hexavalens

Hexavalents is a term used in inorganic chemistry to describe chemical species in which the dominant oxidation state is plus six, or in which six valence electrons participate in bonding around a central atom. In practice, hexavalent species often form six bonds or coordinate to six ligands, frequently adopting octahedral geometries. The concept is widely applied to oxoanions and oxides of certain elements, where the +6 state is common and well defined.

Prominent examples include chromium in Cr(VI) compounds such as chromate (CrO4 2−), dichromate (Cr2O7 2−), and chromium trioxide (CrO3). Molybdenum and tungsten also commonly exist in the +6 state, as in molybdate ions (MoO4 2−) and molybdenum trioxide (MoO3), or tungsten oxoanions such as tungstate (WO4 2−) and tungsten trioxide (WO3). Sulfur in sulfate (SO4 2−) is another well-known hexavalent species, as are uranium in uranyl forms (such as UO2 2+ and UO3). In solution, these hexavalent oxoanions are usually highly oxidizing and can be reduced to lower oxidation states, most notably Cr(VI) to Cr(III).

Occurrence and applications of hexavalent compounds span minerals, industrial pigments, corrosion inhibitors, and catalysts. Hexavalent chromium compounds, for example, have historically been used as pigments and coatings but are subject to stringent health and environmental regulations due to toxicity and carcinogenicity. In contrast, the redox flexibility of hexavalent species underpins their utility in certain catalytic processes and inorganic syntheses, where controlled reduction or oxidation is required.