The Mayer bond order as a tool in inorganic chemistry†

The bonding in molecules is most often described using the classical chemical ideas of covalency (bond multiplicity) and ionicity (atomic charges). The Mayer bond order is a natural extension of the Wiberg bond order, which has proved extremely useful in bonding analysis using semi-empirical computational methods, and the Mulliken population analysis to ab initio theories. The usefulness of the Mayer bond order has been tested in a number of inorganic molecules including sulfur–nitrogen rings, halogen–oxide molecules and transition metal dichloride molecules. The basis set dependence of the Mayer bond order is tested through the case studies presented. It is shown that the bond order can be fully or partially decomposed into the contributions from symmetry types for many interactions of interest to the inorganic chemist. The power of this approach is shown by examining the bonding in a variety of systems and is illustrated by detailed studies of the role of the ring size and electron count on the bonding in S–N rings, the role of hypervalency in the relative stabilities of mixed hydrogen and halogen peroxide isomers and the importance of s–d hybridization in the 3d transition metal dichloride molecules.