Evans, David J., Junk, Peter C., and Smith, Matthew K. (2002) Intramolecular C-H···π interactions influence the conformation of N,N'-dibenzyl-4,13-diaza-18-crown-6 molecules. New Journal of Chemistry, 26. pp. 1043-1048.

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Abstract

Interaction of La(NO3)3 .6H2O, Eu(NO3)3.6H2O, UO2(NO3)2.6H2O or hydrobromic acid with N,N'-dibenzyl-4,13-diaza-18-crown-6 leads to double protonation of the N-containing heterocycle, affording [(H+)2N,N'-dibenzyl-4,13-diaza-18-crown-6][La(N03)5(H20)] (1), [(H+)2N,N'-dibenzyl-4,13-diaza-18-crown-6)[Eu(NO3)5(H2O)] (2), [(H+)2N,N'-dibenzyl-4,13-diaza-18-crown-6][(μ-OH)2{UO2(NO3)2}2] (3) and (H9O4+)2[(H+)2N,N'-dibenzyl-4,13-diaza-18-crown-6]Br4 (5). The X-ray crystal structures of each compound were obtained, revealing unusual C-H...π interactions between the phenyl substituents and two macrocyclic methylene protons that govern the overall conformation of the macrocycle. We also report the X-ray crystal structure of the related [(H2O)2(H+)2N,N'-dibenzyl-4,13-diaza-18-crown-6][UO2Cl4] (4), which, surprisingly, does not have the same conformation of the cation, rather, two molecules of water bind to the inner cavity of the crown ether.

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