Single-Crystal EPR Study of a Cu(II)dialkyldiselenocarbamate. An Example of Noncoinciding Principal Axes

A single‐crystal EPR study of Cu(II)di‐n‐butyldiselenocarbamate magnetically diluted in the corresponding Ni(II) complex is reported. The directions of the principal axes of the ⁶³Cu and ⁷⁷Se hyperfine splitting tensors and the magnitudes of the electron‐spin–nuclear‐spin dipole–dipole interactions along these axes were found to agree satisfactorily with what is expected for a planar complex of approximately $D_{\text{2h}}$ symmetry with one unpaired electron in an antibonding $\sigma$ orbital. The Se hfs data were used to calculate the extent to which the Se $\text{4s}$ and $\text{4p}$ atomic orbitals participate in the orbital of the unpaired electron. It was found that two principal axes of the $g$ tensor do not coincide with the principal axes of the Cu hfs tensor. In addition, the anisotropy in $g$ value reaches a minimum in the plane where the anisotropy in the Cu hfs reaches a maximum. This indicates that the over‐all electronic structure of the complex differs significantly from the structure normally evoked to interpret the EPR parameters of planar Cu(II) complexes, notwithstanding the “normal” hyperfine data. The consequences of the noncoincidence of principal axes for the powder spectrum are discussed. It is shown that the peak positions in the recorded powder spectrum can be accounted for quantitatively using the single‐crystal EPR results.