Lewis base adducts of NpCl4.

Np(IV) Lewis base adducts were prepared by ligand substitution of NpCl4(DME)2. Using acetonitrile and pyridine, NpCl4(MeCN)4 (1) and NpCl4(pyr)4 (2) were isolated, respectively. Addition of t-butylbipyridine and triphenylphosphine oxide generated the respective Lewis base adducts, NpCl4(tBuBipy)2 (3) and NpCl4(OPPh3)2 (4). All species were fully characterized using spectroscopic and structural analyses.

Solution and solid-state characterization of rare silyluranium(III) complexes.

A uranium(III) silylate complex [K(DME)4][UI2{(Si(SiMe3)2SiMe2)2O}] (1) was stabilized by the addition of 18-crown-6, forming [K(18-crown-6)][UI2{(Si(SiMe3)2SiMe2)2O}] (1-crown). Crystallization under multiple conditions resulted in three distinct molecular structures. Compound 1-crown was further characterized in the solution state via1H, 13C, and 29Si NMR spectroscopy, and electronic absorption spectroscopy.

Metal-Ligand Redox Cooperativity in Cerium Amine-/Amido-Phenolate-Type Complexes.

The synthesis and characterization of two cerium complexes of redox-active amine/amido-phenolate-type ligands are reported. A tripodal framework comprising the tris(2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)amino-phenyl) amine (H6Clamp) proligand was synthesized for comparison of its cerium complex with a potassium-cerium heterobimetallic complex of the 4,6-di-tert-butyl-2-[(2,6-diisopropylphenyl)imino]quinone (dippap) proligand. Structural studies indicate differences in the cerium(III) cation coordination spheres, where CeIII(CH3CN)1.5(H3Clamp) (1-Ce(H3Clamp)) exhibits shorter Ce-O distances and longer Ce-N bond distances compared to the analogous distances in K3(THF)3CeIII(dippap)3 (2-Ce(ap)), due to the gross structural differences between the systems. Differences are also evident in the temperature-dependent magnetic properties, where smaller χT products were observed for 2-Ce(ap) compared to 1-Ce(H3Clamp). Solution electrochemical studies for the complexes were interpreted based on ligand- and metal-based oxidation events, and the cerium(III) oxidation of 2-Ce(ap) was observed to be more facile than that of 1-Ce(H3Clamp), behavior that was cautiously attributed to the rigidity of the encrypted 1-Ce(H3Clamp) complex compared to the heterobimetallic framework of 2-Ce(ap). These results contribute to the understanding of how ligand designs can promote facile redox cycling for cerium complexes of redox-active ligands, given the large contraction of cerium-ligand bonds upon oxidation.

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.

Synthesis of BaZrS3 and BaHfS3 Chalcogenide Perovskite Films Using Single-Phase Molecular Precursors at Moderate Temperatures.

Chalcogenide perovskites have garnered interest for applications in semiconductor devices due to their excellent predicted optoelectronic properties and stability. However, high synthesis temperatures have historically made these materials incompatible with the creation of photovoltaic devices. Here, we demonstrate the solution processed synthesis of luminescent BaZrS3 and BaHfS3 chalcogenide perovskite films using single-phase molecular precursors at sulfurization temperatures of 575 °C and sulfurization times as short as one hour. These molecular precursor inks were synthesized using known carbon disulfide insertion chemistry to create Group 4 metal dithiocarbamates, and this chemistry was extended to create species, such as barium dithiocarboxylates, that have never been reported before. These findings, with added future research, have the potential to yield fully solution processed thin films of chalcogenide perovskites for various optoelectronic applications.

Separation of Tellurium from Metal Chalcogenides through Mild Anhydrous Chlorination.

The separation of tellurium from cadmium telluride is examined using a unique combination of mild, anhydrous chlorination and complexation of the subsequent tellurium tetrachloride with 3,5-di-tert-butylcatecholate ligands (dtbc). The resulting tellurium complex, Te(dtbc)2 , is isolated in moderate yield and features a 103 to 104 reduction in cadmium content, as provided by XRF and ICP-MS analysis. Similar results were obtained from zinc telluride. A significant separation between Te, Se, and S was observed after treating a complex mixture of metal chalcogenides with this protocol. These three tunable steps can be applied for future applications of CdTe photovoltaic waste.

Actinide-Oxygen Multiple Bonds from Air: Synthesis and Characterization of a Thorium Oxo Supported by Redox-Active Ligands.

The first non-uranyl, f-element oxo complex synthesized from dioxygen in dry air is presented in this work. The synthesis was accomplished by treating the redox-active thorium amidophenolate complex, [Th(dippap)3][K(15-c-5)2]2 (1-ap crown), with dioxygen in dry air, forming a rare terminal thorium oxo, [O═Th(dippisq)2(dippap)][K(15-c-5)2]2 (2-oxo). Compound 1-ap crown was regenerated by treating 2-oxo with potassium graphite. X-ray crystallography of 2-oxo revealed a comparatively longer bond length for the thorium-oxygen double bond when compared to other thorium oxos. As such, several thorium-oxygen single bonds were synthesized for comparison, including Th(dippisq)2(OSiMe3)2(THF) (4-OSiMe3), Th(OSiMe3)4(bipy)2 (5-OSiMe3), and [Th(OH)2 (dippHap)4][K(15-c-5)2]2 (6-OH). Full spectroscopic and structural characterization of the complexes was performed via 1H NMR spectroscopy, X-ray crystallography, EPR spectroscopy, and electronic absorption spectroscopy as well as SQUID magnetometry, which all confirmed the electronic structure of these complexes.

Solution Deposition for Chalcogenide Perovskites: A Low-Temperature Route to BaMS3 Materials (M = Ti, Zr, Hf).

Chalcogenide perovskites, including BaZrS3, have been suggested as highly stable alternatives to halide perovskites. However, the synthesis of chalcogenide perovskites has proven to be a significant challenge, often relying on excessively high temperatures and methods that are incompatible with device integration. In this study, we developed a solution-based approach to the deposition of BaZrS3. This method utilizes a combination of a soluble barium thiolate and nanoparticulate zirconium hydride. Following solution-based deposition of the precursors and subsequent sulfurization, BaZrS3 can be obtained at temperatures as low as 500 °C. Furthermore, this method was extended to other chalcogenide perovskite (BaHfS3) and perovskite-related (BaTiS3) materials.

Isolation of uranium(III) primary phosphido complexes.

Low-valent uranium(III) primary phosphido complexes supported by hydrotris(3,5-dimethylpyrazolyl)borate (Tp*) were synthesized with phosphines of varying steric and electronic profiles. Compounds were characterized by multinuclear NMR spectroscopy (1H, 11B, 31P NMR), infrared spectroscopy, electronic absorption spectroscopy, X-ray crystallography, and quantum chemical calculations.

Synthesis of Non-Aqueous Neptunium(III) Halide Solvates from NpO2.

Two Np(III) halides, NpI3 (THF)4 and NpBr3 (THF)4 , have been prepared and isolated in high yields as described in this work. Starting with neptunia (NpO2 ), NpCl4 (DME)2 was first generated in an updated, higher yielding synthesis than what was previously reported by using HCl/HF. This material was then reduced with KC8 , followed by subsequent ligand exchange, to generate NpBr3 (THF)4 and NpI3 -(THF)4 . Full characterization by single-crystal X-ray crystallography, 1 H NMR spectroscopy and electronic absorption spectroscopy confirmed the molecular formulas and oxidation states. These trivalent materials are straightforward to synthesize and can be used as starting materials for non-aqueous Np(III) chemistry, obviating the need for rare and restricted Np metal and elemental halogens.

Elucidation of Thorium Redox-Active Ligand Complexes: Evidence for a Thorium-Tri(radical) Species.

A series of thorium(IV) complexes featuring the redox-active 4,6-di-tert-butyl-N-(2,6-di-isopropylphenyl)-o-iminobenzoquinone (dippiq) ligand family have been synthesized and characterized. The neutral iminoquinone ligand was used to generate Th(dippiq)Cl4(dme)2 (1-iq) and Th(dippiq)2Cl4 (2-iq), both of which show dative bonds between the thorium(IV) ion and the ligands. One electron reduction of the ligand forms the unique tris(iminosemiquinone) complex, Th(dippisq)3Cl (3-isq), which features a radical in each ligand. Further reduction furnishes the amidophenolate species, Th(dippap)3]K2(THF)2 (4-ap), which has the ligands in their dianionic form. Attempts to sequester the potassium ions with cryptand resulted in the [Th(dippap)3K][K(crypt)] (4-ap mono crypt) and [Th(dippap)3][K(crypt)]2 (4-ap crypt) species. A bis(amidophenolate) complex was accessed by incorporating bulky triphenylphosphine oxide (OPPh3) ligands to generate Th(dippap)2(OPPh)3 (5-ap). Spectroscopic and structural characterization of each derivative established the +4 oxidation state for thorium with redox chemistry occurring at the ligands rather than the thorium ion. The reported 3-isq complex is unprecedented as it is the first tri(radical) thorium complex with the highest reported magnetic moment for a thorium species as characterized by SQUID magnetometry.

Using Redox-Active Ligands to Generate Actinide Ligand Radical Species.

Using a redox-active dioxophenoxazine ligand, DOPO (DOPO = 2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazine-9-olate), a family of actinide (U, Th, Np, and Pu) and Hf tris(ligand) coordination compounds was synthesized. The full characterization of these species using 1H NMR spectroscopy, electronic absorption spectroscopy, SQUID magnetometry, and X-ray crystallography showed that these compounds are analogous and exist in the form M(DOPOq)2(DOPOsq), where two ligands are of the oxidized quinone form (DOPOq) and the third is of the reduced semiquinone (DOPOsq) form. The electronic structures of these complexes were further investigated using CASSCF calculations, which revealed electronic structures consistent with metals in the +4 formal oxidation state and one unpaired electron localized on one ligand in each complex. Furthermore, f orbitals of the early actinides show a sizable bonding overlap with the ligand 2p orbitals. Notably, this is the first example of a plutonium-ligand radical species and a rare example of magnetic data being recorded for a homogeneous plutonium coordination complex.

Synthesis and Characterization of Tellurium Catecholates and Their N-Oxide Adducts.

Tellurium catecholate complexes were investigated to probe the redox chemistry of tellurium, whose oxidation state can span from -2 to +6. Treating TeO2 with catechols resulted in tellurium coordination complexes in high yields within minutes to hours at room temperature or with extended heating, depending on the ligand substituents, giving Te(IV) complexes of the form Te(C)2, where C = 3,5-di-tert-butylcatecholate, o-catecholate, or tetrachlorocatecholate. The redox behavior of these complexes was investigated through addition of organic oxidants, giving nearly quantitative adducts of pyridine N-oxide or N-methylmorpholine N-oxide with each tellurium complex, the latter set leading to ligand oxidation upon heating. Each compound was characterized crystallographically and computationally, providing data consistent with a mostly electrostatic interaction and very little covalent character between the N-oxide and Te complex. The Te N-oxide bond orders are consistently lower than those with the catechol derivatives, as characterized with the Mayer, Gopinathan-Jug (G-J), and first Nalewajski-Mrozek (N-M1) bond indices. The tellurium lone pair is energetically buried by 1.93-2.81 eV, correlating with the observation that the ligands are more reactive than the tellurium center toward oxidation. This combined experimental and theoretical study finds structure-property relationships between ligand design and reactivity that will aid in future efforts for the recovery of tellurium.

Origin of Bond Elongation in a Uranium(IV) cis-Bis(imido) Complex.

The activation of U-N multiple bonds in an imido analogue of the uranyl ion is accomplished by using a system that is very electron-rich with sterically encumbering ligands. Treating the uranium(VI) trans-bis(imido) UI2(NDIPP)2(THF)3 (DIPP = 2,6-diisopropylphenyl and THF = tetrahydrofuran) with tert-butyl(dimethylsilyl)amide (NTSA) results in a reduction and rearrangement to form the uranium(IV) cis-bis(imido) [U(NDIPP)2(NTSA)2]K2 (1). Compound 1 features long U-N bonds, pointing toward substantial activation of the N═U═N unit, as determined by X-ray crystallography and 1H NMR, IR, and electronic absorption spectroscopies. Computational analyses show that uranium(IV)-imido bonds in 1 are significantly weakened multiple bonds due to polarization toward antibonding and nonbonding orbitals. Such geometric control has important effects on the electronic structures of these species, which could be useful in the recycling of spent nuclear fuels.

Ligand effects on electronic structure and bonding in U(III) coordination complexes: a combined MCD, EPR and computational study.

The trivalent oxidation state of uranium has been shown to undergo unique reactivity, from its ability to activate a variety of small molecules to its role in the catalytic reduction of ethene to ethane amongst others. Central to this unique reactivity and ability to rationally design ligands for isotope separation is the underlying uranium electronic structure. While electronic structure studies of U(iv), U(v), and U(vi) have been extensive, by comparison, analogous studies of more reduced oxidation states such as U(iii) remains underdeveloped. Herein we report a combined MCD and EPR spectroscopic approach along with density functional theory and multireference wavefunction calculations to elucidate the effects of ligand perturbation in three uranium(iii) Tp* complexes. Overall, the experimental and computational insight suggests that the change in ligand environment across this series of U(iii) complexes resulted in only minor perturbations in the uranium electronic structure. This combined approach was also used to redefine the electronic ground state of a U(iii) complex with a redox non-innocent Bipy- ligand. Overall, these studies demonstrate the efficacy of the combined experimental and theoretical approach towards evaluating electronic structure and bonding in U(iii) complexes and provide important insight into the challenges in altering ligand environments to modify bonding and reactivity in uranium coordination chemistry.

Conversion of Trivalent Uranium Anilido to Tetravalent Uranium Imido Species via Oxidative Deprotonation.

Two uranium(III) anilido complexes were synthesized, Tp*2U(NH-C6H4-p-terpyridine) (2-terpy) and Tp*2U(NH-C6H4-p-CH3) (2-ptol), where Tp* = hydrotris(3,5-dimethylpyrazolyl)borate, by protonation of Tp*2UBn (1-Bn; Bn = benzyl) with 4-[2,6-di(pyridin-2-yl)pyridin-4-yl]benzenamine or p-toluidine, respectively. Conversion to the respective uranium(IV) imido species was possible by oxidation and deprotonation, forming Tp*2U(N-C6H4-p-terpyridine) (3-terpy) and Tp*2U(N-C6H4-p-CH3) (3-ptol). These compounds were characterized by multinuclear NMR spectroscopy, IR spectroscopy, electronic absorption spectroscopy, and X-ray crystallography.

Insight into geometric preferences in uranium(VI) mixed tris(imido) systems.

Uranium tris(imido) species have been synthesized using different imido groups in the axial and equatorial positions by treating [(MesPDIMe)U(THF)]2 (1-THF), which is a uranium(iv) dimer that is supported by MesPDIMe tetraanions, with mixed organoazide solutions. While the origin of the geometric preference isn't clear, both steric and electronic factors are likely at play.

Evidence of Alpha Radiolysis in the Formation of a Californium Nitrate Complex.

Well-characterized complexes of transplutonium elements are scarce because of the experimental challenges of working with these elements and the rarity of the isotopes. This leads to a lack of structural and spectroscopic data needed to understand the nature of chemical bonds in these compounds. In this work, the synthesis of Cf(DOPOq )2 (NO3 )(py) (DOPOq =2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazin-9-olate; py=pyridine) is reported, in which the nitrate anion is hypothesized to form through the α-radiolysis-induced reaction of pyridine and/or the ligand. Computational analysis of the electronic structure of the complex reveals that the CfIII -ligand interactions are largely ionic.