2D Water Layers Research Articles

Visualizing Water Monomers and Chiral OH-(H2O) Complexes Infiltrated in a Macroscopic Hydrophobic Teflon Matrix.

Insights into the interaction of fluoroalkyl groups with water are crucial to understanding the polar hydrophobicity of fluorinated compounds, such as Teflon. While an ordered hydrophobic-like 2D water layer has been demonstrated to be present on the surface of macroscopically hydrophobic fluorinated polymers, little is known about how the water infiltrates into the Teflon and what is the molecular structure of the water infiltrated into the Teflon. Using highly sensitive femtosecond sum frequency generation vibrational spectroscopy (SFG-VS), we observe for the first time that monomeric H2O and chiral OH-(H2O) complexes are present in macroscopically hydrophobic Teflon. The species are inhomogeneously distributed inside the Teflon matrix and at the Teflon surface. No water clusters or single-file water "wires" are observed in the matrix. SFG free induction decay (SFG-FID) experiments demonstrate that the OH oscillators of physically absorbed molecular water at the surface dephase on the time scale of <230 fs, whereas the water monomers and hydrated hydroxide ions infiltrated in the Teflon matrix dephase much more slowly (680-830 fs), indicating that the embedded monomeric H2O and OH-(H2O) complexes are decoupled from the outer environment. Our findings can well interpret ultrafast water permeation through fluorous nanochannels and the charging mechanism of Teflon, which may tailor the desired applications of organofluorines.

Static and dynamic water structures at interfaces: A case study with focus on Pt(111).

An accurate atomistic treatment of aqueous solid-liquid interfaces necessitates the explicit description of interfacial water ideally via ab initio molecular dynamics simulations. Many applications, however, still rely on static interfacial water models, e.g., for the computation of (electro)chemical reaction barriers and focus on a single, prototypical structure. In this work, we systematically study the relation between density functional theory-derived static and dynamic interfacial water models with specific focus on the water-Pt(111) interface. We first introduce a general construction protocol for static 2D water layers on any substrate, which we apply to the low indexsurfaces of Pt. Subsequently, we compare these with structures from a broad selection of reference works based on the Smooth Overlap of Atomic Positions descriptor. The analysis reveals some structural overlap between static and dynamic water ensembles; however, static structures tend to overemphasize the in-plane hydrogen bonding network. This feature is especially pronounced for the widely used low-temperature hexagonal ice-like structure. In addition, a complex relation between structure, work function, and adsorption energy is observed, which suggests that the concentration on single, static water models might introduce systematic biases that are likely reduced by averaging over consistently created structural ensembles, as introduced here.

Ordered Water Layer on the Macroscopically Hydrophobic Fluorinated Polymer Surface and Its Ultrafast Vibrational Dynamics.

Hydrophobic-like water monolayers have been predicted at the metal and some polar surfaces by theoretical simulations. However, direct experimental evidence for the presence of this water layer at surfaces, particularly at biomolecule and polymer surfaces, is yet to be validated at room temperature. Here we observe experimentally that an ordered molecular water layer is present at the hydrophobic fluorinated polymer such as polytetrafluoroethylene (PTFE) surface by using sum frequency generation vibrational spectroscopy. The macroscopic hydrophobicity of PTFE surface is actually hydrophilic at the molecular level. The macroscopically hydrophobic character of PTFE is indeed resulting from the hydrophobicity of the ordered two-dimension (2D) water layer, in which cyclic water tetramer structure is found. The water layer at humidity of ≤40% has a vibrational relaxation time of 550 ± 60 fs. The vibrational relaxation time in the frequency range of 3200-3400 cm-1 shows remarkable difference from the interfacial water at the air/H2O interface and the lipid/H2O interface. No discernible frequency dependence of the vibrational relaxation time is observed, indicating the homogeneous dynamics of OH groups in the water layer. These insights into the water layer at the macroscopically hydrophobic surface may contribute to a better understanding of the hydrophobic interaction and interfacial water dynamics.

Supramolecular Aggregation of Tetrameric and Homododecameric Water Clusters in a 1D Cobalt(II) Coordination Polymer Containing 1,2,4,5-Benzenetetracarboxylate

A ternary mixed ligand Co(II) coordination polymer, namely, {[Co(L)(btec)0.5(H2O)]·3H2O}n, (L = 1,4-bis(thiabendazole)butane, H4btec = 1,2,4,5-benzenetetracarboxylic acid) has been hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction analysis. The coordination polymer features a 1D wave-like chain, which is further extended into a 3D supramolecular framework via O–H⋯O hydrogen bonding interactions. It is noteworthy, the chair-shaped homododecamers and quasirectangle teteramers assemble with the 1D loose-string-like water-btec4− chain into a unusual boxing-glove-like 2D water layer. Hirshfeld surface analysis and fingerprint plots show that the coordination polymer is stabilized by O–H⋯O, π⋯π, O–H⋯π, and H⋯H intermolecular interactions. Furthermore, thermal behaviors, luminescence and catalytic properties of the coordination polymer for degradation of methyl orange in a Fenton-like process have been investigated.

An unprecedented mixed valence cobalt(III)/cobalt(II) ion-pair complex ([CoCO3(bipy)2]2[Co(DCA)2]⋅16H2O) with two novel water tapes

An unprecedented mixed valence cobalt(III)/cobalt(II) ion-pair complex, [CoCO3(bipy)2]2[Co(DCA)2]⋅16H2O (1) [bipy = 2,2′-bipyridine, DCA = demethylcantharidate, exo-1,4-epoxy-cyclohexyl-2,3-dicarboxylate group, (C8H8O5)2 −], has been synthesized and characterized by elemental analysis, IR, UV–vis, Thermogravimetric analysis (TGA) and single crystal X-ray diffraction. The crystal structure of 1 consists of three independent molecular moieties: [CoCO3(bipy)2]+, [Co(DCA)2]2–, and water molecules of crystallization. Interestingly, two novel water tapes, one comprises of alternate cyclic water tetramer and octamer, the other is constructed by alternate cyclic water hexamer and carboxylate–water hybrid octamer [(H2O)2(COO)2]2 −, have been detected for the first time in the host framework of 1. The two novel water tapes are linked together by the DCA and carbonate ligands via hydrogen bonds into a 2D water layer, and then the water layers assemble complex ions ([CoCO3(bipy)2]+ and [Co(DCA)2]2 −) through hydrogen bonds, π–π interactions and electrostatic interactions to form the overall 3D metal–organic framework structure.

Conversions between dimeric and polymeric ketopiperazinediacetato complexes constructed by water-layers

Degradations of the layered polymeric products [M2(kpda)2(H2O)4]n·6nH2O (M = Co, 1; Ni, 2; Zn, 3; H2kpda = ketopiperazinediacetic acid, C8H12N2O5) result in the formation of dimeric units [M2(kpda)2(H2O)6]·H2O (M = Co, 4; Ni, 5; Zn, 6) in an ethanol solution, where the layered structures shrink from 11.23 A to 6.22 A. This is attributed to the dehydration of interesting 2D water layers based on X-ray structural analysis. The quasi-interconversion was monitored by IR, NMR measurements and product isolations, which involved complicated hydrated–dehydrated reactions.

First crystallographic report on a novel 2D layer of water pentagons: L5(7) water motif enclathrating [Co(cyclam)Cl2

Abstract X-ray crystallographic study on [CoII(cyclam)Cl2]·3H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane) reveals that the three water molecules form water pentamers, four of such adjacent water pentamers are fused together to form boat-shaped dodecamers (H2O)12 which are further H-bonded to form 2D water layers. Between the successive water layers, H-bonded 1D chains of [Co(cyclam)Cl2] monomers are sandwiched and stacked along the crystallographic c-direction. Thermal studies reveal that the coordinated water molecules are strongly bound to the polymeric framework which can be thermally dehydrated and readsorbed, as evidenced by the PXRD studies of the parent, dehydrated and rehydrated forms of the complex.

A New Coordination Polymer Exhibiting Unique 2D Hydrogen-Bonded (H2O)16 Ring Formation and Water-Dependent Luminescence Properties

A new coordination polymer, [Zn(dpe)(bdc)]·4H(2)O (ZndB; dpe=1,2-bis(4-pyridyl)ethane, bdc(2-)=dianion of benzenedicarboxylic acid), which possesses a 3D metal-organic framework (MOF) has been synthesized and structurally characterized. This 3D MOF is constructed by the assembly of helical channels filled with guest water molecules in both inner and outer regions of the channel. The resulting network also creates a 2D water layer containing hydrogen-bonded (H(2)O)(16) rings as the basic building units. Thermogravimetric and powder X-ray diffraction measurements of ZndB revealed a two-step weight loss of water molecules with a reversible water adsorption/desorption process in the inner channel for the first stage, and irreversible water desorption in the outer channel for the second stage. This spongelike property is manifested by the excimer emission originating from interaction between dpe (π*) and the other dpe (π) of the proximal helical channel, which is highly sensitive to the environmental perturbation. Powder X-ray analyses reveal that the dehydration process induces the readjustment of dpe π-π stacking distance/orientation, which results in dramatic luminescence changes from dim pale blue (λ(em)≈470 nm) upon hydration to bright white-light generation (broad, λ(em)≈500-550 nm) upon water depletion, accompanied by a ≈100-fold increase in the emission intensity.

Syntheses, structural characterization and antimicrobial activities of novel cobalt-pyrazine-2,3-dicarboxylate complexes with N-donor ligands

Abstract Novel cobalt-pyrazine-2,3-dicarboxylate complexes with 1,10-phenanthroline (phen), [Co(pzdca)(phen) 2 ] 2 ·11H 2 O (1) , N,N,N′,N′ -tetramethylethylenediamine (tmen), (H 2 tmen)[Co(pzdca) 2 (tmen)]·9H 2 O (2) and 2,2-dimethylpropane-1,3-diamine (dmpen), [Co(CO 3 )(dmpen) 2 ](pzdca) 0.5 ·H 2 O (3) have been synthesized and characterized by elemental and thermal analyses, spectroscopic (IR and UV–vis) and X-ray diffraction techniques. In 1 and 2 , pyrazine-2,3-dicarboxylate ligand coordinated to the Co(II) ions through one nitrogen atoms of pyrazine ring and oxygen atoms of carboxylate group as a bidentate ligand and distorted octahedral geometries of 1 and 2 are completed by phen and tmen ligands, respectively. In 2 , the tmen molecules exhibit chemically different functions; it coordinated to the Co(II) ion as a bidentate ligand and in the other form it protonated and acts as counter-ion. In complex 3 , Co(III) ion is coordinated by four nitrogen atoms of dmpen and two oxygen atoms of CO 3 ligand and the pzdca behaves as a counter-ion. Furthermore, structures of 1 and 2 contain extensive hydrogen bonding between crystal water molecules to form infinite 2D water layers and 1D water chains, respectively. In vitro antimicrobial activities of new complexes were tested against selected wild type and clinical microorganisms by MIC. Complexes exhibited antimicrobial activity at high concentrations against the bacteria, fungi and clinical isolate tested.

2D water layer enclathrated between Mn(II)–Ni(CN) 4 coordination frameworks

A coordination polymer, {Mn(H 2O) 2[NiCN] 4·4H 2O} n , showed that the coordination layers are stacked on top of each other sandwiching 2D ice layer of boat-shaped hexagonal water clusters [Display omitted] .

Formation of infinite 2D water layers in a crystal host

A self-assembled, (H 2O) 38 cluster stabilized by a mono-nuclear copper(II) complex 1 namely {[Cu(phen) 2(CO 3)]·7H 2O} is characterized by X-ray diffraction studies. The adjacent (H 2O) 38 clusters connect together resulting in an infinite 2D water layer structure. The water morphology is stable at room temperature, but upon thermal decomposition, the water loss is irreversible.

Self-Assembly and Crystal Structures of Supramolecular (H2O)38 Water Morphology in a Coordination Complex Crystal Host

A mono-nuclear copper (II) complex 1, formulated {[Cu(phen)2(CO3)]·7H2O} has been synthesized and characterized by X-ray diffraction studies, FTIR, and thermogravimetric (TG) analysis. However, there is a self-assembly structure of (H2O)38 cluster in this complex 1, and it is worth reporting. The adjacent (H2O)38 clusters connect together resulting in an infinite 2D water layer structure. The water morphology is stable at room temperature, but upon thermal decomposition, the water loss is irreversible. A mono-nuclear copper (II) complex 1, formulated {[Cu(phen)2(CO3)].7H2O} has been synthesized and characterized by X-ray diffraction studies, FTIR, and thermogravimetric (TG) analysis. However, there is a self-assembly structure of (H2O)38 water cluster in this complex 1, and it is worth reporting. The discrete (H2O)38 cluster connects together resulting in an infinite 2D water layer structure. The alternate arrangement of the complex 1 and the 2D water layer produce infinite through-channels along a axis direction, and the part moieties of complex 1 are located inside these channels. The water rings are stable at room temperature, and when thermally decomposes the water loss is irreversible.

Novel L4(6)6(6) water layers trapped in an organic host framework 3-(1H-imidazol-1-yl)-1-phenylpropan-1-one

Using a flexible imidazole derivate ligand 3-(1H-Imidazol-1-yl)-1-phenylpropan-1-one (L), novel 2D (two-dimensional) L4(6)6(6) water layers can be observed, which consist of fused cyclic water tetramers and hexamers. These 2D water layers are also trapped in supramolecular architecture L·3H 2O ( 1). It is interesting that the C–H···π interactions obviously play an important role in stabilizing the packing structure, which also reveal the cooperative interactions between these supramolecular contacts in the construction of 2D water layers.

Regulated Formation of 2D Water Layers with Alternating Six-membered Quasi-planar and Chair Cluster Units by 1D Supramolecular Chain

Abstract Crystals of 4-methylamino-6-oxopyrimidine (1) grown from aqueous alcohol were found to contain 2D water layers consisting of hexameric water clusters with alternating quasi-planar and chair conformations, which are apparently regulated by interactions with the supramolecular aggregate of 1n through hydrogen bonds.

Role of Nonbonding Interactions in the Crystal Growth of Phenazinediamine Tetrahydrate: New Insights into the Occurrence of 2D Water Layers in Crystal Hydrates

Long fibers of 2,3-phenazinediamine tetrahydrate, 1, were grown from aqueous ammoniacal solution containing o-phenylenediamine and catalytic amounts of ammonium molybdate under ambient conditions. Single-crystal analysis of 1 revealed the presence of 2D water layers made of hexameric clusters that are exclusively in the chair conformation similar to that found in hexagonal ice (Ih) on the {0001}; organic molecules were stacked as columns in between water layers dictated through strong supramolecular interactions. We hereby propose an intuitive mechanism to show how nonbonding interactions lead to the crystallization of 1 and other solids exhibiting 2D water sheets. Ab initio calculations at the density functional level for 1 further confirm the origin of their stability.

Well-Resolved, New Water Morphologies Obtained by Modification of the Hydrophilic/Hydrophobic Character and Shapes of the Supporting Layers

The planar coordination complexes [Ag2L2] (L = ophen or obpy, where Hophen = 1H-[1,10]phenanthrolin-2-one and Hobpy = 1H-[2,2']bipyridinyl-6-one) contain both hydrophilic and hydrophobic functional groups. Crystallization of these structurally related complexes in an aqueous medium gives [Ag2(ophen)2]2 x 6H2O (1), [Ag2(obpy)2]3 x 18H2O (2), and [Ag2(obpy)2]2 x 14.5H2O (3). Novel water morphologies are observed in these crystalline hydrates, similar 2D metal-organic layers in which the planar [Ag2L2] complexes as building blocks are stacked alternately together and provide hydrogen bond acceptor sites (O atoms) for anchoring 1D water chains or 2D water layers on their surfaces. In the wavelike metal-organic framework of 1, the wide hydrophobic region renders the formation of 1D water tapes containing four- and six-membered water rings, whereas more complex 2D water layers are sandwiched in 2 and 3, owing to the fact that the surfaces of the supporting layers are more hydrophilic than 1.

Reactive wetting: H2O/Rh(111).

First-principles calculations imply that neither H2O bilayers nor half-dissociated, H2O+OH+H monolayers are thermodynamically stable on clean Rh(111). Thus, the experimental observation that Rh(111) supports a periodic 2D water adlayer needs an explanation. Chemistry involving common surface impurities, notably C atoms, may be the answer. Calculations show they provide favorable binding sites for H atoms detached from H2O. The resulting OH fragments can anchor a 2D water layer to the surface.

Two-dimensional water and ice layers: neutron diffraction studies at 278, 263, and 20 k.

Neutron diffraction elucidates the structures of two-dimensional (2D) water layers (278 K) or 2D ice layers confined in an organic slit-shaped nanospace. The two-dimensional ice phases reported here consist of individual eight-membered rings or folded-chain segments (263 K) and condensed twelve-membered irregular rings (20 K). This is quite different from bulk or other 2D ice structures; the latter usually form hexagonal honeycomb lattices. Both low-temperature structures typically feature water molecules which are surrounded by two or three other water molecules. Neutron diffraction and thermochemical studies indicate a liquid-solid-phase transition around 277 K for two-dimensional D2O layers. A further solid-solid-phase transition occurs between 263 and 20 K.