H2O Ligands Research Articles

Crystal structure of two [Ba(H2O)3](ClO4)2 phases and H2O ligands reorientational motions studied by X-ray single crystal, inelastic and quasielastic incoherent neutron scattering and proton magnetic resonance

XRSCD and NPD measurements indicated that the crystal space group (P63/m) is the same for high and low temperature phases. IINS spectra calculated by the DFT method are in a good agreement with the experimental data. The QENS peaks, registered at 225 and 175K, (above and below the phase transition at TCh=211.3K, respectively) do not show any broadening, what implies that the corresponding reorientational correlation times for 180° jumps of H2O ligands are longer than 10–11s. The 1H NMR line absorption results indicate that above TCh, the ratio of the area under the narrow contribution of the line to the whole line is close to 1:3, what suggests that upon heating of the sample, activation of a much faster than 10−8s rotational (of diffusive nature) motion of the only one of the three H2O ligands per one [Ba(H2O)3](ClO4)2 formula unit occurs.

Synthesis and Characterization of Two New Oxo-centered Trinuclear Complexes of Manganese and Iron

Two new oxo-centered trinuclear complexes, one of them a mixed-valence complex (Mn2MnO(CCl3CO2)6(Py)3) (1) and the other, mixed-metal complex of (Fe2MnO(CCl3CO2)6(H2O)3).NO3 (2) were synthesized by the direct reaction between metal nitrates and trichloroacetic acid. These complexes were characterized by elemental analyses (CHN), atomic absorption spectroscopy and spectral (IR, electronic) studies. These are new types of oxo-bridged mixed-metal complexes in which the carboxylate ligand is trichloroacetic acid. The UV spectra of the complexes exhibited strong bands in the region 213 and 257 nm which are related to the (π → π*) and (n → π*) transitions of the pyridine and H2O ligands, respectively. The IR spectra of these compounds showed two strong stretching vibrations bands, indicating a bridging coordination mode of the carboxylic group of the ligand in the complexes.

Vibrational and reorientational motions of H2O ligands, phase transition and thermal properties of [Sr(H2O)6]Cl2

One phase transition (PT) at TCh=252.9K (on heating) and at TCc=226.5K (on cooling) was detected by DSC for [Sr(H2O)6]Cl2 in 123–295K range. Thermal hysteresis of this PT equals to 26.4K. Entropy change (ΔS) value at this first-order type phase transition equals to ca. 1.5Jmol−1K−1. The temperature dependences of the full width at half maximum (FWHM) values of the infrared bands associated with ρt(H2O)E and δas(HOH)E modes (at ca. 417 and 1628cm−1, respectively) suggest that the observed phase transition is associated with a sudden change of a speed of the H2O reorientational motions. The H2O ligands in the high temperature phase reorientate quickly (correlation times 10−11–10−13s) with the activation energy of ca. 2kJmol−1. Below TCc probably a part of the H2O ligands stop their reorientation, while the remainders continue their fast reorientation but with the activation energy of ca. 8kJmol−1. Far and middle infrared spectra indicated characteristic changes at the vicinity of PT with decreasing of temperature, which suggested lowering of the crystal structure symmetry. Splitting of the band (at 3601cm−1) connected with vas(OH) mode near the TCc suggests lowering of the crystal lattice symmetry. All these facts suggest that the discovered PT is connected both with a change of the reorientational dynamics of the H2O ligands and with the change of the crystal structure.

Toward Understanding the Bonding Character in Complexes of Coinage Metals with Lone-Pair Ligands. CCSD(T) and DFT Computations

We present CCSD(T) interaction energies and the bonding analysis for complexes of Cu, Ag, and Au with the lone-pair ligands H2O, OF2, OMe2, NH3, NF3, NMe3, H2S, SF2, SMe2, PH3, PF3, PCl3, and PMe3 (ML complexes). Both electron correlation and relativistic effects are crucial in the bonding of all complexes. AuPH3, AuPF3, and AuPCl3 (AuPX3) complexes exhibit particularly large relativistic effects, 30-46 kJ/mol. Upon neglecting relativistic effects, the Au-P bonds almost vanish aside from weak long-range van der Waals interactions. Highest binding energies are computed for complexes with Au, followed by Cu and Ag. For all coinage metals the strongest interactions are computed for PX3 ligands followed by SX2 and NX3 OX2 ligands. Upon methylation the interaction energy rises significantly. Metal-thiol complexes, particularly AuSCH3, form a separate class. Exceptional stability of gold complexes is due to large relativistic enhancement of the electron affinity of Au. Along with the electron affinity of a metal, we link the pattern of interaction energies in ML complexes with ionization potentials (IPs) of ligands. Strong interaction with P containing ligands is attributed to their lower IP and the lone pair → metal electron donation accompanied with the back-donation characteristic for P containing ligand. Energy data are accompanied with the natural bond orbital analysis. Computationally less demanding DFT computations with the PBE0 functional provide correct pattern of interaction energies when compared with benchmark CCSD(T) results.

Generation of HO• Radical from Hydrogen Peroxide Catalyzed by Aqua Complexes of the Group III Metals [M(H2O)n]3+ (M = Ga, In, Sc, Y, or La): A Theoretical Study

The mechanism of the rate-limiting stage of alkanes oxidation with hydrogen peroxide, that is, formation of the hydroxyl radicals, catalyzed by aqua complexes, [M(H2O)n]3+ (1), of the group III metals exhibiting a unique stable non-zero oxidation state (M = Ga, In, Sc, Y, or La) was theoretically studied in detail at the DFT level. The mechanism involves the substitution of a H2O ligand for H2O2, protolysis of the coordinated H2O2, substitution of another H2O ligand for H2O2, generation of the hydroxyl radical upon the homolytic O–O bond cleavage in the key complex [M(H2O)(n−2)(H2O2)(OOH)]2+, and closure of the catalytic cycle. The substitution steps proceed via the dissociative mechanism D (M = Ga and Y) or the associative mechanisms A [M = Sc, La, or In (second substitution)] or Ia [M = In (first substitution)]. The general catalytic activity of 1 is determined by three main factors, that is, (i) lability of the complexes, (ii) acidity of the metal-bound ligands, and (iii) the H2O2 activation toward the...

Can the local enzyme scaffold act as an H-donor for a Co(I)[sbnd]H bond formation? The curious case of methionine synthase-bound cob(I)alamin

The density functional calculations and analysis of the existing X-ray crystallographic data have been carried out to gain mechanistic insight into the reactivation cycle of methionine synthase (MetH) enzyme. The calculations were carried out on the cobinamide-type model complexes of cob(I)alamin (Co(I)Cbx) testing H2O and PhOH as possible β-axial ligands. The PhOH motif was used to mimic the tyrosine (Y1139) residue that has been found in the active site of the MetH-bound cob(II)alamin (Co(II)Cbx). The calculations indicate that the β-axial PhOH ligand forms stronger Co(I)H bonds than H2O ligand due to its better H-donor capacity. The calculated redox tuning of Co(I)H interactions on the reduction potential of Co(II)/Co(I) couple (60–800mV vs standard hydrogen electrode (SHE)), irrespective of the β-axial ligand considered, is significantly higher than the biological redox gap between the reduction potential of Co(II)/Co(I) couple and that of the biological reducing agents (50mV vs SHE). The analysis of existing crystallographic data for the reactivation conformation of MetH enzyme (1K7Y (@3.0Å); 1K98 (@3.8Å) and 3IVA (@2.7Å)) indicates that the Y1139 residue and the β-axial H2O ligand in the MetH-bound Co(II)Cbx complex are equidistant from the Co(II) ion (Y1139Co(II)=3.97Å; H2OCo(II)=3.96Å). Taking into account that the Y1139-induced Co(I)H linkages are thermodynamically more stable than the H2O-induced ones, the present calculations suggest that the Y1139 residue may serve as the β-axial ligand in the reactivation conformation of MetH enzyme.

DFT Study of Uranyl Peroxo Complexes with H2O, F–, OH–, CO32-, and NO3–

The structural and electronic properties of monoperoxo and diperoxo uranyl complexes with aquo, fluoride, hydroxo, carbonate, and nitrate ligands have been studied using scalar relativistic density functional theory (DFT). Only the complexes in which the peroxo ligands are coordinated to the uranyl moiety in a bidentate mode were considered. The calculated binding energies confirm that the affinity of the peroxo ligand for the uranyl group far exceeds that of the F(-), OH(-), CO3(2-), NO3(-), and H2O ligands. The formation of the monoperoxo complexes from UO2(H2O)5(2+) and HO2(-) were found to be exothermic in solution. In contrast, the formation of the monouranyl-diperoxo, UO2(O2)2X2(4-) or UO2(O2)2X(4-/3-) (where X is any of F(-), OH(-), CO3(2-), or NO3(-)), complexes were all found to be endothermic in aqueous solution. This suggests that the monoperoxo species are the terminal monouranyl peroxo complexes in solution, in agreement with recent experimental work. Overall, we find that the properties of the uranyl-peroxo complexes conform to well-known trends: the coordination of the peroxo ligand weakens the U-O(yl) bonds, stabilizes the σ(d) orbitals and causes a mixing between the uranyl π- and peroxo σ- and π-orbitals. The weakening of the U-O(yl) bonds upon peroxide coordination results in uranyl stretching vibrational frequencies that are much lower than those obtained after the coordination of carbonato or hydroxo ligands.

Complexation of gold in S3−-rich hydrothermal fluids: Evidence from ab-initio molecular dynamics simulations

Recent Raman spectroscopic studies suggest that S3− is an important sulfur species in magmatic hydrothermal and metamorphic fluids at P>0.5GPa and T>250°C, and may be an important ligand for metal transport (Pokrovski and Dubrovinsky, 2011). Based on static Density Functional Theory calculations, Tossell (2012) confirmed the stability of the S3− ion, and suggested some possible Cu–S3 complexes in the ideal gas phase and in aqueous solution. We investigated the complexation of Au and S3− in aqueous fluids by ab-initio molecular dynamics (MD) simulations. We performed ab-initio MD simulations in aqueous solution at 300°C, 0.5 and 2GPa to investigate the competition among the S3−, HS−, H2S(aq), OH− and H2O ligands for Au+, aiming at evaluating the significance of the ‘exotic’ S3− ligand for Au metallogenesis. The results indicate that, in contrast to results of static calculations that show a symmetric Au–S3 complex with bidentate structure, Au+ forms linear complexes with S3−. The stoichiometry of these complexes depends on pH and fluid composition (e.g., Au(H2O)S3(aq); Au(HS)S3−; Au(OH)S3−; Au(S3)2−). The S3− and bisulfide (HS−) ions are ligands of similar strength for Au+; this confirms Pokrovski and Dubrovinsky's (2011) assumption that such ‘exotic’ ligands may play a major role in promoting Au mobility in magmatic and metamorphic environments.

Synthesis, Crystal Structure, and Electrochemical Properties of Two New Manganese Complexes With a Ligand Derived From 1,2-Propanediamine and 2-Hydroxy-5-Methoxybenzaldehyde

Two new homo binuclear manganese(III) complexes, [Mn (L)(H2O)]2(PF6)2, where [H2L = N,N′-Bis(2-hydroxy-5-methox- ybenzylidene)-propane-1,2-diamine] have been prepared by reaction of N,N′-bis(2-hydroxy-5-methoxybenzylidene)propane-1,2-diamine as a Schiff-base ligand, manganese(II) acetate and ammonium hexafluorophosphate. The complexes were characterized by spectral, structural and electrochemical studies. X-ray structural analysis shows the presence of dimanganese core in the complexes and the binding of the ligands to the manganese(III) is through N2O2. The dimeric unit is formed by a double Mn–O bridge of one molecule with its centrosymmetric homologue. The crystal structure of the complexes indicates that in the solid state the complex adopts an octahedral environment of the imine N and hydroxo O with the one axial H2O ligand around manganese. There are two coordination/chelation environments present around two manganese centers of each binuclear complex. The electronic spectra of the complex show red shift in the d–d transition. The electrochemical reduction of these complex at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Mn(III)–Mn(II) is electrochemically quasireversible in the range of 0 to −1.0 V.

Coordination and Solvation of the Au+ Cation: Infrared Photodissociation Spectroscopy of Mass-Selected Au(H2O)n+ (n = 1–8) Complexes

Gold cation-water complexes with attached argon atoms are produced via a laser vaporization supersonic cluster source. The [Au(H(2)O)(n)Ar(x)](+) (n = 1-8; x = 1 or 2) complexes are each mass selected and studied by infrared photodissociation spectroscopy in the OH stretching frequency region to explore the coordination and solvation structures of the Au(+) cation. Density functional calculations have been performed, and the calculated vibrational spectra are compared to the experimental spectra to identify the gas-phase structures of the Au(H(2)O)(n)(+) complexes. Confirming previous theoretical predications, the first coordination shell of the Au(+) cation contains two water molecules forming a linear O-Au(+)-O arrangement; subsequent water molecules bind to the two H(2)O ligands of the Au(H(2)O)(2)(+) core ion via hydrogen bond forming of the second hydration shell, which is complete at n = 6. For the complexes with n ≤ 7, the experimental spectrum can in general be assigned to the predicted global minimum structure. However, the spectrum suggests that two or more conformers coexist for the n = 8 complex, indicating that the identification of a single global minimum becomes less important upon increasing the number of solvating water molecules.

Understanding Differences in Mechanisms of Action of Fe vs Mn Porphyrins: Comparison of Their Reactivities Towards Cellular Reductants and Reactive Species

Understanding Differences in Mechanisms of Action of Fe vs Mn Porphyrins: Comparison of Their Reactivities Towards Cellular Reductants and Reactive Species Artak Tovmasyan, Tin Weitner, Emily Roberts, Melba Jaramillo, Ivan Spasojevic, Kam Leong, Margaret Tome, Ludmil Benov, and Ines Batinic-Haberle Duke University, University of Arizona, Kuwait University, Kuwait Fe and Mn N-substituted pyridylporphyrins (FePs and MnPs) are successfully studied in models of oxidative stress. Replacement of Mn with Fe in MnSOD enzyme results in dramatic change in metal coordination, which shifts M(III)/M(II) reduction potential, E1/2 out of the region optimal for catalysis of O2dismutation, and results in the loss of enzyme activity. In contrast, both FePs and MnPs have nearly identical E1/2 and thus dismute O2 and reduce ONOO with similarly high rate constants. Yet, there is a distinct difference in metal coordination field: at pH 7.8 axial coordination sites of Mn are occupied with two H2O molecules, while Fe bears H2O and OH ligands. The OH ligand neutralizes a positive charge at the Fe site, and labilizes trans-axial H2O, resulting in enhanced reactivity of FePs. FePs allow SOD-deficient E. coli to grow as good as wild type at up to 1000-fold lower concentrations than MnPs, but become toxic at doses where MnPs are efficient. When combined with ascorbate, MnPs become toxic to E. coli, whereas FePs toxicity is reversed. In a different study, both FePs and MnPs exert up to 10-fold higher toxicity towards cancer vs normal cells; however, FePs are cytotoxic at up to 10-fold lower concentrations than MnPs. When given with ascorbate, MnPs are toxic towards cancer cells (and not towards normal cells), while FePs/ascorbate system is toxic to neither cancer nor normal cells. To understand such large difference in bioactivity of FePs vs MnPs, we explored their reactivity towards cellular reductants. Thiol (cysteine and glutathione) oxidase activity, leading to H2O2 production, was revealed for both MnPs and FePs. The FePs are several-fold more reactive than MnPs, resulting in higher production of H2O2. Yet, FePs are very unstable towards H2O2; “free” Fe released by rapid degradation of FePs results in cell death, presumably via Fenton chemistry. In contrast, MnPs produce less H2O2, are more stable towards it, plus “free” Mn does not undergo Fenton chemistry. With ascorbate in cell medium, FePs are rapidly degraded by H2O2 produced in the medium due to FePs/ascorbate cycling, and in turn have small chance to enter and damage the cell. With MnPs/ascorbate, and due to MnPs higher stability, excessive levels of H2O2 are produced, thus accounting for enhanced cytotoxicity. Unlike cancer cells, normal cells are up to 10-fold less sensitive either to porphyrin or its combination with ascorbate due to the abundance of H2O2-removing systems.

First-principles molecular dynamics study of stepwise hydrolysis reactions of Y3 + cations

First-principles molecular dynamics simulations are carried out to study the stepwise hydrolysis reactions of Y3+-aqua in water. The simulation results reproduce the 8-fold coordinated hydration structure of Y3+. A constrained molecular dynamics method is employed to investigate the hydrolysis reactions, and a thermodynamic integration technique is used to calculate the free-energy profiles. Thus, the stepwise pKa's are derived: pKa1=7.9, pKa2=9.1 and pKa3=10.3, while the fourth hydrolysis is found to be extremely unfavorable. Based on the dissociation constants, the hydrolyzing speciation of Y3+ is constructed. The simulation results also show that in the hydrolysis process, some H2O ligands leave the cation to become part of the bulk solution, which makes the hydration number of Y3+ cations decrease from 8 (Y(H2O)83+) to 7 (Y(OH)(H2O)62+ and Y(OH)2(H2O)5+) and then to 6 (Y(OH)3(H2O)3).

Symmetry-adapted perturbation theory study for some magnesium complexes

A systematic theoretical study on Mg–ligand interactions has been carried out employing both ab initio correlated wave function and density functional methods. The interactions of the Mg(CH3N2)2moiety with BF, CO, N2, NH3, and H2O ligands have been investigated by performing calculations at the B3LYP, MP2, MP4, and CCSD(T)/6–311++G(3df,3pd) levels of theory. Results indicate that the interaction energies of the Mg(CH3N2)2–L complexes increase in the order NH3 > H2O > BF > CO > N2. Symmetry-adapted perturbation theory (SAPT) analysis has been carried out to understand the nature of the forces involved in the bonding. The SAPT results indicate that the stabilities of the Mg–L interactions are attributed mainly to electrostatic effects, while induction and dispersion forces also play a significant role. The evaluated SAPT interaction energies for the Mg(CH3N2)2–L complexes are generally in good agreement with those obtained using the supermolecule CCSD(T) methods, suggesting that SAPT is a proper method to study the intermolecular interactions in these complexes. The results also suggest an explanation for the unique role of Mg2+as a carrier of water molecules that mediate enzymatic hydrolysis reactions.

The geometry of the silver 1,1′-dibenzyl-2,2′-biimidazole complexes

The argentophilic interactions and interactions of weakly coordinated nitrate and water with silver metal were studied by investigating the reaction of 1,1′-dibenzyl-2,2′-biimidazole (Bn2bim) with silver nitrate. Three new silver complexes [Ag4(Bn2bim)4(NO3)2]·4(CH3CH2OH)·2(NO3)·0.5(H2O) (1), [Ag4(Bn2bim)4(H2O)4]·4(NO3) (2) and [Ag4(Bn2bim)4(NO3)4]·6(CH2Cl2)·2(H2O) (3) were synthesized and characterized. Complexes 1-3 have rare tetranuclear twisted closed cyclic structure with four bridging biimidazoles and variable nitrate/water ratio. The interactions between the nitrate ligand and Ag as well as water ligands and Ag are considered to be weak due to the ease of exchanging them. The structure 1 consists of a discrete tetranuclear complex with two short Ag⋯Ag distances of 3.0984(10)Å and 3.1994(10)Å, which indicates argentophilic interactions. The complex 2 forms linear assemblies of tetranuclear moieties via hydrogen bonding through weakly coordinated aqua ligand and NO3− counteranions. Crystallization from a mixture of dichloromethane and n-hexane led to an exchange of H2O ligands to nitrates and formation of a new discrete tetranuclear complex 3. Unlike 1, the more open structures of 2 and 3 did not show any argentophilic interactions. The two shortest Ag⋯Ag distances for complexes 2 and 3 were 4.6508(8)Å and 4.9517(5)Å and 4.5810(5)Å–5.0050(5)Å respectively. The overall energetics and the effect of the H2O molecules and the nitrate anions on the geometries of the Ag complexes were studied by computational DFT methods.

Inside Cover: Watching Water Migration around a Peptide Bond (Angew. Chem. Int. Ed. 27/2012)

The motion of a single water ligand around a peptide bond in acetanilide was probed in real time by time-resolved IR spectroscopy. In their Communication on page 6604 ff., O. Dopfer, M. Fujii et al. observe that triggered by photo-ionization, the H2O ligand is released from the CO site of the peptide linkage and trapped after a migration time of 5 ps at the NH site of the same peptide bond. The migration occurs via an intermediate in which the H2O molecule binds neither to the CO nor the NH site.

Watching Water Migration around a Peptide Bond

A long and winding road: The motion of a single water ligand around a peptide bond in acetanilide was probed in real time by time-resolved IR spectroscopy. Triggered by photoionization, the H2O ligand is released from the CO site of the peptide linkage and trapped after a migration time of 5 ps at the NH site of the same peptide bond (see picture).

Raman light scattering, infrared absorption and DSC studies of the phase transition and vibrational and reorientational dynamics of H2O ligands and ClO4– anions in [Ba(H2O)3](ClO4)2

[Ba(H2O)3](ClO4)2 between 90 and 300 K possesses two solid phases. One phase transition of the first‐order type at: = 211.3 K (on heating) and = 204.6 K (on cooling) was determined by differential scanning calorimetry. The entropy change value (ΔS ≈ 15 Jmol–1 K–1), associated with the observed phase transition, indicates a moderate degree of molecular dynamical disorder. Both, vibrational and reorientational motions of H2O ligands and ClO4– anions, in the high‐temperature and low‐temperature phases, were investigated by Fourier transform far‐infrared and middle‐infrared and Raman light scattering spectroscopies. The temperature dependences of the full‐width at half‐maximum values of the bands associated with ρw(H2O) mode, in both infrared (~570 cm–1) and Raman light scattering (~535 cm–1) spectra, suggest that the observed phase transition is not associated with a sudden change of a speed of the H2O reorientational motions. Ligands reorient fast, with correlation time of the order of several picoseconds, with a mean activation energy value Ea = 5.1 kJ mol–1 in both high and low temperature phases. On the other hand, measurements of temperature dependences of full‐width at half‐maximum values of the infrared band at ~460 cm–1, associated with δd(OClO)E mode, and Raman band at ~1105 cm–1, associated with νas(ClO)F2 mode, revealed the existence of a fast ClO4– reorientation in phase I and in phase II, with the Ea(I) and Ea(II) values equal to 8.0 and 6.5 kJ mol–1, respectively. These reorientational motions of ClO4– are slightly distorted at the TC. Fourier transform far‐infrared and middle‐infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TC, which suggested lowering of the crystal structure symmetry. All these experimental facts suggest that the discovered phase transition is associated with small change of H2O ligands and somewhat major change of ClO4– anions reorientational dynamics, and with insignificant change of the crystal structure, too. Copyright © 2012 John Wiley & Sons, Ltd.

N,N′-dipyridoxyl(ethylenediamine) schiff-base ligand and its square-pyramidal copper(II) complex: Synthesis, experimental and theoretical characterization

A new tetradentate N,N′-dipyridoxyl(1,2-ethylenediamine) [=H2ES] Schiff-base ligand and its Cu(II) salen complex [Cu(ES)(H2O)] are synthesized and characterized by IR, UV-Vis, 1H NMR, mass spectrometry, and elemental analysis. Their optimized geometries and theoretical vibrational frequencies are computed by using the density functional theory method where the B3LYP functional was used. Also, the 1H NMR chemical shifts of the H2ES ligand are calculated at the same computational level. In the optimized structure of the free ligand, two pyridine rings are not in the same plane. In the structure of the complex, the Schiff-base ligand acts as a dianionic tetradentate ligand in the N, N, O−, O− manner, so that the coordinating atoms occupy equatorial positions. The H2O ligand occupies the axial position of the squarepyramidal complex. The calculated results are consistent with the experimental ones, confirming the suitability of the optimized structures for the H2ES ligand and its Cu(II) complex.

Synthesis and supramolecular structure of [Me3Sn(μ-C2N10)SnMe3(H2O)]n, the first metal–organic azotetrazolate

Abstract The first metal–organic azotetrazolate, [Me3Sn(μ-C2N10)SnMe3(H2O)]n (2), was prepared in 61% isolated yield by the reaction of disodium azotetrazolate (Na2AZT⋅ 5H2O, 1) with 2 equivalents of Me3SnCl in aqueous solution. An X-ray diffraction study revealed a novel supramolecular structure of 2 in the crystal. Two different coordination environments around tin result in the formation of an unexpected zig-zag chain structure in the solid state with H2O ligands coordinated to every second Sn atom ligands terminating the alternating corners of the zig-zag chain. Both hydrogen atoms of the coordinated water molecules are engaged in O–H⋅⋅⋅N to different azotetrazolate dianions, leading to an interlocking of the zig-zag chain in a zipper-like overall crystal structure. Despite its fairly low nitrogen content of only 27.48% the title compound was found to be sensitive to both impact and friction.

Studies on solubility of uranyl complexes in supercritical carbon dioxide and its controlling factors using UV-visible and 17O- and 19F-NMR spectroscopy

Solubility of various β-diketonato complexes [Cu(hfa)2, Cr(hfa)3, Zr(hfa)4, Cu(hfa)2H2O, VO(hfa)2H2O, UO2(hfa)2H2O, UO2(hfa)2DMSO, and UO2(dfh)2DMSO (DMSO = dimethyl sulfoxide, hfa = hexafluoroacetylacetonate, dfh = 4H,4H-decafluoroheptane-3,5-dionate)] in supercritical carbon dioxide (scCO2) at 10.0 MPa and 40°C were measured using ultraviolet-visible and nuclear magnetic resonance (NMR) spectrometers equipped with high-pressure cell. The solubility of UO2(hfa)2H2O (4.0 × 10−2 M) and Cu(hfa)2H2O (2.3 × 10−2 M) with H2O ligands was smaller than that of UO2(hfa)2DMSO (1.2 × 10−1 M), UO2(dfh)2DMSO (3.8 × 10−1 M), and Cu(hfa)2 (2.9 × 10−2 M) (M = mol dm−3). The number of yl-oxygen and fluorine atoms also affected the solubility, i.e. the solubility increased in order of Cu(hfa)2H2O < VO(hfa)2H2O (2.5 × 10−2 M) < UO2(hfa)2H2O and in order of Cu(hfa)2 (2.9 × 10−2 M) < Cr(hfa)3 (3.0 × 10−2 M) < Zr(hfa)4 (4.4 × 10−2 M). Moreover, the intermolecular interactions between CO2 and specific atoms (yl-oxygen and fluorine) in β-diketonato complexes were examined by 17O- and 19F-NMR chemical shifts, and the existence of the apparent van der Waals interactions between CO2 and the specific atoms was identified. These results showed that the solubility of β-diketonato complexes in scCO2 was mainly controlled by the strength of CO2-complex interactions.