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1. Crystal structure of bulky-ligand-protected Au24(S-C4H9)16

   K. H. Wijesinghe, A. G. ( September 2022 , Acta crystallographica Section C Structural chemistry)

   Atomically precise thiol­ate-protected gold nanomolecules have attracted inter­est due to their distinct electronic and chemical properties. The structure of these nanomolecules is important for understanding their peculiar properties. Here, we report the X-ray crystal structure of a 24-atom gold nanomolecule protected by 16 tert-butylthiolate ligands. The com­position of Au24(S-C4H9)16 {poly[hexa­deca­kis­(μ-tert-butyl­thiol­ato)tetra­cosa­gold]} was confirmed by X-ray crystallography and electrospray ionization mass spectrometry (ESI–MS). The nanomolecule was synthesized in a one-phase synthesis and crystallized from a hexa­ne–ethanol layered solution. The X-ray structure confirms the 16-atom core protected by two monomeric and two trimeric staples with four bridging ligands. The Au24(S-C4H9)16 cluster follows the shell-closing magic number of 8. 

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2. Ion mobility–tandem mass spectrometry of bulky tert ‐butyl thiol ligated gold nanoparticles

   https://doi.org/10.1002/jms.4998  

   Wijesinghe, Kalpani H. ; Hood, Christopher ; Mattern, Daniell ; Angel, Laurence A. ; Dass, Amala ( February 2024 , Journal of Mass Spectrometry)

   Gold nanoparticles (AuNPs) synthesized in the 1–3 nm range have a specific number of gold core atoms and outer protecting ligands. They have become one of the “hot topics” in recent decades because of their interesting physical and chemical properties. The characterization of their structures is usually achieved by crystal X‐ray diffraction although the structures of some AuNPs remain unknown because they have not been successfully crystallized. An alternative method for studying the structure of AuNPs is electrospray ionization–ion mobility–tandem mass spectrometry (ESI‐IM‐MSMS). This research evaluated how effectively ESI‐IM‐MSMS using the commercially available Waters Synapt XS instrument yielded useful structural information from two AuNPs; Au₂₃(S‐tBu)₁₆and Au₃₀(S‐tBu)₁₈. The study used the maximum range of available collision energies along with ion mobility separation to measure the energy‐dependence of the product ions and their drift times which is a measure of their spatial size. For Au₂₃(S‐tBu)₁₆, the dissociation gave the masses of the outer protecting monomeric [RS–Au–SR] and trimeric [SR–Au–SR–Au–SR–Au–SR] staples where R = tBu, and complete dissociation of the outer layer Au andtBu groups to reveal the Au₁₅S₈core. For Au₃₀(S‐tBu)₁₈, the dissociation products was primarily through the loss of the partial ligands S‐tBu andtBu from the outer protecting layer and the loss of single Au₄(S‐tBu)₄unit. These results showed the that ESI‐IM‐MSMS analysis of the smaller Au₂₃(S‐tBu)₁₆gave information on all it major structural components whereas for Au₃₀(S‐tBu)₁₈, the overall structural information was limited to the ligands of the outer layer.

    

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3. Ligand exchange on Au 38 (SR) 24 : substituent site effects of aromatic thiols

   https://doi.org/10.1039/d0nr01430c  

   Li, Yingwei ; Juarez-Mosqueda, Rosalba ; Song, Yongbo ; Zhang, Yuzhuo ; Chai, Jinsong ; Mpourmpakis, Giannis ; Jin, Rongchao ( May 2020 , Nanoscale)

   Understanding the critical roles of ligands ( e.g. thiolates, SR) in the formation of metal nanoclusters of specific sizes has long been an intriguing task since the report of ligand exchange-induced transformation of Au 38 (SR) 24 into Au 36 (SR′) 24 . Herein, we conduct a systematic study of ligand exchange on Au 38 (SC 2 H 4 Ph) 24 with 21 incoming thiols and reveal that the size/structure preference is dependent on the substituent site. Specifically, ortho -substituted benzenethiols preserve the structure of Au 38 (SR) 24 , while para - or non-substituted benzenethiols cause its transformation into Au 36 (SR) 24 . Strong electron-donating or -withdrawing groups do not make a difference, but they will inhibit full ligand exchange. Moreover, the crystal structure of Au 38 (SR) 24 (SR = 2,4-dimethylbenzenethiolate) exhibits distinctive π⋯π stacking and “anagostic” interactions (indicated by substantially short Au⋯H distances). Theoretical calculations reveal the increased energies of frontier orbitals for aromatic ligand-protected Au 38 , indicating decreased electronic stability. However, this adverse effect could be compensated for by the Au⋯H–C interactions, which improve the geometric stability when ortho -substituted benzenethiols are used. Overall, this work reveals the substituent site effects based on the Au 38 model, and highlights the long-neglected “anagostic” interactions on the surface of Au-SR NCs which improve the structural stability. 

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4. Controlling magnetism of Au 133 (TBBT) 52 nanoclusters at single electron level and implication for nonmetal to metal transition

   https://doi.org/10.1039/c9sc02736j  

   Zeng, Chenjie ; Weitz, Andrew ; Withers, Gayathri ; Higaki, Tatsuya ; Zhao, Shuo ; Chen, Yuxiang ; Gil, Roberto R. ; Hendrich, Michael ; Jin, Rongchao ( October 2019 , Chemical Science)

   The transition from the discrete, excitonic state to the continuous, metallic state in thiolate-protected gold nanoclusters is of fundamental interest and has attracted significant efforts in recent research. Compared with optical and electronic transition behavior, the transition in magnetism from the atomic gold paramagnetism (Au 6s 1 ) to the band behavior is less studied. In this work, the magnetic properties of 1.7 nm [Au 133 (TBBT) 52 ] 0 nanoclusters (where TBBT = 4- tert -butylbenzenethiolate) with 81 nominal “valence electrons” are investigated by electron paramagnetic resonance (EPR) spectroscopy. Quantitative EPR analysis shows that each cluster possesses one unpaired electron (spin), indicating that the electrons fill into discrete orbitals instead of a continuous band, for that one electron in the band would give a much smaller magnetic moment. Therefore, [Au 133 (TBBT) 52 ] 0 possesses a nonmetallic electronic structure. Furthermore, we demonstrate that the unpaired spin can be removed by oxidizing [Au 133 (TBBT) 52 ] 0 to [Au 133 (TBBT) 52 ] + and the nanocluster transforms from paramagnetism to diamagnetism accordingly. The UV-vis absorption spectra remain the same in the process of single-electron loss or addition. Nuclear magnetic resonance (NMR) is applied to probe the charge and magnetic states of Au 133 (TBBT) 52 , and the chemical shifts of 52 surface TBBT ligands are found to be affected by the spin in the gold core. The NMR spectrum of Au 133 (TBBT) 52 shows a 13-fold splitting with 4-fold degeneracy of 52 TBBT ligands, which are correlated to the quasi- D 2 symmetry of the ligand shell. Overall, this work provides important insights into the electronic structure of Au 133 (TBBT) 52 by combining EPR, optical and NMR studies, which will pave the way for further understanding of the transition behavior in metal nanoclusters. 

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5. Seeing luminescence appear as crystals crumble. Isolation and subsequent self-association of individual [(C 6 H 11 NC) 2 Au] + ions in crystals

   https://doi.org/10.1039/d0sc03299a  

   Luong, Lucy M. ; Lowe, Christopher D. ; Adams, Alexandria V. ; Moshayedi, Venoos ; Olmstead, Marilyn M. ; Balch, Alan L. ( November 2020 , Chemical Science)

   null (Ed.)

   Non-luminescent, isostructural crystals of [(C 6 H 11 NC) 2 Au](EF 6 )·C 6 H 6 (E = As, Sb) lose benzene upon standing in air to produce green luminescent (E = As) or blue luminescent (E = Sb) powders. Previous studies have shown that the two-coordinate cation, [(C 6 H 11 NC) 2 Au] + , self-associates to form luminescent crystals that contain linear or nearly linear chains of cations and display unusual polymorphic, vapochromic, and/or thermochromic properties. Here, we report the formation of non-luminescent crystalline salts in which individual [(C 6 H 11 NC) 2 Au] + ions are isolated from one another. In [(C 6 H 11 NC) 2 Au](BArF 24 ) ((BArF 24 ) − is tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) each cation is surrounded by two anions that prohibit any close approach of the gold ions. Crystallization of [(C 6 H 11 NC) 2 Au](EF 6 ) (E = As or Sb, but not P) from benzene solution produces colorless, non-emissive crystals of the solvates [(C 6 H 11 NC) 2 Au](EF 6 )·C 6 H 6 . These two solvates are isostructural and contain columns in which cations and benzene molecules alternate. With the benzene molecules separating the cations, the shortest distances between gold ions are 6.936(2) Å for E = As and 6.9717(19) Å for E = Sb. Upon removal from the mother liquor, these crystals crack due to the loss of benzene from the crystal and form luminescent powders. Crystals of [(C 6 H 11 NC) 2 Au](SbF 6 )·C 6 H 6 that powder out form a pale yellow powder with a blue luminescence with emission spectra and powder X-ray diffraction data that show that the previously characterized [(C 6 H 11 NC) 2 Au](SbF 6 ) is formed. In the process, the distances between the gold( i ) ions decrease to ∼3 Å and half of the cyclohexyl groups move from an axial orientation to an equatorial one. Remarkably, when crystals of [(C 6 H 11 NC) 2 Au](AsF 6 )·C 6 H 6 stand in air, they lose benzene and are converted into the yellow, green-luminescent polymorph of [(C 6 H 11 NC) 2 Au](AsF 6 ) rather than the colorless, blue-luminescent polymorph. Paradoxically, the yellow, green-luminescent powder that forms as well as authentic crystals of the yellow, green-luminescent polymorph of [(C 6 H 11 NC) 2 Au](AsF 6 ) are sensitive to benzene vapor and are converted by exposure to benzene vapor into the colorless, blue-luminescent polymorph. 

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