Iupac Nomenclature Coordination

8 MCQs9-step worked example

Source: NCERT Coordination CompoundsPYQ coverage: NEET 2021, 2022, 2023, 2024, 2025Official key: NTA-verifiedLast reviewed: May 2026

Lesson

The naming trap in IUPAC nomenclature of coordination compounds is deceptively simple: you know the rules individually, but under exam pressure you scramble the order of ligands, botch a multiplicity prefix, or misassign the oxidation state. NEET exploits this — a wrong alphabetical sequence or a missing Roman numeral costs you 5 marks (−1 for the wrong pick plus +4 lost).

The IUPAC naming protocol (NCERT Class 12 Chemistry Chapter 5, page 8) follows a strict sequence:

Cation first, anion second — regardless of which is the complex ion.
Ligands before metal — within the coordination sphere, list ligands alphabetically by their IUPAC ligand name (not by the prefix).
Multiplicity prefixes — di-, tri-, tetra- for simple ligands; bis-, tris-, tetrakis- for ligands whose names already contain a prefix or are polydentate (e.g., bis(ethylenediamine), not diethylenediamine).
Anionic ligands end in -o — chlorido (Cl⁻), cyanido (CN⁻), hydroxido (OH⁻). Neutral ligands keep their name, except aqua (H₂O), ammine (NH₃), carbonyl (CO), nitrosyl (NO).
Metal name — in a cationic or neutral complex, use the English name; in an anionic complex, use the Latin-root name with the suffix -ate (ferrate, cuprate, argentate).
Oxidation state — Roman numeral in parentheses immediately after the metal name. No space.

Watch-out: Alphabetical order uses the ligand name stripped of its prefix. Ammine comes before chlorido because "a" < "c" — even if you write "dichlorido" and "tetraammine," the alphabetical comparison is ammine vs chlorido, not tetra vs di.

For anionic complexes, forgetting the -ate suffix or using the English metal name instead of the Latin root is a common confusion in NEET options.

Practice MCQs

Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.

MCQ 1Easy RecallPractice

In the IUPAC name of a coordination compound, ligands are listed in which order?

MCQ 2Easy RecallPractice

When a coordination compound is anionic, the metal in the name receives which treatment?

MCQ 3Easy RecallPractice

Which of the following ligands is named "ammine" (with double m) in IUPAC nomenclature?

MCQ 4Direct ApplicationPractice

The IUPAC name of [Co(NH₃)₄Cl₂]Cl is:

MCQ 5Direct ApplicationPractice

What is the IUPAC name of K₃[Fe(CN)₆]?

MCQ 6Direct ApplicationPractice

The complex [Cr(en)₂Cl₂]⁺ contains the bidentate ligand ethylenediamine (en). The correct multiplicity prefix for two en ligands in the IUPAC name is:

MCQ 7Concept TrapPractice

A student writes the IUPAC name of [Pt(NH₃)₂Cl(NO₂)] as "diamminechlorido**nitro**platinum(II)." Assuming the ligand is NO₂⁻ bonded through nitrogen, which part of the name is incorrect?

MCQ 8Concept TrapPractice

Two coordination compounds have the formulas [Co(NH₃)₅Br]SO₄ and [Co(NH₃)₅SO₄]Br. In their IUPAC names, which of the following correctly distinguishes them?

Worked Example

Pattern: IUPAC coordination compound naming (pattern P.CHE.U12.IUPAC_COORDINATION_NAMING, observed NEET 2022).

1
Given
- Formula: [CrCl₂(en)₂]Cl - en = ethylenediamine (bidentate, neutral ligand) - Complex ion: [CrCl₂(en)₂]⁺ (cationic, since Cl⁻ is counter ion)
2
Required
IUPAC name of the compound.
3
Concept
IUPAC naming rules for coordination compounds: cation named first, ligands alphabetically before metal, correct prefixes, oxidation state in Roman numerals, -ate suffix only for anionic complexes.
4
Identify components
- Ligands in coordination sphere: 2 Cl⁻ (anionic → chlorido) and 2 en (neutral, polydentate → ethylenediamine) - Counter ion: Cl⁻ (named as chloride) - Central metal: Cr
5
Apply naming rules
**Alphabetical order of ligands:** Compare "chlorido" (c) with "ethylenediamine" (e). c < e, so chlorido comes first. **Multiplicity prefixes:** - 2 × chlorido → dichlorido (simple ligand, use di-) - 2 × ethylenediamine → bis(ethylenediamine) (polydentate ligand whose name contains "di," so use bis- with parentheses) **Oxidation state of Cr:** Complex ion charge = +1. Two Cl⁻ inside contribute −2. Two en are neutral. So Cr + (−2) + 0 = +1 → Cr = +3. **Metal name:** Complex is cationic → use English name: chromium.
6
Assemble the name
Cation: dichloridob is(ethylenediamine)chromium(III) Counter ion: chloride Full name: **Dichloridobis(ethylenediamine)chromium(III) chloride**
7
Final answer
Dichloridobis(ethylenediamine)chromium(III) chloride
8
Common trap
The most frequent error is writing "diethylenediamine" instead of "bis(ethylenediamine)." Because the ligand name ethylenediamine contains the fragment "di," the prefix di- would create ambiguity (diethylenediamine could be misread as a single ligand named "diethylenediamine"). The bis- prefix with parentheses resolves this. A second trap: placing ethylenediamine before chlorido because "en" might be mentally shortened to "e." But alphabetical order uses the full ligand name — chlorido (c) comes before ethylenediamine (e).
9
Similar NEET-style question
Try naming [CoCl₂(en)₂]NO₃ — the logic is identical, but the counter ion changes to nitrate and the metal is cobalt(III). ---

Before solving, remember these

Key Fact

IUPAC nomenclature of coordination compounds

Order: cation first, anion second; ligands in alphabetical order before metal; use Greek prefixes (di, tri, tetra...) for ligand multiplicity; oxidation state in parentheses. Example: [Co(NH₃)₆]Cl₃ = hexaamminecobalt(III) chloride.

-- NCERT Class 12 Chemistry, Ch. 5, p. 8

Formulas

Crystal field splitting (octahedral vs tetrahedral)

Δ_{t} \approx \frac{4}{9} Δ_{o}

Tetrahedral splitting is smaller than octahedral due to fewer/farther ligands.

Symbol	Quantity	SI Unit
Delta_o	octahedral splitting	J or eV
Delta_t	tetrahedral splitting	J or eV

Valid when

Same metal and same ligand
Mostly high-spin tetrahedral due to small Δ_t

Magnetic moment of coordination complex

μ = n (n + 2) BM

Same spin-only formula but n depends on high-spin/low-spin from CFT.

Symbol	Quantity	SI Unit
n	unpaired electrons	-

Valid when

High vs low spin determined by Δ_o vs P
Octahedral (or tetrahedral with Δ_t)

Exam Traps & Common Mistakes

These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.

Trap

High-spin vs low-spin from ligand field

Category: Similar Terms

Student defaults to one spin state. Strong-field ligand (CN⁻, CO, NH₃ for some) → low-spin (Δ > P, electrons pair). Weak-field (F⁻, H₂O, Cl⁻) → high-spin.

When it triggers

Coordination compound with given ligand asking for magnetic moment, color, or spin state.

How to avoid

Memorise spectrochemical series: I⁻ < Br⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O < NH₃ < en < CN⁻ < CO. NH₃, CN⁻, CO usually strong-field. F⁻, H₂O, Cl⁻ usually weak-field.

Mistake

Defaults to high-spin (or low-spin) without checking ligand field strength.

Root cause: concept gap

Correction

Strong-field ligand (CN⁻, CO, NH₃ when applicable): Δ > P → low-spin. Weak-field (F⁻, Cl⁻, H₂O): Δ < P → high-spin. Use spectrochemical series.

Past Year Questions

11 questions from NEET 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.

NEET 2025

The correct order of the wavelength of light absorbed by the following complexes is, A. [Co(NH ) ]3+ B. [Co(CN) ]3– 3 6 6 C. [Cu(H O) ]2+ D. [Ti(H O) ]3+ 2 4 2 6 Choose the correct answer from the options given below:

1C < A < D < B

2B < D < A < C

3B < A < D < C

4C < D < A < B

NTA Answer: Option 3(final)

NEET 2025

Given below are two statements : Statement I : Ferromagnetism is considered as an extreme form of paramagnetism. Statement II : The number of unpaired electrons in a Cr2+ ion (Z = 24) is the same as that of a Nd3+ ion (Z = 60). In the light of the above statements, choose the correct answer from the options given below :

1Statement I is false but Statement II is true

2Both Statement I and Statement II are true

3Both Statement I and Statement II are false

4Statement I is true but Statement II is false

NTA Answer: Option 4(final)

NEET 2024Revised key

The reagents with which glucose does not react to give the corresponding tests/products are A. Tollen’s reagent B. Schiff’s reagent C. HCN D. NH OH 2 E. NaHSO 3 Choose the correct options from the given below:

1B and C

2A and D

3B and E

4E and D

NTA Answer: Option 3(revised_final)

NEET 2024Revised key

Given below are two statements : Statement I: Both [Co(NH ) ]3+ and [CoF ]3– complexes are octahedral but differ in their magnetic behaviour. 3 6 6 Statement II: [Co(NH ) ]3+ is diamagnetic whereas [CoF ]3– is paramagnetic. 3 6 6 In the light of the above statements, choose the correct answer from the options given below:

1Both Statement I and Statement II are true

2Both Statement I and Statement II are false

3Statement I is true but Statement II is false

4Statement I is false but Statement II is true

NTA Answer: Option 1(revised_final)

NEET 2023

Intermolecular forces are forces of attraction and repulsion between interacting particles that will include : A. dipole - dipole forces B. dipole - induced dipole forces C. hydrogen bonding D. covalent bonding E. dispersion forces Choose the most appropriate answer from the options given below :

1A, B, C, D are correct

2A, B, C, E are correct

3A, C, D, E are correct

4B, C, D, E are correct

NTA Answer: Option 2(final)

NEET 2023

Homoleptic complex from the following complexes is

1Diamminechloridonitrito-N-platinum (II)

2Pentaamminecarbonatocobalt (III) chloride

3Triamminetriaquachromium (III) chloride

4Potassium trioxalatoaluminate (III)

NTA Answer: Option 4(final)

NEET 2022

Identify the incorrect statement from the following.

1The shapes of d xy , d yz and d zx orbitals are similar to each other; and d x2−y2 and d z2 are similar to each other.

2All the five 5d orbitals are different in size when compared to the respective 4d orbitals.

3All the five 4d orbitals have shapes similar to the respective 3d orbitals.

4In an atom, all the five 3d orbitals are equal in energy in free state.

NTA Answer: Option 1(final)

NEET 2022

The IUPAC name of the complex- [Ag(H O) ][Ag(CN) ] is: 2 2 2

1diaquasilver(I) dicyanidoargentate(I)

2dicyanidosilver(II) diaquaargentate(II)

3diaquasilver(II) dicyanidoargentate(II)

4dicyanidosilver(I) diaquaargentate(I)

NTA Answer: Option 1(final)

NEET 2022

The order of energy absorbed which is responsible for the color of complexes (A) [Ni(H O) (en) ]2+ 2 2 2 (B) [Ni(H O) (en)]2+ and 2 4 (C) [Ni(en) ]2+ 3 is

1(B) > (A) > (C)

2(A) > (B) > (C)

3(C) > (B) > (A)

4(C) > (A) > (B)

NTA Answer: Option 4(final)

NEET 2021

What is the IUPAC name of the organic compound formed in the following chemical reaction? Acetone ⎯⎯(i)C⎯2H⎯5Mg⎯Br,⎯dry⎯Eth⎯er⎯→Product (ii)H2O,H+

12-methylbutan-2-ol

22-methylpropan-2-ol

3pentan-2-ol

4pentan-3-ol

NTA Answer: Option 1(final)

NEET 2021

Ethylene diaminetetraacetate (EDTA) ion is :

1Tridentate ligand with three "N" donor atoms

2Hexadentate ligand with four "O" and two "N" donor atoms

3Unidentate ligand

4Bidentate ligand with two "N" donor atoms

NTA Answer: Option 2(final)

How NEET usually asks this

Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.

Determine high-spin or low-spin from ligand field strength. Strong-field (CN, CO): low-spin. Weak-field (F, H2O): high-spin.

InterpretationMedium

Common distractors

forgets weak vs strong ligand

Default low-spin always

Apply IUPAC rules: ligands alphabetical, prefixes for multiplicity, oxidation state of metal.

RecallMedium

Common distractors

wrong order ligands

Uses non-alphabetical order

Identify primary and secondary valencies, coordination number from formula. Primary = ionizable ions; secondary = ligands.

InterpretationMedium

Common distractors

counts counter ions as ligands

Treats all attached species as ligands

Sources

NCERT refs: Class 12 Chemistry Chapter 5, p.8

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