Question 20.8: Give a valence bond description of the bonding in [V(NH3)6]^......
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] \overset{\uparrow}{—} \overset{\uparrow}{—} \overset{}{\underset{3d}{—}} — — \underset{4s}{—} — \overset{}{\underset{4p}{—}} —Because [V(NH_{3})_{6}]^{3+} is octahedral, the V^{3+} ion must use either d²sp³ or sp³d² hybrid orbitals in accepting a share in six pairs of electrons from the six NH_{3} ligands. The preferred hybrids are d²sp³ because several 3d orbitals are vacant and d²sp³ hybrids have lower energy than sp³d² hybrids (because the 3d orbitals have lower energy than the 4d orbitals). Thus, [V(NH_{3})_{6}]^{3+} has the following orbital diagram:
[V(NH_{3})_{6}]^{3+}: [Ar] \overset{\uparrow}{—} \overset{\uparrow}{—} \underset{3d}{—} \underset{Six d^2sp^3 bonds to the ligands}{\boxed{\overset{\uparrow\downarrow}{—} \overset{\uparrow\downarrow}{—} \overset{\uparrow\downarrow}{\underset{4s}{—}} \overset{\uparrow\downarrow}{—} \overset{\uparrow\downarrow}{\underset{4p}{—}} \overset{\uparrow\downarrow}{—}}}The complex has two unpaired electrons and is therefore paramagnetic.