Differentiating between F and OH Ligands in Homologous Gold(III) Complexes beyond X‐Ray Crystallography

The homologous fluoride and hydroxide complexes of gold(III) [PPh 4 ][(CF 3 ) 3 AuX] [X = F ( 1 ), OH ( 2 )] have been structurally characterized by single‐crystal X‐ray diffraction methods. Both of them crystallize in the P 2 1 / n space group, yet they are not isomorphous. Despite the intrinsic difficulty to distinguish between F − and OH − by X‐ray diffraction, the ability of the OH ligand in complex 2 to establish intramolecular OH…F hydrogen bonding with one of the CF 3 groups in cis position enables a clear differentiation from the fluoride complex 1 . Given the tendency of late‐transition metal fluorides to undergo hydrolysis, much caution should be taken when ascribing the identity of a fluoride ligand by X‐ray diffraction methods, especially where unusual geometries are implied.