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Cross, Justin N.

Publications and source records attributed to Cross, Justin N..

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Isolation and characterization of a californium metallocene

Californium (Cf) is currently the heaviest element accessible above microgram quantities. Cf isotopes impose severe experimental challenges due to their scarcity and radiological hazards. Consequently, chemical secrets ranging from the accessibility of 5f/6d valence orbitals to engage in bonding, the role of spin–orbit coupling in electronic structure, and reactivity patterns compared to other f elements, remain locked. Organometallic molecules were foundational in elucidating periodicity and bonding trends across the periodic table, with a twenty-first-century renaissance of organometallic thorium (Th) through plutonium (Pu) chemistry, and to a smaller extent americium (Am), transforming chemical understanding. Yet, analogous curium (Cm) to Cf chemistry has lain dormant since the 1970s. Here, we revive air-/moisture-sensitive Cf chemistry through the synthesis and characterization of [Cf(C 5 Me 4 H) 2 Cl 2 K(OEt 2 )] n from two milligrams of 249 Cf. This bent metallocene motif, not previously structurally authenticated beyond uranium (U), contains the first crystallographically characterized Cf–C bond. Analysis suggests the Cf–C bond is largely ionic with a small covalent contribution. Lowered Cf 5f orbital energy versus dysprosium (Dy) 4f in the colourless, isoelectronic and isostructural [Dy(C 5 Me 4 H) 2 Cl 2 K(OEt 2 )] n results in an orange Cf compound, contrasting with the light-green colour typically associated with Cf compounds.

Chemical bonding↗
DOE OSTI2021

Crystallographic characterization of (C 5 H 4 SiMe 3 ) 3 U(BH 4 )

New syntheses have been developed for the synthesis of (borohydrido-κ 3 H)tris­[η 5 -(tri­methyl­sil­yl)cyclo­penta­dien­yl]uranium(IV), [U(BH 4 )(C 8 H 13 Si) 3 ] or Cp' 3 U(BH 4 ) (Cp' = C 5 H 4 SiMe 3 ) and its structure has been determined by single-crystal X-ray crystallography. This compound crystallized in the space group P1¯ and the structure features three η 5 -coordinated Cp' rings and a κ 3 -coordinated (BH 4 ) – ligand.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Origins of the odd optical observables in plutonium and americium tungstates

A series of trivalent f-block tungstates, MW 2 O 7 (OH)(H 2 O) (M = La, Ce, Pr, Nd, and Pu) and AmWO 4 (OH), have been prepared in crystalline form using hydrothermal methods. Both structure types take the form of 3D networks where MW 2 O 7 (OH)(H 2 O) is assembled from infinite chains of distorted tungstate octahedra linked by isolated MO 8 bicapped trigonal prisms; whereas AmWO 4 (OH) is constructed from edge-sharing AmO 8 square antiprisms connected by distorted tungstate trigonal bipyramids. PuW 2 O 7 (OH)(H 2 O) crystallizes as red plates; an atypical color for a Pu( III ) compound. Optical absorption spectra acquired from single crystals show strong, broadband absorption in the visible region. A similar feature is observed for CeW 2 O 7 (OH)(H 2 O), but not for AmWO 4 (OH). Here we demonstrate that these significantly different optical properties do not stem directly from the 5f electrons, as in both systems the valence band has mostly O-2p character and the conduction band has mostly W-5d character. Furthermore, the quasi-particle gap is essentially unaffected by the 5f degrees of freedom. Despite this, our analysis demonstrates that the f-electron covalency effects are quite important and substantially different energetically in PuW 2 O 7 (OH)(H 2 O) and AmWO 4 (OH), indicating that the optical gap alone cannot be used to infer conclusions concerning the f electron contribution to the chemical bond in these systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Advancing Understanding of the +4 Metal Extractant Thenoyltrifluoroacetonate (TTA – ); Synthesis and Structure of M IV TTA 4 (M IV = Zr, Hf, Ce, Th, U, Np, Pu) and M III (TTA) 4 – (M III = Ce, Nd, Sm, Yb)

Thenoyltrifluoroacetone (HTTA)-based extractions represent popular methods for separating microscopic amounts of transuranic actinides (i.e., Np and Pu) from macroscopic actinide matrixes (e.g. bulk uranium). It is well-established that this procedure enables +4 actinides to be selectively removed from +3, + 5, and +6 f-elements. However, even highly skilled and well-trained researchers find this process complicated and (at times) unpredictable. It is difficult to improve the HTTA extraction—or find alternatives—because little is understood about why this separation works. Even the identities of the extracted species are unknown. In addressing this knowledge gap, we report in this paper advances in fundamental understanding of the HTTA-based extraction. This effort included comparatively evaluating HTTA complexation with +4 and +3 metals (M IV = Zr, Hf, Ce, Th, U, Np, and Pu vs M III = Ce, Nd, Sm, and Yb). We observed +4 metals formed neutral complexes of the general formula M IV (TTA) 4 . Meanwhile, +3 metals formed anionic M III (TTA) 4 – species. Characterization of these M(TTA) 4 x– (x = 0, 1) compounds by UV–vis–NIR, IR, 1 H and 19 F NMR, single-crystal X-ray diffraction, and X-ray absorption spectroscopy (both near-edge and extended fine structure) was critical for determining that Np IV (TTA) 4 and Pu IV (TTA) 4 were the primary species extracted by HTTA. Furthermore, this information lays the foundation to begin developing and understanding of why the HTTA extraction works so well. The data suggest that the solubility differences between M IV (TTA) 4 and M III (TTA) 4 – are likely a major contributor to the selectivity of HTTA extractions for +4 cations over +3 metals. Finally and moreover, these results will enable future studies focused on explaining HTTA extractions preference for +4 cations, which increases from Np IV to Pu IV , Hf IV , and Zr IV .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Incipient class II mixed valency in a plutonium solid-state compound

Electron transfer in mixed-valent transition-metal complexes, clusters and materials is ubiquitous in both natural and synthetic systems. The degree to which intervalence charge transfer (IVCT) occurs, dependent on the degree of delocalization, places these within class II or III of the Robin–Day system. In contrast to the d-block, compounds of f-block elements typically exhibit class I behaviour (no IVCT) because of localization of the valence electrons and poor spatial overlap between metal and ligand orbitals. Here, in this paper, we report experimental and computational evidence for delocalization of 5f electrons in the mixed-valent Pu III /Pu IV solid-state compound, Pu 3 (DPA) 5 (H 2 O) 2 (DPA = 2,6-pyridinedicarboxylate). The properties of this compound are benchmarked by the pure Pu III and Pu IV dipicolinate complexes, [Pu III (DPA)(H 2 O) 4 ]Br and Pu IV (DPA) 2 (H 2 O) 3 ·3H 2 O, as well as by a second mixed-valent compound, Pu III [Pu IV (DPA) 3 H 0.5 ] 2 , that falls into class I instead. Metal-to-ligand charge transfer is involved in both the formation of Pu 3 (DPA) 5 (H 2 O) 2 and in the IVCT.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Comparing the 2,2′‐Biphenylenedithiophosphinate Binding of Americium with Neodymium and Europium

Abstract Advancing our understanding of the minor actinides (Am, Cm) versus lanthanides is key for developing advanced nuclear‐fuel cycles. Herein, we describe the preparation of (NBu 4 )Am[S 2 P( t Bu 2 C 12 H 6 )] 4 and two isomorphous lanthanide complexes, namely one with a similar ionic radius (i.e., Nd III ) and an isoelectronic one (Eu III ). The results include the first measurement of an Am−S bond length, with a mean value of 2.921(9) Å, by single‐crystal X‐ray diffraction. Comparison with the Eu III and Nd III complexes revealed subtle electronic differences between the complexes of Am III and the lanthanides.

Cross, Justin N.↗
DOE OSTI2016

Comparing the 2,2'-Biphenylenedithiophosphinate Binding of Americium with Neodymium and Europium

Advancing our understanding of the minor actinides (Am, Cm) versus lanthanides is key for developing advanced nuclear-fuel cycles. Here in this paper, we describe the preparation of (NBu 4 )Am[S 2 P( t Bu 2 C 12 H 6 )] 4 and two isomorphous lanthanide complexes, namely one with a similar ionic radius (i.e., Nd III ) and an isoelectronic one (Eu III ). The results include the first measurement of an Am-S bond length, with a mean value of 2.921(9) Å, by single-crystal X-ray diffraction. Comparison with the Eu III and Nd III complexes revealed subtle electronic differences between the complexes of Am III and the lanthanides.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2016

Nuclear Magnetic Resonance Measurements and Electronic Structure of Pu(IV) in [(Me)4N]2PuCl6

The synthesis, electronic structure, and characterization via single crystal X-ray diffraction, nuclear magnetic resonance (NMR) spectroscopy, and magnetic susceptibility of (Me4N)2PuCl6 are reported. NMR measurements were performed to both search for the direct 239Pu resonance and to obtain local magnetic and electronic information at the Cl site through 35Cl and 37Cl spectra. No signature of 239Pu NMR was observed. The temperature dependence of the Cl spectra was simulated by diagonalizing the Zeeman and quadrupolar Hamiltonians for 35Cl, 37Cl and 14N isotopes. Electronic structure calculations predict a magnetic ?5 triplet ground state of Pu(IV) in the crystalline electric field of the undistorted PuCl6 octahedron. A tetragonal distortion would result in a very small splitting (20 cm-1) of the triplet ground state into a nonmagnetic singlet and a doublet state. The Cl shifts have an inflection point at T = 15 K, differing from the bulk susceptibility, indicating a nonmagnetic crystal field ground state. The Cl spin-lattice relaxation time is constant down to T = 15 K, below which it rapidly increases, also supporting the nonmagnetic crystal field ground state.

Mounce, Andrew M.↗