A differential pulse polarographic study of bismuthIII complexes with macrocyclic ligands 1,4,7,10-tetraazacyclododecane and 1,4,7,10-tetrakis (2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane. An out-of-cell determination of stability constants of polarog

The ligands 1,4,7,10-tetraazacyclododecane (cyclen) and 1,4,7,10-tetrakis (2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane (THP-cyclen) were studied with BiIII by differential pulse polarography (DPP) at the fixed total ligand to total metal concentration ratio and various pH values at 25°C and an ionic strength of 0.5 mol dm−3. The out-of-cell technique was used for the stability constant determination, as the equilibrium of the BiIII–cyclen and BiIII–THP-cyclen systems in aqueous solution is very slow. A polarographic speciation technique based on the data interpretation of a labile part of the metal–ligand system was used. The stability constants of the ML complexes, as log K1, were estimated to be 23.45±0.05 and 21.25±0.05 for BiIII–cyclen and BiIII–THP-cyclen, respectively. The influence of neutral alcoholic oxygen donors on the stability constants is discussed and results obtained in this work are compared with the literature data. The presence or absence of the DPP peaks of reduction of polarographically non-labile complexes BiIII–cyclen and BiIII–THP-cyclen is related to their crystallographic structures.