Oxygen-Donor Metalloligands Induce Slow Magnetization Relaxation in Zero Field for a Cobalt(II) Complex with {CoO₄} Motif.

ABSTRACT: Most 3d metal-based single-molecule magnets (SMMs) use N-ligands or ligands with even softer donors to impart a particular coordination geometry and increase the zero-field splitting parameter |D|, while complexes with hard O-donor ligands showing slow magnetization relaxation are rare. Here, we report that a diamagnetic Ni^II complex of a tetradentate ligand featuring two N-heterocyclic carbene and two alkoxide-O donors, [L^O,ONi], can serve as a {O,O'}-chelating metalloligand to give a trinuclear complex [(L^O,ONi)Co(L^O,ONi)](OTf)₂ (2) with an elongated tetrahedral {Co^IIO₄} core, D = -74.3 cm^-1, and a spin reversal barrier U_eff = 86.9 cm^-1 in the absence of an external dc field. The influence of diamagnetic Ni^II on the electronic structure of the {CoO₄} unit in comparison to [Co(OPh)₄]^2- (A) has been probed with multireference ab initio calculations. These reveal a contrapolarizing effect of the Ni^II, which forms stronger metal-alkoxide bonds than the central Co^II, inducing a change in ligand field splitting and a 5-fold increase in the magnetic anisotropy in 2 compared to A, with an easy magnetization axis along the Ni-Co-Ni vector. This demonstrates a strategy to enhance the SMM properties of 3d metal complexes with hard O-donors by modulating the ligand field character via the coordination of diamagnetic ions and the benefit of robust metalloligands in that regard.

SUBMITTER: Lococciolo G 

PROVIDER: S-EPMC10966742 | biostudies-literature | 2024 Mar

REPOSITORIES: biostudies-literature