---
title: "VBT: [Ni(CN)₄]²⁻ and [Ni(CO)₄]"
subject: "Engineering Chemistry"
chapter: 6
key: "semester_2/engineering_chemistry:vbt-nicn4-nico4"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/vbt-nicn4-nico4
site: BCT Engineering
---

# VBT: [Ni(CN)₄]²⁻ and [Ni(CO)₄]

Engineering Chemistry · Chapter 6: Coordination Complexes

- Asked in: 2073 Bhadra, 5 marks
- Video: [Ni(CO)4, [Ni(CN)4]2-, [NiCl4]2-Structure-Hybridization-diamagnetic-VBT-IUPAC Name - IIT JEE NEET](https://www.youtube.com/watch?v=r_C4yyTUSjM) — AdiChemistry Aditya Vardhan
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/vbt-nicn4-nico4
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-6

## Question

Using VBT, explain as to show the two complexes [Ni(CN)₄]²⁻ and [Ni(CO)₄] have different structure but do not differ in their magnetic behavior.

## Short answer

[Ni(CN)4]2- is square planar (dsp2) and [Ni(CO)4] is tetrahedral (sp3). Both have all electrons paired and are diamagnetic, so magnetic behavior is the same but structures differ due to hybridization.

## Answer

#### [Ni(CN)₄]²⁻
Ni²⁺ is 3d⁸. CN⁻ is a strong-field ligand, so the two unpaired 3d electrons pair up and one 3d orbital becomes empty. One 3d, one 4s and two 4p orbitals mix to give **dsp²** hybrid orbitals.
```text
3d: [↑↓][↑↓][↑↓][↑↓][  ]  4s [ ]  4p [ ][ ]  → dsp²
```
Geometry **square planar**; no unpaired electrons, **diamagnetic**.

#### [Ni(CO)₄]
Ni is in the 0 oxidation state: 3d⁸ 4s². CO is a strong-field ligand, so the 4s electrons shift into 3d, giving 3d¹⁰ (all paired). One 4s and three 4p orbitals are vacant and form **sp³** hybrid orbitals.
```text
3d: [↑↓][↑↓][↑↓][↑↓][↑↓]  4s [ ]  4p [ ][ ][ ]  → sp³
```
Geometry **tetrahedral**; no unpaired electrons, **diamagnetic**.

Both complexes have no unpaired electrons and so show the same (diamagnetic) behaviour, but the different hybridisation (dsp² vs sp³) gives different shapes.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which hybridisation describes [Ni(CN)4]2-?
   A. dsp2
   B. sp3
   C. sp3d2
   D. d2sp3
   Answer: A. One 3d vacated. (Key point: CN-)

2. What is the oxidation state of Ni in Ni(CO)4 and what happens to its electrons?
   A. +2
   B. 0, 3d10 after 4s shifts into 3d
   C. +4
   D. -2
   Answer: B. The correct option is: 0, 3d10 after 4s shifts into 3d. This follows from the answer on ni(co)4 state. (Key point: Ni(CO)4 state)

3. What is the shape of [Ni(CO)4]?
   A. square planar
   B. octahedral
   C. tetrahedral sp3
   D. linear
   Answer: C. The correct option is: tetrahedral sp3. This follows from the answer on ni(co)4 shape. (Key point: Ni(CO)4 shape)

4. What is the magnetic behaviour of both [Ni(CN)4]2- and [Ni(CO)4]?
   A. paramagnetic
   B. one paramagnetic one diamagnetic
   C. ferromagnetic
   D. diamagnetic
   Answer: D. No unpaired. (Key point: Magnetism)

## Related in Engineering Chemistry

- [VBT formation of [Ni(CO)₄] and [Fe(CN)₆]⁴⁻](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Avbt-nico4-fecn6-4) — Engineering Chemistry, chapter 6
- [VBT: magnetism of [Fe(CN)₆]⁴⁻/³⁻ and [Ni(CO)₄]](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Avbt-facts-fecn6-nico4) — Engineering Chemistry, chapter 6
- [VBT for [Ni(CN)₄]²⁻ and its magnetism](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Avbt-nicn4) — Engineering Chemistry, chapter 6
- [Inner/outer orbital complexes; VBT of [Fe(CN)₆]³⁻](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Ainner-outer-vbt-fecn6) — Engineering Chemistry, chapter 6
- [Low vs high spin; VBT of [Ni(CO)₄]](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Alow-high-spin-ni-co4) — Engineering Chemistry, chapter 6
- [Tetrahedral and square planar complexes; [Ni(NH₃)₄]²⁺ VBT](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Atetra-square-vbt-ni-nh3) — Engineering Chemistry, chapter 6

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