R. Dhillon, S. Madbak, F. Ciccone
Jul 1, 1997
Citations
0
Influential Citations
20
Citations
Journal
Journal of the American Chemical Society
Abstract
13C NMR studies are consistent with 1,4,7,10-tetrakis((S)-2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane (ΛS-thpc12) and its eight-coordinate alkali metal complex ions (Λ[M(S-thpc12)]+) existing predominantly as single distorted cubic diastereomers in methanol in accord with structures predicted through molecular orbital calculations. Intramolecular exchange in ΛS-thpc12 is characterized by k(298.2 K) = 34 800 ± 1600 s-1, ΔH⧧ = 53.9 ± 0.6 kJ mol-1, and ΔS⧧ = 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, ΔH⧧ = 21.4 ± 0.2, 26.3 ± 0.5, and 46.3 ± 0.2 kJ mol-1, and ΔS⧧ = −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 Λ[M(S-thpc12)]+, decomplexation is characterized by kd(298.2 K) = 2200 ± 10, 64.3 ± 1.6, and 11 900 ± 300 s-1, ΔHd⧧ = 35.3 ± 0.5, 62.8 ± 0.5, and 41.8 ± 0.4 kJ mol-1, and ΔSd⧧ = −62.6 ± 2.1, 0.3 ± 2.0, and −26.8 ± 1.6 J K-1 ...