Structural, Spectroscopic, and Computational Analysis of Halogen- and Hydrogen-Bonding Effects within a Series of Uranyl Fluorides with 4-Halopyridinium

Reported are the syntheses and characterization of five compounds containing one-dimensional uranyl fluoride chains charge balanced by 4-X-pyridinium (X = H, F, Cl, Br, I) cations. Structural analysis reveals molecular assembly via noncovalent interactions in the second coordination sphere with the X···Oyl interaction distances ranging from 2.987(7) to 3.142(3) Å, all of which are less than or close to the sum of the van der Waals radii. These interactions were probed via luminescence and Raman spectroscopy, where the latter indicates slight differences in the U═O symmetric stretches as a consequence of U═O in-phase and out-of-phase Raman-active stretches. The decrease in the X···Oyl sum of the van der Waals overlap between comparable compounds within the series manifests as a red-shifting trend among the Raman symmetric stretches. Computational density functional theory (DFT)-based frequency, electrostatic potential surfaces (ESPs), and natural bonding orbital (NBO) methods support the observed Raman spectroscopic features and provide a comprehensive rationale for assembly.

Three-Dimensional Noncovalent Interaction Network within [NpO2Cl4]2- Coordination Compounds: Influence on Thermochemical and Vibrational Properties

Noncovalent interactions (NCIs) can influence the stability and chemical properties of pentavalent and hexavalent actinyl (AnO2+/2+) compounds. In this work, the impact of NCIs (actinyl-hydrogen and actinyl-cation interactions) on the enthalpy of formation (ΔHf) and vibrational features was evaluated using Np(VI) tetrachloro compounds as the model system. We calculated the ΔHf values of these solid-state compounds through density functional theory+ thermodynamics (DFT+ T) and validated the results against experimental ΔHf values obtained through isothermal acid calorimetry. Three structural descriptors were evaluated to develop predictors for ΔHf, finding a strong link between ΔHf and hydrogen bond energy (EHtotal) for neptunyl-hydrogen interactions and total electrostatic attraction energy (Eelectrostatictotal) for neptunyl-cation interactions. Finally, we used Raman spectroscopy together with bond order analysis to probe Np=O bond perturbation due to NCIs. Our results showed a strong correlation between the degree of NCIs by axial oxygen and red-shifting of Np=O symmetrical stretch (ν1) wavenumbers and quantitatively demonstrated that NCIs can weaken the Np=O bond. These properties were then compared to those of related U(VI) and Np(V) phases to evaluate the effects of subtle differences in the NCIs and overall properties. In general, the outcomes of our study demonstrated the role of NCIs in stabilizing actinyl solid materials, which consequently governs their thermochemical behaviors and vibrational signatures.

Synthesis, Characterization, and Density Functional Theory Investigation of the Solid-State [UO2Cl4(H2O)]2- Complex

A significant number of solid-state [UO2Cl4]2- coordination compounds have been synthesized and structurally characterized. Yet, despite their purposive relative abundance in aqueous solutions, characterization of aquachlorouranium(VI) complexes remain rare. In the current study, a solid-state uranyl aqua chloro complex ((C4H12N2)2[UO2Cl4(H2O)]Cl2) was synthesized using piperazinium as a charge-balancing ligand, and the structure was determined using single-crystal X-ray diffraction. Using periodic density functional theory, the electronic structure of the [UO2Cl4(H2O)]2- complex was compared to [UO2Cl4]2- to uncover the strengthening of the U═O bond in [UO2Cl4(H2O)]2-. Changes in the strength of the U═O bond were validated further with Raman and IR spectroscopy, where uranyl symmetrical (ν1) and asymmetrical (ν3) stretches were blue-shifted compared to the reference [UO2Cl4]2- complex. Furthermore, the formation energy of the solid-state (C4H12N2)2[UO2Cl4(H2O)]Cl2 complex was calculated to be -287.60 ± 1.75 kJ mol-1 using isothermal acid calorimetry. The demonstrated higher stability relative to the related [UO2Cl4]2- complex was related to the relative stoichiometry of the counterions.

Guiding Principles for the Rational Design of Hybrid Materials: Use of DFT Methodology for Evaluating Non-Covalent Interactions in a Uranyl Tetrahalide Model System

Together with the synthesis and experimental characterization of 14 hybrid materials containing [UO2 X4 ]2- (X=Cl- and Br- ) and organic cations, we report on novel methods for determining correlation trends in their formation enthalpy (ΔHf ) and observed vibrational signatures. ΔHf values were analyzed through isothermal acid calorimetry and a Density Functional Theory+Thermodynamics (DFT+T) approach with results showing good agreement between theory and experiment. Three factors (packing efficiency, cation protonation enthalpy, and hydrogen bonding energy [E H , norm total ${{E}_{H,{\rm { norm}}}^{{\rm { total}}}}$ ]) were assessed as descriptors for trends in ΔHf . Results demonstrated a strong correlation betweenE H , norm total ${E_{{\rm{H}},{\rm{norm}}}^{{\rm{total}}} }$ and ΔHf , highlighting the importance of hydrogen bonding networks in determining the relative stability of solid-state hybrid materials. Lastly, we investigate how hydrogen bonding networks affect the vibrational characteristics of uranyl solid-state materials using experimental Raman and IR spectroscopy and theoretical bond orders and find that hydrogen bonding can red-shift U≡O stretching modes. Overall, the tightly integrated experimental and theoretical studies presented here bridge the trends in macroscopic thermodynamic energies and spectroscopic features with molecular-level details of the geometry and electronic structure. This modeling framework forms a basis for exploring 3D hydrogen bonding as a tunable design feature in the pursuit of supramolecular materials by rational design.

Yet another perspective on hole interactions, part II: lp-hole vs. lp-hole interactions

Most of the experimental and theoretical work in hole interactions (HIs) is mainly focused on exploiting the nature and characteristics of σ and π-holes. In this perspective, we focus our attention on understanding the origin and properties of lone-pair holes. These holes are present on an atom opposite to its lone-pair region. Utilizing some new and old examples, such as X₃N/P⋯F^- (X = F/Cl/Br/I), F-Cl/Br/I⋯H₃P⋯NCH and H₃B-NBr₃ along with other molecular systems, we explored to what extent these lp-holes participate in lp-hole interactions, if they participate at all.

Thermodynamic, Spectroscopic, and Structural Study on a Sodium Uranyl Tri-2-Methoxybenzoate Dodecahydrate Coordination Compound with Considerably Low Solubility in Acidic Conditions

A spontaneous crystallization of an uranium(VI)-organic coordination compound with sodium and 2-methoxybenzoate (2-mba) was observed in acidic solutions, and the solubility product, molecular vibrations, crystal structure, thermal stability, and emission properties of the atypically low-soluble U(VI) complex (Na[UO₂(2-mba)₃]·12H₂O(s)) were fully investigated for the first time. A long-term solubility experiment and speciation modeling gave a solubility product of log K_s,0 = -12.18 ± 0.02 (T = 25 °C and I = 0.1 M NaClO₄), and vibrational analyses confirmed the overall molecular structure of complex and the frequencies of characteristic stretching motions of uranyl moiety as well. The crystal quality of Na[UO₂(2-mba)₃]·12H₂O(s) was improved by a digestion method, and X-ray diffraction analysis of the single crystalline specimen verified that the newly studied uranyl-organic compound contains one-dimensional channels with a diameter of 20 Å along the [001] direction; the sodium and water molecules are arranged in the channel structures. In the coordination environment around uranyl, three aromatic carboxylates are symmetrically bound in the equatorial plane of uranyl coplanarily, and the unit [UO₂(2-mba)₃]^- complexes are further extended along the plane to form the layered-morphologies. The three-dimensional packing of [UO₂(2-mba)₃]^- anions is driven by the parallel-displaced π-stacking of aromatic rings with a centroid-centroid distance of 3.7 Å. Additional thermogravimetric analysis confirmed that the Na[UO₂(2-mba)₃]·12H₂O(s) is stable up to 250 °C, and dehydration and release of the organic ligand were subsequently observed beyond that temperature. Photoluminescence spectrum of the Na[UO₂(2-mba)₃]·12H₂O(s) clearly displayed the characteristic U(VI) emission, and a band spacing between the ground electronic states of U(VI) uranyl was evaluated to be 831 ± 14 cm^-1. Such detailed characterization of the unique Na[UO₂(2-mba)₃]·12H₂O(s) is advancing upon a systematic understanding of the structural effects of the aromatic model ligands on U(VI) complexation, with relevance to the environmental chemistry of U(VI) and crystal engineering for development of diverse uranyl-organic frameworks.

Influence of Metal Coordination on the Gas-Phase Chemistry of the Positional Isomers of Fluorobenzoate Complexes

The fragmentation behaviors of the o-, m-, and p-fluorobenzoate complexes of La³⁺, Ce³⁺, Fe³⁺, Cu²⁺, and UO₂²⁺ were investigated by electrospray ionization mass spectrometry, and the corresponding reaction mechanisms were explored by density functional theory (DFT) calculations. Fluoride transfer product La^IIIFCl₃^-/Ce^IIIFCl₃^- and decarboxylation product La^IIICl₃(C₆H₄F)^-/Ce^IIICl₃(C₆H₄F)^- were observed when the carboxylate precursors La^IIICl₃(C₆H₄FCO₂)^-/Ce^IIICl₃(C₆H₄FCO₂)^- were subjected to collision-induced dissociation. The variation in product ratios, which is not obvious in the meta and para cases, qualitatively follows the increasing overall energy barrier and reaction endothermicity of the two-step CO₂/C₆H₄ elimination mechanism, and this aligns with the increase in U-F distance in the ortho, meta, and para decarboxylation product isomers. In contrast, the mass spectra of Fe^IIICl₃(C₆H₄FCO₂)^-/Cu^IICl₂(C₆H₄FCO₂)^- are dominated by the reduction product FeCl₃^-/CuCl₂^- regardless of the fluorobenzoate isomer. DFT/B3LYP calculations show that the two-step CO₂/C₆H₄F elimination pathways are comparable in energy for all three positional isomers. It is energetically more favorable to give the reduction product than the fluoride transfer product, which is opposite to the lanthanum cases. Although the decarboxylation product was observed for all three U^VIO₂Cl₂(C₆H₄FCO₂)^- isomers, the ortho isomer behaves more similarly to La^IIICl₃(C₆H₄FCO₂)^-/Ce^IIICl₃(C₆H₄FCO₂)^- as evidenced by the formation of U^VIO₂FCl₂^-, and the appearance of U^VO₂Cl₂^- in the cases of the meta and para isomers indicates the similarity with Fe^IIICl₃(C₆H₄FCO₂)^-/Cu^IICl₂(C₆H₄FCO₂)^-. The shorter U-F distance in U^VIO₂Cl₂(o-C₆H₄F)^- causes the decrease in the fluoride transfer barrier and thus makes this process more favorable over o-C₆H₄F radical loss to give U^VO₂Cl₂^-.

Periodic Trends within Actinyl(VI) Nitrates and Their Structures, Vibrational Spectra, and Electronic Properties

A series of actinyl(VI) nitrate salts of the form MAnO₂(NO₃)₃, where M = NH₄⁺ K⁺, Rb⁺, Cs⁺, and Me₄N⁺ and AnO₂²⁺ = U, Np, Pu, and AnO₂(NO₃)₂(H₂O)₂·H₂O, and the uranyl tetranitrates M₂UO₂(NO₃)₄ have been synthesized from aqueous solution and their structures determined using single-crystal X-ray diffraction. Together, these complexes represent an isostructural series of actinide complexes among the salts crystallized with the same charge-compensating cation and have been studied using vibrational spectroscopy including Raman and Fourier-transform infrared. Periodic trends in both the structural properties of these complexes and their vibrational spectra are presented and discussed, in particular the invariant nature of the O≡An≡O asymmetric stretching frequencies observed across the actinyl series. Electronic structure calculations were performed at a variety of levels of theory to aid in the interpretation of the vibrational data and to correlate trends in the data with the underlying electronic properties of these molecules.

A novel symmetric pyrazine (pyz)-bridged uranyl dimer [UO2Cl3(H2O)(Pyz)0.5]22-: synthesis, structure and computational analysis

Herein we report on the synthesis of (HPyz⁺)₂[UO₂Cl₃(H₂O)(Pyz)_0.5]₂·2H₂O which features a novel pyrazine-bridged uranyl dimer, [UO₂Cl₃(H₂O)(Pyz)_0.5]₂^2-. A rigorous computational and experimental analysis of this compound was performed to fully explore the influence of coordination on the electronic structure and potential charge-transfer characteristics of this dimer, revealing a delocalized π-system across the bridging pyrazine and the axial components of both uranyl centers. Electrostatic surface potentials, used to rationalize the observed assembly, indicate a decreased basicity of the uranyl oxo versus [UO₂Cl₄]^2-, and signify a lessened capacity for the terminal -yl oxos of the [UO₂Cl₃(H₂O)(Pyz)_0.5]₂^2- dimer to participate in supramolecular assembly. A combined density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) analysis further evidenced an increase in UO bond strengths within the dimer, which is supported by a blue shift in the characteristic Raman-active uranyl symmetric stretch (ν₁) with respect to the more typically observed [UO₂Cl₄]^2-.

Unveiling the new function of uranyl molecular clusters as fluorometric sensors for UV and X-ray dosimetry

Simple synthetic modulation based on uranyl acetate and phenanthroline has resulted in two uranyl clusters (1 and 2) with different topologies and nuclearities. Notably, the dimeric complex exhibits distinct luminescence quenching upon UV and X-ray irradiation with detection limits of 4.30 × 10^-6 J and 0.32 Gy, respectively. To advance the practical application, 1 was further fabricated with polyvinylidene fluoride into a flexible strip as a UV and X-ray indicator.

Pb-Oxo Interactions in Uranyl Hybrid Materials: A Combined Experimental and Computational Analysis of Bonding and Spectroscopic Properties

Reported are the syntheses and characterization of six new heterometallic UO₂²⁺/Pb²⁺ compounds. These materials feature rare instances of M-oxo interactions, which influence the bonding properties of the uranyl cation. The spectroscopic effects of these interactions were measured using luminescence and Raman spectroscopy. Computational density functional theory-based natural bonding orbital and quantum theory of atoms in molecules methods indicate interactions arise predominantly through charge transfer between cationic units via the electron-donating uranyl O sp^x lone pair orbitals and electron-accepting Pb²⁺ p orbitals. The interaction strength varies as a function of Pb-oxo interaction distance and angle with energy values ranging from 0.47 kcal/mol in the longer contacts to 21.94 kcal/mol in the shorter contacts. Uranyl units with stronger interactions at the oxo display an asymmetric bond weakening and a loss of covalent character in the U═O bonds interacting closely with the Pb²⁺ ion. Luminescence quenching is observed in cases in which strong Pb-oxo interactions are present and is accompanied by red-shifting of the uranyl symmetric Raman stretch. Changes to inner sphere uranyl bonding manifest as a weakening of the U═O bond as a result of interaction with the Pb²⁺ ion. Comprehensive evaluation of the effects of metal ions on uranyl spectra supports modeling efforts probing uranyl bonding and may inform applications such as forensic signatures.

Uranyl(VI) Triflate as Catalyst for the Meerwein-Ponndorf-Verley Reaction

Catalytic transformation of oxygenated compounds is challenging in f-element chemistry due to the high oxophilicity of the f-block metals. We report here the first Meerwein-Ponndorf-Verley (MPV) reduction of carbonyl substrates with uranium-based catalysts, in particular from a series of uranyl(VI) compounds where [UO₂(OTf)₂] (1) displays the greatest efficiency (OTf = trifluoromethanesulfonate). [UO₂(OTf)₂] reduces a series of aromatic and aliphatic aldehydes and ketones into their corresponding alcohols with moderate to excellent yields, using ⁱPrOH as a solvent and a reductant. The reaction proceeds under mild conditions (80 °C) with an optimized catalytic charge of 2.3 mol % and KOⁱPr as a cocatalyst. The reduction of aldehydes (1-10 h) is faster than that of ketones (>15 h). NMR investigations clearly evidence the formation of hemiacetal intermediates with aldehydes, while they are not formed with ketones.

Yet another perspective on hole interactions

Hole interactions are known by different names depending on the key atom of the bond (halogen bond, chalcogen bond, hydrogen bond, etc.), and the geometry of the interaction (σ if in line, π if perpendicular to the Lewis acid plane). However, its origin starts with the creation of a Lewis acid by an underlying covalent bond, which forms an electrostatic depletion and a virtual antibonding orbital, which can create non-covalent interactions with Lewis bases. In this (maybe subjective) perspective, we will claim that hole interactions must be defined via the molecular orbital origin of the molecule. Under this premise we can better explore the richness of such bonding patterns. For that, we will study old, recent and new systems, trying to pinpoint some misinterpretations that are often associated with them. We will use as exemplars the triel bonds, a couple of metal complexes, a discussion on convergent σ-holes, and many cases of anti-electrostatic hole interactions.

Bimetallic uranyl/cobalt(II) isothiocyanates: structure, property and spectroscopic analysis of homo- and heterometallic phases

We report the synthesis and characterization of a family of UO22+/Co2+ isothiocyanate materials containing [UO2(NCS)5]3- and/or [Co(NCS)4]2- building units charged balanced by tetramethylammonium cations and assembled via SS or SOyl non-covalent interactions (NCIs), namely (C4H12N)3[UO2(NCS)5], (C4H12N)2[Co(NCS)4], and (C4H12N)5[Co(NCS)4][UO2(NCS)5]. The homometallic uranyl phase preferentially assembles via SS interactions, whereas in the heterometallic phase SOyl interactions are predominant. The variation in assembly mode is explored using electrostatic surfaces potentials, revealing that the pendant -NCS ligands of the [Co(NCS)4]2- anion is capable of outcompeting those of the [UO2(NCS)5]3- anion. Notably, the heterometallic phase displays atypical blue shifting of the uranyl symmetric stretch in the Raman spectra, which is in contrast to many other compounds featuring non-covalent interactions at uranyl oxygen atoms. A combined experimental and computational (density functional theory and natural bond orbital analyses) approach revealed that coupling of the uranyl symmetric stretch with isothiocyanate modes of equatorial -NCS ligands was responsible for the atypical blue shift in the heterometallic phase.

Neptunium(V) Isothiocyanate Complexes with 4'-Aryl-Substituted 2,2':6',2″-Terpyridines and N,N-Dimethylacetamide as Molecular Ligands

New complexes of neptunyl(V) isothiocyanate with 4'-aryl-substituted 2,2':6',2″-terpyridines (Terpy) and N,N-dimethylacetamide (DMA) were obtained: [(NpO₂)(4'-Ph-Terpy)(DMA)(NCS)]·DMA, [(NpO₂)(4'-(4-(CF₃)C₆H₄)-Terpy)(DMA)(NCS)]·2H₂O·DMA, [(NpO₂)(4'-(3-BrC₆H₄)-Terpy)(DMA)(NCS)]·DMA, and [(NpO₂)(4'-(2-(COOH)C₆H₄)-Terpy)(DMA)(NCS)]·DMA. The structures of the compounds were determined with X-ray diffraction analysis. The neptunium coordination polyhedra were found to be pentagonal bipyramids with O atoms of the NpO₂ groups in the apical positions and the equatorial planes formed by three N atoms of the terpyridine ligand, a N atom of the isothiocyanate anion, and an O atom of DMA. The influence of the substituents of the Ar group on the crystal structure is discussed. The IR spectra contain well-resolved bands of characteristic vibrations of all groups in the complex. The electronic absorption spectra are typical for neptunium(V) complexes and contain an intense narrow absorption band belonging to an f-f transition with a maximum of 988 nm and several long-wave satellites of lower intensity. The substituted terpyridines were shown to be efficient for the extraction of various valence forms of neptunium from the isothiocyanate solutions.

Structural, spectroscopic, and computational evaluations of cation–cation and halogen bonding interactions in heterometallic uranyl hybrid materials

A route for systematically accessing the oxo atoms of the linear uranyl (UO₂²⁺) cation via cation–cation and halogen bonding interactions is detailed, and interaction strengths are probed via structural, vibrational, and computational means.

Structural Diversity of Bipyridinium-Based Uranyl Coordination Polymers: Synthesis, Characterization, and Ion-Exchange Application

As well-known functional groups with excellent electro/photochromic and ion-exchange properties, bipyridinium motifs have been used in functionalized metal-organic coordination polymers, but they are still rarely applied to construct actinide coordination polymers. In this work, we utilized a bipyridinium-based carboxylic acid, 1,1'-bis(4-carboxyphenyl)-4,4'-bipyridinium bis(chloride) ([H₂bcbp]Cl₂), as the organic ligand to assemble with uranyl cations. By the introduction of different kinds of auxiliary ligands and adjustment of the pH, five novel uranyl coordination compounds, 1-5, have been synthesized through hydrothermal reactions. Starting from uranyl ions and terephthalic acid (H₂TP) and H₂bcbp ligands, [(UO₂)₂(bcbp)(TP)₂]·3H₂O (1) has a wave-shaped two-dimensional (2D) structure consisting of dinuclear units connected by terephthalate linkers and further supported by the longer H₂bcbp ligands. [(UO₂)₂(bcbp)(PA)₂]·4H₂O (2) has a zigzag chain of dimeric uranium units, and [(UO₂)₂(bcbp)(bpdc)₂]·5H₂O (3) forms a one-dimensional ribbonlike structure. The 2D structures of [(UO₂)(bcbp)(OH)(H₂O)]·Cl (4) and [(UO₂)(bcbp)Cl]·Cl (5) are similar, both of which are constructed from dinuclear uranyl units and bcbp^2- ligands. Furthermore, the performance for perrhenate removal of compound 4 with a cationic framework is assessed, and we found that compound 4 can efficiently remove ReO₄^- from an aqueous solution in a wide range of pH values. This work extends the library of viologen derivative-based uranyl coordination polymers, provides to some extent broader insights into actinide coordination chemistry of functionalized ligands, and may facilitate the ion-exchange applications of related coordination polymers.

Halogen Bonds in 2,5-Dihalopyridine-Copper(I) Halide Coordination Polymers

Two series of 2,5-dihalopyridine-Cu(I)A (A = I, Br) complexes based on 2-X-5-iodopyridine and 2-X-5-bromopyridine (X = F, Cl, Br and I) are characterized by using single-crystal X-ray diffraction analysis to examine the nature of C2-X2···A-Cu and C5-X5···A-Cu halogen bonds. The reaction of the 2,5-dihalopyridines and Cu(I) salts allows the synthesis of eight 1-D coordination polymers and a discrete structure. The resulting Cu(I)-complexes are linked by C-X···A-Cu halogen bonds forming 3-D supramolecular networks. The C-X···A-Cu halogen bonds formed between halopyridine ligands and copper(I)-bound halide ions are stronger than C-X···X'-C interactions between two 2,5-dihalopyridine ligands. The C5-I5···I-Cu and C5-Br5···Br-Cu halogens bonds are shorter for C2-fluorine than C2-chlorine due to the greater electron-withdrawing power of fluorine. In 2,5-diiodopyridine-Cu(I)Br complex, the shorter C2-I2···Br-Cu [3.473(5) Å] distances are due to the combined polarization of C2-iodine by C2-I2···Cu interactions and para-electronic effects offered by the C5-iodine, whilst the long halogen bond contacts for C5-I5···Br-Cu [3.537(5) Å] are indicative that C2-iodine has a less para-electronic influence on the C5-iodine. In 2-fluoro-5-X-pyridine-Cu(I) complexes, the C2-fluorine is halogen bond passive, while the other C2-halogens in 2,5-dihalopyridine-Cu(I), including C2-chlorine, participate in halogen bonding interactions.

Persistent Superprotonic Conductivity in the Order of 10−1 S·cm−1 Achieved Through Thermally Induced Structural Transformation of a Uranyl Coordination Polymer

Despite tremendous efforts having been made in the exploration of new high-performance proton-conducting materials, systems with superprotonic conductivity higher than 10−1 S·cm−1 are scarcely reported. We show here the utilization of bridging uranyl oxo atoms, traditionally termed cation–cation interaction (CCI), as the hydrogen bond acceptor to build a dense and ordered hydrogen bond network, affording a unique uranyl-based proton-conducting coordination polymer (H3O)4UO2(PO4)2 (HUP-1). This compound contains a densely connected hydronium network that is substantially stabilized by uranyl oxo atoms and exhibits high proton conductivities over a wide temperature range. At 98 °C, 98% relative humidity, a superprotonic conductivity of 1.02 × 10−1 S·cm−1 is observed for the system, one of the highest values reported for a solid-state proton-conducting material. This property originates from the thermally induced phase transformation from HUP-1 to another uranyl compound also with a CCI bond, (H3O)UO2PO4·(H2O)3 (HUP-2), accompanied by the partial generation of phosphorus acid that is further trapped in the structure of HUP-2, demonstrated by solid-state NMR analysis. The superprotonic conductivity of H3PO4@HUP-2 is persistent under the testing condition.

Halogen bonding in UiO-66 frameworks promotes superior chemical warfare agent simulant degradation

Herein, a series of halogenated UiO-66 derivatives was synthesized and analyzed for the breakdown of the chemical warfare agent simulant dimethyl-4-nitrophenyl phosphate (DMNP) to analyze ligand effects. UiO-66-I degrades DMNP at a rate four times faster than the most active previously reported MOFs. MOF defects were quantified and ruled out as a cause for increased activity. Theoretical calculations suggest the enhanced activity of UiO-66-I originates from halogen bonding of the iodine atom to the phosphoester linkage allowing for more rapid hydrolysis of the P-O bond.

Detection and identification of solids, surfaces, and solutions of uranium using vibrational spectroscopy

The purpose of this review is to provide an overview of uranium speciation using vibrational spectroscopy methods including Raman and IR. Uranium is a naturally occurring, radioactive element that is utilized in the nuclear energy and national security sectors. Fundamental uranium chemistry is also an active area of investigation due to ongoing questions regarding the participation of 5f orbitals in bonding, variation in oxidation states and coordination environments, and unique chemical and physical properties. Importantly, uranium speciation affects fate and transportation in the environment, influences bioavailability and toxicity to human health, controls separation processes for nuclear waste, and impacts isotopic partitioning and geochronological dating. This review article provides a thorough discussion of the vibrational modes for U(IV), U(V), and U(VI) and applications of infrared absorption and Raman scattering spectroscopies in the identification and detection of both naturally occurring and synthetic uranium species in solid and solution states. The vibrational frequencies of the uranyl moiety, including both symmetric and asymmetric stretches are sensitive to the coordinating ligands and used to identify individual species in water, organic solvents, and ionic liquids or on the surface of materials. Additionally, vibrational spectroscopy allows for the in situ detection and real-time monitoring of chemical reactions involving uranium. Finally, techniques to enhance uranium species signals with vibrational modes are discussed to expand the application of vibrational spectroscopy to biological, environmental, inorganic, and materials scientists and engineers.

Monomeric thorium chalcogenolates with bipyridine and terpyridine ligands

Thorium chalcogenolates Th(ER)4 react with 2,2'-bipyridine (bipy) to form complexes with the stoichiometry (bipy)2Th(ER)4 (E = S, Se; R = Ph, C6F5). All four compounds have been isolated and characterized by spectroscopic methods and low-temperature single crystal X-ray diffraction. Two of the products, (bipy)2Th(SC6F5)4 and (bipy)2Th(SeC6F5)4, crystallize with lattice solvent, (bipy)2Th(SPh)4 crystallizes with no lattice solvent, and the selenolate (bipy)2Th(SePh)4 crystallizes in two phases, with and without lattice solvent. In all four compounds the available volume for coordination bounded by the two bipy ligands is large enough to allow significant conformational flexibility of thiolate or selenolate ligands. 77Se NMR confirms that the structures of the selenolate products are the same in pyridine solution and in the solid state. Attempts to prepare analogous derivatives with 2,2',6',2''-terpyridine (terpy) were successful only in the isolation of (terpy)(py)Th(SPh)4, the first terpy compound of thorium. These materials are thermochromic, with color attributed to ligand-to-ligand charge transfer excitations.

Pseudohalide Tectons within the Coordination Sphere of the Uranyl Ion: Experimental and Theoretical Study of C-H···O, C-H···S, and Chalcogenide Noncovalent Interactions

A series of uranyl thiocyanate and selenocyanate of the type [R₄N]₃[UO₂(NCS)₅] (R₄ = ⁿBu₄, Me₃Bz, Et₃Bz), [Ph₄P][UO₂(NCS)₃(NO₃)] and [R₄N]₃[UO₂(NCSe)₅] (R₄ = Me₄, ⁿPr₄, Et₃Bz) have been prepared and structurally characterized. The resulting noncovalent interactions have been examined and compared to other examples in the literature. The nature of these interactions is determined by the cation so that when the alkyl groups are small, chalcogenide···chalcogenide interactions are present, but this "switches off" when R = ⁿPr and charge assisted U═O···H-C and S(e)···H-C hydrogen bonding remain the dominant interaction. Increasing the size of the chain to ⁿBu results in only S···H-C interactions. The spectroscopic implications of these chalcogenide interactions have been explored in the vibrational and photophysical properties of the series [R₄N]₃[UO₂(NCS)₅] (R₄ = Me₄, Et₄, ⁿPr₄, ⁿBu₄, Me₃Bz, Et₃Bz), [R₄N]₃[UO₂(NCSe)₅] (R₄ = Me₄, ⁿPr₄, Et₃Bz) and [Et₄N]₄[UO₂(NCSe)₅][NCSe]. The data suggest that U═O···H-C interactions are weak and do not perturb the uranyl moiety. While the chalcogenide interactions do not influence the photophysical properties, a coupling of the U═O and δ(NCS) or δ(NCSe) vibrational modes is observed in the 77 K solid state emission spectra. A theoretical examination of representative examples of Se···Se, C-H···Se, and C-H···O═U by molecular electrostatic potentials and NBO and AIM methodologies gives a deeper understanding of these weak interactions. C-H···Se are individually weak but C-H···O═U interactions are even weaker, supporting the idea that the -yl oxo's are weak Lewis bases. An Atoms in Molecules study suggests that the chalcogenide interaction is similar to lone pair···π or fluorine···fluorine interactions. An oxidation of the NCS ligands to form [(UO₂)(SO₄)₂(H₂O)₄]·3H₂O was also noted.

Probing hydrogen and halogen-oxo interactions in uranyl coordination polymers: a combined crystallographic and computational study

Four uranyl compounds containing either benzoic acid (1), m-chlorobenzoic acid (2), m-bromobenzoic acid (3), or m-iodobenzoic acid (4) are described, and the latter two compounds are used to probe non-covalent interaction strengths via structural, vibrational, and computational means.

Synthesis, structural analysis, and supramolecular assembly of a series of in situ generated uranyl–peroxide complexes with functionalized 2,2′-bipyridine and varied carboxylic acid ligands

Presented herein are eight new binuclear uranyl complexes bridged by in situ generated peroxide ligands and assembled via noncovalent interactions.

Nine isomorphous lanthanide–uranyl f–f bimetallic materials with 2-thiophenecarboxylic acid and terpyridine: structure and concomitant luminescent properties

Concomitant and semi-selective uranyl and lanthanide luminescence observed within a series of f–f bimetallic molecular materials (UO₂²⁺/Ln = Pr–Er).

Crystal structures of uranyl complexes with isobutyrate and isovalerate anions

Types of sodium coordination, depolymerization of metal–oxygen frameworks and coordination sequences are analyzed for establishing correlations between composition and crystal structure in the family of analogous compounds.

A new Pu(iii) coordination geometry in (C5H5NBr)2[PuCl3(H2O)5]·2Cl·2H2O as obtained via supramolecular assembly in aqueous, high chloride media

A novel hydrated Pu(iii) chloride, (C₅H₅NBr)₂[PuCl₃(H₂O)₅]·Cl·2H₂O, is prepared from aqueous media and the non-covalent interaction pairings are rationalized using electrostatic potentials.