A continuous chirality analysis of homoleptic hexacoordinated complexes

Hexacoordinated complexes are generally considered to be potentially chiral if they have at least two bidentate ligands or at lest three different monodentate ligands. Here we draw attention to a neglected general possibility, namely that homoleptic hexacoordinated complexes with molecular structures in between octahedral and trigonal prismatic, following the Bailar twisting route, are chiral, A quantitative evaluation of the degree of chirality of such hexakis(mondenlate) complexes shows that they reach maximum chirality when the trigonal rotation angle of the prism reaches 23°. Model calculations and analysis of experimental X-ray structures are in good agreement. The most chiral of the complexes with monodentate ligands that have been analyzed is [Zr(SC₆H₄-4-OMe)₆]^2-. The validity of the theoritical prediction is also corroborated by an analysis of the chirality of the coordination sphere in twisted tris(chelate) complexes.