EPR and pulse radiolysis studies on electron transfer in transition metal dithiolenes at the surface of colloidal TiO2

One-electron reduction of several transition metal bis-dithiolenes at the s urface of TiO2 particles and in aqueous solutions were studied. Electron Pa ramagnetic Resonance (EPR) was used to study the reduction at the particle surface and the pulse radiolysis technique was employed for aqueous solutio ns. Variable temperature EPR measurements following band-gap excitation of the particles showed the disappearance of signals due to the paramagnetic N i(III) and Cu(II) complexes of 4,5-dimercaptophthalic acid (DMPA), 3,4-dime rcaptotoluene (TDT) and maleonitrile dithiolate (MNT), with the surface ele ctron signals vanishing concomitantly. Similarly, the diamagnetic Cu(III) c omplex of TDT was reduced to the paramagnetic Cu(II) complex. The bimolecul ar rate constants for the reaction of Ni(III)DMPA and Ni(II)MNT with e(aq)( -) were determined to be 4.3 x 10(9) dm(3) mol(-1) s(-1) and 1.3 x 10 10 dM 3 Mol(-1) s(-1). respectively. Pulse radiolysis results were used to distin guish between reduction with electron and (CH2OH)-C-. radical. It is inferr ed that e(aq)(-.) reduces the metal centre while (CH2OH)-C-. adds to the li gand.