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Chemistry · Class 12 Science

Ch 10Coordination Compounds — Class 12 Chemistry, concept-first.

A coordination compound (or complex compound) is a compound in which a central metal atom or ion is bonded to a fixed number of surrounding ions or neutral molecules, called ligands, through coordinate (dative) covalent bonds — bonds in which the ligand alone supplies both electrons of the shared pair, while the metal…

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Key concepts

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Ligands and Denticity

A ligand is an ion or neutral molecule with at least one lone pair on a donor atom, capable of donating that pair to a central metal to form a coordinate bond.

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Chapter contents

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5.1

Introduction to Coordination Compounds

A coordination compound (or complex compound) is a compound in which a central metal atom or ion is bonded to a fixed number of surrounding ions or neutral molecules, called ligands, through coordinat…

5.2

Ligands and Their Classification by Denticity

A ligand is any ion or neutral molecule that possesses at least one lone pair of electrons on a donor atom and is capable of donating that lone pair to a central metal atom or ion to form a coordinate…

5.3

Classification of Ligands by Field Strength: The Spectrochemical Series

Not every ligand affects the energies of a metal's d-orbitals to the same extent. Some ligands split the d-orbital energies only weakly; others split them very strongly.

5.4

Coordination Number

The coordination number of a central metal atom or ion in a complex is the total number of donor atoms directly bonded to it — that is, the total number of coordinate bonds it forms with all of its li…

5.5

Colour of Coordination Compounds

One of the most visually obvious properties of many transition-metal complexes is their intense colour: is a striking purple, is pale blue, is a much deeper blue, and is green.

5.6

Magnetic Properties of Coordination Compounds

Whether a coordination compound behaves as paramagnetic (weakly attracted into an external magnetic field, because it contains one or more unpaired electrons) or diamagnetic (weakly repelled, because…

5.7

Shapes of Coordination Compounds

The overall three-dimensional shape of a coordination entity is determined primarily by its coordination number (Section 5.4), and for two-, four-, and six-coordinate complexes the correlation is gene…

5.8

IUPAC Nomenclature of Mononuclear Coordination Compounds

Coordination compounds are named according to a systematic set of IUPAC rules that let the complete composition and structure of any mononuclear complex be read directly from its name.

5.9

Effective Atomic Number (EAN) Rule

The Effective Atomic Number (EAN) rule, proposed by Sidgwick, is a simple electron-counting rule that offers a rough but useful check on the stability of a coordination entity.

5.10

Werner's Theory of Coordination Compounds

Long before any electronic theory of bonding existed, the Swiss chemist Alfred Werner correctly worked out the structure of coordination compounds in 1893, using purely chemical evidence: how many ion…

5.11

Valence Bond Theory (VBT) of Coordination Compounds

Valence bond theory (VBT), applied to coordination compounds by Linus Pauling, explains both the geometry and the magnetic behaviour of a complex by proposing that the central metal ion makes availabl…

5.12

Crystal Field Theory: Splitting in an Octahedral Field

Crystal field theory (CFT) takes a different, purely electrostatic approach from valence bond theory: it treats each ligand as a point negative charge (or, for a neutral ligand such as , the negative…

5.13

Crystal Field Theory: Splitting in a Tetrahedral Field

When only four ligands surround a metal ion in a tetrahedral arrangement, rather than six in an octahedral one, the geometry of approach relative to the d-orbitals changes completely, with two importa…

5.14

Crystal Field Splitting Energy (CFSE) and High-Spin/Low-Spin Complexes

Once the d-orbitals of a metal ion have been split by the surrounding ligand field (Sections 5.12-5.13), filling them with the metal's actual d-electrons releases a net energetic stabilization compare…

5.15

Structural Isomerism in Coordination Compounds

Structural isomers of a coordination compound share exactly the same overall chemical formula (the same atoms in the same total quantities) but differ in which groups are actually bonded to the metal,…

5.16

Stereoisomerism: Geometrical (cis-trans) Isomerism

Geometrical (cis-trans) isomers have exactly the same set of ligands bonded to the metal in exactly the same way (they are not structural isomers), but differ in how those ligands are spatially arrang…

5.17

Stereoisomerism: Optical Isomerism

Optical isomers, or enantiomers, are pairs of molecules that are non-superimposable mirror images of one another — related to each other exactly the way a person's left and right hand are related.

5.18

Importance and Applications of Coordination Compounds

Coordination compounds are far more than an abstract classroom topic: complex formation underlies practical chemical analysis, the industrial extraction of precious metals, and some of the most essent…

Summary

- Ligands and denticity: a ligand donates a lone pair to the central metal through one or more donor atoms — monodentate (one donor, e.g. , ), bidentate (two donors, e.g.

Sample & Board Papers

Sample papers and previous-year board questions for this subject.

+Show 14 questions14 questions
  1. Q1An aqueous solution of a complex compound of formula Co(NH3)5Br(SO4) reacts readily with aqueous AgNO3 to give a yellowish white precipitate…Preview
  2. Q2What is the state of hybridisation of Fe in [FeF6]3- ion? (a) d2sp3 (b) dsp3 (c) sp3d2 (d) sp3dPreview
  3. Q3Which type of isomerism is shown by the two complexes [Co(NH3)5SO4]Br and [Co(NH3)5Br]SO4? How would you distinguish between the two complex…Preview
  4. Q4In which of the following metal ions is the hybridisation state of the metal sp3d2? (a) [Ni(CN)4]2- (b) [Fe(CN)6]4- (c) [Co(NH3)6]3+ (d) [Fe…Preview
  5. Q5Give two differences in between Double Salt and Complex Salt. **OR** Give two fundamental differences in between Nucleoside and Nucleotide.Preview
  6. Q6The metal atom in the complex compound acts as a (a) Lewis Base (b) Lewis Acid (c) Bronsted Base (d) Bronsted Acid **OR** The paramagnetic c…Preview
  7. Q7What is the valency of the central atom of the complex salt, K4[Fe(CN)6]? **OR** Give the formula of Mohr salt. What type of salt is it?Preview
  8. Q8Complex compounds [Co(NH3)5Cl]SO4 and [Co(NH3)5SO4]Cl show which of the following isomerism? (a) Hydrate isomerism (b) Coordination isomeris…Preview
  9. Q9(i) How would you differentiate between the two complex compounds [Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br by a suitable chemical test? (ii) Writ…Preview
  10. Q10The hybridisation state of the central metal atom of a square planar complex compound is (a) sp3 (b) dsp2 (c) d2sp (d) sp3dPreview
  11. Q11(i) Calculate the oxidation number of central metal atom of the following complex compound: [Cr(NH3)5Cl]SO4. (ii) When aqueous solution of o…Preview
  12. Q12Which type of isomerism is shown by the two complexes [Co(NH3)5SO4]Br and [Co(NH3)5Br]SO4? How would you distinguish between them? [1+1]Preview
  13. Q13What is meant by isomerism? Draw the possible geometrical isomers of [Pt(NH3)2Cl2] and write their IUPAC name.Preview
  14. Q14i) Write two differences with example between double salt and complex salt. ii) What is meant by Chelating effect? Draw the structure of che…Preview

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+Show 18 questions18 questions
  1. Example 1Classify each of the following ligands as monodentate, bidentate, or polydentate, giving the number of donor atoms in each case: (a) $\text{…Free
  2. Example 4Arrange the ligands $\text{I}^-$, $\text{H}_2\text{O}$, $\text{NH}_3$, and $\text{CN}^-$ in increasing order of ligand field strength accord…Free
  3. Example 6Determine the coordination number of the central metal ion in each of the following: (a) $[\text{Co}(\text{NH}_3)_6]\text{Cl}_3$, (b) $[\tex…Free
  4. Example 8$[\text{Sc}(\text{H}_2\text{O})_6]^{3+}$ is colourless, while $[\text{Ti}(\text{H}_2\text{O})_6]^{3+}$ is purple. Account for this differenc…Preview
  5. Example 10Using crystal field theory, determine the electronic configuration and the number of unpaired electrons in $[\text{CoF}_6]^{3-}$ ($\text{Co}…Preview
  6. Example 12Predict the shape and hybridization of the central metal in $[\text{Ni}(\text{CO})_4]$, given that $\text{Ni}$ is in the zero oxidation stat…Preview
  7. Example 14Write the IUPAC name of $\text{K}_4[\text{Fe}(\text{CN})_6]$.Preview
  8. Example 15Write the IUPAC name of $[\text{Co}(\text{NH}_3)_5\text{Cl}]\text{Cl}_2$.Preview
  9. Example 16Write the IUPAC name of $[\text{Cr}(\text{en})_3]\text{Cl}_3$.Preview
  10. Example 19Calculate the Effective Atomic Number (EAN) of iron in $[\text{Fe}(\text{CN})_6]^{4-}$ and state which noble gas it corresponds to.Preview
  11. Example 21According to Werner's theory, identify the primary valence and the secondary valence of cobalt in $\text{CoCl}_3.6\text{NH}_3$, and write it…Preview
  12. Example 23Using valence bond theory, explain why $[\text{Ni}(\text{CN})_4]^{2-}$ is square planar and diamagnetic while $[\text{NiCl}_4]^{2-}$ is tetr…Preview
  13. Example 25Describe how the five degenerate $d$-orbitals of a free metal ion split when six ligands approach it along the Cartesian axes to form an oct…Preview
  14. Example 27$[\text{CoF}_6]^{3-}$ is a high-spin octahedral complex with configuration $t_{2g}^4e_g^2$. Calculate its Crystal Field Stabilization Energy…Preview
  15. Example 29$[\text{Co}(\text{NH}_3)_5\text{Br}]\text{SO}_4$ and $[\text{Co}(\text{NH}_3)_5\text{SO}_4]\text{Br}$ have the same overall composition but…Preview
  16. Example 32$[\text{Co}(\text{NH}_3)_6][\text{Cr}(\text{CN})_6]$ and $[\text{Cr}(\text{NH}_3)_6][\text{Co}(\text{CN})_6]$ have identical overall composi…Preview
  17. Example 33The square planar complex $[\text{Pt}(\text{NH}_3)_2\text{Cl}_2]$ exists as cis and trans geometrical isomers. Describe the arrangement of l…Preview
  18. Example 35$[\text{Co}(\text{en})_3]^{3+}$ shows optical isomerism. Explain why, in terms of molecular symmetry, and describe the relationship between…Preview
+Show 18 questions18 questions
  1. Q2From the ligands $\text{Cl}^-$, $\text{NH}_3$, ethylenediamine ($\text{en}$), and EDTA$^{4-}$, identify which ones are chelating ligands. Ex…Free
  2. Q3The thiocyanate ion ($\text{SCN}^-$) and the nitrite ion ($\text{NO}_2^-$) are both described as ambidentate ligands. Explain what this term…Free
  3. Q5Classify each of the following ligands as a weak-field ligand or a strong-field ligand: $\text{F}^-$, $\text{en}$, $\text{H}_2\text{O}$, $\t…Free
  4. Q7Determine the coordination number of the central metal ion in (a) $[\text{Fe}(\text{C}_2\text{O}_4)_3]^{3-}$, where oxalate is a bidentate l…Preview
  5. Q9Aqueous solutions of most $\text{Zn}^{2+}$ complexes, such as $[\text{Zn}(\text{H}_2\text{O})_6]^{2+}$, are colourless, even though $\text{Z…Preview
  6. Q11Using crystal field theory, determine the electronic configuration and the number of unpaired electrons in $[\text{Co}(\text{NH}_3)_6]^{3+}$…Preview
  7. Q13$[\text{Ni}(\text{CN})_4]^{2-}$ is square planar and diamagnetic, while $[\text{NiCl}_4]^{2-}$ is tetrahedral and paramagnetic, even though…Preview
  8. Q17Write the formula for hexaamminecobalt(III) chloride.Preview
  9. Q18Write the formulas for (a) potassium tetracyanonickelate(II) and (b) tetraamminediaquacobalt(III) nitrate.Preview
  10. Q20Calculate the Effective Atomic Number (EAN) of the central metal in (a) $[\text{Co}(\text{NH}_3)_6]^{3+}$ and (b) $[\text{Ni}(\text{CO})_4]$…Preview
  11. Q22$\text{CoCl}_3.6\text{NH}_3$, $\text{CoCl}_3.5\text{NH}_3$, and $\text{CoCl}_3.4\text{NH}_3$ give 3, 2, and 1 mole of $\text{AgCl}$ respecti…Preview
  12. Q24Using valence bond theory, explain why $[\text{Co}(\text{NH}_3)_6]^{3+}$ is an inner orbital ($d^2sp^3$) diamagnetic octahedral complex, whi…Preview
  13. Q26How does the splitting of the $d$-orbitals in a tetrahedral crystal field differ from that in an octahedral field, both in the order of the…Preview
  14. Q28$\text{Fe}^{2+}$ ($d^6$) forms both $[\text{Fe}(\text{CN})_6]^{4-}$ and $[\text{Fe}(\text{H}_2\text{O})_6]^{2+}$. State the electronic confi…Preview
  15. Q30$\text{CrCl}_3.6\text{H}_2\text{O}$ is known to exist as three different coloured compounds: $[\text{Cr}(\text{H}_2\text{O})_6]\text{Cl}_3$…Preview
  16. Q31$[\text{Co}(\text{NH}_3)_5(\text{NO}_2)]\text{Cl}_2$ and $[\text{Co}(\text{NH}_3)_5(\text{ONO})]\text{Cl}_2$ are isomers of each other. Name…Preview
  17. Q34The octahedral complex $[\text{Co}(\text{NH}_3)_4\text{Cl}_2]^+$ (an $\text{MA}_4\text{B}_2$ type) shows cis and trans geometrical isomerism…Preview
  18. Q36Describe three important applications of coordination compounds, one each in (a) qualitative/quantitative analysis, (b) extraction of a meta…Preview