Which of the following is paramagnetic ?

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V(CO)₆

Fe(CO)₅

Fe₂(CO)₉

Cr(CO)₆

answer is A.

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Detailed Solution

CO is a neutral ligand, so all metal ions are in zero oxidation state.

(i) V(CO)₆

Oxidation state of V is zero and its electronic configuration is [Ar] 3d³ 4s². As CO is a strong ligand, so all electrons of 3d and 4s gets paired leaving one unpaired electrons which is responsible for its paramagnetic behavior.

(ii) Fe(CO)₆

Oxidation state of Fe is zero and its electronic configuration is [Ar] 3d⁶ 4s². As CO is a strong ligand, so all electrons of 3d and 4s gets paired leaving no unpaired electrons, so it is diamagnetic.

(ii) Fe₂(CO)₉

Oxidation state of Fe is zero and its electronic configuration is [Ar] 3d⁶ 4s². Complex is diamagnetic because each Fe has one unpaired electron which combine together and forms a Fe-Fe bond.

(ii) Cr(CO)₆

Oxidation state of Cr is zero and its electronic configuration is [Ar] 3d⁵ 4s¹. As CO is a strong ligand, so all electrons of 3d and 4s gets paired leaving no unpaired electrons, so it is diamagnetic.

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