K. Ohtsu et al., THERMODYNAMICS OF COMPLEXATION OF SODIUM, POTASSIUM, RUBIDIUM, CESIUMAND AMMONIUM-IONS WITH 18-CROWN-6 IN ACETONITRILE AND PROPYLENE CARBONATE, Journal of the Chemical Society. Faraday transactions, 91(24), 1995, pp. 4375-4380
Citations number
28
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 acetonitrile (MeCN) and propylene
carbonate (PC) containing 0.05 mol dm(-3) (C2H5)(4)NCIO4 as a constant
ionic medium at 25 degrees C. The formation of [M(18-crown-6)](+) (M
= Na+, K+, Rb+, Cs+, NH4+) ions was revealed, and their formation cons
tants, reaction enthalpies and entropies were determined. Consistent w
ith the similar donor and acceptor properties of MeCN and PC, the stab
ility of the 18-crown-6-cation complexes is similar in the two solvent
s. However, the enthalpic and entropic behaviour are very different. T
he formation enthalpy of the sodium complex is positive in MeCN, while
negative in PC. The reactions for the potassium, rubidium, caesium an
d ammonium ions are less exothermic in MeCN than in PC. On the other h
and, the formation of the sodium complex in MeCN is accompanied by a m
ore positive entropy change than that in PC. The reaction entropies fo
r the potassium, rubidium, caesium and ammonium systems are positive i
n MeCN, whereas they are negative in PC. Thus, enthalpy-entropy compen
sation results in a similar stability of [M(18-crown-6)](+) (M = Na+,
K+, Rb+, Cs+, NH4+) in MeCN and PC.