Hydrothermal syntheses, structures and magnetic properties of coordination frameworks of divalent transition metals

Abstract

The hydrothermal syntheses, single-crystal X-ray structures and magnetic properties of [Co(C4O4)(H2O)2] (1), [Co3(OH)2(C4O4)2] · 3H2O (2) and [Fe(OH)2(C4O4)] (3) are described. Pale yellow cubes of 1 and brown red crystals of 2 were obtained from the reaction of Co(OH)2 and squaric acid at 200 °C. Brown needle of 3 were obtained similarly from Fe(SO4) · 7H2O, squaric acid and NaOH. 1 consists of a cubic sodalite arrangement with empty cavities where the Co atoms are connected by μ4-squarate and two trans-water molecules each, while 2 and 3 contain metal-hydroxide double-chains of edge-sharing octahedral, brucite-type for 2 and goethite for 3, connected by μ6-squarate. 2 contains water molecules in the channels which can be removed and re-inserted repeatedly without loss of crystallinity. All three compounds possess 3D frameworks made up of coordination and hydrogen bonds. 1 behaves as a paramagnet while 2 and 3 are antiferromagnets and 2 transforms to a ferromagnet reversibly upon dehydration and rehydration. The structures of two one-dimensional polymers employing 2,5-pyridinedicarboxylate, [Co2(H2O)6(2,5-pydc)2] · 2H2O (4) and Cu(2,5-pydc)2 (5), are also reported.