ic0003372_si_002.pdf (866.1 kB)
Trigonal Planar Copper(I) Complex: Synthesis, Structure, and Spectra of a Redox Pair of Novel Copper(II/I) Complexes of Tridentate Bis(benzimidazol-2‘-yl) Ligand Framework as Models for Electron-Transfer Copper Proteins†
journal contribution
posted on 2001-04-03, 00:00 authored by Ramalingam Balamurugan, Mallayan Palaniandavar, R. Srinivasa GopalanThe copper(II) and copper(I) complexes of the chelating ligands 2,6-bis(benzimidazol-2‘-ylthiomethyl)pyridine
(bbtmp) and N,N-bis(benzimidazol-2‘-ylthioethyl)methylamine (bbtma) have been isolated and characterized by
electronic and EPR spectra. The molecular structures of a redox pair of Cu(II/I) complexes, viz., [Cu(bbtmp)(NO3)]NO3, 1, and [Cu(bbtmp)]NO3, 2, and of [Cu(bbtmp)Cl], 3, have been determined by single-crystal X-ray
crystallography. The cation of the green complex [Cu(bbtmp)(NO3)]NO3 possesses an almost perfectly square
planar coordination geometry in which the corners are occupied by the pyridine and two benzimidazole nitrogen
atoms of the bbtmp ligand and an oxygen atom of the nitrate ion. The light-yellow complex [Cu(bbtmp)]NO3
contains copper(I) with trigonal planar coordination geometry constituted by the pyridine and two benzimidazole
nitrogen atoms of the bbtmp ligand. In the yellow chloride complex [Cu(bbtmp)Cl] the asymmetric unit consists
of two complex molecules that are crystallographically independent. The coordination geometry of copper(I) in
these molecules, in contrast to the nitrate, is tetrahedral, with pyridine and two benzimidazole nitrogen atoms of
bbtmp ligand and the chloride ion occupying the apexes. The above coordination structures are unusual in that
the thioether sulfurs are not engaged in coordination and the presence of two seven-membered chelate rings
facilitates strong coordination of the benzimidazole nitrogens and discourage any distortion in Cu(II) coordination
geometry. The solid-state coordination geometries are retained even in solution, as revealed by electronic, EPR,
and 1H NMR spectra. The electrochemical behavior of the present and other similar CuN3 complexes has been
examined, and the thermodynamic aspects of the electrode process are correlated to the stereochemical
reorganizations accompanying the redox changes. The influence of coordinated pyridine and amine nitrogen atoms
on the spectral and electrochemical properties has been discussed.