A nuclear magnetic resonance study of the sodium cryptate formed by 4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane (C211) in various solvents

Abstract

Sodium-23 n.m.r. studies of the exchange of Na⁺ between the solvated and Na⁺·C211 environments show that the cryptate dissociation rate constant k_d(335 K)= 1053.6±4.1, 832.7±5.0 and 554.8±3.2, ΔH^‡= 67.2±0.3, 69.5±0.4 and 83.5±0.5 kJ mol^–1 and ΔS^‡= 12.6±0.7, 17.4±1.2 and 55.9±1.2 J K^–1 mol^–1 in water, dimethyl sulphoxide and dimethylformamide, respectively. Both ¹³C and ²³Na n.m.r. studies indicate that Na⁺·C211 exists predominantly in the exclusive form in solution whereas Li⁺·C211 exists predominantly in the inclusive form. These data are discussed in terms of the two sequential equilibria: [graphics ommitted]. Mechanistic discussion is also extended to larger cryptates.