Structural characterization and gas-phase studies of the [Ag 10 H 8 (L) 6 ] 2+ nanocluster dication.

The reactions between silver salts and borohydrides produce a rich set of products that range from discrete mononuclear compounds through to silver nanoparticles and colloids. Previous studies using electrospray ionization mass spectrometry (ESI-MS) to track the cationic products in solutions containing sodium borohydride, silver(i) tetrafluoroborate and the bisphosphine ligands, L, bis(diphenylphosphino)methane (dppm) and bis(diphenylphosphino)amine (dppa) have identified the dications [Ag ₁₀ H ₈ (L) ₆ ] ²⁺ . Here we isolate and structurally characterize [Ag ₁₀ H ₈ (dppa) ₆ ](BF ₄ ) ₂ , and [Ag ₁₀ H ₈ (dppa) ₆ ](NO ₃ ) ₂ via X-ray crystallography. Both dications have nearly identical structural features consisting of a Ag ₁₀ scaffold with the atoms lying on vertices of a bicapped square antiprism. DFT calculations were carried out to suggest potential sites for the hydrides. Ion-mobility mass spectrometry experiments revealed that [Ag ₁₀ H ₈ (dppa) ₆ ] ²⁺ and [Ag ₁₀ H ₈ (dppm) ₆ ] ²⁺ have similar collision cross sections, while multistage mass spectrometry experiments were used to compare their unimolecular gas-phase chemistry. Although the same initial sequential ligand loss followed by cluster fission and H ₂ evolution is observed, the more acidic N-H of the dppa provides a more labile H for H ₂ loss and H/D scrambling processes as revealed by isotope labelled experiments.