Transition metal thiosulfate complex

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]

Illustrative coordination complexes of thiosulfate.


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]

AgX + 2 S2O32− → [Ag(S2O3)2]3− + X
AgX + 3 S2O32− → [Ag(S2O3)3]5− + X

Sodium aurothiosulfate, Na3Au(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 this purpose with obvious risks.[6]


In the IUPAC Red Book the following terms may be used for thiosulfate as a ligand: trioxido-1κ3O-disulfato(SS)(2−); trioxidosulfidosulfato(2−); thiosulfato; sulfurothioato. In the naming for thiosulfate salts, the final "o" is replaced by "e".[7]


  1. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 715. ISBN 978-0-08-037941-8.
  2. ^ Trachevskii, V. V.; Zimina, S. V.; Rodina, E. P. (2008). "Thiosulfate Metal Complexes". Russian Journal of Coordination Chemistry. 34 (9): 664–669. doi:10.1134/S1070328408090066. S2CID 98593860.
  3. ^ Kubas, G. J.; Ryan, R. R. (1984). "Reduction of Sulfur Dioxide by Cp2MH2 (M = Mo, W) to Cp2M(S2O3) and water. Molecular Structure and Reaction with Acids of an Organometallic Molybdenum-Thiosulfate Complex". Inorganic Chemistry. 23 (20): 3181–3183. doi:10.1021/ic00188a030.
  4. ^ Sowerby, A.L.M., ed. (1961). Dictionary of Photography: A Reference Book for Amateur and Professional Photographers. London: Illife Books Ltd. pp. 324–326.
  5. ^ Karlheinz Keller et al. "Photography" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi: 10.1002/14356007.a20_001
  6. ^ Aylmore MG, Muir DM (2001). "Thiosulfate Leaching of Gold - a Review". Minerals Engineering. 14 (2): 135–174. doi:10.1016/s0892-6875(00)00172-2.
  7. ^ IUPAC Red Book p 329