A Comparative Study of Nickel and Cadmium Coordination Polymers: Framework Topology and Proton Conductivity

Two new coordination polymers (CPs), [Ni2(dip)2(obb)2]⋅2H2O, and [Cd2(dip)2(obb)2(H2O)]⋅5.5H2O, were successfully synthesized via hydrothermal processes utilizing the organic linkers 4,4'-oxybisbenzoate (obb) and 2,6-di(1H-imidazol-1-yl)pyridine (dip). The unique structures of both CPs were confirmed by single-crystal X-ray diffraction studies. Ni-CP presents an intricate three-fold interpenetrated 3D framework, featuring a rare cag topology centered around dinuclear nodes. In contrast, Cd-CP exhibits a distinctive non-interpenetrated 2D framework with an unusual kIa topology. Despite Cd-CP’s water coordination and the inclusion of substantial guest water molecules, it unexpectedly exhibited lower proton conductivity than Ni-CP, which is non-porous and contains much less water content.