Enhancing the chemical flexibility of hybrid perovskites by introducing divalent ligands

Herein we report the synthesis and structures of [(CH3)2NH2]Er(HCO2)2(C2O4) and [(NH2)3C]Er(HCO2)2(C2O4), in which the inclusion of divalent oxalate ligands allows for the exclusive incorporation of A+ and B3+ cations in an ABX3 hybrid perovskite structure for the first time. We rationalise the observed thermal expansion of these materials, including negative thermal expansion, and find evidence for weak antiferromagnetic coupling in [(CH3)2NH2]Er(HCO2)2(C2O4).