Complexation of Bi III by nitrogen donor ligands. A polarographic study

Abstract

Differential pulse polarography was used to determine the formation constants of Bi 3+ at ionic strenght 0.5 and 25°C with the ligands DIEN (1,4,7-triazaheptane), TETREN (1,4,7,10,13-pentaazatridecane), DPA [bis(2-pyridyl)amine], AMPY [2-(amino-methyl)pyridine], and THPED [N,N,N′,N′-tetrakis(2-hydroxypropyl)-1,2-diaminoethane]. The equilibria between Bi 3+ and these ligands were mostly established slowly on the polarographic timescale, so that separate peaks occurred in the differential pulse polarograms for the free metal ion and complexes, simplifying calculation of the formation constants. Values obtained for Bi 3+ were: DIEN, log K 1 = 17.4; log K(ML + H = MLH) = 3.9; log K(ML + OH = MLOH) = 8.1; TETREN, log K 1 = 23.9; log K(ML + OH = MLOH) = 6.9; AMPY, log K 1 = 9.6; THPED, log K 1 = 12.0; log KML + OH = MLOH) = 12.0; DPA, log K 1 = 9.0, log K 2 = 7.4. These results are shown to be reasonable in terms of the formation constant log K 1(NH 3) = 5.0 for Bi 3+ predicted by a dual basicity equation developed previously. A good linear free energy relationship between log K 1 values for Bi III complexes and log K 1 for analogous complexes of the isoelectronic Pb IIion was found, which may be useful in predicting Bi III solution chemistry.