Gold(I,III) chloride is a black solid with the chemical formula
Au4 Cl8. It is an example of a
mixed valence compound
Mixed valence complexes contain an element which is present in more than one oxidation state. Well-known mixed valence compounds include the Creutz–Taube complex, Prussian blue, and molybdenum blue. Many solids are mixed-valency including in ...
as it contains gold in two different
oxidation states
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Co ...
; square-planar gold(III) and almost linear gold(I). The compound is
photosensitive Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and phototoxicity. ...
as well as air- and moisture-sensitive.
Synthesis
Gold(I,III) chloride may be prepared by the reaction of
gold(III) chloride
Gold(III) chloride, traditionally called auric chloride, is a compound of gold and chlorine with the molecular formula . The "III" in the name indicates that the gold has an oxidation state of +3, typical for many gold compounds. Gold(III) c ...
with gold carbonyl chloride
or
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
at room temperature in
thionyl chloride
Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year bein ...
.
: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 P
space group
In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unchan ...
and consist of discrete Au
4Cl
8 molecules with idealised C
2h symmetry
Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definit ...
.
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).
References
Gold compounds
Chlorides
Metal halides
Mixed valence compounds
Light-sensitive chemicals
Gold–halogen compounds
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