Articles written in Journal of Chemical Sciences
Volume 130 Issue 7 July 2018 Article ID 0078
The fixation of carbon dioxide (CO2) is an important global challenge. A significant increase of the atmospheric CO2 due to the industrial emissions and a steady increase in combustion of fossil fuels is widespread environmental concern. This article is a short literature review on the recent developments in the field of CO2 activation and fixation by bioinspired copper(II) catalysts. In our laboratory, copper(II) complexes of bidentate ligands have been reported as catalysts for the fixation of CO2. The molecular structure of one of the complexes has shown unusual trigonal bipyramid geometry (τ, 0.936) by the coordination of two ligand units and a water molecule. All the complexes exhibited a well-defined Cu(II)/Cu(I) redox potentials around 0.352 to 0.401 V in acetonitrile. The rhombic EPR spectra of the complexes indicate the existence of a geometrical equilibrium between trigonal bipyramidal and square pyramidal at 70 K. The d-d transitions around 750–800 and 930–955 nm further supports five coordination geometry in solution. These copper(II) complexes have successfully fixed atmospheric CO2 as CO322- by using Et3N as sacrificial reducing agent and afforded [Cu(L)CO3(H2O)]. The CO322-bound complex has shown a distorted square pyramidal geometry (τ, 0.369) around copper(II) center via the coordination of only one ligand unit, a carbonate, and water molecules. The catalysts are active enough to fix CO2 for eight repeating cycles without any change in the efficiency. The fixation of CO2possibly proceeds via the formation of Cu(I)-species. This is supported by X-ray structure, which reveals distorted tetrahedral geometry by the coordination of two units of ligand.
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