MH2O6n

MH2O6n is a shorthand notation used in coordination chemistry to describe a metal aquo complex in which six water molecules are coordinated to a central metal ion. In formal notation this is written as [M(H2O)6]^n+, with 'M' representing a metal cation and 'n' the overall charge of the complex. The six aquo ligands create an octahedral coordination geometry around M and often define the complex's basic properties in solution.

In aqueous solution, many metal salts dissociate and rapidly form [M(H2O)6]^n+ species. The identity of M and the value of n determine the complex's color, stability, and reactivity. The water ligands can be replaced by other ligands in substitution reactions, and hydrolysis can occur with increasing pH to form hydroxo- or oxo-bridged species.

Spectroscopic and kinetic properties of these aquo complexes vary widely. Transition-metal ions typically show characteristic d–d transitions; ligand lability varies with charge and electronic configuration. Stability constants describe how readily water ligands stay attached versus being displaced.

Although MH2O6n serves as a useful schematic for discussing hydration shells, it is not a formal name. For precise communication, chemists specify the metal, its oxidation state, and the coordinating ligands, e.g., [Fe(H2O)6]3+. The concept remains a core part of understanding aqueous coordination chemistry and metal hydration phenomena.