The sodium perchlorate complex of cis-syn-cis dicyclohexano-24-crown-8 ether. X-ray crystal structure and solution conformations as studied by variable temperature ¹³C NMR spectroscopy at 125 MHz. An example of eight-coordinate sodium

Abstract

Can. J. Chem. 70, 1688 (1992. The major isomer obtained by hydrogenation of dibenzo-24-crown-8 ether is shown to have the cis-syn-cis configuration as determined from the crystal structure of its sodium perchlorate complex. This material possesses eight-coordinate sodium with Na-0 distances ranging from 2.54 to 2.78 A. The complex is shown to exist in a single asymmetric conformation below 240 K as determined by I3C NMR at 125 MHz. From NMR coalescence temperature measurement, the free energy of activation for cyclohexane ring inversion in this complex has been determined to be 51.0 * 1688 (1992). En se basant sur la structure cristalline du perchlorate, on a determine que l'isomkre majeur obtenu par hydrogenation de 1'Cther dibenzo-24-couronne-8 posskde la configurati~n~cis-syn-cis. Dans ce produit, il y a huit atomes de sodium de cordonnes et les distances Na-0 varient de 2,54 a 2,78 A. Grice a la RMN du I3C a 125 MHz, on a dCmontr6 que, 2i une temperature inferieure 240 K, le complexe existe sous une seule conformation asymetrique. Sur la base de mesures de temperatures de coalescence, on a determine que l'energie libre d'interconversion du cyclohexane est egale 2i 51,O c 0,6 kJ/mol.[Traduit par la redaction]

A Review of the Thermodynamics of Complexation of Crown Ethers With Metal Ion

“…larger than 18-crown-6) adapt their conformations for optimized complexation of guest titles. Therefore, the formation of "wrap-around" complexes between some alkali metal ions and crown ethers both in solid state [31] and solution [32], are expected. The numeral and the nature of heteroatoms participating in bind of cation, the nature of substituted groups on the macrocyclic ring, and especially, the solvent properties are of some other important factors [30].…”