Synergic Bonding in Metal-Carbonyl Complexes: 18 flashcards
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1. What is synergic bonding?
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A two-way electron exchange where the metal donates σ electron density to the ligand and the ligand accepts π electron density back from the metal's d-orbitals, with each flow strengthening the other.
2. In the diagram, which direction does the σ bond arrow point?
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From the metal M to the carbon of CO (M → C).
3. Which orbitals of CO accept the π back-bond?
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The π 2px* and π 2py* antibonding orbitals.
4. Which metal orbitals supply electrons for π back-donation?
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The metal's d-orbitals (d-electrons).
5. Name the three ligands identified as forming synergic bonds.
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CO, CN⁻, and NO.
6. Why does σ donation strengthen π back-donation?
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σ donation makes the carbon of CO more electron-rich, so it becomes a better acceptor for π back-donation.
7. Why does π back-donation strengthen σ donation?
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Back-donation makes the metal more electron-poor, increasing its ability to donate σ electron density.
8. What is the synergic effect?
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The mutual reinforcement of σ donation and π back-donation, making the metal–CO bond stronger than either interaction alone.
9. What happens to the C≡O bond when back-donation increases?
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The C≡O bond weakens because electron density fills the π* antibonding orbitals.
10. How does back-bonding affect the IR stretching frequency of CO?
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The IR stretching frequency of CO drops as back-bonding increases.
11. Why are CO, CN⁻, and NO good synergic ligands?
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They have lone pairs for σ donation and accessible π* antibonding orbitals to accept π electron density.
12. What does the label σ* 2pz on the oxygen end of CO indicate?
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That CO has an antibonding orbital available to accept electron density.
13. What is the common mistake about CO in metal bonding?
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Assuming CO only donates its lone pair to the metal and ignoring the π back-bond.
14. Why is synergic bonding central to organometallic chemistry?
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It explains the stability of metal carbonyls and why CO is a common ligand in catalysts and industrial processes.
15. In the diagram, how many π back-bonds are shown and where?
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Two π back-bonds, one above and one below the M–C–O axis.
16. What is the reference line for the π back-bonds in the diagram?
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The M–C–O axis.
17. How many d-orbitals are shown around the metal center in the diagram?
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Four d-orbitals.
18. Why is the metal–CO bond stronger than σ donation alone would predict?
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Because σ donation and π back-donation reinforce each other in synergic bonding.
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