Hexaammine cobalt (III) or `[Co(NH)_6]^(3+)` has `d^2sp^3` hybridization.
Hexaamine cobalt (III) is also sometime termed as "inner orbital" complex because the energy difference between d orbital and s & p orbitals of next shell is very small. In this case, 4s and 4p orbitals have slightly higher energy as compared to 3d orbital.
For this complex cation, the 6 valence electrons of cobalt will occupy the 3d orbital, whereas the 6 ligands (each of which donate a pair of electrons) will occupy 3d, 4s and 4p orbitals in d2sp3 hybridization.
This distribution of electrons causes the shape of the ion to be octahedral.
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