Structural characterization and gas-phase studies of the [AgH(L)] 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 [AgH(L)]. Here we isolate and structurally characterize AgH(dppa), and AgH(dppa)via X-ray crystallography. Both dications have nearly identical structural features consisting of a Ag 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 [AgH(dppa)] and [AgH(dppm)] 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 evolution is observed, the more acidic N-H of the dppa provides a more labile H for H loss and H/D scrambling processes as revealed by isotope labelled experiments.