Cobalt nuclear resonance spectra

The frequencies of the cobalt nuclear resonances of solutions of fourteen cobalt (III) complexes have been measured in a magnetic field of 4370.9G. The temperature coefficient of the nuclear resonance frequency of two of the complexes has been measured, and the effect of variation of solvent studied. The electronic absorption spectra of the complexes have also been measured, and the absorption band shifts which occur when the temperature is changed have been studied for two of the complexes. The nuclear resonance frequencies show a close correlation with the spectrochemical series of the ligands. Following a suggestion by Orgel, a simple interpretation of the chemical shifts is developed in terms of crystal field theory. The theory predicts a linear relation between the cobalt nuclear resonance frequency and the wavelength of the lowest frequency optical absorption maximum of the octahedral complexes. The compounds studied support this prediction. Using measured values of the temperature coefficient of the nuclear resonance frequency and the optical absorption wavelength, the theory permits the temperature dependence of the optical spectrum to be calculated. In the two cases studied the calculations are in satisfactory agreement with experiment. The results provide information about the ‘electronic shielding’ of the cobalt nucleus which leads to an improved value of the cobalt nuclear moment.