An Experimental and Theoretical Investigation on Pentacoordinated Cobalt(III) Complexes with an Intermediate S=1 Spin State: How Halide Ligands Affect their Magnetic Anisotropy

International audienceUnderstanding the factors that control the magnitude and symmetry of magnetic anisotropy should facilitate the rational design of mononuclear metal complexes in the quest for single-molecule magnets (SMMs), based on a single metal ion, with high blocking temperatures and large energy barriers. The best strategy is to define magnetostructural correlations through the investigation of a series of metal complexes. It has been demonstrated that the main contribution to the magnetic anisotropy arises from the spin-orbit coupling (SOC) effect in metal-ion-based systems, so current studies focus particularly on the use of both ligands and metal ions possessing a large SOC. In this context, we report a unique series of halide CoIII complexes, [CoL(X)], with X=Cl, Br, I (CoX) and L=2,2′-(2,2′-bipyridine-6,6′-diyl)bis(1,1-diphenylethanethiolate), which possess a rare intermediate S=1 spin ground state. The S=1 CoIII complexes are attractive species because they possess a remarkably large axial zero-field splitting (defined by D from the following Hamiltonian: H=DSz2), as well as the halide ligands inducing large SOC constants...