C-13 NMR studies are consistent with Delta-1,4,7,10-tetrakis((R)-2-hydroxy-2-phenylethyl)-1,4,7,10-tetraazacyclododecane (Delta R-thpec12) and its eight-coordinate alkali-metal complexes, Delta[M(R-thpec12)](+), existing predominantly as single square antiprismatic Delta diastereomers in dimethylformamide. Molecular orbital calculations show the parallel square oxygen and nitrogen planes to delineate the square antiprismatic structure of Delta R-thpec12 and Delta[M(R-thpec12)](+) where the basket defined by the four phenyl groups of Delta R-thpec12 becomes increasingly shallow as the M+ radius increases from Na+ to Cs+ and the four oxygens move further apart. An intramolecular exchange process, involving double inversion of all four nitrogen centers, occurs in Delta R-thpec12 for which k(298.2 K) = 46300 +/- 1800 s(-1), Delta H double dagger = 40.8 +/- 0.4 kJ mol(-1), and Delta S double dagger = -18.8 +/- 1.7 J K-1 mol(-1). In [M(R-thpec12)](+) this process is characterized by k(298.2 K) = 233 +/- 2, 98 +/- 1, 4900 +/- 100, 33500 +/- 1000, and 34500 +/- 1100 s(-1), Delta H double dagger = 34.6 +/- 0.3, 46.1 +/- 0.2, 42.7 +/- 0.3, 39.1 +/- 0.3, and 38.5 +/-0.3 kJ mol(-1), and Delta S double dagger = -83.5 +/- 1.1, -52.2 +/- 0.7, -31.1 +/- 1.2, -27.2 +/- 1.2, and -28.9 +/- 1.3 J K-1 mol(-1), respectively, when M+ = Li+, Na+, K+, Rb+, and Cs+. For intermolecular ligand exchange on Delta[M(R-thpec12)](+), decomplexation is characterized by k(d)(298.2 K) = 396 +/- 3, 156 +/- 3, and 152000 +/- 6000 s(-1), Delta H-d double dagger = 46.0 +/- 0.3, 62.3 +/- 0.5, and 69.8 +/- 0.5 kJ mol(-1), and Delta S-d double dagger = -40.9 +/- 1.0, 6.0 +/- 1.9, and 88.4 +/- 2.1 J K-1 mol(-1), respectively, when M+ = Li+, Na+, and K+. The stability constant, K, of Delta[M(R-thpec12)](+) varies as M+ changes in the sequence Li+ (3.13 +/-0.05), Na+ (4.25 +/- 0.05), K+ (4.10 +/- 0.05), Rb+ (3.57 +/- 0.05), Cs+ (3.47 +/- 0.05), and Ag+ (8.14 +/- 0.03), where the figures in parentheses are log(K/(dm(3) mol(-1))) determined in dimethylformamide by potentiometric titration at 298.2 K and I = 0.05 mol dm(-3) (NEt4ClO4).