CHIRAL RECOGNITION AMONG TRISDIIMINE - METAL-COMPLEXES .2. ARE CLAY-MINERALS PROCHIRAL ADSORBENTS

Based on a review of crystal structures we propose that with trisphenanthroline complexes the racemic layer is the preferred one, but with trischelate complexes of bipyridyl and related ligands it is the enantiomeric layer. Adsorption of complex cations is fast and kinetically controlled. Intercalation up to the bilayer arrangement is energetically only feasible if the monolayer corresponds to the energetically most favourable two-dimensional packing. Hence the reported chiral recognition power of clay minerals is founded solely in the lateral interactions of the guest-complexes. The clay mineral host is acting as an anion that, while strongly modifying the structure, does promote or merely does not prevent chiral recognition between the guests in the interlayer region. The achiral clay minerals themselves do not have any chiral recognition ability.