Beryllium iodide (BeI₂) is an inorganic compound composed of beryllium and iodine. It is a hygroscopic white solid. It appears as a white to yellowish crystalline solid that is highly hygroscopic, meaning it readily absorbs moisture from the air. The compound is soluble in water, alcohol, and ether, forming acidic solutions due to hydrolysis.
Structurally, beryllium iodide exhibits different arrangements depending on temperature. At room temperature, it typically adopts a polymeric chain structure where each beryllium atom is tetrahedrally coordinated by four iodide ions, while at higher temperatures it can form layered structures. This variation is attributed to the small size and high polarizing power of the beryllium cation (Be²⁺). The Be2+ cation, which is relevant to salt-like BeI2, is characterized by the highest known charge density (Z/r = 6.45), making it one of the hardest cations and a very strong Lewis acid.
Properties
- Chemical formula: BeI2
- Molar mass: 262.82112 g·mol−1
- Appearance: colorless needle-like crystals
- Density: 4.325 g/cm3
- Melting point: 480 °C (896 °F; 753 K)
- Boiling point: 590 °C (1,094 °F; 863 K)
- Solubility in water: reacts with water
- Solubility: Slightly soluble in CS2
- Soluble in ethanol, diethyl ether
Structure
Two forms (polymorphs) of BeI2 are known. Both structures consist tetrahedral Be2+ centers interconnected by doubly bridging iodide ligands. One form consist of edge-sharing polytetrahedra. The other form resembles zinc iodide with interconnected adamantane-like cages.
Reactions
Beryllium iodide can be synthesized by the direct reaction of elemental beryllium with iodine at elevated temperatures or by treating beryllium oxide with hydroiodic acid. It is used mainly in research rather than industry, due to the toxicity of beryllium compounds.
Beryllium iodide can be prepared by reacting beryllium metal with elemental iodine at temperatures of 500 °C to 700 °C:
Be + I2 → BeI2
When the oxidation is conducted on an ether suspension of elemental Be, one obtains colorless dietherate:
Be + I2 + 2 O(C2H5)2 → BeI2(O(C2H5)2)2
The same dietherate is obtained by suspending beryllium iodide in diethyl ether:
BeI2 + 2 O(C2H5)2 → BeI2(O(C2H5)2)2
This ether ligands in BeI2(O(C2H5)2)2 can be displaced by other Lewis bases.
Beryllium iodide reacts with fluorine giving beryllium fluoride and fluorides of iodine, with chlorine giving beryllium chloride, and with bromine giving beryllium bromide.
Occurrences
- Natural occurrence: Beryllium iodide does not occur naturally in the Earth’s crust because beryllium usually occurs in silicate minerals (like beryl and bertrandite) rather than as halides.
- Preparation: It is typically synthesized in laboratories by direct reaction of beryllium metal with iodine at elevated temperatures:
Be+I2→BeI2Be + I₂ → BeI₂Be+I2→BeI2
Applications
Beryllium iodide can be used in the preparation of high-purity beryllium by the decomposition of the compound on a hot tungsten filament. One of its key applications is as a precursor in chemical vapor deposition (CVD) processes for producing beryllium-containing materials. However, handling BeI₂ requires great care, as inhalation or ingestion of beryllium compounds is highly toxic and can cause chronic beryllium disease. Its main significance lies in materials science and academic studies.
