Electrospray mass spectrometry of thiophenolate-capped clusters of CdS, CdSe, and ZnS and of cadmium and zinc thiophenolate complexes: Observation of fragmentation and metal, chalcogenide, and ligand exchange processes

Electrospray mass spectrometry provides a rapid, convenient technique for characterizing and studying the chemistry of anionic metal sulfide thiolate clusters. Negative-ion electrospray mass spectra have been recorded for the thiophenolate-capped clusters [Me4N](4)[E4Cd10(SPh)(16)] (E = S, Se), [Me4N](4)[S4Zn10(SPh)(16)], and [Me4N](2)[S-4-Cd-17(SPh)(28)] and of the metal thiophenolate complexes [Me4N](2)[M(SPh)(4)], [Me4N](2)[M-4(SPh)(10)] (M = Cd, Zn), and [Et4N](2)[Cd4X4(SPh)(6)] (X = Cl, Br, I). The exchanges of M, E, and X which occur in various mixtures of these clusters and complexes and the fragmentation processes have been investigated. In the clusters the M-E bonds involving the sulfide or selenide core remain intact during the observed fragmentation at low cone voltages. At high cone voltages, monoions are ultimately formed by loss of charged species and neutral M(SPh)(2), resulting in almost complete removal of the SPh- ligands from the cluster core. Fragmentation of the ME core unit itself occurs only at very high voltages. The exchange of X in [Et4N](2)[Cd4X4(SPh)(6)] (X = Br, I) gives peaks due to the ions [Cd4InBrm(SPh)(10-(n+m))](2-) (n + m = 0-4) and fragment ions with mixed ligands. The nature of the detected species suggests that the halides only exist as terminal ligands. The exchange of M in [Me4N](2)[M-4-(SPh)(10)] and [Me4N](4)[S4M10(SPh)(16)] results in the mixed-metal complexes [Cd4-nZnn(SPh)(10)](2-) (n = 0-4) and the mixed-metal clusters [S4Cd10-nZnn(SPh)(16)](4-) (n = 0-10). The exchange follows random statistics in [M-4(SPh)(10)](2-) but is biased toward equilibrium association of the same metal in [S4M10(SPh)(16)](4-). The rates of exchange within the different structural elements of [S4M10(SPh)(16)](4-) and [S4M17(SPh)(28)](2-) decrease for the atoms located toward the center of the clusters.