The crystal structures of the cobalt(II) metal–organic frameworks or coordination networks of Co(pdb)(DMF) and Co2(pdi)(DMF)3·2(DMF)·H2O (H2pdb = 3,3′-(phenazine-5,10-diyl)dibenzoic acid; H4pdi = 5,5′-(phenazine-5,10-diyl)diisophthalic acid; DMF = N,N-dimethylformamide) were synthesized solvothermally from cobalt(II) nitrate and the free acid of the linker in DMF. Systematic solvothermal screening demonstrated strong metal- and counterion-dependent framework formation, as crystalline coordination polymers were obtained exclusively from cobalt(II) nitrate, whereas other metal salts and cobalt(II) chloride or sulfate produced no crystalline materials. In catena-(N,N-dimethylformamide)-μ4-3,3′-(phenazine-5,10-diyl)dibenzoate-cobalt(II), Co(pdb)(DMF), the Co2 units, acting as secondary building units, are coordinated by four carboxylate groups from four linkers in a paddle-wheel arrangement, giving a three-dimensional (3D) network with cds (or CdSO4) topology, in which the wide openings are filled by two symmetry-related nets to form a threefold interpenetrated structure. In catena-tris(N,N-dimethylformamide)-μ8-5,5′-(phenazine-5,10-diyl)diisophthalate-dicobalt(II) bis(N,N-dimethylformamide) hydrate, Co2(pdi)(DMF)3·2(DMF)·H2O, there are two different Co atoms, of which only Co2 is connected to each of the four carboxylate groups of the tetracarboxylate linker and, thus, is responsible for 3D network formation. The network topology in Co2(pdi)(DMF)3 is pts (or platinum(II) sulfide) when taking the Co2 atom as a tetrahedral node and the linker as a square-planar fourfold node; however, this arrangement is inverse to the common square-planar metal and tetrahedral linker nodes found in PtS and most pts topologies.
Vollrath et al. (Tue,) studied this question.