Magnetic Anisotropy and Spin Coupling in a Cobalt(II) Dimer with Bioinspired Bridges.

Cobalt-(II) metal complexes constitute a versatile platform for investigating how coordination geometry and spin-orbit coupling determine their magnetic properties. Although numerous cobalt-(II) coordination complexes have been reported in recent literature, only a limited number exhibit comprehensive and quantitatively reliable magnetic characterization. In this work, we investigate the magnetic properties of the hexacoordinated cobalt dimer [Co2(μ-L1H)2(μ-H2O)2(H2O)4]-4NO3·2H2O, where L1H denotes the adenine bridging ligand. The hexacoordinated environment stabilizes a high-spin S = 3/2 configuration for both Co-(II) centers, resulting in strong spin-orbit coupling and significant zero-field splitting, described by axial (D) and rhombic (E) anisotropy parameters. Fits to magnetic susceptibility and magnetization data reveal antiferromagnetic coupling between the Co-(II) ions, with a ratio of E/D ≈ 1/4 and D/k B = 89 K, evidencing pronounced magnetic anisotropy in the system. This behavior is further supported by anisotropic Landé factors g x = g y = 2.5 and g z = 2.4, consistent with easy-plane magnetic anisotropy.