313_Chemistry_Eng_Lesson22.pdf). Content covers sections 22.1–22.7.Complexes such as Na[Ag(CN)₂] and Na₂[Zn(CN)₄] contain a central metal ion surrounded by ligands. They matter in industry (Ziegler–Natta catalyst, metal extraction), medicine (cis-platin, EDTA), and life (chlorophyll Mg complex; haemoglobin Fe complex). This lesson covers Werner’s theory, terminology, IUPAC nomenclature, valence bond theory, crystal field theory, isomerism, and applications.
Before Werner (1893), compounds like CoCl₃·6NH₃, CoCl₃·5NH₃, CoCl₃·4NH₃ were mysterious — different numbers of ionisable Cl⁻ despite similar formulas. Werner proposed:
Six-coordinate complexes are octahedral; four-coordinate may be tetrahedral ([NiCl₄]²⁻) or square planar ([Ni(CN)₄]²⁻).
Ligand: molecule/ion bound to metal via donor atom (Lewis base). Monodentate (H₂O, NH₃, Cl⁻); bidentate (en); polydentate/chelating (EDTA hexadentate). Chelates hold metal like a claw — extra stability.
Coordination number: number of donor atoms around metal (not always number of ligands if polydentate). Coordination sphere: metal + ligands in square brackets. Oxidation number: from charge balance — e.g. [PtCl₆]²⁻ → Pt +4; [Cu(NH₃)₄]²⁺ → Cu +2.
Rules in brief: (1) cation named before anion; (2) ligands first (alphabetical), metal last; (3) anionic ligands end in -o; NH₃ = ammine, H₂O = aqua, CO = carbonyl; (4) di/tri/tetra or bis/tris/tetrakis; (5) metal OS in Roman numerals; (6) complex anion metal name ends in -ate (ferrate, cuprate).
Examples: [Co(H₂O)₆]Cl₃ hexaaquacobalt(III) chloride; K₂[PtCl₆] potassium hexachloroplatinate(IV); K₄[Fe(CN)₆] potassium hexacyanoferrate(II); [Co(en)₂Cl₂]Cl dichlorobis(ethylenediamine)cobalt(III) chloride; Ni(CO)₄ tetracarbonylnickel(0).
More practice: [Co(NH₃)₄Cl₂]⁺ tetraamminedichlorocobalt(III) ion; (NH₄)₃[Cr(NCS)₆] ammonium hexathiocyanatochromate(III); [Cr(en)₃]Cl₃ tris(ethylenediamine)chromium(III) chloride. Formula writing reverse of naming: potassium hexacyanoferrate(III) is K₃[Fe(CN)₆]; tetrachloronickelate(II) is [NiCl₄]²⁻.
Pauling’s VBT: empty metal hybrid orbitals accept ligand lone pairs (σ coordinate bonds). Hybridisation sets geometry and relates to magnetism.
Octahedral: [CoF₆]³⁻ uses outer 4d → sp³d² high-spin paramagnetic (4 unpaired). [Co(NH₃)₆]³⁺ rearranges electrons → inner 3d → d²sp³ low-spin diamagnetic. [Fe(CN)₆]⁴⁻ diamagnetic d²sp³; [Fe(CN)₆]³⁻ paramagnetic (1 unpaired); [Cr(NH₃)₆]³⁺ paramagnetic (3 unpaired, μ ≈ 3.87 BM).
Four-coordinate: [NiCl₄]²⁻ sp³ tetrahedral, 2 unpaired; Ni(CO)₄ sp³ tetrahedral diamagnetic; [Ni(CN)₄]²⁻ dsp² square planar diamagnetic.
VBT explains structure and magnetism well but not colour or quantitative spectra — that needs CFT.
Ligands treated as point charges split the five d orbitals. In octahedral field, ligands on axes raise energy of dx²−y² and dz² (eg) relative to dxy, dxz, dyz (t₂g). Splitting energy = Δ (or Δo).
Spectrochemical series: I⁻ < Br⁻ < Cl⁻ < F⁻ < H₂O < NH₃ < en < NO₂⁻ < CN⁻. Larger Δ for higher charge metal and stronger ligands. If Δ small, electrons occupy eg before pairing → high-spin; if Δ large, pairing first → low-spin (relevant for d⁴–d⁷). Example: [FeF₆]³⁻ high-spin; [Fe(CN)₆]³⁻ low-spin.
Structural: ionisation ([Co(NH₃)₅Br]SO₄ vs [Co(NH₃)₅SO₄]Br); hydrate (three CrCl₃ hydrates with different colours/ionisable Cl); coordination (swap complex cation/anion); linkage (SCN vs NCS).
Stereo: geometrical cis–trans (e.g. [Pt(NH₃)₂Cl₂], MA₄B₂ octahedral); optical enantiomers when no plane of symmetry ([Co(en)₃]³⁺ — rotate plane-polarised light oppositely).
Extraction: Au + CN⁻ + air → [Au(CN)₂]⁻; Zn displaces gold. Ni purified via Ni(CO)₄ (Mond process idea).
Medicine: EDTA chelates Pb²⁺ (lead poisoning); cis-[Pt(NH₃)₂Cl₂] anticancer; sodium nitroprusside lowers blood pressure.
Qualitative analysis: [Ag(NH₃)₂]⁺ dissolves AgCl; [Cu(NH₃)₄]²⁺ deep blue; Ni + DMG → red [Ni(DMG)₂]; Fe complexes (Prussian blue); [CoCl₄]²⁻ colour with HCl.
Must-score topics: Werner primary/secondary valence; CN and OS calculations; full IUPAC names and formulae; VBT hybridisation + magnetism for listed complexes; CFT octahedral splitting, spectrochemical series, high/low spin; isomer types with examples; cis-platin and cyanide extraction.
Links L21 (transition metals, colour, magnetism) to bonding theories that explain those properties in complexes. Practice writing structures for [Co(NH₃)₆]³⁺, [Ni(CN)₄]²⁻, and naming K₃[Fe(CN)₆] / [Cr(en)₃]Cl₃ until automatic.
Intext checkpoints: primary vs secondary valence; CN/OS for [MnCl₆]⁴⁻, [Fe(CN)₆]³⁻, [Ni(en)₃]²⁺; names of [Co(NH₃)₄Cl₂]⁺ and K₄[Fe(CN)₆]; hybridisation of [Fe(CN)₆]³⁻ vs [NiCl₄]²⁻; which is diamagnetic [Ni(CN)₄]²⁻ or [NiCl₄]²⁻; F⁻ vs CN⁻ field strength; hydrate isomers of CrCl₃·6H₂O; cis-platin use; gold cyanide complex. Master these and L22 exam questions become routine.
Most exam-important points from this chapter:
Primary = OS (ionisable); secondary = CN (geometry). Ligands mono/bi/poly; chelates stable. Count donor atoms for CN.
Cation first; ligands alphabetical; metal + Roman OS; -ate if complex anion. Ammine, aqua, carbonyl special names.
d²sp³ inner low-spin vs sp³d² outer high-spin. [NiCl₄]²⁻ sp³ para; [Ni(CN)₄]²⁻ dsp² dia; Ni(CO)₄ sp³ dia.
Octahedral: t₂g below e_g; Δ = hν (colour). Spectrochemical: I⁻ weak … CN⁻ strong. High-spin vs low-spin for d⁴–d⁷.
Ionisation, hydrate, linkage, cis–trans, optical. CN⁻ extracts Au; EDTA chelates Pb; cis-platin cancer; DMG tests Ni.
Extracted from NIOS Chemistry (313) board exam papers in your PDF. Chapter L22 — Coordination Compounds only. Use Model Answer for marking points; Explanation for concept clarity.
4 question(s) · Sources: 313/MAY/205A, 313/MAY/205B, 313/MAY/205C, 313/TUS/105A
PYQ1. Outer orbital complex formation involves — (A) sp3d2 hybridization (B) d2sp3 hybridization (C) sp3 hybridization (D) dsp2 hybridization
Model Answer
Answer: (A) sp3d2 hybridization
Explanation
Outer orbital (high-spin) octahedral complexes use nd orbitals → sp³d² hybridisation.
Source paper: 313/MAY/205A · Q10 · 1 mark(s) · Chapter L22.
PYQ2. Outer orbital complex formation involves — (A) sp3d2 hybridization (B) d2sp3 hybridization (C) sp3 hybridization (D) dsp2 hybridization
Model Answer
Answer: (A) sp3d2 hybridization
Explanation
Outer orbital (high-spin) octahedral complexes use nd orbitals → sp³d² hybridisation.
Source paper: 313/MAY/205B · Q14 · 1 mark(s) · Chapter L22.
PYQ3. Outer orbital complex formation involves — (A) sp3d2 hybridization (B) d2sp3 hybridization (C) sp3 hybridization (D) dsp2 hybridization
Model Answer
Answer: (A) sp3d2 hybridization
Explanation
Outer orbital (high-spin) octahedral complexes use nd orbitals → sp³d² hybridisation.
Source paper: 313/MAY/205C · Q3 · 1 mark(s) · Chapter L22.
PYQ4. Read the passage given below and answer the following questions (out of four attempt any two) : Coordination compounds are the compounds in which a central metal ion is attached to a group of surrounding ligands by coordinate covalent bond. Ligands can be monodentate or polydentate. Polydentate ligands are also called chelating ligands. The geometries of coordination compounds are linear, tetrahedral, square planar and octahedral. [Co(CN) ] and [CoF ] both are octahedral complexes. Then what is the difference between the two? Give a chemical test to distinguish between [Co(NH ) Br]SO and [Co(NH ) SO ]Br . Name any one chelating agent. Identify and name the bidentate ligand in [Co(en)2(H2O)(CN)]– complex ion.
Model Answer
State the precise definition from the L22 notes in 1–2 sentences, include formula/example if marks ≥ 2, and avoid extra theory beyond the ask.
Explanation
Definition questions score for accuracy of wording + one supporting point/example. Do not write full chapter summaries.
How to write for NIOS: Use 30–50 words (VSA) or short objective. Open with definition/equation, then reason, end with conclusion. Paper 313/TUS/105A · Q24 · 2 mark(s) · L22.
Six problems spanning this chapter’s NIOS syllabus. Every question is built from the notes and formula sheet: solve with equations first, then read the formal textbook-style write-up, the easy explanation, and the topic in depth (formulas, meaning, exam tips). If the question says draw, a labelled pencil sketch is provided. Explanations open by default.
Draw an octahedral sketch of ML₆. Define coordination number.
Final answer: CN = number of donor atoms bound to metal
Werner theory: primary and secondary valences; modern: ligands donate pairs to metal.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Metal in the middle with 6 ligands at octahedron corners.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
CN 4 often tetrahedral/square planar.
Linked to chapter notes (L22). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
What is a chelating ligand? Give one example.
Final answer: e.g. en or EDTA
Chelates are more stable (chelate effect).
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
A ligand that grabs the metal with two or more teeth.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
EDTA used in titration/medicine.
Linked to chapter notes (L22). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
Name [Cu(NH₃)₄]²⁺ (simple).
Final answer: Tetraamminecopper(II)
Ligands named first alphabetically, then metal with OS.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Four ammonia on copper +2.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Anionic complexes use -ate ending.
Linked to chapter notes (L22). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
What is ionisation isomerism? Give conceptual example.
Final answer: Different counter ions exchange with ligands
Structural isomerism type in coordination chemistry.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Which ion is stuck on the metal vs free in solution differs.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Test with AgNO₃ etc.
Linked to chapter notes (L22). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
In octahedral field, how do d orbitals split?
Final answer: t₂g lower, e_g higher
Ligand field splits degenerate d orbitals.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
Some d orbitals point at ligands and go higher in energy.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Explains colour and magnetic properties.
Linked to chapter notes (L22). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.
Define homoleptic complex.
Final answer: Only one kind of ligand
Heteroleptic has more than one ligand type.
Working formulas: (see solution steps). State the definition or law first (NIOS style), use SI units, and box the final numerical answer with unit.
All ligands the same vs mixed ligands.
Read once for the idea, once for the numbers. Write the formula, substitute, then simplify. Check whether you used moles, grams, or litres correctly.
Useful classification term.
Linked to chapter notes (L22). Remember: (see solution steps). Most exam errors are unit mix-ups (g vs mol, mL vs L) or wrong mole ratios from the equation.
Write (see solution steps) before substituting. Keep three significant figures until the end when data allow.