Gold(I,III) chloride
# Gold(I,III) chloride

Gold(I,III) chloride is a black solid with the chemical formula $Au_4Cl_8.$ It is an example of a mixed valence compound as it contains gold in two different oxidation states; square-planar gold(III) and almost linear gold(I). The compound is photosensitive as well as air- and moisture-sensitive.

## Synthesis

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.

    $Au_2(CO)Cl_4$ + $Au_2Cl_6$ → $COCl_2$ + $Au_4Cl_8$
    2 $Au_2Cl_6$ + 2 CO → $Au_4Cl_8$ + 2 $COCl_2$

## Structure and properties

Single crystals of gold(I,III) chloride are triclinic with a P1 space group and consist of discrete $Au_4Cl_8$ molecules with idealised $C_{2h}$ symmetry. Within this the Au(I) centers are linearly coordinated with a Cl-Au-Cl bond angle of 175.0° (close to the ideal value of 180°) and an average bond length of 2.30 Å. The Au(III) centers adopt a slightly irregular square-planar conformation with the Au-Cl bond lengths for bridging chlorides (2.33 Å) being slightly longer than those of terminal chlorides (2.24 Å).

