Correlation of Photosubstitution Quantum Efficiencies of [Cr Lm Cln](3-n)+ Complexes with Solvent Properties in Mixed Solvents by Statistical Relationships

Objectives: This investigation focuses on the excited state aquation reactions of a series of [Cr(N)xCly](3-y)+ [(N)x = (en)2, (pn)2, (tn)2, (dien), (trien) and (tetren)] complexes in binary solvent(methanol/water) media. The main objective of this paper is to study the quantum yield (Φ) variation with respect to change of mole fraction (x2)of solvents in aquation reactions of these Cr (III) complexes in mixed solvent media and to interpret the results in the light of statistical analysis to give meaningful qualitative and quantitative treatment.
Study design: The linear solvation energy relationship (LSER) is employed to correlate the Φ data with various empirical solvent parameters in single and multiple statistical equations.
Methodology: Visible light photolysis was carried out for the [Cr Lm Cln](3-n)+ complexes in water containing either methanol (MeOH) or 1,4-dioxane (Diox), x2 (xMeOH/xDiox) 0, 0.029/0.0109 to 0.1602/0.0831, respectively.
Results: Photolysis of these complexes in these binary mixtures is good to excellent for few complexes and poor for the remaining cases. Solvent assisted photolysis in the binary solvent mixtures produced aquated products. In principle, the photoaquation takes place by associative mechanism and quantum yield for this reaction was found to exhibit linear x2 dependence.
Conclusion: In summary, the available model analysis allows a definitive choice of the above two alternative pathways according an increase or decrease in Φ value at higher mole fractions of MeOH/Diox in the medium. This conclusion is more appealing and in order to gain more insight into the problem. This model analysis is extremely important because it can yield both qualitative (bulk solvent effect) and quantitative (short range solvation effect) information that may otherwise be difficult to arrive at.