Thorium Complexes Research Articles

Complexation of ThoriumIV with Fluorinated Heterocyclic β‐Diketones in Aqueous Hydrochloric Solutions

AbstractThe interaction of Thorium(IV) with a group of non‐symmetric CF3‐diketones has been studied by means of electronic absorption spectroscopy in HCl aqueous solutions at I=0.5 M (NaCl) and T=298 K. Six heterocyclic dicarbonyl ligands (2‐thenoyl‐trifluoroacetone, 2‐furoyl‐trifluoroacetone, 2‐selenophen‐trifluoroacetone, 2‐tellurophen‐trifluoroacetone, phenyl‐trifluoroacetone, and 2‐naphthyl‐trifluoroacetone) demonstrate the chelation activity toward ThIV in the acidic pH range. Obtained values of the “true” stability constants lie in the range 6.2–6.8 logarithmic units, respectively. A significant (10–15 nm) bathochromic shift between the maximum absorption wavelength of lanthanide and actinide monocomplexes has been detected. Observed spectral shift increases with the atomic number of substituted chalcogen atoms in the heterocyclic ring of the corresponding ligand: 10 nm for furan, 11 nm for thiophen, 14 nm for selenophen, and 15 nm for tellurophene rings. The complexation with Thorium occurs in an acidic media, where studied ligands do not interact with transition and rare earth metals. Spectral and pH shifts make studied ligands useful reagents for the detection and analytical determination of Thorium in the mixture with other metals without prior separation. Quantum‐chemical simulations (DFT and TD‐DFT) demonstrate that the nine‐ and deco‐coordinated structures of ThoriumIV complexes reproduce experimental values within reasonable errors.

Covalency-Driven Differences in the Hydrogenation Chemistry of Lanthanide- and Actinide-Based Frustrated Lewis Pairs.

The electronic organization of Frustrated Lewis Pairs (FLPs) allows them to activate strong bonds in mechanisms that are usually free of redox events at the Lewis acidic site. The unique 6d/5f manifold of uranium could serve as an interesting FLP acceptor site, but to date FLP-like catalysis with actinide ions is unknown. In this paper, the catalytic, FLP-like hydrogenation reactivity of trivalent uranium complexes is explored in the presence of base-stabilized silylenes. Comparison to isoelectronic, isostructural lanthanide and thorium complexes lends insight into the electronic factors governing dihydrogen activation. Mechanistic studies of the uranium- and lanthanide-catalyzed hydrogenations are presented, including discussion of likely intermediates. Computational modeling of the f-element complexes, combined with experimental comparison to p-block Lewis acids, elucidates the relevance of steric hindrance to productive reactivity with dihydrogen. Consideration of the complete experimental and theoretical evidence provides a clear picture of the electronic and steric factors governing dihydrogen activation by these FLPs.

Covalency parameters for nine-coordinated thorium acylpyrazolone complexes along with their synthesis and crystal features

This study discusses the synthesis and characterization of three thorium complexes with a general composition of [Th(L)4(EtOH)] demonstrated a nine-coordinated geometry in acylpyrazolone chemistry, a novel finding supported by single crystal evidence. A detailed analysis of complex [Th(L2)2(DMF)] was conducted, utilizing single-crystal X-ray diffraction data and Hirshfeld surface area analysis to investigate secondary interactions, exploring the planarity and bonding characteristics of the crystals. Covalency parameters such as the Nephelauxetic ratio, Sinha parameter, bonding parameter, and angular overlap parameter were calculated from electronic spectral data, revealing positive covalency and electron delocalization across the 5f orbital for all complexes. Notably, the presence of solvent bound to the 9th coordination site of the complex suggests potential changes in covalency across different solvents, thereby indirectly impacting chemical characteristics.

Thorium Complexation with Aliphatic and Aromatic Hydroxycarboxylates: A Combined Experimental and Theoretical Study.

Hydroxycarboxylic acids, viz., α-hydroxyisobutyric acid (HIBA) and mandelic acid (MA), have been widely employed as eluents for inner transition metal separation studies. Both extractants have identical functional groups (OH and COOH) with different side-chains. Despite their similarities in binding motifs, they show different retention behaviors for thorium and uranium in liquid chromatography. To understand the mechanism behind the trend, a detailed study on the aqueous phase interaction of thorium with both extractants is carried out by speciation, spectroscopy, and density functional theory-based calculations. Potentiometric titration experiments are carried out to reveal the stability and species formed. Electrospray ionization mass spectrometry is performed to identify the formation of different species by Th with both HIBA and MA. It is seen that for Th-HIBA and Th-MA, the dominating species are ML3 and ML4, respectively. A similar pattern observed in potentiometric speciation analysis supports the tendency of Th to form higher stoichiometric species with MA than with HIBA. The difference in the dominating species thus helps in explaining the reversal in the retention behavior of uranium and thorium in the reverse-phase liquid chromatographic separation. The results obtained are corroborated with extended X-ray absorption fine structure spectroscopic measurements and density functional theory (DFT) calculations.

Synthesis of phosphonic acid and amide functionalized core–shell magnetic composite and its mechanisms for synergistic adsorption of thorium from strongly acidic solution

To develop adsorbents for the preeminent extraction of thorium in strongly acidic solutions is very imperative, due to strong inorganic acids are frequently used in the fuel cycle of thorium. Herein, a robust core–shell magnetic nanocomposite Fe3O4@SiO2/P (MBA-VPA-AM) possessing phosphonic acid and amide was developed via distillation-precipitation copolymerization of N, N'-methylene diacrylamide (MBA), vinylphosphonic acid (VPA) with acrylamide (AM) employing Fe3O4 decorated by SiO2 (Fe3O4@SiO2) as magnetic core. Due to the synergistic effect of phosphonic acid and amide ligand, the sorbent could capture thorium from concentrated HNO3 media efficiently, and the maximum adsorption capacity (qmax) at 4 mol L−1 of HNO3 solution reached up to 232.5 mg g−1, superior to that of all magnetic sorbents reported previously. Furthermore, the sorbent displayed good selectivity towards thorium in the presence of competitive metal ions including La3+, Nd3+, and Ce3+. The excellent thorium sorption behavior in strong hydrogen nitrate solution was merely ascribed to the complexation of thorium with phosphonic acid ligand, and the amide ligand could not complex with thorium, evidenced by XPS, FT-IR and DFT method. However, the presence of amide ligand could enhance the hydrophilicity of the sorbent and the free movement degree of phosphonic acid ligand to a certain extent, both of which could help to promote the thorium sorption on the sorbent in strong HNO3 media. Besides, due to its core–shell structure and superparamagnetism, the sorbent not only exhibited excellent acidic resistance in strong acid medias, but could be magnetically recouped, which could avoid tedious centrifugation or filtration of traditional adsorbents. This work provides a novel strategy to develop magnetic sorbent for the preeminent entrapment of thorium from strong acid solutions.

Reduction of Thorium Tris(amido)arene Complexes: Reversible Double and Single C-C Couplings.

The reduction chemistry of thorium complexes is less explored compared to that of their uranium counterparts. Here, we report the synthesis, characterization, and reduction chemistry of two thorium(IV) complexes, (AdTPBN3)ThCl (1) and (DtbpTPBN3)ThCl(THF) (4) [RTPBN3 = 1,3,5-[2-(RN)C6H4]3C6H3; R = 1-adamantyl (Ad) or 3,5-di-tert-butylphenyl (Dtbp); THF = tetrahydrofuran], supported by tripodal tris(amido)arene ligands with different N-substituents. Reduction of 1 with excessive potassium in n-pentane yielded a double C-C coupling product, [(AdTPBN3)ThK(Et2O)2]2 (3), featuring a unique tetraanionic tricyclic core. On the other hand, reduction of 4 with 1 equiv of KC8 in hexanes/1,2-dimethoxyethane (DME) afforded a single C-C coupling product, [(DtbpTPBN3)Th(DME)]2 (5), with a dianionic bis(cyclohexadienyl) core. The solid- and solution-state structures of dinuclear thorium(IV) complexes 3 and 5 were established by X-ray crystallography and NMR spectroscopy. In addition, reactivity studies show that 3 and 5 can behave as thorium(II) and thorium(III) synthons to reduce organic halides. For instance, 3 and 5 are able to reduce 4 and 2 equiv of benzyl chloride, respectively, to regenerate 1 and 4 with concomitant formation of dibenzyl. Reversible C-C couplings under redox conditions provide an alternative approach to exploiting the potential of thorium arene complexes in redox chemistry.

Synthesis, Characterization, and Reduction of Thorium Pyridinediimine Complexes.

A family of thorium complexes featuring the redox-noninnocent pyridinediimine ligand MesPDIMe was synthesized, including (MesPDIMe)ThCl4 (1-Th), (MesPDIMe)ThCl3(THF) (2-Th), (MesPDIMe)ThCl2(THF)2 (3-Th) and [(MesPDIMe)Th(THF)]2 (5-Th) Full characterization of these species shows that these complexes feature MesPDIMe in four different oxidation states. The electronic structures of these complexes have been explored using 1H NMR and electronic absorption spectroscopies, X-ray crystallography, and SQUID magnetometry where appropriate.

Thermodynamics of Thorium(IV) complexes with N-methylethylenediamine-N,Nʹ,Nʹ-triacetate in aqueous solutions: Potentiometry and microcalorimetry

The thermodynamic parameters of the complexes of Th with N-methylethylenediamine-N,Nʹ,Nʹ-triacetic acid (MEDTA; denoted as H3L with three dissociable protons) were studied. Potentiometry and microcalorimetry were used to determine formation constants and enthalpies, respectively. Thermodynamic analysis revealed two successively formed complexes, namely, ThL+ and ThL22− (L3− denotes the totally deprotonated MEDTA). Results indicated that both complexation reactions were exothermic and driven by entropic force. The first stepwise reaction (Th4+ ​+ ​L3− = ThL+) was mainly driven by entropy with minimal effect on enthalpy change. The second stepwise reaction (ThL+ ​+ ​L3− = ThL22−) was more exothermic and showed less entropic change than the first stepwise reaction. The strong chelation of MEDTA would inhibit the hydrolysis of Th4+ and increase solubility.

Tetravalent Uranium and Thorium Complexes: Elucidating Disparate Reactivities of AnIVCl2 (An = U, Th) Supported by a Pyridine-Decorated Dianionic Ligand.

Although synthesis, reactivity, and bonding of U(IV) and Th(IV) complexes have been extensively studied, direct comparison of fully analogous compounds is rare. Herein, we report corresponding complexes 1-U and 1-Th, in which U(IV) and Th(IV) are supported by the tetradentate pyridine-decorated dianionic ligand N2NN' (1,1,1-trimethyl-N-(2-(((pyridin-2-ylmethyl)(2-((trimethylsilyl)amino)benzyl)amino)methyl)phenyl)silanamine). Although 1-U and 1-Th are structurally very similar, they display disparate reactivities with TMS3SiK (tris(trimethylsilyl)silylpotassium). The reaction of (N2NN')UCl2 (1-U) and 1 equiv of TMS3SiK in THF unexpectedly formed [Cl(N2NN')U]2O (2-U) featuring an unusual bent U-O-U moiety. In contrast, a salt elimination reaction between (N2NN')ThCl2 (1-Th) and 1 equiv of TMS3SiK led to thorium complex 2-Th, in which the pyridyl group has undergone a 1,4-addition nucleophilic attack. Complex 2-Th serves as a synthon for preparing dimetallic bis-azide complex 3-Th by reaction with NaN3. The complexes were characterized by X-ray crystal diffraction, solution NMR, FT-IR, and elemental analysis. Computations of the formation mechanism of 2-U from 1-U suggest reduced U(III) as a key intermediate for promoting the cleavage of the C-O bonds of THF. The inaccessible nature of Th(III) as an intermediate oxidation state explains the very different reactivity of 1-Th versus 1-U. Given that reactants 1-U and 1-Th and products 2-U and 2-Th all comprise tetravalent actinides, this is an unusual case of very disparate reactivity despite no net change in the oxidation state. Complexes 2-U and 3-Th provide a basis for the synthesis of other dinuclear actinide complexes with novel reactivity and properties.

Selective Extraction of Thorium(IV) from Uranium and Rare Earth Elements Using Tetraphenylethane-1,2-diylbis(phosphoramidate).

Tetraphenylethane-1,2-diylbis(phosphoramidate) in conjugation with a room temperature ionic liquid in chloroform medium is reported for the first time in the liquid-liquid extraction of thorium (Th). The extracted Th(IV) is collected as a white solid in the organic medium, thereby facilitating its easy separation. A high distribution ratio (D) of (12.4 ± 0.1) × 103 in 2-8 mol L-1 acidity range and high decontamination factors (α) of Th(IV) from uranium, lanthanides, and a number of transition elements makes this extraction process versatile and selective. A number of experimental investigations in synergism with extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) studies are interpreted to confirm the structure of the chelated complex. A 1:2 metal/ligand complex in which the two oxygen and two nitrogen atoms of each bis(phosphoramidate) molecule satisfying the eight coordination sites of Th(IV) is found to be formed. The extracted white solid thorium complex is easily converted to ThO2 after washing and heating at 1300 °C under O2 atmosphere. This work is expected to find direct application in the thorium fuel cycle, especially in the mining process of thorium from its ores and in the separation of fissile 233U from fertile 232Th in irradiated fuel.

Structural and spectroscopic characterization of thorium pyrasal complexes

To explore the coordination chemistry of thorium, the most abundant radioactive element on earth, we examine the synthesis and characterization of two Th (IV)-pyrasal complexes, L1 “pyrasal” ((2,2'-((1E,1'E)-(pyrazine-2,3-diylbis(azaneylylidene))bis(methaneylylidene))diphenol), and L2 “naphthylpyrasal” (1,1'-((1E,1'E)-(pyrazine-2,3-diylbis(azaneylylidene))bis(methaneylylidene))bis(naphthalen-2-ol). These complexes demonstrate little or no fluorescence when compared to similar naphthylsalophen thorium complexes previously published. Each complex was synthesized and characterized by IR, NMR (1H), and mass spectrometry. The photometric properties of the complexes were characterized using UV–Vis and fluorescence spectroscopy and their solid-state molecular structures were established by single-crystal X-ray crystallography. The electron-withdrawing effects of the pyrazine ring creates changes in the thorium coordination environment resulting in a secondary solid-state extended structure that minimizes the pi-pi stacking. This subsequently causes an overall decrease in the intensity of fluorescence demonstrated previously in by naphthylsalophen thorium complexes.

The interplay of d and f orbitals in the chemistry of the early actinides: High spin versus low spin

Early actinides lie at the borderline between d- and f-block elements. Here we describe the coordination capabilities of thorium featuring characteristics from both blocks. Thus analysis of the recently synthesized monoanion [Cp3Th]− indicates a diamagnetic singlet d2f0 ground state for the central thorium(II) atom. In this species the trigonal (Cp3)3− ligand system provides a strong ligand field for the thorium d-orbitals accounting for the low spin of this system. This differs from the high spin unambiguous f-element analogue, [Cp3U]−. For the d0f0 thorium(IV) complex (η8-C8H8)2Th both π→d and π→f forward bonding is observed, where a comparison with (η8-C8H8)2U is given. This indicates that a borderline element such as thorium can exhibit either d- or f-block character according to the surrounding ligand field.

Electronic Structure Studies and Photophysics of Luminescent Th(IV) Anilido and Imido Complexes

A series of thorium anilide compounds [ThNHArR(TriNOx)] (R = para-OCH3 (1-ArOMe), para-H (1-ArH), para-Cl (1-ArCl), para-CF3 (1-Ar4-CF3), TriNOx3- = tris(2-tert-butylhydroxylaminato)benzylamine), and their corresponding imido compounds [Li(DME)][Th═NArR(TriNOx)] (2-ArR) as well as the alkyl congeners [ThNHAd(TriNOx)] (1-Ad) and [Li(DME)][Th═NAd(TriNOx)] (2-Ad), have been prepared. The para-substituents on the arylimido moiety were introduced for systematic variation of their electron-donating and withdrawing abilities, changes that were evident in measurements of the 13C{1H} NMR chemical shifts of the ipso-C atom of the ArR moiety. Room temperature, solution-state luminescence of the four new thorium imido compounds, along with the previously reported [Li(THF)2][Th═NAr3,5-CF3(TriNOx)] (2-Ar3,5-CF3) and [Li(THF)(Et2O)][Ce═NAr3,5-CF3(TriNOx)] (3-Ar3,5-CF3) have been described. Among these complexes, 2-Ar3,5-CF3 demonstrated the most intense luminescence feature with excitation at 398 nm and emission at 453 nm. The luminescence measurements, together with a time-dependent density functional theory (TD-DFT) study, helped uncover an intra-ligand n → π* transition that was assigned as the origin of the bright blue luminescence; 3-Ar3,5-CF3 has an 1.2 eV redshift in excitation energy compared with its proligand. The weak luminescence of other derivatives (2-ArR and 3-Ar3,5-CF3) was attributed to non-radiative decay from low-lying excited states originating from inter-ligand transitions (2-ArR) or ligand-to-metal charge transfer bands (3-Ar3,5-CF3). Overall, the results expand the range of the thorium imido organometallic compounds and demonstrate that thorium(IV) complexes can support strong ligand luminescence. The results also demonstrate the utility of applying a Th(IV) center for tuning the n → π* luminescence energy and intensity of an associated imido moiety.

Synthesis, characterization, photophysical, and magnetic studies of mixed‐ligand thorium(IV) complex of 2‐hydroxy‐5‐sulfobenzoic acid and 1,10‐phenanthroline

The new eight-coordinate complex of thorium(IV) was synthesized by the reaction of Th(NO3)4.4H2O with 1,10-phenanthroline(phen) and 2-hydroxy-5-sulfobenzoic acid (SSA) by coprecipitation method. An environment friendly chelating agent sulfosalicylic acid (SSA) having oxygen donor atoms, phen with delocalized π-electron system, and N-donor atoms were used during the preparation of complex. The complex was characterized on the basis of elemental analysis, Fourier transform infrared (FTIR) spectroscopy, UV–Vis spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The complex was further assessed for structural and magnetic behavior. The results revealed that the complex has been completely formed as eight coordinated, amorphous in nature, diamagnetic, air stable, granular surface morphology, and water soluble. Furthermore, the FTIR studies of the complex demonstrate coordination of Th(IV) with SSA, phen, and nitrate by the participation of oxygen and nitrogen atoms. According to the results obtained, the changes in the IR spectra indicate that the coordination takes place via nitrogen atoms of phen, oxygen atoms of SSA and nitrate ions, the former two acting as bidentate ligands while as the latter coordinate via the monodentate mode. Moreover, from the emission spectra, the complex also showed emission atom excitation wavelength of 290 nm.

Bonding and Reactivity in Terminal versus Bridging Arenide Complexes of Thorium Acting as ThII Synthons

AbstractThorium redox chemistry is extremely scarce due to the high stability of ThIV. Here we report two unique examples of thorium arenide complexes prepared by reduction of a ThIV‐siloxide complex in presence of naphthalene, the mononuclear arenide complex [K(OSi(OtBu)3)3Th(η6‐C10H8)] (1) and the inverse‐sandwich complex [K(OSi(OtBu)3)3Th]2(μ‐η6,η6‐C10H8)] (2). The electrons stored in these complexes allow the reduction of a broad range of substrates (N2O, AdN3, CO2, HBBN). Higher reactivity was found for the complex 1 which reacts with the diazoolefin IDipp=CN2 to yield the unexpected ThIV amidoalkynyl complex 5 via a terminal N‐heterocyclic vinylidene intermediate. This work showed that arenides can act as convenient redox‐active ligands for implementing thorium‐ligand cooperative multielectron transfer and that the reactivity can be tuned by the arenide binding mode.

Catalytic regeneration of metal-hydrides from their corresponding metal-alkoxides via the hydroboration of carbonates to obtain methanol and diols.

Thorium complexes decorated with 5-, 6-, and 7-membered N-heterocyclic iminato ligands containing mesityl wingtip substitutions have been synthesized and fully characterized. These complexes were found to be efficient in the hydroboration of cyclic and linear organic carbonates with HBpin or 9-BBN promoting their decarbonylation and producing the corresponding boronated diols and methanol. In addition, the hydroboration of CO2 breaks the molecule into "CO" and "O" forming boronated methanol and pinBOBpin. Moreover, the demanding depolymerization of polycarbonates to the corresponding boronated diols and methanol opens the possibility of recycling polymers for energy sources. Increasing the core ring size of the ligands allows a better performance of the complexes. The reaction proceeds with high yields under mild reaction conditions, with low catalyst loading, and short reaction times, and shows a broad applicability scope. The reaction is achieved via the recycling of a high-energy Th-H moiety from a stable Th-OR motif. Experimental evidence and DFT calculations corroborate the formation of the thorium hydride species and the reduction of the carbonate with HBpin to the corresponding Bpin-protected alcohols and H3COBpin through the formate and acetal intermediates.

Experimental and theoretical insight into biphasic extractive mass transfer of thorium into ionic liquid phase using chloroamide ligands

2-chloro-N-methyl-N-phenylacetamide (L1) and 2-chloro-N-(3-methylpyridin-2-yl)acetamide (L2) have been explored for the efficient separation of tetravalent thorium ion (Th4+) from aqueous phase to the ionic liquid phase. Due to the positive inductive effect (+I effect) of alkyl group, the electron density on N in L1 was more compared to that in L2; as evidenced from the distribution ratio values of Th4+ (DThL1 ∼ 180 and DThL2 ∼ 107 at 1 M HNO3). The extraction proceeds via 'cation exchange' mechanism involving 1:3 metal ligand stoichiometry for both the ligands. Each thorium complex was associated with three nitrate ions; thus, making the complex uni-positive in nature. The charge compensation during extractive mass transfer was done by dissolution of one hexyl methylimidazolium cation from ionic liquid phase to aqueous phase. The mass transfer followed slower kinetics, which was attributed to the high viscosity coefficient of ionic liquid. The extraction processes were spontaneous (ΔGL1300K ∼ −16.31 kJ mol−1 and ΔGL2300K ∼ −15.75 kJ mol−1) and endothermic in nature with a significant enhancement in the entropy (ΔSL1300K ∼ 107.98 kJ mol- 1K−1 and ΔSL2300K ∼ 103.54 kJ mol-1K−1). Density functional theory (DFT) calculation revealed the presence of two types of Th-O bond associated with nitrate ion and ligands (Th-OnitrateL1 ∼ 2.511A˚, Th-OligandL1 ∼ 2.411A˚, Th-OnitrateL2 ∼ 2.518A˚ and Th-OligandL2 ∼ 2.422A˚. The higher extraction efficiency of Th4+ for L1 was corroborated from the negative ΔG values calculated for L1 in gas and ionic liquid phase compared to that for L2.

Separation and recovery of Th(IV) from rare earth and other cation solutions using pH-responsive ionic liquids at high acidity condition of 1 M HNO3

Thorium has received widespread attention as a potential nuclear fuel alternative, but it is still a difficult task to extract thorium from strong HNO3 media. Meanwhile, stimulus-responsive materials have received extensive attention in the field of separation due to their special properties. Herein, we designed and synthesized a new type of stimulus responsive ionic liquid (SIL) material and applied it to solve the problem of low thorium extraction efficiency in strong HNO3 media. By utilizing the pH-response performance of SIL, a SIL and thorium complex (SILTh) is found to self-assemble and precipitate out from solution upon simple adjustment of the pH. We found that the extraction efficiency of thorium can reach 99.6% under high acidity and that it can be even higher than 98.8% when the temperature changes. Under experimental conditions, SIL showed a record-breaking maximum extraction capacity for thorium (644.2 mg g−1) with an excellent selectivity for thorium over lanthanide and transition metal in 1 M HNO3 (S>1400). Studies reveal that PO is complexed with thorium, which also explains the high adsorption capacity and selectivity of SIL for thorium under high acidity. Moreover, the pH-response characteristics of SIL are reversible. The pH-responsive SIL material and the extracted thorium can be recovered, and SIL also shows an excellent recycling ability over five cycles, with extraction and recovery efficiencies for Th(IV) of 98.0% and 98.7%, respectively within five cycles, indicating that the material has a good recycling ability. This study explores the possibility of using pH-responsive materials to recover thorium in strong HNO3 media, and provides ideas for the design and synthesis of new materials for the recovery of thorium.

Optical Properties of the Suwannee River Fulvic Acid Complexation with Thorium Using 3D Fluorescence Spectroscopy

The relationship between the complexation amount of thorium (Th) and Suwannee River fulvic acid (SRFA) and the changes in Th concentration and pH were studied using differential spectroscopy and 3D excitation-emission matrix fluorescence spectroscopy (3D EEM). Experiments were performed at different Th concentrations and pH values. In the differential spectra at different concentrations, four bands of aromatic components appeared, and thorium was complexed with the carboxyl groups in SRFA. The 3D EEM spectra showed a fulvic acid-like fluorescence region, a visible-light fulvic acid region, and the blueshift phenomenon. The fluorescence intensity decreased with increasing thorium concentration and increased with increasing pH. The results showed that the amount of complexation of thorium and SRFA increased with increasing thorium concentration, and high pH was not conducive to the complexation of thorium and SRFA.

Cation Complexes of Uranium and Thorium with Cyclooctatetraene: Photochemistry and Decomposition Products.

Ion-molecule complexes of uranium or thorium singly-charged positive ions bound to cyclooctatetraene (COT), i.e., M+(COT)1,2, are produced by laser ablation and studied with UV laser photodissociation. The ions are selected by mass and excited at 355 or 532 nm, and the ionized dissociation products are detected using a reflectron time-of-flight mass spectrometer. The abundant fragments M+(C6H6), M+(C4H4), and M+(C2H2) occur for complexes of both metals, whereas the M+(C4H2), M+(C3H3), and M+(C5H5) fragments are prominent for uranium complexes but not for thorium. Additional experiments investigate the dissociation of M+(benzene)1,2 ions which may be intermediates in the fragmentation of the COT ions. The experiments are complemented by computational quantum chemistry to investigate the structures and energetics of fragment ions. Various cation-π and metallacycle structures are indicated for different fragment ions. The metal ion-ligand bond energies for corresponding complex ions are systematically greater for the thorium species. The computed thermochemistry makes it possible to explain the mechanistic details of the photochemical fragmentation processes and to reveal new actinide organometallic structures.