Site-specific Anchoring of Tetrairon(III) Single Molecule Magnets on Functionalized Si(100) Surfaces

The site-specific reaction of tetrairon(III) propeller-like clusters with tripodal ligands derived from 2-hydroxymethyl-propane-1,3-diol was investigated as a route to graft these single molecule magnets (SMMs) on Si(100). A silicon surface prefunctionalized with a long-chain trimethylol derivative was reacted with [Fe4(OMe)6(tmhd)6] (1) and [Fe4(L)2(tmhd)6] (2), and the reaction course was followed by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-infrared spectroscopy, and atomic force microscopy (Htmhd = 2,2,6,6-tetramethylheptane-3,5-dione, H3L = 2-(4-chloro-phenyl)-2-hydroxymethyl-propane-1,3-diol). Chlorine-marked complex 2 was specifically designed to monitor the ligand-exchange reaction by XPS. This technique showed that the amount of Fe at the surface closely parallels the surface concentration of tripodal receptors. For low receptor concentrations the Cl/Fe atomicratio is halved as compared with solid 2, as expected for intact molecules linked to the surface via one receptor only. For high receptor concentrations, the Cl/Fe ratio drops to zero, as expected for a complete replacement of L3- ligands by surface-bound receptors.