Hybridization and Geometry for Coordination Number 5

$$\begin{aligned} sp^3d &\implies \text{Trigonal Bipyramidal (TBP)} \quad [\text{e.g., } \text{Fe}(\text{CO})_5, \text{ PCl}_5] \\ dsp^3 &\implies \text{Square Pyramidal (SP)} \quad [\text{e.g., } [\text{VO}(\text{acac})_2], [\text{Ni}(\text{CN})_5]^{3-}] \end{aligned}$$

Concept: Five-coordinate complexes utilize inner $$d_{z^2}$$ orbitals for $$dsp^3$$ square pyramidal geometries and outer/inner d-orbitals for trigonal bipyramidal geometries depending on ligand field strength and steric crowding.

Notation:

• $$\text{acac}^-$$ = Acetylacetonate ion (bidentate monoanionic ligand)