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UCHEM Report Summary

Project ID: 612724
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Periodic Report Summary 3 - UCHEM (Frontier Non-Aqueous Uranium Chemistry: Structure, Bonding, Reactivity, and Nanomagnetism)

From a historical perspective, the chemistry of uranium can be considered to lag behind the rest of the periodic table because the rarity and perceived handling problems have restricted or discouraged its use. This is surprising when the fact that uranium plays a central role in nuclear power is appreciated. There are enduring questions regarding how uranium undertakes chemical bonding to other elements and what effect this has on reactivity. The extent of covalency in uranium bonding, that is sharing of electrons, is poorly understood, but could be key to resolving nuclear waste problems since only a small fraction of the volume of nuclear waste is actually radioactive, but separating it is difficult.

The only way to overcome the limitations on our understanding is to prepare families of uranium and thorium molecules and study their properties in-depth. Below we present some selected highlights of research that has been accomplished by this grant.

We have followed up on our ground-breaking terminal uranium nitride work (Science 2012, Nature Chemistry 2013), by developing a new way to make them, thus overcoming the roadblock to progress imposed by the initial breakthrough, but unreliable, method. This allowed us to assemble a family of uranium nitrides that have been exhaustively quantified (Nat. Comm. 2016, 7, 13773). We have prepared analogous U-AsH2, U=AsH, and UAsK2 linkages; these are species made on bulk scale under ambient conditions that prior barely had precedent in spectroscopic matrix isolation experiments at 10 Kelvin so are highly novel (Nat. Chem. 2015, 7, 582). This spurred us to make Th-PH2, Th=PH, Th-P(H)-Th, and Th=P=Th linkages. These represent the first thorium-phosphorus multiple bonds outside of matrix isolation spectroscopic experiments at 5 Kelvin (Nat. Comm. 2016, 7, 12884). More remarkably, given arsenic is larger than phosphorus, we managed to extend this work to producing Th-AsH2, Th=AsH...K, Th-As(H)-Th, and Th=As=Th linkages. Again, most of these were unprecedented outside of fleeting transients in spectroscopic experiments so making them under ambient conditions is a real step forward (Nat. Comm. 2017, 8, 14769). The value of comparative work really emerged with these two studies because they show interesting variations in the quantities of 7s, 5f, and 6d orbital contributions to the bonding that we are still trying to understand. But given that these tensions were not even recognised as even existing before the work we clearly have much to do to elucidate some very fundamental trends in the actinides. Whilst looking at analogous uranium, thorium, and cerium complexes we noticed an unusual feature of those complexes in that even though strong donor ligands were opposite each other in those complexes they were bound closer, not further away as would be usual. This is called the inverse-trans-influence (ITI). This has been thought a niche concept in actinide chemistry for decades, but this work suggests that it has a much broader role to play, which is important in building our framework of understanding in an area that has few rules (Nat. Comm. 2017, 8, 14137).

Thus, this ERC CoG has to date produced a stream of high impact research published in leading international journals.

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United Kingdom
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