R. Uma et al., COPPER(II) COMPLEXES OF NOVEL TRIPODAL LIGANDS CONTAINING PHENOLATE AND BENZIMIDAZOLE PYRIDINE PENDANTS - SYNTHESIS, STRUCTURE, SPECTRA ANDELECTROCHEMICAL-BEHAVIOR, Journal of the Chemical Society. Dalton transactions, (8), 1994, pp. 1219-1226
Mononuclear copper(II) complexes of tri- and tetra-dentate tripodal li
gands containing phenolic hydroxyl and benzimidazole or pyridine group
s have been isolated. They are of the type (CuL(X)].nH2O, [CuL(H2O)]X.
nH2O or [CuL].nH2O where X = Cl-, ClO4-, N3- or NCS- and n = 0-4. The
electronic spectra of all the complexes exhibit a broad absorption ban
d around 14000 cm-1 and the polycrystalline as well as the frozen-solu
tion EPR spectra are axial, indicating square-based geometries. The cr
ystal structure of [CuL(Cl)] [HL = -hydroxy-5-nitrobenzyl)bis(2-pyridy
l-methyl)amine] revealed a square-pyramidal geometry around Cu(II). Th
e mononuclear complex crystallises in the triclinic space group P1BAR
with a = 6.938(1), b = 11.782(6), c = 12.678(3) angstrom and alpha = 1
14.56(3), beta = 92.70(2), gamma = 95.36(2)-degrees. The co-ordination
plane is comprised of one tertiary amine and two pyridine nitrogens a
nd a chloride ion. The phenolate ion unusually occupies the axial site
, possibly due to the electron-withdrawing p-nitro group. The enhanced
pi delocalisation involving the p-nitrophenolate donor elevates the E
1/2 values. The spectral and electrochemical results suggest the order
of donor strength as nitrophenolate < pyridine < benzimidazole in the
tridentate and nitrophenolate < benzimidazole < pyridine in the tetra
dentate ligand complexes.