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Q5.22:
Discuss the nature of bonding in metal carbonyls.
Solution :
1. Fundamental Nature of Metal Carbonyls
Metal carbonyls are coordination complexes where carbon monoxide ($\text{CO}$) acts as a neutral ligand bonded to a transition metal in a low oxidation state (often zero). The bonding in these compounds is unique because it involves a synergistic effect known as synergic bonding, which strengthens the metal-carbon bond while simultaneously weakening the carbon-oxygen bond.
2. The Two-Fold Bonding Mechanism
The bonding arises from two simultaneous orbital interactions:
- $\sigma$-Donation (Metal-Carbon $\sigma$-bond): The lone pair of electrons on the carbon atom of the $\text{CO}$ molecule is donated into an empty hybrid orbital of the transition metal atom. This forms a $\text{M} \leftarrow \text{CO}$ $\sigma$-bond.
- $\pi$-Back-bonding (Metal-Carbon $\pi$-bond): The filled metal $d$-orbitals overlap with the empty antibonding $\pi^*$ molecular orbitals of the $\text{CO}$ ligand. This involves the donation of electron density from the metal to the ligand, forming a $\text{M} \rightarrow \text{CO}$ $\pi$-bond.
3. Visual Representation of Synergic Bonding
4. Consequences of the Synergic Effect
| Interaction | Electronic Effect | Structural Consequence |
|---|---|---|
| $\sigma$-donation | Electron density flows M $\leftarrow$ C | Increases M-C bond order |
| $\pi$-back-donation | Electron density flows M $\rightarrow$ C | Decreases C-O bond order; Increases M-C bond order |
Per the Molecular Orbital Theory, the back-donation of electron density into the $\pi^*$ orbital of $\text{CO}$ results in the reduction of the $\text{C} \equiv \text{O}$ bond order (from 3 towards 2). Consequently, the bond length of $\text{C}-\text{O}$ increases compared to free $\text{CO}$, while the $\text{M}-\text{C}$ bond length decreases, demonstrating partial double-bond character [In accordance with the Dewar-Chatt-Duncanson model].
5. Evidence and Summary
The extent of this bonding can be experimentally verified using Infrared (IR) Spectroscopy. As the metal-to-ligand $\pi$-back-donation increases, the $\text{C}-\text{O}$ stretching frequency decreases. This confirms that the strength of the metal-carbon bond is inversely proportional to the strength of the carbon-oxygen bond.
Final Solution: Bonding in metal carbonyls is characterized by a synergistic interaction consisting of $\sigma$-donation from the $\text{CO}$ ligand to the metal and $\pi$-back-donation from the metal to the empty antibonding $\pi^*$ orbitals of the $\text{CO}$ ligand. This stabilizes the complex through back-bonding, creating a shorter, stronger $\text{M}-\text{C}$ bond and a longer, weaker $\text{C}-\text{O}$ bond.
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.
- Q5.23 (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.
- Q5.4: 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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