Two Uranyl Complexes with Pyromellitic Acid. A Heterometallic Complex with U=O–CuII Interaction

Two uranyl complexes based on pyromellitic acid were hydrothermally synthesized, and their X‐ray single‐crystal diffraction structures were determined. Complex [UO₂(Hbtec)]^–(Himd)⁺ · H₂O ( 1 ) (H₄btec = pyromellitic acid, imd = imidazole), is an ionic complex, which shows a typical (4, 4) topological structure in the space. A heterometallic complex, UO₂Cu(btec)(phen) ( 2 ) (phen = 1,10‐phenanthroline) results from the reaction of uranyl nitrate and copper(II) bromide with pyromellitic acid. The structure of complex 2 revealed that the chains of UO₇ and CuO₃N₂ units were connected to each other through the carboxyl groups and U=O–Cu interactions to create a two‐dimensional framework.     

Spectroscopic characterization of alkaline earth uranyl carbonates

A series of alkaline uranyl carbonates, M[UO₂(CO₃)₃]·nH₂O (M=Mg₂, Ca₂, Sr₂, Ba₂, Na₂Ca, and CaMg) was synthesized and characterized by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS) after nitric acid digestion, X-ray powder diffraction (XRD), and thermal analysis (TGA/DTA). The molecular structure of these compounds was characterized by extended X-ray absorption fine-structure (EXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). Crystalline Ba₂[UO₂(CO₃)₃]·6H₂O was obtained for the first time. The EXAFS analysis showed that this compound consists of (UO₂)(CO₃)₃ clusters similar to the other alkaline earth uranyl carbonates. The average U-Ba distance is 3.90±0.02 Å.Fluorescence wavelengths and life times were measured using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The U-O bond distances determined by EXAFS, TRLFS, XPS, and Raman spectroscopy agree within the experimental uncertainties. The spectroscopic signatures observed could be useful for identifying uranyl carbonate species adsorbed on mineral surfaces.     

Raman spectra of zeolites exchanged with uranyl(VI) cations—II. Zeolite X

The formation of hydrolysed uranyl(VI) species in UO₂X zeolites prepared by various methods has been investigated by Raman spectroscopy. Ion-exchange in aqueous (pH>3) and non-aqueous (anhydrous methanol and uranyl nitrate melts) media resulted in the formation of hydroxy-bridged complexes such as [(UO₂)₃(OH)₄]²⁺, [(UO₂)₃(OH)₅]⁺, and [(UO₂)₄(OH)₇]⁺. Ion-exchange in more acidic media (initial pH < 3) was accompanied by the formation of a disordered phase incorporating UO₃, following extensive collapse of the zeolite framework structure. Cation speciation in the UO₂X system is compared to that in UO₂Y zeolites.     

Reticular Chemistry of Uranyl Phosphonates: Sterically Hindered Phosphonate Ligand Method is Significant for Constructing Zero-Dimensional Secondary Building Units

Designability is an attractive feature for metal–organic frameworks (MOFs) and essential for reticular chemistry, and many ideas are significantly useful in the carboxylate system. Bi-, tri-, and tetra-topic phosphonate ligands are used to achieve framework structures. However, an efficient method for designing phosphonate MOFs is still on the way, especially for uranyl phosphonates, owing to the complicated coordination modes of the phosphonate group. Uranyl phosphonates prefer layer or pillar-layered structures as the topology extension for uranyl units occurs in the plane perpendicular to the linear uranium-oxo bonds and phosphonate ligands favor the formation of compact structures. Therefore, an approach that can construct three-dimensional (3D) uranyl phosphonate MOFs is desired. In this paper, a sterically hindered phosphonate ligand method (SHPL) is described and is successfully used to achieve 3D framework structures of uranyl phosphonates. Four MOF compounds ([AMIM]₂(UO₂)(TppmH₄) ⋅ H₂O ( UPF-101 ), [BMMIM]₂(UO₂)₃(TppmH₄)₂ ⋅ H₂O ( UPF-102 ), [Py14]₂(UO₂)₃(TppmH₄)₂ ⋅ 3 H₂O ( UPF-103 ), and [BMIM](UO₂)₃(TppmH₃)F₂ ⋅ 2 H₂O ( UPF-104 ); [AMIM]=1-allyl-3-methylimidazolium, [BMMIM]=1-butyl-2,3-dimethylimidazolium, [Py14]=N-butyl-N-methylpyrrolidinium, and [BMIM]=1-butyl-3-methylimidazolium) are obtained by ionothermal synthesis, with zero-dimensional nodes of uranyl phosphonates linked by steric tetra-topic ligands, namely tetrakis[4-(dihyroxyphosphoryl)phenyl]methane (TppmH₈), to give 3D framework structures. Characterization by PXRD, UV/Vis, IR, Raman spectroscopy, and thermogravimetry (TG) were also performed.     

Raman,resonance Raman and infrared spectra of potassium uranyl croconate

The Raman, resonance Raman and IR spectra of potassium uranyl croconate, UO₂(H₂O)K₂(C₅O₅)₂ were obtained and interpreted. Several croconate modes are split indicating a substantial decrease in the oxocarbon symmetry, as is to be expected from a recent crystallographic investigation, revealing the coordination of the oxocarbon to be two non-equivalent UO²⁺₂ moieties in a monodentate fashion. In terms of vibrational frequency shifts it can be concluded that the UO²⁺₂ moiety behaves as an isolated oscillator.The resonance Raman results suggest that the strong band centered around 450 nm in the UV—vis spectrum should be assigned to a charge transfer transition from the oxocarbon to the uranyl ion. In fact, as resonance is approached, both uranyl and croconate modes are enhanced. It can also be inferred that the chromophore is rather delocalized into the oxocarbon ring, rather than localized in the carbonyl groups as previously observed for other croconate complexes.     

Preparation de nouveaux difluorodioxophosphates a partir de l’oxyde de difluorure de phosphoryle Partie V. Reactions aur le trioxyde d’uranium

UO₂(PO₂F₂)₂ has been synthesized from the action of P₂O₃F₄ on UO₃ or uranyl nitrate. The monofluorophosphate UO₂(PO₃F) was obtained by thermal decomposition. Infrared and Raman spectroscopic investigation of UO₂(PO₂F₂)₂ suggest a chain structure with oxygen phosphorus-oxygen bridges.     

Unusual case of a polar copper(II) uranyl phosphonate that fluoresces

A polar Cu(II) uranyl diphosphonate, Cu(H₂O)₄(UO₂)₃(H₂O)₂[CH₂(PO₃)₂]₂·5H₂O, has been prepared under mild hydrothermal conditions. This compound has direct linkages between the oxo atoms of the uranyl moieties and the Cu(II) centers. Despite the presence of Cu(II) in the structure, vibronically-coupled emission is still observed, most likely because there are two crystallographically unique uranyl moieties, only one of which bonds to Cu(II).     

3D Uranyl Organic Frameworks Supported by Rigid Octadentate Carboxylate Ligand: Synthesis,Structure Diversity,and Luminescence Properties

Seven three dimensional (3D) uranyl organic frameworks (UOFs), formulated as [NH₄][(UO₂)₃(HTTDS)(H₂O)] ( 1 ), [(UO₂)₄(HTTDS)₂](HIM)₆ ( 2 , IM=imidazole), [(UO₂)₄(TTDS)(H₂O)₂(Phen)₂] ( 3 , Phen=1,10-phenanthroline), [Zn(H₂O)₄]_0.5[(UO₂)₃(HTTDS)(H₂O)₄] ( 4 ), and {(UO₂)₂[Zn(H₂O)₃]₂(TTDS)} ( 5 ), {Zn(UO₂)₂(H₂O)(Dib)_0.5(HDib)(HTTDS)} ( 6 , Dib=1,4-di(1H-imidazol-1-yl)benzene) and [Na]{(UO₂)₄[Cu₃(u₃-OH)(H₂O)₇](TTDS)₂} ( 7 ) have been hydrothermally prepared using a rigid octadentate carboxylate ligand, tetrakis(3,5-dicarboxyphenyl)silicon(H₈TTDS). These UOFs have different 3D self-assembled structures as a function of co-ligands, structure-directing agents and transition metals. The structure of 1 has an infinite ribbon formed by the UO₇ pentagonal bipyramid bridged by carboxylate groups. With further introduction of auxiliary N-donor ligands, different structure of 2 and 3 are formed, in 2 the imidazole serves as space filler, while in 3 the Phen are bound to [UO₂]²⁺ units as co-ligands. The second metal centers were introduced in the syntheses of 4–7 , and in all cases, they are part of the final structures, either as a counterion ( 4 ) or as a component of framework ( 5 − 7 ). Interesting, in 7 , a rare polyoxometalate [Cu₃(μ₃-OH)O₇(O₂CR)₄] cluster was found in the structure. It acts as an inorganic building unit together with the dimer [(UO₂)₂(O₂CR)₄] unit. Those uranyl carboxylates were sufficiently determined by single crystal X-ray diffraction, and their topological structures and luminescence properties were analyzed in detail.     

Isolation of a Star‐Shaped Uranium(V/VI) Cluster from the Anaerobic Photochemical Reduction of Uranyl(VI)

Actinide oxo clusters are an important class of compounds due to their impact on actinide migration in the environment. The photolytic reduction of uranyl(VI) has potential application in catalysis and spent nuclear fuel reprocessing, but the intermediate species involved in this reduction have not yet been elucidated. Here we show that the photolysis of partially hydrated uranyl(VI) in anaerobic conditions leads to the reduction of uranyl(VI), and to the incorporation of the resulting U^V species into the stable mixed‐valent star‐shaped U^VI/U^V oxo cluster [U(UO₂)₅(μ₃‐O)₅(PhCOO)₅(Py)₇] ( 1 ). This cluster is only the second example of a U^VI/U^V cluster and the first one associating uranyl groups to a non‐uranyl(V) center. The U^V center in 1 is stable, while the reaction of uranyl(V) iodide with potassium benzoate leads to immediate disproportionation and formation of the U₁₂^IVU₄^VO₂₄ cluster {[K(Py)₂]₂[K(Py)]₂[U₁₆O₂₄(PhCOO)₂₄(Py)₂]} ( 5 ).     

Reaction of uranyl nitrate with carboxylic diacids under hydrothermal conditions. Crystal structure of complexes with l(+)-tartaric and oxalic acids

l(+)-tartaric acid reacts with uranyl nitrate in the presence of KOH, under mild hydrothermal conditions, to give the complex [UO₂(C₄H₄O₆)(H₂O)] (1), the first uranyl tartrate to be crystallographically characterized. Each tartrate ligand bridges three uranyl ions, one of them in chelating fashion through proximal carboxylate and hydroxyl groups. The resulting assemblage is two-dimensional, with the uranyl pentagonal bipyramidal coordination polyhedra separated from one another. Prolonged heating of an uranyl tartrate solution resulted in oxidative cleavage of the acid and formation of the oxalate complex [(UO₂)₂(C₂O₄)₂(OH)Na(H₂O)₂] (2). The bis-bidentate oxalate and bridging hydroxide groups ensure the formation of sheets with corner-sharing uranyl pentagonal bipyramidal coordination polyhedra, in which six-membered metallacycles encompass the sodium ions. These sheets are assembled into a three-dimensional framework through further oxo-bonding of the sodium ions.     

Uranyl complexes with acetophenone oxime

The interaction of uranyl compounds with acetophenone oxime has been studied. Mixed-ligand uranyl acetophenone oximates have been synthesized. X-ray crystallography shows that, in single crystals of [UO₂(C₈H₈NO)₂{(CH₃)₂SO}₂] and [UO₂(C₈H₈NO)(NO₃){(CH₃)₂SO}₂], acetophenone oxime is coordinated to uranyl as a bidentate chelating ligand.     

Two isomorphous imidazole (Him) complexes: [MCl2(Him)2(H2O)2] (M = Co and Ni)

The structures of aqua­di­chloro­bis(1H‐imidazole)­cobalt(II), [CoCl₂(Him)₂(H₂O)₂] (Him is 1H‐imidazole, C₃H₄N₂), (I), and aqua­di­chloro­bis(1H‐imidazole)­nickel(II), [NiCl₂(Him)₂(H₂O)₂], (II), are isomorphous and consist of monomers with inversion symmetry. The three monodentate ligands (imidazole, chlorine and aqua), together with their symmetry equivalents, define almost perfect octahedra. Hydro­gen‐bonding interactions via the imidazole and aqua H atoms lead to a three‐dimensional network.     

Vibrational spectroscopy of a crystallographically unsettled uranyl carbonate: Structural impact and model

Room-temperature vibrational and photoluminescence (PL) spectra of a natural, rare hydrated calcium copper uranyl carbonate mineral, voglite (Ca₂Cu(UO₂)(CO₃)₄·6H₂O) are recorded and discussed in details. Vibrational spectroscopy gives information about the structure of voglite, which is still missing due to its unknown crystallographic features. By comparison with other uranyl carbonates and sulfates, a strong Raman line occurring at 834 cm⁻¹ is assigned to the ν₁(UO₂)²⁺ symmetric stretching vibration rather than to the ν₂(CO₃)²⁻ out-of-plane bending vibration. The ν₃(UO₂)²⁺ antisymmetric stretching vibration is tentatively identified at 897 cm⁻¹ from infrared (IR) spectroscopy. Several well resolved bands found at 1074,1092, 1381, 1566 cm⁻¹ in the Raman and 1046, 1114, 1145, 1376, 1426, 1510, 1561 cm⁻¹ in the IR are ascribed to symmetric and antisymmetric stretching motions of the carbonate units. The presence of all these intense vibrational bands points to different CO bond lengths. The infrared water band is well structured, suggesting a few different OH moieties in the crystal. Original micro-PL spectra show a manifold of vibronic features whose energy spacing is close to the frequency of the symmetric OUO stretching vibration and confirms the uranium origin of the most intense Raman band. The study suggests that voglite structure has no inversion centers, a low symmetry, and contains molecular units similar to those of the parent phases, andersonite or liebigite, like uranyl tricarbonate clusters (UTC). The existence of these UTCs in voglite is confirmed by density functional theory calculations. A new assignment of all vibrational modes is proposed.     

Design,synthesis and structure of uranyl coordination polymers from 2-D layer to 3-D network structure

Solvothermal reaction of uranyl acetate and succinic acid in DMF resulted in formation of three uranyl coordination polymers, [(UO₂)₄(μ₂-OH)₇(OH)₆]·2(H₂O)·(H₃O)·4NH₂(CH₃)₂ (1), [(UO₂)(μ₂-OH)(OH)₃]·2NH₂(CH₃)₂] (2), and [(DMF)₂(UO₂)(μ₂-OH)₄(UO₂))] (3). The products were characterized by elemental analysis, IR spectroscopy, X-ray single crystal, and powder diffraction. Structural analysis shows that 1 is a layer, 2 and 3 are 3-D network structures.     

Rhenium‐Dicarbonyl‐Nitrosyl‐Komplexe mit Imidazol

Rhenium Dicarbonyl‐Nitrosyl Complexes with Imidazole Different rhenium‐dicarbonyl‐nitrosyl complexes with imidazole (Im) as monodentate ligand have been synthesized and characterized, starting from [NEt₄][ReCl₃(CO)₂(NO)] and [ReCl(μ?Cl)(CO)₂(NO)]₂. Whereas the complexes [ReCl₂(Im)(CO)₂(NO)] and [ReCl(Im)₂(CO)₂(NO)]⁺ were achieved in high yields, the complex [Re(Im)₃(CO)₂(NO)]²⁺ with three imidazole ligands could only be isolated after complete removal of all halide ions (with AgBF₄) in low yield. The synthesis of a corresponding ^99mTc‐dicarbonyl‐nitrosyl complex with imidazole opens a new perspective for such compounds as potential radiopharmaceuticals and alternatives to the already established ^99mTc‐tricarbonyl complexes.     

The Rb analogue of grimselite,Rb6Na2[(UO2)(CO3)3]2(H2O)

The crystal structure of the Rb analogue of grimselite, rubidium sodium uranyl tricarbonate hydrate, Rb₆Na₂[(UO₂)(CO₃)₃]₂(H₂O), consists of a uranyl hexagonal bipyramid that shares three non‐adjacent equatorial edges with carbonate triangles, resulting in a uranyl tricarbonate cluster of composition [(UO₂)(CO₃)₃)]. These uranyl tricarbonate clusters form layers perpendicular to [001] and are interconnected by NaO₈ polyhedra. The title compound is isostructural with grimselite, with a reduced occupancy of the H₂O site (25% versus 50% in grimselite).     

Syntheses and structures of two new uranyl complexes [UO2(DPDPU)2(NO3)2](C6H5CH3) and [UO2(PMBP)2(DPDPU)](CH3C6H4CH3)0.5

Two new uranyl complexes [UO₂(DPDPU)₂(NO₃)₂](C₆H₅CH₃) (1) and [UO₂(PMBP)₂ (DPDPU)](CH₃C₆H₄CH₃)_0.5 (2), (DPDPU?=?N,N′-dipropyl-N,N′-diphenylurea, HPMBP?= 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5) were synthesized and characterized. The coordination geometry of the uranyl atom in 1 is distorted hexagonal bipyramidal, coordinated by two oxygen atoms of two DPDPU molecules and four oxygen atoms of two bidentate nitrate groups. The coordination geometry of the uranyl atom in 2 is distorted pentagonal bipyramidal, coordinated by one oxygen atom of one DPDPU molecule and four oxygen atoms of two chelating PMBP molecules.     

Extraction chemistry of uranyl nitrate and nitric acid in high concentration systems

HNO₃ is extracted in significant quantities by uranyl nitrate solvates with different extractants: TBP (tributyl phosphate), TOPO (trioctyl phosphine oxide) and TDA (tetradecyl ammonium). The effect of diluent nature is not observed on extracting HNO₃ and TBP saturated by uranium at equilibrium with its salt using the diluents (CCl₄, C₆H₅Cl, C₁₂H₂₆, CHCl₃) which are less polar than UO₂(NO₃)₂(TBP)₂. HNO₃ occurs in organic phase as undissociated form and its state is similar to pure anhydrous HNO₃. Solvates of TBP and TDA with uranyl nitrate dissolve HNO₃ without displacement of uranium from organic phase.     

Isopropylammonium Layered Uranyl Chromates: Syntheses and Crystal Structures of [(CH3)2CHNH3]3[(UO2)3(CrO4)2O(OH)3] and[(CH3)2CHNH3]2[(UO2)2(CrO4)3(H2O)]

Two novel isopropylamine‐templated uranyl chromates, [(CH₃)₂CHNH₃]₃[(UO₂)₃(CrO₄)₂O(OH)₃] ( 1 ) and [(CH₃)₂CHNH₃]₂[(UO₂)₂(CrO₄)₃(H₂O)] ( 2 ) were prepared by hydrothermal method at 100 °C. The compounds were characterized by electron microprobe analysis and X‐ray diffraction crystal structure analysis [ 1 : trigonal, P31m, a = 9.646(4), c = 8.469(4) Å, V = 682.4(5) ų; 2 : monoclinic, P2₁/c, a = 11.309(3), b = 11.465(3), c = 17.055(5) Å, β = 99.150(6)°, V = 2183.2(11) ų]. The structure of 1 is based upon trimers of uranyl bipyramids interlinked by CrO₄ tetrahedra to form [(UO₂)₃(CrO₄)₂O(OH)₃]^3– layers, whereas, in the structure of 2 , UO₇ and UO₆(H₂O) pentagonal bipyramids are linked through CrO₄ tetrahedra into the [(UO₂)₂(CrO₄)₃(H₂O)]^2– layers. The structures show many similarities to related uranyl selenate compounds, thus providing additional data on similarities and differences between uranyl sulfates, chromates, selenates, and molybdates.     

Theoretical studies on the complexation of uranyl with typical carboxylate and amidoximate ligands

Understanding of the bonding nature of uranyl and various ligands is the key for designing robust sequestering agents for uranium extraction from seawater. In this paper thermodynamic properties related to the complexation reaction of uranyl(VI) in aqueous solution (i.e. existing in the form of UO₂(H₂O)₅ ²⁺) by several typical ligands (L) including acetate (CH₃CO₂ ^?), bicarbonate (HOCO₂ ^?), carbonate (CO₃ ^2?), CH₃(NH₂)CNO^? (acetamidoximate, AO^?) and glutarimidedioximate (denoted as GDO^2?) have been investigated by using relativistic density functional theory (DFT). The geometries, vibrational frequencies, natural net charges, and bond orders of the formed uranyl-L complexes in aqueous solution are studied. Based on the DFT analysis we show that the binding interaction between uranyl and amidoximate ligand is the strongest among the selected complexes. The thermodynamics of the complexation reaction are examined, and the calculated results show that complexation of uranyl with amidoximate ligands is most preferred thermodynamically. Besides, reaction paths of the substitution complexation of solvated uranyl by acetate and AO^? have been studied, respectively. We have obtained two minima along the reaction path of solvated uranyl with acetate, the monodentate-acetate complex and the bidentate-acetate one, while only one minimum involving monodentate-AO complex has been located for AO^? ligand. Comparing the energy barriers of the two reaction paths, we find that complexation of uranyl with AO^? is more difficult in kinetics, though it is more preferable in thermodynamics. These results show that theoretical studies can help to select efficient ligands with fine-tuned thermodynamic and kinetic properties for binding uranyl in seawater.