Continuous chirality measures of tetracoordinate bis(chelate) metal complexes

The interconversion pathway between the tetrahedron and the square that is represented by the structures of a large variety of tetracoordinate complexes is the achiral spread pathway in the presence of monodentate ligands but the chiral twist pathway in bis-chelated complexes. The chirality of several families of bis-chelated metal complexes is evaluated using the Continuous Chirality Measures methodology. The specific contribution to chirality from the innermost MX₄ shell, as well as from the ligands is analyzed. The maximal expected chirality value for the tetrahedral to square planar route is at a torsion angle of 45°, which is realized in [Cu(p-C₆H₄(p-C₂H₅bipyMe)₂)]²⁺. The chiral behavior of double-stranded helicates is compared to that of analogous mononuclear complexes. The present study shows that chirality is a rather common property of bis-chelated complexes, even in the absence of asymmetric ligands.