Ligand-Coated Vanadium Oxide Clusters: Capturing Gas-Phase Magic Numbers in Solution

Abstract

Subnanometer vanadium oxide clusters in the 10−30 atom size range are produced in the gas phase with laser vaporization, coated with gas-phase ligands, and then captured in solution using a laser vaporization flow reactor. Acetonitrile (MeCN) and tetrahydrofuran (THF) ligands form complexes efficiently with the oxide clusters, rendering them soluble in solutions of these same ligands and other solvents. The structures and compositions of clusters captured in solution are investigated with laser desorption time-of-flight (LD-TOF) mass spectrometry, UV−visible and IR spectroscopy, and density functional theory computations. MeCN forms oxide clusters having the exact stoichiometries found previously to be stable in the gas phase (V3O6, V4O9, and V5O12), in a simple ligand-addition process. THF produces similar oxide cores, but with terminal oxygens displaced. Infrared spectra are consistent with the presence of terminal oxygens for the MeCN complexes and their absence for the THF species. In either case, DFT computations show that the vanadium oxide cores are minimally perturbed by ligand addition. Solutions of both samples exhibit visible photoluminescence with only minor dependence on the ligand, indicating that the core oxide is the source of the emission.