posted on 1999-06-30, 00:00authored byJineun Kim, Mojtaba Shamsipur, Song Z. Huang, Rui H. Huang, James L. Dye
Cesium-133 nuclear magnetic resonance was used as a probe of the interaction of the Cs+ 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 133Cs 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.