metaanhydride

A metaanhydride is a type of inorganic compound characterized by the presence of a central metal atom bonded to two or more anhydride groups, typically derived from oxyacids. These compounds are formed when a metal oxide or hydroxide reacts with an acid anhydride, leading to the elimination of water. The general structure often involves a metal atom coordinated with anionic fragments such as carbonate (CO₃²⁻), sulfate (SO₄²⁻), or phosphate (PO₄³⁻) groups.

Metaanhydrides are commonly encountered in coordination chemistry and solid-state chemistry. A well-known example is aluminum carbonate, Al₂(CO₃)₃, which technically exists only as a metaanhydride due to the instability of its carbonate salt under normal conditions. Similarly, metal sulfates and phosphates often exhibit metaanhydride-like behavior when dehydrated or formed under specific conditions.

These compounds are often unstable in aqueous solutions, as they tend to hydrolyze back into their constituent metal oxides or hydroxides and the corresponding oxyacid. For instance, metal carbonates decompose upon heating or exposure to moisture, releasing carbon dioxide and forming metal oxides. This instability limits their practical applications but makes them useful in certain chemical reactions or as intermediates in synthesis.

Metaanhydrides play a role in mineralogy, where they appear in naturally occurring minerals such as basic carbonates or sulfates. They also have relevance in industrial processes, such as cement production, where calcium metasilicate (CaSiO₃) forms during the hydration of clinker. Despite their limited stability, their study contributes to understanding metal-oxygen bonding and the behavior of coordination complexes in various environments.