HfCl4

Hafnium tetrachloride, chemical formula HfCl4, is a compound of hafnium in the +4 oxidation state. It is a moisture‑sensitive, covalently bonded halide that is volatile and can be handled under dry, inert conditions. In the gas phase it exists as discrete HfCl4 molecules, while in the condensed phase it tends to form polymeric or chloride-bridged networks.

Preparation and occurrence: HfCl4 is typically prepared by direct chlorination of metallic hafnium at elevated temperature, for example Hf + 2 Cl2 → HfCl4. It can also be obtained by chlorinating hafnium-containing precursors under carefully controlled conditions. The compound is commonly used as a starting material for hafnium-containing reagents and materials.

Properties: HfCl4 is a colorless to white solid or low‑melting material that is volatile and readily sublimes. It is soluble in nonpolar organic solvents and can be distilled under dry nitrogen. It hydrolyzes rapidly in the presence of water, producing hafnium oxychlorides and hydrogen chloride.

Reactions and hydrolysis: Exposure to moisture leads to hydrolysis, forming hafnium oxides or oxychloride species and releasing HCl. In solution, hafnium forms various hydrolyzed species depending on pH and ligands, which can ultimately lead to hafnium oxide upon aging.

Uses: HfCl4 serves as a convenient precursor to hafnium oxide (HfO2) and hafnium-containing films used in microelectronics as high‑k dielectrics. It is employed in chemical vapor deposition and atomic layer deposition to deposit hafnium-containing films and as a synthetic starting material for organ hafnium compounds.

Safety: HfCl4 is corrosive and reacts with water to release corrosive HCl. It should be handled under strictly dry, inert conditions with appropriate protective equipment and stored in sealed, moisture‑free containers.