In this week’s issue of Nature magazine Arnold et al. have published an intriguing reactive complex of the notoriously stable uranyl dication [UO₂]⁺ that cleaves C-Si bonds and yields a functionalized U=O bond. This was accomplished by first encapsulating the UO₂ into a cyclic macrocycle, followed by the addition of the metal (either iron or zinc bound to the inner U=O bond) with a silylamide base. The major product is shown in the figure below.

Reprinted by permission from Macmillan Publishers Ltd: Nature, advance online publication, 17 January 2008 (doi:10.1038/nature06467)

Reprinted by permission from Macmillan Publishers Ltd: Nature, advance online publication, 17 January 2008 (doi:10.1038/nature06467)

A solution to the problem of determining the presence of the postulated intermediate might simply be to take mass specs along the course of the reaction; as one described prep takes 42 hours. In the end, this work literally builds the scaffold for future chemists to begin functionalizing uranyl. Although, no mention is given how to un-encapsulate the newly derivatized uranium.

Note 1: Link to article — Reduction and selective oxo group silylation of the uranyl dication

Mitch

The discovery of a new isotope of Bohrium, by Nelson et al., was published yesterday in PRL. In total, 8 events of ²⁶⁰Bh were reported. Unfortunately, the new isotope is not long-lived enough to be of practical chemical interest. A summary of the decay properties is summarized in the Nuclear Trading Card format shown below.

The yellow color signifies the observation that it decays by alpha emission 100% of the time. Fortunately the nuclide decays into ²⁵⁶Db, which is long-lived enough for chemistry, and the results taken with this paper and others updates the known decay properties of Dubnium-256. The updated trading card is below.

In this case the red signifies an ~30% electron capture branch. We hope you enjoy the announcement of a new member to the Bohrium family, and have fun with your new nuclear trading card.

Note 1: Link to article: Lightest Isotope of Bh Produced via the ²⁰⁹Bi(⁵²Cr, n)²⁶⁰Bh Reaction

Mitch

Earlier this week a paper by L. Soderholm et al. in Angewandte Chemie may have solved the great plutonium polymer mystery. Plutonium polymer is the ubiquitous noun often spoken by plutonium chemists in regards to the un-extractable ill-defined hydrous oxides of plutonium that will form in any solution of aqueous plutonium lying about the bench top. Often plutonium polymerization can be inhibited by storing aqueous plutonium solutions at high acid concentrations. It was thought to form from a series of olation reactions:

Plutonium Olation Reaction: Pu—OH + Pu—OH₂ —> Pu—OH—Pu + H₂O

This old hypothesis is put to rest with the isolation of Li₁₄(H₂O)_n[Pu₃₈O₅₆Cl₅₄(H₂O)₈]. This occurred after repeated anion-exchange with an acidified alkaline peroxide solution of plutonium, that then crystallized in the presence of aqueous LiCl. This type of workup is common for samples containing plutonium polymer. The crystal is reported to have the same intracluster packing and structural topology as bulk PuO₂. The crystal structure of the [Pu₃₈O₅₄(H₂O)₈]⁴⁰⁺ is shown below.

Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.: Angewandte Chemie International Edition (Dec 2007).

The Plutonium is in green, oxygen from the oxide in red, and oxygen from water in blue. With this and other evidence of well defined Pu—O clusters and the lack of hard evidence for oxyhydroxides they expect plutonium to condensate through an oxolation reaction.

Plutonium Oxolation Reaction: 2Pu—OH —> Pu—O—Pu + H₂O

The one caveat with this work is that it was performed with the more stable plutonuium-242 (t_1/2=3.7 x 10⁵ y) and not the typical reactor plutonium-239 (t_1/2=2.4 x 10⁴ y). Perhaps in the presence of the >10x more radioactive Pu-239 the nanoclusters would become either too structurally damaged to resolve nice crystalline structures, or more chemically reactive towards hydrous oxide formation or oxyhydroxide formation. Regardless, this work may still lead to better methods of extracting plutonium out of the nuclear fuel cycle and represents a nice resolution to the nebulous plutonium polymer conundrum.

Link to Paper: http://dx.doi.org/10.1002/anie.200704420

Mitch

Baumann et al. have recently reported the discovery of three new isotopes ⁴⁰Mg, ⁴²Al, and ⁴³Al. The discovery is notable for producing an isotope that neither the finite range droplet model (FRDM) nor the Hartree-Fock-Bogoliubov (HFB-8) predicted should be bound.

Of the 3 isotopes, the discovery of ⁴²Al is an unexpected surprise and thusly the most fascinating. As we all know from undergraduate nuclear chemistry the Weizsäcker’s formula contains a pairing term (d) approximately equal to 34*A^-3/4 MeV. The term increases the binding energy for an even number of protons (Z) and neutrons (N), decreases it for an odd Z and N, and of course is zero for an odd atomic number (A). ⁴²Al contains 13-protons and 29-neutrons, lies on the extreme neutron-rich side, and thus was not predicted to exist in a bound state.

Theory can be seen to be in contradiction from experimental data as seen below.

Reprinted by permission from Macmillan Publishers Ltd: Nature 449, 1022 - 1024 (25 Oct 2007).

To the immediate left of the ⁴³Al dot is the collection of ⁴²Al events. The ⁴³Al event had a probability of ~2 x 10^-3 of arising from the Al-42 cluster of events.

The tantalizing conclusion of this work is that the neutron-drip line may reside further than even the next generation nuclear facilities could explore for Z>12.

Link to article: http://dx.doi.org/10.1038/nature06213

Mitch

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Mitch