A theoretical approach to the leaving ligand problem of photosubstitution reactions of hexacoordinate transition metal mixed-ligand complexes

A coordination theory approach to the specific site labilization in ligand photosubstitution reactions has been proposed for hexacoordinate mixed-ligand transition metal complexes. On the basis of molecular orbital theory and the ligand even-distribution assumption, the relative stability of a metal-ligand bond in an excited species is expressed as a function of molecular orbital energy gap resulting from sigma and pi interactions between the metal and ligands, and of the Jahn-Teller effects of the ground and excited species. In terms of the function, some experimental facts have been analyzed. It is likely that the alteration in the electron-pair number upon excitation accounts for the difference between the d(3) type (including d(1-3) and weak field d(4)) and strong field d(6) type (including strong field d(4-7)) complexes in the leaving ligand character. The a and pi interactions may act differently, or even oppositely, on the leaving ligand. The impact of sigma interaction on the leaving ligand has also been assessed for complexes with other electronic configurations.Chemistry, MultidisciplinarySCI(E)0ARTICLE8793-8034