ChemistryCBSE Class 12 · Coordination Compounds

IUPAC Nomenclature of Coordination Compounds

Updated 15 October 2026 · Fact-checked

To name a coordination compound, name the cation first and the anion second. Inside the complex, list ligands alphabetically with prefixes (di, tri; or bis, tris), then the metal with its oxidation state in Roman numerals. An anionic complex ends in -ate, such as ferrate or cobaltate: $K_3[Fe(CN)_6]$ is potassium hexacyanidoferrate(III).

In the name, the cation comes first, then ligands, then the metal, so the arrows cross: the formula writes the metal first, but the name writes it last.

Illustration drawn for QuestionBuddy.

Understand IUPAC Nomenclature of Coordination Compounds

A systematic name lets anyone write the exact formula and structure of a complex. CBSE follows the IUPAC rules used in the NCERT textbook.

Writing formulas. (1) The central atom is written first. (2) The ligands follow in alphabetical order; a ligand's charge does not affect its place. (3) Polydentate ligands are also placed alphabetically, using their abbreviation. (4) The whole complex entity, charged or neutral, is enclosed in square brackets; polyatomic ligands go in parentheses. (5) There is no space between the ligands and the metal inside the bracket. (6) If the complex is charged, the charge is shown outside the bracket as a superscript, and counter-ions are written outside.

Naming: the rules.
1. In an ionic compound, the cation is named first, then the anion, whether or not the complex is the cation.
2. Ligands are named before the metal, in alphabetical order.
3. Ligand names. Neutral ligands keep their normal names, except $H_{2} O$ (aqua), $N H_{3}$ (ammine, double m), CO (carbonyl) and NO (nitrosyl). Anionic ligands end in -o: $C l^{-}$ chlorido, $C N^{-}$ cyanido, $O H^{-}$ hydroxido, $C_{2} O_{4}^{2 -}$ oxalato, $N O_{2}^{-}$ bound through N is nitrito-N, through O is nitrito-O; $S C N^{-}$ through S is thiocyanato-S, through N thiocyanato-N. Positive ligands end in -ium. The ethane-1,2-diamine ligand is abbreviated en.
4. Prefixes. Use di, tri, tetra, penta, hexa to show how many of each simple ligand. If the ligand name already contains a number (ethane-1,2-diamine) or is complicated, use bis, tris, tetrakis and put the ligand name in brackets: tris(ethane-1,2-diamine).
5. Oxidation state of the metal is given in Roman numerals in parentheses right after the metal's name, with no space.
6. Anionic complexes end in -ate. For some metals the Latin root is used: iron → ferrate, copper → cuprate, silver → argentate, gold → aurate, lead → plumbate, tin → stannate. Cobalt → cobaltate, nickel → nickelate, platinum → platinate. Cationic and neutral complexes use the ordinary metal name.
7. A neutral complex is named like a complex cation, with no counter-ion.

Alphabetical order uses the ligand name, not the prefix: in $[C o (N H_{3})_{4} (H_{2} O) C l] C l_{2}$ , 'ammine', 'aqua', 'chlorido' give tetraammineaquachloridocobalt(III) chloride.

Finding the oxidation state. Charge of complex = oxidation state of metal + sum of ligand charges. The complex's charge comes from the counter-ions. In $[C o (e n)_{3}]_{2} (S O_{4})_{3}$ , three sulphates ( $- 6$ ) balance two complex ions, so each is +3; en is neutral, so Co is +3.

Worked names. $[C r (N H_{3})_{3} (H_{2} O)_{3}] C l_{3}$ : triamminetriaquachromium(III) chloride. $[C o (e n)_{3}]_{2} (S O_{4})_{3}$ : tris(ethane-1,2-diamine)cobalt(III) sulphate. $[A g (N H_{3})_{2}] [A g (C N)_{2}]$ : diamminesilver(I) dicyanidoargentate(I). $[P t (N H_{3})_{2} C l (N H_{2} C H_{3})] C l$ : diamminechlorido(methanamine)platinum(II) chloride.

IUPAC Nomenclature of Coordination Compounds: formulas and key facts

Order in a name: $cation \to anion; inside: ligands (A-Z) \to metal (oxidation state)$; Prefixes (di, tri, bis) are ignored for alphabetical order.
Oxidation state of metal: $x = charge of complex - \sum (ligand charges)$; Complex charge comes from the counter-ions.
Neutral ligand names: $H_{2} O aqua, N H_{3} ammine, C O carbonyl, N O nitrosyl, e n ethane-1,2-diamine$; Ammine has double m (only for $N H_{3}$ ).
Anionic ligand names: $C l^{-} chlorido, C N^{-} cyanido, O H^{-} hydroxido, C_{2} O_{4}^{2 -} oxalato, N O_{2}^{-} nitrito-N or nitrito-O$; Ambidentate ligands state the donor atom.
-ate names with Latin roots: $F e \to ferrate, C u \to cuprate, A g \to argentate, A u \to aurate, P b \to plumbate, S n \to stannate$; Only for anionic complexes.

How to solve IUPAC Nomenclature of Coordination Compounds questions

Two question types: give the IUPAC name of a formula, or write the formula from a name. Work in the same fixed order every time.

1Split the compound into cation and anion; find which part is the complex (inside square brackets).
2Find the charge on the complex from the counter-ions, then the metal's oxidation state from the ligand charges.
3Name each ligand (aqua, ammine, chlorido, cyanido …) and count it; choose di/tri or bis/tris.
4Arrange the ligand names alphabetically (ignore multiplying prefixes) and join them without spaces.
5Add the metal: normal name for cationic or neutral complexes, -ate (Latin root where needed) for anionic ones; then the oxidation state in Roman numerals.
6Write the full name: cation first, then anion, with one space between them.
7For formulas from names, reverse the process: metal symbol first, ligands in alphabetical order, square brackets, then enough counter-ions to make the compound neutral.

IUPAC Nomenclature of Coordination Compounds in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Reading a systematic name on a medicine

Suppose a pharmacy student sees the anticancer drug cisplatin listed in a reference book only by its formula, $c i s$ - $[P t (N H_{3})_{2} C l_{2}]$ , and needs to write its IUPAC name and describe the metal centre for a project.

Give the IUPAC name, the oxidation state and coordination number of platinum, and state whether the complex is a cation, an anion or neutral.

Try it first, then show the solutionSolution

Ligands: two $N H_{3}$ (ammine, neutral) and two $C l^{-}$ (chlorido, −1 each).
Complex charge is 0 (no counter-ion), so $x + 2 (0) + 2 (- 1) = 0$ , $x = + 2$ .
Four donor atoms are attached: coordination number 4.
Alphabetical order: ammine, chlorido. Name: diamminedichloridoplatinum(II); prefix cis- describes the geometry.

Answer: cis-Diamminedichloridoplatinum(II); Pt is +2 with coordination number 4; a neutral complex.

Memory hook: The name is a recipe: ligands A to Z, then the metal and its charge in Roman numerals.

Tricks to remember IUPAC Nomenclature of Coordination Compounds

Short memory aids. Say each one aloud once, then use it on a question the same day.

Cation first, always
Like a person's name: first name (cation), then surname (anion), whether or not the complex is first.
Use it when: Ordering the two parts of a name.
Anion? Add -ate
If the complex is negative, the metal name gets -ate: 'Fe goes Ferrate, Cu goes Cuprate, Ag goes Argentate, Au goes Aurate'.
Use it when: Anionic complexes.
A before C before N
Ammine, aqua, carbonyl, chlorido, cyanido, hydroxido, nitrito, oxalato: say them in dictionary order, ignoring di/tri/bis.
Use it when: Getting the ligand order right.

IUPAC Nomenclature of Coordination Compounds: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Name of a familiar salt · 1 mark · MCQBoard level

The IUPAC name of $K_{3} [F e (C N)_{6}]$ is:
(a) potassium hexacyanoiron(III)
(b) potassium hexacyanidoferrate(III)
(c) potassium hexacyanidoferrate(II)
(d) tripotassium hexacyanidoiron(III)

Try it first, then show the solutionSolution

The complex $[F e (C N)_{6}]^{3 -}$ is an anion, so iron becomes ferrate.
$x + 6 (- 1) = - 3$ , so Fe is +3. The number of $K^{+}$ is not stated in the name.

Answer: (b) potassium hexacyanidoferrate(III).

Example 2: Two names · 2 marks · Very short answerBoard level

Write the IUPAC names of (a) $[C o (N H_{3})_{5} C l] C l_{2}$ and (b) $[P t (N H_{3})_{2} C l_{2}]$ .

Try it first, then show the solutionSolution

(a) Complex charge +2 (two $C l^{-}$ outside); $x + 0 - 1 = + 2$ , so Co is +3. Ligands: ammine (5), chlorido (1). Name: pentaamminechloridocobalt(III) chloride (1 mark).
(b) Neutral complex; $x + 0 + 2 (- 1) = 0$ , Pt is +2. Name: diamminedichloridoplatinum(II) (1 mark).

Answer: (a) Pentaamminechloridocobalt(III) chloride. (b) Diamminedichloridoplatinum(II).

Example 3: Formulas from names · 3 marks · Short answerHarder board level

Write the formulas of: (a) pentaammineaquacobalt(III) chloride, (b) sodium hexanitrito-N-cobaltate(III), (c) hexaamminecobalt(III) sulphate.

Try it first, then show the solutionSolution

(a) Co(III) with 5 $N H_{3}$ and 1 $H_{2} O$ (all neutral): complex is +3, so 3 $C l^{-}$ : $[C o (H_{2} O) (N H_{3})_{5}] C l_{3}$ (also written $[C o (N H_{3})_{5} (H_{2} O)] C l_{3}$ ) (1 mark).
(b) Co(III) with 6 $N O_{2}^{-}$ bonded through N: complex charge $3 - 6 = - 3$ , so 3 $N a^{+}$ : $N a_{3} [C o (N O_{2})_{6}]$ (1 mark).
(c) $[C o (N H_{3})_{6}]^{3 +}$ and $S O_{4}^{2 -}$ : lowest common multiple of 3 and 2 is 6, so $[C o (N H_{3})_{6}]_{2} (S O_{4})_{3}$ (1 mark).

Answer: (a) $[C o (H_{2} O) (N H_{3})_{5}] C l_{3}$ . (b) $N a_{3} [C o (N O_{2})_{6}]$ . (c) $[C o (N H_{3})_{6}]_{2} (S O_{4})_{3}$ .

Example 4: Oxidation state, coordination number and name · 3 marks · Short answerHarder board level

For each compound give the oxidation state and coordination number of the metal and the IUPAC name: (a) $[C o (e n)_{3}]_{2} (S O_{4})_{3}$ (b) $K_{2} [P tC l_{6}]$ (c) $[N i (C O)_{4}]$ .

Try it first, then show the solutionSolution

(a) Each complex ion is +3; en neutral; Co +3; en is didentate, so CN $= 3 \times 2 = 6$ . Tris(ethane-1,2-diamine)cobalt(III) sulphate (1 mark).
(b) Complex −2; $x - 6 = - 2$ , Pt +4; CN 6. Potassium hexachloridoplatinate(IV) (1 mark).
(c) CO neutral; Ni 0; CN 4. Tetracarbonylnickel(0) (1 mark).

Answer: (a) +3, 6, tris(ethane-1,2-diamine)cobalt(III) sulphate. (b) +4, 6, potassium hexachloridoplatinate(IV). (c) 0, 4, tetracarbonylnickel(0).

Example 5: From a precipitation test to a name · 3 marks · Short answerHOTS / competency

One mole of a cobalt complex with empirical formula $C o C l_{3} \cdot 4 N H_{3}$ gives one mole of AgCl when treated with excess $A g N O_{3}$ solution. (a) Write its structural formula and IUPAC name. (b) What is the secondary valence of cobalt? (c) How many geometrical isomers can the complex ion have?

Try it first, then show the solutionSolution

(a) Only one $C l^{-}$ is outside the coordination sphere (precipitated as AgCl); the other two are ligands. Formula $[C o (N H_{3})_{4} C l_{2}] C l$ ; name tetraamminedichloridocobalt(III) chloride (1½ marks).
(b) Secondary valence = coordination number = 4 + 2 = 6 (½ mark).
(c) An octahedral $[M A_{4} B_{2}]$ ion has two geometrical isomers: cis (the two Cl adjacent) and trans (opposite) (1 mark).

Answer: (a) $[C o (N H_{3})_{4} C l_{2}] C l$ , tetraamminedichloridocobalt(III) chloride. (b) 6. (c) Two (cis and trans).

Where students lose marks in IUPAC Nomenclature of Coordination Compounds

The slips examiners see most often, and what to write instead.

Mistake: Ordering ligands by prefix or by charge
Wrong working
dichloridotetraamminecobalt(III)
Right working
tetraamminedichloridocobalt(III)
Do this: Alphabetise by the ligand name only: a (ammine) before c (chlorido).
Usually costs: Full mark for the name.
Mistake: Forgetting -ate for an anionic complex
Wrong working
potassium tetracyanidonickel(II)
Right working
potassium tetracyanidonickelate(II)
Do this: Check the sign of the complex before naming the metal.
Usually costs: 1 mark.
Mistake: Wrong oxidation state from ignoring counter-ions
Do this: Work out the complex's charge from the ions outside the bracket first, then subtract ligand charges.
Usually costs: ½ to 1 mark.
Mistake: Spelling 'amine' for $N H_{3}$
Wrong working
tetraaminecopper(II)
Right working
tetraamminecopper(II)
Do this: Ammine (double m) is only for the $N H_{3}$ ligand; amine is an organic compound.
Usually costs: ½ mark in strict marking.

Exam tips

Write the oxidation state as a Roman numeral in brackets with no space: cobalt(III).
Use the NCERT ligand names: chlorido, cyanido, hydroxido, aqua, ammine.
Write one space only between the cation and anion names.
Use bis/tris with brackets for en and other polydentate or complex ligand names.
When asked for a formula, check that the total charge is zero.

Practice questions on IUPAC Nomenclature of Coordination Compounds

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
In IUPAC names, the ligand $C l^{-}$ is called:
(a) chloro (b) chlorine (c) chlorido (d) chloride
Hint
Anionic ligand names end in -o.
Answer
(c) chlorido.
Q2 · 2 marks · Very short answerBoard level
Write the IUPAC names of (a) $[C u (N H_{3})_{4}] S O_{4}$ and (b) $[F e (H_{2} O)_{6}] C l_{2}$ .
Hint
Both complexes are cations.
Answer
(a) Tetraamminecopper(II) sulphate. (b) Hexaaquairon(II) chloride.
Q3 · 2 marks · Very short answerHarder board level
Write the formulas of (a) diamminesilver(I) dicyanidoargentate(I) and (b) sodium trioxalatocobaltate(III).
Hint
Oxalate is $C_{2} O_{4}^{2 -}$ .
Answer
(a) $[A g (N H_{3})_{2}] [A g (C N)_{2}]$ . (b) $N a_{3} [C o (C_{2} O_{4})_{3}]$ (Co +3, three oxalates −6, complex −3).
Q4 · 1 mark · Assertion-reasonHarder board level
Assertion (A): The complex anion in $K_{4} [F e (C N)_{6}]$ is named hexacyanidoferrate(II).
Reason (R): When the complex is an anion, the metal's name ends in -ate, using the Latin root for some metals.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Ferrum is Latin for iron.
Answer
(a).
Q5 · 3 marks · Short answerHarder board level
Give the IUPAC names of (a) $[C o (N H_{3})_{4} (H_{2} O) C l] C l_{2}$ and (b) $[P t (N H_{3})_{4}] [P tC l_{4}]$ . Give the oxidation state of each metal.
Hint
In (b) both cation and anion are complexes.
Answer
(a) Tetraammineaquachloridocobalt(III) chloride; Co +3. (b) Tetraammineplatinum(II) tetrachloridoplatinate(II); Pt +2 in both.
Q6 · 2 marks · Very short answerHarder board level
Correct the following names and explain each error: (a) dichloridotetraammineplatinum(IV) ion for $[P t (N H_{3})_{4} C l_{2}]^{2 +}$ ; (b) potassium hexacyanoiron(III) for $K_{3} [F e (C N)_{6}]$ .
Hint
Alphabetical order; anionic complexes end in -ate.
Answer
(a) Tetraamminedichloridoplatinum(IV) ion: ligands must be alphabetical (ammine before chlorido), ignoring prefixes. (b) Potassium hexacyanidoferrate(III): $C N^{-}$ is cyanido, and the anionic complex takes -ate with the Latin root (ferrate).
Q7 · 3 marks · Short answerHOTS / competency
Three cobalt(III) complexes have empirical formulas $C o C l_{3} \cdot 6 N H_{3}$ , $C o C l_{3} \cdot 5 N H_{3}$ and $C o C l_{3} \cdot 4 N H_{3}$ . With excess $A g N O_{3}$ , one mole of each gives 3, 2 and 1 mol of AgCl respectively. Write the formula and IUPAC name of each, and the number of ions each gives in solution.
Hint
Precipitated chloride lies outside the brackets.
Answer
$[C o (N H_{3})_{6}] C l_{3}$ : hexaamminecobalt(III) chloride, 4 ions. $[C o (N H_{3})_{5} C l] C l_{2}$ : pentaamminechloridocobalt(III) chloride, 3 ions. $[C o (N H_{3})_{4} C l_{2}] C l$ : tetraamminedichloridocobalt(III) chloride, 2 ions.
Q8 · 4 marks · Case-basedHOTS / competency
Read and answer.
Suppose a lab assistant finds four old bottles labelled only with formulas: (P) $[C r (N H_{3})_{3} (H_{2} O)_{3}] C l_{3}$ , (Q) $[F e (C O)_{5}]$ , (R) $[C o (N H_{3})_{5} (O N O)] C l_{2}$ and (S) $K_{2} [N i (C N)_{4}]$ . She must relabel them with IUPAC names.
(a) Name P and Q. (2 marks)
(b) Name R, showing how the donor atom of the nitrite ligand is indicated. (1 mark)
(c) Give the oxidation state of the metal in Q and S. (1 mark)
Hint
ONO means bonding through oxygen.
Answer
(a) P: triamminetriaquachromium(III) chloride. Q: pentacarbonyliron(0). (b) R: pentaamminenitrito-O-cobalt(III) chloride (bonding through O). (c) Q: Fe 0; S: Ni +2.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Name of the $H_{2} O$ ligand?Show answer
Aqua.
2.Latin -ate name for silver?Show answer
Argentate.
3.IUPAC name of $[N i (C O)_{4}]$ ?Show answer
Tetracarbonylnickel(0).
4.Which is named first in an ionic complex compound?Show answer
The cation.
5.Prefix used for three en ligands?Show answer
Tris, as in tris(ethane-1,2-diamine).
6.Oxidation state of Co in $[C o (N H_{3})_{5} C l] C l_{2}$ ?Show answer
+3.

IUPAC Nomenclature of Coordination Compounds: frequently asked questions

How do I name a coordination compound in Class 12?

Name the cation first, then the anion. Within the complex, name ligands alphabetically with numerical prefixes, then the metal (with -ate if the complex is an anion) and its oxidation state in Roman numerals.

Why is iron called ferrate in some names?

When the complex is an anion, the metal takes the -ate ending, and for iron the Latin root 'ferr-' is used, giving ferrate.

Is it chloro or chlorido?

The current IUPAC name used in NCERT is chlorido; similarly cyanido and hydroxido.

Do prefixes like di and tetra count for alphabetical order?

No. Ligands are ordered by their names alone; tetraammine comes before dichlorido because 'ammine' precedes 'chlorido'.

How is the donor atom of an ambidentate ligand shown?

By adding the donor atom's symbol after the ligand name: nitrito-N for M–NO₂ and nitrito-O for M–ONO.