📌 Snapshot
- Establishes Werner's primary/secondary valence framework that underpins all modern coordination chemistry — primary valence is ionisable, secondary valence is the coordination number and is fixed for a metal (NCERT §5.1, p. 119-120).
- Develops the vocabulary CUET routinely tests: coordination entity, ligand (uni/di/poly/ambidentate, chelate), coordination number, coordination sphere/polyhedron, oxidation number, homoleptic vs heteroleptic (NCERT §5.2, p. 121-122).
- Builds IUPAC nomenclature rules for mononuclear complexes — cation-first, ligands alphabetical, anion ligand "-o" ending, "-ate" suffix for anionic complex, Roman-numeral oxidation state (NCERT §5.3, p. 122-124).
- Classifies isomerism (stereo: geometrical + optical; structural: linkage, coordination, ionisation, solvate) and bonding theories (VBT hybridisation sp³/dsp²/d²sp³/sp³d², CFT octahedral t₂g/eₑ splitting Δₒ, tetrahedral splitting Δₜ = 4/9 Δₒ, spectrochemical series, CFSE, colour from d-d transition) (NCERT §5.4-5.5, p. 125-134).
- Closes with biological/industrial importance — chlorophyll (Mg), haemoglobin (Fe), vitamin B₁₂ (Co), cisplatin, EDTA chelation therapy, Wilkinson catalyst (NCERT §5.7, p. 136-137).
📖 Detailed Notes
2.1 Core concepts
- Werner studied CoCl₃·xNH₃ series: 1 mol [Co(NH₃)₆]Cl₃ gave 3 mol AgCl (1:3 electrolyte), 1 mol [CoCl(NH₃)₅]Cl₂ gave 2 mol AgCl (1:2), 1 mol [CoCl₂(NH₃)₄]Cl gave 1 mol AgCl (1:1) — explaining the data needed primary (ionisable) and secondary (non-ionisable, fixed = coordination number) valences (NCERT §5.1, p. 118-119).
- Werner's four postulates: metals show primary + secondary linkages; primary valences are ionisable and satisfied by negative ions; secondary valences are non-ionisable, equal coordination number, satisfied by neutral molecules or negative ions; secondary-linkage groups have characteristic spatial arrangement = coordination polyhedron (NCERT §5.1, p. 119).
- Double salts (carnallite KCl·MgCl₂·6H₂O, Mohr's salt, potash alum) dissociate completely in water, whereas complex ions like [Fe(CN)₆]⁴⁻ do not dissociate into Fe²⁺ and CN⁻ — this distinguishes a complex from a double salt (NCERT §5.1, p. 120).
- Ligands classified by donor atoms: unidentate (Cl⁻, H₂O, NH₃), didentate (en = ethane-1,2-diamine; ox = C₂O₄²⁻), polydentate (N(CH₂CH₂NH₂)₃), hexadentate (EDTA⁴⁻ binds via 2 N + 4 O); ambidentate ligands (NO₂⁻, SCN⁻) have two different donor atoms; chelate complexes (di/polydentate using ≥2 donors on the same metal) are more stable than unidentate analogues (NCERT §5.2, p. 121).
- Coordination number = number of σ-bonded ligand donor atoms; π-bonds are NOT counted. E.g. [PtCl₆]²⁻ CN = 6; [Fe(C₂O₄)₃]³⁻ CN = 6 (since ox is didentate) (NCERT §5.2, p. 121-122).
- Common polyhedra are octahedral (CN 6), tetrahedral and square planar (CN 4); oxidation number written as Roman numeral, e.g. Cu(I) in [Cu(CN)₄]³⁻; homoleptic = one kind of donor ([Co(NH₃)₆]³⁺); heteroleptic = more than one ([Co(NH₃)₄Cl₂]⁺) (NCERT §5.2, p. 122).
- IUPAC naming: cation first; ligands alphabetical before metal; anionic ligand end "-o" (chlorido, cyanido, oxalato); neutral H₂O = aqua, NH₃ = ammine, CO = carbonyl, NO = nitrosyl; "bis/tris/tetrakis" with polyatomic ligands; Roman-numeral oxidation state in parentheses; metal in anionic complex ends in "-ate" (e.g. ferrate, cobaltate) (NCERT §5.3, p. 123-124).
- Worked examples: [Cr(NH₃)₃(H₂O)₃]Cl₃ = triamminetriaquachromium(III) chloride; [Co(en)₃]₂(SO₄)₃ = tris(ethane-1,2-diamine)cobalt(III) sulphate; [Ag(NH₃)₂][Ag(CN)₂] = diamminesilver(I) dicyanidoargentate(I) (NCERT §5.3.2, p. 124).
- Isomerism — stereoisomerism: geometrical (cis-trans in square planar [MX₂L₂], octahedral [MX₂L₄] and [MX₂(L-L)₂]; fac/mer in [Ma₃b₃] octahedral); optical isomerism (non-superimposable mirror images = enantiomers, d and l; common in octahedral with didentate ligands like [Co(en)₃]³⁺ and cis-[PtCl₂(en)₂]²⁺ but NOT in trans-[PtCl₂(en)₂]²⁺) (NCERT §5.4.1-5.4.2, p. 125-127).
- Geometrical isomerism is impossible in tetrahedral complexes because the relative positions of the four unidentate ligands are identical with respect to each other (NCERT Example 5.4, p. 126).
- Structural isomerism — linkage (ambidentate ligand; [Co(NH₃)₅(NO₂)]Cl₂ red −ONO vs yellow −NO₂); coordination (ligand exchange between cation/anion complex, e.g. [Co(NH₃)₆][Cr(CN)₆] vs [Cr(NH₃)₆][Co(CN)₆]); ionisation (counter ion swaps with ligand, e.g. [Co(NH₃)₅(SO₄)]Br vs [Co(NH₃)₅Br]SO₄); solvate/hydrate ([Cr(H₂O)₆]Cl₃ violet vs [Cr(H₂O)₅Cl]Cl₂·H₂O grey-green) (NCERT §5.4.3-5.4.6, p. 127-128).
- Valence Bond Theory: metal uses (n−1)d, ns, np or ns, np, nd orbitals to give hybrids — CN 4 sp³ tetrahedral or dsp² square planar; CN 5 sp³d trigonal bipyramidal; CN 6 d²sp³ (inner orbital / low spin) or sp³d² (outer orbital / high spin) octahedral (NCERT §5.5.1 Table 5.2, p. 128).
- VBT worked examples: [Co(NH₃)₆]³⁺ — Co³⁺ d⁶, d²sp³, diamagnetic, inner orbital low-spin; [CoF₆]³⁻ — sp³d² outer orbital, paramagnetic with 4 unpaired e⁻ high-spin; [NiCl₄]²⁻ — Ni²⁺ d⁸, sp³ tetrahedral, paramagnetic (2 unpaired); [Ni(CO)₄] — Ni(0), sp³ tetrahedral, diamagnetic; [Ni(CN)₄]²⁻ — Ni²⁺ d⁸, dsp² square planar, diamagnetic (NCERT §5.5.1, p. 129-130).
- Limitations of VBT: assumption-heavy; no quantitative magnetic interpretation; doesn't explain colour, thermodynamic/kinetic stability; cannot predict tetrahedral vs square planar; doesn't distinguish weak vs strong ligands (NCERT §5.5.3, p. 131).
- Crystal Field Theory: electrostatic model, ligands = point charges/dipoles, five degenerate d orbitals split in a non-spherical ligand field. Octahedral field: d_{x²−y²} and d_{z²} (eₑ, axial) rise by (3/5)Δₒ; d_{xy}, d_{yz}, d_{xz} (t₂g) fall by (2/5)Δₒ. The energy gap is Δₒ (NCERT §5.5.4(a), p. 131-132).
- Spectrochemical series (increasing field strength): I⁻ < Br⁻ < SCN⁻ < Cl⁻ < S²⁻ < F⁻ < OH⁻ < C₂O₄²⁻ < H₂O < NCS⁻ < EDTA⁴⁻ < NH₃ < en < CN⁻ < CO (NCERT §5.5.4, p. 132).
- For d⁴: if Δₒ < P (pairing energy) → weak field, high-spin t₂g³eₑ¹; if Δₒ > P → strong field, low-spin t₂g⁴eₑ⁰. Strong field ligands form low-spin complexes; d⁴-d⁷ are more stable in strong field than weak field (NCERT §5.5.4(a), p. 132).
- Tetrahedral field: splitting is inverted (e set lower, t₂ higher) and Δₜ = (4/9)Δₒ — too small to force pairing, so low-spin tetrahedral complexes are rarely observed; "g" subscript dropped (no centre of symmetry) (NCERT §5.5.4(b), p. 133).
- Colour from d-d transition: e.g. [Ti(H₂O)₆]³⁺ is d¹; absorbs blue-green light at 498 nm (t₂g¹eₑ⁰ → t₂g⁰eₑ¹) and appears violet (complementary). Without ligand field there is no splitting → no colour: anhydrous CuSO₄ is white, CuSO₄·5H₂O is blue (NCERT §5.5.5, p. 133-134).
- Limitations of CFT: anionic ligands ought to split most strongly (point-charge logic) but in fact sit at the low end of the spectrochemical series; covalent ligand-metal character is ignored — addressed by LFT/MOT (NCERT §5.5.6, p. 135).
- Metal carbonyls: Ni(CO)₄ tetrahedral, Fe(CO)₅ trigonal bipyramidal, Cr(CO)₆ octahedral; Mn₂(CO)₁₀ two square-pyramidal units joined by Mn–Mn; Co₂(CO)₈ has Co–Co bond bridged by 2 CO. M–C bond has σ + π character — σ from CO lone pair into vacant metal orbital, π from filled metal d into vacant π* of CO = synergic bonding (NCERT §5.6, p. 135-136).
- Importance — qualitative/quantitative analysis (EDTA, DMG, cupron); hardness of water by Na₂EDTA titration; extraction of gold/silver via [Au(CN)₂]⁻ and Zn displacement; purification of Ni via [Ni(CO)₄]; biology: chlorophyll (Mg), haemoglobin (Fe), vitamin B₁₂ cyanocobalamine (Co), carboxypeptidase A, carbonic anhydrase; Wilkinson catalyst [(Ph₃P)₃RhCl] for alkene hydrogenation; electroplating from [Ag(CN)₂]⁻ and [Au(CN)₂]⁻; photographic fixing as [Ag(S₂O₃)₂]³⁻; chelate therapy — D-penicillamine and desferrioxime B for excess Cu/Fe, EDTA for lead poisoning, cis-platin for tumours (NCERT §5.7, p. 136-137).
2.2 Definitions to memorise
| Term | Definition | Page |
|---|---|---|
| Coordination entity | Central metal atom/ion bonded to a fixed number of ions/molecules, e.g. [CoCl₃(NH₃)₃] | 121 |
| Central atom/ion | Atom/ion in the entity to which a fixed number of ions/groups are bound in a definite geometry; acts as Lewis acid | 121 |
| Ligand | Ion/molecule bound to the central atom in a coordination entity | 121 |
| Unidentate | Ligand bound through a single donor atom (Cl⁻, H₂O, NH₃) | 121 |
| Didentate | Ligand binding through two donor atoms (en, C₂O₄²⁻) | 121 |
| Polydentate | Ligand with several donor atoms (e.g. N(CH₂CH₂NH₂)₃); EDTA⁴⁻ is hexadentate | 121 |
| Ambidentate | Ligand with two different donor atoms, only one of which ligates at a time (NO₂⁻, SCN⁻) | 121 |
| Chelate ligand | Di/polydentate ligand simultaneously using ≥2 donor atoms on the same metal; chelate complexes are more stable than unidentate analogues | 121 |
| Denticity | Number of ligating groups of a chelate ligand | 121 |
| Coordination number | Number of σ-bonded ligand donor atoms attached to the central metal (π bonds not counted) | 121-122 |
| Coordination sphere | Central atom + attached ligands enclosed in square brackets; ions outside are counter ions | 122 |
| Coordination polyhedron | Spatial arrangement of ligand donor atoms about the central metal — octahedral, tetrahedral, square planar | 122 |
| Oxidation number | Charge the central atom would carry if ligands were removed with their shared electron pairs; Roman numeral in parentheses | 122 |
| Homoleptic | Metal bound to only one kind of donor (e.g. [Co(NH₃)₆]³⁺) | 122 |
| Heteroleptic | Metal bound to more than one kind of donor (e.g. [Co(NH₃)₄Cl₂]⁺) | 122 |
| Enantiomers | Non-superimposable mirror image optical isomers; d (right-rotating) and l (left-rotating) | 126 |
| Crystal field splitting Δₒ | Energy separation between eₑ and t₂g sets in octahedral field; eₑ rises by (3/5)Δₒ, t₂g falls by (2/5)Δₒ | 131-132 |
| Spectrochemical series | Experimental ordering of ligands by field strength: I⁻ < Br⁻ < SCN⁻ < Cl⁻ < S²⁻ < F⁻ < OH⁻ < C₂O₄²⁻ < H₂O < NCS⁻ < EDTA⁴⁻ < NH₃ < en < CN⁻ < CO | 132 |
| Pairing energy P | Energy required to pair two electrons in a single orbital | 132 |
| Synergic bonding | σ donation from ligand to metal + π back-donation from metal d to ligand π* (in metal carbonyls) | 136 |
2.3 Diagrams / processes to remember
- Fig. 5.1 — Shapes of coordination polyhedra (octahedral, square planar, tetrahedral) with M and unidentate L (p. 122).
- Fig. 5.2 / 5.3 / 5.4 — cis-trans isomers of [Pt(NH₃)₂Cl₂], [Co(NH₃)₄Cl₂]⁺, [CoCl₂(en)₂] (p. 125-126).
- Fig. 5.5 — fac and mer isomers of [Co(NH₃)₃(NO₂)₃] (p. 126).
- Fig. 5.6 / 5.7 — Optical d/l isomers of [Co(en)₃]³⁺ and cis-[PtCl₂(en)₂]²⁺ (p. 126).
- Fig. 5.8 — Octahedral d-orbital splitting diagram with t₂g lower (by 2/5 Δₒ) and eₑ upper (by 3/5 Δₒ) (p. 132).
- Fig. 5.9 — Tetrahedral d-orbital splitting (inverted, e lower, t₂ upper, Δₜ = 4/9 Δₒ) (p. 133).
- Fig. 5.10 — d¹ electron transition t₂g¹eₑ⁰ → t₂g⁰eₑ¹ explaining violet colour of [Ti(H₂O)₆]³⁺ (p. 134).
- Fig. 5.11 — Colour change as en progressively replaces H₂O in [Ni(H₂O)₆]²⁺ → [Ni(en)₃]²⁺ (green → pale blue → blue/purple → violet) (p. 134).
- Fig. 5.13 — Structures of Ni(CO)₄, Fe(CO)₅, Cr(CO)₆, Mn₂(CO)₁₀, [Co₂(CO)₈] (p. 136).
- Fig. 5.14 — Synergic bonding (σ ligand → metal + π metal → ligand π*) in carbonyls (p. 136).
2.4 Common confusions / NTA trap points
- Coordination number counts σ-bonded donor atoms only, NOT the number of ligand molecules: en is didentate, so [Co(en)₃]³⁺ has CN = 6, not 3 (NCERT p. 121-122).
- In tetrahedral complexes geometrical isomerism is NOT possible because all four ligands are equivalent in spatial relation; tetrahedral complexes also rarely show low-spin behaviour because Δₜ = (4/9)Δₒ is below pairing energy (p. 126, 133).
- Inner orbital / low spin / spin paired (d²sp³, uses (n−1)d) vs outer orbital / high spin / spin free (sp³d², uses nd): same magnetic moment label can confuse — strong-field ligand (CN⁻, CO) gives inner orbital, weak-field (F⁻, Cl⁻, H₂O) gives outer orbital (p. 129-131).
- NCERT spectrochemical series places anionic ligands (I⁻, Br⁻, Cl⁻, F⁻) at the WEAK end and neutral CO, CN⁻ at the strong end — this contradicts CFT's pure point-charge logic and is one of CFT's stated limitations (p. 132, 135).
- Ionisation isomers and coordination isomers are both "structural" but differ in mechanism — ionisation swaps a ligand with the counter ion of the SAME complex ([Co(NH₃)₅(SO₄)]Br vs [Co(NH₃)₅Br]SO₄), whereas coordination isomers exchange ligands between TWO complex ions of different metals ([Co(NH₃)₆][Cr(CN)₆] vs [Cr(NH₃)₆][Co(CN)₆]) (p. 127-128).
- "g" subscript (t₂g, eₑ) is used only for centrosymmetric geometries — octahedral and square planar — NOT for tetrahedral, whose levels are written as e and t₂ (p. 133).
- EAN rule — Effective Atomic Number = Z − ox. state + 2×CN; classical EAN noble-gas configurations rationalise CN choices but EAN is not always obeyed (NCERT mentions historical relevance).
- Chelate effect — Polydentate (en, EDTA) complexes are more stable than monodentate analogues of equal donor count due to entropy gain on ring formation (p. 138).
2.5 Quick reference table — coordination chemistry essentials
| # | Item | Formula / Detail | Page |
|---|---|---|---|
| 1 | Primary valence | Oxidation state of metal | 120 |
| 2 | Secondary valence | Coordination number | 120 |
| 3 | Δₜ vs Δₒ | Δₜ = (4/9) Δₒ | 133 |
| 4 | Spin-only μ | μ = √[n(n+2)] BM | 130 |
| 5 | Octahedral splitting | t₂g (−0.4Δₒ) / eₑ (+0.6Δₒ) | 133 |
| 6 | Tetrahedral splitting | e (lower) / t₂ (upper) | 133 |
| 7 | Strong-field ligands | CO, CN⁻, NO₂⁻ | 132 |
| 8 | Weak-field ligands | I⁻, Br⁻, Cl⁻, F⁻ | 132 |
| 9 | Inner-orbital complex | d²sp³ low-spin (e.g. [Co(NH₃)₆]³⁺) | 129 |
| 10 | Outer-orbital complex | sp³d² high-spin (e.g. [CoF₆]³⁻) | 129 |
| 11 | Square planar examples | [Ni(CN)₄]²⁻, [PtCl₄]²⁻ | 131 |
| 12 | Tetrahedral examples | [NiCl₄]²⁻, [MnBr₄]²⁻ | 131 |
| 13 | Cis-trans isomerism | Octahedral MA₄B₂ & square planar MA₂B₂ | 126 |
| 14 | Optical isomerism | [Co(en)₃]³⁺, cis-[Co(en)₂Cl₂]⁺ | 127 |
| 15 | Biological complexes | Haemoglobin (Fe-porphyrin), chlorophyll (Mg-porphyrin), B₁₂ (Co), cisplatin (Pt) | 138 |
🎯 Practice MCQs
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Q1. According to Werner's theory of coordination compounds, the secondary valence of a metal is equal to its:
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Answer: C
Werner's third postulate states that the secondary valence is non-ionisable and equals the coordination number, fixed for a metal. Primary valence (option A) is the oxidation state and is ionisable — not the same idea.
Q2. Which of the following pairs correctly identifies the type of ligand?
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Answer: C
EDTA⁴⁻ binds through 2 nitrogen and 4 oxygen donor atoms, making it hexadentate. NH₃ is unidentate, C₂O₄²⁻ is didentate, en is didentate (not ambidentate — ambidentate examples are NO₂⁻ and SCN⁻).
Q3. The IUPAC name of K₃[Fe(C₂O₄)₃] is:
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Answer: A
The cation K⁺ is named first. The complex anion has three C₂O₄²⁻ (charge −6) and total charge −3, so Fe is +3 and the anionic-complex metal takes the "-ate" suffix → ferrate(III). Hence potassium trioxalatoferrate(III).
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Q4. The IUPAC name of the coordination compound [Co(NH₃)₅Cl]Cl₂ is:
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Answer: B
Two Cl⁻ counter ions imply +2 charge on the complex cation; with five neutral NH₃ and one Cl⁻ ligand, Co is +3. Ligands are alphabetical (ammine before chlorido), so the name is pentaamminechloridocobalt(III) chloride.
Q5. Which of the following complexes will show optical isomerism?
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Answer: B
NCERT explicitly states that only the cis-isomer of [PtCl₂(en)₂]²⁺ shows optical activity. The trans-isomer has a plane of symmetry, square planar [Pt(NH₃)₂Cl₂] is achiral, and tetrahedral [Ni(CO)₄] with one ligand type is non-chiral.
Q6. The pair [Co(NH₃)₅(SO₄)]Br and [Co(NH₃)₅Br]SO₄ illustrates which type of isomerism?
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Answer: C
The counter ion and a coordinated ligand have exchanged positions — classic ionisation isomerism. Linkage isomerism requires an ambidentate ligand; coordination isomerism needs two complex ions of different metals; solvate isomerism involves water.
Q7. In the spectrochemical series listed in NCERT, which of the following ligands produces the strongest field?
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Answer: D
NCERT's series is I⁻ < Br⁻ < SCN⁻ < Cl⁻ < S²⁻ < F⁻ < OH⁻ < C₂O₄²⁻ < H₂O < NCS⁻ < EDTA⁴⁻ < NH₃ < en < CN⁻ < CO. CO sits at the strongest-field end.
Q8. In octahedral crystal field splitting, the eₑ orbitals are raised in energy by ____ and the t₂g orbitals are lowered by ____ relative to the spherical-field reference.
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Answer: B
NCERT explicitly states the eₑ pair rises by (3/5)Δₒ and the t₂g triplet falls by (2/5)Δₒ. The (4/9) factor in option D is the tetrahedral relation Δₜ = (4/9)Δₒ, not the eₑ shift.
Q9. For [Co(NH₃)₆]³⁺, Co³⁺ is d⁶. Using valence bond theory, the hybridisation and magnetic behaviour are:
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Answer: B
Six d⁶ electrons pair into the three 3d orbitals, freeing two inner d for d²sp³ hybridisation; no unpaired electron → diamagnetic, inner orbital (low spin). sp³d² (outer orbital) is shown by [CoF₆]³⁻ which is paramagnetic.
Q10. The complex ion [MnBr₄]²⁻ has a spin-only magnetic moment of 5.9 BM. Its geometry is:
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Answer: B
Coordination number is 4, so the complex is tetrahedral (sp³) or square planar (dsp²). A magnetic moment of 5.9 BM implies 5 unpaired electrons, which is only possible if no pairing occurs — that requires the tetrahedral, sp³ arrangement, not the square-planar dsp².
Q11. For an octahedral d⁴ ion in a strong-field environment (Δₒ > P), the electronic configuration and the number of unpaired electrons are:
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Answer: B
Strong-field ligands (Δₒ > P) push the fourth electron into the lower t₂g level rather than the higher eₑ, giving t₂g⁴eₑ⁰ — three of these electrons remain paired in two orbitals and two are unpaired, giving 2 unpaired electrons. Option A is the weak-field (high-spin) case.
Q12. The crystal field splitting in a tetrahedral complex Δₜ is related to that of an octahedral complex Δₒ (same metal, ligands and M–L distance) as:
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Answer: B
NCERT explicitly states Δₜ = (4/9)Δₒ, which is too small to force pairing — hence low-spin tetrahedral complexes are rare.
Q13. The violet colour of [Ti(H₂O)₆]³⁺ is explained by crystal field theory as:
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Answer: B
Ti³⁺ is d¹; the lone electron sits in t₂g, absorbs blue-green (around 498 nm), and is promoted to eₑ. The transmitted (complementary) colour is violet. CFT attributes such colour to d-d transition.
Q14. Match the coordination compound with its biological/medicinal role: | Compound | Role | |---|---| | 1. Chlorophyll | i. Oxygen carrier in blood | | 2. Haemoglobin | ii. Photosynthesis pigment | | 3. Vitamin B₁₂ (cyanocobalamine) | iii. Anti-tumour drug | | 4. cis-platin | iv. Anti-pernicious anaemia factor |
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Answer: A
NCERT states chlorophyll (Mg) is the photosynthesis pigment; haemoglobin (Fe) is the oxygen carrier in blood; vitamin B₁₂ (cyanocobalamine, Co) is the anti-pernicious anaemia factor; cis-platin (Pt) inhibits tumour growth.
Q15. **Assertion (A):** [Ni(CN)₄]²⁻ is diamagnetic while [NiCl₄]²⁻ is paramagnetic, although both have Ni²⁺ and coordination number 4. **Reason (R):** CN⁻ is a strong-field ligand causing d-electron pairing and dsp² square-planar hybridisation, whereas Cl⁻ is a weak-field ligand giving sp³ tetrahedral geometry with unpaired electrons.
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Answer: A
Ni²⁺ is d⁸. With CN⁻ (strong field), electrons pair to free one 3d orbital for dsp² hybridisation, giving square-planar diamagnetic [Ni(CN)₄]²⁻. With Cl⁻ (weak field) no pairing occurs, so sp³ hybridisation gives tetrahedral [NiCl₄]²⁻ with two unpaired electrons (paramagnetic). The reason fully explains the assertion.
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