@article {166, title = {Nanomechanical Investigations of Crystals of Copper Nanocluster Isomorphs: Enhanced Hardness of the Low-Density Analogue}, journal = {Chemistry of Materials}, year = {2025}, month = {01/2025}, type = {Full article}, abstract = {

Atomically precise cluster crystals, with constituent units composed of tens to hundreds of atoms, are important for the construction of miniaturized solid-state devices. Understanding the mechanical characteristics of such crystals is crucial for these applications. In this study, we focused on the nanomechanical properties of crystals of two isomorphic copper nanoclusters (Cu4L4), protected by ortho-carborane-9-thiol, Cu4(oCBT)4, and meta-carborane-9-thiol, Cu4(mCBT)4. These two clusters possess identical square planar Cu4 cores embedded in butterfly-shaped Cu4S4 staples. Load{\textendash}displacement measurements indicated that the crystals of Cu4(oCBT)4 (hardness of \~{}534.31 MPa) were harder than those of Cu4(mCBT)4 (hardness of \~{}335.49 MPa). Despite their lower density, crystals of Cu4(oCBT)4 demonstrated increased hardness, owing to the presence of locked slanted layers that efficiently interacted with each other through various short contact supramolecular interactions. During indentation studies, multiple {\textquotedblleft}pop-in{\textquotedblright} events were observed for the crystals of both clusters, suggesting the dislocation of molecular layers within the crystal lattice. Dynamic mechanical analysis conducted at different loading frequencies indicated that crystals of Cu4(oCBT)4 have a higher storage modulus than Cu4(mCBT)4. Both the crystals are thermally robust, as evident from thermogravimetric analysis and attenuated total reflection-IR analysis. Using density functional theory, we calculated Young{\textquoteright}s modulus (Er) for both crystals at 1 and 2\% strain and found that the high-density isomorph had a lower Er, consistent with experimental data showing Er of Cu4(oCBT)4 and Cu4(mCBT)4 to be 9.79 and 8.54 GPa, respectively. These findings highlight the significant role of subtle structural differences in governing the nanomechanical behavior of isomorphic cluster crystals, paving the way for their rational design in advanced solid-state device applications.

}, keywords = {carborane, Copper, indentation, nanocluster, nanomechanical, thiol, Young{\textquoteright}s modulus}, doi = {https://doi.org/10.1021/acs.chemmater.4c03265}, url = {https://pubs.acs.org/doi/10.1021/acs.chemmater.4c03265}, author = {Amoghavarsha R Kini and Sanghamitra Debta and Arijit Jana and C Aparna and Vivek Yadav and Nataliia Kusiak and Tomas Base and Umesh V Waghmare and Pijush Ghosh and Thalappil Pradeep} } @article {167, title = {Site-specific substitution in atomically precise carboranethiol-protected nanoclusters and concomitant changes in electronic properties}, journal = {Nature Communications}, volume = {16}, year = {2025}, month = {01/2025}, type = {Full article}, chapter = {1197}, abstract = {

We report the synthesis of [Ag17(o1-CBT)12]3- abbreviated as Ag17, a stable 8e$^{-}$ anionic cluster with a unique Ag@Ag12@Ag4 core-shell structure, where o1-CBT is ortho-carborane-1-thiol. By substituting Ag atoms with Au and/or Cu at specific sites we created isostructural clusters [AuAg16(o1-CBT)12]3- (AuAg16), [Ag13Cu4(o1-CBT)12]3- (Ag13Cu4) and [AuAg12Cu4(o1-CBT)12]3- (AuAg12Cu4). These substitutions make systematic modulation of their structural and electronic properties. We show that Au preferentially occupies the core, while Cu localizes in the tetrahedral shell, influencing stability and structural diversity of the clusters. The band gap expands systematically (2.09\ eV for Ag17 to 2.28\ eV for AuAg12Cu4), altering optical absorption and emission. Ultrafast optical measurements reveal longer excited-state lifetimes for Cu-containing clusters, highlighting the effect of heteroatom incorporation. These results demonstrate a tunable platform for designing nanoclusters with tailored electronic properties, with implications for optoelectronics and catalysis.

}, keywords = {Alloy, boron, carborane, Cluster, Copper, gold, luminescence, Metal, silver, Structure, thiol}, doi = {https://doi.org/10.1038/s41467-025-56385-w}, url = {https://www.nature.com/articles/s41467-025-56385-w}, author = {Vivek Yadav and Arijit Jana and Swetashree Acharya and Sami Malola and Harshita Nagar and Ankit Sharma and Amoghavarsha Ramachandra Kini and Sudhadevi Antharjanam and Jan Machacek and Kumaran Nair Valsala Devi Adarsh and Tomas Base and Hannu H{\"a}kkinen and Thalappil Pradeep} } @article {155, title = {Influence of Terminal Carboxyl Group on Structure and Reactivity of Functionalized m-Carboranethiolate Self-Assembled Monolayers}, journal = {Chemistry of Materials}, volume = {32}, year = {2020}, month = {07/2020}, pages = {6800-6809}, type = {Article}, chapter = {6800}, abstract = {

The structure and function of self-assembled monolayers (SAMs) at the nanoscale are determined by the steric and electronic effects of their building blocks. Carboranethiol molecules form pristine monolayers that provide tunable two-dimensional systems to probe lateral and interfacial interactions. Additional ω-functionality, such as carboxyl groups, can be introduced to change the properties of the exposed surfaces. Here, two geometrically similar isomeric m-carborane analogs of m-mercaptobenzoic acid, 1 COOH-7-SH-1,7-C2B10H10 and racem-1-COOH-9-SH-1,7-C2B10H10, are characterized and their SAMs on Au{111} are examined. The latter isomer belongs to the rare group of chiral cage molecules and becomes, to our knowledge, the first example assembled on Au{111}. Although different in symmetry, molecules of both isomers assemble into similar hexagonal surface patterns. The nearest neighbor spacing of 8.4 {\textpm} 0.4 {\r A} is larger than that of non-carboxylated isomers, consistent with the increased steric demands of the carboxyl groups. Computational modeling reproduced this spacing and suggests a tilt relative to the surface normal. However, tilt domains are not observed experimentally, suggesting the presence of strong lateral interactions. Analyses of the influence of the functional groups through the pseudo-aromatic m carborane skeleton showed that the thiol group attached to either carbon or boron atoms increases the carboxyl group acidity in solution. In contrast, the acidity of the exposed carboxyl group in the SAMs decreases upon surface attachment; computational analyses suggest that the driving force of this shift is the dielectric of the environment in the monolayer as a result of confined intermolecular interactions, proximity to the Au surface, and partial desolvation.

}, keywords = {acidity, carborane, carboxyl, monolayer, SAM, self-assembly}, doi = {https://doi.org/10.1021/acs.chemmater.0c02722}, url = {https://pubs.acs.org/doi/10.1021/acs.chemmater.0c02722}, author = {Dominic P Goronzy and Jan Stanek and Erin Avery and Han Guo and Zdenek Bastl and Michal Dusek and Nathan M Gallup and Saliha Gun and Monika Kucerakova and Brian J Levandowski and Jan Machacek and Vaclav Sicha and John C Thomas and Adem Yavuz and K N Houk and M Fatih Danisman and Ersen Mete and Anastassia N Alexandrova and Tomas Base and Paul S Weiss} } @article {152, title = {Formation of Highly Ordered Terminal Alkyne Self-Assembled Monolayers on the Au{111} Surface through Substitution of 1-Decaboranethiolate}, journal = {J. Phys. Chem. C}, volume = {123}, year = {2019}, pages = {1348{\textendash}1353}, abstract = {

The reaction aimed at completing and closing the open cages of 1-decaboranethiol self-assembled monolayers (SAMs) on Au{111} with 4-phenyl-1-butyne results in highly ordered monolayers of 4-phenyl-1-butyne. The initially disordered 1-decaboranethiolate changed into ordered (√3{\texttimes}√3)R 30{\textdegree} lattices on Au{111} typical of alkyne SAMs, indicating the complete substitution of 1-decaboranethiolate moieties, as determined by nanoscale imaging with scanning tunneling microscopy and X-ray photoelectron spectroscopy. Vibrational spectroscopy results indicate that the process happens gradually and that alkynyl groups are not totally oxidized in the ordered 4-phenyl-1-butyne monolayer.

}, keywords = {alkyne, decaborane, gold, self-assembly, surface, thiol}, doi = {10.1021/acs.jpcc.8b11033}, url = {https://pubs.acs.org/doi/10.1021/acs.jpcc.8b11033}, author = {Shenkai Wang and Dominic P Goronzy and Thomas D Young and Natcha Wattanatorn and Logan Stewart and Tomas Base and Paul S Weiss} }