Doubly interpenetrating stereoisomeric three-dimensional frameworks of tripodal neodymium(III) complexes from potentially spacer-controlled enantioselective self-assembly

Abstract

Two three-dimensional frameworks composed of doubly interpenetrating networks of the same topology but different stereoisomeric structures have been constructed from self-assembly of the chiral building block, Δ- or Λ-[Nd(ntb)₂]³⁺, with different spacers bipy and bpen (ntb = tris(2-benzimidazolylmethyl)amine, bipy = 4,4′-bipyridyl, bpen = trans-1,2-bis(4-pyridyl)ethylene). In the crystal structure of [Nd(ntb)₂][ClO₄]₃·3bipy·2H₂O the spacer bipy connects [Nd(ntb)₂]³⁺ cations of the same handedness to generate a chiral network Δ₃-Δ . . . (or Λ₃-Λ . . .){[Nd(ntb)₂]³⁺· 3bipy}_∞, which is interpenetrated further by another identical network. The crystal structure of [Nd(ntb)₂][ClO₄]₃· 3bpen·H₂O shows a topologically similar but achiral framework in which each spacer bpen connects either cations of the same chirality or a pair of enantiomers, thus generating a three-dimensional racemate Δ₂Λ-Λ . . . (or Λ₂Δ-Δ . . .){[Nd(ntb)₂]³⁺·3bpen}_∞. Aggregation of the molecular species is effected by N–H⋯N hydrogen bonds, and the observed enantioselective self-assembly can be rationalized by π⋯π interactions between aromatic rings.