The Hydrothermal NH4/V/P/H2O and K/V/P/N(C2H5)3/H2O Systems at 473 K and the Crystal Structures of NH4VOPO4and (NH4)3V2O3(VO)(PO4)2(HPO4)

Abstract An examination of the NH 4 /VO 5 /P/H 2 O system at 473 K under hydrothermal conditions yielded the (NH 4 ) 3 V 2 O 3 (VO)(PO 4 ) 2 (HPO 4 ) and NH 4 VOPO 4 phases. The crystal structure of the first compound is isotypical with the corresponding Tl + and K + phases. The cations NH + 4 and Tl + have similar coordinations against oxygen. The investigation of the crystal structure of the second compound (space group Pn 2 n ) shows it to be related to other AB O T O 4 phases of the potassium titanyl phosphate type with A =Na + , Ag + , NH + 4 , Rb + , K + , and Tl + , and B =Ti 4+ , V 4+ , Sn 4+ , Fe 4+ , Ge 4+ , Ga 3+ , Zr 4+ , Sb 5+ , and Nb 5+ , and T =P 5+ , Ge 4+ , Si 4+ , and As 5+ , but none of them crystallize in space group Pn 2 n . In the K/V/P/N(C 2 H 5 ) 3 /H 2 O system, three different K phases were found: K 0.5 VOPO 4 ·1.5H 2 O, KVOPO 4 , and K-FVP-1 (Frankfurt vanadium phosphate, one, or for short, FVP-1). The microporous K-FVP-1 compound was synthesized in a similar pH range as the isotypic Na-FVP-1 phase. The V 4+ /V 5+ ratio of K-FVP-1 varies from 3.5(1)/1.5(1) to 1.6(1)/3.4(1) and the corresponding lattice constants range from 16.0013(6) to 15.7665(4) A.