Molecular analogue of the perovskite repeating unit and evidence for direct Mn^III-Ce^IV-Mn^III exchange coupling pathway.

Abstract

The perovskite manganites AMnO₃ and their doped analogues A_1-x B _x MnO₃ (A and B = main group and lanthanide metals) are a fascinating family of magnetic oxides exhibiting a rich variety of properties. They are thus under intense investigation along multiple fronts, one of which is how their structural and physical properties are modified at the nanoscale. Here we show that the molecular compound [Ce₃Mn₈O₈(O₂CPh)₁₈(HO₂CPh)₂] (Ce^III₂Ce^IVMn^III₈; hereafter Ce₃Mn₈) bears a striking structural resemblance to the repeating unit seen in the perovskite manganites. Further, magnetic studies have established that Ce₃Mn₈ exhibits both the combination of pairwise Mn^III₂ ferromagnetic and antiferromagnetic exchange interactions, and the resultant spin vector alignments that are found within the 3-D C-type antiferromagnetic perovskites. First-principles theoretical calculations reveal not only the expected nearest-neighbor Mn^III₂ exchange couplings via superexchange pathways through bridging ligands but also an unusual, direct Mn^III-Ce^IV-Mn^III metal-to-metal channel involving the Ce^IV f orbitals.Perovskite manganites exhibit intriguing but poorly understood properties, including multiferroicity. Here, the authors synthesize a Ce₃Mn₈ cluster that structurally resembles a perovskite repeat unit, and use this molecular analogue to elucidate mechanisms driving bulk perovskite properties.