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

Abstract

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) (H₂L1 = 2,2′-[benzene-1,4-diylbis(methanediylsulfanediyl)]dibenzoic acid, H₂L2 = 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.