Disulfide- and thiol-incorporating copper catenanes: synthesis, deposition onto gold, and surface studies

Two new copper-complexed [2]catenanes have been prepared, both of which consist of two different interlocking rings. In both cases, one of the rings incorporates a disulfide bridge. The other ring contains either a single chelate (phen=1,10-phenanthroline, a bidentate ligand) or two different chelates (phen and terpy, 2,2',6',2"-terpyridine, a tridentate chelate). Deposition of these two complexes on a gold electrode surface was carried out by standard procedures, leading to reductive cleavage of the S-S bridge. The adsorbed species can be viewed as [2]catenanes for which the gold atoms of the electrode surface are an integral fragment of one of the two rings. They yield clear electrochemical responses, but no motion is observed for the catenane incorporating a phen unit and a terpy fragment in one of the two rings, regardless of the metal oxidation state. This is at odds with the behavior of the parent compound in solution, which undergoes ring-gliding motions upon electrochemical reduction or oxidation of the copper center. Near-field microscopy was used to study the deposited layers (STM and AFM). STM images suggest that the molecules do not tend to order at long range on the surface. Polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS) led to promising results: the two catenanes deposited are likely to be oriented perpendicular to the gold surface. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2002/f3636_s.pdf or from the author. 1: Infrared spectra of [Cu.2]+ as a powder (black line, transmission IR spectroscopy) and as a SAM on gold (dotted line, PM-IRRAS). (Spectra offset and scaled for clarity; significant peaks marked with an asterisk.) 2: STM image (819x819 nm2) of a monolayer of [Cu.3]+ on Au(111) on mica.