Crystalline Reflectance Spectra of Ion—Radical Salts at Room Temperature, at 77°, and at 4.2°K. I. Wurster's Blue Perchlorate

Abstract

Polarized reflectance spectra of crystalline Wurster's blue (WB) perchlorate are reported at temperatures above and below the reported phase transition at 190°K of the ion—radical salt. The spectral evidence indicates the position of the first π—π* transition in the solid and uncovers an electronic band associated with the low-temperature phase of the solid in the near-infrared spectral range at approximately 11 000 cm−1. By comparing these spectra with the solution dimer spectrum of WB perchlorate of Hausser and Murrell and by observing the unique polarization of the band in the solid, arguments are advanced in favor of a ``dimer'' model for the solid in the low-temperature phase. Further implications of the observed polarization effects are discussed.