Congratulations to
Sandwich molecule

Collage: A sandwich with an iron ball in the middle

Picture: Peyker /

Ernst Otto Fischer was awarded the Nobel Prize in Chemistry in 1973 for a seemingly impossible molecule called ferrocene. Working at what is now the Technical University of Munich (TUM), Fischer discovered its sandwich-like structure with an iron atom as the filling. This breakthrough helped scientists deepen their understanding of how atoms can bond to each other.

A new kind of chemical bonding

Ernst Otto Fischer could himself barely believe the results of his experiments in 1952 – but no other explanation was possible. An iron atom really was layered between two five-membered hydrocarbon rings, like the filling in a sandwich. The very idea seemed preposterous at the time. Fischer contended that a metal atom was surrounded and “held” by two organic groups. The scientific community had never before come across a molecule with that type of structure and had never even considered it possible. Yet this had to be the reason for the incredible stability of these orange-colored crystals, which only start to break down at a temperature of around 470°C.

The molecule soon came to be known as “ferrocene”. Fischer was awarded the Nobel Prize in 1973 for proving its sandwich structure – and for producing and investigating countless similar molecules with his laboratory team. The discovery of the sandwich compound fundamentally changed our understanding of how atoms can bond to each other. Fischer shared the Nobel Prize with Geoffrey Wilkinson. The English scientist had uncovered the structure of ferrocene in Harvard around the same time and, along with Professor Fischer, is regarded as a pioneer of organometallic chemistry.

It was Wilkinson who nicknamed this extraordinary compound the “molecular sandwich” – a fitting description by all accounts. The Nobel Committee actually presented ferrocene as an iron sphere between two slices of bread.

„They did not prepare the first sandwich but they were the first to grasp the odd nature of the compound and its conceptual importance.“

Nobel prize medal

Nobel committee,1973, at the prize ceremony for Ernst Otto Fischer und Geoffrey Wilkinson

Bild: © ®The Nobel Foundation: Photo: Lovis Engblom

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