RbCuFe(PO4)2.

A new iron phosphate, rubidium copper(II) iron(III) bis-(phosphate), RbCuFe(PO4)2, has been synthesized as single crystals by the flux method. This compound is isostructural with KCuFe(PO4)2 [Badri et al. (2011 ▶), J. Solid State Chem. 184, 937-944]. Its structure is built up from Cu2O8 units of edge-sharing CuO5 polyhedra, inter-connected by FeO6 octa-hedra through common corners to form undulating chains that extend infinitely along the [011] and [01-1] directions. The linkage of such chains is ensured by the PO4 tetra-edra and the resulting three-dimensional framework forms quasi-elliptic tunnels parallel to the [101] direction in which the Rb(+) cations are located.