A transition metal thiosulfate complex is a coordination complex containing one or more thiosulfate ligands. Thiosulfate occurs in nature and is used industrially, so its interactions with metal ions are of some practical interest.[1][2] Three binding modes are common: monodentate (κ1-), O,S-bidentate (κ2-),and bridging (μ-). Typically, thiosulfate complexes are prepared from thiosulfate salts. In some cases, they arise by oxidation of polysulfido complexes, or by binding of sulfur trioxide to sulfido ligands.[3]
Silver-thiosulfate complexes are produced by common photographic fixers. By dissolving silver halides the fixer stabilises the image. The dissolution process entails reactions involving the formation of 1:2 and 1:3 complexes (X = halide):[4] Fixation involves these chemical reactions (X = halide, typically Br−):[5]
Sodium aurothiosulfate dihydrate, Na3[Au(S2O3)2]·2H2O, has been widely discussed in the context of the extraction of gold from its ores. Presently cyanide salts are used on a large scale for that
purpose with obvious risks.[6]
In the IUPAC Red Book the following terms may be used for thiosulfate as a ligand: trioxido-1κ3O-disulfato(S—S)(2−); trioxidosulfidosulfato(2−); thiosulfato; sulfurothioato. In the naming for thiosulfate salts, the final "o" is replaced by "e".[7] Thus, sodium aurothiosulfate could be called trisodium di(thiosulfato)aurate(I).