Synthesis and crystal structure of strontium borate Sr<Subscript>4</Subscript>B<Subscript>14</Subscript>O<Subscript>25</Subscript>

The new compound Sr₄B₁₄O₂₅ (4SrO · 7B₂O₃) corresponding to an oxide ratio of 4: 7 has been identified and synthesized in the SrO-B₂O₃ system. The crystal structure of the compound has been determined (space group Cmc2₁, a = 7.734(5) Å, b = 16.332(5) Å, c = 14.556(5) Å, Z = 4, 702 F(hkl), R = 0.078). The borate anions form a three-dimensional framework consisting of borate groups of two types: three-ring structures (2□, Δ) and BO₃ triangles. Layers formed by 14-membered rings composed of boron-oxygen tetrahedra and triangles packed within the layer according to the herringbone pattern can be distinguished in the framework. The strontium atoms are located on the mirror symmetry planes between these layers. The compound is metastable and decomposes, on long-term storage, into strontium di- and metaborate.     

Structural features of bismuth borates in the system <Emphasis Type="Italic">n</Emphasis>Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-<Emphasis Type="Italic">m</Emphasis>B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The crystal structures of general composition nBi₂O₃-mB₂O₃ were analyzed and systematized with the use of the structures of borate groups. Based on the CNs calculated by the bond valence method, the shapes of bismuth coordination polyhedra derived from an octahedron were suggested. A correlation was found between the number of BO₃ triangles and BO₄ tetrahedra in borate groups, the average CN of Bi atoms, and the degree of distortion of Bi polyhedra as a function of the m: n ratio, as well as between the polarity of BO₄ tetrahedra and noncentrosymmetry of the structures. The role of Bi³⁺ with the active E pair in the manifestation of specific features of the forms of bismuth polyhedra and the types of connection of boron polyhedra was elucidated.     

High-temperature heat capacity and thermodynamic properties of pyrovanadate Pb<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> and orthovanadate Pb<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The heat capacities of Pb₂V₂O₇ and Pb₃(VO₄)₂ as a function of temperature in the range 350–965 K have been studied by the differential scanning calorimetry method. The C_P = f(T) curve for Pb₂V₂O₇ is described by the equation C_p = (230.76 ± 0.51) + (73.60 ± 0.50)×10^-3T ? (18.38 ± 0.54)×10⁵T^-2 in the entire temperature range. For Pb₃(VO₄)₂, there is a well-pronounced extreme point in the C_P = f(T) curve at T = 371.5 K, which is caused by the existence of a structural phase transition. The thermodynamic properties of the oxide compounds have been calculated.     

High-pressure nonstoichiometric phase Sm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

Perovskite-like nonstoichiometric oxide Sm _x Cu₃V₄O₁₂ (space group Im \(\bar 3\), Z = 2, a = 7.276?7.314 Å) with cationic vacancies and a homogeneity region was prepared barothermally (p = 6.0?9.0 GPa, T = 700?1100°C) for the first time. Structural and isotropic thermal parameters, as well as bond lengths and bond angles, were determined. The compound has metal-type conductivity and paramagnetic properties.     

High-temperature heat capacity of stannates Er<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript> and Tm<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript>

Erbium stannate Er₂Sn₂O₇ and thulium stannate Tm₂Sn₂O₇ with a pyrochlore-type structure were produced by solid-phase synthesis by calcining stoichiometric mixtures of the respective oxides in air at 1473 K for 240 and 200 h. The high-temperature heat capacity of Er2Sn2O7 and Tm₂Sn₂O₇ was studied by differential thermal calorimetry at 353–1000 K. From the experimental dependences C _P = f(T), the thermodynamic functions (enthalpy change, entropy change, and reduced Gibbs free energy) of oxide compounds were calculated.     

Synthesis and structure of [UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>){CONH<Subscript>2</Subscript>N(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>}<Subscript>2</Subscript>]

The single crystals of [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] were synthesized and studied by X-ray diffraction. The crystals are monoclinic, a = 7.461(2) Å, b = 8.828(2) Å, c = 11.756(2) Å, β = 107.21(3)°, space group Pc, Z = 2, R = 2.94%. The structure comprises infinite chains [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] extended along [001] and corresponding to the AT¹¹M ₂ ¹ crystallochemical group (A = UO ₂ ²⁺ , T¹¹ = C₂O ₄ ^2? , M¹ = N,N-CONH₂N(CH₃)₂) of uranyl complexes. The chains are connected into a three-dimensional framework by hydrogen bonds involving the oxygen atoms of oxalate and uranyl ions and the N,N-dimethylcarbamide methyl groups.     

Thermodynamic properties and functions of condensed Bi<Subscript>8</Subscript>O<Subscript>11</Subscript>

The values of ΔH°₂₉₈, S°₂₉₈, H°₂₉₈–H°₀, T, ΔH _fus, and C _p(T), as well as the temperature dependences of the Gibbs energy function, are calculated for Bi₈O₁₁ oxide by proven computational methods.     

The thermodynamic properties of the [(Me<Subscript>3</Subscript>Si)<Subscript>7</Subscript>C<Subscript>60</Subscript>]<Subscript>2</Subscript> fullerene complex

The temperature dependence of the heat capacity C _p ^o of the [(Me₃Si)₇C₆₀]₂ fullerene complex was measured for the first time using precision adiabatic vacuum calorimetry over the temperature range 6.7–340 K and high-accuracy differential scanning calorimetry at 320–635 K. For the most part, the error in the C _p ^o values was about ±0.5%. An irreversible endothermic effect caused by the splitting of the dimeric bond between fullerene fragments and the thermal decomposition of the complex was observed at 448–570 K. The thermodynamic characteristics of this transformation were calculated and analyzed. Multifractal analysis of the low-temperature (T < 50 K) heat capacity was performed, and conclusions were drawn concerning the character of the heterodynamicity of the structure. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o (T) ? H ^o (0), S ^o (T) ? S ^o (0), and G ^o (T) ? H ^o (0) over the temperature range from T → 0 to 445 K and estimate the standard entropy of formation of the compound from simple substances at 298.15 K. The standard thermodynamic properties of [(Me₃Si)₇C₆₀]₂ are compared with those of the (C₆₀)₂ dimer, the [(η⁶-Ph₂)₂Cr]⁺[C₆₀]^?? fulleride, and the initial C₆₀ fullerene.     

Structure and some properties of [UO<Subscript>2</Subscript>CrO<Subscript>4</Subscript>{CH<Subscript>3</Subscript>CON(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>}<Subscript>2</Subscript>]

A new complex [UO₂CrO₄{CH₃CON(CH₃)₂}₂] (I) was studied by thermal analysis, IR spectroscopy, and X-ray crystallography. The crystals are monoclinic: a = 13.8108(11) Å, b = 8.6804(7) Å, c = 13.0989(10) Å, β = 104.777(1)°, V = 1518.4(2) ų, space group P2₁/c, Z = 4, R = 2.39%. The structure of I contains infinite chains of the [UO₂CrO₄{CH₃CON(CH₃)₂}₂] composition running along [001]; the complex belongs to the AT¹¹M¹ ₂ crystal-chemical group (A = UO ₂ ²⁺ , T¹¹ = CrO ₄ ^2? , M¹ = CH₃CON(CH₃)₂) of uranyl complexes. The chains are linked into a three-dimensional framework due to hydrogen bonds between oxygen atoms of chromate ions and hydrogen atoms of methyl groups of the dimethylacetamide.     

Thermal properties,phase transitions,vibrational and reorientational dynamics of [Mn(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

[Mn(NH₃)₆](NO₃)₂ crystallizes in the cubic, fluorite (C1) type crystal lattice structure (Fm \( \overline{3} \) m) with a = 11.0056 Å and Z = 4. Two phase transitions of the first-order type were detected. The first registered on DSC curves as a large anomaly at T _C1 ^h  = 207.8 K and T _C1 ^c  = 207.2 K, and the second registered as a smaller anomaly at T _C2 ^h  = 184.4 K and T _C2 ^c  = 160.8 K (where the upper indexes h and c denote heating and cooling of the sample, respectively). The temperature dependence of the full width at half maximum of the band associated with the δ_s(HNH)F_1u mode suggests that the NH₃ ligands in the high temperature and intermediate phase reorientate quickly with correlation times in the order of several picoseconds and with activation energy of 9.9 kJ mol^?1. In the phase transition at T _C2 ^c probably only a some of the NH₃ ligands stop their reorientation, while the remainders continue to reorientate quickly with activation energy of 7.7 kJ mol^?1. Thermal decomposition of the investigated compound starts at 305 K and continues up to 525 K in four main stages (I–IV). In stage I, ²/₆ of all NH₃ ligands were seceded. Stages II and III are connected with an abruption of the next ²/₆ and ¹/₆ of total NH₃, respectively, and [Mn(NH₃)](NO₃)₂ is formed. The last molecule of NH₃ per formula unit is freed at stage IV together with the simultaneous thermal decomposition of the resulting Mn(NO₃)₂ leading to the formation of gaseous products (O₂, H₂O, N₂ and nitrogen oxides) and solid MnO₂.     

Catalytic removal of soot particles over MnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> catalysts prepared by the auto-combustion method

Soot removal for exhaust gas from diesel engine has been addressed due to the more stringent legislation and environmental concerns. MnCo₂O₄ catalysts were systematically prepared using glucose as a fuel via the auto-combustion method and applied for soot removal. The as-prepared samples were characterized by X-ray diffraction (XRD), O₂-temperature-programmed oxidation (TPO) reaction and H₂-temperature-programmed reduction reaction (H₂-TPR). The catalytic activities for soot combustion were evaluated by micro activity test (MAT) with a tight contact mode between soot and catalysts. Compared with catalysts prepared by the solid state method without glucose, auto-combustion method in the presence of glucose can decrease the synthetic temperature, avoiding high temperature treatment and sintering. The catalysts prepared with glucose could catalyze soot oxidation effectively and the derived values of T₁₀, T₅₀, and T₉₀ were 326, 408, and 468 °C in a tight contact mode, respectively, showing a significant drop of T₁₀, T₅₀, and T₉₀ by 156, 177, and 178 °C for non-catalytic reaction.     

High-pressure defect phase La<Subscript>x</Subscript>Cu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

Perovskite-like nonstoichiometric oxide La _x Cu₃V₄O₁₂ (space group Im \(\bar 3\), Z = 2, a = 7.313–7.354 Å) with cation-site vacancies has been prepared for the first time at high pressures (p = 6.0–8.0 GPa) and high temperatures (T = 700–1100°C). The compound has metal-type conductivity and paramagnetic properties, and undergoes a phase transition.     

Theoretical study of V<Subscript>20</Subscript>O<Subscript>50</Subscript> oxovanadate cluster compounds with alkali metal atoms

The energies and structural and spectroscopic characteristics of model М _n V₂₀O₅₀ systems corresponding to compounds of the V₂₀O₅₀ oxovanadate cluster with alkali metal atoms (M = Li, K; n = 1–20) have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, in the K _n V₂₀O₅₀ compounds, all the metal atoms are coordinated in the outer sphere to the edges of the hollow dodecahedral V₂₀O₅₀ cage to form three-center O_t?K?O_t bridges with terminal oxygen atoms. In the Li _n V₂₀O₅₀ compounds, the metal atoms can be coordinated both outside and inside the V₂₀O₅₀ cage. At n = 4, the most favorable isomer is endohedral Li₄O₄@V₂₀O₄₆ in the quintet state (S = 5), in which the four Li atoms are located in the inner cavity of the inverted O₄@V₂₀O₄₆ isomer of the oxovanadate cluster with four O atoms oriented to the cage center and form with them a corrugated eight-membered ring Li₄O₄. The decrease in energy caused by the formation of the endohedral isomer (4Li + V₂₀O₄₅₀ → Li₄O₄@V₂₀O₄₆) is estimated at ~377 kcal/mol. The exohedral isomer 4Li ? V₂₀O₅₀ (S = 5), in which the Li atoms are coordinated to the outside of the V₂₀O₅₀ cage, is ~23 kcal/mol less favorable. For the other members of the Li series with n from 4 to 20, the endohedral isomers with the inner Li₄O₄ ring remain preferable. At n > 4, the extra Li atoms fill the outer sphere of the cage, being coordinated to its edges to form three-center O_t?Li?O_t bridges with terminal oxygen atoms. The specific energy of formation of Li _n V₂₀O₅₀ (by the scheme nLi + V₂₀O₄₅₀ → Li₄O₄@V₂₀O₄₆Li_n-4) per Li atom monotonically decrease from ~98 (n = 2) to ~80 kcal/mol (n = 20). For K _n V₂₀O₅₀, these energies are ~20?25 kcal/mol lower than for the lithium analogues and decrease from ~80 (n = 2) to ~64 kcal/mol (n = 12). The atoms of both alkali metals in the M _n V₂₀O₅₀ systems have large positive effective charges (0.85e?0.92e for K and 0.65e?0.78e for Li), which also monotonically decrease with increasing n. The addition of each alkali metal atom is accompanied by its ionization (М → М⁺) along with the reduction of one of the neighboring pentavalent vanadium atoms to the tetravalent state (V^V → V^IV) and localization of the unpaired electron in its 3d shell. For all Li _n V₂₀O₅₀ complexes, the states with maximal multiplicity and parallel spins are the most preferable.     

High-pressure defect phase Tm<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

Perovskite-related oxide Tm _x Cu₃V₄O₁₂ (space group Im \(\bar 3\), Z = 2, a = 7.262?7.273 Å) with vacancies in the cationic sublattice has been prepared for the first time under barothermal conditions (p = 7.0?9.0 GPa, T = 900?1100°C). Electric resistivity (10–300 K) and magnetic susceptibility (0–300 K) were studied as a function of temperature. Tm _x Cu₃V₄O₁₂ is shown to have a metallic conductivity and paramagnetism.     

Refinement of LiFe<Subscript>5</Subscript>O<Subscript>8</Subscript> crystal structure

The crystal structure and the formation conditions of crystals of the LiFe₅O₈ ordered phase obtained from the solution-melt of the Bi₂O₃-Fe₂O₃-B₂O₃-LiCl quadruple system are refined. The crystals are black, octahedral, of cubic symmetry (space group P4₃32). Unit cell parameters: a = 8.3339(1) Å, V = 578.82(1) ų, Z = 4, d _calc = 4.753 g/cm³. From 6046 of the collected array I _hkl 358 are independent (R _int = 0.0321). As a result of anisotropic refinement of structural parameters, R ₁ factor is found to be 0.0186 (wR ₂ = 0.0467). Lithium atoms are in octahedral environment, Li-O is 2.109(1) Å; iron atoms are of two types: in octahedra with Fe-O (by two) distances of 1.9586(9) Å, 2.0152(9) Å, and 2.0652(10) Å and tetrahedra with Fe-O (three) 1.8848(10) Å and 1.914(2) Å. The structure is of inverted spinel type.     

Synthesis and characterization of a new monophosphate (C<Subscript>6</Subscript>H<Subscript>16</Subscript>N<Subscript>2</Subscript>)(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) ų, Z = 1, and D_x = 1.565 g cm^?3. The crystal structure has been determined and refined to R = 0.030 and R _w(F ²) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H₂PO₄] _n ^n? chains with (C₆H₁₆N₂)²⁺ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, ¹³C and ³¹P MAS NMR spectroscopies and Ab initio calculations.     

Crystal structures of Ti(NH<Subscript>4</Subscript>)<Subscript>2</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript> and Sn(NH<Subscript>4</Subscript>)<Subscript>2</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript>

The characteristics of crystal structures of the titanium(IV) diammonium (Ti(NH₄)₂P₄O₁₃) and tin(IV) diammonium (Sn(NH₄)₂P₄O₁₃) tetraphosphates, which are isostructural with similar silicon(IV) and germanium(IV) salts, have been obtained by the Rietveld method using X-ray powder diffraction data. The compounds crystallize in the triclinic system, space group P \(\overline 1 \), Z = 2, a = 15.0291(7) Å, b = 7.9236(4) Å, c = 5.0754(3) Å, α = 99.168(3)°, β = 97.059(3)°, γ = 83.459(3)° for Ti(NH₄)₂P₄O₁₃ and a = 15.1454(7) Å, b = 8.0103(5) Å, c = 5.1053(3) Å, α = 99.898(6)°, β = 96.806(3)°, γ = 83.881(4)° for Sn(NH₄)₂P₄O₁₃. The structure is refined in the isotropic approximation using the pseudo-Voigt function: R _p = 0.077, R _Bragg = 0.045, R _F = 0.057 for Ti(NH₄)₂P₄O₁₃; R _p = 0.082, R _Bragg = 0.044, R _F = 0.046 for Sn(NH₄)₂P₄O₁₃. The hydrogen atoms of the ammonium cations are placed in the calculated positions. A comparative analysis of the structures of the compounds of the M^IV(NH₄)₂P₄O₁₃ (M^IV = Si, Ge, Ti, Sn) series has been carried out.     

Synthesis and properties of the high-pressure phase CaCu<Subscript>2</Subscript>CoV<Subscript>4</Subscript>O<Subscript>12</Subscript>

Under uniform compression (p = 7.0 GPa) on heating (T = 1100°C), the perovskite-like oxide CaCu₂CoV₄O₁₂ was obtained for the first time. The crystal structure of the compound was determined by X-ray crystallography (space group Im-3, Z = 2, a = 7.3015(5) Å). The main bond lengths and angles were found. It was established that the high-pressure phase CaCu₂CoV₄O₁₂ has metallic conduction. Its magnetic properties were studied.     

High-temperature heat capacity and thermodynamic properties of Pb<Subscript>4</Subscript>V<Subscript>2</Subscript>O<Subscript>9</Subscript> and Pb<Subscript>8</Subscript>V<Subscript>2</Subscript>O<Subscript>13</Subscript>

The molar heat capacity of Pb₄V₂O₉ and Pb₈V₂O₁₃ in the temperature range 350–1000 K was measured by differential scanning calorimetry. It was determined that the plot C_p = f(T) for Pb₈V₂O₁₃ has an extremum within the range 416–516 K, which is due to a phase transition. A correlation was found between the heat capacity and composition of oxides in the PbO–V₂O₅ system. The data obtained allowed one to predict the specific heat capacity value for Pb(VO₃)₂.     

Crystal Structure of New One-Dimensional Triple Molybdate Na<Subscript>2</Subscript>K<Subscript>2</Subscript>Cu(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>

The title compound (disodium dipotassium copper(II) tris-[molybdate (VI)]) is prepared by form melt and characterized by single crystal X-ray diffraction and UV-vis spectroscopy. It crystallizes in the triclinic space group P-1 with a = 7.4946(8) Å, b = 9.3428(9) Å, c = 9.3619(9) Å, α = 92.591(7)°, β = 105.247(9)°, γ = 105.496(9)°, V = 604.7 ų, and Z = 2. Its structure is isotypic with that of Na₄Mn(MoO₄)₃. It is formed by Cu₂O₁₀ distorted bi-octahedral dimers linked by two bridging bidentate Mo₂O₄ tetrahedra and, additionally, two monodentate Mo₁O₄ tetrahedra to form Cu₂Mo₄O₂₀ units. These units are linked by the insertion of Mo₃O₄ tetrahedra to build infinite ribbons disposed along the c axis. All of these ribbons form a one-dimensional framework. Both K1 and K3 cations are located in the inversion center, and all the other atoms are at general positions. The structure model is supported by the bond valence sum (BVS) and charge distribution CHARDI methods. The Cu²⁺ cations adopt the [4+2] CuO₆ Jahn-Teller distortion giving rise to an intense d–d transition in the UV-vis absorption spectra.