TY - JOUR T1 - Competing Intermolecular and Molecule–Surface Interactions: Dipole–Dipole-Driven Patterns in Mixed Carborane Self-Assembled Monolayers JF - Chemistry of Materials Y1 - 2024 A1 - Katherine E. White A1 - Erin M. Avery A1 - Edison Cummings A1 - Zixiang Hong A1 - Jens Langecker A1 - Aliaksei Vetushka A1 - Michal Dusek A1 - Jan Machacek A1 - Jakub Višnák A1 - Jan Endres A1 - Zdenek Bastl A1 - Ersen Mete A1 - Anastassia N. Alexandrova A1 - Tomas Base A1 - Paul S. Weiss KW - 2D assembly KW - boron KW - carborane KW - Cluster Molecules KW - Dipole-dipole KW - Molecular interactions KW - Molecular structure KW - scanning tunneling microscopy KW - Supramolecular chemistry AB -

Carboranedithiol isomers adsorbing with opposite orientations of their dipoles on surfaces are self-assembled together to form mixed monolayers where both lateral dipole–dipole and lateral thiol–thiolate (S–H···S) interactions provide enhanced stability over single-component monolayers. We demonstrate the first instance of the ability to map individual isomers in a mixed monolayer using the model system carboranedithiols on Au{111}. The addition of methyl groups to one isomer provides both an enhanced dipole moment and extra apparent height for differentiation via scanning tunneling microscopy (STM). Associated computational investigations rationalize favorable interactions of mixed pairs and the associated stability changes that arise from these interactions. Both STM images and Monte Carlo simulations yield similarly structured mixed monolayers, where approximately 10% of the molecules have reversed dipole moment orientations but no direct chemical attachment to the surface, leading to homogeneous monolayers with no apparent phase separation. Deprotonating the thiols by depositing the molecules under basic conditions eliminates the lateral S–H···S interactions while accentuating the dipole–dipole forces. The molecular system investigated is composed of isomeric molecules with opposite orientations of dipoles and identical surface packing, which enables the mapping of individual molecules within the mixed monolayers and enables analyses of the contributions of the relatively weak lateral interactions to the overall stability of the assemblies.

VL - 36 UR - https://pubs.acs.org/doi/10.1021/acs.chemmater.3c03210 ER - TY - JOUR T1 - Thermal isomerizations of monothiolated carboranes (HS)C2B10H11 and the solid-state investigation of 9-(HS)-1,2-C2B10H11 and 9-(HS)-1,7-C2B10H11 JF - Journal of Organometallic Chemistry Y1 - 2015 A1 - Tomas Base A1 - Jan Machacek A1 - Zuzana Hajkova A1 - Jens Langecker A1 - John D Kennedy A1 - Michael J Carr KW - carborane KW - Carboranethiol KW - closo-dicarbadodecaborane thiol KW - closo-dicarbadodecaboranes KW - Cluster KW - Dipole KW - Isomer KW - Isomerisation KW - Thermal Stability AB -

At 300-500 C, three C-thiolated closo-dicarbadodecaborane isomers 1-(HS)-1,2-C2B10H11 (1-o), 1-(HS)-1,7-C2B10H11 (1-m), and 1-(HS)-1,12-C2B10H11 (1-p), and two B-thiolated isomers 9-(HS)-1,7-C2B10H11 (9-m) and 9-(HS)-1,2-C2B10H11 (9-o) show two types of reaction: first, removal of an SH group from the closo-dicarbadodecaborane skeleton, and second, skeletal isomerizations from ortho to meta to para that lead to new isomers. A previously unreported SH skip from carbon-to-boron is also observed. The effect of the thiol group on the skeletal rearrangement is discussed. The isomerisation products are assigned on the basis of correlation of their computationally obtained dipole moments with their gas-chromatographic retention times. Computational results on molecular energies for the mono-thiolated species show good agreement between the calculated relative stabilities and the incidence and relative quantities of the isomerization products. Two of the starting B-thiolated isomers, 9-o and 9-m, were characterized using single-crystal X-ray diffraction analyses and their crystallographic packings as well as some selected structural parameters are discussed. All starting compounds were characterized using multinuclear NMR spectroscopy.

UR - http://www.sciencedirect.com/science/article/pii/S0022328X15300462 ER - TY - JOUR T1 - Carbon-substituted 9,12-dimercapto-1,2-dicarba-closo-dodecaboranes via a 9,12-bis(methoxy-methylthio)-1,2-dicarba-closo-dodecaborane precursor JF - Polyhedron Y1 - 2012 A1 - Jens Langecker A1 - Karla Fejfarova A1 - Michal Dusek A1 - Daniel Rentsch A1 - Tomas Base VL - 45 UR - http://www.sciencedirect.com/science/article/pii/S0277538712005207 ER - TY - JOUR T1 - Carboranedithiols: Building Blocks for Self-Assembled Monolayers on Copper Surfaces JF - Langmuir Y1 - 2012 A1 - Tomas Base A1 - Zdenek Bastl A1 - Vladimir Havranek A1 - Jan Machacek A1 - Jens Langecker A1 - Vaclav Malina AB -

Two different positional isomers of 1,2-dicarbacloso-dodecaboranedithiols, 1,2-(HS)2-1,2-C2B10H10 (1) and 9,12-(HS)2-1,2-C2B10H10 (2), have been investigated as cluster building blocks for self-assembled monolayers (SAMs) on copper surfaces. These two isomers represent a convenient system in which the attachment of SH groups at different positions on the skeleton affects their acidic character and thus also determines their reactivity with a copper surface. Isomer 1 exhibited etching of polycrystalline Cu films, and a detailed investigation of the experimental conditions showed that both the acidic character of SH groups and the presence of oxygen at the copper surface play crucial roles in how the surface reaction proceeds: whether toward a self-assembled monolayer or toward copper film etching. We found that each positional isomer requires completely different conditions for the preparation of a SAM on copper surfaces. Optimized conditions for the former isomer required the exposure of a freshly prepared Cu surface to vapor of 1 in vacuum, which avoided the presence of oxygen and moisture. Adsorption from a dichloromethane solution afforded a sparsely covered Cu(0) surface; isomer 1 effectively removes the surface copper(I) oxide, forming a soluble product, but apparently binds only weakly to the clean Cu(0) surface. In contrast, adsorption of the latter, less volatile isomer proceeded better from a dichloromethane solution than from the vapor phase. Isomer 2 was even able to densely cover the copper surface cleaned up by the dichloromethane solution of 1. Both isomers exhibited high capacity to remove oxygen atoms from the surface copper(I) oxide that forms immediately after the exposure of freshly prepared copper films to ambient atmosphere. Isomer 2 showed suppression of Cu film oxidation. A number of methods including X-ray photoelectron spectroscopy (XPS), X-ray Rutherford back scattering (RBS), proton-induced X-ray emission (PIXE) analysis, atomic force microscopy (AFM), cyclic voltammetry, and contact angle measurements were used to investigate the experimental conditions for the preparation of SAMs of both positional isomers on copper surfaces and to shed light on the interaction between these molecules and a polycrystalline copper surface.

VL - 28 UR - http://pubs.acs.org/doi/abs/10.1021%2Fla302334x ER -