Hemibonding of hydroxyl radical and halide anion in aqueous solution

Molecular geometries and properties of the possible reaction products between the hydroxyl radical and the halide anions in aqueous solution were investigated. The formation of two-center three-electron bonding (hemibonding) between the hydroxyl radical and halide anions (Cl, Br, I) was examined by density functional theory (DFT) calculation with a range-separated hybrid (RSH) exchange-correlation functional. The long-range corrected hybrid functional (LC-ωPBE), which have given quantitatively satisfactory results for odd electron systems and excited states, was examined by test calculations for dihalogen radical anions (X(2)(-); X = Cl, Br, I) and hydroxyl radical-water clusters. Equilibrium geometries with hemibonding between the hydroxyl radical and halide anions were located by including four hydrogen-bonded water molecules. Excitation energies and oscillator strengths of σ-σ* transitions calculated by the time-dependent DFT method showed good agreement with observed values. Calculated values of the free energy of reaction on the formation of hydroxyl halide radical anion from the hydroxyl radical and halide anion were endothermic for chloride but exothermic for bromide and iodide, which is consistent with experimental values of equilibrium constants.     

Adsorption studies of mercury on zirconium oxide from aqueous solution

The adsorption of mercury on zirconium oxide from aqueous solution has been studied in relation to concentration of adsorbent and adsorbate. The influence of contact time, buffer composition, pH, and foreign ions was also investigated. Thiosulfate, iodide, thiocyanate, EDTA, cyanide and Li(I) drastically reduced adsorption. Adsorption of other metal ions under the same conditions was also investigated. Based on these data, separation of mercury from antimony and neodymium can be achieved.     

A set of molecular models for alkali and halide ions in aqueous solution

This work presents new molecular models for alkali and halide ions in aqueous solution. The force fields were parameterized with respect to the reduced liquid solution density at 293.15 K and 1 bar, considering all possible ion combinations simultaneously. The experimental target data are reproduced with a high accuracy over a wide range of salinity. The ion models predict structural properties of electrolyte solutions well, such as pair correlation functions and hydration numbers. The force fields provide good predictions of the properties studied here in combination with different models for water.     

Calix[4]pyrroles bearing quinolinium moiety for halide sensing in aqueous solution

Sensing of chloride in aqueous solution with high selectivity is a challenging task and has a great potential for cellular imaging and analytical applications in food chemistry. Supramolecular binding motif calix[4]pyrrole has been conjugated with a known fluorescent probe for chloride – a quinolinium dye - through conformationally flexible and rigid linkers. Effects of the supramolecular host on the properties of the fluorescent dye and vice versa have been investigated by NMR, X-ray crystallographic and spectroscopic methods. New fluorescent probes have demonstrated better binding and quenching properties towards chloride, bromide and iodide in a 1:1 water-methanol mixture as compared to free calix[4]pyrrole and the quinolinium dye.     

Early stages in the growth of small silver clusters in aqueous solution

In this mini-review, the growth of silver nanoclusters following the reduction of silver ions in aqueous solution is studied and some clusters are characterized. A model for the molecular structure of trimer silver clusters is discussed as well as the role of aliphatic alcohol radicalsin the growth of silver nanoclusters.     

Distinguishing metal halide molecular clusters from perovskite magic sized clusters in the synthesis of metal halide perovskite nanostructures

Background

Research into perovskite nanocrystals (PNCs) has uncovered interesting properties compared to their bulk counterparts, including tunable optical properties due to size-dependent quantum confinement effect (QCE). More recently, smaller PNCs with even stronger QCE have been discovered, such as perovskite magic sized clusters (PMSCs) and ligand passivated PbX₂ metal halide molecular clusters (MHMCs) analogous to perovskites.

Objective

This review aims to present recent data comparing and contrasting the optical and structural properties of PQDs, PMSCs, and MHMCs, where CsPbBr₃ PQDs have first excitonic absorption around 520 nm, the corresponding PMSCS have absorption around 420 nm, and ligand passivated MHMCs absorb around 400 nm.

Results

Compared to normal perovskite quantum dots (PQDs), these clusters exhibit both a much bluer optical absorption and emission and larger surface-to-volume (S/V) ratio. Due to their larger S/V ratio, the clusters tend to have more surface defects that require more effective passivation for stability.

Conclusion

Recent study of novel clusters has led to better understanding of their properties. The sharper optical bands of clusters indicate relatively narrow or single size distribution, which, in conjunction with their blue absorption and emission, makes them potentially attractive for applications in fields such as blue single photon emission.     

Synthesis and structural determination of a hexanuclear zirconium glycine compound formed in aqueous solution

Single crystals of a zirconium-glycine compound have been first grown in aqueous solution via an excess acid and extra stabilizer approach. The crystal structure [Zr 6(OH (-)) 8(H 2O) 8(HGly) 4(Gly (-)) 4].(SO 4 (2-)) 6.14H 2O ( CP-1) has been characterized by single-crystal X-ray diffraction. The structure revealed that it is composed of hexa-zirconium octahedral clusters coordinated by eight carboxylic acid groups of glycine. The charge assignment is also consistent with the electronic structure calculations, and the computational result reveals that the Zr 6 core should have no skeleton electrons.     

Structure-directing influence of halide in mercury thiolate clusters

Under identical conditions, the reaction of 2-aminoethanethiol hydrochloride with HgX(2) (X = Cl and Br) in water yielded discrete hexanuclear [Hg(6)Cl(8)(SCH(2)CH(2)NH(3))(8))]Cl(4).4H(2)O (1) and nonanuclear [Hg(9)Br(15)(SCH(2)CH(2)NH(3))(9)](Cl(0.8)Br(0.2))(3) (2) complexes with unusual coordination environments. Compound 1 crystallizes as triclinic with a = 9.434(2) Angstroms, b = 10.999(2) Angstroms, c = 13.675(7) Angstroms, alpha = 92.9(7) degrees, beta = 105.2(7) degrees, and gamma = 96.9(7) degrees, whereas 2 is monoclinic with a = 14.162(3) Angstroms, b = 8.009(16) Angstroms, c = 19.604(4) Angstroms, alpha = gamma = 90.0 degrees, and beta = 92.7(3) degrees. In both cases, it is observed that the halide creates the secondary structure around trinuclear units (dimer in 1 and trimer in 2) through Hg-X bonding. Two independent types of Hg atoms (four- and five-coordinate in 1) and (three- and four-coordinate in 2) are observed. The geometry around Hg is quite variable with bridging thiolate and both bridging and terminal halides. The angles around Hg associated with the S atoms are more obtuse than expected from mercury(II) thiolates with a coordination number of more than 2. Intermolecular hydrogen bonding involving NH(3)(+), water molecules, and the halide atoms is responsible for the three-dimensional network in both compounds. Relatively short Hg...Hg interactions in 1 (3.797 and 3.776 Angstroms) and in 2 (3.605 and 3.750 Angstroms) are also observed. The compounds have been characterized with the help of (1)H and (13)C NMR, UV-Vis, infrared, Raman, and mass spectrometry, thermogravimetric analysis, and single X-ray crystallography.     

Ion mobility measurements of metal halide clusters

The failure of standard solid state methods to determine the structure of very small clusters has been the starting point to adapt the ion chromatography technique to cluster experiments. A new approach combining an ion drift cell and a time-of-flight mass spectrometer for cluster ion mobility measurements is described. In this publication we concentrate on the experimental set-up and the data analysis starting with the time-of-flight mass spectra. Furthermore, first results concerning relative ion mobilities for cesium iodide and sodium iodide clusters will be shown to demonstrate the feasibility of the new tandem instrument.     

Effect of various halide salts on the incompatibility of cyanocobalamin and ascorbic acid in aqueous solution

Combination of cyanocobalamin (VB12) and ascorbic acid (VC) has been widely seen in pharmaceutical products and dietary supplements. However, VB12 has been reported that its behavior in stability in aqueous solution is quite different when VC is mixed. In the present study, we examined the stabilities of these vitamins in acetate buffer (pH 4.8) using high performance liquid chromatography. Degradation of VB12 was not observed in the absence of VC in the buffer. However, when VC was mixed in the VB12 solution, VB12 concentrations decreased in accordance with VC degradation. VB12 and VC degradations were inhibited by adding sodium halides to acetate buffer at pH 4.8. These stabilization effects were also observed in the range from pH 3.5 to 5.3 and by adding potassium, magnesium, and calcium halides. Furthermore, our data demonstrated that increases in the halide anion concentrations and atomic number (Cl-相似文献   

Existence of oriented ion-hydroxide clusters in concentrated aqueous NaCl solution at pH 13

We probe the local electronic structure at solvated Na+ ions in 1 M aqueous NaCl solutions as a function of pH. A dramatic change in the Na+ white line intensity in X-ray absorption is observed for high pH values, reflecting a changing local electronic structure at the Na+ ions when OH- is present. Given the relative abundance of sodium and hydroxide ions, we conclude that one OH- affects at least 2.4+/-0.6 Na+ ions in an electronically noticeable way at pH 13. From the experimental data we infer that spatially extended clusters or networks incorporating Na+ and OH- can exist in the electrolyte solution. The experimental data are complemented by molecular dynamics simulations, which indicate the presence of structured clusters incorporating Na+, OH-, and solvent molecules.     

Characterization of novel vanadium(III)/acetate clusters formed in aqueous solution

We report the first structures of simple acetate complexes of vanadium(III) formed in aqueous solution. Paramagnetic (1)H NMR spectroscopy titration experiments indicate the formation of two major V(III)/acetate complexes in acidic aqueous solution for acetate/V(III) < or =4, pD 3.50. A novel tetranuclear cluster and a trinuclear cluster have been characterized by X-ray diffraction studies. Mass spectrometry measurements show these clusters retain their integrity in solution.     

Chemical bonding and aromaticity in trinuclear transition-metal halide clusters

Trinuclear transition-metal complexes such as Re(3)X(9) (X = Cl, Br, I), with their uniquely featured structure among metal halides, have posed intriguing questions related to multicenter electron delocalization for several decades. Here we report a comprehensive study of the technetium halide clusters [Tc(3)(μ-X)(3)X(6)](0/1-/2-) (X = F, Cl, Br, I), isomorphous with their rhenium congeners, predicted from density functional theory calculations. The chemical bonding and aromaticity in these clusters are analyzed using the recently developed adaptive natural density partitioning method, which indicates that only [Tc(3)X(9)](2-) clusters exhibit aromatic character, stemming from a d-orbital-based π bond delocalized over the three metal centers. We also show that standard methods founded on the nucleus-independent chemical shift concept incorrectly predict the neutral Tc(3)X(9) clusters to be aromatic.     

Anion-pi interaction augments halide binding in solution

1H NMR spectroscopic data and complementary theoretical predictions suggest that a designed receptor exhibits the anion-pi interaction in solution.     

Mechanism of triphosphate hydrolysis in aqueous solution: QM/MM simulations in water clusters

The mechanism of the hydrolysis reaction of the unprotonated methyl triphosphate (MTP) ester in water clusters has been modeled. The effective fragment potential based quantum mechanical-molecular mechanical (QM/MM) approach has been applied in the simulations. It is shown that the minimum energy reaction path is consistent with an assumption of a two-step dissociative-type process similar to the case of the guanosine triphosphate (GTP) hydrolysis in the Ras-GAP protein complex (Grigorenko, B. L.; Nemukhin, A. V.; Topol, I. A.; Cachau, R. E.; Burt, S. K. Proteins: Struct., Funct., Bioinf. 2005, 60, 495). At the first stage, a unified action of environmental molecular groups and the catalytic water molecule leads to a substantial spatial separation of the gamma-phosphate group from the rest of the molecule. At the second stage, inorganic phosphate H2PO4- is formed from water and the metaphosphate anion PO3- through the chain of proton transfers along hydrogen bonds. The estimated activation barriers for MTP in aqueous solution at both stages (20 and 14 kcal/mol) are substantially higher than the corresponding barriers for the GTP hydrolysis in the protein.     

Hydrogen bonds in gas-phase clusters between halide ions and olefins

Gas-phase clustering reactions of halide ions (X- = F-, Cl-, Br-, and I-) with ethylene (C2H4) and propylene (C3H6) were studied with a pulsed electron beam mass spectrometer. Bonding energies of all cluster ions were found to be less than 10 kcal/mol, i.e., no anion-initiated polymerization of C2H4 and C3H6 took place. For the cluster F-(C2H4)n, a small gap in the binding energy is observed between n = 4 and 5 suggesting that the first shell is completed with n = 4. For larger halide ions, the bond energies for the clusters X-(C2H4)n were found to be nearly n independent. For Cl-(C3H6)n a steep decrease in binding energies was observed between n = 2 and 3 and n = 3 and 4. The structure of the cluster ions was investigated by ab initio calculations. X-(C2H4)n complexes were calculated to have hydrogen-bond geometries regardless of the identity of the halide ions, and bidentate (chelate) type geometries of X-(C3H6)1 were found.