Vibrational Perturbations and Ligand–Layer Coupling in a Single Crystal of Au₁₄₄(SC₂H₄Ph)₆₀ Nanocluster

Abstract

We have determined vibrational signatures and optical gap of the Au144(PET)60 (PET: phenylethylthiol, SC2H4Ph) nanocluster solvated in deuterated dichloromethane (DCM-D2, CD2Cl2) and in a single crystal. For crystals, solid-state (13)C NMR and X-ray diffraction were also measured. A revised value of 2200 cm(-1) (0.27 eV) was obtained for the optical gap in both phases. The vibrational spectra of solvated AU144(PET)60 closely resembles that of neat PET, while the crystalline-state spectrum exhibits significant inhomogeneous spectral broadening, frequency shifts, intensity transfer between vibrational modes, and an increase in the overtone and combination transition intensities. Spectral broadening was also observed in the (13)C NMR spectrum. Changes in the intensity are explained due to vibrational coupling of the normal modes induced by the crystal packing, and the vibrational broadening is caused by ligand-environment inhomogeneity in the crystal. This indicates a pseudocrystalline state where the cluster cores are arranged in periodic fashion, while the ligand-layer molecules between the cores form amorphous structures.

Au25(SEt)18, a Nearly Naked Thiolate-Protected Au25 Cluster: Structural Analysis by Single Crystal X-ray Crystallography and Electron Nuclear Double Resonance

“…This was attributed to a possible effect of the charge state or a solid-state effect induced by the presence of the bulky counterion for the anionic state. Interestingly, however, in the neutral cluster Au 25 (SEt) 18 0 we find two couples of linear staples (as shown in Figure 3A) and one couple ( Figure 3B) displaying the same distortion mentioned above for Au 25 , the three ligands are oriented in a, say, downÀupÀdown direction with respect to the plane containing the S(R)ÀAuÀS(R)ÀAuÀS(R) motif. 15 In Au 25 (SC 2 H 4 Ph) 18 À , on the other hand, the orientation is always of the downÀupÀup type.…”

“…After 2 days under stirring, the clusters were separated from the reaction mixture and purified. Au 25 Figure S1 in Supporting Information). 15,26,30 The chemical composition, purity, and monodispersity of Au 25 (SEt) 18 0 were assessed by MALDI-TOF mass spectrometry.…”

“…Mass spectrometry techniques proved to be very effective, particularly matrixassisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry 17 and electrospray ionization (ESI) mass spectrometry. 18, 19 Mass spectra were indeed instrumental to establish the correct cluster formula in advance of the actual structural determination for Au 25 (SR) 18 , 18,19 formerly believed to be Au 38 (SR) 24 . 20 Very recently, structural characteristics of clusters whose single crystal X-ray diffraction structure is still unknown were inferred by different approaches.…”

“…We prepared a monodisperse Au 25 cluster protected by the smallest ligand ever used, ethanethiol. Au 25 (SEt) 18 was fully characterized by MALDI-TOF, UVÀvis, electrochemistry, and 1 H and 13 C NMR spectroscopy of both the anion and the neutral forms. Successful preparation of high-purity samples and single crystals allowed us to obtain the first X-ray structure of a gold cluster protected by a very short alkanethiolate.…”

Structural Information on the Au–S Interface of Thiolate-Protected Gold Clusters: A Raman Spectroscopy Study

“…Experimental Raman spectra were reported by Price and Whetten 13 17 Line broadening in the crystalline state due to ligand-layer coupling was observed as compared to the cluster in solution.…”