RbFe(HAsO4)2 and TlFe(HAsO4)2, two new hydrogenarsenates adopting two closely related structure types

Abstract

Rubidium iron bis[hydrogen arsenate(V)], RbFe(HAsO4)2, and thallium iron bis[hydrogen arsenate(V)], TlFe(HAsO4)2, were grown under mild hydrothermal conditions (T = 493 K, 7 d). RbFe(HAsO4)2 adopts the RbFe(HPO4)2 structure type (space group R\overline{3}c), while TlFe(HAsO4)2 crystallizes in the (NH4)Fe(HPO4)2 structure type (space group P\overline{1}). Both compounds have tetrahedral–octahedral framework topologies. The M + cations are located in channels of the respective framework and are disordered in TlFe(HAsO4)2, which may suggest that the M + cations can move in the channels.