Transition metal sulfito complexes are

coordination compound A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

s containing

sulfite Sulfites or sulphites are compounds that contain the sulfite ion (systematic name: sulfate(IV) ion), . The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are widely used. Sulfites are ...

(SO₃^2-) as a

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

. The inventory is large. Few sulfito complexes have commercial applications, but sulfite is a substrate for the molybdoenzyme

sulfite oxidase Sulfite oxidase () is an enzyme in the mitochondria of all eukaryotes, with exception of the yeasts. It oxidizes sulfite to sulfate and, via cytochrome c, transfers the electrons produced to the electron transport chain, allowing generation of ...

Bonding modes

In principle, sulfite can bond to metal ions via S or O. To some extent, the sulfito ligand resembles nitrito (), which can bind through N or O. Monodentate, ''S''-bonded sulfites are more common than O-bonded sulfito ligands. ''S''-Bonded sulfite is a soft ligand with a strongly trans labilizing effect as indicated by the rapid

aquation Aquation is the chemical reaction involving "incorporation of one or more integral molecules of water" with or without displacement of other atoms or groups. The term is typically employed to refer to reactions of metal complexes where an anion is ...

of to give . In some cases, sulfite serves as a bridging ligand forming M-SO₂-O-M’ linkages.

Examples

* (tetren = ) * (M = Rh, Co, en =

ethylenediamine Ethylenediamine (abbreviated as en when a ligand) is the organic compound with the formula C2H4(NH2)2. This colorless liquid with an ammonia-like odor is a basic amine. It is a widely used building block in chemical synthesis, with approximately ...

) * *

Complexes with modified sulfito ligands

Being dibasic, sulfito ligands are susceptible to ''O''-alkylation and ''O''-protonation. Some examples: * * * *

References

{{Coordination complexes Ligands Sulfites