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Q5.4:
What is meant by unidentate, didentate and ambidentate ligands? Give two examples for each.
Solution :
1. Definition of Ligands and Denticity
In coordination chemistry, a ligand is an ion or molecule attached to a central metal atom or ion to form a coordination complex. The denticity of a ligand refers to the number of donor atoms through which the ligand coordinates to the central metal atom. Ligands are classified based on the number of donor atoms they utilize to form coordinate covalent bonds.
2. Classification of Ligands
| Ligand Type | Definition | Examples |
|---|---|---|
| Unidentate | Ligands that coordinate to the central metal atom through only one donor atom. | $Cl^-$, $NH_3$ |
| Didentate | Ligands that have two donor atoms and can coordinate to the central metal atom through both simultaneously, forming a chelate ring. | $H_2N-CH_2-CH_2-NH_2$ (en), $C_2O_4^{2-}$ (ox) |
| Ambidentate | Monodentate ligands which have two different donor atoms, but only one of them forms a coordinate bond at a time. | $NO_2^-$, $SCN^-$ |
3. Analytical Breakdown of Ligand Types
A. Unidentate Ligands
These ligands possess a single lone pair of electrons available for donation. They form one coordinate bond per ligand molecule.
- Chloride ion ($Cl^-$): Donates electron density from a lone pair on the chlorine atom.
- Ammine ($NH_3$): Donates the lone pair of electrons from the nitrogen atom to the metal orbital.
B. Didentate (Bidentate) Ligands
These ligands possess two distinct donor sites. When both sites attach to the same metal, they form a heterocyclic ring structure known as a chelate [Per Chelate Effect].
- Ethane-1,2-diamine ($en$): $H_2N-CH_2-CH_2-NH_2$. Both nitrogen atoms act as donor sites.
- Oxalate ion ($ox^{2-}$): $C_2O_4^{2-}$. Two oxygen atoms donate electron pairs to the metal center.
C. Ambidentate Ligands
These exhibit linkage isomerism because they possess multiple potential donor atoms, though sterics or electronic factors usually dictate which atom binds.
- Nitrite ion ($NO_2^-$): Can bind via Nitrogen (nitro, $-NO_2$) or via Oxygen (nitrito, $-ONO$).
- Thiocyanate ion ($SCN^-$): Can bind via Sulfur (thiocyanato-S, $-SCN$) or via Nitrogen (isothiocyanato-N, $-NCS$).
4. Structural Visualization of Linkage
Final Solution: Unidentate ligands (e.g., $Cl^-$, $NH_3$) use one donor atom; Didentate ligands (e.g., $en$, $ox^{2-}$) use two donor atoms to form rings; Ambidentate ligands (e.g., $NO_2^-$, $SCN^-$) contain two potential donor sites but coordinate through only one at a time.
More Questions from Class 12 Chemistry Coordination Compounds Exercises
- Q5.1: Explain the bonding in coordination compounds in terms of Werner’s postulates.
- Q5.1: Explain the bonding in coordination compounds in terms of Werner’s postulates.
- Q5.10 (i): Draw the structures of optical isomers of: ([Cr(C_{2}O_{4})_{3}]^{3-})
- Q5.10 (ii): Draw the structures of optical isomers of: ([PtCl_{2}(en)_{2}]^{2+})
- Q5.10 (iii): Draw the structures of optical isomers of: ([Cr(NH_{3})_{2}Cl_{2}(en)]^{+})
- Q5.10(i): Draw the structures of optical isomers of: \([Cr(C_{2}O_{4})_{3}]^{3-}\)
- Q5.10(ii): Draw the structures of optical isomers of: \([PtCl_{2}(en)_{2}]^{2+}\)
- Q5.10(iii): Draw the structures of optical isomers of: \([Cr(NH_{3})_{2}Cl_{2}(en)]^{+}\)
- Q5.11 (i): Draw all the isomers (geometrical and optical) of: ([CoCl_{2}(en)_{2}]^{+})
- Q5.11 (ii): Draw all the isomers (geometrical and optical) of: ([Co(NH_{3})Cl(en)_{2}]^{2+})
- Q5.11 (iii): Draw all the isomers (geometrical and optical) of: ([Co(NH_{3})_{2}Cl_{2}(en)]^{+})
- Q5.11(i): Draw all the isomers (geometrical and optical) of: \([CoCl_{2}(en)_{2}]^{+}\)
- Q5.11(ii): Draw all the isomers (geometrical and optical) of: \([Co(NH_{3})Cl(en)_{2}]^{2+}\)
- Q5.11(iii): Draw all the isomers (geometrical and optical) of: \([Co(NH_{3})_{2}Cl_{2}(en)]^{+}\)
- Q5.12: Write all the geometrical isomers of \([Pt(NH_{3})(Br)(Cl)(py)]\) and how many of these will exhibit optical isomers?
- Q5.12: Write all the geometrical isomers of ([Pt(NH_{3})(Br)(Cl)(py)]) and how many of these will exhibit optical isomers?
- Q5.13: Aqueous copper sulphate solution (blue in colour) gives: (i) a green precipitate with aqueous potassium fluoride and (ii) a bright green solution with aqueous potassium chloride. Explain these experimental results.
- Q5.13: Aqueous copper sulphate solution (blue in colour) gives: (i) a green precipitate with aqueous potassium fluoride and (ii) a bright green solution with aqueous potassium chloride. Explain these experimental results.
- Q5.14: What is the coordination entity formed when excess of aqueous \(KCN\) is added to an aqueous solution of copper sulphate? Why is it that no precipitate of copper sulphide is obtained when \(H_{2}S(g)\) is passed through this solution?
- Q5.14: What is the coordination entity formed when excess of aqueous KCN is added to an aqueous solution of copper sulphate? Why is it that no precipitate of copper sulphide is obtained when ((H_{2}S(g))) is passed through this solution?
- Q5.15 (i): Discuss the nature of bonding on the basis of valence bond theory: ([Fe(CN)_{6}]^{4-})
- Q5.15 (ii): Discuss the nature of bonding on the basis of valence bond theory: ([FeF_{6}]^{3-})
- Q5.15 (iii): Discuss the nature of bonding on the basis of valence bond theory: ([Co(C_{2}O_{4})_{3}]^{3-})
- Q5.15 (iv): Discuss the nature of bonding on the basis of valence bond theory: ([CoF_{6}]^{3-})
- Q5.15(i): Discuss the nature of bonding in the following coordination entities on the basis of valence bond theory: \([Fe(CN)_{6}]^{4-}\)
- Q5.15(ii): Discuss the nature of bonding in the following coordination entities on the basis of valence bond theory: \([FeF_{6}]^{3-}\)
- Q5.15(iii): Discuss the nature of bonding in the following coordination entities on the basis of valence bond theory: \([Co(C_{2}O_{4})_{3}]^{3-}\)
- Q5.15(iv): Discuss the nature of bonding in the following coordination entities on the basis of valence bond theory: \([CoF_{6}]^{3-}\)
- Q5.16: Draw figure to show the splitting of d orbitals in an octahedral crystal field.
- Q5.16: Draw figure to show the splitting of d orbitals in an octahedral crystal field.
- Q5.17: What is spectrochemical series? Explain the difference between a weak field ligand and a strong field ligand.
- Q5.17: What is spectrochemical series? Explain the difference between a weak field ligand and a strong field ligand.
- Q5.18: What is crystal field splitting energy? How does the magnitude of \(\Delta_{o}\) decide the actual configuration of d orbitals in a coordination entity?
- Q5.18: What is crystal field splitting energy? How does the magnitude of (\Delta_{o}) decide the actual configuration of d orbitals in a coordination entity?
- Q5.19: \([Cr(NH_{3})_{6}]^{3+}\) is paramagnetic while \([Ni(CN)_{4}]^{2-}\) is diamagnetic. Explain why?
- Q5.19: ([Cr(NH_{3})_{6}]^{3+}) is paramagnetic while ([Ni(CN)_{4}]^{2-}) is diamagnetic. Explain why?
- Q5.2: \(FeSO_{4}\) solution mixed with \((NH_{4})_{2}SO_{4}\) solution in 1:1 molar ratio gives the test of \(Fe^{2+}\) ion but \(CuSO_{4}\) solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of \(Cu^{2+}\) ion. Explain why?
- Q5.2: ((FeSO_{4})) solution mixed with ((NH_{4})_{2}SO_{4}) solution in 1:1 molar ratio gives the test of ((Fe^{2+})) ion but ((CuSO_{4})) solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of ((Cu^{2+})) ion. Explain why?
- Q5.20: A solution of \([Ni(H_{2}O)_{6}]^{2+}\) is green but a solution of \([Ni(CN)_{4}]^{2-}\) is colourless. Explain.
- Q5.20: A solution of ([Ni(H_{2}O)_{6}]^{2+}) is green but a solution of ([Ni(CN)_{4}]^{2-}) is colourless. Explain.
- Q5.21: \([Fe(CN)_{6}]^{4-}\) and \([Fe(H_{2}O)_{6}]^{2+}\) are of different colours in dilute solutions. Why?
- Q5.21: ([Fe(CN)_{6}]^{4-}) and ([Fe(H_{2}O)_{6}]^{2+}) are of different colours in dilute solutions. Why?
- Q5.22: Discuss the nature of bonding in metal carbonyls.
- Q5.22: Discuss the nature of bonding in metal carbonyls.
- Q5.23 (i): Give the oxidation state, d orbital occupation and coordination number of the central metal ion: (K_{3}[Co(C_{2}O_{4})_{3}])
- Q5.23 (ii): Give the oxidation state, d orbital occupation and coordination number of the central metal ion: (cis-[CrCl_{2}(en)_{2}]Cl)
- Q5.23 (iii): Give the oxidation state, d orbital occupation and coordination number of the central metal ion: ((NH_{4})_{2}[CoF_{4}])
- Q5.23 (iv): Give the oxidation state, d orbital occupation and coordination number of the central metal ion: ([Mn(H_{2}O)_{6}]SO_{4})
- Q5.23(i): Give the oxidation state, d orbital occupation and coordination number of the central metal ion in the following complexes: \(K_{3}[Co(C_{2}O_{4})_{3}]\)
- Q5.23(ii): Give the oxidation state, d orbital occupation and coordination number of the central metal ion in the following complexes: cis-\([CrCl_{2}(en)_{2}]Cl\)
- Q5.23(iii): Give the oxidation state, d orbital occupation and coordination number of the central metal ion in the following complexes: \((NH_{4})_{2}[CoF_{4}]\)
- Q5.23(iv): Give the oxidation state, d orbital occupation and coordination number of the central metal ion in the following complexes: \([Mn(H_{2}O)_{6}]SO_{4}\)
- Q5.24 (i): Write down the IUPAC name for the complex and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex: (K[Cr(H_{2}O)_{2}(C_{2}O_{4})_{2}].3H_{2}O)
- Q5.24 (ii): Write down the IUPAC name for the complex and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex: ([Co(NH_{3})_{5}Cl]Cl_{2})
- Q5.24 (iii): Write down the IUPAC name for the complex and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex: ([CrCl_{3}(py)_{3}])
- Q5.24 (iv): Write down the IUPAC name for the complex and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex: (Cs[FeCl_{4}])
- Q5.24 (v): Write down the IUPAC name for the complex and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex: (K_{4}[Mn(CN)_{6}])
- Q5.24(i): Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex: \(K[Cr(H_{2}O)_{2}(C_{2}O_{4})_{2}].3H_{2}O\)
- Q5.24(ii): Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex: \([Co(NH_{3})_{5}Cl]Cl_{2}\)
- Q5.24(iii): Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex: \([CrCl_{3}(py)_{3}]\)
- Q5.24(iv): Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex: \(Cs[FeCl_{4}]\)
- Q5.24(v): Write down the IUPAC name for each of the following complexes and indicate the oxidation state, electronic configuration and coordination number. Also give stereochemistry and magnetic moment of the complex: \(K_{4}[Mn(CN)_{6}]\)
- Q5.25: Explain the violet colour of the complex \([Ti(H_{2}O)_{6}]^{3+}\) on the basis of crystal field theory.
- Q5.25: Explain the violet colour of the complex ([Ti(H_{2}O)_{6}]^{3+}) on the basis of crystal field theory.
- Q5.26: What is meant by the chelate effect? Give an example.
- Q5.26: What is meant by the chelate effect? Give an example.
- Q5.27: Discuss briefly giving an example in each case the role of coordination compounds in: (i) biological systems (iii) analytical chemistry (ii) medicinal chemistry and (iv) extraction/metallurgy of metals.
- Q5.27(i): Discuss briefly giving an example in each case the role of coordination compounds in: biological systems
- Q5.27(ii): Discuss briefly giving an example in each case the role of coordination compounds in: medicinal chemistry
- Q5.27(iii): Discuss briefly giving an example in each case the role of coordination compounds in: analytical chemistry
- Q5.27(iv): Discuss briefly giving an example in each case the role of coordination compounds in: extraction/metallurgy of metals.
- Q5.28: How many ions are produced from the complex \(Co(NH_{3})_{6}Cl_{2}\) in solution?
- Q5.28: How many ions are produced from the complex (Co(NH_{3})_{6}Cl_{2}) in solution?
- Q5.29: Amongst the following ions which one has the highest magnetic moment value?
- Q5.29: Amongst the following ions which one has the highest magnetic moment value?
- Q5.3: Explain with two examples each of the following: coordination entity, ligand, coordination number, coordination polyhedron, homoleptic and heteroleptic.
- Q5.3: Explain with two examples each of the following: coordination entity, ligand, coordination number, coordination polyhedron, homoleptic and heteroleptic.
- Q5.30: Amongst the following, the most stable complex is
- Q5.30: Amongst the following, the most stable complex is
- Q5.31: What will be the correct order for the wavelengths of absorption in the visible region for the following: \([Ni(NO_{2})_{6}]^{4-}\), \([Ni(NH_{3})_{6}]^{2+}\), \([Ni(H_{2}O)_{6}]^{2+}\)?
- Q5.31: What will be the correct order for the wavelengths of absorption in the visible region for the following: ([Ni(NO_{2})_{6}]^{4-}), ([Ni(NH_{3})_{6}]^{2+}), ([Ni(H_{2}O)_{6}]^{2+})?
- Q5.4: What is meant by unidentate, didentate and ambidentate ligands? Give two examples for each.
- Q5.5 (i): Specify the oxidation numbers of the metals: ([Co(H_{2}O)(CN)(en)_{2}]^{2+})
- Q5.5 (ii): Specify the oxidation numbers of the metals: ([CoBr_{2}(en)_{2}]^{+})
- Q5.5 (iii): Specify the oxidation numbers of the metals: ([PtCl_{4}]^{2-})
- Q5.5 (iv): Specify the oxidation numbers of the metals: (K_{3}[Fe(CN)_{6}])
- Q5.5 (v): Specify the oxidation numbers of the metals: ([Cr(NH_{3})_{3}Cl_{3}])
- Q5.5(i): Specify the oxidation numbers of the metals in the following coordination entities: \([Co(H_{2}O)(CN)(en)_{2}]^{2+}\)
- Q5.5(ii): Specify the oxidation numbers of the metals in the following coordination entities: \([CoBr_{2}(en)_{2}]^{+}\)
- Q5.5(iii): Specify the oxidation numbers of the metals in the following coordination entities: \([PtCl_{4}]^{2-}\)
- Q5.5(iv): Specify the oxidation numbers of the metals in the following coordination entities: \(K_{3}[Fe(CN)_{6}]\)
- Q5.5(v): Specify the oxidation numbers of the metals in the following coordination entities: \([Cr(NH_{3})_{3}Cl_{3}]\)
- Q5.6 (i): Using IUPAC norms write the formulas: Tetrahydroxidozincate(II)
- Q5.6 (ii): Using IUPAC norms write the formulas: Potassium tetrachloridopalladate(II)
- Q5.6 (iii): Using IUPAC norms write the formulas: Diamminedichloridoplatinum(II)
- Q5.6 (iv): Using IUPAC norms write the formulas: Potassium tetracyanidonickelate(II)
- Q5.6 (ix): Using IUPAC norms write the formulas: Tetrabromidocuprate(II)
- Q5.6 (v): Using IUPAC norms write the formulas: Pentaamminenitrito-O-cobalt(III)
- Q5.6 (vi): Using IUPAC norms write the formulas: Hexaamminecobalt(III) sulphate
- Q5.6 (vii): Using IUPAC norms write the formulas: Potassium tri(oxalato)chromate(III)
- Q5.6 (viii): Using IUPAC norms write the formulas: Hexaammineplatinum(IV)
- Q5.6 (x): Using IUPAC norms write the formulas: Pentaamminenitrito-N-cobalt(III)
- Q5.6(i): Using IUPAC norms write the formulas for the following: Tetrahydroxidozincate(II)
- Q5.6(ii): Using IUPAC norms write the formulas for the following: Potassium tetrachloridopalladate(II)
- Q5.6(iii): Using IUPAC norms write the formulas for the following: Diamminedichloridoplatinum(II)
- Q5.6(iv): Using IUPAC norms write the formulas for the following: Potassium tetracyanidonickelate(II)
- Q5.6(ix): Using IUPAC norms write the formulas for the following: Tetrabromidocuprate(II)
- Q5.6(v): Using IUPAC norms write the formulas for the following: Pentaamminenitrito-O-cobalt(III)
- Q5.6(vi): Using IUPAC norms write the formulas for the following: Hexaamminecobalt(III) sulphate
- Q5.6(vii): Using IUPAC norms write the formulas for the following: Potassium tri(oxalato)chromate(III)
- Q5.6(viii): Using IUPAC norms write the formulas for the following: Hexaammineplatinum(IV)
- Q5.6(x): Using IUPAC norms write the formulas for the following: Pentaamminenitrito-N-cobalt(III)
- Q5.7 (i): Using IUPAC norms write the systematic names: ([Co(NH_{3})_{6}]Cl_{3})
- Q5.7 (ii): Using IUPAC norms write the systematic names: ([Pt(NH_{3})_{2}Cl(NH_{2}CH_{3})]Cl)
- Q5.7 (iii): Using IUPAC norms write the systematic names: ([Ti(H_{2}O)_{6}]^{3+})
- Q5.7 (iv): Using IUPAC norms write the systematic names: ([Co(NH_{3})_{4}Cl(NO_{2})]Cl)
- Q5.7 (ix): Using IUPAC norms write the systematic names: ([Ni(CO)_{4}])
- Q5.7 (v): Using IUPAC norms write the systematic names: ([Mn(H_{2}O)_{6}]^{2+})
- Q5.7 (vi): Using IUPAC norms write the systematic names: ([NiCl_{4}]^{2-})
- Q5.7 (vii): Using IUPAC norms write the systematic names: ([Ni(NH_{3})_{6}]Cl_{2})
- Q5.7 (viii): Using IUPAC norms write the systematic names: ([Co(en)_{3}]^{3+})
- Q5.7(i): Using IUPAC norms write the systematic names of the following: \([Co(NH_{3})_{6}]Cl_{3}\)
- Q5.7(ii): Using IUPAC norms write the systematic names of the following: \([Pt(NH_{3})_{2}Cl(NH_{2}CH_{3})]Cl\)
- Q5.7(iii): Using IUPAC norms write the systematic names of the following: \([Ti(H_{2}O)_{6}]^{3+}\)
- Q5.7(iv): Using IUPAC norms write the systematic names of the following: \([Co(NH_{3})_{4}Cl(NO_{2})]Cl\)
- Q5.7(ix): Using IUPAC norms write the systematic names of the following: \([Ni(CO)_{4}]\)
- Q5.7(v): Using IUPAC norms write the systematic names of the following: \([Mn(H_{2}O)_{6}]^{2+}\)
- Q5.7(vi): Using IUPAC norms write the systematic names of the following: \([NiCl_{4}]^{2-}\)
- Q5.7(vii): Using IUPAC norms write the systematic names of the following: \([Ni(NH_{3})_{6}]Cl_{2}\)
- Q5.7(viii): Using IUPAC norms write the systematic names of the following: \([Co(en)_{3}]^{3+}\)
- Q5.8: List various types of isomerism possible for coordination compounds, giving an example of each.
- Q5.8: List various types of isomerism possible for coordination compounds, giving an example of each.
- Q5.9 (i): How many geometrical isomers are possible? ([Cr(C_{2}O_{4})_{3}]^{3-})
- Q5.9 (ii): How many geometrical isomers are possible? ([Co(NH_{3})_{3}Cl_{3}])
- Q5.9(i): How many geometrical isomers are possible in the following coordination entities? \([Cr(C_{2}O_{4})_{3}]^{3-}\)
- Q5.9(ii): How many geometrical isomers are possible in the following coordination entities? \([Co(NH_{3})_{3}Cl_{3}]\)
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