Gold-xanthate monolayers

Organosulfur Adsorbates on Metal and Semiconductor Surfaces. Sulfur compounds (qv) and selenium compounds (qv) have a strong affinity for transition metal surfaces (206—211). The number of reported surface-active organosulfur compounds that form monolayers on gold includes di- -alkyl sulfide (212,213), di- -alkyl disulfides (108), thiophenols (214,215), mercaptopyridines (216), mercaptoanilines (217), thiophenes (217), cysteines (218,219), xanthates (220), thiocarbaminates (220), thiocarbamates (221), thioureas (222), mercaptoimidazoles (223—225), and alkaneselenoles (226) (Fig. 11). However, the most studied, and probably most understood, SAM is that of alkanethiolates on Au(lll) surfaces. 

Fig. 11. Surface-active organosulfur compounds that form monolayers on gold (a) alkanethiol (b) dialkyl disulfide (c) dialkyl sulfide (d) alkyl xanthate ...

Other sulphur(II) compounds also form self-assembled layers on gold and silver surfaces. Alkyl xanthate ions ROCS2 are coordinated to the surface through both S atoms and therefore have good stability. FT-IR analysis revealed that alkane chains in these monolayers are well-packed and ordered. Alkyl xanthates and dithiocarbamates were also reported to form monolayers on the surface of Ag coUoids . Thioalkanoic acids RCOSH form well-packed monolayers on both Au(lll) and Ag(lll) surfaces. However, these monolayers exhibit only short-term stability due to hydrolysis of the thiocarboxyl group. ... 

Figure 16. Suggested coordination and orientation of octyl xanthate on gold at full monolayer coverage. The alkyl chain is tilted 29° away from the surface normal and rotated 40° out of th plane of the paper around the axis of the chain. (From Ihs et al.)...

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