Control of metal ion selectivity in ligands containing neutral oxygen and pyridyl groups

The stabilities of the complexes of the ligand (py)/sub 2/-18-aneN/sub 2/O/sub 4/ (N,N'-bis(o-pyridylmethyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane) at 25/sup 0/C in 0.1 M NaNO/sub 3/ are reported, as well as those of DHEAMP (((bis(2-hydroxyethyl)amino)methyl)-pyridine, with a variety of metal ions. The log K/sub 1/ values for the (py)/sub 2/-18-aneN/sub 2/O/sub 4/ complexes are as follows: Cu/sup 2 +/, 13.55; Ni/sup 2 +/, 8.80; Zn/sup 2 +/, 6.96; Cd/sup 2 +/, 10.96; Ca/sup 2 +/, 3.63; La/sup 3 +/, 3.53; Sr/sup 2 +/, 4.87; Pb/sup 2 +/, 11.67; Ba/sup 2 +/, 4.99. The constants for the protonation equilibria were, for H/sup +/ + L = HL/sup +/, log K = 7.44, for H/sup +/ + HL/sup +/ = H/sub 2/L/sup 2 +/, log K = 6.26, and for H/sup +/ + H/sub 2/L/sup 2 +/ = H/sub 3/L/sup 3 +/, log K = 1.38. For DHEAMP, log K values are as follows: Cu/sup 2 +/, 9.2; Ni/sup 2 +/, 7.34; Zn/sup 2 +/, 5.25; Ca/sup 2 +/, 1.0; La/sup 3 +/, 1.95; Pb/sup 2 +/, 5.43. The protonation equilibria for DHEAMP were, for H/sup +/ + L = HL/sup +/, log K = 6.92, and for H/sup +/ + HL/sup +/ = H/sub 2/L/sup 2more » +/, log K = 1.16. The coordinating properties of ligands with neutral oxygen donors are discussed, and the suitability of (py)/sub 2/-18-aneN/sub 2/O/sub 4/ as a reagent for the treatment of lead poisoning is considered. The control of metal ion selectivity based on metal ion size is discussed, as well as the coordinating properties of ligands based on the 18-aneN/sub 2/O/sub 4/ ring, which have pendant donor groups attached to the nitrogens of the macrocyclic ring.« less