Trihalides
The triiodide does not exist. AuCl3 readily forms out of the elements at temperatures below 254 °C. It is a volatile red solid. The volatile species is the dimer Au2Cl6.. Likewise, AuBr3 can be formed from the elements and exists primarily as the dimer Au2Br6.
Gold(III) fluoride, AuF3, has a unique polymeric helical structure, containing corner-sharing {AuF4} squares.
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