metalcentered

Metal-centered is an adjective used in inorganic and organometallic chemistry to describe processes, electronic states, or reactivity that are primarily localized on the metal atom within a metal-containing species, as opposed to being centered on ligands or the ligand framework.

In coordination chemistry, metal-centered redox refers to changes in the metal's oxidation state and electron count, whereas ligand-centered redox involves oxidation or reduction localized on ligands. In spectroscopy and electronic structure, metal-centered transitions are those that primarily involve the metal’s d-orbitals (such as d–d transitions or metal-based charge-transfer states), while ligand-centered transitions involve electronic excitation within the ligand framework (for example, ligand π to π* or n to π* transitions). Charge-transfer states are often described as metal-to-ligand (MLCT) or ligand-to-metal (LMCT), which are not metal-centered in the strict sense but involve interaction between metal and ligand orbitals.

In catalysis and photochemistry, metal-centered pathways are those where the reactive site is the metal center—changes in oxidation state, radical formation on the metal, or steps that proceed via metal-centered intermediates. Ligand-centered pathways involve transformations occurring predominantly on the ligands or through metal–ligand cooperative effects.

Determining whether a process is metal-centered can involve experimental and computational methods, such as cyclic voltammetry to identify metal-based redox events, UV–visible spectroscopy and EPR to assign electronic states, X-ray absorption spectroscopy to probe metal oxidation states, and density functional theory analyses of orbital localization.

See also: ligand-centered, non-innocent ligands, MLCT, LMCT.