Intramolecular C–H⋯π interactions influence the conformation of N,N′-dibenzyl-4,13-diaza-18-crown-6 molecules

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(NO₃)₅(H₂O)] (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.