Zentralmetallion

Zentralmetallion is a term used in coordination chemistry to denote the central metal ion at the core of a coordination complex or organometallic cluster. The Zentralmetallion is the metal atom or ion to which the surrounding ligands bind, and it often largely determines the chemical and physical properties of the complex.

Its oxidation state, electronic configuration, and nuclear charge influence the geometry, reactivity, and spectroscopic characteristics of the complex. The central metal's identity sets the preferred coordination number and ligand field, which in turn governs color, spin state, catalytic activity, and stability.

Common coordination environments include octahedral and square planar geometries, with coordination numbers typically from 4 to 6, though higher or lower values occur in some systems. The central metal ion can be a transition metal, main-group metal, or lanthanide/actinide, depending on the complex. Examples of central metals in well-known complexes include iron in ferricyanide [Fe(CN)6]3- and ferrocyanide [Fe(CN)6]4-, copper in [Cu(H2O)6]2+, and platinum in [PtCl6]2-.

Zentralmetallions are central to catalysis, bioinorganic processes, and materials science. Their study uses methods such as UV–visible spectroscopy, X-ray crystallography, and electron paramagnetic resonance to determine oxidation states, geometry, and electronic structure. While the term Zentralmetallion is primarily used in German-language literature or theoretical discussions, it corresponds closely to the widely used concept of the central metal ion in English-language coordination chemistry.

See also: coordination complex, ligand, oxidation state, ligand field theory.