Gold(III) compounds are isoelectronic with the corresponding platinum(II) complexes, some of which have strong anti-cancer properties. This information served as the basis for experiments trying to synthesize gold compounds with similar biological effects.
Because Au(III) is easily reduced to Au(I), which either happens during production of the compounds or in vivo, these experiments have not yet been successful.
However, a monomeric gold(I) complex with the bidentate phosphine ligand bis(diphenylphosphino)ethane (DPPE) shows promising anti-cancer properties and is currently undergoing clinical trials.
The gold atom in this complex is tetrahedrally coordinated, which is an unusual coordination environment for gold(I).