Field-induced slow magnetic relaxation of two 1-D compounds containing six-coordinated cobalt(ii) ions: influence of the coordination geometry

Two one-dimensional (1-D) cobalt(ii) compounds, namely, {[Co(L1)(2,2-bipy)]0.5DMF}(n) (1) and {[Co(bimb)(H2O)(4)](L2)2DMF}(n) (2) (H(2)L1 = 2,2-[benzene-1,4-diylbis(methanediylsulfanediyl)]dibenzoic acid, H(2)L2 = 2,2-(1,4-phenylenebis(methylene))bis(sulfanediyl)dinicotinic acid, 2,2-bipy = 2,2-bipyridine, bimb = 1,4-bis(benzoimidazo-1-ly)benzene), have been synthesized using cobalt(ii) salts with long flexible carboxylic acids and N-containing ligands. Compounds 1 and 2 were systematically characterized by elemental analysis, infrared spectroscopy, and single crystal X-ray diffraction analysis. Both compounds display 1-D chain structures with two types of well-separated six-coordinated cobalt(ii) ions possessing the same coordination sphere CoO4N2 but different coordination geometries: distorted trigonal prism and octahedron, respectively, which lead to different magnetic properties. Compound 1 exhibits more significant frequency-dependent signals and larger field-induced slow relaxation magnetization than compound 2. High frequency electron paramagnetic resonance (HF-EPR) studies further demonstrated the large anisotropy of both compounds with D values of -56.2 and +57.5 cm(-1), respectively.