ESI/MS investigation of routes to the formation of silver hydride nanocluster dications [AgxHx−2Ly]2+ and gas-phase unimolecular chemistry of [Ag10H8L6]2+

•ESI/MS of [Ag3(L)3(μ3-BH4)]+ and BH4− yields [Ag8H6L5]2+ & [AgnHn−2L6]2+ (n = 9-15).•CID of [Ag10H8L6]2+ produces [Ag10H8L4]2+.•CID of [Ag10H8L4]2+ gives cluster fission in competition with [Ag10L3]2+ formation.•DFT calculations reveal changes to the cluster core upon ligand loss.•Loss of L from [Ag10H8L4]2+ is endothermic, but further loss of 4H2 is exothermic.

When the bis(diphenylphosphino)methane (dppm) ligated silver hydride nanocluster salt [Ag3(L)3(μ3-H)](BF4)2 is allowed to react with NaBH4 in a methanol/chloroform solution for 5 mins., and then diluted with acetonitrile and subjected to electrospray ionization mass spectrometry (ESI/MS), a range of silver hydride nanocluster dications are observed including: [Ag8H6L5]2+ and [AgxHx−2L6]2+, where x = 9-15 and L = dppm. All of these clusters are no longer present in the ESI mass spectrum at 40 mins after mixing. Multistage mass spectrometry (MSn) experiments were carried out to determine the fragmentation chemistry of [Ag10H8L6]2+ under conditions of collision-induced dissociation (CID). The initial CID reactions involve sequential loss of two ligands (L) to produce [Ag10H8L4]2+. Further isolation and CID of [Ag10H8L4]2+ resulted in a rich series of product ions which arise from three classes of fragmentation reactions: (i) cluster fission to yield complementary ion pairs [Ag10−xH8-(x−1)L4−y] + and [AgxHx−1Ly]+ (x = 1, 2 and 4); (ii) ligand loss associated with cluster fission to yield pairs of singly charged clusters [Ag10−xH8-(x−1)L4−y]+ and [AgxHx−1Ly−1]+ (x = 1-4); (iii) ligand loss with concomitant loss of all the hydrides, presumably as four molecules of hydrogen to give the ligated silver cluster, [Ag10L3]2+. The subsequent fragmentation reactions of the product ions were also examined. Most of the singly charged ligated silver hydride clusters fragment to form [AgxHx−1Ly]+. The exceptions are [Ag9H8L2]+ and [Ag7H6L2]+ which, upon ligand loss also release all of the hydrides to form the ligated silver clusters, [Ag9L]+ and [Ag7L]+ respectively. DFT calculations were carried out to examine how the cluster geometry changes for the following processes: [Ag10H8L6]2+ → [Ag10H8L4]2+ + 2L → [Ag10H8L3]2+ + L → [Ag10L3]2+ + 4H2. Losses of 2 L from [Ag10H8L6]2+ and L from [Ag10H8L4]2+ were calculated to be endothermic by 2.9 and 1.9 eV respectively, but the subsequent loss of 4H2 from [Ag10H8L3]2+ is exothermic by 0.2 eV.

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