Understanding the eighteen-electron rule

摘要

It is pointed out that the preferred closed-shell electron structures, such as those in typical high-symmetry 18-electron systems, are driven both by the bonding contributions to the centre and by the kinetic-energy (nodal-structure) terms in the ligand subsystem, L-n. The latter imposes a filling order s < p < d, even for the MLn complex. Then the 18e principle can be right for the right reasons even without any np contributions at the central atom. (c) 2006 Elsevier B.V. All rights reserved.