The vanadium monophosphates AVOPO_4: Synthesis of a second form #beta#-KVOPO_4 and structural relationships in the series

摘要

A new form of potassium vanadophosphate #beta#-KVOPO_4 has been synthesized using hydrothermal technique which showed the role of the extra adduct, here W or WO_3. The structure of this phase, isotypic to Rb and Cs monophosphates, has been determined from a single crystal X-ray study. Structural relationships between the different monophosphates of the AVOPO_4 series with A = Li, Na, K, Rb, Cs, NH_4 are presented in which K~+ appears as a boundary cation: with cations smaller than K~+ the vanadium(IV) is octahedral and pyramidal with larger ones, both coordinations existing with K~+.