Unusually short Au(III)⋯Au(III) aurophilic contacts between anions. Necessity of counterions

Certain crystals contain unusually short contacts between Au(III) species, sometimes interpreted as unsupported aurophilic interactions. Calculations at various levels of theory, including CCSD(T)/CBS, demonstrate the potentials between anions containing these Au(III) centers are purely repulsive, despite the presence of noncovalent bonding between the Au centers. The occurrence of these anion⋯anion dimers in the crystal structure are dependent on the presence of counterions. On the other hand, rearranging the orientations of the anions relative to one another can yield metastable minima, albeit with energies much higher than a pair of fully dissociated species.