Coordination between cobalt (II) ion and carbonyl group in acetone probed by using DAOSD approach

We applied a newly developed technique of the DAOSD (Double Asynchronous Orthogonal Sample Design) approach to probe weak coordination between Co2+ ions and acetone. Subtle spectral variation on the carbonyl band of acetone and d–d transition band are revealed via cross peaks of 2D asynchronous spectra generated by using the DAOSD approach. These results suggest that coordination occur between cobalt ions and the carbonyl group of acetone. To confirm whether coordination occur between cobalt ions and acetone, EXAFS experiments are utilized. The EXAFS results reveal that a Co2+ is coordinated by six methanol molecules in anhydrous CoCl2/methanol solution. Upon addition of acetone in into the anhydrous CoCl2/methanol solution, the coordination number of Co2+ ion becomes four, and one coordinating oxygen atom is replaced by a chlorine atom. We infer that the decrease in coordination number of Co2+ ion is due to the participation of the carbonyl oxygen of acetone in the coordination since the size of acetone is larger than methanol. This result provides an alternative evidence to support the conclusion that Co2+ ions coordinate with acetone, which is separately obtained from the 2D asynchronous spectra generated by using the DAOSD approach.