Bromine-silicon crystals

X-Ray studies of crystals of pyridine complexes with trimethylsilyl bromide and iodide (264) and of N-methylimidazole adducts to trimethyl-chlorosilane (265) were performed. The tetracoordinate silicon structure of these complexes was proved. The distances between the halogen and silicon atoms in pyridine adducts are 4.359 and 4.559 A for bromine and iodine, respectively, which is approximately 2 A greater than the sum of the covalent radii and significantly longer (0.5 A) than the sum of the van der Waals radii. This result is consistent with the ionic structures of the complexes in the solid state. The distance from silicon to nitrogen (1.86 A) is evidently larger than the length of typical Si—N bonds (1.75 A), which... 

Cobalt Disilicide, CoSi2, results when cobalt is heated in the electric furnace with excess of silicon or with a mixture of copper silicide and silicon.8 It forms dark crystals, probably belonging to the cubic system density 5 3 hardness 4-5. Sulphur has no action on it, and oxygen at 1200° C. only effects a superficial oxidation. It incandesces in fluorine if gently wanned chlorine attacks it at 300° C., and bromine and iodine at dull red heat. Concentrated hydrogen... 

The first fractions will contain some bromine and a small quantity of silicon tetrabromide. The disilicon hexa-bromide distills at a fairly constant temperature, depending upon the pressure employed. Thus a considerable proportion comes over at 130 to 140°, if the pressure is varied from 15 to 20 mm. This material may have a pale-yeUow color, but on redistillation or sublimation a pure-white well-crystallized substance may be obtained (m.p. 95°). Yield 80 per cent based on the bromine used or 60 per cent based on the calcium-silicon alloy. 

Dow has produced a polycarbonate grade for liquid crystal display monitors, incorporating a silicone flame retardant. Formulations containing the silicone additive are said to have better impact strength and temperature resistance than those protected by phosphorus based flame retardants, and better heat and light stability than those containing brominated FRs. 

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