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)(n)-PPh2 (LP) (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+), [Au(8)L(4)n](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. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.