Indium trihydride

Nomenclature

The systematic name indium trihydride, a valid IUPAC name, is constructed according to the compositional nomenclature. Indium trihydride is also used to refer to the related molecular compound indigane and its oligomers. Care should be taken to avoid confusing the two compounds.

Chemical properties

For solid InH₃ a three-dimensional network polymeric structure, where In atoms are connected by In-H-In bridging bonds, is suggested to account for the growth of broad infrared bands when samples of InH₃ and InD₃ produced on a solid hydrogen matrix are warmed. Such a structure is known for solid AlH₃. When heated above −90 °C (−130 °F), indium trihydride decomposes to produce indium–hydrogen alloy and elemental hydrogen. As of 2013, the only known method of synthesising indium trihydride, is the autopolymerisation of indigane below −90 °C (−130 °F).

Indigane

Indigane (also systematically named trihydridoindium), also called indane, is the monomer with the chemical formula InH
3 (also written [InH
3]). It is a colourless gas that cannot persist undiluted. Indigane is the simplest of the indiganes. Unsolvated indigane will spontaneously autopolymerise, first to oligomers, and finally indium trihydride.

It has been observed in matrix isolation. Gas phase stability has been predicted The infrared spectrum was obtained in the gas phase by laser ablation of indium in presence of hydrogen gas Several indium hydride complexes have been reported. Examples of complexes with two hydride ligands replaced by other ligands are K₃[K(Me₂SiO)₇][HIn(Me₃CCH₂)₃]₄ and HIn(2-Me₂NCH₂-C₆H₄)₂.

Lewis Acidity

A number of indium hydride adducts are known. These include 1:1 adducts with four coordinate indium and 2:1 adducts with five coordinate indium. Typically the 1:1 amine complexes are made by the reaction of indium tribromide with lithium hydride to form LiInH₄ in solution which then is reacted with a trialkylammonium chloride. The 2:1 complex with tricyclohexylphosphine (PCy₃) may be produced by reacting the 1:1 trimethylammonium complex with PCy₃. These adducts are not all stable, for example the trimethylammonium complex is stable only below −30 °C or in dilute solution. The 1:1 and 2:1 complexes with of PCy₃ have been characterised crystallographically and the average In-H bond length was found to be 168 pm, which is considerably longer than the corresponding Al-H and Ga-H bonds. Indium hydride is also known to form adducts with carbenes.

The indium atom in indiganes such as indigane can accept an electron-pair donating ligand into the molecule by adduction:

Because of this acceptance of the electron-pair donating ligand (L), indigane has Lewis-acidic character. Indigane can accept one electron-pair from a ligand, as in the case of the tetrahydridoindate(1−) anion (InH−
4).