Isolated heterometallic Cr7Ni rings grafted on Au(111) surface

A study of the deposition of heterometallic antiferromagnetically coupled rings onto gold surfaces is reported. Two new {Cr7Ni} rings, [NH2n Pr-2][Cr7NiF8(3-tpc)(16)] (1) (where 3-tpc = 3-thiophenecarboxylate) and [(BuNH2CH2CH2SH)-Bu-n] [Cr7NiF8((O2CBu)-Bu-t)(16)] (2) have been made and structurally characterized. They have been deposited from the liquid phase on Au(111) and the adsorbed molecules compared by means of scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS). In both cases a two-dimensional distribution of individually accessible {Cr7Ni} heterometallic rings on the gold surface has been obtained, exploiting the direct grafting of sulfur-functionalized clusters. There is a competition between the chemisorption of the {Cr7Ni} clusters and a thiolic self-assembled monolayer (SAM) formed by free ligands. In 2, the presence of a single sulfur ligand should force the molecule to graft with the ring axis normal to the surface. The cluster stability in the STM images and the S-2p energy positions demonstrate, for both functionalizations, the strength of the grafting with the gold surface.