Stereochemistry of five-co-ordination. Part III. Compounds of stoicheiometry bis (unidentate ligand)(tridentate ligand) metal

Abstract

Minimisation of the repulsive energy around five-co-ordinate molecules containing one tridentate and two unidentate ligands shows that neither the symmetrical trigonal bipyramid nor the square pyramid are the expected stereochemistries. For normal tridentate ligands, the predicted stereochemistry (I), contains a mirror plane through the central atom of the tridentate and both unidentate ligands, but the unidentate ligands are not symmetrically arranged on each side of the plane containing the three donor atoms of the tridentate ligand, and this tridentate plane does not contain the metal atom. A second stereochemistry, (II), is possible if the three donor atoms of the tridentate ligand form an equilateral triangle. These predictions agree with the crystal structures of molecules of this type.