The elucidation of the rotational diffusion tensor of a spin probe using NMR and ESR

Abstract A combination of ESR lineshape studies and NMR relaxation time measurements permits the complete elucidation of the rotational diffusion tensor of a spin probe. The technique employs both paramagnetic (Cu(II)) and deuterated diamagnetic (Ni(II)) homologs of bis[pyrollidine- N -carbodithioato]metal(II) complexes. The lineshape and relaxation time measurements were analyzed in terms of spectral densities which in turn were inverted to give the principal elements of the diffusion tensor. The results obtained insights into the pitfalls of the commonly made assumption of isotropic rotational diffusion.