The structure of the fluorite-related phase Ca2Hf7O16

The atomic arrangement in the fluorite-related phase, Ca₂Hf₇O₁₆, has been determined by powder X-ray diffraction. The unit cell is rhombohedral, $\text{R}\text{3}$, with a = 9.5273Å, α = 38.801°, and Z = 1, and its volume is $\text{2}\text{1}\text{4}$ times that of the fluorite subcell from which it is derived. The cations are ordered on the cation sites of the fluorite structure with the calcium ions segregated into discrete layers parallel to the (111) fluorite plane: there is some evidence that the formal anion vacancies are also ordered.     

Defect structure of anion-excess fluorite-related Ca1−xYxF2+x solid solutions

On the basis of the transformation of a cube within a fluorite-type matrix into an archimedean antiprism of the kind found in numerous ordered anion-excess fluorite-related superstructures, a new polyhedral cluster, labeled 4:4:3, [according to B. T. M. Willis, Proc. Br. Ceram. Soc.1, 9 (1964) and A. K. Cheetham, B. E. F. Fender, and M. J. Cooper, J. Phys. C4, 3107 (1971)], is proposed to explain the defect structure and short-range order in Ca_1?xY_xF_2+x solid solution. In agreement with the spectroscopic, dielectric, and electric experiments, this new structural model fits perfectly well the measured occupation numbers for normal F and interstitial F′ and F″ fluorine atoms for the whole range of compositions without requiring the too short F′F′ distances generated by the previously proposed 2:2:2 or 3:4:2 clusters. Such 4:4:3 clusters and nearly identical 4:4:4 or 4:4:5 ones, are probably present in the other highly and moderately doped Ca_1?xLn_xF_2+x solid solutions; they could be precursors for the largest clusters, i.e., ordered microdomains, observed for samples annealed for a long time.     

Theoretical study of polyoxide clusters Sc20O30, P20O50, Ti20O30F20, and V20O30F20

The structural, electronic, and vibrational characteristics and energies of the isolated polyoxide clusters Sc₂₀O₃₀, P₂₀O₅₀, Ti₂₀O₃₀F₂₀, and V₂₀O₃₀F₂₀ and ammonia complexes Sc₂₀O₃₀ · nNH₃ were calculated by the density functional theory B3LYP method with several basis sets. The computation results show that a fullerene-like closo structure I _h with oxygen bridges located above the midpoints of the edges of an empty [M₂₀] dodecahedron is preferable for the Ti₂₀O₃₀F₂₀ and V₂₀O₃₀F₂₀ clusters with four-coordinate metal atoms protected by the outer M-F bonds. This structure with a cage diameter of ∼1 nm and the diameter of nearly planar decagonal faces (windows) of ∼0.5 nm is stable to dissociation into fragments and to strong geometric distortions and retains its closo shape when molecules like NH₃ and anions like H⁻ are attached to the cage. An analogous closo structure is favorable for the P₂₀O₅₀ cluster; however, in this structure, the [P₂₀] cage is severely distorted and all 12 windows are strongly corrugated. For Sc₂₀O₃₀, the I _h dodecahedron with bare three-coordinate Sc atoms corresponds to a local minimum of the potential energy surface, which is 170–200 kcal/mol less favorable than compact puck-shaped isomers in which four- and five-coordinate metal atoms and three- and four-coordinate oxygen atom prevail. “Solvation” of the dodecahedral and puck-shaped Sc₂₀O₃₀ isomers by ammonia molecules strongly decreases the energy gap between the isomers; however, the dodecahedron I _h in all cases remains a high-lying intermediate. According to calculations, most polyoxides under consideration have a high electron affinity (comparable with or higher than that of fullerenes) and is able to add three to five or more alkali-metal atoms to form radical salts in which clusters are in the state of polyanions. Because of large sizes of the [M₂₀] cages and their windows, the interior of the cage (as distinct from fullerenes) can accommodate a considerable number of atoms and several small molecules. The V₂₀O₃₀F₂₀ cluster has 20 unpaired electrons and can be treated as a molecular magnet. The properties of the [M₂₀] cages depend only slightly on the outer substituents. It is suggested that the pattern will be retained upon the substitution of OH groups for the F atoms and that the hydroxo-substituted clusters can bind to each other through hydrogen bridges and serve as building blocks for self-assembly into ordered nanometer and crystalline structures of various dimensions. Original Russian Text ? O.P. Charkin, N.M. Klimenko, D.O. Charkin, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 5, pp. 775–785.     

A new structure type of RE4B4O11F2: High-pressure synthesis and crystal structure of La4B4O11F2

The first lanthanum fluoride borate La₄B₄O₁₁F₂ was obtained in a Walker-type multianvil apparatus at 6 GPa and 1300 °C. La₄B₄O₁₁F₂ crystallizes in the monoclinic space group P2₁/c with the lattice parameters a=778.1(2) pm, b=3573.3(7) pm, c=765.7(2) pm, β=113.92(3)° (Z=8), and represents a new structure type in the class of compounds with the composition RE₄B₄O₁₁F₂. The crystal structure contains BO₄-tetrahedra interconnected with two BO₃-groups via common vertices, B₂O₅-pyroborate units, and isolated BO₃-groups. The structure shows a wave-like modulation along the b-axis. The crystal structure and properties of La₄B₄O₁₁F₂ are discussed and compared to Gd₄B₄O₁₁F₂.     

Theoretical study of polyoxide clusters B20O30, Al20O30, V20O50, Si20O30H20, and Si20O30F20

The structural, electronic, and vibrational characteristics and energies of the isolated polyoxide clusters B₂₀O₃₀, Al₂₀O₃₀, V₂₀O₅₀, Si₂₀O₃₀H₂₀, and Si₂₀O₃₀F₂₀ and their complexes with the H⁻ ion and ammonia complexes Al₂₀O₃₀ · nNH₃ have been calculated by the density functional theory B3LYP method with different basis sets. The computation results show that the symmetric closo structure I _h with oxygen bridges located above the centers of the faces of an empty [M₂₀] dodecahedron is more favorable for V₂₀O₅₀, Si₂₀O₃₀H₂₀, and Si₂₀O₃₀F₂₀. For B₂₀O₃₀, the cage closo isomer is also more favorable than the other isomers, but its structure is severely distorted as compared to a dodecahedron and has a symmetry close to C ₃ . For Al₂₀O₃₀, the I _h structure corresponds to a high-lying local minimum of the potential energy surface. For Al₂₀O₃₀, a set of unusual puckshaped isomers of symmetry C _i , with different numbers of four-coordinate atoms ^IVAl and three-coordinate atoms ^IIIO, was localized; these structures are more than 90 kcal/mol more favorable than the dodecahedron I _h . The most favorable isomer of Al₂₀O₃₀ contains twelve four-coordinate atoms ^IVAl and four five-coordinate atoms ^VAl. The energies of dissociation of the most favorable M₂₀O₃₀ clusters into the M₂O₃ (C _2v ) and M₄O₆ (T _d ) fragments and, in the case of Al₂₀O₃₀, also into the Al₈O₁₂ (O _h ) and Al₁₂O₁₈ (D _3d ) fragments, have been estimated. The conclusion has been drawn that these clusters can, in principle, exist and can be experimentally detected in the isolated state. Analogous calculations have been performed for ammonia complexes Al₂₀O₃₀ · nNH₃ with n varying from 1 to 20. The effect of solvation on the relative stability of the dodecahedral and puckshaped isomers of the Al₂₀O₃₀ cluster is observed. The isomers with ammonia molecules in their first coordination sphere become much closer to one another on the energy scale; however, the dodecahedron remains a considerably less favorable intermediate. Original Russian Text ? O.P. Charkin, N.M. Klimenko, D.O. Charkin, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 4, pp. 624–635.     

Crystal structures of the fluorite-related phases CaHf4O9 and Ca6Hf19O44

Crystal structures for the fluorite-related phases CaHf₄O₉$\text{ф}{}_1$) and Ca₆Hf₁₉O₄₄ ($\text{ф}{}_2$) have been determined from X-ray powder diffraction data. qf₁ is monoclinic, $\text{C2}\text{c}$, with a = 17.698 Å, b = 14.500Å, c = 12.021 Å, β = 119.47° and Z = 16. qf₂ is rhombohedral, $\text{R}\text{3}\text{c}$, with a = 12.058 Å, α = 98.31° and Z = 2.Both phases are superstructures derived from the defect fluorite structure by ordering of the cations and of the anion vacancies. The ordering is such that the calcium ions are always 8-coordinated by oxygen ions, while the hafnium ions may be 6-, 7-, or 8-coordinated. The closest approach of anion vacancies is a $\text{1}\text{2}\text{〈111〉}$ fluorite subcell vector, and in each structure vacancies with this separation form strings.     

Crystal structures of some fluorite-related M7O12 compounds

Powder X-ray diffraction techniques have been used to determine the crystal structures of Ti₃Sc₄O₁₂, Nb_1.5Sc_5.5O₁₂, NbSc₆O₁₁F, NbSc₅HfO₁₂, Zr₃Er₄O₁₂, and Hf₃Sc₄O₁₂ and to reexamine the structures of Zr₃Sc₄O₁₂ and Zr₃Yb₄O₁₂. All the compounds have the same fluorite-related superstructure as reported previously for Pr₇O₁₂, UY₆O₁₂, Zr₃Sc₄O₁₂, and Zr₃Yb₄O₁₂. Most of the compounds exhibit cation ordering, a situation observed previously only in UY₆O₁₂. One-seventh of the cations occupy a set of special sites of symmetry $\text{3}$ and are octahedrally coordinated by oxygen. These cations are of the type that has the smallest available ionic radius. The remaining cations occupy a set of general sites randomly with respect to atom type and are sevenfold coordinated by oxygen. In Hf₃Sc₄O₁₂, only partial ordering of this nature occurs, while it is confirmed that no cation ordering occurs in Zr₃Sc₄O₁₂. Some aspects of the cation order-disorder situation are discussed.     

A study of the thermal decomposition of Se2O2F8 and Te2O2F8, using molecular beam techniques

The thermal decomposition of the vapor phases of the oxygen bridged dimers Se₂O₂F₈ and Te₂O₂F₈ has been studied by mass spectrometry, electric deflection and flight time analysis on a molecular beam generated directly from the decomposition products. Se₂O₂F₈ begins to decompose at ?250°C; the principal products are SeF₄ and O₂, with SeOF₂ as a minor product. Decomposition is complete by ?500°C. There is some decomposition to monomeric SeOF₄ between 200 and 350°C. Te₂O₂F₈ did not begin to decompose until a temperature of 400°C was reached. Again, the principal products observed were TeF₄, O₂, and TeOF₂ with no evidence for decomposition to the monomeric TeOF₄.     

Sol-gel synthesis of K3InF6 and structural characterization of K2InC10O10H6F9, K3InC12O14H4F18 and K3InC12O12F18

K₃InF₆ is synthesized by a sol-gel route starting from indium and potassium acetates dissolved in isopropanol in the stoichiometry 1:3, with trifluoroacetic acid as fluorinating agent. The crystal structures of the organic precursors were solved by X-ray diffraction methods on single crystals. Three organic compounds were isolated and identified: K₂InC₁₀O₁₀H₆F₉, K₃InC₁₂O₁₄H₄F₁₈ and K₃InC₁₂O₁₂F₁₈. The first one, deficient in potassium in comparison with the initial stoichiometry, is unstable. In its crystal structure, acetate as well as trifluoroacetate anions are coordinated to the indium atom. The two other precursors are obtained, respectively, by quick and slow evaporation of the solution. They correspond to the final organic compounds, which give K₃InF₆ by decomposition at high temperature. The crystal structure of K₃InC₁₂O₁₄H₄F₁₈ is characterized by complex anions [In(CF₃COO)₄(OH_x)₂]^(5−2x)− and isolated [CF₃COOH_2−x]^(x−1)− molecules with x=2 or 1, surrounded by K⁺ cations. The crystal structure of K₃InC₁₂O₁₂F₁₈ is only constituted by complex anions [In(CF₃COO)₆]³⁻ and K⁺ cations. For all these compounds, potassium cations ensure only the electroneutrality of the structure. IR spectra of K₂InC₁₀O₁₀H₆F₉ and K₃InC₁₂O₁₂F₁₈ were also performed at room temperature on pulverized crystals.     

Conformational analysis of n-perfluoroalkanes: n-C4F10 and n-C6F14

The vibrational spectra of n-C₄ F₁₀ and n-C₆F₁₄ were investigated in the vapour, liquid and solid phases and the equilibrium conformations of these molecules were determined. Different solid-phase spectra were recorded by changing deposition and/or annealing conditions.     

Magnetic properties of Ca2F2-xMnxO5

Magnetic susceptibility of Ca₂F_2-xMn_xO₅ members crystallizing in two different structures, one having octahedral (O), tetrahedral (T) and square-pyramidal (SP) coordination of transition metal atoms (OTSP structure) and the other having octahedral and tetrahedral coordination (OT structure), has been investigated. Susceptibility behaviour of the oxides with OTSP structure is different from that of the oxides with OT structure. Ca₂Fe_1-33Mn_0-67O₅ with OTSP structure shows an antiferromagnetic ordering while the corresponding oxide with OT structure shows weak ferromagnetism. Contribution No. 398 from the Solid State and Structural Chemistry Unit     

The defect structure of V4As3

The nature of the defect structure of crystals of V₄As₃ has been studied by electron diffraction and electron microscopy methods. Lattice images reveal that planar defects of the chemical twinning type are common in the orthorhombic α-V₄As₃ crystals. Thermal decomposition, yielding negative crystals, was also studied.     

The structure of defect Ru4Si3

The nature of the defect structure of Ru₄Si₃ has been studied with electron diffraction and electron microscopy methods. Lattice image pictures, interpreted with histogram analysis, reveal that planar defects of chemical twinning type are common in the crystals.     

The pyrophosphate NaFeP2O7: A cage structure

The high-temperature form of NaFeP₂O₇ crystallizes in the monoclinic $\text{P2}{}_1\text{c}$ space group with a = 7.3244(13), b = 7.9045(7), c = 9.5745(15), Å, β = 111.858(13)°, and Z = 4. The structure has been refined from 3842 reflections leading to R = 0.040 and R_w = 0.047. The structure of II-NaFeP₂O₇ can be described by alternately stacking layers containing the FeO₆ octahedra and layers formed by the P₂O₇ groups, parallel to (001). Elongated cages are formed where two Na⁺ ions are located. The structure is compared with that of KAlP₂O₇. Both structures are built up from blocks of three polyhedra, [FeP₂O₁₁] or [AlP₂O₁₁], including a small O_octO_tetO_oct angle. These blocks are connected in such a way that several types of tunnels appear in each structure.     

The gas-phase structure of dodecafluorooctahydrothiophene, c-C4F8SF4

The geometric structure of c-C₄F₈SF₄ has been determined by gas-phase electron diffraction. The five-membered ring has the twist form (C₂ symmetry) with a puckering amplitude q = 0.42 (2) Å. The following principle geometric parameters (r_a values) with estimated uncertainties have been derived: (C---C)_av = 1.541(10), S---C = 1.896(7), S---F_e = 1.558(6), S---F_a = 1.594(6) Å, CSC = 90.0(9)°, SCC = 109.1(8)°, CCC = 106.5(12)°, F_aSF_e = 90.5(15)° and F_eSF_e = 87.7(29)°. Vibrational amplitudes for long non-bonded CF and FF distances indicate a high barrier to pseudorotation of the ring.     

Crystal structures of NaBaCr2F9 and NaBaFe2F9: Structural correlations with other enneafluorides,particularly with KPbCr2F9

NaBaCr₂F₉ and NaBaFe₂F₉ are monoclinic (SG $\text{P2}{}_1\text{n}$, No. 14). Lattice constants are found to be a = 7.318(2) Å, b = 17.311(4) Å, c = 5.398(1) Å, β = 91.14°(3) for chromium, and a = 7.363(2) Å, b = 17.527(4) Å, c = 5.484(1) Å, β = 91.50°(5) for iron. The structures were solved from 507 and 1113 X-ray reflections, respectively, for the Cr and Fe compounds; the corresponding R_w values are 0.025 and 0.037. The network is built from tilted double cis chains of octahedra (M₂F₉)^3n?_n [M = Cr, Fe], linked by Na⁺ and Ba²⁺ ions. The structures are compared to the previously described structures, particularly KPbCr₂F₉, whose symmetry and parameters are different. The difference is analyzed first in terms of tilted octahedra, but principally in terms of bond strengths and steric activity of the Pb²⁺ lone pair. A mechanism is proposed for the transformation between the structures of NaBaCr₂F₉ and KPbCr₂F₉.     

Electrical conductivity and defect structure of Nd2O3+x

The electrical conductivity and departure from the stoichiometry of Nd₂O₃ have been measured over the temperature range of 900° to 1100°C and oxygen partial pressure of 1 to 10^?16 atm. The hole conductivity of Nd₂O₃ is found to be proportional to , where n are 4.6, 4.9, and 5.1 at 900°, 1000°, and 1100°C, respectively. From the oxygen partial pressure dependence of the hole conductivity, it is shown that the predominant point defects in nonstoichiometric NdO_1·+x are fully ionized and partially doubly ionized metal vacancies. From the thermogravimetric measurements, the departure from stoichiometry, x in NdO_1·5+x, is 2.0 × 10^?3 at 1000°C and 1 atm. By combining the electrical conductivity and weight change data, it is shown that the hole mobility is 6.3 × 10^?4 (cm²/V·sec) at 1000°C and 1 atm.     

The crystal structure of Ca6Eu2Na2(PO4)6F2

The crystal structure of Ca₆Eu₂Na₂(PO₄)₆F₂ has been determined by single crystal X-ray diffraction. The unit cell constants are $\text{a = 9.385(2), c = 6.893(3)}\text{A}\text{?}$ and the space group is $\text{P6}{}_3\text{m}$. The structure was refined by normal full matrix least squares techniques. The final value of the refinement indicator is R = 0.065, based on 419 reflections.The structure of Ca₆Eu₂Na₂(PO₄)₆F₂ contains disordered cations in both the triangle and column positions. The occupation of the six triangle sites is $\text{1}\text{4}\text{Eu}$ and $\text{3}\text{4}\text{Ca}$ and of the four column sites $\text{1}\text{2}\text{Na}\text{,}\text{4}\text{10}\text{Ca}$, and $\text{1}\text{10}\text{Eu}$.     

锂电池用草酸二氟硼酸锂有机电解液的电化学性能

以草酸锂和三氟化硼乙醚溶液合成了草酸二氟硼酸锂(LiBC₂O₄F₂),并用碳酸二甲酯溶剂萃取和重结晶提纯。LiBC₂O₄F₂有机电解液能在铝箔上形成一层致密的保护膜,这能较好地抑制在高电位时电解液在铝箔上发生氧化反应,而且在很宽的温度范围内LiBC₂O₄F₂基电解液都具有较好的离子电导率。电化学测试结果表明：使用1.0 mol·L^-1 LiBC₂O₄F₂有机电解液的LiMn₂O₄/Li电池首次放电容量为110.2 mAh·g^-1,并且具有比使用LiPF₆有机电解液的LiMn₂O₄/Li电池更好的高低温循环性能和更优良的低温放电性能。     

The defect structure of anion excess CaF2

Neutron scattering and computer simulation techniques have been used to investigate the defect cluster structure of CaF₂ doped with 5% La^3?. The results strongly support the formation of small discrete clusters rather than the superstructures that have been suggested in recent studies of anion excess fluorites. The type of cluster that emerges as dominant comprises an interstitial-dopant dimer (of the 2:2:2 type) which has captured an additional F^? interstitial. The formation of such clusters is supported by recent ITC studies.