l-Cysteine as a Chiral Linker in Lanthanide–Cucurbit[6]uril One-Dimensional Assemblies

The reaction of neodymium, europium, or terbium nitrate with cucurbit[6]uril (CB6) in the presence of the α-amino acid l-cysteine (l-cys) gives the complexes [Nd(l-cys)(CB6)(NO3)(H2O)4]·2NO3·10H2O (1) and {[Ln(l-cys)(CB6)(H2O)5][Ln(l-cys)(CB6)(NO3)(H2O)4]}·5NO3·22H2O with Ln = Eu (2) or Tb (3). 2 and 3 only differ from 1 by the presence of two independent metal ions in slightly different environments. In all cases, each metal atom is bound to the bidentate CB6 and the monodentate l-cys molecules, with the latter being in its zwitterionic form. The ammonium group of l-cys is directed away from CB6 and is involved in ion−dipole and hydrogen bonding interactions with the uncomplexed portal of the neighboring molecule, which gives rise to the formation of chiral one-dimensional assemblies of columnar shape.