Formate-mediated magnetic superexchange in the model hybrid perovskite [(CH3)2NH2]Cu(HCOO)3

Abstract

We have investigated the magnetic and electronic structures of crystalline dimethylammonium copper formate [(CH₃)₂NH₂]Cu(HCOO)₃, a model compound that belongs to a wide class of hybrid organic–inorganic perovskites. We present the results of a combined experimental approach, where neutron diffraction and magnetisation measurements were used to solve the ground state magnetic structure in which the same ligand mediates both antiferromagnetic and ferromagnetic interactions, while the electron charge density distribution and orbital occupancy were determined by high-resolution X-ray diffraction. The latter enabled a microscopic analysis of the chemical bonding, from which we established a detailed correlation between the structural, electronic, and magnetic properties of [(CH₃)₂NH₂]Cu(HCOO)₃, demonstrating the primary role of Cu–O bonding in establishing the nature of the exchange. Our results elucidate the mechanism of magnetic exchange mediated by formate anions, from which we examine the applicability of foundational theories of purely inorganic perovskites and define characteristics that the ligands should meet to support the use of the Goodenough–Kanamori–Anderson rules.