Gold(I,III) chloride is the inorganic compound with the chemical formula Au<sub>4</sub>Cl<sub>8</sub>. It is a mixed valence compound as it contains gold in two oxidation states; square-planar gold(III) and almost linear gold(I). The compound, which is black, is photosensitive as well as air- and moisture-sensitive.
According to the procedure by Calderazzo et al., gold(I,III) chloride may be prepared by the reaction of gold(III) chloride with gold carbonyl chloride or carbon monoxide at room temperature in thionyl chloride.
Single crystals of gold(I,III) chloride are triclinic with a P space group and consist of discrete Au<sub>4</sub>Cl<sub>8</sub> molecules with idealised C<sub>2h</sub> symmetry. Within this the Au(I) centers are linearly coordinated with a Cl-Au-Cl bond angle of 175.0ð (close to the ideal value of 180ð) and an average bond length of 2.30 ÃÂ. The Au(III) centers adopt a slightly irregular square-planar conformation with the Au-Cl bond lengths for bridging chlorides (2.33 à) being slightly longer than those of terminal chlorides (2.24 à).