UPSC Combined Geo-Scientist, Mains · 2020 · Mains Paper I

Q1(g). Triiron dodecacarbonyl

Question

Write the structure of triiron dodecarbonyl. Mention the number of M–M bonds.

Fe₃(CO)₁₂ has a triangular Fe framework with three Fe–Fe bonds; its familiar solid-state structure has ten terminal and two bridging CO ligands.

Two CO ligands bridge the same Fe–Fe edge.
Total electron count before M–M bonding is 3(8)+12(2)=48. Three 18-electron centres require 54 in local counting, so (54-48)/2=3 metal–metal bonds.
Each Fe attains 18 electrons when the two neighbouring metal–metal contributions are included.

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.

CoversTriiron dodecacarbonylMetal clusters