In chemistry, anarsenide is a compound ofarsenic with a lesselectronegative element or elements. Many metals formbinary compounds containing arsenic, and these are called arsenides. They exist with manystoichiometries, and in this respect arsenides are similar tophosphides.[1]
The group 1alkali metals and the group 2,alkaline earth metals, form arsenides with isolated arsenic atoms. They form upon heating arsenic powder with excess sodium givessodium arsenide (Na3As). The structure of Na3As is complex with unusually short Na–Na distances of 328–330 pm which are shorter than in sodium metal. This short distance indicates the complex bonding in these simple phases, i.e. they are not simply salts of As3− anion, for example.[1] The compound LiAs, has a metallic lustre and electrical conductivity indicating some metallic bonding.[1] These compounds are mainly of academic interest. For example, "sodium arsenide" is a structural motif adopted by many compounds with the A3B stoichiometry.
Indicative of their salt-like properties, hydrolysis of alkali metal arsenides givesarsine:
Many arsenides of thegroup 13 elements (group III) are valuable semiconductors.Gallium arsenide (GaAs) features isolated arsenic centers with azincblende structure (wurtzite structure can eventually also form in nanostructures), and with predominantly covalent bonding – it is a III–V semiconductor.
Arsenides of thegroup 12 elements (group II) are also noteworthy.Cadmium arsenide (Cd3As2) was shown to be a three-dimensional (3D) topological Diracsemimetal analogous tographene.[2][3] Cd3As2,Zn3As2 and other compounds of theZn-Cd-P-As quaternary system have very similar crystalline structures, which can be considered distorted mixtures of the zincblende andantifluorite crystalline structures.[4]
Arsenic anionics are known to catenate, that is, form chains, rings, and cages. The mineralskutterudite (CoAs3) features rings that are usually described asAs4−
4.[1] Assigning formaloxidation numbers is difficult because these materials are highly covalent and often are best described withband theory.Sperrylite (PtAs2) is usually described asPt4+
As4−
2. The arsenides of the transition metals are mainly of interest because they contaminate sulfidic ores of commercial interest. The extraction of the metals – nickel, iron, cobalt, copper – entails chemical processes such as smelting that poses environmental risks. In the mineral, arsenic is immobile and poses no environmental risk. Released from the mineral, arsenic is poisonous and mobile.
Partial reduction of arsenic with alkali metals (and related electropositive elements) affords polyarsenic compounds, which are members of theZintl phases.