Solvent control on the electron transfer reaction between CoIII(en)2Br(L)2+-Fe(CN)64- (L = aryl amines) by regression relationships: the PXRD and electrochemical investigations

Solvent shell coupled electron transfer (ET) reaction, principally between Co-III(en)(2)Br(L)(2+) and Fe(CN)(6)(4-) complexes (L = RC6H4NH2; R = m-OCH3, p-F, H, m-CH3, p-CH3, p-OC2H5, and p-OCH3) in H2O/EtOH binary mixed solvents has been investigated. The cobalt(III)-aryl amine complexes have been structurally refined by powder X-ray diffraction (PXRD) data as monoclinic unit cell with a distorted geometry. Cyclic voltammograms of the complexes exhibit Co-III/Co-II and Co-II/Co-I reduction peaks with an indication of participation of electron accepting/donating abilities of RC6H4NH2 in the reduction. The Delta Ep (50-580 mV) and Ic/nu(1/2) (0.12-2.83) values differ for the complexes. ET between Co-III(en)(2)Br(L)(2+) and Fe(CN)(6)(4-) is due to ion pair, {Co-III(en)(2)Br(L)(2+); Fe(CN)(6)(4-)}, formation leading to product via (i) solvent caged ({Co-III center dot center dot center dot Fe-II}, restricted mobility due to RC6H4NH2) and (ii) solvent controlled (electron accepting/donating substituent in aryl ligand concertedly alters the equilibrium: reactants <-> ion pair) mechanisms. Reduction was followed in 0-30% v/v (x(2): x(EtOH) = 0, 0.0159-0.1162) aqueous ethanol solutions at 286, 293, and 300 K. Reaction follows second-order condition and there is a gradation in rate when x(2)=0-0.1162 representing co-solvent influence. This tendency is understood in the attainment of equilibrium and the formed compact ion pair. In order to estimate the solvent influence, the rate data were subjected to linear and multiple regression analyses using Y-s = Y-0 + a(1)X(1) + a(2)X(2) + a(3)X(3)center dot center dot center dot a(n)X(n) correlation relationship. Copyright (C) 2010 John Wiley & Sons, Ltd.