UPSC Civil Services (Mains), Chemistry optional · 2022 · Paper I

Q6(c). Neutral mixed sandwich compound of a d⁶ centre

10 marks
Topic: Coordination chemistry
Answered

Question

[Two pairs of π-donor ring ligands, (I) and (II), drawn in the paper.] Consider the above pairs of π-donor ligands. Identify the d⁶ metal ions/atom among Co(0), Mn(I), Fe(II) and Fe(III) which form neutral mixed sandwich compound. Explain.

Answer in brief

Mn(I): with pair II it forms the neutral 18-electron compound (η⁵-C₅H₅)Mn(η⁶-C₆H₆).

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Topic notes: organometallics: 18-electron rule, oxidative addition, fluxional molecules and Wilkinson's catalyst, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversmixed sandwich compound18-electron rulecyclopentadienylη6-benzene complexorganometallic electron counting

All parts of Question 6

6(a) Metal–metal bonds in Cp₂Fe₂(CO)₄; structure of Bi₅³⁺10 marks
6(b) Pale colours and line-like spectra of lanthanide ions10 marks
6(c) Neutral mixed sandwich compound of a d⁶ centre10 marks
6(d) Separating XeF₆; diborane with NH₃ and with Me₃N10 marks
6(e) Origin of the yellow colour of aqueous FeCl₃10 marks