14N hyperfine coupling (HFC) tensors of some copper(II) complexes having tetrahedrally distorted N2S2 and N2 and trigonal bipyramidal N2O-O2 coordination structures were examined by the angle-selected ENDOR method. By the use of this spectroscopic method, not only the principal values but also the relative orientations with respect to the g tensors were determined from disordered systems. On the basis of the observed 14N HFC tensors, (1) the effects of tetrahedral distortion on 14N HFC constants and the unpaired electron distribution, (2) hybridization of the nitrogen coordinating orbitals, and (3) orientations of the g tensor and the copper unpaired electron orbital in the molecular framework were discussed. In the tetrahedrally distorted cis-N2S2 type complexes, the g⊥ plane was found to be on the S-Cu-S plane. This is attributed to that the orientation of the copper unpaired electron orbital (3d orbital) is tilting toward the S-Cu-S plane and also to that the spin-orbit interactions of the coordinating sulfurs contribute appreciably to the g tensor. The obtained information will be useful for studies of electronic states of the copper binding sites in copper proteins, most of which have distorted coordination structures.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry