Used as a catalyst or starting material in organic synthesis, particularly in carbon-halogen bond formation and coupling reactions requiring a source of iodide and Fe(II) ions. Employed in the preparation of other iron compounds and in laboratory research for studying redox reactions, inorganic chemistry, and coordination chemistry, including magnetic properties of iron compounds. Also utilized in some specialized battery systems and energy storage applications, as well as a reagent in analytical chemistry for detecting certain functional groups. Note: Iron(II) iodide is highly sensitive to air and moisture, requiring handling under inert conditions, which limits its practical applications.