Synthesis, structure, spectra and redox behaviour of copper(II) complexes of certain bis(phenolate) ligands: Phenoxyl radical complexes of copper(II) as models for galactose oxidase

Content Provider	Semantic Scholar
Author	Vaidyanathan, Mathrubootham Palaniandavar, Mallayan Gopalan, R. Srinivasa
Copyright Year	2003
Abstract	Copper(II) complexes of a series of tetradentate tripodal and linear ligands containing two substituted phenolates appended to N,N-dimethylethylenediamine and N,N'-dimethylethylenediamine moieties viz. N,N-dimethyl-N',N'-bis(2-hydroxy-4-nitrobenzyl)ethylenediamine [H 2 (L1)], N,N-dimethyl-N',N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine [H 2 (L2)], N,N-dimethyl-N',N'-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine [H 2 (L3)], N,N'-dimethyl-N,N'-bis(2-hydroxy-4-nitrobenzyl)ethylenediamine [H 2 (L4)], N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine [H 2 (L5)] and N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-di-tert-butylbenzyl)ethylenediamine [H 2 (L6)] have been isolated and characterized by electronic absorption and EPR spectroscopy and cyclic and differential pulse voltammetry. Of these complexes, [Cu(L1)] 2 .2H 2 O 1, [Cu(Ll)(py)] la and [Cu(L4)(H 2 O)].H 2 O 4 have been structurally characterized by X-ray crystallography. The coordination structure of 1 is dimeric with a trigonal bipyramidal distorted square based pyramidal geometry (TBDSBP) around each Cu(II). In complex la also a trigonal bipyramidal distorted square based pyramidal geometry (TBDSBP) around Cu(II) is present. The CuN 2 O 2 basal plane is comprised two phenolates and a tertiary amine nitrogen of H 2 (L1) and an exogenous pyridine nitrogen and the dimethyl substituted amine nitrogen of H 2 (L1) is axially coordinated. In 4, there are two different copper(II) complex molecules in the same unit cell with trigonal bipyramidal distorted square based pyramidal geometry (TBDSBP) around Cu(II). The methyl groups of the ethylenediamine frame are cis to each other in one molecule (A) and are trans to each other in the other molecule (B). The bond lengths and bond angles in the two molecules are different. The ligand field and EPR spectra of all the complexes are consistent with a square-based geometry even in solution. An intense band observed in the range 390-465 nm may originate from Cu(II) → (phenolate)O - (axial) and/or equatorial(phenolate)O - → Cu(II) CT transitions. The g∥ values lie in the range 2.23-2.29 indicating the presence of CuN 2 O 2 or CuNO 3 chromophores. All the complexes show an irreversible Cu I I /Cu I redox process at increased negative E 1 / 2 values, which are consistent with the presence of two coordinated phenolate groups. The oxidation wave(s) occurring in the range 0.06-0.89 V (vs Ag/Ag + ) demonstrate(s) the formation of phenoxyl radical-copper(II) species. The influence of the phenolate substituents on the PhO - → Cu(II) LMCT transition and the Cu(II)-phenolate/Cu(II)-phenoxyl radical redox potentials are discussed. The stability of the radicals is enhanced with the increase in donor ability of the substituents. The relevance of the notable structural and spectral features of the complexes containing two redox active phenolates bound to copper(II) in a square pyramidal environment, to those of galactose and glyoxal oxidases are highlighted.
Starting Page	2210
Ending Page	2222
Page Count	13
File Format	PDF HTM / HTML
Volume Number	42
Alternate Webpage(s)	http://nopr.niscair.res.in/bitstream/123456789/20727/1/IJCA%2042A(9)%202210-2222.pdf
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article