Zirconium(III) iodide is an inorganic compound with the formula ZrI<sub>3</sub>.
Like other group 4 trihalides, zirconium(III) iodide can be prepared from zirconium(IV) iodide by high-temperature reduction with zirconium metal, although incomplete reaction and contamination of the product with excess metal often occurs.
An alternative is to crystallise zirconium(III) iodide from a solution of zirconium(III) in aluminium triiodide. The solution is prepared by reducing a eutectic solution of ZrI<sub>4</sub> in liquid AlI<sub>3</sub> at a temperature of 280âÂÂ300 ðC with metallic zirconium or aluminium.
Zirconium(III) iodide has a lower magnetic moment than is expected for the d<sup>1</sup> metal ion Zr<sup>3+</sup>, indicating non-negligible ZrâÂÂZr bonding.
The crystal structure of zirconium(III) iodide is based on hexagonal close packing of iodide ions with one third of the octahedral interstices occupied by Zr<sup>3+</sup> ions. The structure consists of parallel chains of face-sharing {ZrI<sub>6</sub>} octahedra with unequally spaced metal atoms. The ZrâÂÂZr separation alternates between 3.17 àand 3.51àà.
ZrCl<sub>3</sub>, ZrBr<sub>3</sub> and ZrI<sub>3</sub> adopt structures very similar to the ò-TiCl<sub>3</sub> structure. In all three ZrX<sub>3</sub> there is some elongation of the octahedra along the metal-metal axis, partly due to metal-metal repulsion, but the elongation is most pronounced in the chloride, moderate in the bromide and negligible in the iodide.