Showing papers on "Water cluster published in 2007"
TL;DR: A computational study with the Becke3LYP density functional was carried out to elucidate the mechanisms of Au(I)-catalyzed reactions of enynyl acetates involving tandem [3,3]-rearrangement, Nazarov reaction, and [1,2]-hydrogen shift, showing that water is found to act as a proton shuttle in the proton-transport catalysis strategy.
Abstract: A computational study with the Becke3LYP density functional was carried out to elucidate the mechanisms of Au(I)-catalyzed reactions of enynyl acetates involving tandem [3,3]-rearrangement, Nazarov reaction, and [1,2]-hydrogen shift. Calculations indicate that the [3,3]-rearrangement is a two-step process with activation free energies below 10 kcal/mol for both steps. The following Nazarov-type 4pi electrocyclic ring-closure reaction of a Au-containing dienyl cation is also easy with an activation free energy of 3.2 kcal/mol in CH2Cl2. The final step in the catalytic cycle is a [1,2]-hydride shift, and this step is the rate-limiting step (with a computed activation free energy of 20.2 kcal/mol) when dry CH2Cl2 is used as the solvent. When this tandem reaction was conducted in wet CH2Cl2, the [1,2]-hydride shift step in dry solution turned to a very efficient water-catalyzed [1,2]-hydrogen shift mechanism with an activation free energy of 16.4 kcal/mol. Because of this, the tandem reaction of enynyl acetates was found to be faster in wet CH2Cl2 as compared to the reaction in dry CH2Cl2. Calculations show that a water-catalyzed [1,2]-hydrogen shift adopts a proton-transport catalysis strategy, in which the acetoxy group in the substrate is critical because it acts as either a proton acceptor when one water molecule is involved in catalysis or a proton-relay stabilizer when a water cluster is involved in catalysis. Water is found to act as a proton shuttle in the proton-transport catalysis strategy. Theoretical discovery of the role of the acetoxy group in the water-catalyzed [1,2]-hydrogen shift process suggests that a transition metal-catalyzed reaction involving a similar hydrogen shift step can be accelerated in water or on water with only a marginal effect, unless a proton-accepting group such as an acetoxy group, which can form a hydrogen bond network with water, is present around this reaction's active site.
266 citations
TL;DR: The effect of hydration, messenger atom Ar, and temperature are crucial to elucidating the nature of vibrational spectra of Eigen and Zundel forms and to assigning the vibrational modes of small protonated water clusters.
Abstract: The spectral properties of protonated water clusters, especially the difference between Eigen (H3O+) and Zundel (H5O2+) conformers and the difference between their unhydrated and dominant hydrated forms are investigated with the first principles molecular dynamics simulations as well as with the high level ab initio calculations. The vibrational modes of the excess proton in H3O+ are sensitive to the hydration, while those in H5O2+ are sensitive to the messenger atom such as Ar (which was assumed to be weakly bound to the water cluster during acquisitions of experimental spectra). The spectral feature around ∼2700 cm-1 (experimental value: 2665 cm-1) for the Eigen moiety appears when H3O+ is hydrated. This feature corresponds to the hydrating water interacting with H3O+, so it cannot appear in the Eigen core. Thus, H3O+ alone would be somewhat different from the Eigen forms in water. For the Zundel form (in particular, H5O2+), there have been some differences in spectral features among different experime...
139 citations
Journal Article•
TL;DR: In this article, the appearance energies of a series of protonated water clusters are determined from the photoionization threshold for clusters composed of up to 79 molecules, representing an upper limit of the adiabatic ionization energy of the corresponding parent neutral water cluster in the supersonic molecular beam.
Abstract: Tunable vacuum ultraviolet (VUV) photoionization studies of water clusters are performed using 10-14 eV synchrotron radiation and analyzed by reflectron time-of-flight (TOF) mass spectrometry. Photoionization efficiency (PIE) curves for protonated water clusters (H{sub 2}O){sub n}H{sup +} are measured with 50 meV energy resolution. The appearance energies of a series of protonated water clusters are determined from the photoionization threshold for clusters composed of up to 79 molecules. These appearance energies represent an upper limit of the adiabatic ionization energy of the corresponding parent neutral water cluster in the supersonic molecular beam. The experimental results show a sharp drop in the appearance energy for the small neutral water clusters (from 12.62 {+-} 0.05 to 10.94 {+-} 0.06 eV, for H{sub 2}O and (H{sub 2}O){sub 4}, respectively), followed by a gradual decrease for clusters up to (H{sub 2}O){sub 23} converging to a value of 10.6 eV ({+-}0.2 eV). The dissociation energy to remove a water molecule from the corresponding neutral water cluster is derived through thermodynamic cycles utilizing the dissociation energies of protonated water clusters reported previously in the literature. The experimental results show a gradual decrease of the dissociation energy for removal of one water molecule for small neutral water clustersmore » (3{le}n{le}9). This dissociation energy is discussed within the context of hydrogen bond breaking in a neutral water cluster.« less
123 citations
TL;DR: Infrared multiple photon dissociation spectra for size-selected water cluster anions (H2O)(n)(-), n=15-50, are presented covering the frequency range of 560-1820 cm(-1), suggesting a more delocalized electron binding motif for the larger clusters in which the excess electron interacts with multiple water molecules.
Abstract: Infrared multiple photon dissociation spectra for size-selected water cluster anions (H2O)n−, n=15–50, are presented covering the frequency range of 560–1820cm−1. The cluster ions are trapped and cooled by collisions with ambient He gas at 20K, with the goal of defining the cluster temperature better than in previous investigations of these species. Signal is seen in two frequency regions centered around 700 and 1500–1650cm−1, corresponding to water librational and bending motions, respectively. The bending feature associated with a double-acceptor water molecule binding to the excess electron is clearly seen up to n=35, but above n=25; this feature begins to blueshift and broadens, suggesting a more delocalized electron binding motif for the larger clusters in which the excess electron interacts with multiple water molecules.
79 citations
TL;DR: In this paper, the authors observed that the rigid dodecahedral water cluster encaging a methane molecule has an affinity for other methane molecules diffusing freely in liquid water and can adsorb them by chance.
Abstract: By performing 400 molecular dynamics simulations, we observe that the rigid dodecahedral water cluster (DWC) encaging a methane molecule has an affinity for other methane molecules diffusing freely in liquid water and can adsorb them by chance. Utilizing the affinity, we successfully prepare seven series (200 runs in each series) of DWCs adsorbing 0−12 methane molecules, and study how the adsorbed methane molecules affect the DWC lifetime. The results show that the adsorbed methane molecules can prolong the lifetime of DWC. The structures and dynamics of the DWC and its surroundings are also analyzed. We find that the adsorbed methane molecules slow down the water molecules in both the DWC and its surroundings, reduce the number of H-bonds that tend to break the DWC, and change the H-bond networks of the DWC surroundings from the liquid water structure toward the cagelike structure. On the basis of these observations, a methane aggregation mechanism caused by the DWC adsorbing dissolved methane molecules ...
77 citations
TL;DR: The second generation multi-state empirical valence bond (MS-EVB2) model was employed in a molecular dynamics study based on a high-resolution X-ray structure to simulate the interaction of the excess proton with the channel environment.
Abstract: The mechanism of proton transport in the D-pathway of cytochrome c oxidase (CcO) is further elucidated through examining a protonated water/hydroxyl cluster inside the channel. The second generation multi-state empirical valence bond (MS-EVB2) model was employed in a molecular dynamics study based on a high-resolution X-ray structure to simulate the interaction of the excess proton with the channel environment. Our results indicate that a hydrogen-bonded network consisting of about 5 water molecules surrounded by three side chains and two backbone groups (S197, S200, S201, F108) is involved in storage and translocation of an excess proton to the extracellular side of CcO.
70 citations
TL;DR: In this paper, a 3D infinite supramolecular host was realized in solid in which the water assembly as a whole acted as a building block of the 3D framework with rectangular channels where guest molecules reside.
Abstract: A 3D supramolecular metal-organic host could be realized in solid in which the water assembly as a whole acted as a building block of the 3D framework with rectangular channels where guest molecules reside, adding a new dimension to water cluster research where the role of water has been shifted from its usual behavior of guest to that of a host. The crystal structure of the compound, {[Cu(mal) 2 ](picH) 2 ·5H 2 O} n , 1 [mal = malonate dianion, picH = protonated 2-amino-4-picoline], synthesized from purely aqueous media, shows that the Cu(II)-malonate 2D coordination polymeric sheets are locked together by the water assembly that lines up perpendicular to the Cu(II)-malonate sheets constituting a 3D infinite supramolecular host where within the channels protonated 2-amino-4-picoline auxiliary ligands are accommodated. A spirocyclic tetrameric water chain having a dimeric crown on it describes the composition of the water assembly that runs down the c-axis.
59 citations
TL;DR: An idealized model of the hydrated electron in which six hydroxyl groups arranged in an octahedral pattern point toward the common center is shown to provide the closest match to the experimental parameters, such as isotropic and anisotropic hyperfine coupling constants for the protons, the second moment of the EPR spectra, and the radius of gyration.
Abstract: Density functional theory is used to rationalize magnetic parameters of hydrated electron trapped in alkaline glasses as observed using electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectroscopies. To this end, model water cluster anions (n = 4−8 and n = 20, 24) that localize the electron internally are examined. It is shown that hyperfine coupling tensors of H/D nuclei in the water molecules are defined mainly by the cavity size and the coordination number of the electron; the water molecules in the second solvation shell play a relatively minor role. An idealized model of the hydrated electron (that is usually attributed to L. Kevan) in which six hydroxyl groups arranged in an octahedral pattern point toward the common center is shown to provide the closest match to the experimental parameters, such as isotropic and anisotropic hyperfine coupling constants for the protons (estimated from ESEEM), the second moment of the EPR spectra, and the radius of gyration. ...
57 citations
TL;DR: In this paper, the phase transition of a water cluster confined in a flexible single-walled carbon nanotube was investigated using a classical molecular dynamics (MD) method, where the formation of ice-nanotube is monitored through the structure factor and potential energies.
Abstract: The phase transition of a water cluster confined in a flexible single-walled carbon nanotube is investigated using a classical molecular dynamics (MD) method. The formation of ice-nanotube is monitored through the structure factor and potential energies. The transition temperature and its diameter dependence obtained by the simulations agree well with those of previously reported experiments. The transition temperature of the ice-nanotube was shown to take a maximum value of around room temperature with the number of the ring members n = 5. Potential energy contribution to the phase change is generally dominated by that of the intrinsic water−water interaction, while that of water−carbon interaction plays a significant role in determining the dependence of transition temperature on the nanotube diameter.
55 citations
TL;DR: In this paper, the authors used density functional theory (DFT) with the Becke−Lee−Yang−Parr functional and single-excitation configuration interaction (CIS) methods to generate snapshots of the hydrated electron in liquid water at 300 K.
Abstract: Adiabatic mixed quantum/classical (MQC) molecular dynamics (MD) simulations were used to generate snapshots of the hydrated electron in liquid water at 300 K. Water cluster anions that include two complete solvation shells centered on the hydrated electron were extracted from the MQC MD simulations and embedded in a roughly 18 A × 18 A × 18 A matrix of fractional point charges designed to represent the rest of the solvent. Density functional theory (DFT) with the Becke−Lee−Yang−Parr functional and single-excitation configuration interaction (CIS) methods were then applied to these embedded clusters. The salient feature of these hybrid DFT(CIS)/MQC MD calculations is significant transfer (∼18%) of the excess electron's charge density into the 2p orbitals of oxygen atoms in OH groups forming the solvation cavity. We used the results of these calculations to examine the structure of the singly occupied and the lower unoccupied molecular orbitals, the density of states, the absorption spectra in the visible a...
54 citations
TL;DR: In this article, a series of reproductions of mass spectroscopy data on stepwise binding Gibbs energy, enthalpy and entropy of ion(H 2 O) n, n ǫ = 1ǫ − 6 clusters for a set of monovalent ions has been carried out with the help of bicanonical Monte-Carlo technique.
TL;DR: In this paper, the surface oxygen concentration of pitch-based activated carbon fibers (ACF) was controlled by heat treatment in Ar and H2, and the adsorbed states of water in the nanopores of the three ACFs were investigated by density fluctuation analysis from small-angle X-ray scattering and grand canonical Monte Carlo (GCMC) simulation.
Abstract: The surface oxygen concentration of pitch-based activated carbon fibers (ACF) was controlled by heat treatment in Ar and H2. The surface oxygen-to-carbon ratio was determined by X-ray photoelectron spectroscopy; the O/C ratios of the as-received ACF, the ACF treated in Ar, and the ACF treated in H2 were 0.07, 0.03, and 0.02, respectively. The adsorbed states of water in the nanopores of the three ACFs were investigated by density fluctuation analysis from small-angle X-ray scattering and grand canonical Monte Carlo (GCMC) simulation. Although the adsorption isotherms of the three ACFs at 303 K have almost similar features, their density fluctuation profiles with filling differ. The density fluctuations in the course of adsorption showed that the cluster size of the adsorbed water increased with the decrease in the number of surface oxygens. Radial distributions calculated from the snapshots of the GCMC simulation suggested that the water structure has a short-range order with hydrogen bonding. The island ...
TL;DR: A temperature dependent analysis of the vibrational spectrum of the protonated 21-water cluster using the ab initio molecular dynamics method called atom-centered density matrix propagation finds that even at low temperatures, finite temperature dynamical averaging greatly influences the spectral results.
Abstract: A temperature dependent analysis of the vibrational spectrum of the protonated 21-water cluster is provided using the ab initio molecular dynamics method called atom-centered density matrix propagation. It is found that even at low temperatures, finite temperature dynamical averaging greatly influences the spectral results. While the current publication deals with an analysis of the vibrational spectrum at many internal temperatures, the general conclusions are consistent with those in an earlier publication [Iyengar et al., J. Chem. Phys.123, 084309 (2005)]. Furthermore, a critical spectral region (below 1500cm−1) is found for this system, where the key vibrations of the protonated species can be detected.
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TL;DR: In this paper, the first order phase transition of a water cluster confined in a dynamic single-walled carbon nanotube was investigated using a classical molecular dynamics (MD) method.
Abstract: The first order phase transition of a water cluster confined in a dynamic single-walled carbon nanotube is investigated using a classical molecular dynamics (MD) method. The formation of ice-nanotube is monitored through the structure factor and potential energies. The transition temperature and its diameter dependence obtained by the simulations agree well with those of previously reported experiments. The transition temperature of the ice-nanotube was shown to take a maximum value of around room temperature with the number of the ring members n=5. Potential energy contribution to the phase change is generally dominated by that of the intrinsic water-water interaction, while that of water-carbon interaction plays a significant role on determining the dependence of transition temperature on the nanotube diameter.
TL;DR: The energetic stability and dynamical evolution of the system at different internal temperatures and the corresponding "dynamically averaged" vibrational density of states are studied to discuss the conditions under which the pentavalent oxygen may be observed using vibrational action spectroscopy.
Abstract: In this study, we construct the hydroxide water cluster, OH-(H2O)6, that (a) could support a stable hydroxide ion with a four-coordinated (pentavalent) hydroxide oxygen and (b) displays hydroxide ion migration. We study the energetic stability and dynamical evolution of the system at different internal temperatures and analyze the corresponding "dynamically averaged" vibrational density of states to discuss the conditions under which the pentavalent oxygen may be observed using vibrational action spectroscopy. We also provide an alternate hydroxide migration mechanism.
TL;DR: Formation of the macroscopically-infinite hydrogen-bonded water network in various aqueous systems occurs via 3D percolation transition when the probability of finding a spanning water cluster exceeds 95%.
Abstract: Formation of the macroscopically-infinite hydrogen-bonded water network in various aqueous systems occurs via 3D percolation transition when the probability of finding a spanning water cluster exceeds 95%. As a result, in a wide interval of water content below the percolation threshold, rarefied quasi-2D water networks span over the mesoscopic length scale. Formation and topology of spanning water networks, which affect various properties of aqueous systems, can be described within the framework of the percolation theory.
TL;DR: Experimental evidence suggests that acidic dissociation takes place in the cluster, but the H3O+ ion remains rather immobile.
Abstract: Photodissociation of water clusters doped with HX(X=Br,Cl), molecules has been studied in a molecular beam experiment. The HX(H2O)n clusters are dissociated with 193nm laser pulses, and the H fragments are ionized at 243.07nm and their time-of-flight distributions are measured. Experiments with deuterated species DBr(H2O)n and HBr(D2O)n suggest that the photodissociation signal originates from the presence of the HX molecule on the water cluster, but does not come directly from a photolysis of the HX molecule. The H fragment is proposed to originate from the hydronium molecule H3O. Possible mechanisms of the H3O production are discussed. Experimental evidence suggests that acidic dissociation takes place in the cluster, but the H3O+ ion remains rather immobile.
TL;DR: In this article, a well-resolved discrete water dodecameric cluster containing core cyclic chair-conformational hexamer has been observed within a metal-organic network built from the combination of 4,4′-bipyridine and 4, 4′-dipyrine-N,N′-oxide linkers.
Abstract: A well-resolved discrete water dodecameric cluster containing core cyclic chair-conformational hexamer has been observed within a metal–organic network built from the combination of 4,4′-bipyridine and 4,4′-dipyridine-N,N′-dioxide linkers.
TL;DR: Two crystal structures of cyclic water hexamers are reported in this article, one with a bicyclic cryptand and the other with a tricyclic host, where the water molecules lie between the cryptands.
Abstract: Two crystal structures of cyclic water hexamers are reported, one with a bicyclic cryptand and the other with a tricyclic host. In the bicycle structure, the water molecules lie between the cryptands. In the tricycle structure, the hexameric water cluster is almost totally encapsulated within the host framework.
TL;DR: The electron capture dynamics of halocarbon and its water complex have been investigated by means of the full dimensional direct density functional theory molecular dynamics method in order to shed light on the mechanism of electron capture of a Halocarbon adsorbed on the ice surface.
Abstract: The electron capture dynamics of halocarbon and its water complex have been investigated by means of the full dimensional direct density functional theory molecular dynamics method in order to shed light on the mechanism of electron capture of a halocarbon adsorbed on the ice surface. The CF2Cl2 molecule and a cyclic water trimer (H2O)3 were used as halocarbon and water cluster, respectively. The dynamics calculation of CF2Cl2 showed that both C–Cl bonds are largely elongated after the electron capture, while one of the Cl atoms is dissociated from CF2Cl2− as a Cl− ion. Almost all total available energy was transferred into the internal modes of the parent CF2Cl radical on the product state, while the relative translational energy of Cl− was significantly low due to the elongation of two C–Cl bonds. In the case of a halocarbon-water cluster system, the geometry optimization of neutral complex CF2Cl2(H2O)3 showed that one of the Cl atoms interacts with n orbital of water molecules of trimer and the other C...
TL;DR: In this article, the effect of hydrogen bond functionalized backbone and ligating topologies on the resultant supramolecular architectures in mixed ligand systems containing dicarboxylates as counter bridging anions was explored.
Abstract: Four coordination polymers, namely [{(H2O)4Co(μ-L1)2}·fumarate·2H2O]n1, [{(H2O)3(μ-fumarate)Co(μ-L1)2}·fumarate·2H2O]n2, [{(H2O)4Co(μ-L2)2}·terephthalate·3H2O]n3 and [{(H2O)4Co(μ-L2)2}·terephthalate·10H2O]n4 (L1 = N-(3-pyridyl)nicotinamide, L2 = N-(4-pyridyl)isonicotinamide) have been synthesized and structurally characterized mainly by single crystal X-ray diffraction techniques in order to explore the effect of hydrogen bond functionalized backbone and ligating topologies on the resultant supramolecular architectures in mixed ligand systems containing dicarboxylates as counter bridging anions. Interestingly, the counter bridging anions fumarate and terephthalate failed to coordinate to the metal centers in 1 and 3–4, respectively; fumarate, however, terminally connects to the metal centers in 2 resulting in the ladder topology. A (H2O)14 water cluster, having unprecedented topology, has been found entrapped in the lattice of 4.
TL;DR: The vibrational predissociation spectra of the two more strongly electron binding forms of the (H2O)8- anion are obtained in the HOH intramolecular bending region by deconvoluting the overlapping spectra obtained from a mixed ensemble using a population modulation scheme in which the low electron binding isomer (II) is removed from the ion packet prior to spectroscopic analysis.
Abstract: The vibrational predissociation spectra of the two more strongly electron binding forms of the (H2O)8− anion are obtained in the HOH intramolecular bending region. This is accomplished by deconvoluting the overlapping spectra obtained from a mixed ensemble using a population modulation scheme in which the low electron binding isomer (II) is removed from the ion packet prior to spectroscopic analysis. By choosing the energy of the photodepletion laser to lie between the vertical detachment energies of the two isomers, the contribution from isomer II can be quantitatively eliminated, leaving the population of I largely unaffected. The low binding energies involved in the application of the method to the water cluster anions necessitate that this should be carried out in the midinfrared, thus requiring two tunable ir laser systems for implementation. The isolated spectrum of isomer 1 displays a strong, redshifted feature associated with a double H-bond acceptor (AA) water molecule in direct contact with the ...
TL;DR: The measured vibrational OH-stretch spectra of size-selected Na(H2O)n clusters for n=8, 10, 16, and 20 are compared with first-principle calculations, which account for the interaction of the sodium cation, the electron, and the water molecules with the hydrogen-bonded network.
Abstract: The measured vibrational OH-stretch spectra of size-selected Na(H2O)n clusters for n=8, 10, 16, and 20 are compared with first-principle calculations, which account for the interaction of the sodium cation, the electron, and the water molecules with the hydrogen-bonded network. The calculated harmonic frequencies are corrected by comparing similar results obtained for pure water clusters with experiment. The experimental spectra are dominated by intensity peaks between 3350 and 3550 cm(-1), which result from the interaction of the H atoms with the delocalized electron cloud. The calculations, which are all based upon the average spectra of the four lowest-energy isomers, indicate that most of the peaks at the lower end of this range (3217 cm(-1) for n=8) originate from the interaction of one H atom with the electron distribution in a configuration with a single hydrogen-bonding acceptor. Those at the upper end (3563 cm(-1) for n=8) come from similar interactions with two acceptors. The doublets, which arise from the interaction of both H atoms with the electron, appear in the red-shifted part of the spectrum. They are with 3369/3443 cm(-1) quite pronounced for n=8 but slowly vanish for the larger clusters where they mix with the other spectral interactions of the hydrogen-bonded network, namely, the fingerprints of the free, the double, and the single donor OH positions known from pure water cluster spectroscopy. For all investigated sizes, the electron is sitting at the surface of the clusters.
TL;DR: The authors found that in the magic number clusters, the surface protonated sites are energetically favored over their internal counterparts and the excess proton prefers to take the form of H(3)O(+) despite the fact that the proton affinity of methanol is greater than that of water.
Abstract: Infrared spectra of large-sized protonated methanol-water mixed clusters, H+(MeOH)m(H2O)n (m=1–4, n=4–22), were measured in the OH stretch region. The free OH stretch bands of the water moiety converged to a single peak due to the three-coordinated sites at the sizes of m+n=21, which is the magic number of the protonated water cluster. This is a spectroscopic signature for the formation of the three-dimensional cage structure in the mixed cluster, and it demonstrates the compatibility of a small number of methanol molecules with water in the hydrogen-bonded cage formation. Density functional theory calculations were carried out to examine the relative stability and structures of selected isomers of the mixed clusters. The calculation results supported the microscopic compatibility of methanol and water in the hydrogen-bonded cage development. The authors also found that in the magic number clusters, the surface protonated sites are energetically favored over their internal counterparts and the excess prot...
TL;DR: In this paper, the lattice water molecules, forming a 1D water cluster, function as glue to form a 3D supramolecular network through an extended hydrogen bonding.
Abstract: The coordination polymer, {[Co(tart)(phen)]·6H2O}n (1) (tart, tartrate dianion; phen, 1,10-phenanthroline) has been synthesized and characterized by single-crystal X-ray structure determination, magnetic measurement and thermal analysis. The structural analyses reveal two adjacent parallel 1D–[Co(phen)-tart-Co(phen)]– coordination polymers zipped through π-π interactions. The lattice water molecules, forming a 1D water cluster, function as glue to form a 3D supramolecular network through an extended hydrogen bonding. A comparison highlighting the structural differences with the corresponding 2,2′-bipyridine (bpy) derivative, {[Co(tart)(bpy)]·5H2O}n (2) containing a less amount of lattice water molecules is discussed. The variable-temperature magnetic study of 1 has been carried out and interpretation of the already reported complex 2 has been re-visited: both polymers 1 and 2 show weak antiferromagnetic interaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
TL;DR: In this paper, a hexanuclear zinc complex [Zn6(HL)6(H2L)6]6+ with multifunctional ligand 4-(2pyridyl)-6-(4-pyrideyl)-2-aminopyrimidine (H 2L) leads to a unique water cluster (H2O)26 composed of a clathrate core and six dangling water molecules.
Abstract: The reaction of Zn(NO3)2·6H2O with multifunctional ligand 4-(2-pyridyl)-6-(4-pyridyl)-2-aminopyrimidine (H2L) leads to a circular hexanuclear zinc complex [Zn6(HL)6(H2L)6](NO3)6·26H2O (1), confirmed by single-crystal X-ray diffraction. In the [Zn6(HL)6(H2L)6]6+ cation, six zinc centers are arranged in a chairlike conformation and 12 ligands fulfill bridging and terminal functions, respectively. The particular interest of complex 1 is the formation of a unique water cluster (H2O)26 composed of a clathrate (H2O)20 core and six dangling water molecules, and the clathrate (H2O)20 core is structurally similar to the famous “Bucky water” (H2O)20. Furthermore, the water molecules and the nitrate ions are assembled into an interesting negative three-dimensional (3D) framework through hydrogen bonds, and the [Zn6(HL)6(H2L)6]6+ cations just locate in the cavities of the anionic 3D network. To gain insight into the stability of (H2O)20 observed in complex 1, we isolate the water cluster from its environments and com...
TL;DR: In this article, the authors studied the sorption and diffusion of water in the plastic-bonded explosive PBX 9501 and each of its components, and found that the equilibrium amount of water sorbed per gram of sample is linear in the relative humidity at low relative humidity but curves upwards at higher relative humidity.
Abstract: In preparation for studying the hydrolytic degradation of Estane® 5703 in the plastic-bonded explosive PBX 9501, the sorption (solubility) and diffusion of water in PBX 9501 and each of its components are studied experimentally and modeled theoretically. Experiments are reported that measure the weight gain or loss due to a change in the relative humidity (RH). For all of the components, the equilibrium amount of water sorbed per gram of sample is linear in the RH at low relative humidities but curves upwards at higher relative humidities. This behavior is modeled with a water cluster model. Diffusion coefficients are determined by modeling the time dependence of the water concentrations assuming Fickian diffusion, and that fits the data for some of the materials. However, all the samples that contain the explosive HMX show much more complicated behavior at high relative humidities, and that is presented and discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
TL;DR: The reactions of water cluster anions (H2O)n-, n = 30-70, with hydrogen chloride have been studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and represents an example for supramolecular self-organization in the gas phase.
Abstract: The reactions of water cluster anions (H2O)n-, n = 30−70, with hydrogen chloride have been studied by Fourier transform ion cyclotron resonance (FT−ICR) mass spectrometry. The first HCl taken up by the clusters is presumably ionically dissolved. The solvated electron recombines with the proton, which is thereby reduced to atomic hydrogen and evaporates from the cluster. This process is accompanied by blackbody radiation and collision induced loss of water molecules. Subsequent collisions lead to uptake of HCl and loss of H2O, yielding mixed clusters Cl-(HCl)m(H2O)n until they are saturated with HCl. Those saturated clusters lose H2O and HCl in a characteristic sequence. The final stage of the reaction, involving clusters with m = 0−4 and n = 0−6, is studied in detail with density functional theory calculations. The Cl-(HCl)4(H2O)6 cluster represents an example for supramolecular self-organization in the gas phase: it consists of a tetrahedral Cl-(HCl)4, connected on one side of the tetrahedron to a compa...
TL;DR: In this paper, semiempirical, ab initio and density functional theory calculations are used to locate many low-energy minima on the potential energy surface of the CH 2 OHCOOH-(H 2 O) 16 complex.
TL;DR: In this article, a decameric water cluster in compound of [Ni (phen)3Cr2O7 ǫ·5H2O] has been synthesized and structurally characterized by single-crystal X-ray diffraction.