C-13 NMR studies are consistent with 1,4,7,10-tetrakis((S)-2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane (Lambda S-thpc12) and its eight-coordinate alkali metal complex ions (Lambda[M(S-thpc12)](+)) existing predominantly as single distorted cubic diastereomers in methanol in accord with structures predicted through molecular orbital calculations. Intramolecular exchange in Lambda S-thpc12 is characterized by k(298.2 K) = 34 800 +/- 1600 s(-1), Delta H-double dagger = 53.9 +/- 0.6 kJ mol(-1), and Delta S-double dagger = 22.8 +/- 2.5 J K-1 mol(-1) in methanol. This process is slowed in [M(S-thpc12)](+), for which k(298.2 K) = 332 +/- 6, 125 +/- 2, and 3020 +/- 30 s(-1), Delta H-double dagger = 21.4 +/- 0.2, 26.3 +/- 0.5, and 46.3 +/- 0.2 kJ mol(-1), and Delta S-double dagger = -125 +/- 1, -116 +/- 2, and -23.1 +/- 0.9 J K-1 mol(-1), respectively, when M+ = Li+, Na+, and K+. For intermolecular ligand exchange on Lambda[M(S-thpc12)](+), decomplexation is characterized by k(d)(298.2 K) = 2200 +/- 10, 64.3 +/- 1.6, and 11 900 +/- 300 s(-1), Delta H-d(double dagger) = 35.3 +/- 0.5, 62.8 +/- 0.5, and 41.8 +/- 0.4 kJ mol(-1), and Delta S-d(double dagger) = -62.6 +/- 2.1, 0.3 +/- 2.0, and -26.8 +/- 1.6 J K-1 mol(-1), respectively, when M+ = Li+, Na+, and K+. The stability constant, K, of [M(S-thpc12)](+) varies as M+ changes in the sequence Li+ (4.0 +/- 0.1), Na+ (4.8 +/- 0.1), K+ (3.5 +/- 0.1), Rb+ (3.4 +/- 0.1), Cs+ (3.2 +/- 0.1), and Ag+ (12.8 +/- 0.1), where the figures in parentheses are log(K/dm(3) mol(-1)) determined in methanol by potentiometric titration at 298.2 K and I = 0.05 mol dm(-3) (NEt4ClO4). Stability constants in acetonitrile, propylene carbonate, and dimethylformamide are also reported.