Thermochromism and Magnetic Susceptibility of Copper(II) Anthracene-9-carboxylate

We investigated the thermochromism of copper(II) anthracene-9-carboxylate experimentally and theoretically. We performed X-ray crystal structure analysis at 233 and 113 K, measured magnetic susceptibility for 300-2 K, diffuse reflection spectra at 300 and 77 K, and spectra of the molecule in EPA solution at 300 and 77 K. DFT and TD-DFT calculations were performed to discuss magnetic properties and electronic spectra. The thermochromism was ascribed to a decrease in occupancy in the triplet state at 300 K due to a drop in temperature, since the LMCT band of the triplet state ((LMCT)-L-3) at 510 nm diminished with a decrease in the population of triplet state at lower temperature. The assignment of electronic absorption bands and the nature of chemical bonding are discussed with the results of DFT and TD-DFT calculation.