Vyacheslav N. Baumer

Two polymorphs of 2-(4-chlorophenyl)-4-methylchromenium perchlorate.

Crystallization (from ethyl acetate solution) of 2-(4-chlorophenyl)-4-methylchromenium perchlorate, C(16)H(12)ClO(+).;ClO(4)(-), (I), yields two monoclinic polymorphs with the space groups P2(1)/n [polymorph (Ia)] and P2(1)/c [polymorph (Ib)]; in both cases, Z = 4. Cations and anions, disordered in polymorph (Ib), form ion pairs in both polymorphs as a result of Cl-O...pi interactions. Related by a centre of symmetry, neighbouring ion pairs in polymorph (Ia) are linked via pi-pi interactions between cationic fragments, and the resulting dimers are linked through a network of C-H...O(perchlorate) interactions between adjacent cations and anions. The ion pairs in polymorph (Ib), arranged in pairs of columns along the a axis, are linked through a network of C-H...O(perchlorate), C-Cl...pi, pi-pi and C-Cl...O(perchlorate) interactions. The aromatic skeletons in polymorph (Ia) are parallel in the cationic fragments involved in dimers, but nonparallel in adjacent ion pairs not constituting dimers. In polymorph (Ib), these skeletons are parallel in pairs of columns, but nonparallel in adjacent pairs of columns; this is visible as a herring-bone pattern. Differences in the crystal structures of the polymorphs are most probably the cause of their different colours.

Structure-driven mixed-site borate–phosphate K5Ta8BP4O34: synthesis, structural, spectroscopic and theoretical study

Tungstate bronze (TB) related borate–phosphate K5Ta8BP4O34 is afforded from boron-enriched potassium–molybdate flux. It was found to crystallize [space group P2/c (no. 13), a = 1384.36(5), b = 640.99(2), c = 2054.75(8) pm, β = 125.007(2)°, V = 1493.44(9) × 106 pm3] isotypically with the K5MIV2Nb6P5O34 (M = Ti, Zr) group of compounds. Revealed by X-ray structural analysis, occupational disorder of boron and phosphorus atoms over two crystallographically distinct positions was explained by the decrease of tetrahedral distortions. The calculated electronic structure of title compound was found to be similar to that reported for UV-Vis active niobium phosphate photocatalysts for full water decomposition. Transformation of the parental [Ta8BP4O34] framework at incongruent melting (T = 1618 K) into MIMI′2MV6P3O24-type phosphates was detected leading to a subtle structural relationship of phosphates bearing TB building features.

Novel modification of anhydrous transition metal oxalates from powder diffraction

The known metal-C2O4 structures may be divided into two modifications, α and β. The α-modification has an order-disorder struxture, revealing one-dimensional disordering of the metal-oxalate chains, and the β-modification is ordered. The crystal structures of orthorhombic γ-MnC2O4 {poly[μ-oxalato-manganese(II)]; space group Pmna, a = 7.1333 (1), b = 5.8787 (1), c = 9.0186 (2) Å, V = 378.19 (1) Å3, Z = 4 and Dx = 2.511 Mg m-3} and γ-CdC2O4 {poly[μ-oxalato-cadmium(II)]; space group Pmna, a = 7.3218 (1), b = 6.0231 (1), c = 9.2546 (2) Å, V = 408.13 (1) Å3, Z = 4 and Dx = 3.262 Mg m-3} have been obtained from powder diffraction patterns. The structures are isostructural. Each metal atom in each structure is coordinated by seven O atoms which belong to five oxalate ions. The crystal packing, which contains noticeable cavities in the [101] and [001] directions, is not close packed and essentially differs from the known disordered α- and ordered β-modifications of transition metal oxalates. This modification seems to be metastable. It was found that a spontaneous γ→β phase transition takes place for γ-CdC2O4.

Synthesis and structure of monoclinic bismuth vanadate doped with molybdenum

The synthetic conditions of BiVO₄:Mo crystallization in the molten salts of K-Bi-V-Mo-O have been studied. The compound crystallizes in the monoclinic system, space group I2/a, with unit cell parameters a = 5.1153(3), b = 11.7012(1), c = 5.1878(1) Å, β = 90.24(1)°, Z = 4 representing scheelite-related structure. The formula of the compound established to be Bi_0.98V_0.95Mo_0.05O₄.

Synthesis, structure and luminescence properties of lanthanide compounds grown from phosphate-molybdate molten systems

The main crystallization trends of complex oxide compounds of lanthanides from alkaline phosphate-molybdate (tungstate) melts have been studied in light of structure - luminescence properties relationships. The regions of formation M^I3Ln(PO<inf>4</inf>)<inf>2</inf>, LnPO<inf>4</inf>, K<inf>2</inf>Ln(PO<inf>4</inf>)(M^VIO<inf>4</inf>), M^IM^III(M^VIO<inf>4</inf>)<inf>2</inf> from self flux systems M^I-P-Ln-O (M^I-alkaline metal; M^VI-Mo, W) have been defined. The influence of M^I/M^VI ratio in the initial melt has been shown to play the key role in solid phase formation and structural peculiarities of LnOx polyhedral condensation of compounds obtained.

Synthesis and structural investigations of tantalates phosphates in the flux system Na 2 O-P 2 O 5 -Ta 2 O 5 -MoO 3

The complex sodium-tantalum phosphates (Na<inf>2</inf>Ta<inf>6</inf>P<inf>4</inf>O<inf>26</inf>, Na<inf>3</inf>Ta<inf>7</inf>P<inf>4</inf>O<inf>29</inf>, Na<inf>4</inf>Ta<inf>8</inf>P<inf>4</inf>O<inf>32</inf>) have been synthesized using the flux method in the quasi-quaternary system Na<inf>2</inf>O-P<inf>2</inf>O<inf>5</inf>-Ta<inf>2</inf>O<inf>5</inf>-MoO<inf>3</inf>. These compounds are isostructural with family of sodium-niobium phosphates Na<inf>x</inf>Nb<inf>2m</inf>P<inf>4</inf>O<inf>6m+8</inf> and tightly related to monophosphate tungsten bronzes (MPTB<inf>p</inf>) with pentagonal-shaped tunnels. The structure of these phosphates has been investigated by X-ray powder and single crystal diffraction. Their three-dimensional frameworks consist of slabs of corner-shared TaO<inf>6</inf> distorted octahedra connected via isolated PO<inf>4</inf> tetrahedra and delimit pentagonal tunnels running along c, where Na atoms are located. The solid state band gap measurements gave reasonable prospects for its photocatalytic activity.

Synthesis and structural relationship of complex tantalum phosphates in the flux system K 2 O-P 2 O 5 -Ta 2 O 5 -MoO 3

Single crystals of K<inf>2</inf>Ta<inf>4</inf>O<inf>11</inf> (I), K(TaO<inf>2</inf>)<inf>2</inf>PO<inf>4</inf> (II) and K<inf>3</inf>Ta<inf>5</inf>O<inf>11</inf>(PO<inf>4</inf>)<inf>2</inf> (III) were synthesized by flux-aided method in the pseudo-quaternary system K<inf>2</inf>O-P<inf>2</inf>O<inf>5</inf>-Ta<inf>2</inf>O<inf>5</inf>-MoO<inf>3</inf>. Tight interrelation of their crystal structures has been found via X-ray diffraction study. Experimental solid-state band gap measurements revealed its semiconductor nature corroborated with DFT calculations. Local structure of PO<inf>4</inf> groups in (II) and (III) compounds was probed with ³¹P MAS NMR spectroscopy.

Phase formation in the flux systems K 2 O-P 2 O 5 -Fe 2 O 3 -M II O-MoO 3

KMg<inf>0.09</inf>Fe<inf>1.91</inf>(PO<inf>4</inf>)<inf>2</inf> is isotypic with KM^IIFe(PO<inf>4</inf>)<inf>2</inf> (M^II - Fe, Cu) (monoclinic system, space group P 2<inf>1</inf>/n). The framework is built up from [FeO<inf>5</inf>] and [Fe(Mg)O<inf>6</inf>] polyhedra sharing vertices, edges and connected by two types of bridging PO<inf>4</inf> tetrahedra. The K atoms are nine-coordinated and are located in hexagonal channels running along the direction of c-axis.