Electron spin resonance and electron nuclear double resonance study of mixed crystals of benzophenone and diphenylnitroxide.

An e.s.r. and ENDOR study of diphenylnitroxide in benzophenone crystals is presented. Different paramagnetic species due to the isolated radicals, strongly coupled radical pairs, clusters of three and four radicals and finally weakly coupled radical pairs have been detected. From crystal-like ENDOR spectra in crystalline powders the proton hyperfine tensors have been obtained, and the conformation of the radical has been deduced to be slightly different from that of benzophenone. 14N and 1H ENDOR analysis in single crystals has given the result that the diphenylnitroxide radical is substituted isostructurally for the host molecules, but that a rearrangement of the radical orientation is present when two or more radicals occupy adjacent positions in the host structure.