Si6O18

Si6O18 is the chemical formula used in silicate chemistry to denote a hexasilicate oxide cluster. It is not the name of a single widely recognized mineral, but rather a stoichiometric composition that can appear as a fragment of a silicate network or as a charged cluster in solution.

Structure and bonding

The six silicon atoms in such clusters are typically four-coordinated to oxygen through SiO4 tetrahedra that share oxygen atoms with each other. The overall connectivity results in extensive bridging between tetrahedra, giving a condensed silicate core. With oxide ligands as O2−, the cluster generally carries a net negative charge in its bare form, and charge balance is achieved in salts or through protonation. Consequently, [Si6O18]n− species and protonated variants such as HxSi6O18 are observed in different chemical environments.

Occurrence and context

Si6O18 is discussed mainly as a structural motif in silicate oligomer chemistry, in geochemical modelling of silicate solutions, and in studies of condensation processes in sols and gels. It serves as a representative building block for understanding how small silicate units link to form larger networks, rather than as a standalone mineral with a fixed crystal structure.

Characterization and synthesis

In laboratory contexts, hexasilicate-like clusters can be generated or detected in solution by condensation reactions of silicate precursors and analyzed by spectroscopic methods or mass spectrometry. The exact geometry and charge state depend on synthesis conditions, pH, and counterions present.

See also

Silicate chemistry, silicate oligomers, polyox silicates.