zerovalent

Zerovalent describes chemical species whose oxidation state is zero. In chemistry, oxidation states are formal charges assigned to atoms in a compound to reflect electron transfer during reactions. Zerovalent species include elements in their elemental form and certain organometallic or coordination compounds in which the metal center is formally in the zero oxidation state. In practice, zerovalent species are often stabilized by ligands or protective environments that prevent rapid oxidation.

Zerovalent metals occur in several contexts. Elemental metals such as iron, nickel, or palladium can be considered zerovalent when viewed in their pure, uncharged state, though in many practical settings they exist as alloys or in compounds where the formal oxidation state is not zero. Organometallic chemistry also provides zerovalent metal centers, for example zero-valent nickel or palladium complexes stabilized by ligands such as carbon monoxide or phosphines. In these complexes, the metal center is formally in oxidation state zero, which influences reactivity and catalytic properties. Zerovalent metals in nanoparticulate or coated forms are common in industrial and environmental contexts.

One notable application is zerovalent iron (ZVI), widely used in environmental remediation to reduce and immobilize contaminants in groundwater, including chlorinated solvents and certain metal pollutants. Zerovalent metals serve as reducing agents in organic synthesis and catalysis, where the zero oxidation state enables electron transfer to substrates. Stability is a key consideration: zerovalent species are typically prone to oxidation by air and moisture, often requiring protective ligands, coatings, or inert atmospheres to maintain their reactive, low-oxidation-state character.