HYPERFINE INTERACTIONS OF COORDINATING NITROGENS IN THE COPPER(II) COMPLEXES HAVING A N2S2 DONOR SET AND BLUE COPPER PROTEINS

Hyperfine coupling (hfc) parameters for coordinating nitrogens in some copper(II) complexes with planar and tetrahedrally distorted N2S2 coordination structures were obtained from their single-crystal-like ENDOR spectra. They are compared with those obtained for the N4-, cis- and trans-N2O2-, and NO3-type copper(II) complexes reported in a previous paper. The hfc parameters of coordinating nitrogens in the nitrogen and oxygen donor systems are mainly determined by deformation of the copper orbital containing the unpaired electron caused by the ligand field of the coordinating atoms, but in the N2S2 systems, spin distribution onto the sulfurs also makes an appreciable contribution to the 14N hfc’s, in addition to the effect of deformation of the copper orbital. Little difference was observed in the nitrogen hfc parameters between the systems containing thioether and thiol sulfurs, between cis-N2S2 and trans-N2S2 donor configurations, and between the planar and tetrahedrally distorted structures, but appreciable differences were observed between the sp2-type nitrogens and the sp3-type ones. The nitrogen hfc’s in some blue copper proteins reported in literature are discussed in connection with the above results, and the largely different two l4N hfc’s observed for the proteins are shown to be explained qualitatively by the large deformation of the copper orbital containing the unpaired electron due to the existence of a trigonal-pyramidal or trigonal-bipyramidal coordination structure. © 1990, American Chemical Society. All rights reserved.