UPSC Combined Geo-Scientist, Mains · 2017 · Mains Paper I

Q1(d). Eighteen-electron counts

Question

Identify the organometallic compound which obeys the 18 electron rule. (i) [(η⁷-C₇H₇)Mo(CO)₃]⁺ (ii) [(η⁵-C₅H₅)Fe(CO)₂I].

Both displayed compounds have 18 valence electrons.

Use one counting convention consistently.
For the neutral iron compound, Fe contributes 8, η⁵-Cp 5, two CO ligands 4 and I 1: 8+5+4+1=18.
An ionic check for the latter uses Fe(II), d⁶, Cp⁻ as a 6-electron donor, I⁻ as a 2-electron donor and two CO as 4: 6+6+2+4=18.

The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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