Question

The number of unpaired electron(s) of chromium in [($\eta^6$-C$_6$H$_6$)Cr(CO)$_3$] is _ _ _. (answer in integer)

Hint:

Metal carbonyl complexes usually follow the 18-electron rule and are generally diamagnetic due to strong field CO ligands

Answer 1

Correct Answer: 0

Step 1: Oxidation state of chromium.
Benzene and the three carbonyls are all neutral, so chromium is in the zero state.

Step 2: Electron count and field.
This is an 18 electron complex and carbon monoxide is a strong field ligand, so all electrons pair up.

Step 3: Unpaired electrons.
With everything paired the count of unpaired electrons is zero.

Step 4: Answer.
\[ \boxed{0} \]