Which of the following organometallic compound is `sigma` and `pi`-bonded?

Options

A. `[Fe(eta^(5) - C_(5)H_(5))_(2)]`
B. `K[PtCI_(3)(eta^(2) - C_(2)H)_(4)]`
C. `[Co(CO)_(5)NH_(3)]^(2+)`
D. `AI(CH_(3))_(3)`

Answer

C

Explanation

All carbonyls are `sigma` and `pi` bonded in nature because the metal - carbon bond in metal carbonyls possesses both `sigma` and `pi` character. The `M-C` `sigma` bond is formed by the donation of ion pair of electrons on the carbonyl carbon into a vacant orbital of the metal. The `M-C` `pi` bonds is formed by the donation of a pair of electrons from a filled d orbital of metal into the vacant antibonding `pi^(*)` orbital of carbon monoxide.