Transformation of Au₁₄₄(SCH₂CH₂Ph)₆₀ to Au₁₃₃(SPh-tBu)₅₂ Nanomolecules: Theoretical and Experimental Study

Abstract

Ultrastable gold nanomolecule Au144(SCH2CH2Ph)60 upon etching with excess tert-butylbenzenethiol undergoes a core-size conversion and compositional change to form an entirely new core of Au133(SPh-tBu)52. This conversion was studied using high-resolution electrospray mass spectrometry which shows that the core size conversion is initiated after 22 ligand exchanges, suggesting a relatively high stability of the Au144(SCH2CH2Ph)38(SPh-tBu)22 intermediate. The Au144 → Au133 core size conversion is surprisingly different from the Au144 → Au99 core conversion reported in the case of thiophenol, -SPh. Theoretical analysis and ab initio molecular dynamics simulations show that rigid p-tBu groups play a crucial role by reducing the cluster structural freedom, and protecting the cluster from adsorption of exogenous and reactive species, thus rationalizing the kinetic factors that stabilize the Au133 core size. This 144-atom to 133-atom nanomolecule's compositional change is reflected in optical spectroscopy and electrochemistry.

Ligand Structure Determines Nanoparticles' Atomic Structure, Metal-Ligand Interface and Properties

“…Thiophenol is a classic example of aromatic thiol. TBBT thiol is found to have similar aromatic ligand effect with minimal variation of the end product except for instance reported case where, Au 133 (SR) 52 (Nimmala et al, 2015 ) is reported with TBBT, but not with thiophenol. This is expected as the surface availability of the nanomolecule decreases as the size increases steric effect by para -tert-butyl groups becomes significant compared to smaller core-size Au 36 (SR) 24 .…”

“…Thus, ligand effects are not necessarily due to only the ligands' bulkiness but also due to the aromaticity and electronic nature of the ligand structure. Experimentally, we have shown that in the presence of the aromatic TBBT ligand Au 144 (SCH 2 CH 2 Ph) 60 transforms to a new core-size to give Au 133 (SPh- t Bu) 52 (Nimmala et al, 2015 ). We hypothesize the effect of aromatic phenyl rings contribute a favorable inter-ligand interaction while para-tertiary groups create steric repulsion and kinetic effects and trigger the core-size conversion to Au 133 (SPh- t Bu) 52 .…”

Isolation and Total Structure Determination of an All‐Alkynyl‐Protected Gold Nanocluster Au144

“…[22,23] Formore than two decades, investigations were performed in the absence of precise structural information. It was reported that thiolate-protected Au 144 clusters show promising catalytic activities [24][25][26][27][28] and electrochemiluminescence, [29,30] and can be employed as precursors in the synthesis of Au 99 [31] and Au 133 [12,13,32] nanoclusters.M oreover,A u 144 has applications in organic solar cell [33] and floating memory devices, [34] etc.More importantly, it was also found that thiolate-protected Au 144 exhibits both molecular and bulklike behaviors,w ith its size in the critical transition range.F or example,A u 144 (SR) 60 exhibits ah ighly structured UV-vis-NIR spectrum with absorption bands over the entire region. [35,36] This spectrum indicates the molecular nature of Au 144 ,and was also supported by density functional theory (DFT) calculations.…”

Ab initio molecular dynamics studies of Au38(SR)24 isomers under heating

“…Here it is important to point out that the temperature of fragmentation that could be measured experimentally might significantly differ from the values reported here since all the stabilizations arising from the ligands (such as ligand-ligand interactions and steric effects) have been omitted for practical purposes. Moreover, and despite the large number of observations of core-size conversion of MPC upon ligand exchange under heating [14,[49][50][51], to the best of our knowledge there are not reports on the fragmentation of this type of systems caused solely by the effect of temperature. In addition, modeling the time scales involve in the fragmentation of MPC at room temperature is unfeasible by using ab initio calculations.…”