Coordination Compounds Class 12 Notes for IIT JEE & NEET
eSaral Academic and Editorial Team
Summary
Coordination Compounds Class 12 notes cover Werner’s theory, ligands and coordination number, IUPAC nomenclature, isomerism, valence bond theory (VBT), crystal field theory (CFT), colour, magnetic properties and the importance of coordination compounds. This page gives corrected tables, solved examples and handwritten notes for CBSE boards, JEE Main and NEET.
Coordination Compounds is one of the most concept-based chapters of Class 12 Chemistry. In the current NCERT book, it is Unit 5 of 10. Older books number it Chapter 9. These Coordination Compounds Class 12 notes follow the chapter in the same order as the textbook, from theory to bonding and applications.
Coordination Compounds Class 12 Notes: Chapter Overview and Syllabus
The chapter covers:
- Werner’s theory, ligands, coordination number and denticity
- IUPAC nomenclature of mononuclear coordination compounds
- Isomerism: structural and stereoisomerism
- Bonding: valence bond approach and the basic ideas of crystal field theory
- Colour and magnetic properties
- Importance of coordination compounds: qualitative analysis, extraction of metals, biological systems and medicine
The EAN (effective atomic number) rule and the 18-electron rule are not part of the NCERT chapter, the CBSE syllabus or the JEE Main syllabus, so treat them as extra reading. Check the latest syllabus of your exam.
Coordination Compounds Class 12 Notes
India's Best Exam Preparation for Class 12th - Download Now
India's Best Exam Preparation for Class 12th - Download Now
India's Best Exam Preparation for Class 12th - Download Now
India's Best Exam Preparation for Class 12th - Download Now
What Do Boards, JEE and NEET Ask from Coordination Compounds Class 12 Notes?
Exam | Typical focus |
|---|---|
CBSE boards | Werner’s theory, nomenclature, isomerism, VBT hybridisation, basic CFT, importance of complexes |
JEE Main | Nomenclature, isomerism, VBT and CFT (high and low spin, unpaired electrons), magnetic moment, colour |
JEE Advanced | Stereoisomerism, CFT splitting, spin states, structure-based reasoning |
NEET | Nomenclature, magnetic properties, hybridisation, and the biological role of complexes |
The number of questions varies each year, so check previous years’ papers.
Tip from the eSaral Chemistry team: Do not memorise names. Learn the naming rules, and apply the same steps every time. Practise both directions: name from formula, and formula from name.
Werner’s Theory in Coordination Compounds Class 12 Notes
Alfred Werner proposed the first systematic theory of coordination compounds in 1893, and he received the Nobel Prize in Chemistry in 1913.
Postulates of Werner’s Theory
- A metal in a coordination compound shows two types of valency: primary and secondary.
- Primary valency is ionisable and is satisfied by negative ions. It corresponds to the oxidation state of the metal.
- Secondary valency is non-ionisable and is satisfied by ligands (neutral molecules or negative ions) attached directly to the metal. It equals the coordination number.
- Secondary valencies are directional, so they give the complex its geometry, while primary valencies are non-directional.
Example: [Co(NH₃)₆]Cl₃
- Primary valency: 3 (satisfied by 3 Cl⁻ ions)
- Secondary valency, or coordination number: 6 (satisfied by 6 NH₃ molecules)
- Geometry: octahedral
Werner supported his theory by studying ionisation in solution. [Co(NH₃)₆]Cl₃ gives 4 ions (1 complex cation and 3 Cl⁻), while [Co(NH₃)₄Cl₂]Cl gives only 2 ions (1 complex cation and 1 Cl⁻). This shows which chloride ions are inside the coordination sphere.
Key Terms in Coordination Compounds Class 12 Notes: Ligands, Central Metal and Coordination Number
- Central metal atom or ion: the atom or ion at the centre that accepts electron pairs from the ligands, for example Fe²⁺, Co³⁺, Pt²⁺ and Cu²⁺.
- Coordination sphere: the central metal and its ligands, written in square brackets.
- Coordination number: the number of ligand donor atoms bonded to the central metal. Common values are 2 (linear), 4 (tetrahedral or square planar) and 6 (octahedral).
- Homoleptic complex: all ligands are the same, as in [Co(NH₃)₆]³⁺. Heteroleptic complex: different ligands, as in [Co(NH₃)₄Cl₂]⁺.
Types of Ligands
Ligand type | Number of donor atoms | Examples |
|---|---|---|
Monodentate | 1 | Cl⁻, NH₃, H₂O, CN⁻, CO |
Bidentate | 2 | en (ethane-1,2-diamine), oxalate (C₂O₄²⁻) |
Tridentate | 3 | dien (diethylenetriamine) |
Tetradentate | 4 | trien |
Hexadentate | 6 | EDTA |
Ambidentate | 1 (with two possible donor atoms) | SCN⁻ (through S or N), NO₂⁻ (through N or O) |
Chelate complexes form when a bidentate or polydentate ligand binds to the same metal and forms a ring. They are more stable than similar complexes with monodentate ligands (the chelate effect).
IUPAC Nomenclature in Coordination Compounds Class 12 Notes
Rules for Naming a Coordination Compound
- Name the cation first and the anion second.
- Inside the complex, name the ligands first in alphabetical order (ignoring the prefixes di, tri and so on), and then the central metal.
- Anionic ligands end in -o (chlorido, cyanido, hydroxido, oxalato). Neutral ligands keep their names, except H₂O (aqua), NH₃ (ammine), CO (carbonyl) and NO (nitrosyl).
- Use di, tri, tetra, penta and hexa for the number of simple ligands. Use bis, tris and tetrakis for complex ligands, such as ethane-1,2-diamine.
- Show the oxidation state of the metal in Roman numerals in brackets after its name.
- If the complex ion is an anion, the metal name ends in -ate (for example ferrate, cuprate, argentate and aurate).
Worked Examples
Formula | IUPAC name |
|---|---|
[Co(NH₃)₆]Cl₃ | Hexaamminecobalt(III) chloride |
K₄[Fe(CN)₆] | Potassium hexacyanidoferrate(II) |
[Pt(NH₃)₂Cl₂] | Diamminedichloridoplatinum(II) |
[CoCl₂(en)₂]Cl | Dichloridobis(ethane-1,2-diamine)cobalt(III) chloride |
[Cr(H₂O)₄Cl₂]Cl | Tetraaquadichloridochromium(III) chloride |
Tip: the most common error is the alphabetical order of ligands. The order is by the first letter of the ligand name: ammine, aqua, chlorido, en. So “ammine” comes before “aqua”, and “aqua” comes before “chlorido” and “en”.
Isomerism in Coordination Compounds Class 12 Notes
Structural Isomerism
Type | Description | Example |
|---|---|---|
Ionisation isomerism | Different ions inside and outside the coordination sphere | [Co(NH₃)₅Br]SO₄ and [Co(NH₃)₅SO₄]Br |
Hydrate (solvate) isomerism | Water inside or outside the coordination sphere | [Cr(H₂O)₆]Cl₃ and [Cr(H₂O)₅Cl]Cl₂·H₂O |
Linkage isomerism | An ambidentate ligand binds through a different atom | [Co(NH₃)₅NO₂]Cl₂ and [Co(NH₃)₅ONO]Cl₂ |
Coordination isomerism | Ligands are exchanged between the cationic and anionic complexes | [Co(NH₃)₆][Cr(CN)₆] and [Cr(NH₃)₆][Co(CN)₆] |
Stereoisomerism
- Geometrical isomerism (cis–trans): square planar MA₂B₂ complexes, such as [Pt(NH₃)₂Cl₂], and octahedral MA₄B₂ complexes have cis and trans forms. Octahedral MA₃B₃ complexes have facial (fac) and meridional (mer) forms. Tetrahedral complexes do not show geometrical isomerism.
- Optical isomerism: complexes with no plane of symmetry are optically active. [Co(en)₃]³⁺ and cis-[CoCl₂(en)₂]⁺ show optical isomerism (d and l forms), while the trans form of [CoCl₂(en)₂]⁺ does not.
Valence Bond Theory (VBT) in Coordination Compounds Class 12 Notes
VBT explains the geometry and magnetic behaviour of a complex through hybridisation of the metal orbitals.
Coordination number | Hybridisation | Geometry | Example |
|---|---|---|---|
2 | sp | Linear | [Ag(NH₃)₂]⁺ |
4 | sp³ | Tetrahedral | [NiCl₄]²⁻ |
4 | dsp² | Square planar | [Ni(CN)₄]²⁻ |
6 | sp³d² | Octahedral (outer orbital) | [CoF₆]³⁻ |
6 | d²sp³ | Octahedral (inner orbital) | [Co(NH₃)₆]³⁺ |
- Outer orbital complexes (sp³d²) use 4s, 4p and 4d orbitals. They are high spin and paramagnetic, and they form with weak field ligands.
- Inner orbital complexes (d²sp³) use 3d, 4s and 4p orbitals. They are low spin, and they form with strong field ligands.
Crystal Field Theory (CFT) in Coordination Compounds Class 12 Notes
CFT treats ligands as point charges, and it explains the splitting of the d orbitals when the ligands approach the metal.
Octahedral field: the d orbitals split into a lower-energy t₂g set (d_xy, d_xz, d_yz) and a higher-energy e_g set (d_z², d_x²−y²). The energy gap is Δ_o.
- Strong field ligands cause a large Δ_o, and electrons pair up in the t₂g orbitals (low spin).
- Weak field ligands cause a small Δ_o, and electrons occupy the e_g orbitals before they pair (high spin).
- For d⁴ to d⁷ ions, the complex is high spin if Δ_o is smaller than the pairing energy, and low spin if it is larger.
Spectrochemical series (partial, from weak to strong): I⁻ < Br⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O < NH₃ < en < CN⁻ < CO
Tetrahedral field: the splitting is Δ_t = (4/9) Δ_o, which is small, so tetrahedral complexes are almost always high spin.
Colour and Magnetic Properties in Coordination Compounds Class 12 Notes
Why Are Coordination Compounds Coloured?
The colour comes from d–d transitions. An electron absorbs visible light and moves from a t₂g orbital to an e_g orbital, and the colour we see is the complementary colour of the light absorbed. For example, [Ti(H₂O)₆]³⁺ absorbs in the blue-green region and appears violet. Complexes of d⁰ ions (such as Sc³⁺) and d¹⁰ ions (such as Zn²⁺) have no d–d transitions, so they are usually colourless. A strong colour can also come from charge transfer, as in KMnO₄ (Mn is d⁰).
Magnetic Properties
- Paramagnetic: unpaired electrons are present, and the complex is attracted by a magnetic field.
- Diamagnetic: all electrons are paired.
- Spin-only magnetic moment: μ = √[n(n + 2)] BM, where n is the number of unpaired electrons.
Unpaired electrons (n) | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
μ (BM) | 1.73 | 2.83 | 3.87 | 4.90 | 5.92 |
Complex | Metal ion | Spin state | Unpaired electrons |
|---|---|---|---|
[Co(NH₃)₆]³⁺ | Co³⁺ (d⁶) | Low spin | 0 |
[CoF₆]³⁻ | Co³⁺ (d⁶) | High spin | 4 |
[Fe(CN)₆]⁴⁻ | Fe²⁺ (d⁶) | Low spin | 0 |
[Fe(CN)₆]³⁻ | Fe³⁺ (d⁵) | Low spin | 1 |
[FeF₆]³⁻ | Fe³⁺ (d⁵) | High spin | 5 |
[Ni(CN)₄]²⁻ | Ni²⁺ (d⁸) | Square planar | 0 |
[NiCl₄]²⁻ | Ni²⁺ (d⁸) | Tetrahedral | 2 |
Importance and Applications in Coordination Compounds Class 12 Notes
Biological Importance
Complex | Metal | Role |
|---|---|---|
Haemoglobin | Fe²⁺ | Transports oxygen in the blood |
Chlorophyll | Mg²⁺ | Photosynthesis |
Vitamin B₁₂ (cyanocobalamin) | Co³⁺ | Needed for red blood cell formation |
Carbonic anhydrase | Zn²⁺ | Enzyme that helps to remove CO₂ |
Carbon monoxide is poisonous because it binds to the iron of haemoglobin more strongly than oxygen does, forming carboxyhaemoglobin.
Industrial and Medical Applications
- Cisplatin, cis-[Pt(NH₃)₂Cl₂], is an anticancer drug. The trans isomer is inactive.
- EDTA is used in the treatment of lead poisoning and in the titration of water hardness.
- Wilkinson’s catalyst, [RhCl(PPh₃)₃], is used in hydrogenation.
- Extraction of metals: silver and gold form the cyanide complexes [Ag(CN)₂]⁻ and [Au(CN)₂]⁻.
- Photography: sodium thiosulphate dissolves unexposed AgBr by forming a soluble complex.
- Qualitative analysis: the deep blue [Cu(NH₃)₄]²⁺ is a test for Cu²⁺, and dimethylglyoxime gives a red precipitate with Ni²⁺.
Important Facts in Coordination Compounds Class 12 Notes
Concept | Key point |
|---|---|
Werner’s primary valency | Equals the oxidation state of the metal |
Werner’s secondary valency | Equals the coordination number |
Chelate effect | Polydentate ligands form more stable complexes |
Strong field ligands | Large Δ_o, so low spin |
Weak field ligands | Small Δ_o, so high spin |
Tetrahedral vs octahedral splitting | Δ_t = (4/9) Δ_o |
Cisplatin | cis isomer is active and the trans isomer is inactive |
Colour | d⁰ and d¹⁰ complexes are usually colourless |
Magnetic moment | μ = √[n(n + 2)] BM |
Solved Examples from Coordination Compounds Class 12 Notes
These solved examples follow the rules in the Coordination Compounds Class 12 notes above.
Q1. Write the IUPAC name of [Co(NH₃)₄Cl₂]Cl.
Oxidation state of Co: x + 0 + 2(−1) = +1, so x = +3. Name: tetraamminedichloridocobalt(III) chloride.
Q2. Write the IUPAC name of K₃[Fe(CN)₆].
Name: potassium hexacyanidoferrate(III), because the complex ion is an anion and iron is Fe³⁺.
Q3. Write the formula of sodium tetrahydroxidozincate(II).
Zn²⁺ with four OH⁻ gives [Zn(OH)₄]²⁻, so two Na⁺ are needed. Formula: Na₂[Zn(OH)₄].
Q4. Find the number of unpaired electrons and the magnetic moment of [CoF₆]³⁻.
Co³⁺ is d⁶, and F⁻ is a weak field ligand, so the complex is high spin (t₂g⁴ e_g²) with 4 unpaired electrons. μ = √(4 × 6) = √24 ≈ 4.90 BM.
Q5. How many moles of AgCl are precipitated when excess AgNO₃ is added to one mole of [Co(NH₃)₅Cl]Cl₂?
Only the two Cl⁻ outside the coordination sphere are precipitated, so 2 moles of AgCl are formed.
Common Mistakes in Coordination Compounds Class 12 Notes Problems
Mistake | Correct approach |
|---|---|
Writing ligands in the wrong order in a name | Use alphabetical order by ligand name, ignoring di, tri and so on |
Using “di” for ethane-1,2-diamine | Use “bis” for ligands that already contain a numerical prefix or are complex |
Forgetting “-ate” for an anionic complex | Name the metal with “-ate”, as in ferrate, and show the oxidation state |
Mixing up strong field and Δ_o | Strong field means large Δ_o, which gives low spin |
Using the wrong formula for the magnetic moment | μ = √[n(n + 2)] BM, with n as the number of unpaired electrons |
Counting ions outside the coordination sphere wrongly | Only the species outside the brackets ionise in solution |
How to Study Coordination Compounds Class 12 Notes
- Read the NCERT chapter first, and learn the naming rules. You can download the book from the NCERT Class 12 books page.
- Learn the VBT table and the CFT rules together, and practise finding the number of unpaired electrons.
- Practise nomenclature in both directions every day for a week.
- Revise the chapter with eSaral’s Class 12 Chemistry notes, and then solve previous year questions.
Frequently Asked Questions
What are the most important topics in Coordination Compounds Class 12 notes for JEE Main?
In Coordination Compounds Class 12 notes, IUPAC nomenclature, isomerism (especially geometrical and optical), the VBT hybridisation table, CFT splitting and spin states, the spin-only magnetic moment and colour are the key topics. Practise finding the number of unpaired electrons for different complexes.
How many questions come from Coordination Compounds in NEET?
In Coordination Compounds Class 12 notes, the NEET focus is clear: NEET asks questions from this chapter, usually on nomenclature, hybridisation and magnetic properties, and on the biological role of complexes such as haemoglobin, chlorophyll and vitamin B₁₂. The count varies by year, so check previous years’ papers.
What is the difference between inner orbital and outer orbital complexes?
In Coordination Compounds Class 12 notes, inner orbital complexes use d²sp³ hybridisation (inner 3d orbitals), are low spin and are formed with strong field ligands, as in [Co(NH₃)₆]³⁺. Outer orbital complexes use sp³d² hybridisation (outer 4d orbitals), are high spin and paramagnetic, and are formed with weak field ligands, as in [CoF₆]³⁻.
What is the spectrochemical series, and why does it matter?
The spectrochemical series ranks ligands by the crystal field splitting they produce: I⁻ < Br⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O < NH₃ < en < CN⁻ < CO. Strong field ligands give a large Δ_o and low spin complexes with fewer unpaired electrons. JEE often asks whether a complex is high or low spin. This is covered in the Coordination Compounds Class 12 notes on eSaral.
Why are d⁰ and d¹⁰ complexes colourless?
Colour comes from d–d transitions. In a d⁰ ion there are no d electrons to excite, and in a d¹⁰ ion all the d orbitals are full, so no d–d transition is possible. Such complexes absorb no visible light and appear colourless, unless a charge-transfer transition gives colour, as in KMnO₄.
Which chapter number is Coordination Compounds in Class 12 Chemistry?
In the current NCERT Class 12 Chemistry book, it is Unit 5 of 10. Older books number it Chapter 9. These Coordination Compounds Class 12 notes use the current numbering, so follow the chapter name.
How do you write the IUPAC name of a coordination compound?
In Coordination Compounds Class 12 notes, name the cation first, then the anion. Inside the complex, list the ligands in alphabetical order, then the metal, and show the oxidation state in Roman numerals. Use “-ate” for an anionic complex, and use bis, tris and tetrakis for complex ligands. For example, K₄[Fe(CN)₆] is potassium hexacyanidoferrate(II).
How do you calculate the magnetic moment of a complex?
In Coordination Compounds Class 12 notes, find the number of unpaired electrons (n) from the spin state of the metal ion, and use μ = √[n(n + 2)] BM. For example, a complex with 4 unpaired electrons has μ = √24 ≈ 4.90 BM.
Where can I find more notes on Coordination Compounds on eSaral?
eSaral has Coordination Compounds Class 12 notes on this page, the NCERT book for Class 12 and the Class 12 Chemistry notes hub, all linked on this page.
Team eSaral
eSaral Academic and Editorial Team
Team eSaral is the collective author profile for educational content created by eSaral’s teachers and academic contributors. The team draws on expertise from IIT graduates, doctors, experienced educators and subject specialists to develop resources for JEE, NEET and school students. Our articles aim to explain concepts clearly and help students study with confidence.
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