Theoretical aspects of the enantiomeric resolution of dimetallo helicates with different surface topologies on cellulose columns

Cellulose has been used to separate the enantiomers of a range of dimetallo coordination compounds with different surface topologies. The compounds are all approximately cylindrical in shape, but are based on octahedral coordination at the metals and are also helical. When separation has been achieved, the first eluted enantiomer has always been proven to have a negative circular dichroism (CD) signal for its longest wavelength metal to ligand charge transfer band. In order to understand the underlying basis for the elution order, gas phase molecular dynamics and snap-shot minimisations of each enantiomer with the repeat unit of cellulose, glucose, have been undertaken. For new dimetallo helicates, it is important to have a quick assessment of the enantiomeric identity of the first eluted compound. To this end, the coupled-oscillator model of CD has been applied to relate the signs of the CD signals to the identity of the enantiomers. This correlation is consistent with crystallographic data for the first eluted enantiomer of the parent compound.