H2Si2O5

H2Si2O5 is the chemical formula for a compound sometimes referred to as metasilicic acid or pyrosilicic acid. It is a hypothetical or unstable silicic acid. Silicic acids are a group of compounds derived from silicic acid, H4SiO4, with the general formula SiO2·nH2O. In the case of H2Si2O5, it can be considered as a condensation product of two molecules of silicic acid, with the elimination of one molecule of water.

H2Si2O5 is not commonly encountered as a stable, isolable substance. It tends to readily polymerize or decompose. Its existence is often discussed in theoretical contexts related to the chemistry of silicon and oxygen. In aqueous solutions, silicic acids exist in equilibrium, and more complex polysilicic acids can form. H2Si2O5 would represent an early stage in this polymerization process.

While direct synthesis and isolation of pure H2Si2O5 are difficult, related silicon-oxygen structures are fundamental to many mineral and material sciences. The Si2O5 unit itself can be thought of as two silicon atoms bonded to each other and bridged by oxygen atoms, with additional oxygen atoms bonded to each silicon, and hydrogen atoms attached to some of the oxygen atoms. The precise structure and stability are influenced by factors such as pH and temperature.