Syntheses, structures, and magnetism of new vanadium and iron fluoride phosphates Ax(NH4)3-xM4(PO4)2F7(OH)2 (A=K, Rb, Cs, and M= V, Fe) containing novel structural motifs

Abstract

Five new vanadium and iron fluoride phosphates Ax(NH4)3-xM4(PO4)2F7(OH)2 (A = K, Rb, Cs, and M = V, Fe) were prepared through hydrothermal redox reactions. All compounds crystallize in the monoclinic crystal system, space group P21/m. The crystal structure constitutes three-dimensional frameworks with channels extending along [001] where A+ or (NH4)+ ions reside in the channels. Novel structural motifs are made up of ∞[M4O8F7(OH)2]10− chains formed by corner-shared cubane M4 clusters. In the isostructural series, the interconnection between these units feature corner-shared cubane M4 S = 1 spin-chains (M = V3+) and corner-shared cubane M4 S = 5/2 spin-chain (M = Fe3+), which all promote antiferromagnetic (AFM) interactions.