Artem A. Babaryk

Diazole-based powdered cocrystal featuring a helical hydrogen-bonded network: structure determination from PXRD, solid-state NMR and computer modeling.

We present the structure of a new equimolar 1:1 cocrystal formed by 3,5-dimethyl-1H-pyrazole (dmpz) and 4,5-dimethyl-1H-imidazole (dmim), determined by means of powder X-ray diffraction data combined with solid-state NMR that provided insight into topological details of hydrogen bonding connectivities and weak interactions such as CH···π contacts. The use of various 1D/2D (13)C, (15)N and (1)H high-resolution solid-state NMR techniques provided structural insight on local length scales revealing internuclear proximities and relative orientations between the dmim and dmpz molecular building blocks of the studied cocrystal. Molecular modeling and DFT calculations were also employed to generate meaningful structures. DFT refinement was able to decrease the figure of merit R(F(2)) from ~11% (PXRD only) to 5.4%. An attempt was made to rationalize the role of NH···N and CH···π contacts in stabilizing the reported cocrystal. For this purpose four imidazole derivatives with distinct placement of methyl substituents were reacted with dmpz to understand the effect of methylation in blocking or enabling certain intermolecular contacts. Only one imidazole derivative (dmim) was able to incorporate into the dmpz trimeric motif thus resulting in a cocrystal, which contains both hydrophobic (methyl groups) and hydrophilic components that self-assemble to form an atypical 1D network of helicoidal hydrogen bonded pattern, featuring structural similarities with alpha-helix arrangements in proteins. The 1:1 dmpz···dmim compound I is the first example of a cocrystal formed by two different azoles.

Polyanionic identity of Ca2Zn2(V3O10)(VO4) photocatalyst manifested by X-ray powder diffraction and periodic boundary density functional theory calculations

The structure of photocatalytic and photoluminescent binary vanadate of the general formula “CaZnV2O7” has been investigated using X-ray powder diffraction. The compound is built up of isolated [V3O10], and [VO4] being this complex trivanadate–vanadate, in opposition to previous suggestions on isostructurality “CaMV2O7”, M – Mg or Co (Murashova et al., 1991, 36, 617–621). The present model has been confirmed by theoretical calculations. Thermal analysis and scanning electron microscopy have been performed, and the electronic structure analysis has been found to be in agreement with the experimental observations.

The triple pyrophosphate Cs3CaFe(P2O7)2.

The complex phosphate tricaesium calcium iron bis(diphosphate), Cs(3)CaFe(P(2)O(7))(2), has been prepared by the flux method. Isolated [FeO(5)] and [CaO(6)] polyhedra are linked by two types of P(2)O(7) groups into a three-dimensional framework. The latter is penetrated by hexagonal channels along the a axis where three Cs atoms are located. Calculations of caesium Voronoi-Dirichlet polyhedra give coordination schemes for the three Cs atoms as [8 + 3], [9 + 1] and [9 + 4]. The structure includes features of both two- and three-dimensional frameworks of caesium double pyrophosphates.

K2Ta4O11 (“kalitantite”): a wide band gap semiconductor synthesized in molybdate flux medium

The successful application of molybdate flux for the crystal growth of complex tantalum oxide, verbi causa kalitantite, was shown at a submillimetre scale. The structure was determined via X-ray single crystal refinements (space group Rc, a = 627.32(2) pm, c = 3685.75(13) pm, V = 1256.11(7) pm3 × 10−6, Z = 6) to be an α-U3O8-type layered compound presenting the general formula Mx(Nb,Ta)3n+1O8n+3 (where n = 1 in the case of M being Na, Ca or Ag and n = 2 when M is La–Eu, Y or Bi), thus corroborating earlier studies. Experimental evaluations and complementary ab initio calculations revealed the semiconductor nature of K2Ta4O11. The former were used to explain the vibrational spectrum in the mid-infrared range of wavenumbers.

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.

Some titanium phosphates as host materials: a crystallographic perspective

Santiago Garcia-Granda1, Jorge García-Glez2, Camino Trobajo2, Zakariae Amghouz3, Sergei A. Khainakov4, Conchi O. Ania5, José B. Parra5, Artem A. Babaryk6, Iván da Silva7, Germán R. Castro8 1Physical And Analytical Chemistry Department, University Oviedo, Oviedo, Spain, 2Departments of Analytical and Physical Chemistry and Organic and Inorganic Chemistry, University of Oviedo-CINN, Oviedo, Spain, 3Department of Materials Science and Metallurgical Engineering, University of Oviedo, University Campus, Gijón, Spain, 4Scientific and Technical Services, University of Oviedo, Oviedo, Spain, 5ADPOR Group, Carbon National Institute (INCAR, CSIC), Oviedo, Spain, 6Faculty of Chemistry, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine, 7ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxfordshire, United Kingdom, 8SpLine, Spanish CRG Beamline, ESRF, Grenoble, France E-mail: sgg@uniovi.es

Synthesis and photocatalytic properties of U 3 O 8 -type complex oxides Ag 2 M 4 O 11 (M = Nb, Ta)

The Ag₂Nb₄O₁₁ (space group R3c, a = 6.1521(3) Å, c = 37.0455(7) Å) and Ag₂Ta₄O11 (space group R-3c, a = 6.21021(5) Å, c = 36.8708(3) Å) were prepared by conventional solid-state reaction. Their optical absorption, photocatalytic activity and electronic structure are reported.

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.

Reinvestigation of KMg1/3Nb2/3OPO4

The crystal structure of potassium magnesium niobium oxide phosphate, KMg1/3Nb2/3OPO4, which was described in the space group P4322 [McCarron & Calabrese, (1993 ▶). J. Solid State Chem. 102, 354–361], has been redetermined in the revised space group P41. Accordingly, the assignment of the space group P4322 and, therefore, localization of K at a single half-occupied position, as noted in the previous study, proved to be an artifact. As a consequence, two major and two minor positions of K are observed due to the splitting along [001], as first noted for KTiOPO4 structure analogues. It has been shown that the geometry of the {M II 1/3Nb2/3O6/2}∞ framework is almost unaffected by the lowering of symmetry.