Q7(b)(i). M–C and C–O bond orders in Ni(CO)₄, [Co(CO)₄]⁻ and [Fe(CO)₄]²⁻
The bond orders of some metal carbonyls are: Ni(CO)₄, M–C 1.33 and C–O 2.64; [Co(CO)₄]⁻, M–C 1.89 and C–O 2.14; [Fe(CO)₄]²⁻, M–C 2.16 and C–O 1.85. Explain the above facts.
Answer in brief
The three species are isoelectronic (d¹⁰, tetrahedral, 18 electrons); from Ni(0) to Co(−I) to Fe(−II) the metal carries more negative charge and back-donates more into CO π*, so M–C bond order rises and C–O bond order falls.
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Coversmetal carbonylsπ back-donationsynergic bondingCO stretching frequencyisoelectronic carbonylates
All parts of Question 7
- 7(a) Splitting of d orbitals in a square-planar field10 marks
- 7(b)(i) M–C and C–O bond orders in Ni(CO)₄, [Co(CO)₄]⁻ and [Fe(CO)₄]²⁻10 marks
- 7(b)(ii) Identify A, B and C5 marks
- 7(c)(i) [CoF₆]³⁻ paramagnetic, [Co(CN)₆]³⁻ diamagnetic10 marks
- 7(c)(ii) Structures and magnetic behaviour of Co₂(CO)₈15 marks