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Metal-Ligand Multiple Bonding in Thorium Phosphorus and Thorium Arsenic Complexes
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Activation of Water by Thorium Cation: A Guided Ion Beam and Quantum Chemical Study
The reaction of atomic thorium cations with deuterated water as a function of kinetic energy from thermal to 10 eV was studied using guided ion beam tandem mass spectrometry. At thermal energies, both ThO{sup +} + D{sub 2} and DThO{sup +} + D are formed in barrierless exothermic processes and reproduce results in the literature obtained using ion cyclotron resonance mass spectrometry. As the energy is increased, the branching ratio between these two channels changes such that the dominant product changes from ThO{sup +} to DThO{sup +} and back to ThO{sup +}, until ThD{sup +} + OD is energetically available and is the dominant product channel. To help understand these experimental results, a variety of theoretical approaches were tried and used to establish a potential energy surface, which compares well with previous theoretical studies. Utilizing the theoretical results, the kinetic energy dependent branching ratio between the ThO{sup +} + D{sub 2} and DThO{sup +} + D channels was calculated using both RRKM and phase space theory (PST). The results indicate that consideration of angular momentum conservation (as in PST) and spin-orbit corrected energies are needed to reproduce experimental results quantitatively. The PST modeling also provides relative energies for the two competing transition states that lead to the primary products, for which theory provides reasonable agreement. .
Third minima in thorium and uranium isotopes in a self-consistent theory
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Ab Initio Calculations on the Ground and Excited Electronic States of Thorium–Ammonia, Thorium–Aza-Crown, and Thorium–Crown Ether Complexes
Positively charged metal–ammonia complexes are known to host peripheral, diffuse electrons around their molecular skeleton. The resulting neutral species form materials known as expanded or liquid metals. Alkali, alkaline earth, and transition metals have been investigated previously in experimental and theoretical studies of both the gas and condensed phase. This work is the first ab initio exploration of an f-block metal–ammonia complex. The ground and excited states are calculated for Th0–3+ complexes with ammonia, crown ethers, and aza-crown ethers. For Th3+ complexes, the one valence electron Th populates the metal’s 6d or 7f orbitals. For Th0–2+, the additional electrons prefer occupation of the outer s- and p-type orbitals of the complex, except Th(NH3)10, which uniquely places all four electrons in outer orbitals of the complex. Although thorium coordinates up to ten ammonia ligands, octa-coordinated complexes are more stable. Crown ether complexes have a similar electronic spectrum to ammonia complexes, but excitations of electrons in the outer orbitals of the complex are higher in energy. Aza-crown ethers disfavor the orbitals perpendicular to the crowns, attributed to the N-H bonds pointing along the plane of the crowns.
Solid-state syntheses and single-crystal characterizations of three tetravalent thorium and uranium silicates
Colorless crystals of ThSiO{sub 4} (huttonite) (1) and (Ca{sub 0.5}Na{sub 0.5}){sub 2}NaThSi{sub 8}O{sub 20} (2) have been synthesized by the solid-state reactions of ThO{sub 2}, CaSiO{sub 3}, and Na{sub 2}WO{sub 4} at 1073 K. Green crystals of (Ca{sub 0.5}Na{sub 0.5}){sub 2}NaUSi{sub 8}O{sub 20} (3) have been synthesized by the solid-state reactions of UO{sub 2}, CaSiO{sub 3}, and Na{sub 2}WO{sub 4} at 1003 K. All three compounds have been characterized by single-crystal X-ray diffraction. Compound 1 adopts a monazite-type three-dimensional condensed structure, which is built from edge- and corner-shared ThO{sub 9} polyhedra and SiO{sub 4} tetrahedra. Compounds 2 and 3 are isostructural and they crystallize in a steacyite-type structure. The structure consists of discrete pseudocubic [Si{sub 8}O{sub 20}]{sup 8−} polyanions, which are connected by An{sup 4+} cations into a three-dimensional framework. Each An atom coordinates to eight monodentate [Si{sub 8}O{sub 20}]{sup 8−} moieties in a square antiprismatic geometry. Na{sup +} and Ca{sup 2+} ions reside in the void within the framework. Raman spectra of 1, 2, and 3 were collected on single crystal samples. 1 displays more complex vibrational bands than thorite. Raman spectra of 2 and 3 are analogous with most of vibrational bands located at almost the same regions. - Graphical abstract: A Raman spectrum and crystal structures of (Ca{sub 0.5}Na{sub 0.5}){sub 2}NaAnSi{sub 8}O{sub 20} (An=Th, U), which contain pseudocubic [Si{sub 8}O{sub 20}]{sup 8−} polyanions and eight-coordinate An{sup 4+} cations. - Highlights: • Single crystal growth of three tetravalent actinide silicates from melts. • Single-crystal structures and Raman spectra of (Ca{sub 0.5}Na{sub 0.5}){sub 2}NaAnSi{sub 8}O{sub 20} (An=Th, U). • First report of Raman spectrum of huttonite on single crystal samples.
Verification study of thorium cross section in MVP calculation of thorium based fuel core using experimental data
Considering the importance of thorium data and concerning about the accuracy of Th-232 cross section library, a series of experiments of thorium critical core carried out at KUCA facility of Kyoto Univ. Research Reactor Inst. have been analyzed. The core was composed of pure thorium plates and 93% enriched uranium plates, solid polyethylene moderator with hydro to U-235 ratio of 140 and Th-232 to U-235 ratio of 15.2. Calculations of the effective multiplication factor, control rod worth, reactivity worth of Th plates have been conducted by MVP code using JENDL-4.0 library [1]. At the experiment site, after achieving the critical state with 51 fuel rods inserted inside the reactor, the measurements of the reactivity worth of control rod and thorium sample are carried out. By comparing with the experimental data, the calculation overestimates the effective multiplication factor about 0.90%. Reactivity worth of the control rods evaluation using MVP is acceptable with the maximum discrepancy about the statistical error of the measured data. The calculated results agree to the measurement ones within the difference range of 3.1% for the reactivity worth of one Th plate. From this investigation, further experiments and research on Th-232 cross section library need to be conducted to provide more reliable data for thorium based fuel core design and safety calculation. (authors)
Probing the Electronic Structure of a Thorium Nitride Complex by Solid-State 15N NMR Spectroscopy
The solid-state 15N NMR powder spectra of the thorium nitride complex, [K(18-crown-6)(THF)2][(R2N)3Th(m-15N)(Th(NR2)3] ([K][1-15N], R = SiMe3), and the thorium amide complex, [Th(NR2)3(15NH2)] (2-15N) were recorded. The spectrum for [K][1-15N] represents the first reported solid-state 15N NMR data for an actinide nitride complex. The experimentally measured tensor spans are 847 ppm for [K][1-15N] and 237 ppm for 2-15N. Both shielding tensors exhibit a near-zero asymmetry parameter, which for [K][1-15N] is consistent with a local rotational symmetry of its 15N-labelled nitride ligand. For 2-15N, the lack of asymmetry can be rationalized by a quasi-free Th-NH2 bond rotation in the solid-state. DFT calculations overestimate the tensor span somewhat for [K][1-15N], but provide isotropic shifts in good agreement with both the solid-state and solution values for both complexes. Natural localized molecular orbital (NLMO) analyses of the nuclear shielding reveal that the larger tensor span in [K][1-15N] vs. 2-15N is primarily a consequence of more pronounced covalency of the N-Th bonds, and large spin-orbit coupling due to significant Th 5f orbital contribution to those bonds, impacting the principal components of the shielding tensor perpendicular to the Th-N-Th axis. Overall, our analysis confirms the involvement of the 5f orbitals in Th-N multiple bonds, and further demonstrates the value of solid-state NMR spectroscopy for interrogating actinide-ligand bonding.
Synthetic Control of Thorium Polyoxo-Clusters in Metal–Organic Frameworks toward New Thorium-Based Materials
Control over the assembly of thorium-based polyoxo-clusters remains a great challenge because of their quick olation and oxolation reactions. Here, we report the synthesis and isolation of two pure phase thorium polyoxocluster-based metal-organic frameworks (Th-MOFs), ThNU-1008 and Th-NU-1011. Crystal structures of these ThMOFs reveal two distinct 8-connected polyoxo-clusters: a hexanuclear cluster [Th 6 (μ 3 -O) 4 (OH) 4 (H 2 O) 6 (HCOO) 4 ] was observed in Th-NU-1008 and a tetranuclear cluster [Th 4 (μ 3 -) 2 (OH) 4 (DMF) 2 (H 2 O) 4 ] in Th-NU-1011 which has never been reported before among thorium species. In both Th-NU-1008 and Th-NU-1011, the tetratopic linker, 1,4-dibromo-2,3,5,6-tetrakis(4-carboxyphenyl) benzene, joins the clusters together, forming two three-periodic networks, each with csq topology. The Brunauer-Emmett-Teller (BET) surface areas calculated from the Ar isotherms are approximately 800 and 700 m 2 g -1 for Th-NU-1008 and Th-NU-1011, respectively. Because the linkers are oriented orthogonal to each other in the two respective MOFs, a 32 Å hexagonal channel is observed in Th-NU-1008 while a 15 Å channel is observed in Th-NU-1011. This work opens a new avenue to construct unexplored Th-MOF materials with targeted polyoxo-cluster structures.
Thorium chelators for targeted alpha therapy: Rapid chelation of thorium-226
We report one of the main challenges in targeted alpha therapy is assuring delivery of the α-particle dose to the targeted cells. Thus, it is critical to identify ligands for α-emitting radiometals that will form complexes that are very stable, both in vitro and in vivo. In this investigation, thorium-227 (t 1/2 = 18.70 days) chelation of ligands containing hydroxypyridinonate (HOPO) or picolinic acid (pa) moieties and the stability of the resultant complexes were studied. Chelation reactions were followed by reversed-phased HPLC and gamma spectroscopy. Studies revealed that high 227 Th chelation yields could be obtained within 2.5 h or less with ligands containing four Me-3,2-HOPO moieties, 1 (83%) and 2 (65%), and also with ligands containing pa moieties, H 4 octapa 3 (65%) and H 4 py4pa 6 (87%). No reaction occurred with H 4 neunpa-p-Bn-NO 2 4, and the chelation reaction with another pa ligand H 4 pypa 5 gave inconsistent yields with a very broad radio-HPLC peak. The ligands spermine-(Me-3,2-HOPO) 4 1, H 4 octapa 3, and H 4 py4pa 6 had high stability (i.e., 87% of 227 Th still bound to the ligand) in phosphate-buffered saline at room temperature over a 6-day period. Preliminary studies with ligand 6 demonstrated efficient chelation of thorium-226 (t 1/2 = 30.57 min) when heated to 80°C for 5 min.
Evaluation of ultra-low background materials for uranium and thorium using ICP-MS
An increasing number of physics experiments require low background materials for their construction. The presence of Uranium and Thorium and their progeny in these materials present a variety of unwanted background sources for these experiments. The sensitivity of the experiments continues to drive the necessary levels of detection ever lower as well. This requirement for greater sensitivity has rendered direct radioassay impractical in many cases requiring large quantities of material, frequently many kilograms, and prolonged counting times, often months. Other assay techniques have been employed such as Neutron Activation Analysis but this requires access to expensive facilities and instrumentation and can be further complicated and delayed by the formation of unwanted radionuclides. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is a useful tool and recent advancements have increased the sensitivity particularly in the elemental high mass range of U and Th. Unlike direct radioassay, ICP-MS is a destructive technique since it requires the sample to be in liquid form which is aspirated into a high temperature plasma. But it benefits in that it usually requires a very small sample, typically about a gram. This paper discusses how a variety of low background materials such as copper, polymers, and fused silica are made amenable to ICP-MS assay and how the arduous task of maintaining low backgrounds of U and Th is achieved.
X-ray Crystal Structure of Thorium Tetrahydroborate, Th(BH 4 ) 4 , and Computational Studies of An(BH 4 ) 4 (An = Th, U)
Here the crystal structure of Th(BH 4 ) 4 is described. Two of the four BH 4 – ions are terminal and tridentate (κ 3 ), whereas the other two bridge between neighboring Th IV centers in a κ 2 ,κ 2 (i.e., bis-bidentate) fashion. Thus, each thorium center is bound to six BH 4 – groups by 14 Th–H bonds. The six boron atoms describe a distorted octahedron in which the κ 3 -BH 4 – ions are mutually cis; the 14 ligating hydrogen atoms define a highly distorted bicapped hexagonal antiprism. The thorium centers are linked into a polymer consisting of interconnected helical chains wound about 4-fold screw axes. The structures of An(BH 4 ) 4 (An = Th, U) were also investigated by DFT. The geometries of [An(BH 4 ) 6 ] 2– , [An3(BH 4 ) 16 ] 4– , and [An 5 (BH 4 ) 26 ] 6– fragments of the polymeric structures were optimized at the B3LYP and/or PBE levels. Most calculated geometries are 14-coordinate and agree with the experimental structures, but isolated [Th(BH 4 ) 6 ] 2– units are predicted to feature 16-coordinate Th IV centers.
Formation of Methane versus Benzene in the Reactions of (C 5 Me 5 ) 2 Th(CH 3 ) 2 with [CH 3 PPh 3 ]X (X=Cl, Br, I) Yielding Thorium‐Carbene or Thorium‐Ylide Complexes
Abstract The reaction of (C 5 Me 5 ) 2 Th(CH 3 ) 2 with the phosphonium salts [CH 3 PPh 3 ]X (X=Cl, Br, I) was investigated. When X=Br and I, two equivalents of methane are liberated to afford (C 5 Me 5 ) 2 Th[CHPPh 3 ]X, rare terminal phosphorano‐stabilized carbenes with thorium. These complexes feature the shortest thorium–carbon bonds (≈2.30 Å) reported to date, and electronic structure calculations show some degree of multiple bonding. However, when X=Cl, only one equivalent of methane is lost with concomitant formation of benzene from an unstable phosphorus(V) intermediate, yielding (C 5 Me 5 ) 2 Th[κ 2 ‐(C,C′)‐(CH 2 )(CH 2 )PPh 2 ]Cl. Density functional theory (DFT) investigations of the reaction energy profiles for [CH 3 PPh 3 ]X, X=Cl and I showed that in the case of iodide, thermodynamics prevents the production of benzene and favors formation of the carbene.
Influence of Countercation Hydration Enthalpies on the Formation of Molecular Complexes: A Thorium–Nitrate Example
The influence of countercations (A(n+)) in directing the composition of monomeric metalligand (ML) complexes that precipitate from solution are often overlooked despite the wide usage of A(n+) in materials synthesis. Herein, we describe a correlation between the composition of ML complexes and A(+) hydration enthalpies found for two related series of thorium (Th)-nitrate molecular compounds obtained by evaporating acidic aqueous Th-nitrate solutions in the presence of A(+) counterions. Analyses of their chemical composition and solid-state structures demonstrate that A(+) not only affects the overall solid-state packing of the Th-nitrato complexes but also influences the composition of the Th-nitrato monomeric anions themselves. Trends in composition and structure are found to correlate with A(+) hydration enthalpies, such that the A(+) with smaller hydration enthalpies associate with less hydrated and more anionic Th-nitrato complexes. This perspective, broader than the general assumption of size and charge as the dominant influence of A(n+), opens a new avenue for the design and synthesis of targeted metal-ligand complexes.
Thorium amidates function as single-source molecular precursors for thorium dioxide
Here, we report the synthesis of four homoleptic thorium(IV) amidate complexes as single-source molecular precursors for thorium dioxide. Each can be sublimed at atmospheric pressure, with the substituents on the amidate ligands significantly impacting their volatility and thermal stability. These complexes decompose via alkene elimination to give ThO 2 without need for a secondary oxygen source. ThO 2 samples formed from pyrolysis of C-alkyl amidates were found to have higher purity and crystallinity than ThO 2 samples formed from C-aryl amidates.
Experimental and computational investigation of the bond energy of thorium dicarbonyl cation and theoretical elucidation of its isomerization mechanism to the thermodynamically most stable isomer, thorium oxide ketenylidene cation, OTh + CCO
Collision-induced dissociation (CID) of [Th,2C,2O] + with Xe is performed using a guided ion beam tandem mass spectrometer (GIBMS). The only products observed are ThCO + and Th + by sequential loss of CO ligands. The experimental findings and theoretical calculations support that the structure of [Th,2C,2O] + is the bent homoleptic thorium dicarbonyl cation, Th + (CO) 2 , having quartet spin, which is both thermodynamically and kinetically stable enough in the gas phase to be observed in our GIBMS instrument. Analysis of the kinetic energy-dependent cross sections for this CID reaction yields the first experimental determination of the bond dissociation energy (BDE) of (CO)Th + –CO at 0 K as 1.05 ± 0.09 eV. A theoretical BDE calculated at the CCSD(T) level with cc-pVXZ (X = T and Q) basis sets and a complete basis set (CBS) extrapolation is in very good agreement with the experimental result. Although the doublet spin bent thorium oxide ketenylidene cation, OTh + CCO, is calculated to be the most thermodynamically stable structure, it is not observed in our experiment where [Th,2C,2O] + is formed by association of Th + and CO in a direct current discharge flow tube (DC/FT) ion source. Potential energy profiles of both quartet and doublet spin are constructed to elucidate the isomerization mechanism of Th + (CO) 2 to OTh + CCO. The failure to observe OTh + CCO is attributed to a barrier associated with C–C bond formation, which makes OTh + CCO kinetically inaccessible under our experimental conditions. Furthermore, chemical bonding patterns in low-lying states of linear and bent Th + (CO) 2 and OTh + CCO isomers are also investigated.
Correction: Thorium amidates function as single-source molecular precursors for thorium dioxide
Correction for ‘Thorium amidates function as single-source molecular precursors for thorium dioxide’ by Mark D. Straub et al. , Chem. Commun. , 2021, 57 , 4954–4957, https://doi.org/10.1039/D1CC00867F.