The vanadium monophosphates AVOPO(4): Synthesis of a second form beta-KVOPO4 and structural relationships in the series

A new form of potassium vanadophosphate beta -KVOPO4 has been synthesized u sing hydrothermal technique which showed the role of the extra adduct, here W or WO3. The structure of this phase, isotypic to Rb and Ca monophosphate s, has been determined from a single crystal X-ray study. Structural relati onships between the different monophosphates of the AVOPO(4) series with A = Li, Na, K, Rb, Cs, NH4 are presented in which K+ appears as a boundary ca tion: with cations smaller than K+ the vanadium(IV) is octahedral and pyram idal with larger ones, both coordinations existing with K+. (C) 2001 Editio ns scientifiques et medicales Elsevier SAS. All rights reserved.