COMPLEXATION OF BI-III BY NITROGEN DONOR LIGANDS - A POLAROGRAPHIC STUDY

Differential pulse polarography was used to determine the formation co nstants of Bi3+ at ionic strength 0.5 and 25 degrees C with the ligand s DIEN (1,4,7-triazaheptane), TETREN(1,4,7,10,13-pentaazatridecane), D PA [bis(2-pyridyl) amine], AMPY [2-(aminomethyl) pyridine], and THPED ',N'-tetrakis(2-hydroxypropyl)-1,2-diaminoethane]. The equilibria betw een Bi3+ and these ligands were mostly established slowly on the polar ographic timescale, so that separate peaks occurred in the differentia l pulse polarograms for the free metal ion and complexes, simplifying calculation of the formation constants. Values obtained for Bi3+ 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 K(ML+ OH = MLOH) = 12.0; DPA, log K -1 = 9.0, log K-2 = 7.4. These results are shown to be reasonable in t erms of the formation constant log K-1(NH3) = 5.0 for Bi3+ predicted b y a dual basicity equation developed previously. A good linear free en ergy relationship between log K-1 values for Bi-III complexes and log K-1 for analogous complexes of the isoelectronic Pb-II ion was found, which may be useful in predicting Bi-III solution chemistry.