Gold trihalides

Figure 6-45. High-spin and low-spin electronic configuration of gold trihalides and the splitting of the low-spin E state of gold trihalides.

Table 28.3 is a list of the known halides only gold forms a pentahalide and trihalides and, with... 

All four monohalides of gold have been prepared but the fluoride only by mass spectrometric methods. AuCl and AuBr are formed by heating the trihalides to no more than 150°C and Aul by heating the metal and iodine. At higher temperatures they dissociate into the elements. Aul is a chain polymer which features linear 2-coordinate Au with Au-I 262 pm and the angle Au-I-Au 72°. 

Silver iodide is the only silver halide with an adamantine structure, the two elements having covalent radii in the ratio 1.34 1.33. Both AgCl (1.34 0.99) and AgBr (1.34 1.14) have a rock-salt structure and an ionic character. Gold (I) fluoride is unknown, and the chloride, bromide, iodide decrease in stability in that order, the formation of Aul being endothermic (d H, 5.52 kcal). With the exception of Aul, all are converted by water to the trihalide and metal, the chloride the most readily, possibly because the most soluble. 

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