Beryllium halide

Anhydrous beryllium halides are covalent. The fluoride, Bep2, is obtained as a glass (sublimation point 1073 K) from the thermal decomposition of [NH4]2[BeF4], itself prepared from BeO and NH3 in an excess of aqueous HF. Molten Bep2 is virtually a non-conductor of electricity, and the fact that sohd Bep2 adopts a P-cristobalite structure 

A deliquescent substance absorbs water from the surrounding air and eventually forms a liquid. 

In the vapour state above 1020 K, BeCl2 is monomeric and has a linear structure. At lower temperatures, the vapour also contains planar dimers. We return to the structures of gas-phase BeX2 molecules later in the section. BeCl2 forms colourless, deliquescent crystals containing infinite chains the coordination environment of each Be centre is tetrahedral and the Be-Cl distances are longer than in the 

Each Be centre will be in a trigonal planar environment. 

The recrystaUization of BeCl2 from diethyl ether solutions leads to a Lewis acid-hase adduct. Draw the likely structure of the adduct and rationalize its formation in terms of the electron-accepting properties of BeCl2. 

Anhydrous BeCl2 (mp 688 K, bp 793 K) can be prepared by reaction 12.18. This is a standard method of preparing a metal chloride that cannot be made by dehydration of hydrates obtained from aqueous media. In the case of Be, [Be(OH2)4l is formed and attempted dehydration of [Be(OH2)4]Cl2 yields the hydroxide, not the chloride (eq. 12.19). 

A deliquescent substance absorbs water from the surrounding 

Blue cobalt-dyed silica gel spheres these turn pink when water 

Drying agents that react irreversibly with H2O 

Typically, anhydrous salts that absorb water as solvate are suitable for removing water from solvents. Anhydrous 

Suggest a structure for a dimer of BeCl2 and explain how its formation illustrates BeCl2 acting as a Lewis acid. 

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Beryllium Halides. The properties of the fluoride differ sharply from those of the chloride, bromide, and iodide. BeryUium fluoride is essentiaUy an ionic compound, whereas the other three haUdes are largely covalent. The fluoroberyUate anion is very stable. 

Anhydrous beryllium halides cannot be obtained from reactions in aqueous solutions because of the formation of hydrates such as [Be(H20)4]F2 and the subsequent hydrolysis which attends attempted dehydration. Thermal decomposition of (NH4)2Bep4 is the best route for BeFr, and BeCl2 is conveniently made from the oxide... 

The beryllium halides are stable compounds and consequently their reducti on by hydrogen i s not a practical method of obtaining the metal. Pi Good beryllium deposits are obtained by the pyrolysis of the alkyls as follows ... 

Metallic beryllium is produced by reduction of beryllium halide with sodium, potassium or magnesium. Commercially, it is obtained primarily from its ore, beryl. Beryllium oxide is separated from silica and alumina in ore by melting the ore, quenching the solid solution, and solubilizing in sulfuric acid at high temperatures and pressure. Silica and alumina are removed by pH adjustment. Beryllium is converted to its hydroxide. Alternatively, beryl is roasted with complex fluoride. The products are dissolved in water and then pH is adjusted to produce beryllium hydroxide. 

Beryllium halide alternatively may be reduced to the metal or converted to alloy by electrolysis. 

Ammino-derivatives of Beryllium and Magnesium Salts—Derivatives of Beryllium Halides—Derivatives of Magnesium Halides. 

The alkaline earths, particularly the lighter ones, have more definite water coordination, and a probable coordination number of 4. The heats of sublimation (Table I) of the magnesium salts are about 50 kcal/mole or higher, those for the calcium halides are over 60 kcal/mole, and for the heavier alkaline earths they run over 70 kcal/mole. For the beryllium halides other than the fluoride, however, the values are 30 to 33 kcal/mole. In... 

Beryllium halides have been found to form complexes with several aldehydes, ketones and esters.74 Antipyrine, which acts as a monodentate carbonyl ligand, dissolves alkaline earth metal salts to give solid products of the type MX2-6ap (M24 = Mg, Ca, Sr X = C102 M24 = Mg, Ca X = BFT). The X-ray structure of Mg(C104)2-6ap confirms the monodentation and shows the magnesium to be octahedrally coordinated. 

From the facts of the formation of beryllium dialkyls by the continuous heating of alkylberyllium halides and of the formation of the latter when beryllium dialkyls are treated with beryllium halides (99), the following equilibrium was suggested (R = alkyl, X=halogen) ... 

Beryllium halides are Lewis acids that form adducts with many types of electron pair donors (amines, ethers, phosphines, etc.), and they readily form complex ions. For example, the BeF42 ion results from the reaction... 

The ethereal solutions of these iodides do not fume in air, and removal of the solvent gives a liquid, which on further heating evolves dense white fumes, probably of beryllium oxide. Heating changes the alkyl beryllium halides to beryllium dialkyls. All the alkyl halide compounds are decomposed by water, with formation of the corresponding hydrocarbon. When carbon dioxide is passed through ethereal beryllium methyl iodide for three hours, the solution still gives a positive test and no acetic acid is found after hydrolysis. Acetanilide is formed from beryllium methyl iodide and phenyl isocyanate. 

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