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.

Synthesis, Structure and Photoluminescence Properties of Cd and Cd-Ln Pentafluorobenzoates with 2,2′:6′,2′-Terpyridine Derivatives

Six new complexes [Cd(tpy)(pfb)2] (1, tpy = 2,2′:6′,2″-terpyridine), [Ln2Cd2(tpy)2(pfb)10] (Ln = Eu (2Eu), Tb (2Tb)), [Ln2Cd2(tbtpy)2(pfb)10]·2MeCN (Ln = Eu (3Eu), Tb (3Tb), tbtpy = 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine), [Eu2Cd2(tppz)(pfb)10]n (4, tppz = 2,3,5,6-tetra-(pyridin-2-yl)pyrazine) based on pentafluorobenzoic acid (Hpfb) have been prepared and investigated. The effect of tridentate ligands on geometry heterometallic scaffolds synthesized complexes is discussed. The supramolecular crystal structures of the new compounds are stabilized by π-π, C-F···π, C-H···O, C-H...F, F….F interactions. Non-covalent interactions have been studied using Hirschfeld surface analysis. The obtained compounds were characterized by single-crystal and powder X-ray diffraction, luminescence spectroscopy, IR spectroscopy, CHN analysis. Complexes 2Ln and 3Ln exhibit metal-centered photoluminescence, but the presence of ligand luminescence bands indicates incomplete energy transfer from the d-block to the lanthanide ion.

Noncomplexed Cucurbituril-Mediated Structural Evolution of Layered Uranyl Terephthalate Compounds

Template synthesis is one of the most feasible ways to explore new uranyl compounds with intriguing structures and properties. Here we demonstrate the preparation of six novel "sandwichlike" uranyl coordination polymers (UCPs) based on two-dimensional uranyl-terephthalate acid (H₂TP) networks using CBn (n = 5, 6, 8) as template ligands in the presence of different cations (Na⁺, K⁺, Cs⁺, or H₂N(CH₃)₂⁺). Compound 1 ([UO₂(TP)₂][Na₂(CB5)(H₂O)](H₂O)₅) is composed of layered uranyl-TP networks with the complex of CB5 and sodium cations as template ligands. In compound 2 ([(UO₂)₂(TP)₃]₂(CB6)(H₂O)₁₀), CB6 located between uranyl-TP networks contacts them by π-π interactions and hydrogen bonds. Compound 3 ([(UO₂)₂(TP)₃]₂[Na₂(H₂O)₁₀(CB6)]) is the same as compound 2 except for sodium cations bonding with CB6. Similarly in compound 4 ([(UO₂)₂(TP)₃][Cs(H₂O)₃(CB6)]), CB6 is a capsulelike structure capped with two cesium cations and interacts with uranyl-TP networks through π-π and C-H···π interactions. Compound 5 ([(UO₂)₂(TP)₃(HCOO)₂][K(H₂O)₂(CB5)]₂[H₂N(CH₃)₂]₂(CB6)(H₂O)₆) consists of both templates of CB6 and CB5 in which each CB5 is capped with one potassium cation while the H₂N(CH₃)₂⁺ cation is held at CB6 portals. In compound 6 ([(UO₂)₂(TP)₃]₂[UO₂(TP)₂(H₂O)₂][Cs(CB8)₃(H₂O)₄](H₂O)₁₆), CB8 ligands are connected by cesium cations to form a triangle motif and are further located between the uranyl-TP networks as template agents. All of the 2D layered structures with free CBn or cation-anchored CBn intercalate into the laminates of uranyl-terephthalate and shows a cucurbituril-mediated structural evolution. The regulating role of CBn as structure-directing template agents for the construction of layered UCPs through outer-surface interactions with layers of uranyl terephthalate is demonstrated, especially for the case of CB6 with contractive interlayer spacing.

In situ nitroso formation induced structural diversity of uranyl coordination polymers

This work presents three possible pathways that could exist in the in situ reaction system. Structural analysis of these compounds revealed that the introduction of nitroso group exerted significant influences on the conformations of ligands, skeletons and 3D structures.

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).

Utilizing bifurcated halogen-bonding interactions with the uranyl oxo group in the assembly of a UO2–3-bromo-5-iodobenzoic acid coordination polymer

The synthesis and crystal structure of a new uranyl coordination polymer featuring 3-bromo-5-iodobenzoic acid is described and the luminescent and vibrational properties of the material have been explored. Compound (1), [UO2(C7H3BrIO2)2]n, features dimeric uranyl units chelated and then linked by 3-bromo-5-iodobenzoic acid ligands to form a one-dimensional coordination polymer that is subsequently assembledviabifurcated halogen-bonding interactions with uranyl oxo atoms to form a supramolecular three-dimensional network. The asymmetric, bifurcated halogen-bonding interaction in (1) is notable as it represents the first observation of this synthon in a uranyl hybrid material. Raman and IR spectroscopy showed that halogen-bonding interactions with the uranyl oxo atoms result in small shifts in υ1and υ3frequencies, whereas luminescence spectra collected at an excitation wavelength of 420 nm reveal partially resolved uranyl emission.

Harnessing uranyl oxo atoms via halogen bonding interactions in molecular uranyl materials featuring 2,5-diiodobenzoic acid and N-donor capping ligands

The supramolecular assembly of molecular uranyl species via halogen-oxo interactions and spectroscopic manifestations thereof are probed in the solid state.

The role of intermolecular interactions involving halogens in the supramolecular architecture of a series of Mn(ii) coordination compounds

This study reveals the role of halogen-involving interactions in structural changes of supramolecular assemblies of manganese(ii) complexes including N-(4-halo)phenyl picolinamide ligands.

Controlling dimensionality via a dual ligand strategy in Ln-thiophene-2,5-dicarboxylic acid-terpyridine coordination polymers

Eleven new lanthanide-2,5-TDC-terpyridine coordination polymers which employ a dual ligand strategy have been synthesized and characterized by single crystal and powder X-ray diffraction as well as luminescence spectroscopy.

Synthesis, spectral characterization, structural studies, molecular docking and antimicrobial evaluation of new dioxidouranium(vi) complexes incorporating tetradentate N2O2 Schiff base ligands

Two new uranyl(vi) Schiff base complexes were synthesized and characterized by physicochemical and spectroscopic methods. The antimicrobial activities of these complexes were also investigated against microorganisms.