MIXED-LIGAND COPPER(II) COMPLEXES WITH POSITIVE REDOX POTENTIALS

Mixed-ligand complexes formed by reaction of Cu(CIO,), with 3-(2-pyrid yl)-5,6-diphenyl-1,2,4-triazine (dppt) as primary ligand and 2,2'-bipy ridine (bipy), 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthr oline (dmp), N,N-bis(pyrid-2-ylmethyl)amine (dipica), N,N-bis(benzimid azol-2-ylmethyl)amine (bba), 1,3-bis(2-benzimidazolyl)-2-thiapropane ( bbms) and 1,5-bis(benzimidazolyl)-3-thiapentane (bbes) as the secondar y ligands have been isolated. They are of the type [Cu(dppt)L](ClO4)(2 ) . nH(2)O, where n = 0 or 2. All complexes exhibit only one ligand fi eld band and their cryogenic solution e.p.r. spectra are axial, with < (v)over bar (max>) and g(parallel to) values diagnostic of a square-ba sed geometry. The spectral and redox data are consistent with facial c oordination of the tridentate ligands. All the complexes exhibit a pos itive redox potential (versus n.h.e.). The weak sigma-bonding of dppt, caused by the highly electron-withdrawing phenyl rings, the strong pi -back bonding involving phen and dmp, and interligand repulsions appea r to be responsible for the relatively positive Cu-II/Cu-I redox poten tials.