Trimethylantimony diiodide

The preparation of trimethylantimony diiodide is identical to that of trimethylantimony dichloride up to the point of the addition of chlorine. Instead of a gas inlet tube, an addition funnel is mounted on the flask containing the ice-cold distillate of ethyl ether and trimethylstibine. For a reaction carried out on the basis of 0.25 mol of anhydrous antimony(III) chloride, a solution of 63,5 g. (0.25 mol) of iodine in 400 ml. of ethyl ether is prepared. This solution is added dropwise to the cold distillate. Stirring is maintained and the addition is continued until the color of iodine persists. The precipitate of trimethylantimony diiodide is filtered off on a fritted Buchner fuimel and washed with ethyl ether. The jdeld of the crude product is 47.7 to 65.3 g. (45.0 to 61.8% of theoretical based upon antimony (III) chloride). The diiodide may be recrystallized from ethanol. Anal. Calcd. for (CH3) 3Sbl2 Sb, 28.95 C, 8.55 H, 2.16. Found Sb, 29.31 C, 8.16 H, 2.25. The checkers report that the foregoing syntheses are also satisfactory using one-half the amounts prescribed. 

Trimethylantimony dichloride, dibromide, and diiodide have been shown to consist of trigonal bipyramidal molecules with the halogens at the apices and the methyl groups in the planar positions. Although melting points have been reported for these compounds from time to time, they are not reproducible because the compounds loose methyl halide upon heating. This reaction is useful for the prepa- 

These compounds may then be halogenated to the trihalides such as dimethylantimony trichloride. 

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