Unusual intramolecular CH⋯O hydrogen bonding interaction between a sterically bulky amide and uranyl oxygen

Abstract

The selective separation of toxic heavy metals such as uranyl can be accomplished using ligands with stereognostic hydrogen bonding interactions to the uranyl oxo group, as proposed by Raymond and co-workers (T. S. Franczyk, K. R. Czerwinski and K. N. Raymond, J. Am. Chem. Soc., 1992, 114, 8138–8146). Recently, several ligands possessing this weak interaction have been proposed involving the hydrogen bonding of NH and OH based moieties with uranyl oxygen. We herein report the structurally and spectroscopically characterized CH⋯O hydrogen bonding using a sterically bulky amide based ligand. In conjunction with experiments, electronic structure calculations are carried out to understand the structure, binding and the strength of the CH⋯O hydrogen bonding interactions. This weak interaction is mainly due to the steric effect caused by a bulky substituent around the donor group which has direct relevance in designing novel ligands in nuclear waste management processes. Although the kinetics are very slow, the ligand is also highly selective to uranyl in the presence of other interfering ions such as lanthanides.