A study of the self-assembly of 1,4-benzenedimethanethiol (BDMT; HS-CH(2)-(C(6)H(4))-CH(2)-SH) monolayers on gold is presented. Self-assembled monolayers (SAMs) are characterized by reflection-absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE) measurements. The ensemble of measurements consistently shows that well-organized BDMT SAMs, with "standing-up" molecules, can be obtained on high quality gold films with incubation in n-hexane provided that N(2)-degassed solutions are used and all preparation steps are performed at 60 degrees C in the absence of ambient light. SE data indicate that the optical interface properties of the BDMT-Au system are different from those of simple alkanethiol SAMs. A possible mechanism for the formation of the "standing-up" phase from the lying-down phase via a hydrogen exchange reaction involving chemisorbed lying-down and free dithiol molecules is discussed.

The Ta(dCHtBu)(CH 2 tBu) 3 complex 1 reacts with the OH groups of a MCM-41 mesoporous silica dehydroxylated at 500 °C to form the monosiloxy surface species [(tSiO)Ta(dCHtBu)(CH 2 tBu) 2 ] 2, with evolution of 1 equiv per Ta of neopentane. Complex 2 leads to a mixture of supported tantalum hydrides [(tSiO) 2 Ta(H) x ] (x ) 1, 3), 3, by treatment under hydrogen at 150 °C. These surface complexes were characterized by the combined use of several techniques such as IR and EXAFS spectroscopies as well as 1 H MAS, 13 C CP/MAS, 2D 1 H-13 C HETCOR, and J-resolved solid-state NMR and mass balance analysis. The surface tantalum hydrides evolve reversibly to the monohydride species (tSiO) 2 Ta-H by heating at 150 °C under vacuum; they lead progressively to the complete formation of the supported trisiloxy tantalum complex (tSiO) 3 Ta by heating under hydrogen (600 Torr) up to 500 °C. They can activate at 150 °C the C-H bond of CH 4 to form first the surface tantalum methyl species [(tSiO) 2 Ta-(CH 3 ) x ] with liberation of H 2 . The initially rapid decrease of the ν(Ta-H) bands followed by a slower rate indicates the presence of a distribution of Ta-H sites of various reactivity. The combined use of 13 C CP/MAS solid-state NMR and 100% 13 C-labeled methane affords the observation of methylidene and methylidyne species on a few tantalum sites, which indicates the occurrence of an R-H elimination process. In parallel, a progressive transfer of methyl groups from tantalum to neighboring siloxane bridges was also evidenced, which grows with temperature; this process is reasonably accompanied by the formation of the trisiloxy tantalum complex (tSiO) 3 Ta.

A comparative study on the adsorption of buthanedithiol (BDT), hexanedithiol (HDT), and nonanedithiol (NDT) on Au(111) from ethanolic and n-hexane solutions and two different preparation procedures is presented. SAM characterization is based on reflection-absorption infrared spectroscopy, electrochemistry, X-ray photoelectron spectroscopy, and time of flight direct recoil spectroscopy. Results indicate that one can obtain a standing-up phase of dithiols and that the amount of the precursor lying-down phase decreases from BDT to NDT, irrespective of the solvent and self-assembly conditions. A good ordering of the hydrocarbon chains in the standing-up configuration is observed for HDT and NDT when the system is prepared in degassed n-hexane with all operations carried out in the dark. Disulfide bridges at the free SH terminal groups are formed for HDT and to a lesser extent for NDT prepared in ethanol in the presence of oxygen, but we found no evidence of ordered multilayer formation in our experiments. No disulfides were observed for BDT that only forms the lying-down phase. Our results demonstrate the key role of the chain length and the procedure (solvent nature and oxygen presence) in controlling the surface structure and chemistry of SAMs dithiols on Au(111).