NMR AND POTENTIOMETRIC DETERMINATION OF THE HIGH PK VALUES AND PROTONATION SEQUENCE OF DIPYRIDINO-HEXAAZA-28-CROWN-8 AND ITS INTERACTIONS WITH SELENATE, SULFATE AND NITRATE IONS IN AQUEOUS-SOLUTION

The aqueous protonation and anion-binding (SeO4(2-), SO4(2-), and NO3-) constants of the macrocyclic polyamine ligand, dipyridino-hexaaza-28-crown-8(L), were measured in 0.1M KC1 using a potentiometric titration technique. The protonation sequence of the aza groups of L was studied in D2O from the chemical shifts of the nonlabile protons so as to find the charge distribution geometry as a function of pD. The study indicates that in 0.1M KC1 fully protonated L forms stable 1:1 complexes with SeO4(2-) (log K = 3.68) and SO4(2-) (log K = 3.55), but not with NO3- (log K < 1.5). All of the amine pK values were above 6.3, thus allowing the use of the protonated form of this ligand over a wide pH range.