THE AFFINITY OF LEAD(II) FOR NITROGEN-DONOR LIGANDS

Abstract
The following formation constants are reported for lead(II) with imidazole (lm) at 25°C in 0.5 M 1mHNO3: log K 1 1.10 ± 0.04, log K 2 0.99 ± 0.04. The pK a of 1m in 0.5 M ImHNO3 at 25°C is 6.972 ± 0.003. log K 1 for tead(II) with Im is fairly close to log K 1 (NH3) 1.6 for lead(II) predicted using a model of the chelate effect based on the asymmetry of the standard state. Since log K 1 (lm) and log K 1 (NH3) for any one metalion are invariably close together, the agreement in log K 1 for the lead(II) Im and NH3 complexes indicates that the model can be used to estimate the formation constants of complexes that cannot exist in water because of hydrolysis.