triwertigen

Triwertigen (from German tri- "three" and -wertig "valent") refers to atoms, ions or chemical species that exhibit a valence or oxidation state of three. In chemistry the term is commonly used to describe trivalent cations with a +3 charge (for example Al3+, Fe3+, Cr3+) and elements that typically form three bonds in covalent compounds (for example nitrogen in many organic compounds).

Trivalent ions frequently occur as hydrated complexes in aqueous solution, e.g. Al(H2O)6^3+, and show characteristic coordination chemistry. Although the formal valence is three, coordination numbers often exceed three because ligands occupy available coordination sites; six-coordinate (octahedral) complexes are common for many trivalent transition metals. Trivalency should be distinguished from oxidation state concepts and actual bonding, which can be covalent, ionic or mixed.

Trivalent species are important in materials, catalysis and biology. Fe3+ participates in redox cycling in proteins and transport, Cr3+ is a component of some catalytic systems and trace nutrition, and Al3+ influences water chemistry and mineralogy. Chemical properties such as hydrolysis tendency, complex stability and redox behavior vary with ionic radius, charge density and ligand type. Toxicity and environmental behavior also differ markedly between trivalent and other oxidation states (for example chromium(III) is much less toxic than chromium(VI)). Analytical identification relies on spectroscopy, precipitation reactions and electrochemical methods.