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Search for complex anion Lewis bases species in The Chemical Thesaurus

Complex anion Lewis base species behave as charged hard spheres that form ionic charge-controlled complexes (ie act as non-nucleophilic counter ions), or they behave as donors of hard/soft ligands, X^–.

Ligand substitution – in which a nucleophilic Lewis Base displaces a nucleofugal ligand – is common and ligand symbiosis considerations/effects are very important.

There are four subclasses of complex anion Lewis base:

X = Halogen anion which gives rise to the synthetically useful non-basic, non-nucleophilic, non-interfering anionic spectator counter ions:

[BF₄]^–    [SbF₆]^–    [AsF₆]^–    [FeBr₄]^–

X = Hydride ion which gives rise to species which act as donors of nucleophilic hydride ion, [BH₄]^– and [AlH₄]^–, as long as there is not a Brønsted Acidic proton available or H₂ is generated.

M = Heavy metal (Fe or Cr as opposed to B or Al). Such complex anions are much studied in classical inorganic coordination chemistry. Transition metals centres often exhibit multiple oxidation states. These are better considered as type 23 Lewis acid/base complexes.

X = Oxygen heavy metal species with oxygen ligands are commonly used as oxidising agents.

Families of ligand replacement congeneric series are common: