eighteenelectron
Eighteenelectron is a term used in inorganic and organometallic chemistry to describe species that achieve an eighteen-electron configuration around a central metal atom or ion. The concept is most closely associated with the 18-electron rule, a heuristic that helps predict the stability and reactivity of many transition-metal complexes. When a metal center reaches 18 valence electrons through its own d-electrons plus electrons donated by ligands, the complex often assumes a closed-shell, noble-gas-like configuration that enhances stability.
Calculation of an eighteen-electron count involves determining the metal’s valence electrons and adding the electrons donated
The eighteen-electron rule is a useful guide but not universal. While many low-oxidation-state, carbonyl-rich complexes conform
See also: eighteen-electron rule, electron counting, organometallic chemistry.