# Arsinide

An arsinide, arsanide, dihydridoarsenate(1−) or arsanyl compound is a chemical derivative of arsine, where one hydrogen atom is replaced with a metal or cation. The arsinide ion has formula AsH−2. It can be considered as a ligand with name arsenido or arsanido. Few chemists study arsanyl compounds, as they are both toxic and unstable. The IUPAC names are arsanide and dihydridoarsenate(1−). For the ligand the name is arsanido. The neutral −AsH$_2$ group is termed arsanyl.

## Formation

Alkali metal arsinides can form by bubbling arsine through a liquid ammonia solution of alkali metal such as sodium, potassium or alkaline earth metal such as calcium.
Arsinides are also formed when arsine reacts with thin layers of alkali metals.
The arsine may reduce some compounds to metals, so for example an attempt to make an indium arsinide results in metallic indium.

## Reactions

When heated, metal hydrogen arsinide and metal dihydrogen arsinide compounds lose hydrogen to become a metal arsenide:
    NaAsH$_2$ → NaAs + H$_2$
With lithium dihydrogen arsinide LiAsH$_2$, it can also lose arsine AsH$_3$ to become dilithium hydrogen arsinide Li$_2$AsH:
    2 LiAsH$_2$ → Li$_2$AsH + AsH$_3$
These reactions take place even at room temperature, and result in a discolouration of the original chemical.
Sodium dihydrogen arsinide NaAsH$_2$ reacts with alkyl halides RX (where X = F, Cl, Br, I, and R is alkyl) to make dialkylarsine AsHR$_2$. Potassium dihydrogen arsinide KAsH$_2$ reacts with alkyl halides to make trialkylarsine AsR$_3$.
Sodium dihydrogen arsinide NaAsH$_2$ reacts with diethyl carbonate (CH$_3$CH$_2$O)$_2$CO to yield the 2-arsaethynolate [OCAs]$^−$ ion, (analogous with cyanate [OCN]$^−$ ion) which can be crystallised with the sodium ion Na$^+$ and 18-crown-6.
Arsinides react with water to yield arsine AsH$_3$:
    KAsH$_2$ + H$_2$O → KOH + AsH$_3$
Potassium dihydrogen arsinide KAsH$_2$ reacts with halobenzenes C$_6$H$_5$X, where X = Cl, Br, I (chlorobenzene C$_6$H$_5$Cl, bromobenzene C$_6$H$_5$Br, iodobenzene C$_6$H$_5$I) to produce benzene C$_6$H$_6$, tetraphenyldiarsine (C$_6$H$_5$)$_2$As−As(C$_6$H$_5$)$_2$ and triphenylarsine As(C$_6$H$_5$)$_3$.
Potassium dihydrogen arsinide KAsH$_2$ reacts with a silyl halide, e.g. chlorosilane SiH$_3$Cl, producing trisilylarsine.
Potassium dihydrogen arsinide KAsH$_2$ reacts with H$_2$As−BH$_2$·N(CH$_3$)$_3$ and a crown ether resulting in [K(C$_{12}$H$_{24}$O$_6$)]$^+$[H$_2$As−BH$_2$−AsH$_2$]$^−$.

## List

| Formula | Name | Crystal system | Space group | Unit cell (Å) | Comment |
| LiAsH$_2$ | Lithium arsanide | | | | |
| Li$_2$AsH | Dilithium arsanide | | | | decomposition at 0°C |
| LiAsH$_2$·2NH$_3$ | | | | | |
| LiAsH$_2$·4NH$_3$ | | | | | |
| NaAsH$_2$ | Sodium arsanide | | | | white; decomposition at room temperature |
| Na$_2$AsH | Disodium arsanide | | | | |
| NaAsH$_2$·2NH$_3$ | | | | | |
| NaAsH$_2$·4NH$_3$ | | | | | |
| Li$^+$[Al(AsH$_2$)$_4$]$^−$ | Lithium tetraarsanidoaluminate | | | | |
| (Dipp$_2$Nacnac)Al(AsH$_2$)$_2$ Dipp$_2$Nacnac=HC[C(Me)N(2,6-iPr$_2$C$_6$H$_3$)]$_2$ | | | | | |
| IDipp⋅AlH$_2$AsH$_2$ IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) | | monoclinic | I2/a | | colourless |
| IDipp⋅AlH(AsH$_2$)$_2$ | | monoclinic | I2/a | a 18.3591 b 9.0485 c 34.4864 β 91.580° | |
| KAsH$_2$ | Potassium arsanide | | | | stable to 80°C; decomposition at 90°C |
| Ca(AsH$_2$)$_2$ | Calcium arsanide | | | | |
| (Dipp$_2$Nacnac)Ga(AsH$_2$)$_2$ | | | | | |
| IDipp⋅GaH$_2$AsH$_2$ | | monoclinic | I2/a | | colourless |
| IDipp⋅GaH(AsH$_2$)$_2$ | | monoclinic | I2/a | a 18.465 b 9.1493 c 34.661 β 91.509° | |
| Th(Tren$^{TRIPS}$)AsH$_2$ | | | | | Th-As 3.065 Å |
| U(Tren$^{TRIPS}$)AsH$_2$ | | | | | U-As 3.004 Å |

## Related

The hydrogen atoms in the arsinide anion may be substituted by organic or other groups which can then also produce ions, for example by methyl −CH$_3$, like in potassium methyl arsinide (K$^+$CH$_3$AsH$^−$), or by trimethylsilyl −Si(CH$_3$)$_3$. The doubly bonded ligand =AsH (or AsH$^{2−}$) is called arsinidene.