DFT Calculation of the Structure of the Coordination Unit of Chlrophyll-Containing Proteins

In a DFT/B3LYP study (6-31G(d) basis set), the structure, IR spectra, and thermodynamic parameters of Mg-porphin-imidazole and Mg-khlorin-imidazole complexes, serving as models of the coordination unit of chlorophyll in proteins, have been calculated. When an axial ligand is added, the Mg atom goes out of the plane of the tetrapyrrole macrocycle, the deviation being 0.34 Å. The frequency of the out-of-plane vibrations of Mg in the complexes increased by 50 cm⁻¹, and the frequencies of the two in-plane vibrations decreased by 25 cm^{− 1}–30 cm⁻¹. IR vibrational spectra have been simulated.Original Russian Text Copyright © 2004 by M. D. Elkin, O. D. Ziganshina, K. V. Berezin, and V. V. Nechaev__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1132–1135, November–December, 2004.     

The role of neutral defects in the structural chemistry of liquid water

For defective water associates with an extra hydrogen atom (n-defective associates), size and structure effects on ionization potentials compared to defectless (normal) associates of similar structures have been investigated by quantum chemical and molecular mechanics methods. The ionization potentials of small n defective water associates increase (from fractions of eV to 7 eV–8 eV) with the number of water molecules in the associate. These are most probably the source of a hydrated electron that are responsible for the ensuing equilibrium between all defects in liquid water: neutral n and p defects and ion defects (H _aq ⁺ , OH _aq ^– , e _aq ^– ). Delocalization of an odd electron in defective associates stabilizes the latter and promotes their recombinations, forming hydrated water molecules, hydrogen peroxide, and gaseous hydrogen. Structural instability of fullerene (H₂O)₂₀ relative to normal associates has been found. This compound is stabilized by the endo inclusion of a hydrogen atom, and exo fixation of the hydrogen atom gives rise to an extra source of hydrated electrons.Original Russian Text Copyright © 2004 by G. A. Domrachev, D. A. Selivanovskii, E. G. Domracheva, L. G. Domracheva, A. I. Lazarev, P. A. Stunzhas, S. F. Shishkanov, and V. L. VaksTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 670–677, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

DFT and CI Studies of Electronic Structure and Photoionization of Sc,Ti, V,Cr, and Co Tris-β-diketonate Complexes

Orbital structure calculations were performed in the density functional theory (DFT) approximation for neutral complexes of Sc, Ti, V, Cr, and Co tris-β-diketonates; for the first three compounds, the structures of the ground ionic states and ionization energies were calculated in the CI approximation with decomposition on the orbitals of DFT. The sequence of the highest occupied orbitals found by this procedure coincides with the order of bands in the PES spectrum, while in the SCF-HF ab initio method, it does not. After the electron removal, all orbitals are stabilized by about 4.5 eV; for the vanadium complex, the removal of one d electron leads to the greatest stabilization of the remaining occupied orbital, which is essentially a d orbital. In CI calculations, using the DFT orbitals for decomposition does not lead to significantly better agreement with experiment when compared to the single-determinantal approximation and to the CI method with orbitals of the ab initio approximation.Original Russian Text Copyright © 2004 by I. S. Osmushko and V. I. Vovna__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 783–791, September–October, 2004.     

Coordination Polyhedra RuXn (X = O,S, Se,Te) in Crystal Structures

Crystal-chemical analysis of 312 compounds containing complexes [Ru _a X _b ] ^z– (X = O, S, Se, Te) is performed using Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres. In most of these complexes, Ru atoms have coordination number (CN) 6 and form RuX₆ octahedra. However, only with respect to oxygen do the Ru(V)–Ru(VII) atoms exhibit CN 5 or 4 with trigonal-bipyramidal and tetrahedral coordination, respectively.The effect of the valence state of the Ru atoms on their stereochemistry is considered. The important role of the Ru–Ru interactions in the structure of the Ru(II)–Ru(V) compounds is established. As a result of the Ru–Ru interactions, the RuX₆ octahedra are linked through a face or common edge or give O₅Ru–RuO_- dimers in which every metal atom occupies one of the vertices of an octahedron formed by the neighboring Ru atom.The dependence of the Ru–Ru and Ru–O bond orders on their lengths is established on the basis of a crystal-structure analysis and the 18-electron rule.     

Electronic effects of substituents on the conformational characteristics of the 1,2-dihydropyridine ring

The electronic effects of substituents on the conformational characteristics of the 1,2-dihydropyridine ring were investigated by the MP2/6-31G(d) quantum chemical method. Introduction of a nitro group leads to a flattening of the ring; on the potential energy surface, the minimum corresponding to the conformer with an axial orientation of the NH hydrogen atom vanishes. An opposite tendency is observed in amino derivatives. Intramolecular interactions are analyzed to see how they affect the the equilibrium geometry and the energy characteristics of the dihydroheterocycle.Original Russian Text Copyright © 2004 O. V. Shishkin and R. I. ZubatyukTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 589–594, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Spectroscopic Investigation of Sublimated Products of Ultradisperse Polytetrafluoroethylene

The structure of fractions isolated by thermal sublimation of ultradisperse polytetrafluoroethylene (UPTFE) powder has been studied by IR spectroscopy. At 50°C–160°C, fractions of highly amorphous fragments are condensed on a cold receiver; the fragments are constructed from branched chains with terminal olefin groups. Fractions isolated at 300°C and higher are close in structure to PTFE and are highly crystalline. It is assumed that sample amorphism is due to the irregular distribution of the fractions of fragments with terminal olefin and lateral fluoromethyl groups in the structures.Original Russian Text Copyright © 2004 by L. N. Ignatieva, A. K. Tsvetnikov, O. N. Gorbenko, T. A. Kaidalova, and V. M. Buznik__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 830–836, September–October, 2004.     

Crystal and Molecular Structure of <Emphasis Type="Italic">Bis</Emphasis>(2,3-pentamethylene-3,4-dihydro-4-oxoquinazolinium) Tetrachlorocuprate(II) Sesquihydrate

The structure of bis-(2,3-pentamethylene-3,4-dihydro-4-oxoquinazolinium) tetrachlorocuprate (II) sesquihydrate, (C₁₃H₁₅N₂O)₂[CuCl₄]·1.5H₂O, was determined by single crystal X-ray diffraction. In contrast to the previously studied analogs, the compound contains crystallization water molecules.Original Russian Text Copyright © 2004 by K. K. Turgunov, B. Tashkhodzhaev, L. V. Molchanov, and Kh. M. Shakhidoyatov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 955–959, September–October, 2004.     

Relaxation Effect of Basis Orbitals on the Properties of Atomic and Molecular Hydrogen Systems

The effect of orbital relaxation on the properties of atomic and molecular hydrogen systems H, H ₂ ⁺ , H₂, H ₂ ⁻ , and H ₃ ⁺ calculated using the minimal basis set, the split valence shell basis set including the polarization function, and an extended basis set of grouped natural orbitals is considered. Inclusion of orbital relaxation in calculations results in a decreased total energy and more accurate energies of electron affinity. The strongest effect is produced on the calculated characteristics of the anions. The calculated activation energy of the radical reaction of hydrogen elimination. H₂ + H = H + H₂ depends strongly on the degree to which electron correlation is taken into account. Due to inclusion of orbital relaxation, the activation energy also approximates the experimental value, although to a lesser extent. The semiempirical PM3 method fails to adequately describe the transition state of this reaction, but this disadvantage is eliminated by using the exponent of the relaxed orbital of hydrogen.Original Russian Text Copyright © 2004 by A. I. Ermakov, A. E. Merkulov, A. A. Svechnikova, and V. V. Belousov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 979–985, November–December, 2004.     

X-Ray Investigation of Chiral β-Hydroxyketone Derived From (+)-Isomenthone

X-ray analysis was carried out to study the molecular structure of β-hydroxyketone, which is one of the minor products of selective aldol condensation of (−)-menthone with 4-carbomethoxybenzaldehyde. The cyclohexanone ring of the compound has a practically undistorted chair conformation with an axial orientation of the 1-methyl group and the bulkiest 2-[1′-hydroxy-1′ -(4-carbomethoxyphenyl)]methyl substituent and the equatorial orientation of the isopropyl group in the 4 position. The stereochemical configuration was found to be (1R,2R,4 R, 1′ S), supporting that the compound belongs to the group of (+)-isomenthones; i.e., the starting (-)-menthone undergoes (to a certain extent) epimerization under the reaction conditions used. In crystal, there is intermolecular hydrogen bonding >C=O...HO- (the -O...H- bond length is 2.15 Å). The molecular conformation in hydroxyketone crystals differs from the one which prevails in solutions (according to previous NMR data) and which is characterized by an inverted cyclohexanone ring and intramolecular hydrogen bonding >C=O...HO.Original Russian Text Copyright © 2004 by S. V. Shishkina, T. G. Drushlyak, L. A. Kutulya, N. S. Pivnenko, and O. V. Shishkin__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 933–940, September–October, 2004.     

Basis Set Orbital Relaxation in Atomic and Molecular Hydrogen Systems

Orbital relaxation (OR) amounts to variation of the orbital exponents in hydrogen molecules and ions relative to the exponents of the isolated atom; it is represented as the sum of the one- and two-center contributions depending on the effective atomic charge and on the presence of other atoms in the molecule. The procedure for isolating the contributions of the exponent includes treatment of the OR of hydrogen in a special set of neutral and charged atoms and molecules with certain multiplicities of their electronic states. Within the framework of the spin-unrestricted Hartree-Fock method, we found and discussed the optimal values of the exponents of the basis orbitals of hydrogen atoms and molecules using the minimal split valence-shell basis set, the basis set that includes the polarization function, and the expanded set of grouped natural orbitals. A simple energy model is suggested for OR. Expressions are derived for evaluating the exponents of the relaxed orbitals in hydrogen-containing systems.Original Russian Text Copyright © 2004 by A. I. Ermakov, A. E. Merkulov, A. A. Svechnikova, and V. V. Belousov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 973–978, November–December, 2004.     

Synthesis,Structure and Properties of Some 3d-Element Complexes with 2-[2-(Hydroxybenzylidene)-amino]-2-hydoxymethylpropane-1,3-diol

2-[2-(Hydroxybenzylidene)-amino]-2-hydoxymethylpropane-1,3-diol (HL) reacts with cobalt, nickel, copper and zinc chlorides, bromides and acetates in water–ethanol solutions and gives MLX · nH₂O and ML₂ · nH₂O complexes (M = Co, Ni, Cu, Zn; X = Cl, Br; n = 0–5). Single crystals of CuLBr were grown, and its crystal structure was determined by X-ray diffraction analysis. The crystals are tetragonal, a = 17.024(2), c = 8.720(2) Å, space group P 2₁ c, Z = 8, R ₁ = 0.0349. In the structure of this complex, the copper atom coordinates the deprotonated HL molecule. The coordination polyhedron of the central atom is an elongated tetragonal pyramid. Its base is built of the imine nitrogen atom, phenolic and alcoholic oxygen atoms, and bromine atom. The apex of the pyramid is occupied by the bromine atom of the adjacent complex connected with the initial complex by the plane of sliding reflection. Thus, the crystal contains infinite chains of complexes running along the c axis, the complexes being united by both bridging bromine atoms and O–H···O hydrogen bonds. The conclusions on the compositions and structures of the remaining compounds were made on the basis of elemental and combined thermal analyses, IR spectroscopy, and magnetic chemistry data. The copper halide complexes were found to have dimeric, and the other metal complexes monomeric, structures. In the synthesized complexes, the azomethine HL can function as a bidentate or tridentate ligand. The thermolysis of the coordination compounds proceeds through the stages of elimination of crystal water molecules (75–90°C) or inner-sphere water molecules (145–155°C) and complete thermal destruction (485–550°C).     

Verfeinerung der Kristallstruktur von Te2O3(SO4)

The crystal structure of ditellurium(IV)-trioxide sulfate, Te₂O₃(SO₄)—space group Pmn2₁–C _2v ⁷ ;a=8.879 (2),b=6.936 (2),c=4.646 (4) Å,Z=2—has been determined and refined by least-squares, using three-dimensionalX-ray data (1188 independent reflexions) to a final R-value of 6.3%.The crystal structure comprises puckered tellurium(IV)—oxygen layers in which the tellurium atoms are linked together by three oxygen bridges (Te–O 1.907, 1.945, 2.011 Å). The SO₄ groups are arranged between these layers. Two oxygen atoms of each SO₄ group are bonded to two adjacent tellurium atoms of one layer [Te–O(S) 2.270 Å] and the tellurium atoms show a (3+1) coordination. A third oxygen atom of the SO₄ group is in weak interaction with two adjacent tellurium atoms of the same layer (Te–O 2.603 Å) whereas the fourth oxygen atom has distances of 2.866 Å to two adjacent tellurium atoms of the next layer and effects a very weak interaction between the

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Herrn Prof. Dr.R. Kieffer zu seinem 70. Geburtstag gewidmet.     

Reduction of substituted N-(o-nitrophenyl)glycines with tin(II) chloride

The reduction of substituted N-(o-nitrophenyl)glycines with tin(II) chloride results in closure of a 1,2,3,4-tetrahydropyrazine ring. Depending on the conditions, either the product contains no chlorine atom or the chlorine atom in the product occupies the ortho position with respect to the NHC(O) group.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1706–1708.Original Russian Text Copyright © 2004 by Vlaskina, Perevalov.This revised version was published online in April 2005 with a corrected cover date.     

Quantum-chemical study of potassium and ammonium hexafluorozirconates

A number of fluorozirconate clusters serving as structural models for K₂ZrF₆ and (NH₄)₂ZrF₆ crystals were investigated by the Hartree-Fock ab initio method. Based on the results of quantum-chemical calculations it is shown that the differences in the structure of these compounds and in the behavior of the temperature dependence of the second moment of the ¹⁹F NMR spectra are due to differences in the binding between the cation and anion sublattices. A mechanism responsible for ionic mobility is suggested.Original Russian Text Copyright © 2004 by E. I. Voit, A. V. Voit, V. Ya. Kavun, and V. I. SergienkoTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 644–650, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Synthesis and crystal structures of anhydrous lithium and ammonium hypophosphites

Conditions of synthesis (temperature, precursors) have been selected to grow crystals of anhydrous lithium and ammonium hypophosphites. The crystal structure of LiH₂PO₂ has been determined. Cell parameters and atomic positions in (NH₄)H₂PO₂ at room temperature and at 100 K have been refined. By their oxygen atoms the hypophosphite anions serve to bridge the four cations. Each oxygen atom is bonded to two cations, creating puckered layers parallel to the (001) planes. The structures show much similarity in the general arrangement, but differ in the type of the tetrahedral cation-anion bonds. In LiH₂PO₂, the Li-O bond is ionic (1.933(4) Å); in (NH₄)H₂PO₂, N-H...O is a hydrogen bond (2.846(1) Å).Original Russian Text Copyright © 2004 by M. I. Naumova, N. V. Kuratieva, D. Yu. Naumov, and N. V. PodberezskayaTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 491–496, May–June 2004.     

QSPR Modeling of the Reactivity Parameters of Monomers in Radical Copolymerizations

For a series of monomers, QSPR test analysis is performed by optimizing the correlation weights of the local invariants of molecular graphs representing monomer structures in order to construct models of the reactivity parameters of monomers Q and e. This approach may be used as a tool in reactivity predictions for monomers for which no experimental data on Q and e are available.Original Russian Text Copyright © 2004 by A. A. Toropov, V. O. Kudyshkin, N. L. Voropaeva, I. N. Ruban, and S. Sh. Rashidova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 994–998, November–December, 2004.     

Synthesis of nonequilibrium Ir<Subscript>x</Subscript>Re<Subscript>1-x</Subscript> solid solutions. Crystal structure of [Ir(NH<Subscript>3</Subscript>)<Subscript>5</Subscript>Cl]<Subscript>2</Subscript>[ReCl<Subscript>6</Subscript>]Cl<Subscript>2</Subscript>

Synthesis of five binary complex salts with an [Ir(NH₃)₅Cl]²⁺ complex cation is described. The counterions are [ReCl₆]^2–, [IrCl₆]^2–, [ReBr₆]^2–, and Cl^–. A polycrystal X-ray diffraction study has been performed for [Ir(NH₃)₅Cl]₂[ReCl₆]Cl₂, and its crystal structure has been determined. A series of Ir _x Re_1–x phases (0.5 x > 1) were obtained by reductive thermolysis. For the Ir-Re system, the history of the V/Z(x) dependence has been refined.Original Russian Text Copyright © 2004 by S. A. Gromilov, S. V. Korenev, I. V. Korolkov, K. V. Yusenko, and I. A. BaidinaTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 508–515, May–June 2004.     

Quantum-chemical investigation of nature of neutral intermolecular hydrogen bond in complex H3PO...HF

Results are presented from modeling the complex H₃PO...HF by the ab initio Hartree-Fock-Roothaan method. A generalized method is proposed for the quantitative fragmentary analysis of molecular orbitals (MOs). It is shown that when the complex is formed, the chemical bond between the phosphine oxide and the HF molecule is formed by means of a shift of the electron pair of the -bond of the HF to a 2p orbital of the O atom and the formation of a bonding three-center MO localized on the O, H, and F atoms, and also through a shift of an electron pair from the O atom to a 2p orbital of the F atom and the formation of a nonbonding MO localized on the O and F atoms.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 38–41, January–February, 1992.     

Structural Peculiarities of Dioxane Media in H/D Isotope Effects of Water Solvation at 288.15K-318.15K

Using the data of precision densimetry measurements for diluted solutions of H₂O and D₂O in 1,4-dioxane (1,4-DX) at 288.15 K-318.15 K we calculated the limiting partial molar volumes of the H/D isotopomers of water in dioxane and the excess molar volumes of the stated systems. The water molecules dispersed in 1,4-DX form complexes H-bonded into associates whose packing coefficient slightly exceeds that of the structural aggregates in liquid H₂O and D₂O. It is concluded that the structure of 1,4-DX is loosened and concomitantly undergoes volume expansion caused by the water microimpurities. The differentiating temperature effect on the volume solvation effects of H₂O and D₂O in 1,4-DX has been found.Original Russian Text Copyright © 2004 by. E. V. Ivanov, E. Yu. Lebedeva, and V. K. Abrosimov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 852–861, September–October, 2004.     

Isotope Effect on Fractional Dilatability of Solute Water as an Indicator of the H-Bonding Ability of an Aprotic Dipolar Solvent

Based on experimental data about the density of very dilute solutions of H₂O and D₂O in 1,4-dioxane, hexamethylphosphotriamide, and acetonitrile at 278.15 K-318.15 K we determined the limiting partial molar volume (error ±0.03 cm³·mol⁻¹) and dilatability of the water component. A correlation equation has been derived which relates the isotope effect (IE) in the limiting excess partial molar dilatability of water to the energy of the H₂O-solvent hydrogen bond. The stated IE may be used as a “structural indicator” for evaluating the ability of an aprotic dipolar solvent to undergo specific interactions through hydrogen bonding.Original Russian Text Copyright © 2004 by E. V. Ivanov, V. K. Abrosimov, and E. Yu. Lebedeva__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1020–1026, November–December, 2004.