One correction- FES also has no right angles, according to phenix-dev-3885/modules/chem_data/geostd/f/data_FES.cif and high resolution structure 1rie.pdb Edward Berry wrote on 4/18/2022 2:45 PM:
Have you seen: Iron–sulfur clusters have no right angles Nigel W. Moriarty and Paul D. Adams, Acta Cryst. (2019). D75, 16–20 <https://urldefense.com/v3/__http://journals.iucr.org/d/issues/2019/01/00/rr5... >
The Phenix F3S library worked well for our Complex II structures a few years back. And those structures definitely confirm that the angles are not 90* for F3S. (FES Fe2S2 has close to right angles, I think) You have to be sure that the atoms are arranged in the same way as in the model or the restraints will try to invert your cluster;, and that the Cys ligands connect to the right irons. Ed