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)]-, detected and characterized by FTICR mass spectrometry. These ions, ranging in size from [CoS2]- to [Co38S24]-, possess a slightly curved composition 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 map. Series a is a linear progression of triplets of ions with the compositions [FenSn-1]-, [FenSn]-, and [FenSn+1]-, for n = 3-10, while ions in the unprecedented series b contain an additional S5, namely [FenSn+5]- and [FeSn+6]- for n = 1-7. Ions in series a are probably globular clusters, while each ion in series b could contain an additional chelating polysulfide ligand or could evince a structural principle of extended 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 and core structures for clusters in crystals, the much greater range and number of compositions observed for gaseous clusters presage possibilities for synthesis of new and unexpected clusters in condensed phases. Electronic structures are considered in comparison with those of [NixSy]- and [CuxSy]-, revealing that the valence electron population per metal is largely independent of the metal identity, and decreases from about 15 at x = 5 to about 12.5 for clusters with 37 metal atoms. This is consistent with increased concentration of metal atoms and metal-metal bonding in the cores of larger clusters.