Racemic Assembly of Octahedral Metallomesogens via Δ-Λ Chiral Interaction: Detection of Novel VCD Signals in Quasi-Racemate.

The liquid crystalline columnar assemblies have been developed by using racemic metal complexes with Δ, Λ chirality (M-C8, M = Ru or Ir) as mesogens. A racemic M-C8 exhibits rectangular columnar (Col) and hexagonal columnar (Col) phases upon cooling from their isotropic phases, which are analyzed by the combination of grazing-incidence X-ray diffraction (GI-XRD) measurements and molecular dynamics (MD) simulation. In the Col phase, with lattice parameter a = 3.2 nm, single molecules are proposed to stack and form columns. By contrast, a large lattice with dimensions a = 12.4 nm and b = 2.6 nm is formed in the Col phase. MD simulations demonstrated that two columns, each formed by the alternating stacking of Δ and Λ isomers, form a pair that subsequently assembles to construct a rectangular lattice. The paired columns are proposed to separate into individual columns in the Col phase at the higher temperature, with each column behaving independently. A quasi-racemic assembly of Δ-Ru-C8 and Λ-Ir-C8 or vice versa is further prepared via the Δ-Λ interaction. It is found to have the same structure as rac-M-C8 and exhibit different vibrational circular dichroism (VCD) signals from the individual enantiomers.