Sandwich and mixed sandwich complexes of the cesium ion with crown ethers in nitromethane

Cesium-133 nuclear magnetic resonance was used as a probe of the interaction of the Csi ion with the crown ethers 18C6, 15C5, 12C4, and with HMHCY (hexamethyl hexacyclen) in nitromethane solution with thiocyanate as the counterion. A study of the Cs-133 chemical shift as a function of crown to Cs+ mole ratio showed that the complexation reactions occur stepwise. Formation of a 1:1 complex is followed by the addition of a second complexant molecule to form a sandwich cation. In the case of 18C6, there is strong evidence for the intermediate formation of a 3:2 adduct. The formation constants of sandwich complexes that contain two molecules each of 18C6, 15C5, and HMHCY and various mixed sandwiches of these complexants (and also 12C4) in solution were evaluted from the mole ratio data. The crystal structure of the mixed sandwich salts Cs+(18C6)(12C4)SCN-. 2(CH3OH) and Rb+(18C6)(12C4)I-. H2O were also determined.