Chemical Overview

 Gold Thiolate Chemistry

Monovalent gold is highly 'thiophilic' and unsurprisingly complexes containing sulfur play an important role in many applications of gold compounds (Self Assembly Monolayers, drugs for arthritis therapy). For this reason there is always an incentive to encourage research into ligands for gold that contain this element and its heavier congeners.





The ligand 2,5-dimercapto-1,3,4-thiadiazole (also known as Bismuthiol I; see below) has been employed, as the trivial name suggests, in the complexation of metals and was once the reagent of choice for the analytical determination of bismuth ions. The presence of three sulfur binding sites and two more at nitrogen presents the possibility of a diverse and fascinating chemistry as the tendency of gold to form compounds with sulfur and nitrogen donors is well documented. The phenomenon of sub-van der Waals gold-gold distances in gold(I) complexes (2.7-3.7Å) has been investigated heavily and is especially remarkable as the gold centres are formally closed shell systems. Recent reports suggest that 'soft' donors (e.g. iodide or thiolate ligands) bound to the gold centre result in shorter Au-Au distances than 'harder' donors such as chloride or oxygen donors. The complex [(Me3PAu)2(SSS)] (shown on the right) was formed through reaction of bismuthiol I with chlorogoldtrimethylphosphine in the presence of base. The structure reveals that the gold centres are coordinated solely to the outer sulfur donors and that short 'aurophilic' interactions (3.0Å) are present leading to an extended supramolecular structure.

Bismuthiol I

The discovery and theoretical study of gold-gold contacts has produced considerable interest in their effect on the electronic and optical properties (luminescence) of gold complexes with a view to applications such as luminescent tagging and optical devices. The quest to understand the nature of such intermolecular interactions in gold complexes is therefore of considerable importance.

The complex shown in the bottom right [(dpph)Au2(2SSS)] was formed using a chelating bisphosphine (dpph = 1,6-bis(diphenylphosphino)hexane) resulting in a flexible 16-membered ring system. This compound also displays short intermolecular gold-gold contacts despite the steric bulk of the phosphine ligands. Interestingly, ring formation is favoured over a possible polymeric product.


An extention of this work was the investigation of phosphine-free bismuthiolate complexes such as [(tBuNCAu)2(SSS)] which shows a highly complex supramolecular structure in the solid state shown schematically below.

On gentle heating both in solution and in the solid state, this network breaks down through loss of the (relatively volatile) isocyanide ligand to give polymeric material. Heating more vigorously results in an even deposition of gold metal on the surface of the vessel. This represents a controllable, stepwise conversion from gold complex to elemental gold through a polymeric intermediate.


Further details of this work can be found in the following articles:

J. D. E. T. Wilton-Ely, A. Schier, N. W. Mitzel and H. Schmidbaur. Diversity in the structural chemistry of (phosphine)gold(I)-1,3,4-thiadiazole-2,5-dithiolates ("Bismuthiolates I"). Inorg. Chem., 2001, 41, 6266.

J. D. E. T. Wilton-Ely, A. Schier and H. Schmidbaur. The close-knit supramolecular network of [bis(tert-butylisocyanide)gold(I)]1,3,4-thiadiazole-2,5-disulfide. Organometallics, 2001, 20, 1895.

J. D. E. T. Wilton-Ely, S. Hofreiter, N. W. Mitzel and H. Schmidbaur. Thiolate Complexes of Gold(I) Based on a Tris(phosphine) Support. Z. Naturforsch., 2001, 56b, 1257.