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Tamil Nadu Board of Secondary EducationHSC Science Class 12

Based on VB theory explain why [Cr(NHX3)X6]X3+ is paramagnetic, while [Ni(CN)X4]X2− is diamagnetic. - Chemistry

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Question

Based on VB theory explain why \[\ce{[Cr(NH3)6]^3+}\] is paramagnetic, while \[\ce{[Ni(CN)4]^2-}\] is diamagnetic.

Answer in Brief

Solution

1. \[\ce{[Cr(NH3)6]^3+}\]

In this complex, Cr is in the +3 oxidation state. Electronic configuration of Cr atom. Electronic configuration of Cr3+ ion 

Hybridisation and formation of [Cr(NH3)6]3+ Complex

Due to the presence of three unpaired electrons in [Cr(NH3)6]3+ it behaves as a paramagnetic substance.

The spin magnetic moment,

µs = `"g" sqrt(3(3 + 2)) = "g" sqrt(15)` = 3.87 BM

[Cr(NH3)6]3+ is an inner orbital octahedral complex.

2. \[\ce{[Ni(CN)4]^2-}\]

In this complex, Ni is in the +2 oxidation state. Electronic configuration of Ni atom. Electronic configuration of Ni2+ ion. Hybridisation and formation of \[\ce{[Ni(CN)4]^2-}\] Complex

Since CN is a strong field ligand, hence the electrons in 3d orbitals are forced to pair up and there is no unpaired electron in [Ni(CN)4]2, hence it should be a diamagnetic substance.

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Definition of Important Terms Pertaining to Co-ordination Compounds
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Chapter 5: Coordination Chemistry - Evaluation [Page 172]

APPEARS IN

Samacheer Kalvi Chemistry - Volume 1 and 2 [English] Class 12 TN Board
Chapter 5 Coordination Chemistry
Evaluation | Q 5. | Page 172
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