Conductometric study of complex formations between some substituted pyrimidines and some metal ions in acetonitrile and the determination of thermodynamic parameters

The complexation reactions between Cr3+, Cd2+, Co2+, Ni2+, Hg2+, Zn2+, Pb2+,and Ag+ metal ions with diethyl-3-(4-hydroxy-6-methylpyrimidin-2-yl) guanidine (L1), 2-amino,4-hydroxy,6-methylpyrimidine (L2), and 2-(diethylamin),4-hydroxy,6-methylpyrimidine (L3) in acetonitrile (AN) were studied using a conductometric method. The formation constants of the resulting complexes were determined from computer fitting conductance-mole ratio data. The results revealed that the formation constants of L1 with metal ions are varying in order of Cr3+ > Pb2+ > Zn2+ > Co2+ > Hg2+ > Ag+ ~ Cd2+ > Ni2+. For L2 and L3 the sequence of complex formation constants are follow as Cr3+ > Pb2+ > Zn2+ > Co2+ > Cd2+ > Hg2+ > Ag+ > Ni2+ and Cr3+ > Pb2+ > Zn2+ > Co2+ > Ni2+ ~ Hg2+ ~ Cd2+ ~ Ag+, respectively. The values of the thermodynamic parameters (ΔH, ΔS and ΔG) for complexation reactions were obtained from the temperature dependence of the stability constants. In all cases, the complexes were found to be enthalpy stabilized but entropy destabilized. In addition, some ab-initio quantum-mechanical calculations were carried out, in order to obtain a clue about the degree tendency of ligands to metal ions.