Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 12
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[NiCl4]2− is paramagnetic, while [Ni(CO)4] is diamagnetic, though both are tetrahedral. Why? (Atomic number of Ni = 28) - Chemistry

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[NiCl4]2− is paramagnetic, while [Ni(CO)4] is diamagnetic, though both are tetrahedral. Why? (Atomic number of Ni = 28)

Why is [NiCl4]2– paramagnetic but [Ni(CO)4] is diamagnetic ? (At. nos. : Cr = 24, Co = 27, Ni = 28)

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Solution 1

In [NiCl4]2−, Ni is in the +2 state. Cl is a ligand which is a weak field ligand which does not cause pairing of unpaired 3d electrons. Hence, it is paramagnetic. In [Ni(CO)4], Ni has 0 oxidation state. CO is a strong field ligand, which causes pairing of unpaired 3d electrons. No unpaired electrons are present in this case. So, it is diamagnetic.

Solution 2

In [NiCl4]2−, the oxidation state of Ni is +2. Chloride is a weak field ligand and does not cause pairing up of electrons against the Hund's rule of maximum multiplicity. As a result, two unpaired electrons are present in the valence d-orbitals of Ni which impart paramagnetic character to the complex. On the other hand, carbonyl is a strong field ligand and causes pairing up of electrons against the Hund's rule of maximum multiplicity. As a result, no unpaired electrons are present and hence, the complex is diamagnetic.

Solution 3

[NiCl4]2− and [Ni(CO)4] both are tetrahedral. But their magnetic characters are different. This is due to difference in the nature of ligands.

Ni+2 = [Ar] 4s03d8

Ni+2 has 2 unpaired electrons hence, this complex is paramagnetic.

In Ni(CO)4, Ni is in the zero oxidation state i.e., it has a configuration of 3d84s2.

[Ni(CO)4]

Ni = [Ar] 4s2 3d8

But CO is a strong field ligand. Therefore, it causes the pairing of unpaired 3d electrons. Also, it causes the 4s electrons to shift to the 3d orbital, thereby giving rise to sp3 hybridization. Since, no unpaired electrons are present in this case, [Ni(CO)4] is diamagnetic.

Concept: Bonding in Coordination Compounds - Magnetic Properties of Coordination Compounds
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