Term: eighteen-electron rule
https://doi.org/10.1351/goldbook.E01913

Definition:
An electron-counting rule to which an overwhelming majority of stable diamagnetic transition metal complexes adhere. The number of nonbonded electrons at the metal plus the number of electrons in the metal-ligand bonds should be 18. The 18 electron rule in transition metal chemistry is a full analogue of the 'Lewis octet rule'.

Related Terms:
1) stable (http://doi.org/10.1351/goldbook.S05900).
2) diamagnetic (http://doi.org/10.1351/goldbook.D01668).
3) lewis octet rule (http://doi.org/10.1351/goldbook.LT07065).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1108 (https://doi.org/10.1351/pac199466051077)

Citation: 'eighteen-electron rule' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.E01913

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