VBT Anomalies & Exceptions

Exceptional Profiles:

$$\begin{aligned} [\text{Cu}(\text{NH}_3)_4]^{2+} &\implies dsp^2 \text{ Hybridization (Square Planar, Paramagnetic with } n=1) \\ [\text{Ni}(\text{CO})_4] &\implies sp^3 \text{ Hybridization (Tetrahedral, Diamagnetic with } n=0) \end{aligned}$$

Concept: Captures specific metal-ligand systems where unexpected electronic excitations or migrations occur; Copper(II) excites its single $$3d$$ electron to a $$4p$$ orbital to clear a $$3d$$ orbital, while Nickel(0) migrates its $$4s^2$$ pair back into the $$3d$$ shell.

Notation:

• $$[\text{Cu}(\text{NH}_3)_4]^{2+}$$ = Tetraamminecopper(II) cation ($$d^9$$ system);
• $$[\text{Ni}(\text{CO})_4]$$ = Tetracarbonylnickel(0) complex ($$3d^8 4s^2 \to 3d^{10}$$).