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Yu, Xiaojuan

Publications and source records attributed to Yu, Xiaojuan.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Comparison of Ce( iv )/Th( iv )-alkynyl complexes and observation of a trans -influence ligand series for Ce( iv )

Organometallic cerium(iv) complexes have been challenging to isolate and characterize due to the strongly oxidizing nature of the cerium(iv) cation. Herein, we report two cerium(iv) alkynyl complexes, [Ce(TriNOx)(C[triple bond, length as m-dash]C-SiMe3)] (1-CeTMS) and [Ce(TriNOx)(C[triple bond, length as m-dash]C-Ph)] (1-CePh) (TriNOx3- = tris(2-tert-butylhydroxylaminato)benzylamine), that include terminal alkyne moieties. The isostructural thorium analogue [Th(TriNOx)(C[triple bond, length as m-dash]C-SiMe3)] (1-ThTMS) was also synthesized and compared with 1-CeTMS in bond distance, 13C-NMR spectra, vibrational spectra and electronic structure. The Ce-C bond distances were 2.501(3) Å for 1-CePh and 2.513(5) Å for 1-CeTMS on the shorter end of the few reported CeIV-C single bonds (2.478(3)-2.705(2) Å), possibly indicating significant Ce 5d- and 4f-orbital involvement. 13C-NMR spectroscopy was also consistent with Ce-C covalency, with significantly deshielded resonances ranging from 185-213 ppm. Such 13C-NMR shifts demonstrate a strong influence from spin-orbit coupling (SOC) effects, corroborated by computational studies. Raman analysis showed ν C[triple bond, length as m-dash]C stretching frequencies of 2000 cm-1 (1-CeTMS) and 2052 cm-1 (1-CePh), indicating the cerium(iv)-alkynyl interaction, compared to the parent HC[triple bond, length as m-dash]CPh (IR = 2105 cm-1 and Raman = 2104 cm-1). L3-edge X-ray absorption measurements revealed a predominant Ce(iv) electronic configuration, and magnetic measurements revealed temperature-independent paramagnetism. Electrochemical studies similarly revealed the electron donating ability of the alkynyl ligands, stronger than either fluoride or imido ligands for the Ce(iv)(TriNOx)-framework, with a cerium(iv/iii) reduction potential of E pc = -1.58 to -1.66 V vs. Fc/Fc+. Evidence for a trans-influence has been observed by evaluating a series including previously reported [CeIV(TriNOx)X]+/0 complexes with axial ligands X = THF, I-, Br-, Cl-, F-, -C[triple bond, length as m-dash]C-Ph, -C[triple bond, length as m-dash]C-SiMe3, -NH(3,5-(CF3)2-Ar), -OSiPh3, -N(M(L))(3,5-(CF3)2-Ar) [M(L) = Li(TMEDA), K(DME)2 or Cs(2,2,2-crypt)]. These data stand in contrast with previous reports of an inverse trans-influence at cerium(iv) and point to differences in involvement of cerium 4f- versus 5d-orbitals in the electronic structures of the complexes.

Yang, Qiaomu↗
DOE OSTI2025

4f-orbital covalency enables a single-crystal-to-single-crystal ring-opening isomerization in a CeIV–cyclopropenyl complex

Metal–ligand bonding interactions for f-element compounds are typically highly polarized with only minor covalent character. Whereas the 5d/6d orbitals are known to be chemically accessible for dative bonding, recent quantum chemical and spectroscopic analyses have indicated appreciable 4f/5f-orbital involvement in certain metal–ligand bonds. However, 4f-orbital covalency has not been compellingly linked to distinctive modes of chemical reactivity via rigorous comparative study and mechanistic investigation. Here a series of MIV–cyclopropenyl complexes (M = Ti, Zr, Ce, Hf, Th) are described, wherein the cerium congener exhibits a 4f-covalent Ce=Cα interaction, causing a ring-opening isomerization reaction through a single-crystal-to-single-crystal transformation. The results provide evidence for 4f-orbital covalency by demonstrating its expression in the reactivity of an f-element complex within an isostructural series of tetravalent d- and f-block metal complexes. They also provide new directions for the study of orbital covalency effects of molecular compounds in solid-state chemical transformations.

Vincenzini, Brett D↗
DOE OSTI2024

Facile Oxidation of Ce(III) to Ce(IV) Using Cu(I) Salts

The synthesis, luminescence, and electrochemical properties of the Ce(III) compound, [(C 5 Me 5 )2(2,6- i Pr 2 C 6 H 3 O)Ce(THF)], 1, were investigated. Based on the electrochemical data, treatment of 1 with CuX (X = Cl, Br, I) results in the formation of the corresponding Ce(IV) complexes, [(C 5 Me 5 ) 2 (2,6- i Pr 2 C 6 H 3 O)Ce(X)]. Each complex has been characterized using NMR, IR, and UV−vis spectroscopy as well as structurally determined using X-ray crystallography. Additionally, the treatment of [(C 5 Me 5 ) 2 (2,6- i Pr 2 C 6 H 3 O)Ce(Br)] with AgF results in the formation of the putative [(C 5 Me 5 ) 2 (2,6- i Pr 2 C 6 H 3 O)Ce(F)]. Furthermore, the electronic structure of these Ce(IV)−X complexes was investigated by bond analyses and the Ce(IV)−F moiety using quantum chemistry NMR calculations.

Aromatic compounds↗
DOE OSTI2024

Exploring Spin‐Orbit Effects in a [Cu 6 Tl] + Nanocluster Featuring an Uncommon Tl−H Interaction

Reaction of [CuH(PPh 3 )] 6 with 1 equiv. of Tl(OTf) results in formation of [Cu 6 TlH 6 (PPh 3 ) 6 ][OTf] ([1]OTf]), which can be isolated in good yields. Variable-temperature 1 H NMR spectroscopy, in combination with density functional theory (DFT) calculations, confirms the presence of a rare Tl−H orbital interaction. According to DFT, the 1 H chemical shift of the Tl-adjacent hydride ligands of [1] + includes 7.7 ppm of deshielding due to spin-orbit effects from the heavy Tl atom. In conclusion, this study provides valuable new insights into a rare class of metal hydrides, given that [1][OTf] is only the third isolable species reported to contain a Tl−H interaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Quantifying Actinide–Carbon Bond Covalency in a Uranyl–Aryl Complex Utilizing Solution 13 C NMR Spectroscopy

Reaction of [UO 2 Cl 2 (THF) 2 ] 2 with in situ generated LiFmes (FmesH = 1,3,5-(CF 3 ) 3 C 6 H 3 ) in Et 2 O resulted in the formation of the uranyl aryl complexes [Li(THF) 3 ][UO 2 (Fmes) 3 ] ([Li(THF) 3 ][1]) and [Li(Et 2 O) 3 (THF)][UO 2 (Fmes) 3 ] ([Li(Et 2 O) 3 (THF)][1]) in good to moderate yields after crystallization from hexanes and Et 2 O, respectively. Both complexes were characterized by X-ray crystallography and NMR spectroscopy. DFT calculations reveal that the C ispo resonance in [1] – exhibits a deshielding of 51 ppm from spin–orbit coupling effects originating at uranium, which indicates an appreciable covalency in the U–C bonding interaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Magnetic Properties of Tetravalent Pu in the Perovskites BaPuO 3 and SrPuO 3

BaPuO 3 and SrPuO 3 were synthesized, and their structures were refined in the orthorhombic space group Pbnm , a common distortion from the classic $Pm\bar{3}$m over barm cubic perovskite. Magnetic-susceptibility measurements, obtained as a function of temperature over the range of 1.8-320 K, exhibit temperature-dependent behavior, with evidence of long-range magnetic order at temperatures higher than their lanthanide and actinide analogues: BaPuO 3 below 164(1) K and SrPuO 3 below 76(1) K. Effective moments of 1.66(10)μ B for BaPuO 3 and 1.84(8)μ B for SrPuO 3 were obtained by fitting their paramagnetic susceptibilities using the Curie-Weiss law. Further, both are below the free-ion value of 2.68 μ B expected for a Pu 4+ 5 $\mid$ 4 ground level. Ab initio wave function calculations, performed at the relativistic complete active space level including spin-orbit coupling and with an embedded cluster approach that neglects interactions between Pu centers, were used to generate embedded-cluster Pu 4+ magnetic susceptibilities. The calculations agree well with experimental data at higher temperatures, providing evidence that a single-ion representation is sufficient to account for the observed paramagnetic behavior without the need to invoke charge transfer, disproportionation, strong covalent bonding, or other more complex electronic behavior.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

U–C Bond Insertion, Ring-Opening, and C–H Activation in a Uranium Bis(diisopropylamino)cyclopropenylidene (BAC) Adduct

Reaction of [U(NR 2 ) 3 ] (R = SiMe 3 ) with 1 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) in Et 2 O results in the formation of [(NR 2 ) 3 U(BAC)] (1), which can be isolated in modest yields. Thermolysis of 1 in C 6 D 6 at 85 °C results in the formation of the ring-opened U(IV) product, [(NR 2 ) 2 U{N(R)(SiMe 2 CH=C(NiPr 2 )C(NiPr 2 )=CH)}] (2), which can be isolated in low yields. Mechanistic studies suggest that the formation of 2 proceeds via dissociation of BAC from 1 to regenerate [U(NR 2 ) 3 ], which converts into [U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] at the elevated temperatures. BAC then inserts into the U–C bond of [U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] to generate a cyclopropenyl intermediate, which undergoes ring opening and C–H activation to afford the final product, 2. We hypothesize that the ring-opening generates an unobserved carbene intermediate. Notably, thermolysis of a 1:1 mixture of independently prepared [U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] and BAC results in clean formation of 2, providing strong support for the proposed mechanism. The formulations of both 1 and 2 were confirmed by X-ray crystallography. Finally, theoretical calculations indicate that the hypothesized uranium carbene intermediate features strong U–C bonding, potentially with some carbyne character in the electronic structure.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Overexpression of a gibberellin 20-oxidase gene in poplar xylem led to an increase in the size of nanocellulose fibrils and improved paper properties

Cellulose, the major component of secondary cell walls, is the most abundant renewable long-chain polymer on earth. Nanocellulose has become a prominent nano-reinforcement agent for polymer matrices in various industries. We report the generation of transgenic hybrid poplar overexpressing the Arabidopsis gibberellin 20-oxidase1 gene driven by a xylem-specific promoter to increase gibberellin (GA) biosynthesis in wood. X-ray diffraction (XRD) and sum frequency generation spectroscopic (SFG) analyses showed that cellulose in transgenic trees was less crystalline, but the crystal size was larger. The nanocellulose fibrils prepared from transgenic wood had an increased size compared to those from wild type. When such fibrils were used as a reinforcing agent in sheet paper preparation, the mechanical strength of the paper was significantly enhanced. Engineering the GA pathway can therefore affect nanocellulose properties, providing a new strategy for expanding nanocellulose applications.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

USc 2 C 2 and USc 2 NC Clusters with U–C Triple Bond Character Stabilized Inside Fullerene Cages

The chemistry of f-block metal–carbon multiple bonds is underdeveloped compared to well-established carbene complexes of the d-block transition metals. Herein, we report two new actinide-rare earth mixed metal carbides and nitrogen carbide cluster fullerenes, USc 2 C 2 @D 5h (6)-C 80 and USc 2 NC@D 5h (6)-C 80 , which contain U–C bonds with triple bond character and were successfully synthesized and characterized by mass spectrometry, UV–vis–NIR spectroscopy, Fourier transform infrared spectroscopy, single crystal X-ray diffraction, and DFT calculations. Crystallographic studies show that the two previously unreported clusters, USc 2 C 2 and USc 2 NC, are stabilized in the D 5h (6)-C 80 carbon cage and adopt unique trifoliate configurations, in which C 2 /NC units are almost vertically inserted into the plane defined by the U and two Sc atoms. Combined experimental and theoretical studies further reveal the bonding structure of USc 2 C 2 and USc 2 NC, which contain C=U(VI)=C and C=U(V)=N bonding motifs. The electronic structures of the two compounds are determined as U 6+ (Sc 2 ) 6+ (C 4– ) 2 @D 5h (6)-C 80 4– and U 5+ (Sc 2 ) 6+ (N) 3– (C) 4– @D 5h (6)-C 80 4– , respectively. Quantum-chemical studies confirm that the U–C bonds in both molecules show unprecedented multicenter triple-bond character. Furthermore, the discovery of this unique U–C multiple bond offers a deeper understanding of the fundamentals of uranium chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Synthesis and Characterization of a Bridging Cerium(IV) Nitride Complex

Complexes featuring lanthanide–ligand multiple bonds are rare and highly reactive. They are important synthetic targets to understand 4f/5d-bonding in comparison to d-block and actinide congeners. Herein, the isolation and characterization of a bridging cerium(IV)-nitride complex: [(TriNOx)Ce(Li 2 μ-N)Ce(TriNOx)][BAr F 4 ] is reported, the first example of a molecular cerium-nitride. The compound was isolated by deprotonating a monometallic cerium(IV)-ammonia complex: [Ce IV (NH 3 )(TriNOx)][BAr F 4 ]. The average Ce=N bond length of [(TriNOx)Ce(Li 2 μ-N)Ce(TriNOx)][BAr F 4 ] was 2.117(3) Å. Vibrational studies of the 15 N-isotopomer exhibited a shift of the Ce=N=Ce asymmetric stretch from ν = 644 cm –1 to 640 cm –1 , and X-ray spectroscopic studies confirm the +4 oxidation state of cerium. Furthermore, computational analyses showed strong involvement of the cerium 4f shell in bonding with overall 16% and 11% cerium weight in the σ- and π-bonds of the Ce=N=Ce fragment, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

ThC 2 @C 82 versus Th@C 84 : unexpected formation of triangular thorium carbide cluster inside fullerenes

Synthesis of the first thorium-containing clusterfullerenes, ThC 2 @C s (6)–C 82 and ThC 2 @C 2 (5)–C 82 , is reported. These two novel actinide fullerene compounds were characterized by mass spectrometry, single-crystal X-ray diffraction crystallography, UV–vis–NIR spectroscopy, and theoretical calculations. Crystallographic studies reveal that the encapsulated ThC 2 clusters in both C s (6)–C 82 and C 2 (5)–C 82 feature a novel bonding structure with one thorium metal center connected by a C≡C unit, forming an isosceles triangular configuration, which has not been hitherto observed for endohedral fullerenes or for solid phase thorium carbides. Electronic structure calculations assign a formal electronic structure of [Th 4+ (C 2 ) 2- ] 2+ @[C 82 ] 2- , with pronounced donation bonding from (C 2 ) 2- to Th 4+ , secondary backbonding from the fullerene to thorium and Th–C double bond character in both compounds. This work presents a new family of endohedral fullerenes, MC 2 @C 2n-2 , being unexpected isomers of MC 2n , and provides broader understanding of thorium bonding.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ring-opening of a thorium cyclopropenyl complex generates a transient thorium-bound carbene

The reaction of [Cp 3 ThCl] with in situ generated 1-lithium-3,3-diphenylcyclopropene results in the formation of [Cp 3 Th(3,3-diphenylcyclopropenyl)] (1), in good yields. Thermolysis of 1 results in isomerization to the ring-opened product, [Cp 3 Th(3-phenyl-1H-inden-1-yl)] (3) via a hypothesized carbene intermediate. This transformation represents a new mode of reactivity of 3,3-diphenylcyclopropene with the actinides, improving our ability to use this reagent as a carbene source. Here, a combined DFT and 13 C{ 1 H} NMR analysis of 1 shows a spin–orbit induced downfield shift at C α due to participation of the 5f orbitals in the Th–C bond.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Spin–Orbit Natural Transition Orbitals and Spin-Forbidden Transitions

Natural transition orbitals (NTOs) are in widespread use for visualizing and analyzing electronic transitions. Here, the present work introduces the analysis of formally spin-forbidden transitions with the help of complex-valued spin-orbit (SO) NTOs. The analysis specifically focuses on the components in such transitions that cause their intensity to be non-zero because of SO coupling. Transition properties such as transition dipole moments are partitioned into SO-NTO hole-particle pairs, such that contributions to the intensity from specific occupied and unoccupied orbitals are obtained. The method has been implemented within the restricted active space (RAS) self-consistent field wave function theory framework, with SO coupling treated by RAS state interaction. SO-NTOs have a broad range of potential applications, which is illustrated by the T 2 -S 1 state mixing in pyrazine, spin-forbidden vs. spin-allowed 4f–5d transitions in the Tb 3+ ion, and the phosphorescence of tris(2-phenylpyridine) iridium [Ir(ppy) 3 ].

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Covalency of Trivalent Actinide Ions with Different Donor Ligands: Do Density Functional and Multiconfigurational Wavefunction Calculations Corroborate the Observed “Breaks”?

A comprehensive ab initio study of periodic actinide–ligand bonding trends for trivalent actinides is performed. Relativistic density functional theory (DFT) and complete active-space (CAS) self-consistent field wavefunction calculations are used to dissect the chemical bonding in the [AnCl 6 ] 3– , [An(CN) 6 ] 3– , [An(NCS) 6 ] 3– , [An(S 2 PMe 2 ) 3 ], [An(DPA) 3 ] 3– , and [An(HOPO)] – series of actinide (An = U–Es) complexes. Except for some differences for the early actinide complexes with DPA, bond orders and excess 5f-shell populations from donation bonding show qualitatively similar trends in 5f n active-space CAS vs DFT calculations. The influence of spin–orbit coupling on donation bonding is small for the tested systems. Along the actinide series, chemically soft vs chemically harder ligands exhibit clear differences in bonding trends. There are pronounced changes in the 5f populations when moving from Pu to Am or Cm, which correlate with previously noted “breaks” in chemical trends. As a result, bonding involving 5f becomes very weak beyond Cm/Bk. We propose that Cm(III) is a borderline case among the trivalent actinides that can be meaningfully considered to be involved in ground-state 5f covalent bonding.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗