A Porous Coordination Polymer Assembled from 8-Connected {CoII₃(OH)} Clusters and Isonicotinate: Multiple Active Metal Sites, Apical Ligand Substitution, H₂ Adsorption, and Magnetism

A microporous coordination polymer, namely, [Co(3)(ina)(4)(OH)(C(2)H(5)OH)(3)](NO(3))·C(2)H(5)OH·(H(2)O)(3) (1, or MCF-38, ina = isonicotinate), with 8-connected {Co(3)(OH)} clusters as the structural secondary building units, has been solvothermally synthesized. The hydroxo-centered Co(II) cluster involves multiple active metal sites. The interesting apical ligand substitutions have been directly observed, and the corresponding products of [Co(3)(ina)(4)(OH)(G)(x)(H(2)O)(n)](NO(3))·G·(H(2)O)(m) (1 ⊃ PrOH, G = PrOH, x = 2, n = 1, m = 3; 1 ⊃ BuOH, G = BuOH, x = 2, n = 1, m = 1, and 1 ⊃ MeOH, G = MeOH, x = 3, n = 0, m = 7) have also been obtained by solvothermal syntheses or crystal-to-crystal transformations. High-pressure H(2) adsorption measurement at 77 K reveals that activated 1 can absorb 2.2 wt % H(2) at 5 bar. The relative H(2) absorption at low pressure (86% of the storage capacity at 1 bar) is higher than the corresponding values reported for some typical porous coordination polymers. The magnetic studies of 1 show a dominant antiferromagnetic coupling between Co(II) ions of intra- and inter-cluster.