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(μ₃-OH)₂]_n·5nH₂O (1) and [Co₃(2,4-pydc)₂(μ₃-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 Δ-chains. However, in comparison with only two crystallographically independent Co^II ions in a unit of 2, three crystallographically independent Co^II ions are found in an asymmetric unit of 1, where their Δ-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.