Bonding in d-block metal complexes: valence bond theory

Hybridization schemes

   Although VB theory in the form developed by Pauling in the 1930s is not much used now in discussing d-block metal complexes, the terminology and many of the ideas have been retained and some knowledge of the theory remains essential.

   These same hybridization schemes can be used to describe the bonding in d-block metal complexes (Table 1.1); an empty hybrid orbital on the metal centre can accept a pair of electrons from a ligand to form a σ-bond.   The choice of particular p or d atomic orbitals may depend on the definition of the axes with respect to the molecular framework, e.g. in linear ML₂, the M–L vectors are defined to lie along the z axis.  We have included the cube in Table 1.1 only to point out the required use of an f orbital.

Fig. 1.1 (a) The six M^_L vectors of an octahedral complex [ML₆]^n‏+ can be defined to lie along the x, y and z axes. (b) The five d orbitals; the d_z² and d_x²_{- y}² atomic orbitals point directly along the axes, but the d_xy, d_yz and d_xz  atomic orbitals point between them.

Table 1.1 Hybridization schemes for the σ-bonding frameworks of different geometrical configurations of ligand donor atoms.