High-Resolution Solid-State Oxygen-17 NMR of Actinide-Bearing Compounds: An Insight into the 5f Chemistry

Abstract

A massive interest has been generated lately by the improvement of solid-state magic-angle spinning (MAS) NMR methods for the study of a broad range of paramagnetic organic and inorganic materials. The open-shell cations at the origin of this paramagnetism can be metals, transition metals, or rare-earth elements. Actinide-bearing compounds and their 5f unpaired electrons remain elusive in this intensive research area due to their well-known high radiotoxicity. A dedicated effort enabling the handling of these highly radioactive materials now allows their analysis using high-resolution MAS NMR (>55 kHz). Here, the study of the local structure of a series of actinide dioxides, namely, ThO2, UO2, NpO2, PuO2, and AmO2, using solid-state 17O MAS NMR is reported. An important increase of the spectral resolution is found due to the removal of the dipolar broadening proving the efficiency of this technique for structural analysis. The NMR parameters in these systems with numerous and unpaired 5f electrons were interpreted using an empirical approach. Single-ion model calculations were performed for the first time to determine the z component of electron spin on each of the actinide atoms, which is proportional to the shifts. A similar variation thereof was observed only for the heavier actinides of this study.

A 17O paramagnetic NMR study of Sm2O3, Eu2O3, and Sm/Eu-substituted CeO2

“…4 Nonetheless, the sensitivity of paramagnetic 17 O NMR spectra to distances from, and the electronic and magnetic properties of, the paramagnetic centre has enabled insights in recent years into materials as diverse as metal-organic frameworks, 5 battery materials, 6 mixed ionic-electronic conductors, 7,8 and phases of geological and radiochemical relevance. 9,10 In these studies, computational results from periodic DFT calculations have also played a critical role, aiding in spectral assignment. Nonetheless, the behaviour of paramagnetic Lanthanides can have very large electron magnetic moments due to partial filling of the seven f-orbitals; moreover, the f-orbitals are contracted and hence do not interact strongly with bonded atoms, so that there is minimal crystal field splitting and therefore no driving force to undergo electron pairing and reduce the magnetic moment.…”

Probing thePu4+magnetic moment inPuF4withF19

“…The NMR shifts of nuclei interacting with paramagnetic d-or f-electron centers have been discussed in detail by Shulman and Jaccarino. 20 Gabuda et al 29 and Martel et al 35 have proposed that the field dependent anisotropic hyperfine shifts in paramagnetic tetravalent actinide systems can be approximated as a dipolar field produced by localized, unpaired electrons at the An 4+ sites…”

Lattice thermal expansion of Pu1−y Am y O2−x plutonium–americium mixed oxides

“…Lattice parameter (Å ) Pu 1Ày Am y O 2 This study Literature y = 0.018 5.3954 (5) 5.396 (1) for y = 0 (Zachariasen, 1949) 5.396 (1) for y = 0 (Drummond & Welch, 1957) 5.396 (1) for y = 0 (Gardner et al, 1965) 5.4026 (6) for y = 0 (Molen & White, 1967) 5.3948 for y = 0 (Nutt & Tokar, 1972) 5.3953 (4) for y = 0 (Noe & Fuger, 1974) 5.3954 (4) for y = 0 (Yamashita et al, 1997) 5.3975 for y = 0 (Haschke et al, 2000) 5.3977 for y = 0 (Martel et al, 2014) 5.400 (1) for y = 0.008 (Belin et al, 2013) y = 0.077 5.3948 (5) 5.397 for y = 0.09 (Miwa et al, 2007) 5.409 (1) for y = 0.1 (Belin et al, 2013) y = 0.21 5.3916 (5) 5.392 (1) (Jankowiak et al, 2009) 5.411 (1) for y = 0.2 (Belin et al, 2013) y = 0.49 5.3859 (5) 5.386 (1) (Jankowiak et al, 2009) 5.383 (1) for y = 0.5 (Otobe et al, 2009) y = 0.80 5.3800 (5) 5.379 (1) (Jankowiak et al, 2009) y = 1.00 5.3755 (5) 5.377 (3) (Zachariasen, 1949) 5.383 (1) (Templeton & Dauben, 1953) 5.377 (Keller, 1967) 5.3772 (4) (Chikalla & Eyring, 1968) 5.3733 (Fahey et al, 1974) 5.3724 (4) (Hurtgen & Fuger, 1977) 5.375 (1) (Prieur et al, 2011) 5.375 (1) (Lebreton et al, 2012) 5.375 (1) (Epifano et al, 2016(Epifano et al, , 2017 to confirm that our samples were stoichiometric, i.e. exhibited an O/M ratio equal to 2.00, at room temperature regardless of the americium content.…”