Bimetallic M^V₂Cu^II₃ (M = Mo, W) coordination complexes based on octacyanometalates: Structures and magnetic variations tuned by chelated tetradentate macrocyclic ligands

Four octacyanometalate-based bimetallic Cu-M (M = Mo, W) assemblies coordinated by tetradentate macrocyclic ligands were prepared via self-assembly process in a stoichiometric ratio of [M(CN)₈]^3- and Cu(macrocycle)²⁺ and characterized in terms of structures and magnetic properties. The crystal structures are varied depending on the macrocycles used. The employment of cyclam with no pendant groups produced a one-dimensional chain (1) with a rope-ladder pattern, whereas macrocycles with side groups allowed for the formation of two-dimensional honeycomb-like architectures (2-4). From the crystal structures, the variations in apical Cu-N_ax lengths and Cu-N_ax-C_ax angles on the bridging pathways are observed, which arises from the existence of side groups on macrocyclic ligands. The magnetic results reveal that all of the prepared compounds show ferromagnetic couplings between magnetic centers transmitted through CN bridges under the present structural parameters. Comparing the magnetic strength of the Cu-Mo (3d-4d; 2) and Cu-W (3d-5d; 3) complexes supports that 3d-5d magnetic coupling is stronger than 3d-4d because the 5d orbital is more diffuse than 4d. The magnetic analyses for 1-4 and related complexes tentatively suggest that, when the Cu-N_ax distances are long enough, the axial Cu-N_ax bond length in the bridging route may be one of the major structural parameters to determine the magnitude of the ferromagnetic exchange coupling.