摘要：

Gas-phase metal sulfide cluster anions *Keith Fisher, Ian Dance, Gary Willett and MaNu YiSchool qj' Chemistry, University of New South Wales, Sydney 2052, AustruliaThe formation of metal sulfide cluster anions by laser ablation of solids has been examined for most of thefirst-row transition metals. Maps of the compositions of the clusters [M,S,] - show well defined continuousdistributions of x us. y for each metal, and the slope of each distribution is related to the position of the metalin the transition series. The 290 new molecular forms of metal sulfides range in size up to [ C U ~ ~ S , ~ ] - . Fourier-transform ion cyclotron resonance mass spectrometry revealed that the cluster anions have lifetimes of up to100 s in vacao. Experiments concentrating on the copper-sulfur anions showed their resistance to dissociationon energised collision with argon, and their general lack of reactivity, except with sulfur-containing reactants.In experiments designed to produce mixed-metal anions, cobalt has been shown to substitute for copper inmany of the smaller anions. Geometrical structures and structural principles for the copper sulfide clusters arerevealed by non-local density functional calculations.Metal sulfides normally occur as non-molecular solids, or asclusters ligated by terminal heteroligands.' How then canmolecular forms of binary metal sulfides be generated? Inthis discussion we describe results from our experimentaland theoretical research programmes in gas-phase inorganicchemistry, which reveal the formation and properties of anionicclusters [M,S,] - .These pristine molecular metal sulfides haveno heteroligands, and are devoid of all the many externalinfluences which occur in condensed phase systems. The furtherquestions we are investigating include: (a) what are thecompositions of the [MAS,] - which are stable, and how do theyvary with the identity of M?; (b) what are the inherent stabilitiesof the [M,S,]-, and how do they dissociate?; ( c ) how do the[MAS,lp behave with reactants able to function as ligands, aselectron-transfer agents, and/or as proton-transfer reagents?;( d ) what are the structures of the [M,S,]-, and whatgeometrical factors confer stability?In attempting to answer these questions we use laser ablation(LA) of binary transition-metal sulfides, and observe the anionsformed using Fourier-transform ion cyclotron resonance(FTICR) mass spectrometry.Our laser ablation studies ofmetal sulfides have involved Ag,S,, Ni2S3,3 CuS, Cu,S, andKCU,S,,~ FeS,' COS,~ and V2S3, Cr2S3 and MnS; the last threesystems are not yet published. A brief preliminary report of thegeneration and structure of some metal chalcogenide clustershas been published.6 These laser ablation studies have yielded alarge variety of stable metal sulfide cluster anions. For instancecopper sulfide anions4 have been identified up to [CU,,S,~]~,with two major series of anions of formulae [Cu,, - ,S,] ~ and[Cu,, - ,S,] both appearing in the laser ablation spectra ofseveral different copper sulfide compounds.In the ion-trapping cell of the FTTCR mass spectrometer weare able to store and treat these ions for several seconds,attesting to their inherent stability.Mass spectrometers usingmagnetic and electric sectors, or time-of-flight mass spectro-meters, produce and observe ions in micro- or milli-secondswhereas in FTICR the observation of the ions has a detectionwindow of at least 100 ms up to 100 s. One disadvantage of thetechniques is that reactions can be studied only at very lowpressure.A range of source materials can be used for the generation of* Basis of the presentation given at Dalton Discussion No. I , 3rdp5thJanuary 1996, University of Southampton, UK.Non-SI uriits enzployed: Torr % 133 Pa, bar = lo5 Pa, CV z1.60 x 10 " J .metal sulfide clusters by laser ablation, although the highvacuum required for good ion detection in FTICR does notallow the use of elemental sulfur, and the magnetic fieldprecludes ferromagnetic samples.Many binary and ternarymetal sulfides can be used, as can mixtures with metals, andmixtures of metal powder and

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