K. Ozutsumi et al., THERMODYNAMICS OF COMPLEXATION OF 18-CROWN-6 WITH SODIUM, POTASSIUM, RUBIDIUM, CESIUM AND AMMONIUM-IONS IN N,N-DIMETHYLFORMAMIDE, Journal of the Chemical Society. Faraday transactions, 90(1), 1994, pp. 127-131
Citations number
39
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
The complexation of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6)
with sodium, potassium, rubidium, caesium and ammonium ions has been
studied by titration calorimetry in N,N-dimethylformamide (DMF) contai
ning 0.1 mol dm(-3) (C2H5)(4)NClO4 as a constant ionic medium at 25 de
grees C, The calorimetric titration data were well explained in terms
of the formation of the [M(18-crown-6)](+) (M = Na+, K+, Rb+, Cs+, NH4
+) and [Cs(18-cronw-6)(2)](+) complexes, and their formation constants
, enthalpies and entropies were determined. The stability of the [M(18
-crown-6)](+) (M = Na+, K+, Rb+, Cs+, NH4+) complexes is much more pro
nounced In DMF than In water. The formation entropies are similar for
the sodium and potassium complexes' in DMF and water, but are smaller
for the rubidium, caesium and ammonium complexes in DMF than for the c
orresponding complexes in water. The stabilization of the [M(18-crown-
6)](+) complexes is thus due to the more exothermic complexation in DM
F than in water. Because the solvation of the univalent cations is exp
ected to be enhanced to a greater extent in DMF than in water owing to
the relatively large electron-pair donating ability of DMF, the more
exothermic complexation in DMF than in water is ascribed to the differ
ent solvation of 18-crown-6 in the two solvents, i.e. 18-crown-6 is mu
ch more stabilized in water by forming hydrogen bonds with water molec
ules.