Mechanistic studies on six-membered chelate complexes. Aquation of some dichlorobis(substituted biguanide)rhodium(III) nitrates

Abstract Studies on the aquation of dichlorobis(substituted biguanide)rhodium(III) complexes were carried out in aqueous and aqueous methanol media by conductometric method. The release of chlorides in all the complexes takes place in a steppe manner and rates of each step were determined by a graphical method. Rates of aquation decrease with any substituent and remain nearly equal for all the substituents for both steps. Inductive effect does not seem to be responsible as it changes very little with substitution. In aqueous methanol, rates decrease with increased percentage of methanol for the unsubstituted biguanide complex, but the reverse is true for the phenyl substituted complex. This is due to the greater solvation of phenyl complex in the organic enriched solvent. From various factors it was indicated that the probability of bond formation in the transition state is greater with substituted complexes.