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, [Co2(L)3(HCO2)·MeOH]n (1), [Co5(L)6(OH)2(NO3)2·2H2O]n (2), and [CoL(HCO2)]n (3) [L = (E)-3-(pyridin-3-yl)­acrylate],
have been successfully synthesized. In these complexes, each CoII cluster is linked by twelve L ligands with
different connectivities to generate unique topological nets. In 1, two formate anions link four CoII ions forming
a tetranuclear cluster, and each of the tetranuclear clusters is connected
to eight neighbors by L ligands, giving an 8-connected
36418536 net. In 2,
the pentanuclear cluster is formed by five CoII 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 CoII ions with six syn,syn,anti formate
anions and six syn syn carboxylate groups. Magnetic studies indicated
that domain antiferromagnetic interactions exist between CoII ions, and spin competition exists in 2 and 3.