Syntheses, crystal structures and magnetic properties of three novel cobalt(ii) complexes containing imidazole derivative groups

Abstract

Three Co(II) complexes with the formulas: {[Co2(Bib)3Cl2]Cl(CH3COO)}.CH3OH.H2O (1), [Co2(Bib)3Cl2]Cl2.(CH3OH)2.H2O, (2) and [Co3K1(Tib)2(CH3COO)6]PF6 (3), were obtained by self-assembly of a cobalt(II) salt with Bib and Tib (Bib = 1,3-bis(4,5-dihydro-1H-imidazol-2-yl)benzene; Tib = 1,3,5-tris(4,5-dihydro-1H-imidazol-2-yl)benzene) and were structurally and magnetically characterized. X-Ray single-crystal diffraction showed that each Co(II) ion was in a highly distorted tetrahedral coordination geometry with a cis-trans ratio of 1 : 2 from the Bib ligand, which functioned in a bidentate fashion in the binuclear triple-helical [Co2(Bib)3Cl2]2+ cations in 1 and 2. In the [Co3K1(Tib)2(CH3COO)6]- anions in 3, each Co(II) ion was also in a highly distorted tetrahedral coordination geometry and the Tib ligands acted in an offset fashion in C, C, C and A, A, A coordination to the Co(II) ions with pi-pi stacking interactions between two benzene rings from the Tib ligand in the cluster cation. Each Tib ligand in a cluster unit acted as a tridentate entity to coordinate three Co(II) ions resulting in a cylinder-like cluster structure. The intermolecular hydrogen bonds in the solid-state resulted in the well-shaped 2D layer network which formed a honeycomb in 1, the 3D supramolecular architecture which was connected to the 2D sheet into 3D in 2 and the 3D supramolecular architecture, which was extended into a well-shaped 2D honeycomb layer network in 3. The results from magnetic data, in the high-temperature region, showed that 1 and 2 obeyed the Curie-Weiss law with a Weiss constants theta = -12.3, and -9.8 K and a Curie constants C = 5.31 and 5.32 cm3 K mo1(-1), respectively, indicating antiferromagnetic interactions between adjacent cobalt(II) ions. Both complex 1 and 2 showed magnetic ordering at low temperature due to the canting effect. The zero-field AC magnetic susceptibility measurements for 1 and 2 displayed a maximum which was frequency dependent owing to a slow relaxation process, which could be caused by either domain wall movements or spin-glass behaviours.