---
title: "Tetrahedral and square planar complexes; [Ni(NH₃)₄]²⁺ VBT"
subject: "Engineering Chemistry"
chapter: 6
key: "semester_2/engineering_chemistry:tetra-square-vbt-ni-nh3"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/tetra-square-vbt-ni-nh3
site: BCT Engineering
---

# Tetrahedral and square planar complexes; [Ni(NH₃)₄]²⁺ VBT

Engineering Chemistry · Chapter 6: Coordination Complexes

- Asked in: 2071 Magh
- Video: [[Ni(CO)4] is tetrahedral and [Ni(CN)4]2-  is Square Planar ?Why coordinate compound VBT](https://www.youtube.com/watch?v=La_CXLjcsaw) — Vicky Science Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/tetra-square-vbt-ni-nh3
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-6

## Question

What are the tetrahedral and square planar complexes? [?] formation of [Ni(NH₃)₄]²⁺ on the basis of valence bond theory [and predict its magnetic beh]avior.

## Short answer

Tetrahedral complexes use sp³ hybrids (109.5°), square planar use dsp² hybrids (90°). For [Ni(NH₃)₄]²⁺, Ni²⁺ (3d⁸) uses sp³ hybridization, giving tetrahedral geometry and two unpaired electrons, so it is paramagnetic (μ ≈ 2.83 BM).

## Answer

**Reading:** the question is "What are tetrahedral and square planar complexes? Explain the formation of [Ni(NH₃)₄]²⁺ on the basis of valence bond theory and predict its magnetic behaviour."

#### Tetrahedral and square planar complexes
Both have coordination number 4.
- **Tetrahedral:** the metal uses sp³ hybrid orbitals, with the ligands at the corners of a tetrahedron (bond angle 109.5°). With weak-field ligands these complexes usually have unpaired electrons. Examples: [NiCl₄]²⁻, [Ni(CO)₄].
- **Square planar:** the metal uses dsp² hybrid orbitals, with the ligands at the corners of a square (bond angle 90°). This shape is common for d⁸ ions with strong-field ligands. Examples: [Ni(CN)₄]²⁻, [PtCl₄]²⁻.

#### [Ni(NH₃)₄]²⁺
Ni²⁺ is 3d⁸. Here NH₃ is treated as a ligand that does not force pairing of the 3d electrons, so the two unpaired electrons remain. One 4s and three 4p orbitals form four **sp³** hybrids that accept the NH₃ lone pairs.
```text
3d: [↑↓][↑↓][↑↓][↑ ][↑ ]  4s [ ]  4p [ ][ ][ ] → sp³
```
- **Geometry:** tetrahedral.
- **Magnetism:** two unpaired electrons, so **paramagnetic**, μ = 2.83 BM.

## Check yourself

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

1. Which hybridisation and bond angle describe tetrahedral complexes?
   A. dsp2, 90
   B. sp3d2
   C. d2sp3
   D. sp3, 109.5 deg
   Answer: D. The correct option is: sp3, 109.5 deg. This follows from the answer on tetrahedral. (Key point: Tetrahedral)

2. Which hybridisation and bond angle describe square planar complexes?
   A. dsp2, 90 deg
   B. sp3
   C. sp3d
   D. d2sp3
   Answer: A. The correct option is: dsp2, 90 deg. This follows from the answer on square. (Key point: Square)

3. What is the magnetic behaviour and moment of [Ni(NH3)4]2+?
   A. diamagnetic
   B. 1.73 BM
   C. paramagnetic, 2.83 BM
   D. 4.90 BM
   Answer: C. The correct option is: paramagnetic, 2.83 BM. This follows from the answer on magnet. (Key point: Magnet)

## Related in Engineering Chemistry

- [VBT for [Ni(NH₃)₆]²⁺: geometry and magnetism](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Avbt-nih36) — Engineering Chemistry, chapter 6, asked 2×
- [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
- [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
- [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
- [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
- [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