MxCO3n

MxCO3n is a symbolic notation used to denote a family of carbonate-containing solids in which metal cations, collectively represented as M, are linked by carbonate groups (CO3). The exact composition and structure of these materials depend on the identity and oxidation state of the metal, as well as the ratio x to n in the formula Mx(CO3)n. The term encompasses simple metal carbonates with fixed 1:1 stoichiometry, as well as mixed-metal carbonates and polymeric carbonate frameworks in which carbonate units bridge multiple metal centers.

Structural motifs in MxCO3n can vary from discrete salts to extended networks. In simple cases, a metal carbonate may adopt a one-to-one relationship with carbonate, forming isolated units such as MCO3. In more complex variants, carbonate groups act as multidentate bridges, generating polymeric chains, layered structures, or three-dimensional frameworks. The resulting materials often exhibit characteristic carbonate vibrational modes detectable by infrared spectroscopy, with bands near 1400–1500 cm−1 (carbonate stretching) and around 850–900 cm−1 (out-of-plane bending).

Synthesis of MxCO3n-type materials typically involves precipitation or co-precipitation of metal cations with carbonate sources from aqueous or solvent systems, and in many cases can be enhanced by hydrothermal or solvothermal methods to improve crystallinity. Thermal analysis shows that heating these carbonates generally releases CO2 and leaves behind metal oxides or mixed-oxide phases, depending on composition and conditions.

Applications explored for carbonate-based materials include ceramic precursors, catalysts, and potential CO2 capture or storage materials. The study of MxCO3n also informs understanding of natural carbonate minerals, mixed-metal carbonates, and carbonate-containing coordination polymers.

See also: calcium carbonate, magnesium carbonate, dolomite, mixed-metal carbonates, metal carbonate frameworks.

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