Structure, spectra and redox behaviour of copper(II) complexes of bis(benzimidazolyl)diamine ligands

The linear quadridentate ligand N,N′-bis(benzimidazol-2-ylethyl)ethane-1,2-diamine (L1) and its 1-methylbenzimidazole analogue (L2) and homologues form 1 : 1 complexes with Cu(ClO4)2; L1 also forms complexes of the types CuL1X2 where X = NO3, PF6, Br or Cl and CuL1(X)Y where X = Cl or Br and Y = ClO4 or Br. Deep blue CuL1Br2·2H2O crystallizes in the monoclinic space group C2/c with Z= 4, a= 9.919(2), b= 16.626(3), c= 14.102(3)A and β= 94.39(2)°. The structure was solved by Patterson and Fourier difference methods and refined by the least-squres technique to R= 0.064 for 2195 independent reflections with I > 1.5σ(I). The molecule lies on a two-fold axis symmetrically around CuII. The co-ordination around CuII is found to be square planar with two amino nitrogens and two benzimidazole nitrogens forming the equatorial plane [Cu–N 1.983(3) and 2.037(4)A]. The bromides are at longer distances [3.349(1)A] in axial sites. Ligand field and EPR spectra indicate that one bromide or chloride ion is axially co-ordinated to CuII in [CuL1]2+. This ion exhibits quasi-reversible redox behaviour. Electrochemical studies of the dihalides in methanol have established the presence of [CuL1X2], [CuL1(X)]+ and [CuL1]2+ in equilibrium. In complexes with 565 [CuL4]2+[L4=N,N′-bis(benzimidazol-2-ylmethyl)ethane-1,2-diamine] and 555 [CuL3]2+[L3=N,N′-bis(1-methylbenzimidazol-2-ylmethyl)propane-1,3-diamine] chelate rings, CuII does not seem to lie in the N4 square plane, as revealed by their low A∥ values and irreversible electrochemical behaviour. The CuII–CuI redox potentials in methanol are in the order [CuL1]2+ < [CuL3]2+ < [CuL4]2+; this illustrates that six-membered chelate rings are suitable to stabilize CuII, when Cu–N σ interactions are favourable.

[1]  W. Hatfield,et al.  A novel copper(II) complex containing the ligand 1,2-bis(2,2'-bipyridyl-6-yl)ethane : structural, magnetic, redox, and spectral properties , 1990 .

[2]  R. O'brien,et al.  New tripodal Cu(II) complexes containing imidazole ligands , 1990 .

[3]  Yihua Zhang,et al.  Synthesis and structural characterization of the copper(II) complex with N,N'-bis-(1-benzimidazolylethyl) ethylenediamine , 1989 .

[4]  A. W. Addison,et al.  Copper complexes of some tetradentate pyrazolyl amines , 1988 .

[5]  E. Baker,et al.  Blue copper proteins. The copper site in azurin from Alcaligenes denitrificans , 1986 .

[6]  K. Wieghardt,et al.  Ferromagnetic intramolecular interactions in a bis(.mu.-bromo)-bridged copper(II) dimeric compound: crystal structure and molecular structure determination, electron paramagnetic resonance studies, and magnetic susceptibility measurements on bis(.mu.-bromo)bis(diethylenetriamine)copper(II)] perchlor , 1985 .

[7]  J. Lehn,et al.  Synthesis, spectroscopic properties, and X-ray structure of [1,7-bis(5-methylimidazol-4-yl)-2,6-dithiaheptane]dichlorocopper(II): a compound with unusually long copper(II)-thioether bonds , 1984 .

[8]  T. Rao,et al.  Spectroscopy and Structure of Thiolate and Thioether Complexes of Copper(II) and the Relationship of Their Redox Chemistry to That of Certain Copper Proteins , 1984 .

[9]  E. Solomon,et al.  EPR studies of the "EPR-nondetectable" met derivative of hemocyanin: perturbations and displacement of the endogenous bridge in the coupled binuclear copper active site , 1984 .

[10]  T. Nageswara Rao,et al.  Pentacoordinate copper complexes of nitrogen-sulfur donors: structural chemistry of two complexes of bis(2-(2-benzimidazolyl)ethyl) sulfide with the sulfur alternatively in equatorial and axial coordination modes , 1983 .

[11]  F. Urbach,et al.  Copper(II) complexes with tetradentate bis(pyridyl)-dithioether and bis(pyridyl)-diamine ligands. Effect of thio ether donors on the electronic absorption spectra, redox behavior, and EPR parameters of copper(II) complexes , 1983 .

[12]  J. Guss,et al.  Structure of oxidized poplar plastocyanin at 1.6 A resolution. , 1983, Journal of molecular biology.

[13]  J. Reedijk,et al.  Copper(I) and copper(II) complexes of a new tetradentate chelating ligand containing imidazole and thio ether groups. The x-ray structure of trigonal-bipyramidal [(1,6-bis(N-benzylimidazol-2-yl)-2,5-dithiahexane-N,N,S,S)]bromocopper(II) bromide , 1982 .

[14]  M. Carpenter,et al.  Coordination sphere flexibility at copper: chemistry of a unipositive copper(II) macrocycle, [Cu(cyclops)]+ , 1978 .

[15]  M. Murata,et al.  X-ray crystal structure analysis of plastocyanin at 2.7 Å resolution , 1978, Nature.

[16]  H. Yokoi,et al.  Spectroscopic and redox properties of pseudotetrahedral copper(II) complexes. Their relation to copper proteins , 1977 .

[17]  L. A. Ochrymowycz,et al.  Letter: Redox properties of copper-thiaether complexes. Comparison to blue copper protein behavior. , 1976, Journal of the American Chemical Society.

[18]  A. Lever,et al.  Relation between electronic spectra and heat of formation of some copper-polyamine complexes and the macrocyclic effect , 1976 .

[19]  Y. Nonaka,et al.  Factors Affecting: the Line-width of Nitrogen Superhyperfine Structure in the ESR Spectra of Copper(II) Complexes , 1974 .

[20]  F. S. Mathews,et al.  A semi-empirical method of absorption correction , 1968 .