MS13-P01 Crystal chemical features in the row of phosphates and vanadates with alkaline and transition metals Galina Kiriukhina (Department of Crystallography, Lomonosov Moscow State University, Moscow, Russia) Olga Yakubovich (Department of Crystallography, Lomonosov Moscow State University, Moscow, Russia)email:   New crystals were synthesized under hydrothermal conditions, simulating natural middle-temperature hydrothermal zones (T = 230–280 °C; P = 70–100 atm) using complex vanadate/phosphate systems with transition M = Mn, Co, Ni, Cu and alkaline cations A = Na, K, Rb, or NH4, and Cl-, F-, CO32- mineralizers. The X-ray spectral analysis (JEOL SEM with EDS) provided the chemical composition of the crystals. The crystal structures were determined by single-crystal X-ray diffraction (XCalibur-S-CCD diffractometer). Most of new compounds were found out to be new synthetic modifications of minerals alluaudite KCuMn3(VO4)3, niahite NH4MnPO4×H2O, mahnertite K2.5Cu5Cl(PO4)4(OH)0.5(VO2)·H2O, phosphoellenbergerite Na0.91Co6[HPO4][H0.36PO4](OH)3, elpasolite Rb2NaAlF6, and (NH4)2[(V,P)2O6] with pyroxene structure type; others are «mineralogically probable» phosphates RbCuAl(PO4)2, Na2Ni3(OH)2(PO4)2, Rb2Mn3(H2O)2[P2O7]2, (Al,V)4(P4O12)3.
   In accordance with Sandomirsky-Belov principles [1], applied to classification of phosphates with amphoteric oxo-complexes [2], the crystal chemical function of amphoteric metal atoms in all new structures was revealed [3]. In five crystal structures the octahedral complexes of amphoteric metals in the lowest oxidation state build the cationic part of the structure, forming structure fragments of different dimensionality. These are isolated 0D (Al,V)O6 polyhedra in tetraphosphate (Al,V)4(P4O12)3, 1D columns of MnO6 octahedra in diphosphate Rb2Mn3(H2O)2[P2O7]2, 2D layers of MnO6, or NiO6 octahedra in new polymorphic modification of niachite NH4MnPO4⋅H2O and Na2Ni3(OH)2(PO4)2, respectively, and 3D framework of CoO6 octahedra in synthetic phosphohellenebergerite Na0.91Co6[HPO4][H0.36PO4](OH)3.
   In the compounds containing several types of amphoteric metals, its coordination environment and crystal chemical function depends on electronegativity. Thus, in the RbCu[Al(PO4)2] structure the mixed-type anion framework is built of the AlO5 and PO4 polyhedra, while the columns of CuO6 octahedra form the cationic part of the structure. The main fragment of the alluaudite KCuMn3(VO4)3 structure is the cationic framework of MnO6 octahedra and flat CuO4 groups, which is reinforced with anionic VO4 orthotetrahedra.
   In the vanadyl-phosphate analogue of mahnertite K2.5Cu5Cl(PO4)4(OH)0.5(VO2)·H2O, the copper and vanadium operate as anion formers and build the anionic framework of mixed type together with PO4 tetrahedra. The anion-forming function of amphoteric vanadium is also established in the structure of vanadate analogue of pyroxene (NH4)2[(V,P)2O6].
The reported study was funded by RFBR according to the research project № 18-35-00623.

[1] Sandomirsky P.A., Belov N.V. (1984). Crystal chemistry of the mixed anionic radicals. M: Science.

[2] Yakubovich O.V. (2008). Z. Kristallogr. 223. 126–131. 

[3] Kiriukhina G.V. (2016). PhD thesis, Lomonosov Moscow State University, Moscow, Russia.
Keywords: Transition metal phosphates and vanadates, amphoteric oxo-complexes