Metal Ion Modulation of Structural Interpenetration and Magnetic Properties in Mn(II), Co(II), and Ni(II) Coordination Polymers with bnn Topology

Three novel coordination polymers based on Mn(II), Co(II), and Ni(II) were synthesized under hydrothermal conditions using a rigid dicarboxylate ligand (bcpt^2–) and a flexible bis(imidazole) ligand (bib). Despite employing the same ligands and conditions, the resulting structures exhibit distinct 3D bnn-type frameworks with 4-fold (Mn) and 3-fold (Co, Ni) interpenetration. This structural divergence stems from differences in metal coordination preferences and ligand conformations. Magnetic studies reveal the coexistence of weak ferromagnetic interactions and spin-canted antiferromagnetism in all compounds. Temperature-dependent ZFC/FC magnetization and field-dependent susceptibility measurements indicate long-range magnetic ordering and field-induced spin canting, particularly influenced by the metal centers and their anisotropies. The results reveal how metal ion selection directly impacts framework architecture and magnetic behavior, thus informing strategies for constructing multifunctional coordination materials with tailored properties.