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{pC2H5bipyMe}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.