Bond lengths in organometallic and coordination complexes: Substituent effects

The literature data on substituent influence on the bond lengths obtained from X-ray crystallography or quantum chemical calculations for 32 series of the intermolecular, intramolecular as well as transition metal complexes have been considered, using the correlation analysis. Generally the bond lengths were first established to depend on the joint influence of the inductive, resonance, polarizability, and steric effects of substituents. The presence or otherwise of one or the other effects as well as the relation between their contributions to the overall change in bond length are determined by the type of series. The reason for the occurrence of the polarizability effect (an electrostatic ion–dipole interaction) is the appearance of an excess charge on the atoms of bond studied as a result of the charge transfer from the donor centre of the complex to the acceptor one. The contribution of the polarizability effect may be as great as 55%.