Ligand-stabilized, atomically precise gold nanoclusters with a metal core of a uniform size of just 1-3 nm constitute an interesting class of nanomaterials with versatile possibilities for applications due to their size-dependent properties and modifiable ligand layers. The key to extending the usability of the clusters in applications is to understand the chemical bonding in the ligand layer as a function of cluster size and ligand structure. Previously, it has been shown that monodispersed gold nanoclusters, stabilized by meta-mercaptobenzoic acid (m-MBA or 3-MBA) ligands and with sizes of 68-144 gold atoms, show ambient stability. Here we show that a combination of nuclear magnetic resonance spectroscopy, UV-vis absorption, infrared spectroscopy, molecular dynamics simulations, and density functional theory calculations reveals a distinct chemistry in the ligand layer, absent in other known thiol-stabilized gold nanoclusters. Our results imply a low-symmetry C ligand layer of 3-MBA around the gold core of Au and Au and suggest that 3-MBA protects the metal core not only by the covalent S-Au bond formation but also via weak π-Au and O═C-OH···Au interactions. The π-Au and -OH···Au interactions have a strength of the order of a hydrogen bond and thus are dynamic in water at ambient temperature. The -OH···Au interaction was identified by a distinct carbonyl stretch frequency that is distinct for 3-MBA-protected gold clusters, but is missing in the previously studied Au(p-MBA) cluster. These thiol-gold interactions can be used to explain a remarkably low ligand density on the surface of the metal core of these clusters. Our results lay a foundation to understand functionalization of atomically precise ligand-stabilized gold nanoclusters via a route where weak ligand-metal interfacial interactions are sacrificed for covalent bonding.

The B ̃−X ̃laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of the atmospherically important β-monofluoro ethoxy (MFEO), β,β-difluoro ethoxy (DFEO), and β,β,β-trifluoro ethoxy (TFEO) radicals were recorded with vibronic resolution under jet-cooled conditions. To simulate the spectra, Franck−Condon factors were obtained from quantum chemical computations carried out at the CAM-B3LYP/6-311++G(d,p) level of theory. The simulations reproduce well both the LIF and DF spectra. Both conformers (G and T) of MFEO and one (G) of the two conformers of DFEO contribute to the LIF spectrum. A comparison between the experimental and calculated spectra confirms the expected longrange field effects of the CH x F 3−x group on electronic transition energies and bond strengths, especially in the excited electronic (B ̃) state. Although TFEO has only one conformer, its LIF spectrum is highly congested, which is attributed to the interaction between CO stretch and the −CF 3 internal rotation.

The B -X laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of the atmospherically important β-monofluoro ethoxy (MFEO), β,β-difluoro ethoxy (DFEO), and β,β,β-trifluoro ethoxy (TFEO) radicals were recorded with vibronic resolution under jet-cooled conditions. To simulate the spectra, Franck-Condon factors were obtained from quantum chemical computations carried out at the CAM-B3LYP/6-311++G(d,p) level of theory. The simulations reproduce well both the LIF and DF spectra. Both conformers (G and T) of MFEO and one (G) of the two conformers of DFEO contribute to the LIF spectrum. A comparison between the experimental and calculated spectra confirms the expected long-range field effects of the CH X F 3−X group on electronic transition energies and bond strengths, especially in the excited electronic ( B) state. Although TFEO has only one conformer, its LIF spectrum is highly congested, which is attributed to the interaction between CO stretch and the -CF 3 internal rotation.

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