diodide

Diodide is a term encountered in inorganic and polyhalide chemistry. It is not a standardized IUPAC name, but a descriptive label used to refer to species containing two iodide-related units. Depending on the context, diodide may denote either a dianionic fragment containing two iodide units or a coordination complex in which two iodide ligands are bound to a metal center.

In coordination chemistry, diiodide commonly refers to a complex of a metal with two iodide ligands, often written as M(I)2. Such species are discussed in the same literature that covers other metal halide complexes and may appear in solid state or in solution, depending on the metal and ligands involved.

In polyhalide chemistry, diodide might denote a dianionic polyiodide fragment comprising two iodide units linked in a larger anion. This usage is less standardized than the concept of discrete diiodide complexes and is typically encountered alongside other polyiodide species such as I3−, I5−, and related aggregates that form in concentrated iodine solutions or specific salt matrices.

Characterization of diodide-containing systems relies on techniques common to inorganic chemistry, including X-ray crystallography for structural determination, and spectroscopic methods such as UV-Vis and Raman or IR to probe electronic structure and bonding. The interpretation of oxidation states and bonding in diodide species is context-dependent, varying with whether the focus is on a metal complex or a polyiodide anion.

See also: iodide, diiodine, polyiodide, I3−.

References: literature on metal halide complexes and polyhalide chemistry.