Phosphorus polyphosphides

Examples of the anionic structures in polyphosphides, polyarsenides and poly antimonides. For comparison, recall the structures of red and black phosphorus and of arsenic (pp. 108, 109 and 110). Stereo image for NaPs... 

Figure I. Some homoatomic phosphorus units in metal polyphosphides as examples for polyanionic clusters.

Homonuclear aggregates of phosphorus atoms exist in many forms discrete molecules, covalent networks in crystals, polyphosphide anions, and phosphorus fragments in molecular compounds. 

The hydrogen of this phosphide appears to have a slight acidic character, since the phosphide dissolves in alcoholic alkalies giving deep red solutions which contain polyphosphides, similar to those which are formed by the action of alcoholic alkali on finely divided scarlet phosphorus. These compounds are easily hydrolysed by dilution, or by the addition of acids, with the precipitation of a yellow or reddish mixture of solid hydrogen phosphide and scarlet phosphorus (which possibly contains a suboxide or P4H.OH8,4). 

As a ligand, elemental phosphorus not only appears in the oligomeric forms present in its polymorphs (like P4), but as P with n covering a large range from n = 1 to at least n = 6, and as the corresponding cations and anions (the polyphosphides). 

Table 6 gives a survey on the range of M-P distances. The upper limits are uncertain because the selected distances are only compared with atomic radii and take not into account the topology (convex polyhedra procedure). The M-P coordination in sohd phosphides demonstrates both coordination and donor functions in isolated complex compounds (cf the (E15) complexes, stabihzed in the coordination sphere of transition metals). This is especially true with the polyphosphides. An extreme is CU2P3I2 (see Section 6.5.7), which is an adduct of Cul and elemental phosphorus (charge transfer complex). Chains of polycychc... 

Figure 2 Donor properties of polyphosphides and phosphanes metal atoms, filled circles phosphorus atoms, open circles substituents R indicated by lines, (a)/r, jj, jj -P2R4 (h)j) -P3 (c)/r, , jj -P4R4 (A) (e)/r,(j ,jj -P6 (f) -P4 (g) /r-P7R3 ...

Crystalline [([18]crown-6)K][P(CN)2] is the preferred material for further reactions. In the P4-disproportionation reaction, crown ether potassium polyphosphides are formed as the second product. Their composition and solubility depend on the stoichiometry used. The intense red color of the solution in early stages of the reaction is caused by an intermediate high concentration of soluble polyphosphides. The final equilibrium concentration of these phosphides can contaminate and color the isolated dicyanophosphide. To avoid this contamination, the remaining soluble polyphosphides are converted to insoluble ones by an excess of white phosphorus. 

Alternatively, the black precipitate formed after the first 24 hr is separated, and the excess phosphorus is added to the clear red filtrate. During the second 24 hr period of boiling some more of the black polyphosphide precipitate forms. [([18]crown-6)K] [P(CN)2] is obtained in colorless and analytically pure form but in a somewhat reduced yield, 6.2 g (64%). 

Trilithium heptaphosphide, dilithium hexadecaphosphide, and trisodium henicosaphosphide are polyphosphides with isolated anions in the solid state as well as in solution. These metalated poly phosphorus compounds are of interest because of their structural relationship to the phosphorus hydrides (phosphanes) and organophosphanes P.R and particularly because of their potential use as building blocks for the syntheses of polyphosphorus compounds. 

In all of these reactions the major by-product was an insoluble, non-melting, amorphous, yellow solid containing 40-60% phosphorus. The observation that the polyphosphide intermediates react further with additional phosphorus points to an analogy with the well known reaction of (NH4)2 S with sulfur to give ammonium polysulfrdes 8)... 

The preparation and structure of magnesium polyphosphide, MgP4, have been described. The compound was prepared by the reaction of gaseous phosphorus with the phosphide MgaP2 at 600 °C in a sealed silica tube. Evidence for a primitive monoclinic cell was obtained from electron microdiffraction. Refinement of X-ray powder diffraction data showed that the compound is isostructural with... 

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