Binuclear Cobalt(II) Complex and Cobalt(II) Coordination Polymer of Bidentate Ligand 1,3-Bis(2-benzimidazolyl)benzene: Crystal Structures and Magnetic Properties

Two cobalt(II) complexes, Co-2(MBimB)(2)Cl-4 center dot 2H(2)O center dot EDA (1) (MBimB=1,3-bis(2-benzimidazolyl)benzene, EDA=ethylenediamine) and [Co(MBimB)Cl-2], (2), have been synthesized based on the rigid ligand MBimB and characterized by single crystal X-ray diffraction. In complex 1, two MBimB molecules adopt "cis" conformation and bridge two cobalt(I) ions to form a binuclear metallaycyclic framework. In complex 2, MBimB ligand adopts "trans" conformation and bridges two adjacent cobalt(II) ions into 1D zigzag chain. Magnetic susceptibility of 1 and 2 showed ferromagnetic coupling firstly and then antiferromagnetic coupling as the temperature decreases. Compared to complex 2, stronger ferromagnetic interaction and/or spin-orbital coupling between the cobalt(I) ions in 1 can be ascribed to the shorter distance of Co center dot center dot center dot Co and enhanced intervening aromatic pi-system between the metal centers. CCDC: 993989, 1; 993990, 2.