Metal valence-electron counting and the 18-electron heuristic
Neutral-fragment and oxidation-state counting consistently allocate ligand and metal electrons when their conventions are used throughout.
Key knowledge
Neutral-fragment and oxidation-state counting consistently allocate ligand and metal electrons when their conventions are used throughout. In ionic counting the metal d count is its group number minus oxidation state, with ligand donations added separately. The 18-electron pattern is useful for many transition-metal complexes, but a stable square-planar platinum(II) complex can have 16 electrons.
Values and equations
nd = g−OS; Nval = nd+ΣL dL
- nd
- formal metal d-electron count in ionic bookkeeping electron count
- g
- metal group number 1
- OS
- formal oxidation state 1
- dL
- electron donation assigned to ligand L by the chosen ionic convention electron count
- Nval
- total valence-electron count electron count
Conditions and scope
- Electron counts are bookkeeping, not measured charge or a universal stability criterion.
- Bridging ligands and metal–metal bonds need their stated counting conventions; do not mix neutral and ionic donations.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read both counting methods and cis-PtCl2(NH3)2 example; excluded conflation of every below-18 complex with coordinative unsaturation and homoleptic/heteroleptic wording used for bond cleavage.
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Entry details
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- uni-chem-valence-electron-counting
- Revision
- core.1
- Structured reference record
- University core expansion