Comparison of H3PW12O40 and H4SiW12O40 heteropolyacids supported on silica by 1H MAS NMR

International audienc

Aromatic interactions in hydrotris(indazolyl)borate organometallic complexes: control of an alkyne ligand orientation in the crystal

International audienc

Functionalization of polyoxometalates: from Lindqvist to Keggin derivatives. 2. Investigation of the reactivity of arylamines, organo-hydrazines and tolylisocyanate towards [PW12-xMxO40]n- Keggin anions

International audienc

Self-Assembly of 1,4-Benzenedimethanethiol Self-Assembled Monolayers on Gold

A study of the self-assembly of 1,4-benzenedimethanethiol (BDMT; HS-CH2-(C6H4)-CH2-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 \u201cstanding-up\u201d molecules, can be obtained on high quality gold films with incubation in n-hexane provided thatN2-degassed solutions are used and all preparation steps are performed at 60\ub0C 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.Apossible mechanism for the formation of the \u201cstanding-up\u201d phase from the lying-down phase via a hydrogen exchange reaction involving chemisorbed lying-down and free dithiol molecules is discussed

UPS, XPS, and NEXAFS Study of Self-Assembly of Standing 1,4 Benzenedimethanethiol SAMs on Gold

We report a study of the self-assembly of 1,4-benzenedimethanethiol monolayers on gold formed in n-hexane solution held at 60 °C for 30 min and in dark conditions. The valence band characteristics, the thickness of the layer, and the orientation of the molecules were analyzed at a synchrotron using high resolution photoelectron spectroscopy and near edge X-ray adsorption spectroscopy. These measurements unambiguously attest the formation of a single layer with molecules arranged in the upright position and presenting a free SH group at the outer interface. Near edge X-ray absorption fine structure (NEXAFS) measurements suggest that the molecular axis is oriented at 24° with respect to the surface normal. In addition, valence band features could be successfully associated to specific molecular orbital contributions thanks to the comparison with theoretically calculated density of states projected on the different molecular units

On the self assembly of short chain alkanedithiols

A study of the self-assembly of nonane-alkanedithiol monolayers on gold in n-hexane and ethanol solvents is presented. Self-assembled monolayers (SAMs) are characterised by reflection\u2013absorption infrared spectroscopy (RAIRS), sum frequency generation (SFG) and spectroscopic ellipsometry (SE) measurements. Data obtained for alkanethiols SAMs are also shown for comparison. The measurements show that nicely organized HSC9SH SAMs can be obtained in n-hexane provided that N2-degassed solutions are used and all preparation steps are performed in the absence of ambient light. SFG measurements show that these SAMs have free standing SH groups. Use of an un-degassed and/or light-exposed n-hexane solutions leads to a worse layer organization. Preparation in ethanol, even in degassed solutions with processing in the dark, leads to poorly organized layers and no sign of free \u2013SH groups was observed

Surface Organometallic Chemistry of Titanium: Synthesis, Characterization, and Reactivity of (Si-O)nTi(CH2C(CH3)3)4-n (n =1, 2) Grafted on Aerosil Silica and MCM-41

International audienceThe reaction of tetrakisneopentyl titanium, TiNp4 (1), with the surface of partially dehydroxylated Aerosil silica and MCM-41 and the reactivity of the resultant supported titanium alkyl product with water, alcohols, and oxygen are reported. Two methods of preparation have been investigated and compared for the grafting of TiNp4: (i) reaction of the support with the vapor of the sublimed complex and (ii) impregnation of the support with a solution of the complex. The second method appeared to be more reliable for “larger scale” preparations. The surface species thus obtained were characterized by infrared spectroscopy, solid state NMR, XAFS, elemental analysis, and various test reactions. Whereas on an Aerosil silica partially dehydroxylated at 500 °C, SiO2-(500), the surface complex is a monopodal titanium trisalkyl complex, SiO−Ti[CH2C(CH3)3]3, 2a, a bipodal titanium bisalkyl complex, (SiO)2Ti[CH2C(CH3)3]2, 2b, is obtained as the major species (ca. 65%) with 2a on MCM-41(500). The reason for this difference in behavior is discussed on the basis of the surface structure. The results obtained from hydrolysis confirmed the structure proposed for the supported alkyl complexes. For the reaction of the alkyl surface complexes with alcohols (MeOH, EtOH, tBuOH), the surface compounds obtained were characterized by the same techniques and by XPS and UV−vis. The results are consistent with the formation of monosiloxytrisalkoxy titanium complexes on SiO2-(500), SiO−Ti(OR)3, 3aOR, and of SiO−Ti(OtBu)3, 3aOtBu, and (SiO)2Ti(OtBu)2, 3bOtBu, on MCM-41(500), after reaction with tBuOH. The supported titanium alkyl, 2a, also reacts with oxygen, leading mainly to SiO−Ti[OCH2C(CH3)3]3, probably via an unstable surface compound such as SiO−Ti[OCH2C(CH3)3]2[OOCH2C(CH3)3], resulting from the incorporation of two molecules of oxygen in 2a