GAS-PHASE METAL CHALCOGENIDE CLUSTER IONS - A NEW [COXSY]- SERIES UP TO [CO38S24]- AND 2 [FEXSY]- SERIES

Laser (1064 nm) ablation of CoS yields 83 gaseous ions [Co(x)S(y)]-, d etected and characterized by FTICR mass spectrometry. These ions, rang ing in size from [CoS2]- to [Co38S24]-, possess a slightly curved comp osition distribution on the x/y plot, with x/y approximately 1.6. The same technique applied to FeS and KFeS2, yields 45 [Fe(x)S(y)]- ions, which are distributed in two distinct regions of the x/y composition m ap. Series a is a linear progression of triplets of ions with the comp ositions [FenSn-1]-, [FenSn]-, and [FenSn+1]-, for n = 3-10, while ion s in the unprecedented series b contain an additional S5, namely [FenS n+5]- and [FeSn+6]- for n = 1-7. Ions in series a are probably globula r clusters, while each ion in series b could contain an additional che lating polysulfide ligand or could evince a structural principle of ex tended chains or ribbons of linked tetrahedra. Collisionally activated dissociation measurements for the smaller ions reveal stability for [ Fe6S6]-, [Co5S5]-, and [Co3S3]-. Cluster structures are postulated for representative ions throughout the composition range. Although there are analogies between probable gas-phase structures of the clusters an d core structures for clusters in crystals, the much greater range and number of compositions observed for gaseous clusters presage possibil ities for synthesis of new and unexpected clusters in condensed phases . Electronic structures are considered in comparison with those of [Ni xSy]- and [CuxSy]-, revealing that the valence electron population per metal is largely independent of the metal identity, and decreases fro m about 15 at x = 5 to about 12.5 for clusters with 37 metal atoms. Th is is consistent with increased concentration of metal atoms and metal -metal bonding in the cores of larger clusters.