FACIAL COORDINATION IN BIS[BIS(BENZIMIDAZOL-2-YLMETHYL)AMINE]COPPER(II) PERCHLORATE DIHYDRATE - SYNTHESIS, STRUCTURE, SPECTRA AND REDOX BEHAVIOR

The 1:1 and 1:2 cooper(II) complexes with the tridentate compound bis( benzimidazol-2-ylmethyl)amine (L(1)) and its benzimidazole (L(2)) and amine (L(3)) N-methyl-substituted derivatives have been prepared and t heir spectroscopic properties studied. While the 1:1 complexes are of the type CuLX(2) nH(2)O (X = C/O-4(-), NO3-, Cl- or Br-), the 1:2 comp lexes are of the type CuL(2) (ClO4)(2) nH(2)O (L = L(1) or L(3), n = 0 -4). In all these complexes L acts as a tridentate ligand with the ami ne nitrogen and both the benzimidazole nitrogens co-ordinating to Cu-I I. The complex [CuL(2)(1)][ClO4](2) 2H(2)O crystallises in the monocli nic space group P2(1)/c with a = 9.828(2), b = 9.546(2) and c = 19.906 (2) Angstrom and beta = 95.71(1)degrees, for Z = 2. The R value is 0.0 635 for 2180 significant reflections. The copper(II) ion has an elonga ted octahedral geometry with four equatorial benzimidazole and two lon g-distance axial amine N donors. The Cu-N-bzim and Cu-N-amine distance s are 2.011(4) and 2.597(6) Angstrom respectively. Factors favouring f acial co-ordination to tridentate ligands are discussed. The 1:1 compl exes involve meridonal co-ordination of the ligands, with square-based geometry as revealed by ligand-field and EPR spectral properties. The NMe substitution as in CuL(3)(ClO4)(2) confers low V ($) over tilde$$ (max) and high E(1/2) for the cu(II)-Cu-I couple. Most of the 1:1 comp lexes are less reversible but exhibit E(1/2) values more positive than those of the corresponding 1:2 complexes.