Studies on Complexation of Resorcinol with Some Divalent Transition Metal Ions and Aliphatic Dicarboxylic Acids in Aqueous Media

The binary and ternary complexes of Cu2+, Ni2+, Co2+ and Zn2+ metal ions with resorcinol (R) as primary ligand and some biologically important aliphatic dicarboxylic acids (adipic, succinic, malic, malonic, maleic, tartaric and oxalic acids) as secondary ligands were studied in aqueous solution at 25 °C and I=0.1 mol⋅dm−3 NaNO3 using the potentiometric technique. The formation of different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes is inferred from the corresponding potentiometric pH-titration curves. The ternary complex formation was found to take place in a stepwise manner. The protonation constants of the ligands were determined and used for determining the stability constants of the different complexes formed in aqueous solutions. The lower stability of the 1:2 binary complexes compared to the corresponding 1:1 systems of all ligands studied were in accordance with statistical considerations. The order of stability of the complexes formed in solution was investigated in terms of the nature of the resorcinol, carboxylic acid, and metal ion used. The values of Δlog 10K, percentage of relative stabilization (% R.S.), and log 10X for mixed-ligand complexes studied have been evaluated and discussed. The concentration distribution of the various species formed in solution was evaluated. The mode of chelation of the ternary complexes was ascertained by conductivity measurements.