Using electrospray ionization-tandem mass spectrometry to explore formation and gas-phase chemistry of silver nanoclusters generated from the reaction of silver salts with NaBH4in the presence of bis(diphenylarsino)methane

Electrospray ionization-mass spectrometry (ESI-MS) of mixtures of AgBF(4)or AgNO(3)with the capping ligand bis(diphenylarsino)methane ((Ph2As)(2)CH2= dpam) in a solution of acetonitrile revealed the formation of the following cations: [Ag(CH3CN)(dpam)](+), [Ag(dpam)(2)](+), [Ag-2(Cl)(dpam)(2)](+), and [Ag-3(Cl)(2)(dpam)(3)](+). Addition of NaBH(4)to these solutions results in the formation of the cluster cations [Ag-2(BH4)(dpam)(2)](+), [Ag-2(BH4)(dpam)(3)](+), [Ag-3(H)(BH4)(dpam)(3)](+), [Ag-3(BH4)(2)(dpam)(3)](+), [Ag-3(H)(Cl)(dpam)(3)](+), and [Ag-3(I)(BH4)(dpam)(3)](+), as established by ESI-MS. Use of NaBD(4)confirmed that borohydride is the source of the hydride in these clusters. An Orbitrap Fusion LUMOS mass spectrometer was used to explore the gas-phase unimolecular chemistry of selected clusters via multistage mass spectrometry (MSn) experiments employing low-energy collision-induced dissociation (CID) and high-energy collision-induced dissociation (HCD) experiments. The borohydride containing clusters fragment via two competing pathways: (i) ligand loss and (ii) B-H bond activation involving BH(3)loss. Density functional theory (DFT) calculations were used to calculate the energetics of the optimized structures for all precursor ions, fragment ions, and neutrals and to estimate the reaction endothermicities. Generally, there is reasonable agreement between the most abundant product ion formed and the predicted endothermicity of the associated reaction channel. The DFT calculations predicted that the novel dimer [Ag-2(BH4)(dpam)(2)](+)has a paddlewheel structure in which the dpam and BH(4)(-)ligands bridge both silver centers.

Automated summary

Electrospray ionization-mass spectrometry (ESI-MS) analysis of mixtures of AgBF(4) or AgNO(3) with the capping ligand bis(diphenylarsino)methane ((Ph2As)2CH2= dpam) in acetonitrile solution revealed the formation of various cations. Addition of NaBH(4) resulted in the formation of cluster cations, confirmed to be sourced from borohydride. Density functional theory (DFT) calculations and mass spectrometry experiments showed the fragmentation pathways of borohydride-containing clusters and predicted the structure of a novel dimer cluster.