Gas-Phase Structural and Optical Properties of Homo- and Heterobimetallic Rhombic Dodecahedral Nanoclusters [Ag14–nCun(C≡CtBu)12X]+ (X = Cl and Br): Ion Mobility, VUV and UV Spectroscopy, and DFT Calculations

Abstract

The rhombic dodecahedral nanocluster [Ag14(C≡CtBu)12Cl]+, which has been structurally characterized using X-ray crystallography, was transferred to the gas phase using electrospray ionization, where it was characterized by ion mobility (IM), vacuum ultraviolet (VUV), and ultraviolet (UV) spectroscopies in conjunction with DFT calculations. IM reveals a single peak, and modeling of the collision cross-section with the X-ray structure suggests that the cluster maintains its condensed phase structure upon transfer to the gas phase. The VUV spectra exhibit rich fragmentation, including: photoionization to give [Ag14(C≡CtBu)12Cl]2+• with an onset of 8.84 ± 0.08 eV; cluster fission fragmentation via losses of (AgC≡CtBu)n and (AgC≡CtBu)n−1(AgCl); and via reductive elimination of (tBuC≡C)2. Apart from channels associated with photoionization, similar fragment ions are observed in the UVPD spectra, although their relative intensities differ. The TDDFT absorption spectra are symmetry-allowed transitions including Au → Ag, Eu → Ag, and Eu → Eg irreducible representations. Comparing the collision cross-sections with the X-ray structures for the related clusters [Ag8Cu6(C≡CtBu)12Cl]+, [Ag14(C≡CtBu)12Br]+, and [Ag8Cu6(C≡CtBu)12Br]+ suggests that they maintain their condensed-phase structures in the gas phase. The VUV spectra of [Ag8Cu6(C≡CtBu)12Cl]+ and [Ag14(C≡CtBu)12Br]+ exhibit similar fragmentation channels and ionization onsets (8.86 ± 0.03 and 8.86 ± 0.05, respectively) compared with [Ag14(C≡CtBu)12Cl]+.