Water Hexamer Research Articles

OHO Hydrogen Bond Geometries and NMR Chemical Shifts: From Equilibrium Structures to Geometric H/D Isotope Effects, with Applications for Water, Protonated Water, and Compressed Ice

AbstractHydrogen bond geometries and 1H NMR chemical shifts of OHO hydrogen‐bonded systems have been analyzed using an improved valence bond order model. This model predicts that the heavy atom hydrogen bond coordinate q2 = r1 + r2 is a function of the proton coordinate q1 = (r1 ‐ r2), where r1 and r2 represent the OH and the HO distances.In the first part, it is shown that this correlation reproduces published equilibrium geometries of the Zundel cation H5O2+ as well as those of water clusters in the gas phase and embedded in the fullerene C180. Using the example of the water hexamer, it is shown that changing the level of calculation shifts the calculated geometries along the correlation curve, but not away from the curve. In order to take quantum zero‐point vibrational effects (QZPVE) into account, an empirical correction is proposed. It is shown that this correction properly describes the calculated classical and quantum hydrogen bond geometries of compressed ice as well as calculated geometric H/D isotope effects. The improved valence bond order model is used to analyze a large number of OHO hydrogen bond geometries contained in the Cambridge Structural Database.In the second part, a relation between the geometries and the 1H NMR chemical shieldings of OHO hydrogen bonded systems is established using the valence bond order model. GIAO calculations of the isolated symmetric Zundel cation where H is located in the hydrogen bond center show only a small dependence of the chemical shifts on the O…O distance. This result is rationalized in terms of neighbor group effects and deshielding in the naked proton. The consequence is that the 1H NMR chemical shifts are not much affected by QZPVE. Calculations on water clusters indicate that the influence of the chemical environment of the OHO hydrogen bonds on their 1H NMR chemical shifts is smaller for the strong hydrogen bond regime but large for the weak hydrogen bond regime. A simple chemical shift vs. q1 relation is then used to calculate the average chemical shifts of water clusters in the regime of fast hydrogen bond exchange between hydrogen bonded and free OH groups. It is shown that average chemical shifts of about 6 ppm are possible as the clusters considered exhibit a broad distribution of stronger and weaker hydrogen bonds. The implications for water in organic solvents and for liquid water are discussed, based on published data on the 1H chemical shift distribution in the latter.

Assembly of Silver(I) Two- and Three-Dimensional Coordination Networks with Complementary Tridentate Heteroaryl Ethynide Ligands

Three pairs of complementary nitrogen heteroaryl ligands [2,6-(C[triple bond]C)(2)-py and 2-C[triple bond]C-pym; 2,5-(C[triple bond]C)(2)-py and 2-C[triple bond]C-pyz; 3,5-(C[triple bond]C)(2)-py and 5-C[triple bond]C-pym (py = pyridine, pyz = pyrazine, pym = pyrimidine)], wherein a ring nitrogen atom in one is interchanged with a carbon atom bearing an ethynyl substituent in the other, have been used to generate seven silver(I) complexes (1-7), in which silver infinite chains and two-dimensional coordination networks bridged by heteroaryl ethynide ligands were obtained as pre-programmed. The relative positions and bonding preference between the ethynide group and ring nitrogen atom act as controlling factors to produce various structural building units for the formation of multidimensional coordination networks. The fusion of C[triple bond]C[symbol: see text]Ag(n) (n = 3, 4) building units yields multinuclear silver aggregates in 1-6 whose nuclearities range from seven to twelve. The crystal structure of 7 displays a honeycomb layer composed of Ag(4) baskets alternately linked by pyrimidinyl-5-ethynide ligands. In addition, complex 1 features an infinite chain composed of an alternate arrangement of twist-boat water hexamers and bridging silver atoms.

Formation and photodestruction of dual dipole-bound anion (H2O)6{e−}CH3NO2

A new type of dipole-bound anion composed of water and nitromethane (CH(3)NO(2)) is formed via the incorporation of CH(3)NO(2) into argon-solvated water hexamer anions, (H(2)O)(6) (-)Ar(m). The reaction proceeds as an Ar-mediated process such that an effective energy dissipation through sequential Ar evaporation gives rise to the formation of [CH(3)NO(2)(H(2)O)(6)](-). Photoelectron spectroscopy is employed to probe the electronic properties of the [CH(3)NO(2)(H(2)O)(6)](-) anion, which reveals that the dipole-bound nature of (H(2)O)(6) (-) remains almost intact in the product anion; the vertical detachment energy of [CH(3)NO(2)(H(2)O)(6)](-) is determined to be 0.65+/-0.02 eV. This spectroscopic finding, together with other suggestive evidences, allows us to refer to [CH(3)NO(2)(H(2)O)(6)](-) as a dual dipole-bound anion described as (H(2)O)(6){e(-)}CH(3)NO(2), where the diffuse excess electron interacts with both the (H(2)O)(6) and CH(3)NO(2) moieties via the electron-dipole interactions. The photodestruction of (H(2)O)(6){e(-)}CH(3)NO(2) at 2134 nm (0.58 eV) occurs with a competition between electron detachment and fragmentation. The latter leads exclusively to the formation of CH(3)NO(2) (-)(H(2)O)(3), indicating that the dual dipole-bound anion serves as a precursor to the hydrated valence anion of CH(3)NO(2).

The dynamics of water hexamer isomerization

The dynamics of water hexamer isomerization was analyzed by classic molecular dynamics using TIP4P and TIP5P empirical interaction potentials. Periodic jump transitions between structural isomers occurred as the internal energy of the cluster grew. Structures prevailing over the energy intervals corresponding to the quasi-liquid and quasi-solid cluster phases were determined. The lifetimes of structural isomers were found.

Improvement in hydrogen bond description using van der Waals-corrected DFT: The case of small water clusters

The method recently developed to include van der Waals interactions in DFT (Density Functional Theory) using Wannier functions is applied to small water clusters, characterized by hydrogen-bonding interactions. In particular, water hexamer represents a critical test case since it is relevant for the condensed phases of water and has four low-energy isomers with similar binding energies. We are able to achieve results close to those obtained by high-level quantum chemistry methods and we find that inclusion of van der Waals effects is crucial for an appropriate description of the hydrogen bonds and to get accurate dissociation energy estimates. The relevance of these results for DFT simulations of liquid water is finally discussed.

Dynamically Polarizable Water Potential Based on Multipole Moments Trained by Machine Learning.

It is widely accepted that correctly accounting for polarization within simulations involving water is critical if the structural, dynamic, and thermodynamic properties of such systems are to be accurately reproduced. We propose a novel potential for the water dimer, trimer, tetramer, pentamer, and hexamer that includes polarization explicitly, for use in molecular dynamics simulations. Using thousands of dimer, trimer, tetramer, pentamer, and hexamer clusters sampled from a molecular dynamics simulation lacking polarization, we train (artificial) neural networks (NNs) to predict the atomic multipole moments of a central water molecule. The input of the neural nets consists solely of the coordinates of the water molecules surrounding the central water. The multipole moments are calculated by the atomic partitioning defined by quantum chemical topology (QCT). This method gives a dynamic multipolar representation of the water electron density without explicit polarizabilities. Instead, the required knowledge is stored in the neural net. Furthermore, there is no need to perform iterative calculations to self-consistency during the simulation nor is there a need include damping terms in order to avoid a polarization catastrophe.

Synthesis, structure, and properties of dinuclear copper (II) complex with a (H2O)12 cluster

A novel dinuclear Cu (II) complex with pyrazole-based ligand, which contain supramolecular (H 2 O) 12 morphology. The hydrogen-bonding association leads to the formation of the infinite morphology of water molecules along the c -axis. A novel pyrazole complex, namely [Cu 2 (4,4′-bpy) 2 (2,2′-bpy)(L) 2 ]·6H 2 O has been synthesized under mild condition (4,4′-bpy = 4,4′-bipyridine, 2,2′-bpy = 2,2′-bipyridine). We report the structural evidence in the solid state of discrete water hexamers chair-like conformation. These units were found to act as supramolecular glue in the aggregation of dinuclear copper (II) complex to give a three dimensional network through hydrogen-bonding. The preliminary investigation on the electrochemical property and fluorescence property of the complex are presented.

Formation of nanoporous and non-porous organic–inorganic hybrid materials incorporating α-Keggin phosphotungstate anion: X-ray crystal structure of a 3D polymeric complex [{Na 6(C 9H 5O 6) 3(H 2O) 15}{PW 12O 40}] ∞ with a ‘Ball-in-Bowl’ type molecular structure

Two different synthetic approaches to prepare inclusion complexes of Keggin anion [PW 12O 40] 3− and [Cu 3(BTC) 2(H 2O) 3] n (also known as HKUST-1) have resulted in the formation of two different materials [Cu 3(C 9H 3O 6) 2(H 2O) 3] 2Na 3PW 12O 40· nH 2O ( 1) and [Na 6(BTC-H 2) 3(H 2O) 15][PW 12O 40] ( 2). Compound 1 is a thermally stable, nanoporous material with a type 1 adsorption isotherm. It contains the well-known MOF material [Cu 3(BTC) 2(H 2O) 3] n with half of its pores occupied by the guest Keggin anion. The second product 2 is a crystalline, 3D coordination polymer with a composition of [Na 6(BTC-H 2) 3(H 2O) 15][PW 12O 40] (where BTC-H 3 stands for 1,3,5-benzene-tricarboxylic acid) and is a non-porous, highly water soluble and thermally unstable material. The compound 1 was prepared hydrothermally using precursors of HKUST-1 and Na 3[(PW 12O 40)] whereas 2 was obtained at room temperature from aqueous solutions containing [Cu 3(BTC) 2(H 2O) 3] n and Na 3[(PW 12O 40)] salts. The molecular structure of 2 is unique and features two distinct elements: an anionic Keggin ion [PW 12O 40] 3− and a “bowl type” hexameric [Na 6(C 9H 5O 6) 3(H 2O) 15] 3+ macrocation which is formed by coordination of Na + ions by (BTC-H 2) − anions and water molecules. The macrocation extends in three dimensions due to Y type (BTC-H 2) − to form a porous MOF offering triangular voids. In this framework the globular Keggin ions support themselves above these voids by coordinating to Na + ions and render it completely nonporous. The complex has an unusual structure in the sense that the polyoxoanion is coordinated to [Na 6(C 9H 5O 6) 3(H 2O) 15] 3+ ions by using the three terminal oxygen atoms in a single M 3O 13 triplet, when each one of them is also bridging between two Na + ions. In the crystal structure the POM anion is encapsulated by six octahedrally disposed (BTC-H 2) − moieties. H-bonding interactions among water molecules produce supramolecular water hexamers and dimers.

A novel (3,4,10)-connected three-dimensional hydrogen-bonded supramolecular network containing a cyclic water hexamer

The title compound, 4,4'-(1,1,1,3,3,3-hexafluoroisopropylidene)diphthalic acid hexahydrate, C(19)H(10)F(6)O(8).6H(2)O, crystallizes in the centrosymmetric space group Pbcn, with half of the diphthalic acid residue and three water molecules in the asymmetric unit. The organic molecule is located on a crystallographic twofold axis. In the solid, cyclic water hexamers in chair conformations have crystallographically imposed inversion symmetry. Strong O-H...O hydrogen bonds between the hexamers and organic molecules result in a unique three-dimensional supramolecular network [O...O = 2.554 (2)-2.913 (2) A]. This compound represents the first example of a (3,4,4,10)-connected four-nodal supramolecular topology with the Schläfli symbol (4(3).5.6.7)(2)(4(3).5(2).7)(2)(4(3))(2)(4(6).5(6).6(2).7(8).8(14).9(9)).

CCSD(T) Complete Basis Set Limit Relative Energies for Low-Lying Water Hexamer Structures

MP2 and CCSD(T) complete basis set (CBS) limit relative electronic energies (DeltaE(e)) have been determined for eight low-lying structures of the water hexamer by combining explicitly correlated MP2-R12 computations with higher-order correlation corrections from CCSD(T) calculations. Higher-order correlation effects are quite substantial and increase DeltaE(e) by at least +0.19 kcal mol(-1) and as much as +0.59 kcal mol(-1). The effects from zero-point vibrational energy (ZPVE) have been assessed from unscaled harmonic vibrational frequencies computed at the MP2 level with a correlation consistent triple-zeta basis set (cc-pVTZ for H and aug-cc-pVTZ for O). ZPVE effects are even more significant than higher-order correlation effects and are uniformly negative, decreasing the relative energies by -0.16 kcal mol(-1) to -1.61 kcal mol(-1). Although it has been widely accepted that the cage becomes the lowest-energy structure after ZPVE effects are included [Nature 1996, 381, 501-503], the prism is consistently the most stable structure in this work, lying 0.06 kcal mol(-1) below the nearly isoenergetic cage isomer at the electronic MP2 CBS limit, 0.25 kcal mol(-1) below at the electronic CCSD(T) CBS limit, and 0.09 kcal mol(-1) below at the harmonic ZPVE corrected CCSD(T) CBS limit. Moreover, application of any uniform scaling factor less than unity to correct for anharmonicity further stabilizes the prism and increases the relative energies of the other structures.

Optimal construction of a fast and accurate polarisable water potential based on multipole moments trained by machine learning

To model liquid water correctly and to reproduce its structural, dynamic and thermodynamic properties warrants models that account accurately for electronic polarisation. We have previously demonstrated that polarisation can be represented by fluctuating multipole moments (derived by quantum chemical topology) predicted by multilayer perceptrons (MLPs) in response to the local structure of the cluster. Here we further develop this methodology of modeling polarisation enabling control of the balance between accuracy, in terms of errors in Coulomb energy and computing time. First, the predictive ability and speed of two additional machine learning methods, radial basis function neural networks (RBFNN) and Kriging, are assessed with respect to our previous MLP based polarisable water models, for water dimer, trimer, tetramer, pentamer and hexamer clusters. Compared to MLPs, we find that RBFNNs achieve a 14-26% decrease in median Coulomb energy error, with a factor 2.5-3 slowdown in speed, whilst Kriging achieves a 40-67% decrease in median energy error with a 6.5-8.5 factor slowdown in speed. Then, these compromises between accuracy and speed are improved upon through a simple multi-objective optimisation to identify Pareto-optimal combinations. Compared to the Kriging results, combinations are found that are no less accurate (at the 90th energy error percentile), yet are 58% faster for the dimer, and 26% faster for the pentamer.

An interwoven Fe3L3trigonal metallamacrocycle from an in situligand hydrolysis reaction

Through an in situ hydrolysis reaction of the bishydrazone ligand H4L1 [H4L1=(HOC6H4)CH=NNHCO(C5H3N)CONHN[double bond, length as m-dash]CH(C6H4OH)], in the presence of Fe(III) ions, an interwoven trigonal metallamacrocycle [Fe3L3(H2O)3].9H2O () [H3L=(HOC6H4)CH=NNHCO(C5H3N)CO2H] containing unusually double-layered capsule-like water hexamers was obtained and characterized by elemental analysis, FT-IR, TGA, ESI-MS and X-ray crystallography.

The first crystallographic observation of up to the third hydration layer of Cu(II) ion in an unusual ‘water-cation layer’ templated by an Anderson polyoxometallate

This constitutes the first crystallographic observation of hydrated Cu(II) ion retaining up to its third hydration layer which, along with the chair form water hexamer, builds up a unique water-cation layer. Moreover, an unprecedented supramolecular honeycomb network of [Cu(phen)3]2+ units templated by Anderson polyoxometallate units occupy the intervening spaces between successive water layers. Complex 1 is a rare example of parallel interpenetration of a 2D π–π network and a 3D pillar-layered hydrogen bonded network.

Coordination polymers with pyridine-2,4,6-tricarboxylic acid and alkaline-earth/lanthanide/transition metals: synthesis and X-ray structures

Pyridine-2,4,6-tricarboxylic acid (ptcH(3)) reacts with Cd(II), Mn(II), Ni(II), Mg(II), Ca(II), Sr(II), Ba(II), Dy(III) salts forming different products depending on the reaction conditions. In the presence of pyridine at room temperature the acetate, chloride or nitrate salt of Cd(II) breaks the ligand to form an open framework structure with the empirical formula, {[Cd(Ox)(H(2)O)(2)]H(2)O}(n) (Ox = oxalate), 1. In the absence of pyridine, no crystalline compound could be isolated at room temperature (RT). However, under hydrothermal conditions and in the absence of pyridine, a discrete tetrameric complex with the formula, {[Cd(2)(cda)(2)(H(2)O)(4)](H(2)O)(3)}(2) (cdaH(2) = 4-hydroxypyridine-2,6-dicarboxylic acid), 2, is formed where the carboxylate group at the 4-position of the ligand is reduced to a hydroxyl group. When Ni(II), Mn(II), Mg(II), Ca(II), Sr(II), Ba(II), Dy(III) salts are used in place of Cd(II), no crystalline product could be isolated at RT. But under hydrothermal conditions, coordination polymers ({[Ni(1.5)(ptc)(pip)(0.5)(H(2)O)(4)].H(2)O}(n), (pip = piperazine), 3; {Mn(1.5)(ptc).2H(2)O}(n), 4; {Mg(3)(ptc)(2).8H(2)O}(n), 5; {[Mg(ptc)(H(2)O)(2)].1/2[Mg(H(2)O)(6)].H(2)O}(n), 6; {Ca(1.5)(ptc).2H(2)O}(n), 7; {Sr(1.5)(ptc).5H(2)O}(n), 8; {[Ba(ptc)(H(2)O)][Ba(ptcH(2))H(2)O]}(n), 9; {[Dy(ptc).3H(2)O].H(2)O}(n), 10) are formed. The structures exhibit different dimensionality depending on the nature of the metal ions. In 1 a discrete acyclic water hexamer is also identified. All the compounds are characterized in the solid state by X-ray crystallography, IR and elemental analysis.

Water adsorption on clean Ni(111) andp(2×2)-Ni(111)-Osurfaces calculated from first principles

A systematic and comprehensive analysis of the adsorption of water monomers, small water clusters, and water thin films on clean and oxygen-predosed Ni(111) surfaces is performed. For the clean Ni surface, the formation of water hexamers (and possibly also incommensurate icelike bilayers) is favored. The total-energy results as well as the calculated vibrational frequencies for water adsorbed on the $p(2\ifmmode\times\else\texttimes\fi{}2)\text{-Ni}(111)\text{-O}$ surface suggest a reinterpretation of recent experimental data [M. Nakamura and M. Ito, Phys. Rev. Lett. 94, 035501 (2005)] in terms of single water monomers adsorbed on top of Ni and the formation of (islands of) an icelike bilayer.

On the accuracy of density-functional theory exchange-correlation functionals for H bonds in small water clusters. II. The water hexamer and van der Waals interactions

Second order Møller-Plesset perturbation theory at the complete basis set limit and diffusion quantum Monte Carlo are used to examine several low energy isomers of the water hexamer. Both approaches predict the so-called prism to be the lowest energy isomer, followed by cage, book, and cyclic isomers. The energies of the four isomers are very similar, all being within 10-15 meV/H(2)O. These reference data are then used to evaluate the performance of several density-functional theory exchange-correlation (xc) functionals. A subset of the xc functionals tested for smaller water clusters [I. Santra et al., J. Chem. Phys. 127, 184104 (2007)] has been considered. While certain functionals do a reasonable job at predicting the absolute dissociation energies of the various isomers (coming within 10-20 meV/H(2)O), none predict the correct energetic ordering of the four isomers nor does any predict the correct low total energy isomer. All xc functionals tested either predict the book or cyclic isomers to have the largest dissociation energies. A many-body decomposition of the total interaction energies within the hexamers leads to the conclusion that the failure lies in the poor description of van der Waals (dispersion) forces in the xc functionals considered. It is shown that the addition of an empirical pairwise (attractive) C(6)R(-6) correction to certain functionals allows for an improved energetic ordering of the hexamers. The relevance of these results to density-functional simulations of liquid water is also briefly discussed.

Photoelectron imaging study of vibrationally mediated electron autodetachment in the type I isomer of the water hexamer anion

We exploit the high collection efficiency of negative ion photoelectron imaging for low energy electrons to monitor the energy and angular distributions of the photoelectrons arising from vibrational excitation of the water hexamer anion in the vicinity of the OH stretching fundamentals. Photoelectrons from the low electron binding energy isomer (type II) appear as a smoothly varying outer ring with the anisotropic angular distribution expected for direct photodetachment. The higher binding isomer (type I) yields very slow electrons that are strongly modulated through the OH stretching resonances, which are discussed in the context of a statistical (IVR-based) ejection mechanism.

Counter cation Al 3+ assisting formation of a 2D water sheet that contains both cyclic water hexamers in boat and chair conformations and cyclic water tetramers in an Anderson-type polyoxometalate [Al(H 2O) 6][Al(OH) 6Mo 6O 18]·10H 2O

For the first time, a 2D water sheet that contains both cyclic water hexamers around Al 3+ in boat and chair conformations and cyclic water tetramers was crystallographically observed in an Anderson-type supramolecular complex, [Al(H 2O) 6][Al(OH) 6Mo 6O 18]·10H 2O 1, in which the element type of both the counter cation and the heteroatom of the polyanion are the same, that is Aluminum. The counter cation Al 3+ is coordinated by six water molecules forming a nearly ideal octahedron. The octahedron is then hydrogen-bonded to its surrounding lattice water molecules producing a novel Al 3+-containing 1D water chain composed of both boat- and chair-like water hexamers. More interestingly and importantly, the water chains further on join together through a parallelogram composed of four water molecules to yield a unique 2D water sheet.

Uranyl interaction with the hydrated (1 1 1) nickel face: A periodic density functional theory investigation

Periodic DFT calculations using plane waves basis sets with the GGA formalism were performed in order to study the behavior of the UO 2 2 + uranyl ion at the water–Ni(1 1 1) interface. First, the adsorption of water molecules interacting with an optimized surface model has been studied. At low coverage, isolated water molecules adsorb preferentially on top of the surface nickel atoms, the plane defined by the H 2O molecule being almost parallel to the surface. When the water coverage increases from 1/9 ML to 2/3 ML (ML = monolayer coverage), hydrogen bonds are created leading to the formation of water hexamers, as suggested experimentally on Ni(1 1 1) and other metallic surfaces [A. Michaelides, A. Alavi, D.A. King, Physical Review B 69 (2004) 113404. M. Nakamura, M. Ito, Chemical Physics Letters 325 (2000) 293–298]. Higher water coverage induces the formation of an additional water layer physisorbed over the cyclic hexamers. In a second step, the behavior of UO 2 2 + with respect to the hydrated Ni(1 1 1) face has been investigated. Evidence that two adsorption modes can take place was put forward: a first one with an outer sphere adsorption mechanism, where two water molecules of the uranyl ion first hydration shell are shared with four water hexamers, and a second one through a strong Ni–O −yle bond formation. Even though the second surface complex is energetically the most stable, the necessary activation energy to reach it makes it improbable.

H‐Bonded Porous Supramolecular Network of a CuII Complex Assisted by Assembled 2D Sheet of Chair Form Hexameric Water Cluster

AbstractThe supramolecular network of the complex having the formula [Cu(nicot)2·2NH3·2H2O]·6H2O 1 has been synthesized by transmetallation of the Zn–nicotinate complex by CuII ions and its crystallization in an ionic liquid. The supramolecular network of 1 shows unique H‐bonding in the sense that it not only participates in the formation of nanoporous 2D chains but also forms cyclic hexameric water cluster that adopt an ice‐like chair conformation, which together with octanuclear H‐bonded rings extend the network into a 3D open framework. X‐ray structural analysis, FTIR, thermal analysis, EPR and magnetic properties have been used to characterize this compound. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)