Solvent effects on the charge transfer complexes between p-chloranil and 2,2' -bipyridine and 1,10-phenanthroline

Department of Chemistry, Fakirchand College, Diamond Harbour-743 331, 24-Pargana (S), India Department of Chemistry, Kalyani University, Kalyani-741 235, India E-mail : sujitc!ahiri @yahoo.com Manuscript received 16 August 2004 Complex formation between p-chloranil (Cl-Q) and the heterocyclic aromatic donors like 2,2'-bipyridine (hipy) and 1,10- phenanthroline (phen) were studied in different aliphatic and aromatic solvents. The complexes are found to he considerably stable in different solvents. The comparable values of both Cl-Q + bipy and Cl-Q + phen suggest that the complexes are similar in nature. Acceptor being the same for both the complexes, the differences in Gibbs energy changes for the Cl-Q + bipy and Cl-Q + phen complexes reflect the differences of the Gibbs energy values of the complexes and donors. The differences in the Gibbs energy values for the two complexes arise from the greater resonance stabilization and coplanarity of phen compared to bipy. However, the change from trans-form of' bipy to cis-form is likely to make Cl-Q + bipy complex coplanar. The effect of solvents on the stability of the complexes has been found to be marginal but similar. The association constants of the complexes are greater in aliphatic solvents compared to those in aromatic solvents where the values are almost the same. Attempts to correlate ΔG0 values with different solvent parameters like 1/ɛ, (ɛ-1)/(2ɛ-l) and ET (30) values have been made. Two straight lines, one for aliphatic solvents and other for aromatic solvents has been obtained. But no singular parameter is capable of giving satisfactory explanation regarding the solvent effects of the complexes