Synthesis and gas-phase uni- and bi-molecular reactivity of bisphosphine ligated gold clusters, [AuxLy]n+

The condensed phase synthesis of bis-phosphine Ph2P(CH2)nPPh2 (Ln) (n = 3–6) protected gold clusters containing 6–11 gold core atoms was monitored via electrospray ionisation mass spectrometry (ESI-MS) and UV–vis spectroscopy. The size of the methylene spacer, n, which influences the ligand conformational flexibility, not only dictates Au cluster size, Au:L stoichiometry, and heterogeneity of the cluster mixture formed, but also influences the kinetics of cluster growth. Thus for n = 3, the cluster growth is relatively slow and [Au11L5n]3+ is the main cluster formed after equilibrium in ca. 7 days. For n = 4, the cluster growth rate is intermediate between n = 3 and n = 5 or 6 and [Au11L5n]3+, [Au10L4n]2+, [Au8L4n]2+ and [Au6L3n]2+ are the main clusters formed after equilibrium in ca. 24 h. For n = 5 or 6, the cluster growth rate is relatively fast and [Au10L4n]2+, [Au8L4n]2+ and [Au6L3n]2+ are the main clusters formed after equilibrium in less than 1 h.Low-energy collision induced dissociation (CID) of each of the gold cluster cations was carried out in an ion trap mass spectrometer with the aim of “synthesising” a range of novel gas-phase [AuxLyn]z+ (x = 3, 5–11; y = 1–5 and z = 1–3) clusters via ligand loss and core fission fragmentation pathways. The reactivity of mass selected gold cluster cations was studied via ion-molecule reactions using various neutral reagents in order to determine possible reactive sites. The observed reactivity of some of these clusters appears to relate to previously determined X-ray structures. Thus the lack of reactivity of [Au11L5n]3+ and [Au8L4n]2+ towards a range of neutrals can be attributed to the fact that all their surface gold atoms are capped by a phosphine group.

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► Novel bisphosphine protected gold cluster cations [AuxLyn]z+ (x = 3, 5–11; y = 1–5 and z = 1–3).
► Gas phase ion-molecule reactions using various neutral reagents were used to provide information on possible reactive sites in the clusters.
► The observed lack of reactivity of several of these clusters is consistent with previously determined X-ray structures.
► Gold atoms are not available for reaction when they are capped with phosphine groups.