Mg2ionin

Note: Mg2ionin is not a standard chemical name; this article describes the magnesium(II) ion, Mg2+, the common divalent cation of magnesium.

Mg2+ ion, or magnesium(II) ion, is a divalent cation with the chemical formula Mg2+. In aqueous solution it exists predominantly as the hexaaqua complex [Mg(H2O)6]2+ and is a hard Lewis acid with high charge density. Its ionic radius is small for a divalent cation, influencing its coordination chemistry and interactions with oxygen-containing ligands.

Mg2+ is abundant in the Earth's crust and seawater and is essential for biology. It acts as a critical cofactor for hundreds of enzymes, stabilizes adenosine triphosphate (ATP) by coordinating phosphate groups, and supports the structures of nucleic acids and ribosomes. In plants, magnesium sits at the center of chlorophyll.

Coordination chemistry: Mg2+ commonly adopts six-coordinate, octahedral complexes, especially in water. Ligand exchange is relatively slow due to its strong hydration shell. It forms complexes with phosphate, carbonate, ATP, citrate, and EDTA. The first hydrolysis of [Mg(H2O)6]2+ has a pKa around 11.4, reflecting its preference for remaining hydrated at physiological pH.

Applications and health: Magnesium salts supply Mg2+ in fertilizers and medicines (antacids, laxatives). In industry and water treatment, Mg2+ contributes to hardness and scaling. Adequate dietary magnesium is important for neuromuscular and cardiovascular function; excessive intake can cause diarrhea or hypermagnesemia in extreme cases.