Rubidium iron bis-[hydrogen arsenate(V)], RbFe(HAsO4)2, and thallium iron bis-[hydrogen arsenate(V)], TlFe(HAsO4)2, were grown under mild hydro-thermal conditions (T = 493 K, 7 d). RbFe(HAsO4)2 adopts the RbFe(HPO4)2 structure type (space group Rc), while TlFe(HAsO4)2 crystallizes in the (NH4)Fe(HPO4)2 structure type (space group P ). Both compounds have tetra-hedral-octa-hedral 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.
Keywords: RbFe(HAsO4)2; TlFe(HAsO4)2; arsenate; cation disorder; crystal structure; framework structure; hydrogenarsenate(V).