P6O18

P6O18 is a phosphorus oxide described in some theoretical discussions as a condensed form consisting of six phosphorus atoms and eighteen oxygen atoms. It is part of the broader exploration of polyphosphorus oxides that extend beyond the well-characterized P4O10 (phosphorus pentoxide) and related species. Unlike P4O10, P6O18 is not associated with a widely accepted, experimentally established structure or synthesis.

Structure and bonding in P6O18 are topics of speculation. Proposed models envision a network in which P–O–P linkages connect multiple phosphorus centers, potentially forming cage-like or extended framework motifs. As with many highly condensed oxide species of phosphorus, the average oxidation state of phosphorus would be near +6, and the material would be expected to be highly reactive toward moisture and reducing environments. However, no single structural consensus has been established, and multiple hypothetical geometries have been explored in theoretical studies.

Synthesis and occurrence are similarly uncertain. P6O18 has not been reported as a stable, isolable solid under standard laboratory conditions. If it exists, it would likely arise only under highly anhydrous, high-temperature or gas-phase conditions, or as an intermediate in deeper dehydration or condensation sequences of phosphoric acid derivatives. Its practical preparation, isolation, and characterisation remain unsettled topics in phosphorus oxide chemistry.

Reactivity of any such condensed oxide would be governed by its high affinity for water and potential propensity to hydrolyze to phosphoric acid or polyphosphoric species. Consequently, P6O18 is primarily of theoretical and academic interest, contributing to the understanding of how phosphorus atoms can assemble with oxygen into highly connected networks. Related, better-characterized compounds include P4O10 and its polyphosphoryl derivatives.