The Diffuse Reflection Spectra of Bentonites Colored with Various Aromatic Compounds and Related Ion-radical Salts

Bentonites colored with each of the following aromatic compounds were examined by the method of diffuse reflection in the range from 4 to 30 kK: benzidine, 4,4′-dihydroxybiphenyl, 4,4′-dimethoxybiphenyl, perylene, tetrathiotetracene, and phenothiazine. By comparison with the spectra of the related ion-radical salts, the oxidation of the aromatic compounds to the mono- and/or di-valent cations could be proven in all of them. Except in the case of phenothiazine, the species in the colored clays was found to be drastically modified by moisture. In addition, the spectra of the copper-arene complexes recently reported by Mortland et al. were measured. The oxidation of perylene, tetrathiotetracene, and phenothiazine was found to proceed to a greater extent in the copperexchanged clays.