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(N-pyridyl amide) (L) 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 CoL2 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 SO42– 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.