EFFECT OF-COORDINATING LIGANDS IN THE RADIATION-CHEMICAL STUDIES OF (1-HYDROXYPROLINATE)(ETHYLENEDIAMINE) PALLADIUM(II) CHLORIDE COMPLEX INAQUEOUS-SOLUTION

To understand the role of coordinating ligands in stabilizing the oxid ation state of the metal centre in Pd(II) complexes during their react ion with e(aq)(-) and (OH)-O-., steady state and pulse radiolysis inve stigations on [Pd(en)(1-hypro)](+), where en = ethylenediamine and 1-h ypro = 4-hydroxy-1-prolinate, were carried out in aqueous medium. Fine Pd metal precipitation is observed with e(aq)(-) while with (OH)-O-. a new optically active species having a positive Cotton effect in the 250 nm region is formed which is in confirmation with the optical abso rption measurements. Pulse radiolysis studies, on reaction of OH radic al, showed the formation of a transient species (lambda(max) = 290, 34 0 nm, k(f) = 5.3 x 10(9) dm(3) mol(-1) s(-1) k(d) = 2.2 x 10(2) s(-1)) . The rate constant for reaction of e(aq)(-) with the complex was 2.4 x 10(10) dm(3) mol(-1) s(-1) without any transient band in 270-600 nm region. A comparison of these results with those reported earlier for various Pd complexes, clearly establishes the role of vacant pi orbit als available on the bipyridyl ligand in stabilizing the oxidation sta te of Pd(II) during their reaction with e(aq)(-). These studies also c onfirm the site of attack of e(aq)(-) and (OH)-O-. to be the Pd metal centre in complexes with coordinating ligands lacking vacant pi orbit als. Copyright (C) 1996 Elsevier Science Ltd.