Structural characterization and gas-phase studies of the [Ag10H8(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 [Ag10H8(L)(6)](2+). Here we isolate and structurally characterize [Ag10H8(dppa)(6)](BF4)(2), and [Ag10H8(dppa)(6)](NO3)(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 [Ag10H8(dppa)(6)](2+) and [Ag10H8(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.