Two new Rb-Ga arsenates: RbGa(HAsO

The crystal structures of hydro-thermally synthesized (T = 493 K, 7-9 d) rubidium gallium bis-[hydrogenarsenate(V)], RbGa(HAsO4)2, and rubidium digallium arsenic(V) hexa-[hydrogenarsenate(V)], RbGa2As(HAsO4)6, were solved by single-crystal X-ray diffraction. Both compounds have tetra-hedral-octa-hedral framework topologies. The M+ cations are located in channels of the respective framework. RbGa(HAsO4)2 crystallizes in the RbFe(HPO4)2 structure type (Rc), while RbGa2As(HAsO4)6 adopts the structure type of RbAl2As(HAsO4)6 (Rc), which represents a modification of the RbFe(HPO4)2 structure type. In this modification, one third of the M3+O6 octa-hedra are replaced by AsO6 octa-hedra, and two thirds of the voids in the structure, which are usually filled by M+ cations, remain empty to achieve charge balance.