Complexation of monovalent metal ions by 4,7,13,16-tetraoxa-1,10-diazabicyclo[8.8.8]hexacosane in a range of solvents. A potentiometric titration and nuclear magnetic resonance study (original) (raw)

1992, Inorganic Chemistry

Complexation of Li+, Na+, K+, Rb+, Cs+, Ag+, and TI+ by 4,7,13,16-tetraoxa-1,10-diazabicyclo[8.8.8]hexacosane (C22Cs) to form the cryptate [M.C22C8]+ has been studied in five solvents by potentiometric titration and 7Li and 23Na NMR spectroscopy. A considerable variation in the stability of [M.C22Cs]+ occurs as M+ is varied in the sequence the figuresin bracketsarelog (Kldm3mol-1) andKis theapparent stabilityconstant of [M.C22Cs]+ in acetonitrile and dimethylformamide, respectively, at 298.2 K. The exchange of Na+ on [Na.C22C8]+, determined by 23Na NMR spectroscopy, is characterized by kd(298.2 K) = 443 f 5, 1253 f 7, and 10 800 f 300 s-1, AHd* = 38.2 f 0.6,37.1 f 0.3, and 46.8 f 0.6 kJ mol-I, and A, !&* = -66 f 2, -61 f 1, and-1 1 f 2 J K-l mol-', respectively, in acetonitrile, pyridine, and methanol. In dimethylformamide the [Na.C22Cs]+ exchange rate is in the very fast regime of the 23Na NMR time scale, and in acetonitrile, methanol, dimethylformamide, and pyridine the [Li.C22Cs]+ exchange rate is in the very fast regime of the 7Li NMR time scale. These data are discussed in terms of the effects of cryptand structure and of metal ion and solvent characteristics on cryptate stability and lability. 100.4412-4416. (26) Lincoln, S. F.; Horn, E.; Snow, M. R.; Hambley, T. W.; Brereton, M.; (27) Mathieu, F.; Metz, B.; Moras, D.; Weiss, R.