Å, c = 13.7214(5) Å, α = 65.700(1)°, β = 83.429(1)°, γ = 63.545(1)°, V = 1938.4(1) ų, Z = 2, GOOF = 1.013, R₁ = 0.0456, and wR₂ = 0.1032. Structural analysis shows that the distances among the adjacent zinc atoms are 3.282(1) Å and 3.213(1) Å. The zinc atoms are in distorted square pyramidal and trigonal bipyramidal coordinations.

The novel bimetallic compound [Cu(bappz)(µ-NC)Ni(CN) ₃]×H ₂O (bappz = 1,4-bis(3-aminopropyl)piperazine) is prepared by the reaction of Cu(NO ₃) ₂×3H ₂O, bappz, and K ₂[Ni(CN) ₄] in water. The complex is characterized by IR spectroscopy and single crystal X-ray diffraction. The neutral [Cu(bappz)(µ-NC)Ni(CN) ₃] complex assumes a cyanide-bridged binuclear structure in which the nickel(II) ion is four-coordinated by carbon atoms from four cyano groups (one of them forms a bridge) in a square planar arrangement, whereas the copper(II) ion is five-coordinated by four bappz nitrogen and one cyanide nitrogen atoms in a distorted square-pyramidal geometry.

The crystal structure of bis(4-benzoyl-3-methyl-1-phenyl-4,5-dihydro-1 H-pyrazol-5-onato)-(ethanol)-dioxourane(VI) ethanol solvate [UO ₂L ₂(C ₂H ₅OH)]×C ₂H ₅OH (I), where HL is 4-benzoyl-3-methyl-1-phenyl-4,5-dihydro-1 H-pyrazol-5-one, is determined. The asymmetric part on the unit cell of the crystal structure of I contains the complex of uranyl ion with two bidentately coordinated L‾ ions and coordinated molecule of ethanol. In the outer coordination sphere of the central atom, the solvated ethanol molecule is located. The coordination polyhedron of the uranium atom in complex I is a pentagonal bipyramid. Its equatorial plane is composed of oxygen atoms of HL and ethanol. In the axial positions of the metal coordination polyhedron the oxygen atoms are located. In the crystal, the complexes of the studied compound are linked together via hydrogen bonds of the outer-sphere ethanol molecule in chains along the [100] direction. Between the chains in the crystal, the van der Waals interaction occurs.

The crystal structure of the C ₂H ₁₆N ₁₁NdO ₁₇ complex ( I) is established by X-ray crystallography. Compound ( I) crystallizes in the monoclinic system, space group C2/ c, a = 10.8926(6) Å, b = 9.0003(6) Å, c = 20.4621(11) Å, α = 90°, β = 94.535(3)°, γ = 90°, V = 1999.8(2) Å ³, and Z = 4. The guanidinium N-H and water H atoms are engaged in hydrogen bonds with an oxygen atom of the nitrate groups attached on neodymium (Nd). This has resulted in the formation of a three dimensional network. Based on the Cambridge Structural Database, this is the first structurally-characterized neodymium nitrate anion bonded to the [(NH ₂) ₃C] ⁺ cation.

The interaction of 1,10-diaza-18-crown-6 (L) with boron trifluoride etherate results in the formation of a complex of the composition (LH ₂)[BF ₄] ₂ whose structure is established by single crystal X-ray diffraction. The supramolecular structure of the perching type complex is stabilized by interionic NH⋯F Н-bonds (N⋯F 2.715(11)-2.964(9) Å).

Polyoxometalate complexes are investigated by the separation methods of capillary electrophoresis and ion-pair high-performance liquid chromatography (HPLC) using as an example the separation of model mixtures of heteropolytungstates and actual mixtures of heteropolymolybdate synthesis products of various compositions. The capabilities of the methods to separate complexes with similar structures and compositions are shown, provided that the separation conditions are optimized. For electrophoretic separation, there is a possibility of increasing the resolution of the signals by modifying the inner surface of the capillary.

The technique for interpreting magneto-ellipsometric measurements is proposed. The model of a homogeneous semi-infinite medium for reflecting layered magnetic structures in the presence of the magnetic field in the configuration of the magneto-optical equatorial Kerr effect is considered. Based on the analysis of the Fresnel coefficients with regard to the magneto-optical parameter Q appearing in the off-diagonal elements of the permittivity tensor, the expressions are obtained using which the refraction ( n) and absorption ( k) coefficients, the real ( Q ₁) and imaginary ( Q ₂) parts of the magneto-optical parameter can be found from the ellipsometric (ψ ₀ and Δ ₀) and magneto-ellipsometric (ψ ₀ + δψ and Δ ₀ + δΔ) measurements. The results will allow to measure and analyze the magnetic characteristics such as hysteresis loops and the coercitive force of layered nanostructures using the conventional ellipsometric equipment.

A method for preparing carbon material by carbonizing walnut shell at 700 °C is developed. The sorbent surface is negatively charged. Using scanning electron microscopy it is found that in carbonization the structuring of the sample surface occurs. A method for isolating flavonoids from the herb of St John's wort ( Hypericum perforatum L.) is optimized. The content of the sum of flavonoids in terms of rutin equivalent is 20-50 mg%. The phytocomposition is prepared and the structure of the obtained phytosorbent is studied; the degree of immobilization of biologically active substances is determined.

The voltammetry methods cover a variety of research, identification, and analysis areas based on the voltage-current dependence, with different materials used as electrodes. In this work, using cyclic voltammetry on a smooth platinum electrode by polarization in a wide range of potentials, the composition and properties of methanesulfonic acid (MSA) are studied.

Effect of the pH in the synthesis of ammonium titanate gel and the temperature of xerogel dehydration on the phase composition, degree of crystallinity, and dispersion of photoactive TiO ₂ powders is investigated. The possibility of preparing a metastable anatase modification of TiO ₂ with high crystallinity is shown. The textural, adsorption, and photocatalytic characteristics of the obtained dispersions are studied. Using atomic force microscopy (AFM) and spectral turbidimetry, the presence of particle aggregates and intergrowns causing the TiO ₂ coloring by organic dyes in the aqueous dispersions of photocatalysts is found.

A review is made of the physicochemical factors causing the variability of the properties of inorganic solid phases having the same stoichiometry of the elemental composition, but different actual structures. These factors lead to spatial inhomogeneity in the composition and structure of the solid phases and determine the time profile of the stoichiograms and kinetic dependences for the dissolution of these substances in the dynamic differential dissolution (DD) mode. A discussion is given of the results obtained by mathematical simulation of dynamic dissolution of solid phase mixtures, which show how the selectivity and efficiency of the separation of the phase mixtures depends on their dispersion ability. Various aspects are considered of the use of the DD method for detecting spatial inhomogeneity manifestations in the composition and structure of solids and materials.

The standardless stoichiographic differential dissolution (DD) method is used for phase analysis of superfine multicomponent oxide precursors of Fe-Co MWCNT synthesis catalysts obtained by the Pechini method. The analysis identifies the individual phases in the studied samples of Fe ₂Co/Al ₂O ₃, Fe ₂Co/MgO, and Fe ₂Co/CaCO ₃ and determines their stoichiometric composition and quantitative content. It is found that the samples are a complex mixture of superfine oxide phases the composition of which corresponds to a spinel structure and may simultaneously include both active (Fe and Co) and carrier elements (Al and Mg) to form solid solutions. It is only the Fe ₂Co/CaCO ₃ samples that contain a carrier-free phase the composition of which corresponds to a spinel structure.

An overview is given of the works on the creation of original high-precision oscillation methods for an integrated study of physicochemical characteristics and crystallization/melting of solutions and melts. Some experimental results are presented for viscosity and crystallization/melting in the region of stable and metastable states at high temperatures. Dozens of new compounds and phases are found in the studied oxide systems. It is shown that one high-precision experiment can determine more than ten parameters and characteristics of the studied systems in the region of stable and metastable states. In many cases the proposed oscillation methods are found to be much more accurate and informative than the existing methods.

In the work the properties of grain-oriented layers of the cubic phase of silicon carbide and SiGeC nanoscale basic region formed under them at the inner boundary of the 3C-SiC/SiGeC/Si(100) heterojunction are discussed. The structures are obtained in the process of low-temperature (below 1000 °С) carbidization of the silicon surface in vacuum with the use of molecular beams of hydrides and hydrocarbons. The main attention is focused on the discussion of the composition, microstructure, and surface morphology of the layers. The light-emitting properties of the structures in the band-edge photoluminescence from silicon are studied. The diode characteristics of the heterojunction are also studied. Mathematical modeling methods are employed to investigate the band structure of the heterojunction under different injection level conditions of non-equilibrium charge carriers to the basic region of the system.