In chemistry, a phosphide is a compound of phosphorus with a less electronegative element or elements. Binary compounds are formed with the majority of less electronegative elements with the exception of Hg, Pb, Sb, Bi, Te, Po. Typically there are a range of stoichiometries with each element; for example, potassium has nine phosphides (K3P, K4P3, K5P4, KP, K4P6, K3P7, K3P11, KP10.3, KP15) and nickel has eight (Ni3P, Ni5P2, Ni12P5, Ni2P, Ni5P4, NiP, NiP2, NiP3).
- principally ionic with P3– ions. Examples are the group 1 (e.g. Na
3P) and group 2 (e.g. Ca
2) metal phosphides.
- polyphosphides with, for example, dumbbell P4−
2 ions; cluster P3−
11 ions; polymeric chain anions (e.g. the helical (P−
n ion) and complex sheet or 3-D anions.
- compounds with individual P atoms in a metal lattice that can be semiconducting (e.g. GaP) through to metallic (e.g. TaP) in terms of electrical conductance.
Two polyphosphide ions, P4−
3 found in K
3 and P5−
4 found in K5P4, are radical anions with an odd number of valence electrons making both compounds paramagnetic.
There are many ways to prepare phosphide compounds. The most general and common way that this is done is through the heating of the metal to be bound to phosphorus and red phosphorus (P) under inert atmospheric conditions or vacuum. In principle, all metal phosphides and polyphosphides can be synthesized from elemental phosphorus and the respective metal element in stoichiometric forms. However, the synthesis is complicated due to several problems. The exothermic reactions are often explosive due to local overheating. Oxidized metals, or even just an oxidized layer on the exterior of the metal, causes extreme and unacceptably high temperatures for beginning phosphorination. Hydrothermal reactions to generate nickel phosphides have produced pure and well crystallized nickel phosphide compounds, Ni2P and Ni12P5. These compounds were synthesized through a solid-liquid reaction between NiCl2∙12H2O and red phosphorus at 200 °C for 24 and 48 hours, respectively.
- Aluminium phosphide (AlP)
- Indium phosphide (InP)
- Calcium phosphide (Ca3P2)
- Copper phosphide (Cu3P)
- Magnesium phosphide (Mg3P2)
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