Si2O7n

Si₂O₇ⁿ⁻ (disilicate ion) is a polyatomic anion composed of two silicon atoms bonded to seven oxygen atoms, forming a structural unit within silicate minerals and glasses. This anion belongs to the broader class of silicates, which are among the most abundant and structurally diverse compounds in the Earth's crust. The general formula Si₂O₇ⁿ⁻ represents a repeating unit where the charge (n) varies depending on the bonding environment, typically ranging from -2 to -6, though -6 is the most common in isolated disilicate groups.

The disilicate ion is characterized by two silicon-oxygen tetrahedra (SiO₄) sharing a single oxygen atom, creating a structure known as a "double tetrahedron." This sharing reduces the overall negative charge compared to isolated SiO₄⁴⁻ units, leading to a more stable configuration in crystalline and amorphous materials. Disilicates are found in various minerals, such as thortveitite (Sc₂Si₂O₇) and hemimorphite (Zn₄Si₂O₇(OH)₂·H₂O), where they contribute to the mineral's physical and chemical properties.

In industrial applications, disilicate structures play a role in the production of ceramics, glass, and refractories. For example, certain types of glass, such as borosilicate glass, incorporate silicate units to enhance thermal stability and resistance to chemical corrosion. The anion's flexibility in bonding also allows it to integrate into complex silicate networks, influencing properties like melting point, viscosity, and mechanical strength.

From a structural chemistry perspective, the disilicate ion exemplifies how silicon-oxygen bonding can form extended frameworks. Its study is fundamental to understanding the behavior of silicates in geological processes, materials science, and synthetic chemistry. The anion's versatility underscores its importance in both natural and engineered systems.