Gallium Halides - Intermediate Halides

Intermediate Halides

Intermediate chlorides, bromides and iodides exist. They contain gallium in oxidation states +1, +2 and +3.

Ga₃Cl₇

This compound contains the Ga₂Cl₇− ion, which has a structure similar to the dichromate, Cr₂O₇2−, ion with two tetrahedrally coordinated gallium atoms sharing a corner. The compound can be formulated as gallium(I) heptachlorodigallate(III), GaI GaIII₂Cl₇.

unit cell of Ga3Cl7	part of the crystal structure	structure of −

GaCl₂, GaBr₂ and GaI₂

These are the best known and most studied intermediate halides. They contain gallium in oxidation states +1 and +3 and are formulated GaIGaIIIX₄. The dihalides are unstable in the presence of water disproportionating to gallium metal and gallium(III) entities. They are soluble in aromatic solvents, where arene complexes have been isolated and the arene is η6 coordinated to the Ga+ ion. With some ligands, L, e.g. dioxane, a neutral complex, Ga₂X₂L₂, with a gallium-gallium bond is produced. These compounds have been used as a route into gallium chain and cluster compounds.

Ga₂Br₃ and Ga₂I₃

These are formulated GaI₂ GaII₂Br₆ and GaI₂ GaII₂I₆ respectively. Both anions contain a gallium-gallium bond where gallium has a formal oxidation state of +2. The Ga₂Br₆2− anion is eclipsed like the In₂Br₆2− anion in In₂Br₃ whereas the Ga₂I₆2− anion is isostructural with Si₂Cl₆ with a staggered conformation.