ALKALI-METAL COMPLEXES OF A PENDANT-ARM TETRAAZA MACROCYCLE - EQUILIBRIUM, INTERMOLECULAR AND INTRAMOLECULAR EXCHANGE PROCESSES

The stabilities log(K/dm(3) mol(-1)) of [ML(1)](+) formed by kis(2-hyd roxyethyl)-1,4,7.10-tetraazacyclododecane (L(1)) were found to vary wi th M(+) in the sequence Li+ (8.07 +/- 0.05 and 8.90 +/- 0.05), Na+ (6. 66 +/- 0.05 and 7.49 +/- 0.05), K+ (3.40 +/- 0.05 and 5.91 +/- 0.05), Rb+ (3.00 +/- 0.05 and 4.23 +/- 0.05), Cs+ (2.90 +/- 0.05 and 4.04 +/- 0.05) and Ag+ (9.35 +/- 0.04 and 14.00 +/- 0.05), in acetonitrile and propylene carbonate, respectively, determined by potentiometric titra tion at 298.2 K and I = 0.05 mol dm(-3) (NEt(4)ClO(4)). Complexes of t he parent macrocycle 1,4,7,10-tetraazacyclopodecane (L(2)) are less st able. For the monomolecular decomplexation of [NaL(1)](+) in acetonitr ile and propylene carbonate the values k(d) (298.2 K) = 78.5 +/- 1.0 a nd 26.1 +/- 0.6 s(-1), Delta H-d(double dagger) = 49.2 +/- 0.3 and 57. 7 +/- 0.4 kJ mol(-1), and Delta S-d(double dagger) = -43.7 +/- 0.9 and -24.0 +/- 1.0 JK(-1) mol(-1), respectively, were determined by Na-23 NMR spectroscopy. Carbon-13 NMR spectroscopy showed that for the enant iomerisation of square-antiprismatic [LiL(1)](+), [NaL(1)](+) and [KL( 1)](+) in methanol, k(c) (298.2 K) = 18 300 +/- 3100, 7100 +/- 220 and 7010 +/- 200 s(-1), Delta H-e(double dagger) = 41.3 +/- 1.3, 24.6 +/- 0.5 and 53.7 +/- 0.6 kJ mol(-1), and Delta S-e(double dagger) = -24.8 +/- 5.9, -88.6 +/- 1.8 and 8.8 +/- 2.35 JK(-1) mol(-1), respectively. For [LiL(1)](+) and [NaL(1)](+), enantiomerisation occurs much more r apidly than intermolecular exchange of L(1), but for [KL(1)](+) enanti omerisation occurs predominantly through intermolecular exchange of L( 1).