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

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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.

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