Synthesis, characterization and electrochemical studies of heterobimetallic complexes of schiff base ligands containing vanadium (II) or nickel (II) and molybdenum (II) centers
Situma, S. M.
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In recent times polynuclear complexes have generated a lot of interest in the minds of chemists because of their many applications, they have found use as catalysts. in molecular electronics and are also of biological importance. The work reported in this thesis involved synthesis, characterization and electrochemical studies of heterobimetallic complexes of vanadium and nickel metal ions incorporated in schiff base ligands. The schiff base ligands were synthesized by condensation of either 2,5- or 2,4-dimethylbenzaldehyde and salicylaldehyde with various á-)-diamines (I molar equivalents), giving both "para" and "meta" (with respect to the oxygen atom of the central co-ordination site) ligands, respectively. Individual schiff base ligands were reacted with Vanadyl sulphate in ethanol (1 molar equivalents) to yield mainly red/or green monometallic complexes. The red/or green complexes were further reacted with [MO(NO)L*Cl2 (L*=hydrotris(3,5-dimethylpyrazolyl)borate} to yield wine red bimetallic complexes. The complexes were characterized using physical techniques and found to be paramagnetic. The electrochemical studies showed that there is a small cathodic shift of reduction potentials of molybdenum redox center in the presence of the Vanadyl ion. The lengthening of the polymethylene carbon of the ligand did not have a detectable effect on the reduction potentials. The nickel schiff base complexes were synthesized in a similar manner to their vanadium analogues by reacting schiff bases with nickel(II) chloride hexahydrate to form mainly red/or brown monometallics. The monometallics were further reacted with [Mo(NO)L*CI2 to yield blue or wine red bimetallic complexes. The nickel complexes CV although reversible, gave voltammogrammes with peaks that were in some cases not well resolved. They appeared as a merger of Mo(NO);+ and that of Nit+ reduction potentials. Differential pulses voltammetry timescale gave similar results to those of CV except that the peaks were well resolved. The electrochemical studies showed that there was minimal interaction between the two metal centres. The reduction potentials were also found to be solvent dependent as the metal centres reduced at slightly more cathodic potentials in McCN than the corresponding DCM potentials by 20 - 50 mV. In conclusion we were able to synthesize and characterize the heterobimetallic complexes of vanadium (ii) or nickel (ii) and Mo(NO)L*Cl2 using the Schiff bases as the ligand, and determined their electrochemical behavior