Tantalum(IV) iodide

Tantalum iodide is an inorganic compound with the chemical formula TaI₄. It dissolves in water to give a green solution, but the color fades when left in the air and produces a white precipitate.

Preparation

Tantalum iodide can be prepared by the reduction reaction of tantalum(V) iodide and tantalum. If pyridine is used as the reducing agent, there is an adduct TaI₄₂.
Tantalum iodide can also be obtained by reacting tantalum iodide with aluminum, magnesium or calcium at 380 °C. Ta₆I₁₄ is also formed. This makes it difficult to produce a very pure crystallized tantalum iodide.

Tantalum iodide is a black solid. It has a crystal structure isotypic to that of niobium(IV) iodide. Single-crystalline tantalum iodide was first obtained in 2008 by Rafal Wiglusz and Gerd Meyer as a chance product of a reaction in a tantalum ampoule that was supposed to lead to the product RbI₁₂. The single crystal has a triclinic crystal structure with space group P1 with two formula units per unit cell. The crystal structure differs from that of other transition metal tetraiodides, which usually have a MI_4/2I_2/1 chain structure, as it consists of TaI₆ octahedra bridged over a common surface to form a dimer. Two such dimers bridge over a common edge to form a tetramer.