Catenane Structures of Homoleptic Thioglycolic Acid-Protected Gold Nanoclusters Evidenced by Ion Mobility-Mass Spectrometry and DFT Calculations

Abstract

Thiolate-protected metal nanoclusters have highly size- and structure-dependent physicochemical properties and are a promising class of nanomaterials. As a consequence, for the rationalization of their synthesis and for the design of new clusters with tailored properties, a precise characterization of their composition and structure at the atomic level is required. We report a combined ion mobility-mass spectrometry approach with density functional theory (DFT) calculations for determination of the structural and optical properties of ultra-small gold nanoclusters protected by thioglycolic acid (TGA) as ligand molecules, Au₁₀(TGA)₁₀. Collision cross-section (CCS) measurements are reported for two charge states. DFT optimized geometrical structures are used to compute CCSs. The comparison of the experimentally- and theoretically-determined CCSs allows concluding that such nanoclusters have catenane structures.

Keywords: DFT calculations; catenane; gold nanoclusters; ion mobility; thiolate.

Figure 1

Experimental absorption spectra of Au₁₀(SR)₁₀ nanoclusters (NCs) (with SR = thioglycolic acid (TGA)and SG (see [7]). (Inset) Electrospray ionization ESI mass spectrum of the as-synthesized Au₁₀(TGA)₁₀ NCs.

Figure 2

TD-DFT absorption spectrum and structure for three lowest energy isomers of Au₁₀(TGA)₁₀ shown in (a–c) respectively. Leading excitations responsible for the characteristic features of absorption are illustrated on the right side. HOMO-LUMO for isomers I, II, and III are 4.54, 4.62, and 5.55 eV, respectively.