EPR spectra were obtained for 13 spin-labeled pyridines coordinated to chromium(III) tetraphenylporphyrin chloride. In fluid solution weak electron-electron exchange interaction caused broadening of the nitroxyl signal and stronger interaction caused resolved splitting. Resolved spin-spin splitting was observed in frozen solution. Values of the exchange coupling constant, J, between ±0.005 and ±0.27 cm-1 were obtained by computer simulation of the frozen-solution spectra. The stronger exchange interaction for 4-substituted pyridines than for analogous 3-substituted pyridines is consistent with πdelocalization of the unpaired spin density from the metal into the pyridine ring, π delocalization was also dominant in the vanadyl trifluoroacetylacetonate complexes of these spin-labeled pyridines. The values of J for the Cr(III) (S = 3/2) complexes were 1/2to 2/3 of the values observed for the vanadyl (S = 1/2) complexes of the same spin-labeled pyridines.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry