Challenges in Modelling and Optimization of Stability Constants in the Study of Metal Complexes with Monoprotonated Ligands Part II:A Glass-Electrode Potentiometric and Polarographic Study of the Copper(II)/2-Hydroxy-3-[(2-hydroxy-1,1-dimethylethyl)a

摘要

The influence of 2-hydroxy-3-[(2-hydroxy-1,1-dimethylethyl)amino]propane-1-sulfonia acid (AMPSO=HL)on systems containing copper(II)was studied by glass-electrode potentiometry (GEP)and direct-current polarography (DCP),at fixed total-ligand-to-total-metal-concentration ratios and various pH values (25 deg C,0.1M KNO_3 medium).The predicted model ([CuL]~+,[CuL(OH)],[CuL_2],[CuL_2(OH)]~-,[CuL_2(OH)_2]~(2-),and [CuL_3]~-)and the overall stability constants for species found were obtained by combining results from both electrochemical techniques.The last five complexes are reported for the first time.For the species [CuL]~+,[CuL_2],[CuL_3]~-,and [CuL_2(OH)_2]~(2-),it was possible to determine stability constants with reasonable certainty and their values,as logbeta,were found to be 4.62+-0.04,9.5+-0.1,13.4+-0.1,and 21.2+-0.1,respectively.For the species [CuL(OH)]and [CuL_2(OH)]~-,stability constants 11.7+-0.2 and 15.6+-0.2,respectively.For the species [CuL(OH)]and [CuL_2(OH)]~-,stability constants 11.7+-0.2 and 15.6+-0.2,rspectively,are presented as indicative values.It was demonstrated that AMPSO buffer may decrease the Cu~(2+)concentration by ten orders of magnitude by forming complexes with Cu~(2+).For the first time,the correction in DCP waves for the adsorption of the ligand and quasi-reversibility of the metal allowed to determine stability-constant values that are in good agreement with the values obtained by GEP.The importance of graphic analysis of data and significance of employing two analytical techniques was demonstrated;neither GEP nor DCP would be able to provide the correct M/L/OH~- model and reiable stability constants when used independently.