Hexagonal Bipyramidal Coordination Research Articles

Optical vibrational spectra and proposed crystal structure of ε-UO3

ε-UO3 is an exotic polymorph in the uranium trioxide system with an undetermined crystal structure and limited optical vibrational spectroscopic data. To improve understanding of this compound, we synthesize and investigate the crystal structure and optical vibrational spectra of ε-UO3. Infrared spectra collected for ε-UO3 are in good agreement with previously published results, and our studies extend the available data into the low-energy (600–100 cm–1) regime. For the first time, Raman spectra are presented for ε-UO3 using both 785 and 532 nm excitation wavelengths. Previous reports suggest an impurity phase may be present in ε-UO3 produced by calcination of U3O8; however, spectral center-of-mass calculations, principal component analyses, and Raman spectroscopic mapping employed to investigate this possibility indicate that the product of U3O8 calcined in O3(g) in this work is likely phase-pure. A possible novel structure solution for ε-UO3 is determined via Rietveld refinement of powder X-ray diffraction data and is triclinic, P-1, with a = 4.01 Å, b = 3.85 Å, c = 4.18 Å, and α = 98.26°, β = 90.41°, γ = 120.46° (Rwp = 8.30%). The asymmetric unit of ε-UO3 consists of U(VI) in hexagonal bipyramidal coordination with displaced equatorial oxygen. Further analysis reveals that the structure of ε-UO3 is best described by a 2 × 1 × 2 supercell structure in P-1 with a = 8.03 Å, b = 3.86 Å, c = 8.37 Å with α = 98.26°, β = 90.41°, and γ = 120.46°, although a higher-symmetry structure is possible. Optical vibrational spectroscopic and structural measurements of ε-UO3 presented here furthers our understanding of this complex uranium oxide and clarifies the origin of reported structural similarity to U3O8.

Rare cis‐Dioxido Uranyl Framework Crystalline Complexes: Synthesis, Structure, Characterization and Properties

AbstractThe trans‐dioxido uranyl frameworks named as [(UO2)(Aip)(DMA)] (1), H[(UO2)(Aib)3] (2) and rare cis‐dioxido [(UO2)Co(Suc)2(H2O)4] (3), and [(UO2)Ni(Suc)2(H2O)4] (4) have been synthesized, which based on 5‐aminoisophthalic acid (H2Aip), 3‐aminobenzoic acid (HAib), and succinic acid (H2Suc) as ligands. They were characterized by Fourier Transform Infrared spectra, UV‐vis absorption spectra, single‐crystal X‐ray diffraction, powder X‐ray diffraction and thermogravimetry analysis. It was found that uranium ion of the complex 1 is in the pentagonal bipyramidal coordination environment, while those of the complexes 2–4 are in the hexagonal bipyramidal coordination environment. Complexes 1, 3, and 4 are 3D network structures, 2 is a discrete structure. In particular, geometry of O=U=O for 1 and 2 are trans, ones for 3 and 4 are cis. The highest removal rate of methylene blue was almost to 96 % by complex 1 as an adsorbent, which illustrates that potential application on dye adsorption.

Stabilization of Plutonium(V) Within a Crown Ether Inclusion Complex

Crystalline coordination complexes of actinides, especially in atypical oxidation states, are not only fundamentally important for expanding the notably limited knowledge on the bonding nature of a...

Synthesis of Anhydrous Acetates for the Components of Nuclear Fuel Recycling in Dialkylimidazolium Acetate Ionic Liquids.

A series of anhydrous acetate salts with uranium {[C2C1im][UO2(OAc)3] (1), [C2C2im][UO2(OAc)3] (2), and [C4C1im][UO2(OAc)3] (3)}, lanthanides {[C2C2im]2[La(OAc)5] (4) and [C2C1im]2[Nd(OAc)5] (5)}, and strontium {[C2C1im]n[Sr(OAc)3]n (6)} (where C2C1im = 1-ethyl-3-methylimidazolium, C2C2im = 1,3-diethylimidazolium, C4C1im = 1-butyl-3-methylimidazolium, and OAc = acetate) have been prepared and structurally characterized. Both lanthanides and strontium are common components of the nuclear fuel waste, and their separation from uranium is an important but still challenging task. A new synthetic approach with dialkylimidazolium acetate ionic liquids (ILs) as the solvent has been developed for the direct synthesis of homoleptic acetates from the corresponding hydrates and, unexpectedly, hardly soluble f-element oxides. Although the group of characterized compounds shows perfect structural variability, all actinide and lanthanide metal ions form monomeric complex anions where the metal cation coordinates to five ligands including two oxygen atoms in the case of uranium, as is commonly observed for uranyl compounds. Crystallographic analyses revealed that the complex [UO2(OAc)3]- anions possess rather standard D3h symmetry featuring a hexagonal-bipyramidal coordination environment, while the lanthanide anions [Ln(OAc)5]2- are fully asymmetric and the Ln3+ cations are 10-coordinated in the form of a distorted bicapped tetragonal antiprism. This is the first report of lanthanide ions coordinated in this fashion. For Sr2+, 9-fold coordination through oxygen atoms in the form of a strongly distorted tricapped trigonal prism is observed. The crystallization of anhydrous, homoleptic, anionic acetate complexes from such a large variety of different metal salts appears to be due to the properties of dialkylimidazolium acetate ILs themselves, including enhanced basicity from the high concentration of free anions and their greater affinity for hydrogen-bonding solutes relative to metal cations.

Novel Uranyl Coordination Polymers Based on Quinoline-Containing Dicarboxylate by Altering Auxiliary Ligands: From 1D Chain to 3D Framework

Novel uranyl coordination polymers, UO2(bqdc)(phen)·H2O (1), [UO2(μ-OH)(bqdc)(H2bpy)0.5(H2O)] (2), Na[(UO2)2(bqdc)3Na(H2O)2] (3), and [Na(bqdc)0.5(bpp)(H2O)] (4) (H2bqdc = 2,2′-biquinoline-4,4′-dicarboxylic acid; phen = 1,10-phenanthroline; bpy = 4,4′-bipyridine; bpp = 1,3-di(4-pyridyl)propane), with bqdc2– ligands have been successfully synthesized by hydrothermal reactions and characterized by single-crystal X-ray diffraction, Infrared spectroscopy (IR), thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD). The topological structures feature 1D chain to 3D framework by altering N-donor ancillary ligands. Compound 1 shows a 1D wave-shaped zigzag chain structure and further extends to a two-dimensional (2D) layer through π···π interactions between the quinoline ring of bqdc2– ligand and benzene ring of phen ligand. The uranium adopts an approximate hexagonal bipyramidal coordination geometry with the equatorial plane warped to the unusual chair conformation. Compound 2 features rectangula...

Correlation between intermolecular hydrogen bonds and melting points of uranyl nitrate complexes with cyclic urea derivatives

To clarify requirements for forming UO2(NO3)2(CU)2 (CU: cyclic urea derivative) and UO2(NO3)2(NRP)2 (NRP: N-alkylated pyrrolidone derivative) with high melting points (mps), molecular and crystal structures of UO2(NO3)2(0a)2 (0a: 2-imidazolidone), UO2(NO3)2(0b)2 (0b: tetrahydro-2-pyrimidone) and UO2(NO3)2(1a)2 (1a: 1-methyl-2-imidazolidone) were determined by means of single crystal X-ray analysis. Melting points (mps) of these complexes were compared with each other and those of other UO2(NO3)2(CU)2 and UO2(NO3)2(NRP)2. As a result, the uranyl nitrate complexes with 0a, 0b and 1a exhibit typical structural properties of UO2(NO3)2L2 (L: unidentate ligand); i.e., hexagonal bipyramidal coordination geometry, and two bidentate NO3− and two CUs located at trans positions in an equatorial plane of UO22+ ion. Several intermolecular N–H⋯O hydrogen bonds (HBs) were found in the crystal structures of UO2(NO3)2(0a)2, UO2(NO3)2(0b)2 and UO2(NO3)2(1a)2. In contrast, no intermolecular C–H⋯O HBs were formed in these crystal structures. The intermolecular HBs were discussed in connection with mps of UO2(NO3)2(CU)2 and UO2(NO3)2(NRP)2 including those reported previously. The mp tends to increase as the number of N–H⋯O HBs per molecule increases, whereas effects of C–H⋯O HBs on the mps is not very significant. These results suggest that the intermolecular N–H⋯O HBs strongly contribute to form a uranyl nitrate complex with high mps.

Crystal structure of μ-peroxido-κ(4) O (1),O (2):O (1'),O (2')-bis-[(nitrato-κO)(2,2':6',2''-terpyridine-κ(3) N,N',N'')dioxidouranium(VI)

In the title dimeric complex, [{UO2(NO3)(C15H11N3)}2O2], a peroxide ion bridges the two uran­yl(VI) [O=U=O]2+ ions. The O—O bond length of the peroxide is 1.485 (6) Å and the mid-point of this bond is located at the inversion centre of the dimer. The U atom exhibits a distorted hexa­gonal–bipyramidal coordination geometry with two uran­yl(VI) O atoms occupying the axial positions and one O atom of the monodentate nitrate ion, both O atoms of the peroxide ion and the three N atoms of the chelating tridentate 2,2′:6′,2′′-terpyridine (terpy) ligand in the equatorial positions. Two of the N atoms of the terpy ligand lie above and below the mean plane containing the equatorial ligand atoms and the U atom [deviations from the mean plane: maximum 0.500 (2), minimum −0.472 (2) and r.m.s. = 0.2910 Å]. The dihedral angle between the terpy ligand and the mean plane is 35.61 (7)°. The bond lengths around the U atom decrease in the order U—N > U—Onitrate > U—Operoxo > U=O. The dimeric complexes pack in a three-dimensional network held together by weak π–π inter­actions [centroid–centroid distance = 3.659 (3) Å] between pyridyl rings of the terpy ligands in neighbouring dimers, together with inter­molecular C—H⋯O and C—H⋯π inter­actions. Weak intra­molecular C—H⋯O inter­actions are also observed.

Uranyl(VI) binding by bis(2-hydroxyaryl)diimine and bis(2-hydroxyaryl)diamine ligand derivatives. Synthetic, X-ray, DFT and solvent extraction studies

The interaction of uranyl(VI) nitrate with a series of bis(2-hydroxyaryl)imine (H2L1–H2L5) and bis(2-hydroxyaryl)amine (H2L8, H2L9) derivatives incorporating 1,3-dimethylenebenzene or 1,3-dimethylenecyclohexane bridges between nitrogen sites is reported. Crystalline complexes of type [UO2(H2L)(NO3)2] (where H2L is H2L1–H2L4) were isolated from methanol. X-ray structures of the complexes of H2L1, H2L2 and H2L4 show that each of these neutral ligands bind to their respective UO22+ centres in a bidentate fashion in which coordination only occurs via each ligand’s hydroxy functions. Two bidentate nitrate anions complete the metal’s coordination sphere in each complex to yield hexagonal bipyramidal coordination geometries. A density functional theory (DFT) investigation of [UO2(H2L1)(NO3)2] in a simulated methanol environment is in accord with this complex maintaining its solid state conformation in solution. Solvent extraction experiments (water/chloroform) employing H2L1–H2L7 in the organic phase and uranyl(VI) nitrate in the aqueous phase showed that both amine derivatives, H2L8 and H2L9, yielded enhanced extraction of UO22+ over the corresponding imine derivatives, H2L1 and H2L2. These results were further compared with those obtained for the corresponding Schiff bases incorporating 1,2-phenylene and 1,2-cyclohexane bridged ligands, H2L6 and H2L7; these more rigid systems also yielded enhanced extraction of UO22+ relative to the more flexible Schiff bases H2L1–H2L5. A very significant synergistic enhancement of the extraction of UO22+ by H2L1–H2L4 and H2L7 was observed in the presence of a 10-fold excess of n-octanoic acid; the influence of pH on extraction efficiency was also investigated. A parallel set of experiments employing H2L1–H2L9 as extractants for europium(III) nitrate indicated a clear uptake preference for UO22+ over Eu3+ in all cases; separation of the uranyl ion from the rare earths is an important objective in mineral processing.

Structural features of two polymorphs of ammonium uranyl crotonate

X-ray crystallography, FTIR spectroscopy and thermal analysis were conducted for crystals of two polymorphs of NH4UO2(C3H5COO)3, which are the first examples of uranyl tricarboxylate complexes with ions of unsaturated aliphatic monocarboxylic acid. The main structural units of both polymorphs are anionic complexes [UO2(C3H5COO)3]−. Uranium atoms adopt hexagonal bipyramidal coordination polyhedron, and crotonate ions realize bidentate cyclic type of coordination. Due to different packing of ammonium ions and [UO2(C3H5COO)3]− complexes triclinic crystals of α-polymorph have layer structure and cubic crystals of β-polymorph have three dimensional structure. Features of three dimensional packing of R+ ions and [UO2L3]− complexes in structures of 25 known R[UO2L3] compounds are discussed.

Diaquadinitratouranyl(VI) enforces the O(phenoxo)2O(methoxy)2 compartment of 3-methoxysalicylaldehyde-diamine ligands to interact with water molecules

This report presents the syntheses, characterization and crystal structures of [{CuIIL1}2·{(UVIO2)(NO3)2(H2O)2}] (1), [{CuIIL2}2·{(UVIO2)(NO3)2(H2O)2}]·2H2O (2) and [{CuIIL3}2·{(UVIO2)(NO3)2(H2O)2}]·2H2O (3) derived from three 3-methoxysalicylaldehyde-diamine Schiff base compartmental ligands H2L1, H2L2 and H2L3, in which the diimine moieties come from ethylenediamine, trans-1,2-diaminocyclohexane and ortho-phenylenediamine, respectively. Compounds 2 and 3 crystallize in triclinic crystal system having P1¯ space group, while compound 1 crystallizes in monoclinic symmetry with space group P21/c. The three structures are similar. The two coordinated water molecules in diaquadinitratouranyl(VI) occupy the two trans positions in the hexagonal basal plane of the hexagonal bipyramidal coordination environment. Each of these two water molecules interact, by forming bifurcated hydrogen bonds, with each of the two O(phenoxo)2O(methoxy)2 compartments resulting in the stabilization of the [1×2+1×1] trimetallic self-assemblies. The d–d spectra of 1–3 and the corresponding mononuclear copper(II) complexes [CuIIL1(H2O)]/[CuIIL2(H2O)]/[CuIIL3(H2O)] have been recorded. The previously proposed but little addressed correlation of d–d band position with the displacement of the copper(II) center from the least-squares basal plane has been highlighted, revealing the utilization of this correlation accompanied with the FT-IR data to judge the nature of water molecule in the mononuclear complexes. The unique features in the composition of 1–3 have been discussed.

Uranyl(VI)–Acetylacetonate Coordination Compounds with Various N-Heterocyclic Ligands

Abstract Seven uranyl(VI) complexes, [UO2(acac)2(L)] [L = 4-methylpyridine (1), 4-ethylpyridine (2), 2,4-dimethylpyridine (3), (−)-nicotine (4), and imidazole (5)], [{UO2(acac)2}2(4,4′-bipyridine)] (6), and [(2,2′-bipyridine)2H][UO2(acac)(NO3)2] (7) have been synthesized and characterized crystallographically. The coordination geometry of U has a UNO6 pentagonal-bipyramidal coordination in 1–6, and a UO8 hexagonal-bipyramidal coordination in 7.

Pb(18‐crown‐6)Cl2 and Hg(18‐crown‐6)I2: Molecular Dihalides Trapped in a Crown Ether

AbstractPb(18‐crown‐6)Cl2 and Hg(18‐crown‐6)I2 are obtained as transparent colourless crystals of needle and hexagonal shape, respectively, by isothermal evaporation of their dichloromethane solutions. Pb(18‐crown‐6)Cl2 crystallizes with the trigonal crystal system [$R{\bar 3}$, no. 148, a = b = 1176.3(2), c = 1191.8(3) pm, V = 1428.2(5) 106·pm3, Z = 3] whereas Hg(18‐crown‐6)I2 crystallizes with the orthorhombic crystal system (Pnma, no. 62, a = 1613.9(2) pm, b = 2822.2(5) pm, c = 841.3(1) pm, V = 3832(1)106·pm3, Z = 8). Both compounds are characterized by linear MX2 (HgI2 or PbCl2) molecular units which are encrypted by the crown ether. In both cases, the divalent metal ion resides in the middle of the crown ether resulting in a hexagonal bipyramidal coordination environment for the metal cations. The molecular symmetry comes close to D3d. Hg(18‐crown‐6)I2 and Pb(18‐crown‐6)Cl2 differ in the way the single MX2@18‐crown‐6 units are packed. Whereas the Hg(18‐crown‐6)I2 molecules are arranged in a (distorted) cubic closest packing, the Pb(18‐crown‐6)Cl2 molecules adopt a hexagonal closest packing.

Dioxouranium(VI) complexes with 2,6-acetylpyridinebenzoylhydrazones and -semicarbazones

Benzoylhydrazones and semicarbazones derived from 2,6-diacetylpyridine react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu 4] 2[UO 2Cl 4] to form air-stable complexes. 2,6-Diacetylpyridinebis(benzoylhydrazone) (H 2L 1), 2,6-diacetylpyridinebis(N4-phenylsemicarbazone) (H 2L 2) and the asymmetric proligand 2,6-diacetylpyridine(benzoylhydrazone)(N4-phenylsemicarbazone) (H 2L 3) give yellow products of the composition [UO 2(L)]. The neutral compounds contain doubly deprotonated ligands and possess uranium atoms with distorted pentagonal-bipyramidal coordination spheres. The equatorial coordination spheres of the metal atoms can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting complexes have hexagonal-bipyramidal coordination environments with the oxo ligands in axial positions. X-ray diffraction studies on [UO 2(L 1)(DMSO)], [UO 2(L 2)], [UO 2(L 2)(DMSO)] and [UO 2(L 3)] show relatively short U–O bonds to the benzoylic oxygen atoms between 2.273(6) and 2.368(5) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U–N bond lengths: 2.502(7)–2.671(7) Å). The addition of a sixth ligand to the equatorial coordination sphere results in a lengthening of the metal–pyridine bonds.

Uranyl coordination environment in hydrophobic ionic liquids: an in situ investigation.

Different inner-sphere coordination environments are observed for the uranyl nitrate complexes formed with octyl-phenyl-N,N-diisobutylcarbamoylmethylphosphine oxide and tributyl phosphate in dodecane and in the hydrophobic ionic liquids (ILs) [C(4)mim][PF(6)] and [C(8)mim][N(SO(2)CF(3))(2)]. Qualitative differences in the coordination environment of the extracted uranyl species are implied by changes in peak intensity patterns and locations for uranyl UV-visible spectral bands when the solvent is changed. EXAFS data for uranyl complexes in dodecane solutions is consistent with hexagonal bipyramidal coordination and the existence of UO(2)(NO(3))(2)(CMPO)(2). In contrast, the complexes formed when uranyl is transferred from aqueous nitric acid solutions into the ILs exhibit an average equatorial coordination number of approximately 4.5. Liquid/liquid extraction results for uranyl in both ILs indicate a net stoichiometry of UO(2)(NO(3))(CMPO)(+). The concentration of the IL cation in the aqueous phase increases in proportion to the amount of UO(2)(NO(3))(CMPO)(+) in the IL phase, supporting a predominantly cation exchange mechanism for partitioning in the IL systems.

Synthesis and structure of the amidate-bridged platinumuranium bimetallic complex [Pt{ [formula omitted]H 2} 2(PPh 3) 2]·UO 2(NO 3) 2

The reaction of the β-propiolactam-derived platinum(II) amidate complex [Pt{ NC(O)CH 2C H 2} 2(PPh 3) 2] with uranyl nitrate gives the coordination complex [Pt{ NC(O)CH 2C H 2} 2(PPh 3) 2]·UO 2(NO 3) 2, which was characterised by a single-crystal X-ray diffraction study. The lactam carbonyl groups are coordinated to the linear uranyl group, forming an eight-membered ring, with the uranium also having two bidentate nitrates, completing a hexagonal bipyramidal coordination geometry. The platinum and uranium coordination planes are almost perpendicular, at an angle of 85.4(1)°.

Characterization, luminescence and crystal structure of uranyl nitrate complexes with diphenyl- N-ethylphosphine amide and tripiperidinephosphine oxide

The uranyl complexes UO 2(NO 3) 2L 2 (L=DPEPA ( 1) diphenyl- N, N-ethylphosphine amide and TPPPO ( 2) tripiperidine oxide) have been prepared. Spectroscopic studies indicate that L is bound to the uranyl group via the phosphoryl oxygen atom. The crystal structures of ( 1) and ( 2) show a hexagonal-bipyramidal coordination about uranium. The luminescence properties of the compounds have been also investigated.

Comparison of divalent dimethoxyethane-solvated thulium and samarium diiodides in hexamethylphosphoramide and pyridine: Isolation of the cations { [TmI2 (HMPA) 4] [I] (pyridine) 5} and { [TmI (HMPA) 4 (pyridine) ] [I] 2} and a single crystal containing both linear and bent dimethoxyethane-solvated SmI2

The highly reducing nature of TmI2 (DME) 3 is shown by comparison with SmI2 in its reactions in hexamethylphosphoramide (HMPA) and pyridine. Addition of 4 equiv. of HMPA to green TmI2 (DME) 3 in dimethoxyethane (DME) forms pale yellow solids which dissolve in pyridine and can be isolated as TmI3 (HMPA) 4, 1. Recrystallization of 1 from pyridine yields { [TmI2 (HMPA) 4] [I] (pyridine) 5} , 2, or { [TmI (HMPA) 4 (pyridine) ] [I] 2} , 3, depending upon conditions. Both 2 and 3 crystallize with distorted octahedral geometries around thulium. Addition of HMPA to TmI3 in DME also forms 1. TmI2 (DME) 2, formed by the loss of DME from TmI2 (DME) 3 under vacuum, reacts with pyridine to form intensely colored materials, which have magnetic moments consistent with the presence of Tm (III) . In comparison, SmI2 (THF) 2 dissolves in a mixture of pyridine and DME and can be recrystallized as divalent SmI2 (DME) 3, 4. 4 crystallizes with both linear and bent I-Sm-I arrangements in the same crystal. In the former case a hexagonal bipyramidal coordination geometry is present and in the latter a dodecahedral geometry is observed.

Preparation and Crystal Structure of Lithium Nitride Chloride Li4NCl

Li4NCl was prepared from Li3N and dry OH-free LiCl at 450°C. It is found to be the more nitrogen-rich of two compounds in the quasi-binary system Li3−2xN1−xClx. Following unit cell indexing using laboratory X-ray powder data, the previously unknown structure of the title compound was solved from neutron powder diffraction data recorded using the flat-cone and powder diffractometer E2 at the Berlin BERII reactor. Li4NCl crystallizes in the hexagonal rhombohedral space groupR3=m(No. 166),a=366.225(4),c=1977.18(4) pm with three formula units per unit cell. Its structure comprises a 1:1-ordering variant of a cubic close anion packing, N3−and Cl−forming layers perpendicular to [001]. Li atoms occupy all the triangular voids of the N layers and all the NCl3-tetrahedral holes. Nitrogen is in lithium nitride-like hexagonal bipyramidal coordination by Li, the equatorial six-membered ring being slightly puckered, while Cl is in distorted octahedral coordination. Calculation of the Madelung part of the lattice energy shows that the nitrogen hexagonal bipyramidal coordination polyhedron, peculiar for Li4NCl and the Li3N parent structure, is in agreement with a simple ionic picture and does not imply any covalent bonding.

Synthesis, thermogravimetry and X-ray analysis of uranyl benzoate and butyrate derivatives

The structures of the complexes Na[UO 2(C 6H 5COO) 3].C 6H 5COOH · H 2O ( 1) and Ca[UO 2(C 2H 5COO) 3] 2 · 6H 2O ( 2) have been determined by X-ray diffraction techniques. Complex 1 crystallizes in the triclinic system, space group P 1 with a = 9.443(2), b = 12.141 (3), c = 14.205(3) Å, α = 109.81(2), β = 107.47(2), γ = 93.70(2)° and d calc = 1.84 g cm −3 with Z = 2, R = 0.023, R w = 0.030 for 6819 observed reflections ( I ⩾ 3 σI). Complex 2 crystallizes in the monoclinic system space group P2 1/ c with a = 15.564(2), b = 12.697 (3), c = 18.238(3) Å, β = 94.73(3)° and d calc = 2.08 g cm −3 with Z = 4, R = 0.047, R w = 0.062 for 5813 observed reflections ( I ⩾ 3 σI). Both compounds present the usual hexagonal bipyramidal coordination geometry around uranium ions, with three bidentate chelating benzoate or butyrate ligands occupying the equatorial plane in 1 and 2 respectively. Different sets of interactions between the sodium ions and the uranyl complex anions in 1 and calcium ions and the respective uranyl anions in 2 are present in the two structures. X-ray powder patterns and thermogravimetric analyses further characterize the two compounds.

An Inclusion Complex of Uranyl in a Diazacrown: (Diaza-18-crown-6)2+.2CF3SO3− and [UO2(diaza-18-crown-6)]+.CF3SO3−

The structures of two compounds involving the macrocycle 1, 4, 10, 13-tetraoxa-7, 16-diazacyclooctadecane (diaza-18-crown-6, C 12 H 26 N 2 O 4 ) are reported. In 1, 4, 10, 13-tetraoxa-7, 16-diazoniacyclooctadecane bis(trifluoromethanesulfonate), C 12 H 28 N 2 O 4 2+ .2CF 3 SO 3 − , (I), the two N atoms are protonated, resulting in a ring conformation different to that of the neutral crown. The second compound, dioxo[1, 4, 10, 13-tetraoxa-7, 16-diazocyclooctadecanido(1 −)]uranium trifluoromethane-sulfonate, [UO 2 (C 12 H 25 N 2 O 4 )]CF 3 SO 3 , (II), is composed of [UO 2 (diaza-18-crown-6)] + cations and CF 3 SO 3 − anions. The linear uranyl moiety is included into the macrocycle with hexagonal-bipyramidal coordination geometry; one of the N atoms is deprotonated and the two N atoms are thus at different distances from the U atom and have different geometries