COMPLEXATION OF ALKALI-METAL IONS BY THE PENDANT ARM MACROCYCLIC LIGAND 1,4,7,10-TETRAKIS(2-HYDROXYETHYL)-1,4,7,10-TETRAAZACYCLODODECANE - A POTENTIOMETRIC TITRATION AND NUCLEAR-MAGNETIC-RESONANCE STUDY

Complexation of Li+, Na+, K+, Rb+, Cs+, and Ag+ by the pendant arm macrocyclic ligand 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane (thec12) has been studied in methanol and dimethylformamide. A substantial variation in the stability of [M(thec12)]+ occurs as M+ is varied in the sequence Li+ (3.09 +/- 0.06 and 2.99 +/- 0. 1 2), Na+ (4.53 +/- 0.06 and 3.37 +/- 0.06), K+ (2.43 +/- 0.08 and 1.59 +/- 0.11), Rb+ (2.20 +/- 0.10 and 1.39 +/- 0.09), Cs+ (1.90 +/- 0.10 and 1.23 +/- 0.08), and Ag+ (12.57 +/- 0.04 and 11.16 +/- 0.05), where the figures in parentheses are log (K/dm3 Mol-1) and K represents the apparent stability constants of [M(thec12)]+ in methanol and dimethylformamide, respectively, determined by potentiometric titration at 298.2 K. For [Li(thec12)]+ and [Na(thec12)]+ the monomolecular decomplexation processes in methanol are characterized by k(d)(298.2 K) = 729 +/- 17 and 209 +/- 3 s-1, DELTAH(d)double dagger = 38.0 +/- 0.7 and 68.3 +/- 1.4 kJ mol-1, and DELTAS(d)double dagger = -62.8 +/- 1.2 and 28.4 +/- 0.8 J K-1 mol-1, respectively, determined by Li-7 and Na-23 NMR spectroscopy. The analogous parameters determined in dimethylformamide are k(d)(298.2 K) = 587 +/- 31 and 299 +/- 7 s-1, DELTAH(d)double dagger = 41.8 +/- 0.7 and 56.4 +/- 0.7 kJ mol-1, and DELTAS(d)double dagger = -51.9 +/- 3.3 and -8.4 +/- 2.4.JK-1 mol-1. These data are compared with those obtained for other alkali metal complexes, which together demonstrate a range of different mechanisms through which selectivity occurs in alkali metal ion complexation.