A 3D porous cobalt-organic framework exhibiting spin-canted antiferromagnetism and field-induced spin-flop transition

Two 3D cobalt-organic frameworks formulated as [Co3(2,4-pydc)2(micro3-OH)2]n.5nH2O (1) and [Co3(2,4-pydc)2(micro3-OH)2(H2O)]n.7nH2O (2) (2,4-pydc=pyridine-2,4-dicarboxylate) have been hydrothermally synthesized and characterized. Both compounds 1 and 2 exhibit the 3D porous frameworks with hydroxyl-bridged metal Delta-chains. However, in comparison with only two crystallographically independent CoII ions in a unit of 2, three crystallographically independent CoII ions are found in an asymmetric unit of 1, where their Delta-chains are constructed by two types of vertexes sharing quadrangles formed via edge-sharing triangles. Magnetic studies show that 1 exhibits spin-canted antiferomagnetism and a field-induced spin-flop transition while 2 behaves as a normal antiferromagnet. The magnetic properties are largely retained by the porous frameworks of dehydrated 1 and 2 compounds. Gas adsorption measurements indicate that both the dehydrated compounds absorb H2 into their pores.