Does cyclopentadienyl iron dicarbonyl dimer have a metal–metal bond? Who’s asking?

•I summarize the history of [CpFe(CO)2]2.•I present arguments for representing [CpFe(CO)2]2 with an Fe–Fe bond.•I draw an analogy between representation of molecules and translation.

In a 2012 essay, Green, Green and Parkin noted that certain bridged carbonyl complexes, including [CpFe(CO)2]2 (Cp = η5-cyclopentadienyl), are commonly depicted with an explicitly-drawn metal–metal bond in textbooks, and presented a rationale for why that constitutes a misrepresentation. Here I briefly summarize the history of that compound, in which Cotton played a major part, and try to show that there are at least equally valid justifications for keeping the M–M bond in the picture. More generally, I will argue against the idea of a single “best” representation of a complex molecule, by drawing upon analogies to literary translation.

Graphical abstractIn a 2012 essay, Green, Green and Parkin noted that certain bridged carbonyl complexes, including [CpFe(CO)2]2 (Cp = η5-cyclopentadienyl), are commonly depicted with an explicitly-drawn metal–metal bond in textbooks, and presented a rationale for why that constitutes a misrepresentation. Here I briefly summarize the history of that compound, in which Cotton played a major part, and try to show that there are at least equally valid justifications for keeping the M–M bond in the picture. More generally, I will argue against the idea of a single “best” representation of a complex molecule, by drawing upon analogies to literary translation.Figure optionsDownload full-size imageDownload as PowerPoint slide