Formation and stability of transition metal chelates with 2-(2-hydroxyphenyl) benzoxazole and other ligands

Department of Chemistry, Chi tanya Bharathi Institute of Technology, Gandipet, Hyderabad-500 075, India E-mail: vrr9@yahoo.com Department of Chemistry, University College of Engineering, Osmania University, Hyderabad-500 007, India Manuscript received 19 September 2007, accepted 27 September 2007 The formation equilibria of (1 : 1 and 1 : 2) binary chelates, ML and ML2 and (1 : 1 : 1) ternary chelates, MAL where, M = CoII , NiII and ZnII ; L = 2-(2-hydroxyphenyl)benzoxazole (HPBO) and A = glycine, alanine, proline and histidine have been studied pH-metrically in aqueous-dioxane (50% v/v) medium at 30 ºC and 0.1 M (KNO3) ionic strength. The formation constants of the complexes were evaluated. The relative stabilities of the ternary complexes were expressed in tenns of the parameter Δlog K and various factors influencing the formation and stability of complexes are discussed. The thermodynamic parameters (ΔH, ΔS and ΔG) associated with the ternary systems were also evaluated by determining the formation constants at 20, 30 and 40 ºC and 0.1 M KNO3 ionic strength. All the parameters were found to be favourable for the complexation