VOLTAMMETRIC STUDIES OF THE REACTIONS OF IMIDAZOLIDINE NITROXYL FREE-RADICAL WITH VANADIUM PENTOXIDE, CHROMIUM(III) ACETATE AND MANGANESE(III) ACETYLACETONATE

This work demonstrated the synthesis and voltammetric studies of imida zolidine nitroxyl free radical (LH) complexes of chromium, manganese a nd vanadium. Hall-wave potentials of solutions containing the three me tal-LH as well as the metal free ligand (LH) ranged between -0.18 and -0.20 V (vs. Ag/AgCl) for the reduction process. At a potential window ranging from -0.10 to +1.00 V no oxidation peak was observed for LH. However, LH accepts an electron readily, leading to both forward and r everse peaks. It is not clear whether the added electron pairs up with the unpaired electron on the ligand radical or possibly for ms an ion radical. On the other hand Cr-LH, Mn-LH and V-LH solutions undergo ox idation within the same potential range. A value of n ranging from 0.6 2 to 1.2 was obtained from a plot of E-app versus log[i/i(d)-i], which gave linear relationship for the reduction of the four solutions, sug gesting fast electron transfer front the electrode to the M-LH or meta l free ligand. Reduction of the three metal-ligand solutions exhibited certain degree of electrode reversibility depending on the scan rate. Absence of an anodic peak at low scan rates suggested fast electron t ransfer followed by a homogeneous chemical reaction (EC mechanism). wh ich removed the oxidized species from the surface of the electrode. Th e pseudo-first-order rate constants for the M-LH anion radical ranged from 0.025 to 0.087 s(-1). Overall, k(f) increased in the order: V-LH< Cr-LH<Mn-LH.