Two Dihydroxo-Bridged Plutonium(IV) Nitrate Dimers and Their Relevance to Trends in Tetravalent Ion Hydrolysis and Condensation

We report the room temperature synthesis
and structural characterization of a μ2-hydroxo-bridged
PuIV dimer obtained from an acidic nitric acid solution.
The discrete Pu2(OH)2(NO3)6(H2O)4 moiety crystallized with two distinct
crystal structures, [Pu2(OH)2(NO3)6(H2O)4]2·11H2O (1) and Pu2(OH)2(NO3)6(H2O)4·2H2O (2), which differ primarily in the number of incorporated
water molecules. High-energy X-ray scattering (HEXS) data obtained
from the mother liquor showed evidence of a correlation at 3.7(1)
Å but only after concentration of the stock solution. This distance
is consistent with the dihydroxo-bridged distance of 3.799(1) Å
seen in the solid-state structure as well as with the known Pu–Pu
distance in PuO2. The structural characterization of a
dihydroxo-bridged Pu moiety is discussed in terms of its relevance
to the underlying mechanisms of tetravalent metal-ion condensation.