Electromerism is a type of
isomerism between a pair of
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
s (electromers, electro-isomers) differing in the way
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no ...
s are distributed among the atoms and the connecting chemical bonds. In some literature electromerism is equated to
valence tautomerism, a term usually reserved for tautomerism involving reconnecting chemical bonds.
One group of electromers are excited electronic states but isomerism is usually limited to ground state molecules. Another group of electromers are also called redox isomers: metal ions that can exchange their
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
with their ligands (see
non-innocent ligand
In chemistry, a (redox) non-innocent ligand is a ligand in a metal complex where the oxidation state is not
clear. Typically, complexes containing non-innocent ligands are redox active at mild potentials. The concept assumes that redox reactions ...
). One of the first instances was a cobalt bis(quinone) complex described by Buchanan and Pierpont in 1980 with a cobalt(II) complex in
chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which both the Reagent, reactants and Product (chemistry), products are present in concentrations which have no further tendency to change with time, so that there is no observable chan ...
with the cobalt(III) complex. Ligands commonly found are based on
dioxolenes,
phenoxyl radicals and
polychlorotriphenylmethyl radicals.
Metalloporphyrins have also been studied. A set of electromers not requiring redox-active ligands have been described as well as a set without a metal. A new group of electromers has also been described recently.
References
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Isomerism