Transition metal sulfate complex

Transition metal sulfate complexes or sulfato complexes are coordination complexes with one or more sulfate ligands. Sulfate binds to metals through one, two, three, or all four oxygen atoms. Common are complexes where sulfate is unidentate or chelating bidentate. Examples are respectively [Co(tren)(NH3)(SO4)]+ (tren = tris(2-aminoethyl)amine) and Co(phen)2SO4. All four oxygen atoms of sulfate bond to metals in some Dawson-type polyoxometalates, e.g. [S2Mo18O62]4-.

Sulfate as a counterion
Being the conjugate base of a strong acid (sulfuric acid), sulfate is not basic. It is more commonly a counterion in coordination chemistry. Tutton's salts, with the formula M'2M(SO4)2(H2O)6 (M' = K+, etc.; M = Fe2+, etc.), illustrate the ability of water to outcompete sulfate as a ligand for M2+. Similarly alums, such as chrome alum ([K(H2O)6][Cr(H2O)6][SO4]2), features [Cr(H2O)6](3+) with noncoordinated sulfate. In a related vein, some sulfato complexes confirmed by X-ray crystallography, convert to simple aquo complexes when dissolved in water. Copper(II) sulfate examplifies this behavior, sulfate is bonded to copper in the crystal but dissociates upon dissolution.

Synthesis


Sulfato complexes are commonly produced by reaction of metal sulfates with other ligands.

In some cases, sulfato complexes are produced from sulfur dioxide:
 * Pt(O2)(PPh3)2 + SO2 -> Pt(SO4)(PPh3)2 (PPh3 = triphenylphosphine)

Sulfato complexes also arise by air-oxidation of metal sulfides.

Reactions
Sulfato complexes are susceptible to protonation of uncoordinated oxygen atoms.