---
title: "IUPAC names of four complexes"
subject: "Engineering Chemistry"
chapter: 6
key: "semester_2/engineering_chemistry:iupac-names-2072"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/iupac-names-2072
site: BCT Engineering
---

# IUPAC names of four complexes

Engineering Chemistry · Chapter 6: Coordination Complexes

- Asked in: 2072 Asoj, 2 marks
- Video: [Naming Coordination Compounds - Chemistry](https://www.youtube.com/watch?v=yeNtqjE0dJw) — The Organic Chemistry Tutor
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/iupac-names-2072
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-6

## Question

Name the following complexes by IUPAC system
i) [Cr(H₂O)₅Cl]Cl₂
ii) [Co(en)₃]Br₃
iii) K₂[NiCl₄]
iv) [Cr(C₆H₆)₂]

## Short answer

i) pentaaquachlorochromium(III) chloride, ii) tris(ethylenediamine)cobalt(III) bromide, iii) potassium tetrachloronickelate(II), iv) bis(benzene)chromium(0).

## Answer

i) [Cr(H₂O)₅Cl]Cl₂: **pentaaquachlorochromium(III) chloride**
ii) [Co(en)₃]Br₃: **tris(ethylenediamine)cobalt(III) bromide**
iii) K₂[NiCl₄]: **potassium tetrachloronickelate(II)**
iv) [Cr(C₆H₆)₂]: **bis(benzene)chromium(0)**

Rules used: ligands are named in alphabetical order before the metal; anionic complexes end in "-ate"; the oxidation state is written in Roman numerals in brackets; for complex cations or neutral complexes the metal name is unchanged.

## Check yourself

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

1. In what order are ligands named in IUPAC names?
   A. alphabetically
   B. by charge
   C. by size
   D. random
   Answer: A. The correct option is: alphabetically. This follows from the answer on alphabetical. (Key point: Alphabetical)

2. What ending does the metal name take in an anionic complex?
   A. -ium
   B. -ate
   C. -ide
   D. -ous
   Answer: B. The correct option is: -ate. This follows from the answer on anionic. (Key point: Anionic)

3. What is the IUPAC name of [Co(en)3]Br3?
   A. tris(ethylenediamine)cobaltate(III) bromide
   B. tri-ethylenediaminecobalt(II) bromide
   C. tris(ethylenediamine)cobalt(III) bromide
   D. cobalt tris bromide
   Answer: C. The correct option is: tris(ethylenediamine)cobalt(III) bromide. This follows from the answer on name. (Key point: Name)

4. What is the IUPAC name of [Cr(C6H6)2]?
   A. bis(benzene)chromium(II)
   B. dibenzenechromate
   C. chromium dibenzene
   D. bis(benzene)chromium(0)
   Answer: D. The correct option is: bis(benzene)chromium(0). This follows from the answer on zero. (Key point: Zero)

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