Perovzalates: a family of perovskite-related oxalates

A family of hybrid Perovskite-oxalates (“Perovzalates”) of general composition A^ILi₃M^II(C₂O₄)₃ (A = K⁺, Rb⁺, Cs⁺; M = Fe²⁺, Co²⁺, Ni²⁺) are presented. All eight new compounds are isostructural with the previously reported examples NH₄Li₃Fe(C₂O₄)₃ and KLi₃Fe(C₂O₄)₃, crystallising in the rhombohedral space group Rc, with a ∼11.3–11.6 Å, c ∼14.8–15.2 Å. In contrast to other families of “hybrid perovskites” such as the formates, these compounds can be regarded as closer structural relatives to inorganic (oxide) perovskites, in the sense that they contain direct linkages of the octahedral sites via bridging oxygen atoms (of the oxalate groups). It is of note, therefore, that monoatomic cations as large as Cs⁺ can be incorporated into the perovskite-like A sites of this structure type, which is not feasible in traditional ABO₃ perovskites; indeed CsLi₃Ni(C₂O₄)₃ appears to exhibit the ‘mostly tightly bound’ 12-coordinate Cs⁺ ion in an oxide environment, according to a bond valence analysis.