Influence of water-methanol solvation assembly and the key consequences on the photo reduction of CoIII(L)33+ (L = (NH3)2, en, pn) complexes via ion-pair formation

Cobalt(III) complexes of general formulae Co(L)(3)(3+), where L refers to (NH3)(2), en (1,2-diamino ethane) and pn (1,2-diamino propane) have been subjected to photolysis (excitation wavelength;lambda = 254 nm) in water-methanol mixtures (0, 5, 10, 15, 20, 25 and 30% (v/v) methanol). In each mixture as the mole fraction of water surpassed, the observed quantum yield values were triggered. Therefore, Phi(Co(II)) measured in the binary solvents were subjected to Linear Solvation Energy Relationship (LSER) to model the Phi(Co(II)) data using the measured empirical solvent parameters in order to break open the solvation effects of excited state reactivities. The photo reduction is solvent dependent; has the form log Phi(Co(II)) =a(0)+a(1)X(1) (X-1 =chi(MeOH) or epsilon(-1)(r)). Effect of solvent polarity in Grunwald-Winstein correlations (r(2) = 0.950) is discussed by linear regression analysis incorporating solvent ionizing power (Y-GW) scale and Phi(Co(II)) profile. Major causes for these phenomena are investigated in terms of long range solvation effects, in conjunction with short range solvation effects. Distinct border lines between the two are derived from photolysis yields in six solvent mixtures using the results of log Phi(Co(II)) =a(0)+a(1)X(1)+a(2)X(2)+... plots, where X-1, X-2 etc. are independent variables (like E-T(N), DNN, alpha, beta, and pi*) representing physicochemical characteristics of solvent. These plots show appreciable correlation of data, which were quantified to unravel solvation effects.