Magnetic Properties of Some Iminoxyl Polyradicals. III. Exchange Interaction in Iminoxyl Biradicals

Abstract

The EPR spectra of TEMPAD and Sulfite biradicals in a dilute solution have been reasonably interpreted in terms of the variation in the ratio of the intra-molecular exchange interaction to the ¹⁴N hyperfine interaction. Comparing these spectra with the theoretical ones, the authors have estimated the intra-molecular exchange interactions as 10.0·A=2×10⁻²k and 3.0·A=5×10⁻³k respectively. The magnetic susceptibility of the TEMPAD biradical exhibits a broad maximum at a temperature of 16.5°K, while 50 and 75% TEMPAD diluted in corresponding diamine have no maximum in the temperature range measured. The magnetic susceptibility of the sulfite biradical also shows a broad maximum at 15.0°K, in spite of the weak intra-molecular exchange interaction. These results indicate that the origin of the short-range ordering is the inter-molecular exchange interaction between unpaired electrons in different molecules.