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/kB = 89 K, evidencing pronounced magnetic anisotropy in the system. This behavior is further supported by anisotropic Landé factors gx = gy = 2.5 and gz = 2.4, consistent with easy-plane magnetic anisotropy.