Cation, Solvent, and Substituent Effects on the Optical Spectra of Alkali Metal Salts of Arylthiolate Anions

Abstract

Abstract The optical spectra of the alkali metal salts of arylthiolate anions have been studied in the two aprotic solvents, tetrahydrofuran (THF) and dimethylformamide (DMF). In the former solvent the position of the absorption maxima depends on the size of the counter cations, even at low temperatures (−72 to −76 °C); nearly linear relationships were observed between the inverse of the alkali metal radius (rc) and the wave number of the transition (\ ildeνmax) for both room and low temperatures. The intercepts for the extrapolation of both lines for 1/rc→0 agree with the \ ildeνmax of the ion pairs observed in DMF at room temperature, and the absorption maxima for this solvent are independent of the size of the counter cations. Thus, the existence of contact ion pairs in THF over the temperature range investigated and that of the solvent-separated ion pairs in DMF at room temperature were revealed. In the latter solvent, however, a hypsochromic shift was observed on lowering the temperature. The substituent effect of arylthiolate anions and the solvent effect of dimethoxyethane and dioxane on the absorption maxima are also discussed. From an inspection of optical spectral data it has been suggested that negative charge of arylthiolate anions is localized mainly on the sulfur atom.