Carbon in boron carbide: The crystal structure of B<Subscript>11.4</Subscript>C<Subscript>3.6</Subscript>

A single crystal of boron carbide obtained from a self-propagating high-temperature synthesis (SHS) product was studied by X-ray crystallography: B_11.4C_3.6, a = 5.594(2) Å, c = 11.977(7) Å, V = 324.6(7) ų, space group R3m, Z = 3, ρ_calcd = 2.56 g/cm³, R = 0.048. The content of carbon in the single crystal was estimated at ～24 at % from analysis of the unit cell parameters, bond lengths, and the volume of B_{12 ? x} C _x icosahedra, which demonstrated the possibility of obtaining by SHS carbon-rich boron carbide crystals due to the substitution of carbon atoms for boron atoms in icosahedra. Comparison of the X-ray crystallographic data for single crystals of boron carbide with the results of quantum-chemical calculations (an ab initio method (the 3–21G basis set) with geometry optimization) showed that the C-B-C group in a crystal has a nonlinear structure.     

Stability of polyhedral borane anions and carboranes

Polyhedral borane anions and carboranes that can be constructed formally from the interaction of rings and caps will be stable with six interstitial electrons. Interstitial electron count is obtained by summing the number of π electrons of the ring and the electrons of the caps involved in ring cap binding. Thus B₇H₇ ⁻² (D_5h) has 6 interstitial electrons (none from the B₅H₅ ring, two each from the twobh caps and two negative charge),mndo calculations on isoelectronic pyramidal molecules B₆H₆ ⁻⁴ (C_5v), B₅H₅CH⁻³ (C_5v), B₅H₅ ⁻⁴ (C_4v), B₄H₄CH⁻³ (C_4v), B₄H₄ ⁻⁴ (T _d) and B₃H₃CH⁻³ (C_3v) suggests a criterion based on the out-of-plane bendings of the ring B-H bonds to select the best combination of borocycles and BH or CH caps. Three-membered borocycle prefers CH cap, five-membered borocycle prefers BH cap. The preference of four-membered ring for BH or CH cap is not as pronounced. The extra stability of B₁₂H₁₂ ⁻² arises from the geometry of the icosahedron. The relative stabilities ofnido andcloso carboranes follow from these rules.     

Chemical behavior of positive mouns in diamagnetic metal acetylacetonate solid solutions

Diamagnetic muon yields (P _D) in (Al _x Co_1−x )(acac)₃ and (Ga _x Co_1−x )(acac)₃ systems were investigated. Both in (Al _x Co_1−x )(acac)₃ and (Ga _x Co_1−x )(acac)₃, Co(acac)₃ was more influential on diamagnetic muon yield than Al(acac)₃ and Ga(acac)₃. Zerofield muon spin relaxation rate suggests that the diamagnetic muon resides in the vicinity of Co(acac)₃ molecules.     

Calculations of thermodynamic stability of CpCoC<Subscript>2</Subscript>B<Subscript>9</Subscript>H<Subscript>11</Subscript> cobaltacarborane isomers

Quantum-chemical calculations of the geometry and energies of nine possible isomers of 12-vertex cobaltacarborane CpCoC₂B₉H₁₁ (1) were carried out by the DFT method (PBEPBE/DGDZVP/DGA1). Thermodynamic stability of the isomers increases with increasing distance between the carbon atoms in the cage and is virtually independent of the position of the CpCo vertex. The relative stabilities of the 1,2,3-(17.57 kcal mol⁻¹), 1,2,4-(3.72 kcal mol⁻¹), and 1,2,9-isomers of 1 (0 kcal mol⁻¹) are similar to the corresponding values for the ortho (17.61 kcal mol⁻¹), meta (3.21 kcal mol⁻¹), and para isomers (0 kcal mol⁻¹) of carborane C₂B₁₀H₁₂. The results of the present study confirm a close similarity of the CpCo and BH fragments in metallacarborane chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1557–1559, July, 2005.     

Interface microstructure and diffusion kinetics in diffusion bonded Mg/Al joint

The interface microstructure, formation of diffusion bonded joint and regulation of atom diffusion were studied by means of scanning electron microscope (SEM), energy dispersion spectroscopy (EDS) and electron probe microanalyser (EPMA). The experimental results indicated that an obvious interfacial transition zone was formed between Mg and Al, and there are three intermetallic layers Mg₁₇Al₁₂, MgAl and Mg₂Al₃ in this zone. Diffusion activation energy of Mg and Al in the above layers was lower than that in the Mg and Al base metals. The thickness (x) of each layer can be expressed as x ² = 4.14exp(−28780/RT)(t−t ₀), x ² = 31.4exp(−25550/RT)(t−t ₀) and x ² = 0.6exp(−22600/RT)(t−t ₀) corresponding to Mg₁₇Al₁₂, MgAl and Mg₂Al₃ with heating temperature (T) and holding time (t).     

Development of Cocatalysts for Photocatalytic Overall Water Splitting on (Ga1? x Zn x )(N1? x O x ) Solid Solution

The development of cocatalysts promoting overall water splitting on (Ga_1−x Zn _x )(N_1−x O _x ) solid solution photocatalyst is presented. The (Ga_1−x Zn _x )(N_1−x O _x ) is a stable visible-light-driven photocatalyst for stoichiometric water splitting upon loading with a suitable nanoparticulate cocatalyst. Loading with a combination of Cr and Rh oxides, Rh_2−y Cr _y O₃, is demonstrated to raise the quantum efficiency of (Ga_1−x Zn _x )(N_1−x O _x ) for overall water splitting to 2.5% at 420–440 nm. This represents a 10-fold increase in efficiency over the highest efficiency previously obtained using nanoparticulate RuO₂ as a cocatalyst. In addition to the composition, the dispersion and size of cocatalyst nanoparticles are identified as important factors affecting the degree of enhancement for stoichiometric water splitting. Kazuhiko Maeda—Research Fellow of the Japan Society for the Promotion of Science (JSPS).     

An ab initio Molecular Orbital Study of the Conformational Properties of all-( Z )-Cyclododeca-1,4,7,10-tetraene

 Ab initio HF/6-31G^* and MP2/6-31G^*//HF/6-31G^* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C _4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C _s) and twist (C _2h) conformers and requires about 22.3 kJ · mol⁻¹. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol⁻¹. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries of the title compound are in good agreement with the results of ab initio methods.     

Thermal conversions of chitosanium dodecahydro-<Emphasis Type="Italic">closo</Emphasis>-dodecaborate

The thermal behavior of chitosanium dodecahydro-closo-dodecaborate, (C₆O₄H₉NH₃)₂B₁₂H₁₂, was studied by thermal analysis, X-ray diffraction, and IR and X-ray photoelectron spectroscopy. As this compound is heated at a rate above 10–20 K/min, it ignites at a temperature of about 300°C. As the compound is heated to 1000°C at a rate below 10 K/min in an inert atmosphere, it yields a mixture of carbon and amorphous boron and/or boron carbides. The presence of a small amount of boron oxide in the product is explained by the formation of a partially oxidized hydroborate anion at the early stages of (C₆O₄H₉NH₃)₂B₁₂H₁₂ decomposition via the interaction between oxygen of the chitosanium cation and the B₁₂H₁₂²⁻ anion. Heating the initial compound in air at a rate below 10 K/min yields carbon and boron oxide as the main products. Molten boron oxide protects boron and/or boron carbides and boron nitride forming in small amounts in the particle bulk from oxidation.     

Structural and electronic properties of aln and bn wide-gap semiconductors and their B<Subscript>x</Subscript>Al<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N solid solutions

The structural and electronic properties of B_xAl_1−x N solid solutions (x = 0.25, 0.5, 0.75) were examined by calculating the electronic energy structure by the local coherent potential method within the framework of multiple scattering theory. The charge is transferred from aluminum to nitrogen atoms and increases with the content of boron atoms. The concentration dependences of the structural and electronic properties of these solutions are discussed. __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 5, pp. 822–829, September–October, 2005.     

Crystal structure of [MnII (1,10-C12H8N2)3]2+[(B9C2H11)CoIII(B8C2H10)CoIII(B9C2H11)]2?·CH3CN

A novel compound, [MnPhen₃][(B₉C₂H₁₁)Co(B₈C₂H₁₀)Co(B₉C₂H₁₁)]· CH₃CN (Phen = 1,10-phenantroline), comprising a Co(III) dicobaltacarborane cluster anion has been prepared and characterized by single crystal X-ray diffraction. Crystal data are the following: C₄₄H₅₉B₂₆N₇Co₂Mn, M = 1139.84, triclinic, space group , unit cell parameters: a = 13.2465(11) Å, b = 14.521(2) Å, c = 15.2536(15) Å; α = 77.027(9)°, β = 88.500(8)°, γ = 77.274(9)°; V = 2788.5(5) ų, Z = 2, d _calc = 1.358 g/cm³, T = 295 K, F(000) = 1162, μ = 0.853 mm⁻¹. The structure was solved by the direct and Fourier methods and refined anisotropically (isotropically for hydrogen atoms) using the full-matrix technique to final factors R ₁ = 0.0374, wR ₂ = 0.0915 for 7397 I _hkl ≥2σ_I of 9779 I _hkl measured (diffractometer Enraf-Nonius CAD-4, λMoK _α , graphite monochromator, θ/2θ-scanning). The structure is formed from [MnPhen₃]²⁺ cations, [(B₉C₂H₁₁)×Co(B₈C₂H₁₀)Co(B₉C₂H₁₁)]₂₋ anions, and acetonitrile molecules CH₃CN. Central Mn atom in the cation has a distorted octahedral coordination environment formed by six nitrogen atoms of three bi-dentate Phen ligands, average Mn-N bond length being 2.263(2) Å. The anion has a chain-like structure built from three icosahedra sharing common vertices occupied by the cobalt atoms. The central icosahedron including ten light atoms (8B, 2C) provides two vertices for the cobalt atoms shared with the other icosahedra having 11 light atoms (9B, 2C). The arrangement of-C₂-groups in the anion corresponds to a quasi-gauche-configuration of asymmetric sandwich complexes of both cobalt atoms. Original Russian Text Copyright ? 2005 by T. M. Polyanskaya, V. V. Volkov, and M. K. Drozdova __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 4, pp.730–740, July–August, 2005.     

An ab initio Molecular Orbital Study of the Conformational Properties of all-(Z)-Cyclododeca-1,4,7,10-tetraene

Summary.  Ab initio HF/6-31G^* and MP2/6-31G^*//HF/6-31G^* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C _4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C _s) and twist (C _2h) conformers and requires about 22.3 kJ · mol⁻¹. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol⁻¹. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries of the title compound are in good agreement with the results of ab initio methods. Received July 9, 2001. Accepted September 26, 2001     

Quantum-chemical calculation of a spillover model on a graphite support

The simplest quantum-chemical models of hydrogen spillover over a graphite-like surface as a proton or radical have been considered. The condensed planar C₂₄H₁₂ molecule was used as a model surface. Theab initio calculations of the interaction of hydrogen with the model surface were carried out by the restricted Hartree-Fock (HF) method in the STO-3G and 6-31 G^* basis sets. The radical hydrogen can not bind to such a surface, whereas the proton binds to it with an energy release of 186 kcal mol⁻¹. The activation energy of the transfer of the proton between two neighboring carbon atoms (10 kcal mol⁻¹) has been determined. The simplest model of the hydrogen migration as a proton over the model surface can be used for describing the spillover of hydrogen over the graphite surface. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 428–430, March, 1997.     

Singlet-triplet splitting of divalent five-membered fused rings C<Subscript>12</Subscript>H<Subscript>8</Subscript>M (M = C,Si, Ge,Sn, and Pb): Application in nanocomplex synthesis

Energy differences, ΔX _s−t (X = E, H, and G) (ΔX _s−t = X(singlet) − X(triplet)) between singlet (s) and triplet (t) states of C₁₂H₈M were calculated at B3LYP/6-311+G*. The DFT calculations indicated that the ΔG _s−t between singlet (s) and triplet (t) states of C₁₂H₈M were increased from M = C to M = Pb. The ΔG _s−t of C₁₂H₈M was compared with its analogue C₄H₄M through replacement of heavy atoms from M = C to M = Pb. Configurations of the electrons in orbitals (σ² or π²) for the singlet state of C₁₂H₈M were discussed.     

Hydrogenation of B 120/? : A Planar-to-Icosahedral Structural Transition in B12H n0/? (n?=?1–6) Boron Hydride Clusters

A systematic density functional theory and wave function theory investigation performed in this work reveals a planar-to-icosahedral structural transition between n = 4–5 in the partially hydrogenated B₁₂H _n ^0/− clusters (n = 1–6) upon hydrogenation of all-boron B₁₂^0/−. Coupled cluster calculations with triple excitations (CCSD(T)) indicate that a distorted icosahedral B₁₂H₆ cluster with C₂ symmetry is overwhelmingly favored (by 35 kcal/mol) over the recently proposed perfectly planar borozene (D_3h B₁₂H₆) (Szwacki et al., Nanoscale Res Lett 4:1085, 2009) which proves to be a high-lying local minimum. A similar 2D–3D structural transition occurs to the corresponding boron boronyl analogues of B₁₂(BO) _n with n –BO terminals. Detailed adaptive natural density partitioning (AdNDP) analyses reveal the bonding patterns of these quasi-planar or cage-like clusters which are characterized with delocalized σ and π molecular orbitals. The electron detachment energies of the concerned anions and excitation energies of the neutrals are also predicted to facilitate their future experimental characterizations.     

Structure of complex salts [Co(NH3)6][Rh(NO2)6] and [Co(NH3)6][(NO2)3Rh(μ-NO2)1+x(μ-OH)2?xRh(NO2)3]·(2-x)(H2O), x = 0.17

The structures of two salts [Co(NH₃)₆][Rh(NO₂)₆] (I) and [Co(NH₃)₆][(NO₂)₃Rh(μ-NO₂)_1+x (μ-OH)_2−x Rh(NO₂)₃]·(2−x)(H₂O), x = 0.17 (II) are solved. Single crystals of the salts are obtained by the counter diffusion method through the gel of aqueous solutions of [Co(NH₃)₆]Cl₃ and Na₃[Rh(NO₂)₆]. The structure of [Co(NH₃)₆][Rh(NO₂)₆] is consistent with the diffraction data for a polycrystalline sample of poorly soluble fine salt formed in the exchange reaction between aqueous solutions of [Co(NH₃)₆]Cl₃ and Na₃[Rh(NO₂)₆]. The structure of [Co(NH₃)₆][(NO₂)₃Rh(μ-NO₂)_1+x (μ-OH)_2−x Rh(NO₂)₃]·(2−x)(H₂O), x = 0.17 exhibits the stabilizing effect of a large cation in the formation of novel, unknown previously coordination ions: [(NO₂)₃Rh(μ-NO₂)(μ-OH)₂Rh(NO₂)₃]³⁻ and [(NO₂)₃Rh(μ-NO₂)₂(μ-OH)Rh(NO₂)₃]³⁻.     

Boron–Sulfur and Boron–Selenium Compounds—From Unique Molecular Structural Principles to Novel Polymeric Materials

An immensely broad scope of structural motifs is covered by the intriguing chemistry of boron–sulfur and boron–selenium compounds. Characteristic structural features of the binary boron sulfides can be applied to understand and rationalize the three-dimensional atomic arrangement in macromolecular anionic frameworks such as that of Li_6+2x[B₁₀S₁₈]S_x (x≈2, shown in the picture; ○: S, •: B, ○: Li). Of interest are also the ion dynamics of lithium thioborates and a persubstituted B₁₂ icosahedron that was prepared by high-temperature synthesis and features a characteristic planar B₃Se₂ ring at the chelating ligand.     

Radiation telomerization of tetrafluoroethylene in tetrahydrofuran

According to DSC, DTG, and GPC data, H(CF₂CF₂)nC₄H₇O telomers with a chain length of n = 1−4 and T _b ≈ 170−200°C were formed during the radiolysis of a binary mixture of tetrafluoroethylene + tetrahydrofuran in a molar ratio of (0.37–2)/1 between the reactants at room temperature. IR spectroscopy and quantum-chemical calculations demonstrated that telomerization occurred with chain transfer through the α-hydrogen of the furan ring.     

A Novel Boron-Rich Scandium Borocarbide; Sc4.5−xB57−y+zC3.5−z(x=0.27, y=1.1, z=0.2)

A novel ternary boron-rich scandium borocarbide Sc_4.5−xB_57−y+zC_3.5−z (x=0.27, y=1.1, z=0.2) was found. Single crystals were obtained by the floating zone method by adding a small amount of Si. Single-crystal structure analysis revealed that the compound has an orthorhombic structure with lattice constants of a=1.73040(6), b=1.60738(6) and c=1.44829(6) nm and space group Pbam (No. 55). The crystal composition ScB_13.3C_0.78Si_0.008 calculated from the structure analysis agreed with the measured composition of ScB_12.9C_0.72Si_0.004. The orthorhombic crystal structure is a new structure type of boron-rich borides and there are six structurally independent B₁₂ icosahedra I1—I6, one B₈/B₉ polyhedron and nine bridging sites all which interconnect each other to form a three-dimensional boron framework. The main structural feature of the boron framework structure can be understood as a layer structure where two kinds of boron icosahedron network layer L1 and L2 stack each other along the c-axis. There are seven structurally independent Sc sites in the open spaces between the boron icosahedron network layers.     

Synthesis,Characterization, Structural and Theoretical Analysis of a New Rare‐Earth Boride Carbide: Lu3BC3

Lu₃BC₃ is prepared by arc‐melting of the elements. The silver colored compound crystallizes in the space group Cmcm (Z = 4, a = 4.9788(3) Å, b = 5.0109(3) Å, c = 15.669(1) Å). The crystal structure contains discrete carbon atoms and CBC units in octahedra and bicapped cubes of metal atoms, respectively. The structural analysis is consistent with the group oxidation states (Lu³⁺)₃(C^4–)(CBC^5–). Extended Hückel and LAPW calculations have been performed. Although a semiconducting behavior could be anticipated, the valence band and the conduction band are touching according to LAPW calculations in agreement with the observed metallic conductivity of the compound.     

Thermal Decomposition Studies of Mixed Rare Earth Hydrogen Selenite Crystals

Mixed rare earth hydrogen selenite crystals, neodymium praseodymium hydrogen selenite (Nd_xPr_1−x(HSeO₃)(SeO₃)⋅2H₂O), Neodymium samarium hydrogen selenite (Nd_xSm_1−x(HSeO₃)(SeO₃)⋅2H₂O) and praseodymium samarium hydrogen selenite (Pr_xSm_1−x(HSeO₃)(SeO₃)⋅2H₂O) were prepared by gel diffusion technique. Simultaneous thermogravimetric and differential thermal analysis were carried out on the grown crystals. Decomposition is observed to occurs in six steps, which gives the evidence of successive losses of H₂O and SeO₂. The final product due to decomposition is a mixed rare earth oxides. FT-IR spectrum of the crystal samples heated at different temperatures complemented to the TG-DTA results. This revised version was published online in July 2006 with corrections to the Cover Date.