Alfredo Tlahuice-Flores

On the structure of the thiolated Au6Ag7 cluster

The structure of the Au15-thiolate cluster has been elucidated using a DFT approach, and it is demonstrated to comprise a Au4-tetrahedron core protected solely by the combination of two concatenated staple motifs. The longer motif efficiently wraps the core, and threads the shorter one. The structural assignment is supported by comparison to the powder X-ray diffraction pattern and, via time dependent-DFT calculations, to the optical and chiroptical (CD) absorption spectra. The calculated CD spectrum features a characteristic strong peak centered at 3.48 eV in accordance with the experimental profile. These results confirm the existence of long Au(I)-thiolate motifs as protecting units of small thiolated gold clusters with a thiolate-to-gold ratio comparable to the Au15(SR)13 cluster.

Structure of the thiolated Au130 cluster.

The structure of the recently discovered Au130-thiolate and -dithiolate clusters is explored in a combined experiment-theory approach. Rapid electron diffraction in scanning/transmission electron microscopy (STEM) enables atomic-resolution imaging of the gold core and the comparison with density functional theory (DFT)-optimized realistic structure models. The results are consistent with a 105-atom truncated-decahedral core protected by 25 short staple motifs, incorporating disulfide bridges linking the dithiolate ligands. The optimized structure also accounts, via time-dependent DFT (TD-DFT) simulation, for the distinctive optical absorption spectrum, and rationalizes the special stability underlying the selective formation of the Au130 cluster in high yield. The structure is distinct from, yet shares some features with, each of the known Au102 and Au144/Au146 systems.

Structure & bonding of the gold-subhalide cluster I-Au144Cl60[z].

The structure and bonding of the gold-subhalide compounds Au144Cl60([z]) are related to those of the ubiquitous thiolated gold clusters, or Faradaurates, by iso-electronic substitution of thiolate by chloride. Exact I-symmetry holds for the [z] = [2+,4+] charge-states, in accordance with new electrospray mass spectrometry measurements and the predicted electron shell filling. The high symmetry facilitates analysis of the global structure as well as the bonding network, with some striking results.

Normal modes of Au25(SCH3)18 −, Ag12Au13(SCH3)18 − and Ag25(SCH3)18 − clusters

This report contains a theoretical study on the atomic structure and normal modes of , and clusters based on density functional theory with generalised gradient approximations. It is shown that their calculated infrared (IR) spectra have features, which allow to distinguish them. Therefore, it was found that the Ag–S stretching and CH3 umbrella modes are intense in the IR spectrum of the cluster.

Ligand effects on the optical and chiroptical properties of the thiolated Au18 cluster

The effect of chiral and achiral ligands protecting the inner Au9 core of the Au18(SR)14 cluster is studied based on density functional theory (DFT) and its corrected long-range interaction (DFT-D) approach. It was found that the electronic properties (energy levels) depend on the specific ligands, which induce distinct distortions on the Au-S framework. However, the substitution of S-c-C6H11 as SCH3 ligands may be considered to be correct given the obtained resemblance to the displayed bonding, optical and chiroptical properties. A further comparison of the CD and UV spectra displayed by the Au18 cluster protected by chiral and achiral ligands attests that more intense profiles are featured by ligands including phenyl rings and/or oxygen atoms such that the Au18 cluster protected by either achiral meta-mercaptobenzoic acid (m-MBA) or achiral SPh ligands displays more intense UV and CD signals. These results provide new insight into the effect of ligands on thiolated gold clusters.