A molecular model for the structure of copper complexes on hydrous oxide surfaces: An ENDOR study of ternary Cu(II) complexes on δ-Alumina

Abstract

An ENDOR study of ternary copper(II) complexes on δ-alumina is reported. From EPR results, it is concluded, that copper has a pseudo square planar coordination geometry. The presence of protons of both axially and equatorially coordinated water is indicated by proton ENDOR data, the corresponding CuO(H 2O) distances are estimated to be 2.6(1) and 2.0(1) Å, respectively. The observed nitrogen hyperfine couplings in the ternary complexes are typical for equatorially coordinated ligands. These ENDOR data together with the EPR results allow the development of a model for the molecular structure of the surface complex. The copper and nitrogen hyperfine data are interpreted in terms of an LCAOMO model. The resulting spin density distribution is similar to that found in related copper complexes in solution or diamagnetic host matrices. The nitrogen quadrupole data are discussed in the framework of the Townes-Dailey theory.