ELECTRON SPIN RESONANCE STUDIES OF A WEAKLY COUPLED BIRADICAL

Abstract : ELECTRON SPIN RESONANCE, INCLUDING ITS TEMPERATURE DEPENDENCE, HAS BEEN STUDIED IN SEVERAL SOLID SALTS DERIVED FROM ALPHA,ALPHA,BETA,BETATETRAKIS-(4-DIMETHYLAMINOPHENYL)-ETHYLENE(I). THE PARAMAGNETISM APPEARS TO RESULT FROM THERMAL EXCITATION TO LOW LYING TRIPLET ELECTRONIC STATES IN WHICH THE UNPAIRED ELECTRONS ARE ONLY WEAKLY COUPLED. EXCITATION ENERGIES OF 4.5 AND 8.6 KCAL/MOLE ARE FOUND FOR THE I-DIIODIDE AND THE I-DINITRATE, RESPECTIVELY. IT IS SUGGESTED THAT THE AVERAGING OUT OF HYPERFINE AND ELECTRON DIPOLE-DIPOLE SPLITTINGS RESULTS FROM DELOCALIZATION OF THE UNPAIRED ELECTRONS AND FROM EXCHANGE INTERACTIONS WHICH MAY BE AIDED BY THE DIFFUSION OF THE PARAMAGNETIC SPECIES WHICH RESULTS FROM THE THERMAL EXCITATION AND DEACTIVATION