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Co-Ordination Compounds – JEE Main Formula Sheet & Class 12 Notes | IUPAC Naming, VBT, CFT, Isomerism
This is the complete JEE Main Formula Sheet and Class 12 Formula Sheet for Co-Ordination Compounds — Chapter 22 from the Aakash Rapid Revision & Formula Bank. This chapter covers the foundational theory and applied chemistry of coordination compounds: Werner's theory, IUPAC nomenclature of coordination compounds, types of ligands, Valence Bond Theory (VBT) of coordination compounds including inner and outer orbital complexes, Crystal Field Theory (CFT) and crystal field splitting in coordination compounds, isomerism in coordination compounds (structural and stereo), the effective atomic number (EAN) rule, stability of coordination compounds, and the biological and industrial importance of coordination compounds. Co-Ordination Compounds consistently contributes 4–6 questions in JEE Main every year — covering IUPAC naming, hybridisation of central metal in coordination compounds, type of isomerism, and crystal field stabilisation energy (CFSE). Download the Free PDF below for all formulas, rules, naming conventions, and theory details of coordination compounds in one exam-ready reference.
Topics Covered in This Co-Ordination Compounds Formula Sheet
Co-Ordination Compounds JEE Main Formula Sheet PDF Preview
Scroll to explore all Co-Ordination Compounds formulas — JEE Main & Class 12 Formula Sheet for coordination compounds
Introduction: Why Co-Ordination Compounds Is a High-Value Chapter for JEE Main
Co-Ordination compounds — also written as coordination compounds or complex compounds — represent one of the most intellectually rich areas of inorganic chemistry in the Class 12 syllabus. For JEE Main, coordination compounds consistently deliver 4–6 questions per session, covering everything from IUPAC nomenclature of coordination compounds to crystal field theory, isomerism in coordination compounds, and hybridisation of the central metal atom. This makes the co-ordination compounds chapter one of the most reward-per-hour chapters in the entire JEE Main inorganic chemistry section.
What makes coordination compounds fascinating — and manageable — is that a small number of core rules governs a very wide range of question types. The IUPAC naming rules for coordination compounds, once learned systematically, handle every naming question regardless of how complex the compound appears. The spectrochemical series, once memorised, instantly classifies any ligand as strong-field or weak-field and predicts whether a complex is inner orbital (low-spin) or outer orbital (high-spin). Crystal field splitting in octahedral and tetrahedral coordination compounds follows a simple d-orbital energy level diagram that, when understood, answers CFSE questions and magnetic property questions in one step.
Download the Free PDF of the co-ordination compounds formula sheet to access all IUPAC naming rules, ligand types, hybridisation tables, CFT diagrams, and isomerism examples in one structured JEE Main revision reference.
Overview of the Co-Ordination Compounds Chapter
The co-ordination compounds chapter builds from simple definitions toward progressively more theory-intensive content. It starts with Werner's theory of coordination compounds — the historical foundation that first explained why CoCl₃·6NH₃ does not behave like three separate ions in solution. It then covers the vocabulary of coordination chemistry: central metal, ligand, coordination number, coordination sphere. From there it moves to IUPAC nomenclature of coordination compounds — a rule-based system that every JEE Main student must master — and then to two major bonding theories: Valence Bond Theory (VBT) and Crystal Field Theory (CFT). The chapter closes with isomerism in coordination compounds, stability of complexes, and applications.
Each section builds on the previous one. Understanding coordination number is necessary for applying IUPAC naming rules. Understanding ligand field strength (spectrochemical series) is necessary for applying VBT and CFT correctly. Understanding geometry is necessary for predicting isomerism. This sequential logic means that investing in understanding the early definitions pays dividends across all later sections. Download the Free PDF of coordination compounds notes for a complete sequential summary.
Key Concepts in Co-Ordination Compounds
Werner's Theory of Coordination Compounds — Primary and Secondary Valence
Why Werner's Theory of Coordination Compounds Is the Starting Point for JEE Main
Alfred Werner (Nobel Prize, 1913) proposed the first systematic theory to explain the structure and bonding of coordination compounds. Before Werner's theory, the behaviour of compounds like CoCl₃·6NH₃ was mysterious — they did not lose their ammonia on heating and conductivity measurements showed fewer ions than expected for simple salts. Werner's theory of coordination compounds resolved all these puzzles.
Werner's postulates for coordination compounds: Every metal in a coordination compound has two types of valence — primary valence (ionisable valence, corresponds to the oxidation state of the metal — satisfied by anions that ionise in solution) and secondary valence (non-ionisable, directional valence, corresponds to coordination number — satisfied by ligands that coordinate directly to the metal and do not ionise). In coordination compounds, the secondary valence is always satisfied by ligands pointing in fixed spatial directions around the metal — giving coordination compounds their characteristic geometry. Example: In [Co(NH₃)₆]Cl₃ (hexamminecobalt(III) chloride), Co has primary valence = 3 (satisfied by 3 Cl⁻ ions outside the coordination sphere) and secondary valence = 6 (satisfied by 6 NH₃ molecules inside the coordination sphere). Only 3 Cl⁻ ions are free in solution — conductivity confirms this. Werner's theory of coordination compounds correctly predicted that compounds with the same formula but different structures should have different conductivities and different numbers of ions in solution — this was later confirmed experimentally.
Ligands in Coordination Compounds — Types, Names, and Classification
Why Ligand Classification Is Essential for IUPAC Naming and JEE Main Questions on Coordination Compounds
A ligand in a coordination compound is any atom, ion, or molecule that donates a lone pair of electrons to the central metal atom or ion to form a coordinate bond. Ligands in coordination compounds are classified by the number of donor atoms (teeth) they use to bond to the metal — this is called denticity.
Monodentate ligands (coordination compounds): bond through only one donor atom. Examples — NH₃ (ammine), H₂O (aqua), CO (carbonyl), NO (nitrosyl), CN⁻ (cyano), Cl⁻ (chlorido), Br⁻ (bromido), F⁻ (fluorido), I⁻ (iodido), OH⁻ (hydroxido), NO₂⁻ (nitrito-N or nitrito-O), SCN⁻ (thiocyanato-S or thiocyanato-N). Bidentate ligands in coordination compounds: bond through two donor atoms simultaneously. Examples — en (ethylenediamine, H₂N–CH₂–CH₂–NH₂, two N donors), ox²⁻ (oxalate, C₂O₄²⁻, two O donors), acac⁻ (acetylacetonate, two O donors), gly⁻ (glycinate, one N + one O). Polydentate ligands in coordination compounds: bond through three or more donor atoms. Examples — EDTA⁴⁻ (ethylenediaminetetraacetate — hexadentate, 2N + 4O donors, forms very stable chelate complexes with most metal ions), DIEN (diethylenetriamine — tridentate, 3N), TRIEN (triethylenetetramine — tetradentate). Ambidentate ligands in coordination compounds: have two different possible donor atoms but coordinate through only one at a time. Examples — CN⁻ (can bind through C: isocyano, or through N: cyano), NO₂⁻ (nitrito-N: nitro complex; nitrito-O: nitrito complex), SCN⁻ (thiocyanato-S or thiocyanato-N). Ambidentate ligands are involved in linkage isomerism in coordination compounds. Download the Free PDF for the complete ligand classification table for coordination compounds.
IUPAC Nomenclature of Coordination Compounds — Complete Rules for JEE Main
Why IUPAC Naming of Coordination Compounds Is One of the Highest-Tested Skills in JEE Main
The IUPAC nomenclature of coordination compounds follows a systematic set of rules. Mastering these naming rules for coordination compounds is one of the most reliable ways to secure marks in JEE Main — naming questions appear every year and follow the same rule sequence every time.
IUPAC naming rules for coordination compounds — step by step:
Rule 1 — Cation before anion: Name the cation (positive ion) before the anion — same as for all ionic compounds. If the complex is the cation, name it first. If the complex is the anion, name the simple cation first.
Rule 2 — Inside the coordination sphere, name ligands before the metal: Name all ligands first (alphabetically, ignoring multiplying prefixes like di-, tri-), then name the central metal atom.
Rule 3 — Ligand names in IUPAC nomenclature of coordination compounds: Anionic ligands: change the -ide ending to -ido (Cl⁻ = chlorido, Br⁻ = bromido, F⁻ = fluorido, CN⁻ = cyanido, OH⁻ = hydroxido, O²⁻ = oxido, SO₄²⁻ = sulphato, NO₂⁻ bonded through N = nitro, through O = nitrito, SCN⁻ through S = thiocyanato, through N = isothiocyanato). Neutral ligands use their molecule names with special cases: H₂O = aqua, NH₃ = ammine, CO = carbonyl, NO = nitrosyl, NO⁺ = nitrosonium, C₂H₄ = ethylene. Cationic ligands: add the suffix -ium (e.g., hydrazinium N₂H₅⁺).
Rule 4 — Multiplying prefixes: Use di-, tri-, tetra-, penta-, hexa- for simple ligands. Use bis-, tris-, tetrakis-, pentakis-, hexakis- for ligands whose names already contain a multiplying prefix (e.g., bis(ethylenediamine) not diethylenediamine, to avoid ambiguity).
Rule 5 — Metal name for coordination compounds: For cationic or neutral coordination compounds, use the English name of the metal followed by the oxidation state in Roman numerals in parentheses: e.g., cobalt(III), iron(II), copper(II). For anionic coordination compounds (complex anion), add the suffix -ate to the metal name (often using the Latin root): ferrate (Fe), cuprate (Cu), argentate (Ag), aurate (Au), plumbate (Pb), stannate (Sn), chromate (Cr), manganate (Mn), cobaltate (Co), nickelate (Ni), zincate (Zn), platinate (Pt).
IUPAC naming examples for coordination compounds: [Co(NH₃)₆]Cl₃ = hexaamminecobalt(III) chloride. [Co(NH₃)₅Cl]Cl₂ = pentaamminechloridocobalt(III) chloride. [Fe(CN)₆]⁴⁻ = hexacyanidoferrate(II) ion. [Pt(NH₃)₂Cl₂] = diamminedichloridoplatinum(II). [CoCl₂(en)₂]⁺ = dichloridobis(ethylenediamine)cobalt(III) ion. K₄[Fe(CN)₆] = potassium hexacyanidoferrate(II). [Cr(H₂O)₄Cl₂]Cl = tetraaquadichloridochromium(III) chloride. Na₂[PtCl₄] = sodium tetrachloridoplatinate(II). Download the Free PDF for the complete IUPAC naming table for coordination compounds with 20+ worked examples.
Valence Bond Theory (VBT) of Coordination Compounds — Inner and Outer Orbital Complexes
Why VBT Hybridisation of Coordination Compounds Is a Core JEE Main Question Type
Valence Bond Theory (VBT) of coordination compounds explains bonding in coordination compounds in terms of hybridisation and overlap. The central metal atom or ion provides empty hybrid orbitals (formed by combining atomic orbitals) that accept lone pairs from ligands to form coordinate bonds. The type of hybridisation determines the geometry and magnetic properties of the coordination compound.
Common hybridisations in coordination compounds: Coordination number 2 → sp hybridisation → linear geometry (e.g., [Ag(NH₃)₂]⁺, [AuCl₂]⁻). Coordination number 4 → sp³ → tetrahedral (e.g., [NiCl₄]²⁻, [CoCl₄]²⁻), OR → dsp² → square planar (e.g., [Ni(CN)₄]²⁻, [PdCl₄]²⁻, [Pt(NH₃)₂Cl₂]). Coordination number 6 → d²sp³ → octahedral inner orbital complex (e.g., [Co(NH₃)₆]³⁺, [Fe(CN)₆]⁴⁻), OR → sp³d² → octahedral outer orbital complex (e.g., [CoF₆]³⁻, [Fe(H₂O)₆]³⁺).
Inner orbital vs outer orbital complexes in VBT of coordination compounds: When the inner d-orbitals (of the (n-1)d type — e.g., 3d for first series) are used in hybridisation, the complex is an inner orbital complex (uses d²sp³ hybridisation — 3d + 4s + 4p). Inner orbital complexes form with strong-field ligands (CN⁻, CO, NO⁺, en, NH₃) that force electron pairing in d-orbitals, giving fewer unpaired electrons → low-spin, diamagnetic or weakly paramagnetic. When the outer d-orbitals (of the nd type — e.g., 4d for first series) are used, the complex is an outer orbital complex (uses sp³d² hybridisation — 4s + 4p + 4d). Outer orbital complexes form with weak-field ligands (F⁻, Cl⁻, Br⁻, I⁻, H₂O, OH⁻) that do not force pairing → high-spin, strongly paramagnetic.
Key examples in coordination compounds VBT: [Fe(CN)₆]⁴⁻ — Fe²⁺ = 3d⁶; CN⁻ is strong-field → forces pairing → 3d⁶ → 0 unpaired → d²sp³ → diamagnetic inner orbital complex. [Fe(H₂O)₆]²⁺ — Fe²⁺ = 3d⁶; H₂O is weak-field → no forced pairing → 3d⁶ maintains 4 unpaired → sp³d² → paramagnetic outer orbital complex. [Ni(CN)₄]²⁻ — Ni²⁺ = 3d⁸ → strong CN⁻ forces pairing → 3d⁸ → 0 unpaired in a pair forced → dsp² → square planar, diamagnetic. [NiCl₄]²⁻ — Ni²⁺ = 3d⁸; Cl⁻ weak field → sp³ → tetrahedral, 2 unpaired, paramagnetic. Download the Free PDF for the complete VBT hybridisation table for coordination compounds.
Crystal Field Theory (CFT) of Coordination Compounds — Octahedral and Tetrahedral Splitting
Why Crystal Field Theory Is the Most Conceptual JEE Main Section in Coordination Compounds
Crystal Field Theory (CFT) of coordination compounds treats the interaction between ligands and the central metal as purely electrostatic — ligands are treated as point charges or point dipoles that create an electric field (crystal field) around the metal. This crystal field breaks the degeneracy of the five d-orbitals into groups of different energies — a phenomenon called crystal field splitting in coordination compounds.
Crystal field splitting in octahedral coordination compounds: In an octahedral complex, six ligands approach along the ±x, ±y, and ±z axes. The d-orbitals that point directly toward the ligands along these axes (dx²−y² and dz²) are destabilised — they experience maximum repulsion from the negatively charged ligands. The other three d-orbitals (dxy, dxz, dyz) that point between the axes are stabilised — they experience less repulsion. The result is that the five d-orbitals split into two sets: the eg set (dx²−y² and dz², at higher energy, destabilised by +0.6Δo or +6Dq) and the t₂g set (dxy, dxz, dyz, at lower energy, stabilised by –0.4Δo or –4Dq). The energy gap between t₂g and eg is called the crystal field splitting energy Δo (or 10Dq) for octahedral coordination compounds. The centre of gravity of the five d-orbitals is maintained (the weighted average energy is the same as before splitting). Crystal Field Stabilisation Energy (CFSE) in octahedral coordination compounds = (number of electrons in t₂g) × (–0.4Δo) + (number of electrons in eg) × (+0.6Δo) + pairing energy correction (if applicable). For example, d⁶ low-spin: t₂g⁶eg⁰ → CFSE = 6×(–0.4Δo) + 0 = –2.4Δo.
Crystal field splitting in tetrahedral coordination compounds: In a tetrahedral complex, the four ligands do not approach along the axes — they approach from the corners of a tetrahedron. The d-orbitals that point between the axes (dxy, dxz, dyz — called e set in tetrahedral field, note the opposite labelling from octahedral) are now closer to the ligands and are destabilised. The dx²−y² and dz² (t₂ set in tetrahedral) are stabilised. The tetrahedral crystal field splitting energy Δt = (4/9)Δo — significantly smaller than octahedral splitting for the same metal and ligands. Because Δt is small, tetrahedral coordination compounds are almost always high-spin regardless of ligand strength. The spectrochemical series (weak to strong field): I⁻ < Br⁻ < S²⁻ < SCN⁻ < Cl⁻ < NO₃⁻ < F⁻ < OH⁻ < C₂O₄²⁻ < H₂O < NCS⁻ < en < NH₃ < bipy < phen < NO₂⁻ < CN⁻ < CO. Download the Free PDF for d-orbital energy level diagrams and CFSE tables for coordination compounds in both octahedral and tetrahedral geometries.
EAN Rule — Effective Atomic Number in Coordination Compounds
Why the EAN Rule Is a Direct JEE Main Formula Application Question for Coordination Compounds
The Effective Atomic Number (EAN) rule for coordination compounds, proposed by Sidgwick, states that stable coordination compounds tend to form when the total number of electrons on the central metal (metal electrons + electrons donated by ligands) equals the atomic number of the next noble gas. This total number of electrons is the EAN.
EAN calculation for coordination compounds: EAN = (number of electrons on the metal in its oxidation state) + (number of electrons donated by all ligands). Each monodentate ligand donates 2 electrons (one lone pair); CN⁻, CO, NO⁺ each donate 2. For a neutral metal complex: EAN = atomic number of metal – oxidation state + 2 × (coordination number). Example: [Fe(CO)₅] — Fe⁰ has 26 electrons; 5 CO ligands donate 5×2 = 10 electrons; EAN = 26 + 10 = 36 = Kr (noble gas). Stable! [Ni(CO)₄] — Ni⁰ has 28 electrons; 4 CO donate 8 electrons; EAN = 28 + 8 = 36 = Kr. Stable! [Co(NH₃)₆]³⁺ — Co³⁺ has 24 electrons; 6 NH₃ donate 12; EAN = 24 + 12 = 36 = Kr. The EAN rule works best for metal carbonyl and nitrosyl complexes where back-bonding is important. It does not always predict stability of ionic complexes reliably. Download the Free PDF for EAN calculations for common coordination compounds.
Isomerism in Coordination Compounds — Structural and Stereoisomerism
Why Isomerism in Coordination Compounds Is the Highest-Difficulty JEE Main Topic in This Chapter
Coordination compounds exhibit a rich variety of isomerism — far more diverse than typical organic isomerism. JEE Main tests isomerism in coordination compounds both through identification questions (which type of isomerism is shown by a given pair?) and through counting questions (how many isomers of a given complex exist?). The two main categories are structural isomerism and stereoisomerism in coordination compounds.
Structural isomerism in coordination compounds:
Ionisation isomerism in coordination compounds: compounds with the same molecular formula but different ions inside and outside the coordination sphere. Example: [Co(NH₃)₅Br]SO₄ (ionises to give SO₄²⁻ in solution, precipitated by Ba²⁺) vs. [Co(NH₃)₅SO₄]Br (ionises to give Br⁻, precipitated by AgNO₃). Both have the same formula C₅N₅H₁₅BrSO₄Co³⁺ overall but different ionic species in solution.
Hydrate isomerism (solvate isomerism) in coordination compounds: different numbers of water molecules inside vs. outside the coordination sphere. Classic example: CrCl₃·6H₂O exists as three isomers — [Cr(H₂O)₆]Cl₃ (violet, 3 Cl⁻ precipitable), [Cr(H₂O)₅Cl]Cl₂·H₂O (grey-green, 2 Cl⁻ precipitable), [Cr(H₂O)₄Cl₂]Cl·2H₂O (dark green, 1 Cl⁻ precipitable).
Linkage isomerism in coordination compounds: arises with ambidentate ligands — different donor atoms of the same ligand coordinate to the metal. Example: [Co(NH₃)₅NO₂]Cl₂ (pentaamminenitrito-N-cobalt(III) chloride — N donates) vs. [Co(NH₃)₅ONO]Cl₂ (pentaamminenitrito-O-cobalt(III) chloride — O donates). Also: [Co(NH₃)₅SCN]²⁺ (thiocyanato-S) vs. [Co(NH₃)₅NCS]²⁺ (isothiocyanato-N).
Coordination isomerism in coordination compounds: both cation and anion are complex ions, but the ligands are distributed differently between them. Example: [Co(NH₃)₆][Cr(CN)₆] vs. [Cr(NH₃)₆][Co(CN)₆].
Stereoisomerism in coordination compounds — geometrical (cis-trans) isomerism: Occurs in square planar and octahedral coordination compounds. In square planar MA₂B₂ type: cis (same ligands on the same side) and trans (same ligands across) isomers. Example: [Pt(NH₃)₂Cl₂] — cis-platin (anticancer drug) vs. trans-platin. In octahedral MA₄B₂ type: cis (two B adjacent, 90° apart) and trans (two B opposite, 180° apart). MA₃B₃ type: fac (facial — three A in one face of octahedron) and mer (meridional — three A in a plane containing the metal).
Stereoisomerism — optical isomerism in coordination compounds: A coordination compound is optically active if it is non-superimposable on its mirror image (chiral). Octahedral complexes with two or three bidentate ligands are commonly optically active. Example: [Co(en)₃]³⁺ (tris(ethylenediamine)cobalt(III) — has Δ (right-handed, levorotatory) and Λ (left-handed, dextrorotatory) enantiomers). cis-[Co(en)₂Cl₂]⁺ is optically active; trans-[Co(en)₂Cl₂]⁺ has a plane of symmetry and is optically inactive. Download the Free PDF for isomerism diagrams and worked examples in coordination compounds.
Stability of Coordination Compounds and Important Applications
Why Stability Constants and Applications of Coordination Compounds Are JEE Main and Board Exam Questions
The stability of a coordination compound in solution is measured by its stability constant (formation constant, Kf) — the equilibrium constant for the formation of the complex from its components. A higher Kf means the coordination compound is more stable. For [Ag(CN)₂]⁻: Ag⁺ + 2CN⁻ ⇌ [Ag(CN)₂]⁻; Kf = [[Ag(CN)₂]⁻] / [Ag⁺][CN⁻]² — a very large value (≈ 10²¹) means this complex is extremely stable. The reciprocal of Kf is the instability constant (Kd) — the dissociation constant of the coordination compound. A lower instability constant means a more stable complex. Factors increasing stability of coordination compounds: higher charge on the metal, smaller metal ion size (higher charge density), chelate effect (polydentate ligands form more stable complexes than monodentate, due to entropic advantage — releasing more free solvent molecules on chelation increases entropy), large CFSE.
Applications of coordination compounds in JEE Main and daily life: Metallurgy — cyanide process for extracting gold and silver uses Na[Au(CN)₂] and Na[Ag(CN)₂] coordination compounds. Analytical chemistry — qualitative tests for metal ions use coordination compound formation: [Cu(NH₃)₄]²⁺ (deep blue) identifies Cu²⁺; [Fe(SCN)]²⁺ (blood red) identifies Fe³⁺; K₃[Fe(CN)₆] (potassium hexacyanoferrate(III)) + Fe²⁺ → Turnbull's blue (identification of Fe²⁺); K₄[Fe(CN)₆] (potassium hexacyanoferrate(II)) + Fe³⁺ → Prussian blue (identification of Fe³⁺). Medicine — cis-platin (cis-[Pt(NH₃)₂Cl₂]) is a major anticancer drug used in chemotherapy. EDTA coordination compounds are used in lead poisoning treatment (chelation therapy). Chlorophyll is a Mg–porphyrin coordination compound (magnesium at the centre — essential for photosynthesis). Haemoglobin is an Fe–porphyrin coordination compound (iron at the centre — essential for O₂ transport). Vitamin B₁₂ (cyanocobalamin) is a Co–corrin coordination compound. Photography — Na₂S₂O₃ (hypo, sodium thiosulphate) acts as a fixing agent by forming a stable coordination compound with AgBr: AgBr + 2Na₂S₂O₃ → Na₃[Ag(S₂O₃)₂] + NaBr. Download the Free PDF for the complete applications table for coordination compounds.
Download Free PDF — Co-Ordination Compounds Formula Sheet
All IUPAC naming rules for coordination compounds, ligand classification tables, VBT hybridisation table for coordination compounds, CFT energy level diagrams, CFSE calculation steps, all types of isomerism in coordination compounds with examples, EAN calculations, stability constant expressions, and applications of coordination compounds are compiled in the Aakash Rapid Revision & Formula Bank PDF for co-ordination compounds — structured specifically for JEE Main, CBSE boards, and NEET.
Why Co-Ordination Compounds Is a High-Return Chapter for JEE Main
Four reasons make co-ordination compounds one of the most reliably rewarding chapters in JEE Main inorganic chemistry.
IUPAC naming of coordination compounds is a pure rule-application skill. The IUPAC nomenclature of coordination compounds follows a fixed sequence — cation first, ligands in alphabetical order before the metal, anionic ligands end in -ido, neutral ligands use special names (aqua, ammine, carbonyl, nitrosyl), metal name in -ate for anionic complexes with Roman numeral OS. Once these IUPAC naming rules for coordination compounds are internalised, every naming question in JEE Main becomes a straightforward application, taking under a minute.
VBT hybridisation of coordination compounds is directly testable. Given a coordination compound and its ligands, determining the hybridisation of the central metal (d²sp³ vs sp³d², or dsp² vs sp³) requires only two steps: write the metal ion configuration, identify the ligand field strength from the spectrochemical series, and apply the inner/outer orbital complex rule. This gives hybridisation, geometry, and number of unpaired electrons simultaneously — answering multiple sub-questions from one analysis.
Isomerism in coordination compounds covers multiple JEE Main question types. From identifying which type of structural isomerism a pair of coordination compounds exhibits, to predicting optical activity of a given complex, to counting geometrical isomers of octahedral coordination compounds — these question types appear in every JEE Main session. A systematic approach to isomerism in coordination compounds that covers ionisation, hydrate, linkage, coordination, geometrical (cis/trans, fac/mer), and optical isomerism guarantees coverage of every possible question variant.
Applications of coordination compounds connect the chapter to biology and medicine. Questions about haemoglobin as a coordination compound, cis-platin as an anticancer coordination compound, EDTA in chelation therapy, and the cyanide process in metallurgy are all factual one-mark questions that are systematically tested. Download the Free PDF for coordination compounds to have all applications in one place.
Who Should Use This Co-Ordination Compounds Formula Sheet?
Learning Outcomes After Completing Co-Ordination Compounds
After working through this chapter using the formula sheet and notes above, a student should be able to accomplish the following confidently for coordination compounds.
For definitions and Werner's theory: state Werner's two types of valence in coordination compounds, explain how Werner's theory accounts for the conductivity of CoCl₃·xNH₃ compounds, define coordination number, central metal, ligand, chelate, ambidentate ligand, and coordination sphere in coordination compounds.
For IUPAC nomenclature of coordination compounds: apply all IUPAC naming rules to name any given coordination compound formula, and write the formula of any coordination compound given its IUPAC name. Name anionic ligands (ending in -ido), neutral ligands (aqua, ammine, carbonyl, nitrosyl), and identify when to use the metal -ate suffix in the IUPAC name of a coordination compound.
For VBT and CFT of coordination compounds: determine whether a given coordination compound uses inner or outer orbital hybridisation based on ligand field strength. Write the hybridisation (d²sp³, sp³d², dsp², sp³) and predict the geometry and number of unpaired electrons for any given coordination compound. Calculate CFSE for any d-electron configuration in octahedral and tetrahedral coordination compounds using the t₂g/eg filling rules.
For isomerism in coordination compounds: identify the type of structural isomerism (ionisation, hydrate, linkage, coordination) shown by a given pair of coordination compounds. Draw and name all geometrical isomers (cis/trans, fac/mer) of given octahedral and square planar coordination compounds. Determine whether a given coordination compound is optically active and explain why. Download the Free PDF for coordination compounds to test all these learning outcomes before your exam.
Get the Free PDF for Co-Ordination Compounds — Quick Revision
Whether you are preparing for JEE Main, CBSE Class 12 boards, or NEET, having a focused formula sheet for co-ordination compounds is essential — this chapter delivers consistent marks in every exam when systematically prepared. The Aakash Rapid Revision & Formula Bank PDF for co-ordination compounds brings all IUPAC naming rules, ligand types, VBT and CFT tables, isomerism examples, and application facts into one structured, exam-ready reference.
Conclusion — Master the Rules, Own the Marks
Co-ordination compounds is a chapter where systematic rule mastery converts directly into exam marks. The IUPAC naming rules for coordination compounds are finite and completely learnable. The ligand classification (monodentate, bidentate, ambidentate, chelating) is a fixed vocabulary. The spectrochemical series gives a clear ranking of ligand field strengths. The hybridisation rules (strong field → inner orbital → d²sp³; weak field → outer orbital → sp³d²) require only the metal ion configuration and the spectrochemical series. The CFSE formula (each t₂g electron contributes –0.4Δo, each eg electron +0.6Δo) is one line of mathematics applied to a d-electron count.
The isomerism section of coordination compounds takes the most careful attention — not because it is harder, but because it has the most subtypes. Treating each isomerism type in coordination compounds systematically (what structural difference defines it? what example demonstrates it?) and connecting geometrical isomerism to geometry (only in square planar and octahedral, not tetrahedral MA₄) makes the classification reliable. Optical isomerism in coordination compounds follows from symmetry — if a complex has no plane, axis, or centre of symmetry, it is chiral and optically active.
Use this page, the concept boxes, and the Free PDF Download for co-ordination compounds as your complete revision reference. Combine conceptual understanding with practice on previous JEE Main coordination compounds questions, and this chapter will deliver some of the most reliably earned marks in the entire chemistry paper.
Frequently Asked Questions — Co-Ordination Compounds
What are the IUPAC naming rules for coordination compounds?
The IUPAC nomenclature of coordination compounds follows these key rules in sequence. First, name the cation before the anion (same as for all ionic compounds). Second, inside the coordination sphere, name all ligands before the central metal atom. Third, name ligands in alphabetical order (ignoring multiplying prefixes like di-, tri- when alphabetising). Fourth, use specific ligand names: anionic ligands get the suffix -ido (chlorido for Cl⁻, cyanido for CN⁻, hydroxido for OH⁻, bromido for Br⁻); neutral ligands use aqua (H₂O), ammine (NH₃), carbonyl (CO), and nitrosyl (NO). Fifth, for cationic or neutral complexes, use the English name of the metal followed by the oxidation state in Roman numerals in parentheses (e.g., cobalt(III), iron(II)). For anionic complexes, add the Latin-derived suffix -ate to the metal name (ferrate, cuprate, argentate, aurate, platinate, chromate, cobaltate, nickelate, zincate). Finally, use di-, tri- for simple ligands and bis-, tris- for complex ligand names that already contain a multiplying prefix (e.g., bis(ethylenediamine), not diethylenediamine).
What is the difference between inner orbital and outer orbital complexes in VBT of coordination compounds?
In Valence Bond Theory (VBT) of coordination compounds, the hybridisation of the central metal determines whether the complex is inner or outer orbital. Inner orbital complexes use the (n-1)d orbitals of the metal in hybridisation — for first-series transition metals, these are 3d orbitals combined with 4s and 4p to give d²sp³ hybridisation. This occurs when strong-field ligands (CN⁻, CO, NH₃, en) force electron pairing in the inner 3d orbitals, creating empty inner d-orbitals for hybridisation. Inner orbital complexes are low-spin — they have fewer unpaired electrons and are weakly paramagnetic or diamagnetic. Outer orbital complexes use the nd orbitals (4d for first-series metals) in hybridisation — sp³d² hybridisation using 4s, 4p, and 4d. This occurs with weak-field ligands (F⁻, Cl⁻, H₂O, OH⁻) that do not force pairing, so the 3d electrons remain with maximum unpaired electrons and the outer 4d orbitals are used. Outer orbital complexes are high-spin — maximum unpaired electrons, strongly paramagnetic. Both give octahedral geometry, but their magnetic properties and stability differ significantly.
How do you calculate CFSE in octahedral coordination compounds?
Crystal Field Stabilisation Energy (CFSE) in octahedral coordination compounds is calculated by distributing the d-electrons into the t₂g and eg sets and applying the energy contributions: each electron in the t₂g set contributes –0.4Δo (stabilised) and each electron in the eg set contributes +0.6Δo (destabilised). To find CFSE: (1) determine the d-electron count for the metal ion (remove 4s electrons first, then count remaining 3d); (2) decide whether the complex is high-spin or low-spin based on the spectrochemical series (strong-field ligand → low-spin filling, following Aufbau in t₂g before eg; weak-field ligand → high-spin filling, following Hund's rule across all five d-orbitals first); (3) count electrons in t₂g and eg; (4) calculate CFSE = (t₂g electrons × –0.4Δo) + (eg electrons × +0.6Δo). Example for low-spin d⁶ (strong field): t₂g⁶eg⁰ → CFSE = 6×(–0.4Δo) + 0 = –2.4Δo. Example for high-spin d⁶ (weak field): t₂g⁴eg² → CFSE = 4×(–0.4Δo) + 2×(+0.6Δo) = –1.6Δo + 1.2Δo = –0.4Δo. Higher negative CFSE means greater stabilisation and a more stable coordination compound.
What are the different types of isomerism in coordination compounds?
Isomerism in coordination compounds is classified into two main types: structural isomerism and stereoisomerism. Structural isomerism in coordination compounds includes: ionisation isomerism (same formula but different ions inside/outside the coordination sphere — distinguished by AgNO₃ or BaCl₂ precipitation tests), hydrate/solvate isomerism (different numbers of water molecules inside vs outside — the classic example is the three isomers of CrCl₃·6H₂O showing violet, grey-green, and dark green colours), linkage isomerism (ambidentate ligand coordinates through different donor atoms — e.g., nitro vs nitrito forms, thiocyanato-S vs thiocyanato-N), and coordination isomerism (ligands distributed differently between a complex cation and complex anion). Stereoisomerism in coordination compounds includes: geometrical (cis-trans) isomerism in square planar MA₂B₂ types and in octahedral MA₄B₂ and MA₃B₃ types (fac and mer forms), and optical isomerism in chiral complexes — octahedral complexes with two or three bidentate ligands like [Co(en)₃]³⁺ and cis-[Co(en)₂Cl₂]⁺ are optically active.
What is the spectrochemical series and how is it used in coordination compounds?
The spectrochemical series is an empirical ranking of ligands in order of their ability to split the d-orbital energy levels in coordination compounds — from weak-field (small crystal field splitting energy Δo) to strong-field (large Δo). The order from weak to strong field is approximately: I⁻ < Br⁻ < S²⁻ < SCN⁻ < Cl⁻ < NO₃⁻ < F⁻ < OH⁻ < C₂O₄²⁻ < H₂O < NCS⁻ < en < NH₃ < bipy < phen < NO₂⁻ < CN⁻ < CO. In VBT of coordination compounds, strong-field ligands (CO, CN⁻, NO₂⁻, en, NH₃) give inner orbital complexes (d²sp³, low-spin) while weak-field ligands (F⁻, Cl⁻, H₂O, OH⁻) give outer orbital complexes (sp³d², high-spin). In CFT of coordination compounds, a large Δo (strong-field) means the energy cost of pairing is less than the crystal field splitting — electrons pair up in t₂g (low-spin), giving fewer unpaired electrons and smaller magnetic moment. A small Δo (weak-field) means electrons follow Hund's rule across all d-orbitals (high-spin), giving more unpaired electrons and larger magnetic moment.
Why is cis-platin used as an anticancer drug while trans-platin is not?
cis-Platin is cis-[Pt(NH₃)₂Cl₂] — a square planar coordination compound where the two chloride ligands are on the same side (cis) and the two ammonia ligands are on the same side. Its anticancer activity arises from its ability to bind to DNA: the two cis-positioned chlorido ligands are sequentially replaced by water molecules under the low-chloride conditions inside cancer cells, and the resulting diaqua complex then forms crosslinks between two adjacent guanine bases on the same strand of DNA (intrastrand crosslinks). These crosslinks distort the DNA double helix, preventing replication and transcription, and triggering apoptosis (programmed cell death) of the rapidly dividing cancer cells. trans-Platin — trans-[Pt(NH₃)₂Cl₂] — cannot form these intrastrand crosslinks in the same geometry because the two leaving chlorido groups are on opposite sides of the platinum. It forms different types of DNA crosslinks that the cell can repair, so it has no useful anticancer activity and is actually more toxic to normal cells without the therapeutic benefit. This is a classic example of how geometrical isomerism in coordination compounds directly determines biological activity.
What is the EAN rule for coordination compounds and when does it fail?
The Effective Atomic Number (EAN) rule, proposed by Sidgwick for coordination compounds, states that stable complexes tend to form when the total number of electrons on the central metal (metal electrons + ligand-donated electrons) equals the atomic number of the next noble gas. To calculate EAN: take the number of electrons on the metal in its current oxidation state, then add 2 electrons for each ligand (each monodentate ligand donates 1 lone pair = 2 electrons). Examples where EAN rule works well for coordination compounds: [Fe(CO)₅] → EAN = 26 + 10 = 36 (Kr); [Ni(CO)₄] → EAN = 28 + 8 = 36 (Kr); [Cr(CO)₆] → EAN = 24 + 12 = 36 (Kr). The EAN rule works best for metal carbonyls, nitrosyls, and organometallic coordination compounds where back-bonding is important. It fails for many ionic coordination compounds — for example, [Co(NH₃)₆]³⁺ gives EAN = 24 + 12 = 36 (Kr — works here), but many common coordination compounds like [Cu(NH₃)₄]²⁺ (EAN = 27 + 8 = 35, not a noble gas) are quite stable despite not satisfying the EAN rule. The EAN rule is therefore a useful guide but not a universal predictor of stability for coordination compounds.
How do you determine the oxidation state of the central metal in a coordination compound?
To find the oxidation state of the central metal in a coordination compound, use the principle that the sum of oxidation states of all components of a neutral coordination compound is zero, and the sum within a coordination ion equals the ion's charge. Identify the charge of each component: neutral ligands (H₂O, NH₃, CO, NO) contribute 0; anionic ligands contribute their charge (Cl⁻ = –1, CN⁻ = –1, SO₄²⁻ = –2, ox²⁻ = –2, en = 0 since it's neutral). Set up the equation: (metal OS) + (sum of ligand charges) = total charge of coordination entity. Example: In [Co(NH₃)₅Cl]²⁺ — Co(OS) + 5(0) + 1(–1) = +2 → Co = +3. In K₄[Fe(CN)₆] — the complex ion is [Fe(CN)₆]⁴⁻ → Fe(OS) + 6(–1) = –4 → Fe = +2. In [Cr(H₂O)₄Cl₂]Cl — the complex ion is [Cr(H₂O)₄Cl₂]⁺ → Cr(OS) + 4(0) + 2(–1) = +1 → Cr = +3. Note: in coordination compounds, NO can act as NO⁺ (+1) or NO⁻ (–1) or NO (0) depending on the context — this must be given or inferred from the overall charge of the coordination compound.
What is the chelate effect in coordination compounds and why does it make chelate complexes more stable?
The chelate effect in coordination compounds refers to the extra stability of chelate complexes (formed with polydentate ligands) compared to analogous complexes with the equivalent number of monodentate ligands. For example, [Ni(en)₃]²⁺ (with three bidentate en ligands) is much more stable than [Ni(NH₃)₆]²⁺ (with six monodentate NH₃), even though both satisfy coordination number 6 and use N as donor atoms. The chelate effect in coordination compounds is primarily an entropy effect (thermodynamic origin). When a polydentate ligand replaces several monodentate ligands, the number of free molecules in solution increases — for example, replacing 6 NH₃ by 3 en releases 3 additional molecules to solution, increasing the translational entropy of the system (ΔS becomes more positive). By ΔG = ΔH – TΔS, a more positive TΔS term makes ΔG more negative, meaning the chelate formation is more thermodynamically spontaneous. The enthalpy of chelate complexes is not significantly different from analogous non-chelate complexes — it is entirely the entropy advantage that drives the chelate effect in coordination compounds. EDTA (hexadentate, 6 donor atoms) chelates are the most stable because replacing 6 separate ligands with one EDTA molecule creates the maximum entropy gain.
What is linkage isomerism in coordination compounds and which ligands give rise to it?
Linkage isomerism in coordination compounds arises when an ambidentate ligand can coordinate to the central metal through either of two different donor atoms. The two coordination compounds have the same molecular formula but differ in which atom of the ambidentate ligand is bonded to the metal — giving different physical and chemical properties. The most common ambidentate ligands that give linkage isomerism in coordination compounds are: NO₂⁻ (nitrite ion) — can bond through N (nitro complex, written as –NO₂, suffix in IUPAC name: nitrito-N) giving e.g. [Co(NH₃)₅NO₂]Cl₂ (pentaamminenitrito-N-cobalt(III) chloride, yellow), or through O (nitrito complex, written as –ONO, suffix: nitrito-O) giving [Co(NH₃)₅ONO]Cl₂ (pentaamminenitrito-O-cobalt(III) chloride, red). SCN⁻ (thiocyanate ion) — can bond through S (thiocyanato-S) or through N (isothiocyanato-N). CN⁻ — bonds through C (cyano) or through N (isocyano). These linkage isomers in coordination compounds have different colours, different reactivity, and interconvert under appropriate conditions. The nitro (N-bonded) form of nitrite is thermodynamically more stable than the nitrito (O-bonded) form in most cobalt coordination compounds.
Related Formula Sheets — JEE Main & Class 12 Chemistry
Co-Ordination Compounds – JEE Main Formula Sheet & Class 12 Notes | IUPAC Naming, VBT, CFT, Isomerism
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