1,1.1-Trihalides monohalides

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°. 

Deposition by the hydrogen reducti on of the trihalides (A1X3) i s not practical because of the stability ofthe latter, but is possible through the disproportionation ofthe monohalides. This is a difficultprocedure which has been largely supersededby the decomposition of the aluminum alkyls mentioned above. ... 

Also studied was the effect of ether, which behaves as a retarder, on the polymerization. The retardation is most marked with the di- and trihalides and least with the monohalide and Zr (allyl) 4. In fact if large amounts of ether are present from the preparation, Zr(allyl)2Br2 shows hardly any activity at all. To avoid any possibility of contamination by ether, the halides in Table XI were prepared from pure ether-free Zr(allyl)4 in toluene by reaction with propargyl bromide. 

Trigeminal trihalides are completely reduced by catalytic hydrogenation over palladium [62] and Raney nickel [63], and partially reduced to dihalides or monohalides by electrolysis using mercury cathode [57 ], by aluminum... 

Similar reactions occur with other halogens. Monohalides of indium include chloride, bromide and iodide. Monohalides are obtained by passing indium trihalides over heated indium ... 

Boron subhalides are binary compounds of boron and the halogens, where the atomic ratio of halogen to boron is less than 3. The boron monohalides, BC1, [20583-55-5], bromoborane(l) [19961-29-6], BBr, and iodoborane(l) [13842-56-3], BI, are unstable species that have been observed spectroscopically when the respective trihalides were subjected to a discharge (5). Boron dihalide radicals have been studied, and structural and thermochemical data for these species ( BX2) have been deduced (5). 

Alkyl tellurium halides, RTeX, in general, have no importance as starting materials for the preparation of alkyl tellurium trihalides. The alkyl tellurium halides are synthesized from dialkyl ditellurium compounds and elemental halogens. When alkyl tellurium trihalides are the desired products, there is no reason to prepare the monohalides first. However, when the tellurium monohalide is formed during the introduction of tellurium into an organic molecule, the reaction of this primary product with halogens is the method of choice for the preparation of the tellurium trihalides. This situation is realized for 3-oxo-l-propen-l-yl tellurium halides2,3. 

Alkyl and aryl tellurium trihalides with stabilizing electron-donor groups in the molecule that coordinate to the tellurium atom are not reduced by disodium sulfite3 or hypophosphorous acid4 to ditellurium compounds but only to tellurium monohalides. 

The monohalides of aluminum are produced as short-lived diatomic species in the gas phase by the reaction of the trihalides with aluminum at 1000 °C. The instability of these... 

Metastable solutions of the monohalides AIX and GaX (X = Cl, Br, I) have been prepared using this technique, and oligomeric species (MX) -Em containing a variety of donors (E) have been crystallised. The solutions disproportionate to the trihalide and the metal (equation 2) when warmed to temperatures in the range -40 to 4-50 °C, depending on the halide, the donor, and the concentration. Species with oxidation states both higher and lower than +1 (i.e. on the path to both disproportionation products) have been isolated. The reduced species (0 < Nox < 1) are discussed in the section on metalloid clusters, and the monohahdes and more oxidized species (1 < Nox < 3) are discussed here. A sonochemical synthesis of a subvalent galhum species, possibly Gal, has also been developed. ... 

Diphenyl-3-oxo-l-propen-l-yl tellurium tribromide was reduced by hypophosphorous acid to the corresponding tellurium bromide . These oxopropenyl tellurium trihalides lose halogen on slight heating and are converted to the tellurium monohalides. ... 

Carbothermic reduction in the presence of an alloying element, such as copper, iron, or silicon, to decrease aluminum vapor pressures decreases volatility problems but requires a further stage to recover aluminum from the alloy product. It may be selectively dissolved from the alloy with a more volatile metal, such as mercury, lead, or zinc, and then the aluminum recovered by distillation. Or, the tendency for aluminum halides to form more volatile monohalides at high temperatures, which revert to the trihalides at lower temperatures (Eq. 12.25) may be employed. 

The monohalides have layer structures consisting of sheets of metal and halogen atoms sequenced XMMX... XMMX... and are metallic conductors in a direction parallel to the layers compare this with the conductivity of graphite (see Section 13.4). The di- and trihalides disproportionate (equations 22.18 and 22.19). 

In Klemm and Dierks procedure, excess In metal is allowed to react with the corresponding trihalides, and the resultant monohalides are distilled off in vacuum. 

The monohalides are useful reducing agents for the preparation of a number of intermediate zirconium chloride and bromide phases since their reactivities are considerably greater than those of the refractory metal. Thus, ZrX-ZrX4 reactions have been used to obtain the trihalides in 100% yields as well as ZrCl2(3f -NbS2 type) and a different polytype of ZrBr2. ... 

The most stable halides of boron and aluminum are the trihalides for thallium, the monohalides (TlX) are the most stable. Similarly, the most stable oxides of boron and aluminum are of the formula M2O3 for thallium, the most stable oxide is TI2O. Comment on this chemistry. 

With the exception of the metal and its alloys, aluminium occurs only in oxidation number +3 at normal temperatures the monohalides, formed by heating the trihalides with the metal, disproportionate on cooling. 

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