ChemInform Abstract: Hydration, Ion Pairing, and Sandwich Motifs in Ammonium Nitrate Complexes of Crown Ethers.

Abstract

structure structure (organic substances) K 9000 -025Hydration, Ion Pairing, and Sandwich Motifs in Ammonium Nitrate Complexes of Crown Ethers.-Ammonium nitrate coordinates to 18-crown-6 to form a complex of 1:1 stoichiometry through a near-ideal 'tripod' arrangement of hydrogen bonds to alternate crown ether oxygen atoms. An additional bonding interaction between the crown ether-bound ammonium ion and the counterion is influenced by the extent of hydration, relatively insignificant in aqueous solution, but significant in anhydrous media. Hence it follows that water plays a potentially significant role in dictating the structural details of cation-crown ether complexes. In contrast, ammonium nitrate forms complexes with 15-crown-5 and benzo-15-crown-5 of 1:2 stoichiometry which show sandwich-type structure, with the ammonium cation complexed between two roughly parallel crown ether rings. -(DOXSEE, KENNETH M.; FRANCIS JR., PERRY E.; WEAKLEY, TIMOTHY J. R.; Tetrahedron 56 (2000) 36, 6683-6691; Dep. Chem., Univ. Oreg., Eugene, OR 97403, USA; EN)