AsI3 ARSENIC TRIIODIDE

AsI3 ARSENIC TRIIODIDE 71.126 9.4809E-02 -4.3607E-11 7.6722E-14 -5.0239E-17 298 419 solid... 

Arsenic triiodide is soluble in carbon disulphide, alcohol, ether, chloroform, benzene, toluene and the xylenes.5 The solution in carbon disulphide gradually darkens owing to absorption of oxygen and liberation of iodine.6 With alcohol at 150° C. ethyl iodide is formed. In methylene iodide 5 the triiodide dissolves to the extent of 17-4 parts of AsI3 in 100 parts of solvent at 12° C. The dipole moment in various solvents has been determined.7... 

Arsenic triiodide (arsenic(HI) iodide), Asl3, can be precipitated from a hot solution of trivalent arsenic in hydrochloric acid by the addition of potassium iodide, or it can be formed by treating elemental arsenic with a solution of iodine in carbon disulfide. It is not as easily hydrolyzed as the other arsenic halides, but it decomposes slowly in air at 100 °C (rapidly at 200°C) to give a mixture of iodine, arsenic trioxide, and elemental arsenic. Solutions of AsI3 are unstable, particularly in the presence of moisture. 

Crystalline arsenic triiodide consists of discrete ASI3 molecules, which are stacked such that the iodine atoms are hexagonally close packed. The arsenic atoms are octahedrally surrounded by iodine, but with the arsenic off-centre resulting in two sets of d(As— I) (Table 9) three bonds of 2.59 A and three of 3.47 A (c/. Asia vapour, d(As— I) 2.56 A). Arsenic(HI) triastatine has not yet (mid-1986) been reported, although it would be surprising if the synthesis has not been attempted. 

J Estimate the As—I bond length from the data in Figure 7.6, and compare your value to the experimental As—I bond length in arsenic triiodide, ASI3,2.55 A. 

Arsenic triiodide can be precipitated with much I" from, say, half-M As in rather concentrated HCl. The ASI3 in air slowly liberates I2. 

Solutions of arsenic triiodide ASI3 have no action on aluminium at room temperature. 

Ammonia is slowly absorbed by the triiodide and a voluminous yellow substance is produced8 which, if kept over sulphuric acid, loses ammonia until the composition corresponds with the tetrammino-triiodide, AsIg.ANHg. At 0° C. more ammonia can be absorbed to yield the dodecammino-compound, AsI3.12NH3. If ammonia is passed into a solution of the triiodide in benzene or ether, a voluminous white precipitate, of composition 2AsI3.9NH3, is formed.8 The existence of these ammines as definite compounds has not been established.10 With phosphine, arsenic phosphide is produced ... 

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