Spectroscopic Identification of Disordered Molecular Cations in Defect Perovskite‐like A\(Ln\)(HCO\(_2\))(C\(_2\)O\(_4\))\(_{1.5}\) (\(Ln\) = Tb‐Er) Phases

This work reports a new series of A\(Ln\)(HCO\(_2\))(C\(_2\)O\(_4\))\(_{1.5}\) (A = [(CH\(_3\))\(_2\)NH\(_2\)]\(^+\) and Ln\(^{3+}\) = Tb\(^{3+}\)-Er\(^{3+}\)) compounds made solvothermally. These \({Cmce}\) phases combine monovalent and divalent ligands, which enables a scarce combination of A\(^+\) and B\(^{3+}\) cations in a hybrid perovskite-like compound. The ratio of ligands leads to ordered anion vacancies, which alternate with oxalate linkers along the \(c\)-axis. The A-site cations are disordered and cannot be identified crystallographically, likely a result of the larger pores of these frameworks compared to the recently reported AEr(HCO\(_2\))\(_2\)(C\(_2\)O\(_4\)) phases. Neutron and infrared spectroscopy, supported by elemental composition, enables these cations to be identified as [(CH\(_3\))\(_2\)NH\(_2\)]\(^+\) molecules. Magnetic property measurements suggest these materials have weak antiferromagnetic interactions but remain paramagnetic to 1.8 K.