Collect. Czech. Chem. Commun. 1983, 48, 2509-2517

The effect of counterion on alkali ion-crown complex formation: A near-paradox in dissociating solvents

Jiří Závada, Václav Pechanec and Oldřich Kocián

Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6


Contrary to the widespread belief that counterion influences stability of charged complexes only in poorly solvating media, a dramatic effect of anion was discovered, ebulliometrically, in 0.6 molal M+X--C2H5OH (M = K, Na, Li; X = SCN, OC2H5) and in 0.6 molal M+X--H2O (M = K; X = SCN, OH) solution upon complexing with 18-crown-6,15-crown-5 and 12-crown-4. Out of the nine crown-MSCN combinations examined in the ethanolic solution, seven yielded 1 : 1 (18-crown-6-KSCN, 18-crown-6-NaSCN, 15-crown-5-NaSCN, 15-crown-5-LiSCN, 12-crown-4-KSCN) or 2 : 1 (15-crown-5-KSCN, 12-crown-4-NaSCN) complexes quantitatively, whereas the corresponding crown-MOC2H5 combinations did not complex at all or the complexation was very incomplete. An analogous situation was found in the aqueous solution, with KSCN complexing 18-crown-6 quantitatively or 15-crown-5 and 12-crown-4 partly, whereas KOH did not yield complexes with any of the three crowns. Evidence is presented that the observed effect of anion does not originate from ion-pairing.