The electrons of each individual iron atom possess a tiny magnetic moment, the so-called spin. When several iron atoms meet in a catalyst, the way their spins are oriented relative to each other is crucial. A research team at the University of Vienna was able to decipher the mode of action of an iron-based catalyst using quantum mechanical calculations. One promising candidate is MIL-101(Fe), a metal-organic framework (MOF) in which three iron atoms are arranged in a triangular shape around a central oxygen atom. Until now, it was assumed that the spins of the three iron atoms are aligned in parallel to each other.