Diastereomeric Δ-1,4,7,10-Tetrakis((R)-2-hydroxy-2-phenylethyl)- 1,4,7,10-tetraazacyclododecane and Its Alkali-Metal Complex Ions. A Potentiometric Titration, Nuclear Magnetic Resonance, and Molecular Orbital Study

13 C NMR studies are consistent with Δ-1,4,7,10-tetrakis(( R )-2-hydroxy-2-phenylethyl)-1,4,7,10-tetraazacyclododecane (Δ R- thpec12) and its eight-coordinate alkali-metal complexes, Δ[M( R -thpec12)] +, existing predominantly as single square antiprismatic Δ diastereomers in dimethylformamide. Molecular orbital calculations show the parallel square oxygen and nitrogen planes to delineate the square antiprismatic structure of Δ R- thpec12 and Δ[M( R -thpec12)] + where the basket defined by the four phenyl groups of Δ 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 Δ R- thpec12 for which k (298.2 K) = 46300 ± 1800 s - 1, Δ H ⧧ = 40.8 ± 0.4 kJ mol - 1, and Δ S ⧧ = −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, Δ H ⧧ = 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 Δ S ⧧ = −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 Δ[M( R -thpec12)] +, decomplexation is characterized by k d (298.2 K) = 396 ± 3, 156 ± 3, and 152000 ± 6000 s - 1, Δ H d ⧧ = 46.0 ± 0.3, 62.3 ± 0.5, and 69.8 ± 0.5 kJ mol - 1, and Δ S d ⧧ = −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 Δ[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 (NEt 4 ClO 4 ).