Overview

Arsenic triiodide is an inorganic compound with the formula AsI3. It contains arsenic in the +3 oxidation state bonded to three iodide atoms and belongs to the family of arsenic trihalides. AsI3 is a dense, iodine‑containing material that is less commonly encountered than the chloride or bromide analogues and is handled primarily in laboratory settings.

Structure and properties

The molecule is best described as a pyramidal As(III) center coordinated to three iodide ligands, giving a geometry typical of trivalent pnictogen halides. It is largely covalent rather than ionic, has a high molecular mass and strong absorption of light due to the heavy iodine atoms. AsI3 is moisture sensitive: it can hydrolyze on contact with water to produce arsenous acid and hydrogen iodide, and it may decompose on heating.

Preparation

Common laboratory routes prepare AsI3 by direct combination of elemental arsenic and iodine under controlled conditions or by halide exchange using arsenic trichloride and an iodide source. Procedures are carried out with exclusion of moisture and oxygen to avoid hydrolysis and side reactions. For practical guidance consult specialized synthesis references or safety datasheets via chemical safety resources.

Uses and handling

AsI3 has limited commercial applications; it is mainly used as a precursor in research to prepare other arsenic-containing compounds or as a reagent in specific synthetic transformations. Because arsenic compounds are highly toxic, handling requires strict controls: gloves, eye protection, fume hood, and disposal as hazardous waste. Further information on health hazards and exposure prevention can be found at safety guidance and related databases.

Notable distinctions

  • Compared with lighter arsenic trihalides, AsI3 is less volatile and more susceptible to thermal decomposition.
  • The large iodide ligands influence reactivity and solubility relative to AsCl3 and AsBr3.
  • As a +3 arsenic compound it contrasts chemically with arsenic(V) species that show different redox and hydrolytic behaviour; see general arsenic chemistry at arsenic overview and halide comparisons at iodide chemistry.

Summary: Arsenic triiodide is a covalent arsenic(III) halide of niche use, notable for its heavy-atom character, moisture sensitivity, and significant toxicity; it is primarily encountered in controlled laboratory contexts.