Bonds Involving d Valence Orbitals

There are many structures in which the central atom requires one or more valence orbitals to complete a set of a bonding orbitals. The most important of these structures are square planar, trigonal bipyramidal, square pyramidal, and octahedral examples are shown in Fig. 9-1. Transition-metal ions have available a very stable set of d valence orbitals. The bonding in complexes formed between transition-metal ions and a large number of molecules and other ions undoubtedly involves d orbitals. In this chapter we shall describe the bonding between metal ions and ligands in certain representative metal conjplexes. 

The Ti + ion forms a stable complex ion with six water molecules. The structure around the Ti + ion is octahedral, as shown in Fig. 9-2. 

The titanium has five 3, one 4, and three 4p valence orbitals that can be used in constructing molecular orbitals. Each water molecule must furnish one a valence orbital, which, in accord with the discussion in Chapter VIII, is approximately an rp hybrid orbital. We shall not specify the exact s and p character of the water or valence orbital, however, but simply refer to it as a. 

The metal orbitals thkt can form a molecular orbitals are 

and 4p. Since the sign of the 4s orbital does not change over the boundary surface, the proper linear combination of ligand orbitals for 4s is 

---