Indium halides
Indium trichloride is a starting point in the production of trimethylindium which is used in the semiconductor industry.
The structure of the red form has not been determined by X-ray crystallography, however spectroscopic evidence indicates that indium may be six coordinate.
[citation needed] A surprising number of intermediate chlorides and bromides are known, but only one iodide, and no difluoride.
Early work on the chlorides and bromides involved investigations of the binary phase diagrams of the trihalides and the related monohalide.
The majority of the previously reported chlorides and bromides have now either had their existence and structures confirmed by X Ray diffraction studies or have been consigned to history.
Perhaps the most unexpected case of mistaken identity was the surprising result that a careful reinvestigation of the InCl/InCl3 binary phase diagram did not find InCl2.
The InII2Br6 anion has an eclipsed ethane like structure with a metal-metal bond length of 270 pm.
The solid monohalides InCl, InBr and InI are all unstable with respect to water, decomposing to the metal and indium(III) species.
They fall between gallium(I) compounds, which are more reactive and thallium(I) that are stable with respect to water.
Up until relatively recently the monohalides have been scientific curiosities, however with the discovery that they can be used to prepare indium cluster and chain compounds they are now attracting much more interest.
The room temperature form of InCl is yellow, with a cubic distorted NaCl structure.
Solutions of InI in a pyridine/m-xylene mixture are stable below 243 K.[15] The trihalides are Lewis Acids and form addition compounds with ligands.
For InF3 there are few examples known however for the other halides addition compounds with tetrahedral, trigonal bipyramidal and octahedral coordination geometries are known.
Additionally there are examples of indium with square planar geometry in the InX52− ion.
The square planar geometry of InCl2−5 was the first found for a main group element.
The salt LiInF4 has been prepared,[17][18] however it has an unusual layer structure with octahedrally coordinated indium center.
The InCl2−5 ion has been found to be square pyramidal in the salt (NEt4)2InCl5, with the same structure as (NEt4)2 TlCl5, but is trigonal bipyramidal in tetraphenylphosphonium pentachloroindate acetonitrile solvate.
[20] The InBr2−5 ion has similarly been found square pyramidal, albeit distorted, in the Bis(4-chloropyridinium) salt [21] and trigonal bipyramidal [22] in Bi37InBr48.
[5] The caesium salts of In2Cl3−9 and In2Br3−9 both contain binuclear anions with octahedrally coordinated Indium atoms.
