Jm. Hughes et al., CHARACTERIZATION OF HIGH-NUCLEARITY CLOSE-PACKED ANIONIC PLATINUM CARBONYL CLUSTERS BY CF-252 PLASMA DESORPTION MASS-SPECTROMETRY, International journal of mass spectrometry and ion processes, 126, 1993, pp. 197-210
Citations number
24
Categorie Soggetti
Spectroscopy,"Physics, Atomic, Molecular & Chemical
Cf-252-plasma desorption mass spectrometry has been used to investigat
e a series of high nuclearity, di- and tetraanionic platinum carbonyl
clusters containing Pt19, Pt24, Pt26 and Pt38 closest-packed metal cor
es. Abundant singly-charged negative ions produced by loss of an elect
ron, form an envelope of peaks corresponding to successive losses of c
arbonyl ligands from the intact metal core. A remarkable series of oli
gomeric negative ions formed by self-condensation of the metal core ar
e also observed for the dianionic clusters that extend beyond m/z 50 0
00. Slightly less abundant positive parent and oligomer ions are also
observed for these clusters. The oligomer peaks extend beyond m/z 100
000 in the spectrum of the Pt26 ClUster. The astonishing formation of
these positively charged aggregates that contain in excess of 500 Pt a
toms is even more remarkable because there is no incorporation of the
associated cation despite the strong presence of the cation in the pos
itive ion spectrum. These investigations have established that Cf-252-
PDMS can be used to unequivocally identify the platinum stoichiometry
of these high nuclearity clusters, thus providing a new tool in the va
st array of spectroscopic techniques used to structurally characterize
solution-soluble metal clusters. The unusual ions formed by this clas
s of compounds represent the largest positive and negative ions observ
ed by Cf-252-PDMS. They may also provide a probe of the complex reacti
ons that occur in the fission fragment track and in the ejected plume
of neutrals and ions. These large Pt clusters give quite good intensit
ies even at m/z > 50000 where the mechanism for detection must involve
potential electron emission. The electronic structure of these metal
clusters may be revealing a new aspect of potential emission where the
Fermi level structure of the incident ion plays a role.