Coordination Polymers Containing Tubular, Layered, and Diamondoid Networks: Redox, Luminescence, and Electron Paramagnetic Resonance Activities

Coordination polymeric (CP) materials are of interest due their versatile applications in various fields. CP-based materials have a great potential to act as multifunctional materials given their diversified nature. A series of CPs was found to exhibit a combination of luminescence, redox, and electron paramagnetic resonance (EPR) activities with potential for multifunctional materials. In particular, four new CPs of Cu­(II) and Co­(II) containing bis­(<i>N</i>-pyridyl amide) (<b>L</b>) and dicarboxylates have been synthesized and characterized by single-crystal X-ray and other techniques. The CPs were found to exhibit two types of two-dimensional (2D)-networks and one each of one-dimensional (1D) and three-dimensional (3D) networks. Interestingly the 1D-coordination polymer contains a tubular network which is formed by linking Co<b>L</b>₂ macrocycles by 1,3-benzene-dicarboxylate anions. In one of the 2D-layers, the Cu­(II) center was found to form an interesting trimeric secondary building unit via bridging of carboxylates and SO₄^2– and propagates a 2D-layer that contains no cavities. The Co­(II) complex also exhibits a 2D-layer containing rectangular cavities which are eventually filled by interdigitation of layers. The 3D-CP exhibits a pseudo diamondoid network containing two types of arms which differ in their length hugely, and the networks are triply interpenetrated. Interestingly, two types of water tetramers were found in the 1D-tubular network and 2D-layer containing rectangular grids. The electrochemical measurements (cyclic voltammetry and differential pulse voltammetry), EPR, and luminescence of CPs as well as ligands were explored. These studies indicate that all four CPs serve as redox active electrode materials. Among the four CPs, the CP containing interpenetrated diamondoid network was found to exhibit higher electrochemical performance. The present work emphasizes that the interactions between metal ions and organic linkers play an important role in electrochemical performances of the materials. Further the EPR spectral properties and luminescence properties of CPs were found to follow similar trends. The dimension of the network was found to correlate with their observed properties, i.e., 3D > 2D > 1D