Solvent-induced synthesis of cobalt(ii) coordination polymers based on a rigid ligand and flexible carboxylic acid ligands: syntheses, structures and magnetic properties

Abstract

Five new cobalt(II) coordination architectures, {[Co(L)₂(H₂O)₂]·2H₂O·2NO₃}_n (1), {[Co(L)(ppda)]·2H₂O}_n (2), {[Co₂(L)(ppda)₂]₂·H₂O}_n (3), {[Co(L)(nba)]·5H₂O}_n (4), and {[Co(L)(oba)]₂·3H₂O}_n (5), have been constructed from the rigid ligand L [L = 2,8-di(1H-imidazol-1-yl)dibenzofuran] and different flexible carboxylic acid ligands [H₂ppda = 4,4′-(perfluoropropane-2,2-diyl)dibenzoic acid, H₂nba = 4,4′-azanediyldibenzoic acid, and H₂oba = 4,4′-oxydibenzoic acid]. Depending on the nature of the solvent systems, these five different coordination polymers were synthesized and characterized by single-crystal X-ray diffraction, IR, PXRD and elemental analysis. Compounds 1, 2 and 3 were obtained by a one-pot method, and then we utilized the solvent-induced effect to obtain almost pure crystals of 1–3, respectively. Compound 1 is an infinite 1D chain which is formed by L ligands and Co atoms. Compound 3 contains a [Co₂(CO₂)₄] secondary building unit (SBU), and can be topologically represented as a 6-connected 2-fold interpenetrating pcu net with the point symbol of {4¹²·6³}. Compound 4 can be characterized as a 4-connected sql tetragonal planar network with the point symbol of {4⁴·6²}. In compounds 2 and 5, there is a 1D chain which is formed by flexible carboxylic acid ligands and Co atoms; then the 1D chain is linked by L ligands in the tilting direction, leading to the formation of a 2D layer. Furthermore, UV-vis, TGA and magnetic properties have been investigated in detail.