The affinity of bismuth(III) for nitrogen-donor ligands

Abstract

Differential pulse polarography has been used to determine the formation constants of Bi3+ at ionic strength 0.5 mol dm–3 and 25 °C with the ligands glycine, trien (triethylenetetramine), bipy (2,2′-bipyridine), [15]aneN4(1,4,8,12-tetraazacyclopentadecane) and triethanolamine. The equilibria between Bi3+ and these ligands are established slowly on the polarographic time-scale, so that separate peaks occur in the differential pulse polarograms for free metal ion and complex, greatly simplifying calculation of the formation constants. Stability constant values (log K1) for the complexes of BiIII with these ligands were 10.0 (glycinate), 21.9 (trien), 4.5 (bipy) and 9.2 (triethanolamine). For the macrocycle [15]aneN4, log K1(M3++ L ⇌ ML3+)= 23.5; for the equilibria ML3++ OH–⇌ ML(OH)2+ and ML3++ H+⇌ M(HL)4+, values of log K were 8.5 and 3.5 respectively. These results are shown to be reasonable in terms of the formation constant log K1(NH3)= 5.0 for Bi3+ predicted by a dual basicity equation developed previously.