Gas-phase synthesis and deposition of metal–bipyridine complex [M–bpy1–2]+ (M = Ag, Cu)

Abstract

Controllable synthesis of organometallic clusters in the gas phase is a topic of reasonable interest with precisely tunable properties depending on sizes, compositions, and intra-cluster charge-transfer interactions. Here, we have prepared small Ag_n⁺ and Cu_n⁺ clusters by using a customized magnetron sputtering (MagS) source and observed the gas-phase reactions with 2,2′-bipyridine. It is found that the small silver and copper clusters readily react with bipyridine and form products of [M–bpy_1–2]⁺ (M = Ag, Cu). Quantum chemistry calculations reveal that the bipyridine in both [Ag–bpy_1–2]⁺ and [Cu–bpy_1–2]⁺ takes on cis-conformation with altered N–C–C–N dihedral angles, which is in contrast to the trans-conformation of a free 2,2′-bipyridine molecule itself. In order to unveil the principle of conformational transition, we have fully studied the interactions between the nitrogen atoms of bipyridine and the cationic Ag⁺ and Cu⁺, calculated the donor–acceptor orbital overlaps, and analyzed the correlation of their frontier molecular orbital energy levels. Furthermore, by using a soft-landing strategy, we have managed to deposit the [Cu–bpy₂]⁺ complex onto the glass substrates coated with Ag nanoparticles, and recorded the surface-enhanced Raman scattering spectra.