Differential Refractometric Studies on Some Strong and Weak Molecular Complexes

Abstract

Abstract A more adequate model has been developed to determine the equilibrium constant (K1) and stoichiometry of molecular complexes. This model involves the assumption: &Δφ_a/C_D°={K_1C_A°/α(1+K_1C_A°)}-{K_1Δφ_a/(1+K_1C_A°)^2} &Δφ_d/C_D°={K_1C_A°/α(1+K_1C_A°))}-{K_1Δφ_d/(1+K_1C_A°)^2} where Δφa difference in the refraction per cm3 of solution and acceptor; Δφd is the difference in the refraction per cm3 of solution and donor; α is the extent of electronic polarization. CA° and CD° are the initial concentrations of acceptor and donor respectively. This model has been verified on some strong and weak complexes and was found better than that of earlier methods. Δφa, Δφd, and ΔΩCDA (refraction per cm3 due to chargetransfer complex) have also been used to Yoshida and \barOsawa’s method. The K1 obtained from the plot of Δφa or Δφd versus molar ratio of solutes were found more reliable for weak complexes than K1 calculated from Yoshida and \barOsawa’s plot. From these plots the percentage of contribution of donor or acceptor in total 30% solute aggregation as proposed by Yoshida and \barOsawa has been calculated. It is also noted that Yoshida and \barOsawa’s method may give the reliable value for strong complexes but for weak complexes only differential refractometric method can provide the best values.