Trilithium Heptaphosphide, Dilithium Hexadecaphosphide, and Trisodium Henicosaphosphide

TRILITHIUM HEPTAPHOSPHIDE, DILITHIUM HEXADECAPHOSPHIDE, AND TRISODIUM HENICOSAPHOSPHIDE 

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. 

The increasing complexity of these homoatomic anions is well reflected by the following systematic names  

The compound LiaP7 was first prepared by the action of butyllithium on diphosphane. The route given below, however, is a much better approach it is based on a nucleophilic cleavage of white phosphorus with lithium dihydrogen phosphide. The latter is readily available by the reaction of butyllithium and phosphine.  

A high yield of Li2P 6 is obtained in the reaction of P4 and LiPHj if the stoichiometric ratio of reactants and the reaction time are significantly modified. The formation of the P ion has also been observed in the reaction of Na3P7 with (Ph4P)Cl (ref. 8) and in the decomposition of U2HP7 and LiH2P7.  

The structural peculiarity of trilithium heptaphosphide is its fluctuating anion.On account of the structural similarity to the hydrocarbon bullvalene, the P7 ion is capable of a degenerate Cope rearrangement and at room temperature has to be described by 1680 valence-tautomeric forms of equal structure. 

The ions P, and Pi, exhibit a striking resemblance to structural units of Hittorfs phosphorus.  

---