321 research outputs found
Organometallic Neptunium Chemistry
Fifty years have passed since the foundation of organometallic neptunium chemistry, and yet only a handful of complexes have been reported, and even fewer fully characterised. Yet increasingly, combined synthetic/spectroscopic/computational studies are demonstrating how covalently binding, soft, carbocyclic organometallic ligands provide an excellent platform for advancing the fundamental understanding of the differences in orbital contributions and covalency in f-block metal – ligand bonding. Understanding the subtleties are key to the safe handling and separations of the highly radioactive nuclei. This review describes the complexes that have been synthesised to date, presents a critical assessment on the successes and difficulties in their analysis, and the bonding information they have provided. Because of the recent work to start new Np air-sensitive inorganic chemistry labs, the importance of radioactivity, the basics of Np decay and its ramifications (including the radiochemical synthesis of one organometallic) and the available anhydrous starting materials are also surveyed. The review also highlights a range of instances in which important differences in the chemical behaviour between Np and its closest neighbours, uranium and plutonium, are found.JRC.G.I.5-Advanced Nuclear Knowledg
Destruction of chemical warfare agent simulants by air and moisture stable metal NHC complexes
The cooperative effect of both NHC and metal centre has been found to destroy chemical warfare agent (CWA) simulants. Choice of both the metal and NHC is key to these transformations as simple, monodentate N-heterocyclic carbenes in combination with silver or vanadium can promote stoichiometric destruction, whilst bidentate, aryloxide-tethered NHC complexes of silver and alkali metals promote breakdown under mild heating. Iron–NHC complexes generated in situ are competent catalysts for the destruction of each of the three targetted CWA simulants
Controlling uranyl oxo group interactions to group 14 elements using polypyrrolic Schiff-base macrocyclic ligands
Heterodinuclear uranyl/group 14 complexes of the aryl- and anthracenyl-linked Schiff-base macrocyclic ligands LMe and LA were synthesised by reaction of UO2(H2L) with M{N(SiMe3)2}2 (M = Ge, Sn, Pb). For complexes of the anthracenyl-linked ligand (LA) the group 14 metal sits out of the N4-donor plane by up to 0.7 Å resulting in relatively short M⋯OUO distances which decrease down the group; however, the solid state structures and IR spectroscopic analyses suggest little interaction occurs between the oxo and group 14 metal. In contrast, the smaller aryl-linked ligand (LMe) enforces greater interaction between the metals; only the PbII complex was cleanly accessible although this complex was relatively unstable in the presence of HN(SiMe3)2 and some organic oxidants. In this case, the equatorial coordination of pyridine-N-oxide causes a 0.08 Å elongation of the endo UO bond and a clear interaction of the uranyl ion with the Pb(II) cation in the second donor compartment
Uranyl to Uranium(IV) Conversion through Manipulation of Axial and Equatorial Ligands
The controlled manipulation of the axial oxo and equatorial halide ligands in the uranyl dipyrrin complex, UO2Cl(L), allows the uranyl reduction potential to be shifted by 1.53 V into the range accessible to naturally occurring reductants that are present during uranium remediation and storage processes. Abstraction of the equatorial halide ligand to form the uranyl cation causes a 780 mV positive shift in the UV/UIV reduction potential. Borane functionalization of the axial oxo groups causes the spontaneous homolysis of the equatorial U–Cl bond and a further 750 mV shift of this potential. The combined effect of chloride loss and borane coordination to the oxo groups allows reduction of UVI to UIV by H2 or other very mild reductants such as Cp*2Fe. The reduction with H2 is accompanied by a B–C bond cleavage process in the oxo-coordinated borane
Metal-Metal Bonding in Uranium-Group 10 Complexes
Heterobimetallic
complexes containing short uranium–group
10 metal bonds have been prepared from monometallic IU<sup>IV</sup>(OAr<sup>P</sup>-κ<sup>2</sup><i>O</i>,<i>P</i>)<sub>3</sub> (<b>2</b>) {[Ar<sup>P</sup>O]<sup>−</sup> = 2-<i>tert</i>-butyl-4-methyl-6-(diphenylphosphino)Âphenolate}.
The U–M bond in IU<sup>IV</sup>(μ-OAr<sup>P</sup>-1κ<sup>1</sup><i>O</i>,2κ<sup>1</sup><i>P</i>)<sub>3</sub>M<sup>0</sup>, M = Ni (<b>3–Ni</b>), Pd (<b>3–Pd</b>), and Pt (<b>3–Pt</b>), has been
investigated by experimental and DFT computational methods. Comparisons
of <b>3–Ni</b> with two further U–Ni complexes
XU<sup>IV</sup>(μ-OAr<sup>P</sup>-1κ<sup>1</sup><i>O</i>,2κ<sup>1</sup><i>P</i>)<sub>3</sub>Ni<sup>0</sup>, X = Me<sub>3</sub>SiO (<b>4</b>) and F (<b>5</b>), was also possible via iodide substitution. All complexes were
characterized by variable-temperature NMR spectroscopy, electrochemistry,
and single crystal X-ray diffraction. The U–M bonds are significantly
shorter than any other crystallographically characterized d–f-block
bimetallic, even though the ligand flexes to allow a variable U–M
separation. Excellent agreement is found between the experimental
and computed structures for <b>3–Ni</b> and <b>3–Pd</b>. Natural population analysis and natural localized molecular orbital
(NLMO) compositions indicate that U employs both 5f and 6d orbitals
in covalent bonding to a significant extent. Quantum theory of atoms-in-molecules
analysis reveals U–M bond critical point properties typical
of metallic bonding and a larger delocalization index (bond order)
for the less polar U–Ni bond than U–Pd. Electrochemical
studies agree with the computational analyses and the X-ray structural
data for the U–X adducts <b>3–Ni</b>, <b>4</b>, and <b>5</b>. The data show a trend in uranium–metal
bond strength that decreases from <b>3–Ni</b> down to <b>3–Pt</b> and suggest that exchanging the iodide for a fluoride
strengthens the metal–metal bond. Despite short U–TM
(transition metal) distances, four other computational approaches
also suggest low U–TM bond orders, reflecting highly transition
metal localized valence NLMOs. These are more so for <b>3–Pd</b> than <b>3–Ni</b>, consistent with slightly larger U–TM
bond orders in the latter. Computational studies of the model systems
(PH<sub>3</sub>)<sub>3</sub>MUÂ(OH)<sub>3</sub>I (M = Ni, Pd) reveal
longer and weaker unsupported U–TM bonds vs <b>3</b>
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