Tuning the Subunits and Topologies in Cluster-Based Cobalt-Organic Frameworks by Varying the Reaction Conditions

Different ways of anions introduction were applied to construct cluster-based frameworks, owning to the versatile coordination ability of the formate anion and its sensitivity to the pH value of the reaction system. Three tetra-, penta-, and hexanuclear cluster-based cobalt-organic frameworks, [Co-2 (L)(3)(HCO2) center dot MeOH](n) (1), [Co-5(L)(6)(OH)(2)(NO3)(2)center dot 2H(2)O](n) (2), and [CoL(HCO2)](n), (3) [L = (E)-3-(pyridin-3-yl)acrylate], have been successfully synthesized. In these complexes, each Co-II cluster is linked by twelve L ligands with different connectivities to generate unique topological nets. In 1, two formate anions link four Co-II ions forming a tetranuclear cluster, and each of the tetranuclear clusters is connected to eight neighbors by L ligands, giving an 8-connected 3(6)4(18)5(3)6 net. In 2, the pentanuclear cluster is formed by five Co-II ions linked through two OH- and six carboxylate groups, which are further connected by L ligands to afford a pcu (primitive cubic lattice) net. Different from 1 and 2, complex 3 is a 2-fold interpenetrating pcu net based on hexanuclear clusters, which are formed by the linkage of six Co-II ions with six syn,syn,anti formate anions and six syn syn carboxylate groups. Magnetic studies indicated that domain antiferromagnetic interactions exist between Co-II ions, and spin competition exists in 2 and 3.