Enhancing the chemical flexibility of hybrid perovskites by introducing divalent ligands

Herein we report the synthesis and structures of [(CH\(_3\))\(_2\)NH\(_2\)]Er(HCO\(_2\))\(_2\)(C\(_2\)O\(_4\)) and [(NH\(_2\))\(_3\)C]Er(HCO\(_2\))\(_2\)(C\(_2\)O\(_4\)), in which the inclusion of divalent oxalate ligands allows for the exclusive incorporation of A\(^+\) and B\(^{3+}\) cations in an ABX\(_3\) 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 [(CH\(_3\))\(_2\)NH\(_2\)]Er(HCO\(_2\))\(_2\)(C\(_2\)O\(_4\)).