Phosphide

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A portion of the structure of Cu3P, highlighting the highly crosslinked nature common to many transition metal phosphides (Cu = orange, P = purple).

In chemistry, a phosphide is a compound containing the P3- ion or its equivalent. Many different phosphides are known, with widely differing structures.[1] Most commonly encountered on the binary phosphides, i.e. those materials consisting only of phosphorus and a less electronegative element. Numerous are polyphosphides, which are solids consisting of anionic chains or clusters of phosphorus. Phosphides are known with the majority of less electronegative elements with the exception of Hg, Pb, Sb, Bi, Te, and Po.[2] Finally, some phosphides are molecular.

Binary mono-phosphides[edit]

Examples are the group 1 include Na
3
P
. Notable examples include aluminium phosphide (AlP) and calcium phosphide (Ca3P2), which used as pesticides, exploiting their tendency to release toxic phosphine upon hydrolysis. Magnesium phosphide (Mg3P2) also is moisture sensitive. Indium phosphide (InP) and GaP are used as a semi-conductors, often in combination of related arsenides.[3] Copper phosphide (Cu3P) illustrates a rare stoichiometry for a phosphide. These species are insoluble in all solvents - they are 3-dimensional solid state polymers. For those with electropositive metals, the materials hydrolyze:

Ca3P2 + 3 H2O → 3 Ca(OH)2 + 2 PH3
Coordination environment around Cu in Cu3P. Two pairs of Cu atoms are eclipsed.

Polyphosphides[edit]

These species contain P-P bonds. The simplest polyphosphides contain P4−
2
ions;. Others contain the cluster P3−
11
ions and polymeric chain anions (e.g. the helical (P
)
n
ion) and complex sheet or 3-D anions.[4] The range of structures is extensive. Potassium has nine phosphides: K3P, K4P3, K5P4, KP, K4P6, K3P7, K3P11, KP10.3, KP15. Eight mono- and polyphosphides of nickel has eight (Ni3P, Ni5P2, Ni12P5, Ni2P, Ni5P4, NiP, NiP2, NiP3).[2]

Two polyphosphide ions, P4−
3
found in K
4
P
3
and P5−
4
found in K5P4, are radical anions with an odd number of valence electrons making both compounds paramagnetic.[2]

Preparation of phosphide and polyphosphide materials[edit]

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.[5] 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.[6]

Structure of terminal phosphido complexes of Mo.

.

Molecular phosphides[edit]

Compounds with triple bonds between a metal and phosphorus are rare. The main examples have the formula Mo(P)(NR2)3, where R is bulky organic substituent.[7]

Natural examples[edit]

Schreibersite (Fe,Ni)3P is a common mineral in some meteorites.[8][9]

References[edit]

  1. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  2. ^ a b c H.G. Von Schnering, W. Hönle Phosphides - Solid-state Chemistry Encyclopedia of Inorganic Chemistry Ed. R. Bruce King (1994) John Wiley & Sons ISBN 0-471-93620-0
  3. ^ C. S. Blackman; C. J. Carmalt; S. A. O'Neill; I. P. Parkin; K. C. Molloy; L. Apostolico (2003). "Chemical vapour deposition of group Vb metal phosphide thin films". J. Mater. Chem. 13: 1930–1935. doi:10.1039/b304084b. 
  4. ^ W. Jeitschko, M. H. Möller "Phosphides and Polyphosphides of the Transition Metals" Phosphorus and Sulfur and the Related Elements 1987, Volume 30, pages 413-416. doi:10.1080/03086648708080608
  5. ^ von Schnering, Hans-Georg; Hönle, Wolfgang (1988). "Bridging Chasms with Phosphides". Chem. Rev. 88: 243–273. doi:10.1021/cr00083a012. 
  6. ^ Liu, Zongyi; Huang, Xiang; Zhu, Zhibin; Dai, Jinhui (2010). "A simple mild hydrothermal route for the synthesis of nickel phosphide powders". Ceramics International 36 (3): 1155–1158. doi:10.1016/j.ceramint.2009.12.015. 
  7. ^ Cossairt, B. M.; Piro, N. A.; Cummins, C. C., "Early-Transition-Metal-Mediated Activation and Transformation of White Phosphorus", Chem. Rev. 2010, volume 110, p. 4164. doi:10.1021/cr9003709
  8. ^ Mindat
  9. ^ Handbook of Mineralogy