Correlation between infrared spectra and magnetic and optical properties of potassium chloranil. Effects of phase transition and solvation processes

The results of a study of the variation of the infrared spectrum of the potassium salt of chloranil (KCA) accompanying the temperature dependent phase transition and the hydration process are presented. Four strong absorptions, absent in the spectrum of the room temperature phase of KCA, are observed in the spectrum of the low temperature phase as well as in that of the hydrous form. In both cases they are attributable to a strong activation in infrared of the totally symmetric modes of the CA anion. These modifications of the infrared spectra are correlated with the strengthening of the charge transfer (CT) interaction among radical anions which accompanies the phase transition or hydration process as revealed by the parallel abrupt variation of the magnetic susceptibility and intensity of the CT band. The appearance of the new infrared bands is accounted for in terms of the Ferguson-Person vibronic model applied to a radical-radical self-dimer. © 1977.