A dinuclear Co(iii)/Co(ii) complex based on the H2pmide ligand showing field-induced SMM behaviour

Abstract

We report the synthesis, structural characterization and SMM behaviour of a new mixed valence Co(II)/Co(III) dinuclear complex bearing the H₂pmide ligand. Well defined molecule pairs are observed in the crystal structure, bound through H-bond interactions directed by aqua ligands. From DC magnetometry data, a spin-only Hamiltonian approach including an axial zero-field splitting term seems to be enough for reasonable modelling, with a sizeable D parameter close to 40 cm⁻¹. The first order orbital contribution is extensively quenched due to strong distortion from octahedral symmetry of the Co(II) site. Quantum computation at the CASSCF level supports this interpretation. To model low temperature magnetization data, the H-bond intermolecular exchange interaction is required, with a magnitude close to −1 cm⁻¹, well supported by broken-symmetry DFT computation. This exchange is highly anisotropic due to the existence of a well isolated Kramers doublet at the Co(II) site. AC magnetic susceptibility shows field-induced SMM behaviour with competing Orbach and Raman relaxation pathways as well as a quantum tunnelling process at the lowest probed temperatures. The Orbach thermal barrier agrees with the expected one from combined experimental and quantum computed DC magnetometry analysis.