Construction of Metal−Organic Frameworks with Tetranuclear Metal Clusters: Hydrothermal Synthesis, Structure, and Magnetic Properties

Five novel coordination polymers [Co₄(OABDC)₂(OH)₂(H₂O)₄]_n·(H₂O)_4.4n (1), [Ni₄(OABDC)₂(OH)₂(H₂O)₄]_n·(H₂O)_4n (2) (OABDC = 5-oxyacetateisophthalate), [Co₂(OABDC)(bpe)(OH)]_n·(H₂O)_2.9n (3), [Zn₂(OABDC)(bpe)(OH)]_n·(H₂O)_3.5n (4) (bpe = 1,2-bis(4-pyridyl)ethylene), and [Co₂(OABDC)(bpy)(OH)]_n·(H₂O)_2.2n (5) (bpy = 4,4′-bipyridine) have been acquired at similar hydrothermal conditions. All compounds are constructed from tetranuclear [M₄(μ₃-OH)₂] (M = Co for 1, 3, and 5, Ni for 2, Zn for 4) clusters. Compounds 1 and 2 are isomorphous, in which the M₄(OH)₂ units act as 6-connected nodes and the frameworks are two-dimensional (2D) (3,6)-connected nets with the rare CdI₂ type. If considering the strong H-bond interactions between neighboring layers, both exhibit three-dimensional (3D) microporous networks with channels running along the [100] direction. Complexes 3 and 4 are also isomorphous, in which the 2D CdI₂-based layer was pillared by bpe spacers; thus channels occur along the [100] direction. While adopting bpy instead of the bpe ligand, smaller channels are observed along the [100] direction for 5. The last three compounds all feature 3D networks with one of the scarce (3,8)-connected (4³)₂.(4⁶.6¹⁸.8⁴) topologies. Magnetic susceptibility measurements indicate that compound 1 shows strong antiferromagnetic behavior, while 2 exhibits strong ferromagnetic behavior.