Thermodynamic Studies of Complexes of Amlodipine Besylate with Ni2+, Mg2+, Co2+ and Ca2+ cations in pure and in mixed binary solvent systems at 303.15, 313.15 and 323.15 K by Conductometric Method

The present work relates to the complexation reaction between Amlodipine Besylate[AML] with Ni 2+ , Mg 2+ , Co 2+ and Ca 2+ cation in dimethylsulfoxide (DMSO), pure methanol (MeOH) and their binary mixtures(DMSO-MeOH and DMSO-Water) by conductometric method. The conductance data show that the stoichiometry of the complexes formed between AML with Ni 2+ , Mg 2+ , Co 2+ and Ca 2+ cation in pure DMSO, pure MeOHas well as in the binary solvent mixtures was 1:1. The stability of AML complexes with Ni 2+ , Mg 2+ , Co 2+ and Ca 2+ metal ion was observed to be sensitive to the nature of the solvent system. In case of DMSO-Water binary solvent systems there was a linear change in LogKf values but in case of DMSO-MeOH binary solvent systems non linear change in LogKf values observed.The negative values of ΔG 0 show that the reaction is spontaneous and ability of the AML ligand to form stable complexes. However, the result shows positive value of ΔH 0 which indicates that enthalpy is not driving force for the formation of the complexes. Furthermore, the positive value of ΔS 0 indicates that entropy is a driving force for the complexation. The values of ΔH 0 and ΔS 0 for formation of the complexes were obtained from temperature dependence of the stability constants.