Tj. Kemp et al., FORMATION AND DECOMPOSITION OF URANIUM-OXYGEN CLUSTERS IN FAST-ATOM-BOMBARDMENT OD DIOXOURANIUM(VI) SALTS, Journal of the Chemical Society. Dalton transactions, (5), 1995, pp. 885-889
Fast atom bombardment (FAB) of uranyl salts in involatile organic matr
ices produced a long series of clusters of general formula [(UO2)(x)O-
y](+) with x reaching nearly 40. For each value of x there is a series
of values of y, with some value of y exhibiting: the greatest abundan
ce for each x value. Smaller clusters (x less than or equal to 22) wit
h even values of x show a stoichiometry of O:U of 2.5:1, while larger
clusters (x greater than or equal to 24) show a reduced O:U ratio. All
clusters with odd values of x adopt a O:U ratio of less than 2.5:1. N
ear x = 24, odd-even effects appeared in the relative intensities of t
he clusters. As x --> 40 ail cluster series tend to a final stoichiome
try of O:U = 2.5:1. The collision-induced decomposition (CID) of [(UO2
)(x)O-y](+) produced long sequences of progressively smaller clusters
via the loss of UO2, UO3 and UO4 moieties; the detection of particular
clusters depends on the collision-gas (argon) pressure. Odd-even alte
rnation effects are apparent in the CID spectra. Clusters of general f
ormula [(ThO2)(x)](+) were produced by FA of thorium(lv) nitrate, with
x reaching 20; odd-even alternation effects are prominent when x grea
ter than or equal to 14. The; relatively complex behaviour exhibited b
y U-O clusters is associated with electronic effects, particularly the
existence and relative stabilities of the +6, +5 and +4 oxidation sta
tes of uranium, as also manifested in U-O systems in the solid state,
with which comparison can be made.