Metal–Metal Interactions in Hexagonal Perovskites Containing Bimetallic Face-Sharing Bioctahedra

Abstract Recent studies have revealed metal-to-metal and intervalence-charge transfer transitions in cation ordered 6H perovskites with Cs3M+M2+M3+Cl9 stoichiometry. The structure and properties of two new members of this family, Cs3NaMnVCl9 and Cs3NaMnCrCl9, are reported here. In both compounds Na+ ions occupy sites in octahedra that share only corners, electronically isolating face-sharing M2Cl9 bioctahedral clusters. Analysis of synchrotron X-ray and neutron powder diffraction patterns reveals no sign of long-range ordering of the Mn2+ and V3+/Cr3+ ions, suggesting a random orientation of bimetallic Mn2+M3+Cl94– clusters. Magnetometry studies reveal paramagnetic behavior in both compounds, with negative Weiss temperatures and effective moments that closely align with expected values based on spin-only moments. No sign of long-range magnetic order is observed in either compound down to at least 2 K. The optical absorption spectra feature d-to-d transitions, ligand-to-metal charge transfer (LMCT), and metal-to-metal charge transfer (MMCT) transitions. Cs3NaMnVCl9 exhibits a Mn2+ to V3+ MMCT transition at ∼1390 nm (∼0.9 eV), whereas the comparable MMCT transition in Cs3NaMnCrCl9 falls at a much higher energy and cannot be resolved due to overlap with the LMCT transition. The striking difference in MMCT energy can be attributed to differences in the electron configuration of V3+ (t2g2eg0) and Cr3+ (t2g3eg0).