F. de Jong

Chemistry of crown ethers: Complexation with alkali metal trichloro(ethylene)platinum(II) salts

Abstract A novel method has been developed for the determination of the complexation constants of crown ethers with alkali salts. It comprises the equilibration of crown ether ( 1–7 ) solutions in deuterochloroform with solid trichloro(ethylene)platinum(II) salts (Na + , K + , Rb + , Cs + ) and the PMR spectroscopic determination of the equilibrium ratio of complex to free crown ether from the relative intensities of the ethylene and crown ether protons. The solubility of uncomplexes salt was determined independently by atomic absorption spectrometry. The major advantages of this method over others are: (i) complexation constants in apolar solvents are obtained from a direct solid-liquid transition, (ii) the cation in the salt can be varied, and (iii) a simple detection technique can be used for monitoring the complexation. The PMR spectra indicate that there are three types of complex, depending on the ratio of the diameter of the crown ether cavity to that of the cation. If this ratio is small ( 1.0) the polyether ring is twisted around the cation.

A nesting conformation of the 5′-bromo-1′,3′-xylyl-18-crown-5·tert-butylammonium hexafluorophosphate complex; the correlation of the structures of crown ether complexes in the solid state and in solution

Single-crystal X-ray analysis of the 5′-bromo-1′,3′-xylyl-18-crown-5· tert-butylammonium hexafluorophosphate complex shows that the complex is of the “nesting” type in which the cation and the aryl group are on the same face of the macroring and that the macroring has a (ag+a) (ag−a) (ag+a) (ag−a)(ag+a) (ag−a) conformation.