Single Crystal and Powder EPR Studies on Copper(II) Bis(di-n-butyldiselenocarbamate)

Copper(II) bis(di‐n‐butyldiselenocarbamate) is studied in single crystals, diamagnetically diluted by Ni(II) bis(di‐n‐butyldiselenocarbamate), in polycrystalline samples and in frozen solutions by means of EPR. The EPR spectra show that in the unit cell two magnetic nonequivalent Cu(dbsc)₂ molecules are to be found and that ⁷⁷Se ligand hyperfine splitting can be detected. The principal axes of the g and the copper‐hfs tensor do not coincide. A spin Hamiltonian for this case is given. Contrary to the copper‐hfs and the ⁷⁷Se‐hfs tensors, which were found to be in agreement with what is expected for a planar complex of approximately D_2h symmetry, the behavior of the g tensor is significantly different with respect to analogous CuS₄ compounds. This indicates that the electronic structure of the complex differs remarkably from the structure of planar Cu(II) complexes; consequently, the symmetry is C_2h. The Se‐hfs data were used to estimate the degree of covalency in the $\mathrm{Cu}–\mathrm{Se}$ σ bond. This was compared with parameters for some analogous sulfur complexes. In the spectra of the polycrystalline samples the anomaly in the behavior of the tensors is obviously in accord with the single crystal EPR results.