Self-Assembled p-Carborane Analogue of p-Mercaptobenzoic Acid on Au{111}

Abstract

The p-carborane cluster analogue of p-mercaptobenzoic acid, 1-HS-12-COOH-1,12-C 2 B 10 H 10 , has been synthesized and characterized using nuclear magnetic resonance spectroscopy, single-crystal X-ray diffraction analysis, quantum-chemical calculations, and scanning tunneling microscopy. The single-crystal structure and selected packing aspects are discussed and presented in comparison with the two-dimensional periodic arrangements. Scanning tunneling micrographs, recorded under ambient conditions, are used to compare pure monolayers of 1-HS-1,12-C 2 B 10 H 11 to coadsorbed monolayers of both the parental precursor and carboxyl-functionalized pcarboranethiolate on Au{111}. Monolayers of both constituents are further characterized by X-ray photoelectron spectroscopy, which shows good agreement between the stoichiometry of each pure monolayer and the nominal stoichiometries of the respective molecules. Results indicate that most of the molecules of both derivatives adsorb as thiolates but that a small fraction of each adsorbs as thiols, without complete SH bond scission, and consequently are labile relative to desorption. Wetting-angle measurements confirm the hydrophilic character of monolayers containing the carboxylic acid constituents. Mixed self-assembled monolayers with functionalized constituents of high axial symmetry provide a convenient basis for grafting two-and three-dimensional structures.

Adsorption of oriented carborane dipoles on a silver surface

“…Quantification of these components is provided in the Supporting Information (Table S2). Species unbound to a silver surface, or bound very weakly (physically adsorbed), with the binding energy value of S 2p photoelectrons typical for a free thiol group (∼164.0 eV) , were not observed. The binding energy value of the main thiolate sulfur component in B ‐modified silver surface appears slightly lower compared to the respective component in A ‐modified silver surface, which can be rationalized by the electron donating and accepting effects of the caboranyl backbones in B and A , respectively (Fig.…”

A van der Waals density functional investigation of carboranethiol self-assembled monolayers on Au(111)

“…Hence, SAMs of CTs and their derivatives have attracted increasing interest in recent years. [47][48][49][50][51][52][53][54][55][56][57][58] Recently, Lübben and coworkers have demonstrated that by using pure and mixed SAMs of two carborane dithiol isomers [1,2-(HS 2 )-1,2-C 2 B 10 H 10 and 9,12-(HS 2 )-1,2-C 2 B 10 H 10 ] with opposite dipole moments, the surface potential of silver surfaces could be tuned. Weiss et al, on the other hand, used two CT isomers [1-HS-1,7-C 2 B 10 H 11 (M1) and 9-HS-1,7-C 2 B 10 H 11 (M9), see figure 1 for naming of CT isomers] and were able to tune the gold work function over a range of 0.8 eV by preparing mixed SAMs of these two isomers in different ratios.…”

Atomic Structure of Self-Assembled Monolayer of Thiolates on a Tetragonal Au92 Nanocrystal

“…[1][2][3][4] However, the atomic structures of SAMs, including the nature of Au-S bonds and their patterning modes, still remain elusive. 5 Surface characterization techniques in combination of theoretical calculation are the common approach to decipher the structural enigma of SAMs, and significant progress has been made in the past 30 years.…”

“…For example, the Au-S bond length is fixed at 2.35 ± 0.05 Å, and the Au-S-Au angle is 87 ± 5 o , as averaged from the 28 bridging thiolates in Au 92 (TBBT) 44 ( Figure S6). This 3 gives rise to the span of underneath Au-Au atoms of ~3.2 Å. Therefore, the underlying Au lattice in (100) SAMs is slightly reconstructed (Figure 2D), i.e., the Au-Au bonds beneath the sulfur bridges are stretched, while the adjacent Au-Au bonds become contracted.…”