Overview

Zinc iodide is an inorganic compound with the formula ZnI2. It is typically a colourless to pale yellow crystalline solid and is composed of zinc cations and iodide anions. The compound is hygroscopic and readily dissolves in water and many polar organic solvents, providing a convenient source of Zn2+ and I− in solution. In many contexts it behaves as a Lewis acid and as a source of nucleophilic iodide in synthetic chemistry.

Structure and physical properties

In the solid state ZnI2 often adopts a polymeric arrangement in which iodide ligands bridge between zinc centers, creating extended networks rather than isolated ion pairs. Zinc is frequently four-coordinate in these materials, surrounded by iodide atoms in a roughly tetrahedral environment, although coordination can vary with temperature and phase. In solution the species present depend on concentration and solvent; coordination and aggregation equilibria are common.

Preparation

Common laboratory preparations include direct combination of elemental zinc and iodine or treatment of zinc oxide or carbonate with hydroiodic acid. Products are typically purified by recrystallisation from suitable solvents and must be protected from moisture to avoid hydrolysis and uptake of water.

Uses

  • As a reagent in organic and inorganic synthesis where zinc(II) acts as a Lewis acid and iodide can function as a nucleophile or leaving group.
  • In specialized electrochemical studies and rechargeable zinc–iodine battery research because of the reversible chemistry between zinc and iodine species.
  • In analytical and preparative protocols where a soluble iodide or the combined reactivity of Zn2+ and I− is required.

Safety and handling

Like other soluble iodides, zinc iodide should be handled with appropriate precautions. Ingestion or prolonged exposure to iodide can affect thyroid function in sensitive individuals, and zinc salts are toxic at high doses; skin and eye contact should be avoided. Store the compound in a well-sealed container in a dry environment, preferably in a desiccator or under inert atmosphere if prolonged storage is required. Consult material safety data and technical references for detailed guidance: zinc, iodide, and compound-specific safety information.

For experimental work, follow standard laboratory practice, wear appropriate personal protective equipment, and refer to product datasheets and published literature for reaction-specific advice.