Copper (II) complexes of sterically hindered phenolate ligands as structural models for the active site in gala oxidase and glyoxal oxidase: X-ray crystal structure and spectral and redox properties

摘要

Copper (II) complexes of a series of tripodal ligands containing a phenolate moiety, viz. 2-(bis(1-methylbenzidazol-2-yl)aminomethyl)-4-nitrophenol [H(L~1)] and N,N-dimethyl-N'-(pyrid-2-ylmethyl)-N'(2-hydroxy-4-nitrobenzy)-ethylenediamine [HL~2] have been isolated and characterised by electronic absorption and EPR spectroscopy and cyclic and differential pulse voltammetry. The X-ray crystal distructure of the binuclear perchlorate complex [Cu(L~2)]_2(Clo_4)_4 reveals a square based pyramidal distorted trigonal bipyramidal (SBPDTB) coordination geometry around Cu(II).The CuN_2O trigonal coordination plane is comprised of N,N-dimethyl substuted aminek nitrogen , and the phenolate ion from the second coordiantion sphere resulting in the dimerisation . The ligand field and EPR spectra of all the complexes are consistent with a square-based geolmetry in solution. An intense band observed around 390 nm may originate from Cu(8II)->O~- (phenolate , axial ) and/or equatorial (phenolate )O~--> Cu(II) CT transitions. The g|| values lie in the range 2.24-2.28 indicating the presence of CuN_2O_2 or CuN_3O chromophores . The incorporation of sterically hindered N,N-dimethyl substituted nitrogen and bulky 1-methylbenzimidazole groups tends to enhance the trigonal distortion and raise the Cu(II)/Cu(I) redox potential