When does gold behave as a halogen? Predicted uranium tetraauride and other MAu₄ tetrahedral species, (M = Ti, Zr, Hf, Th)

Quantum chemical calculations suggest that a series of molecules with the general formula MAu₄ are stable, where M = U, Th, and a group-4 atom. They correspond to Au in the formal valence state -1 and indicate that gold can act as a ligand similar to the halogen series. Of the MAu₄ species studied, UAu₄, the first predicted mixed gold uranium compound, has a short M-Au bond distance, 2.71 Å, which would locate Au between Br and I from the bond length point of view in the U-tetrahalide series. Energetically, the U-Au bond is weaker than the corresponding U-Br and U-I bonds.