- Iron(II) chloride (FeCl₂), also known as ferrous chloride, is an inorganic compound consisting of iron in the +2 oxidation state and chloride ions. It typically occurs as a pale green or off-white crystalline solid in its anhydrous form, while its tetrahydrate form (FeCl₂·4H₂O) appears as greenish-blue crystals. FeCl₂ is highly soluble in water, forming pale green solutions that can darken upon exposure to air due to oxidation of Fe²⁺ to Fe³⁺, resulting in the formation of iron(III) compounds such as FeCl₃ or iron oxides/hydroxides.
- This compound plays a critical role in inorganic and coordination chemistry, acting as a reductant and a precursor to various iron-based complexes. In aqueous solutions, Fe²⁺ exists as the [Fe(H₂O)₆]²⁺ complex, which can participate in a range of redox and ligand-substitution reactions. FeCl₂ is paramagnetic due to its d⁶ electronic configuration and is sensitive to air and moisture, often requiring storage under inert atmospheres to prevent oxidation.
- Iron(II) chloride is used in a variety of industrial applications. It serves as a flocculant in wastewater treatment, where it helps to remove impurities and phosphates by precipitating suspended particles. It is also employed in dye production, metallurgy, and organic synthesis. In the lab, FeCl₂ is used to prepare organometallic and coordination compounds, including catalysts and reagents for carbon-carbon bond formation, especially in Grignard-type or cross-coupling reactions involving iron catalysis.
- FeCl₂ can be synthesized by reacting iron metal with hydrochloric acid, producing hydrogen gas as a byproduct:
- Fe + 2HCl → FeCl₂ + H₂↑
- Alternatively, it can be formed through the reduction of iron(III) chloride (FeCl₃) using iron metal or another reducing agent. The compound must be handled carefully, as exposure to oxygen can lead to contamination with iron(III) salts.
- From a toxicological perspective, iron(II) chloride is irritating to the skin, eyes, and respiratory system, and ingestion of large amounts may lead to iron poisoning, which is particularly dangerous in children. Chronic exposure can lead to systemic effects such as liver or gastrointestinal damage. Proper storage, ventilation, and use of personal protective equipment are essential when working with FeCl₂.
