Question 20.10: Describing the Bonding in Complexes in Terms of Valence Bond......
Describing the Bonding in Complexes in Terms of Valence Bond Hybrid Orbitals
Give a valence bond description of the bonding in [V(NH_3)_6]^{3+}. Include orbital diagrams for the free metal ion and the metal ion in the complex. Tell which hybrid orbitals the metal ion uses and the number of unpaired electrons present.
STRATEGY AND SOLUTION
The free V^{3+} ion has the electron configuration [Ar] 3d² and the orbital diagram
V^{3+}: \ [Ar] \frac{\uparrow}{} \frac{\uparrow}{} \frac{}{3d} – – \ \ \frac{}{4s} \ \ – \frac{}{4p} –Because [V(NH_3)_6]^{3+} is octahedral, the V^{3+} ion must use either d² sp³ or sp³ d² hybrid orbitals in accepting a share in six pairs of electrons from the six NH_3 ligands. The preferred hybrids are d² sp³ because several 3d orbitals are vacant and d² sp³ hybrids have lower energy than sp³ d² hybrids (because the 3d orbitals have lower energy than the 4d orbitals). Thus, [V(NH_3)_6]^{3+} has the following orbital diagram: (the photo below)
The complex has two unpaired electrons and is therefore paramagnetic.
