SYNTHESIS, STRUCTURE, SPECTRA AND REDOX ACTIVITIES OF MODEL COMPOUNDSFOR METHANOGENIC BACTERIA

Synthetically accessible benzimidazoles have been synthesized and the benzimidazole ligands were complexed with nickel(II) nitrate. A nickel (II) complex of N,N'-bis(benzimidazole-2-ylethyl)ethylenediamine was c rystallized in single-crystal form and the structure was investigated by X-ray crystallography, The structure of the complex is bicapped axi al coordinated octahedral. Ni(bbes)(2)(2+) [bbes = bis(benzimidazole-2 -ylethyl)sulfide] exhibits broad low energy bands in electronic spectr a and high redox potential in cyclic voltammetry (CV) rather than Ni(e nbzim)(2+) [enbzim = N,N'-bis(benzimidazol-2-ylethyl)ethylene where hi gh energy well separated bands were observed in the visible region and a more negative redox potential was detected in CV. Experimental stud ies show that an increasing amount of pi-orbital interaction with the Ni(2+)ion, irrespective of chelate ring may favour the higher redox po tential. The higher redox potential of methanogenic bacterial [Ni(II)/ Ni(I)] than nickel compounds is one of the main factors for the degrad ation of organic biodegradable compounds and the further transformatio n to methane.