Polyphosphide anions

Almost all metals form phosphides, and over 200 different binary compounds are now known. In addition, there are many ternary mixed-metal phosphides. These phosphides consist of metal cations and phosphide anions. In addition to some simple anions (P3-, P -, P ), there are many polyphosphide anions that exist in the form of rings, cages, and chains, as shown in Fig. 15.3.4. 

In some metal phosphides, the polyphosphide anions constitute infinite chains and sheets, as shown in Fig. 15.3.5. 

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The existence of a variety of other polyphosphide anions has been demonstrated. For example, P and P have been identified in LaP2 (72). Infinite chain stmctures for the polyphosphide anion have been reported for compounds such as KP and thallium pentaphosphide [11093-99-5] TIP. Cage anions such as P that include triply linked phosphoms atoms are found in Li P. ... 

Figure 12.11 Schematic representation of the structures of polycyclic polyphosphide anions (open circles P, shaded circles P") (a) Pj ", (b) fPj Xr, (c) P8 i. (d) Pii -...

Polycyclic polyphosphanes are often best prepared by direct protonation of the corresponding polyphosphide anions (Figs. 12.11 and 12.12)... 

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

Adamantane-shaped anions P o are believed to be present in the solid-state structure of Cu4SnP,o [24,66]. Linear polyphosphide anions such as some of those indicated in Table 4.8 have been shown to exist in metaUophosphorus compounds (Chapter 8.3). Pentaphosphide chain anions Pg " have been obtained from metaUophosphorus ring compounds (Chapter 8.16) (Table 4.8). 

Tetraphospholyl anions are known and electrically conducting polyphosphide anions may be capable of synthesis. 

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... 

Sometimes rather complicated structures occur in the anionic part of a structure. For example, approximately 50 different binary polyphosphides are known only for the alkali and alkaline earth metals, which, in part, also adopt different modifications. In addition, there are more than 120 binary polyphosphides of other metals. Fig. 13.2 conveys an impression of how manifold the structures are. 

Examples of the anionic structures in polyphosphides, polyarsenides and poly antimonides. 

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). 

Coordination to metals follows the usual trends. The transition metals try to achieve octahedral coordination (with a few exceptions), but the cations of the electropositive group 1-3 elements exhibit a rich variety. The coordination polyhedra are determined by radius ratios more than by topological preferences. For polyphosphides in general, all P atoms are involved in M-P interactions according to the number of lone pairs present. The anionic (lb)P and (2b)P as well as the neutral (3b)P° species adopt quasi-tetrahedral coordination, especially if main-group cations are involved. Only a few exceptions are known, for example Li3P7. With more covalent M-P bonds, the number (m + n) of available lone pairs of a polyanion P " is strongly related to the metal coordination number that is, CN(M) < m + n). If CN(M) > m + n), ion-ion and ion-dipole interactions dominate. The relation <7[M-(2b)P] > <7[M-(3b)P] is true in most cases. 

From reaction in solutions, a variety of polyphosphides is obtained that are not known as solvent-free binary compounds (Table 7). Several have been characterized by P NMR spectroscopy in solution, for example, Pi9 and P26" , which have no counterparts in binary systems. LiPs forms a to(P5 ) polyanion in the solid state, but the corresponding anion in solution is monomeric Ps, an analogue of the cyclopentadienyl anion. The helical polyanions do(P7 ) of LiP and NaP have no monomeric counterpart in the solution here the anion is present as R2P7. Adding simply a salt (KI), trimeric P2i is formed as a finite anion in solution and it can be isolated as a solvated salt. 

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. 

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