Guest Water Molecules Research Articles

Solvent-directed Structure Variation from Mononuclear to Bis-methoxo-bridged Binuclear Copper (II) Compound: Crystal Structures and Proton-conduction

In ethanol, the reaction of 2-(methylthio)-4-(pyridin-2-yl)pyrimidine) with Cu(NO3)2 (2-MTPP) yielded a mononuclear Cu(II) coordination compound [(C10H9N3S)2CuNO3]NO3.H2O. In contrast, a discrete bis-methoxo-bridged binuclear Cu(II) coordination compound resulted when ethanol was substituted by methanol. [(C10 H9 N3S)2CuNO3]NO3.H2O and [(C10 H9 N3S)(CH3O) CuNO3]2 have been structurally investigated by single crystal X-ray diffraction. In [(C10H9N3S)2CuNO3]NO3.H2O, uncoordinated nitrate anions and water guest molecules form an interesting one-dimensional hydrogen-bonded chain that is accommodated into an open rhomboidal channel constructed by [Cu(NO3)(2-MTPP)2]+ cations. In [(C10H9N3S)(CH3O)CuNO3]2, binuclear molecules are arrayed in a linear fashion via C–H…O hydrogen bonding interactions. Moreover, [(C10H9N3S)2CuNO3]NO3.H2O has a proton-conductive property with a room-temperature conductivity of 4.96×10−8 S cm−1.

Synthesis, crystal structure and luminescent property of heterometallic d10–d8 porous complex

One new heterometallic complex [Cd2Cu(BTC)2(H2O)2]⋅2H2O (1) (BTC=benzene-1,3,5-tricarboxylate), has been synthesized and characterized by elemental analysis and single-crystal X-ray diffraction techniques. The structure indicates that the complex 1 crystallizes in triclinic, space group Pī, in which, the carboxylate groups of BTC ligand adopt μ2–η1:η1, and μ2–η2:η1 coordination modes, bridging Cd(II) and Cu(II) atoms to generate 2D Cd-BTC bilayer then to a (4,6)-connected open 3D framework with 1D channels occupied by guest water molecules. In addition, thermal gravimetric analysis (TGA) and luminescent property of 1 were investigated.

Hydrothermal synthesis, structure, porosity, and luminescent properties of 3D coordination polymer of holmium with 1,4-phenylenediacetic acid [Ho2(PDA)3(H2O)] n ·2nH2O

Coordination polymer formulated as [Ho2(PDA)3(H2O)] n ·2nH2O having three-dimensional network was hydrothermally synthesized (H2PDA is 1,4-phenylenediacetic acid). The polymer crystallizes in the monoclinic space group P 21/c, unit cell parameters: a = 21.7025(2) Ǻ, b = 10.03560(10) Ǻ, c = 14.03430(10) Ǻ, β = 91.7110(10)° (Z = 4), and exhibits a three-dimensional porous framework. The polymer contains two and four crystallographically independent holmium(III) ions and 1,4-phenylenediacetate anions, respectively. The two types of Ho(III) ions adopt an extended zigzag orientation and act as nodes alternately, while three different carboxylate (COO−) groups bridge two adjacent Ho(III) ions. The coordination polymer chains are reinforced by well-directed hydrogen bonds involving guest water molecules. The polymer is mesoporous in nature with average pore size diameter of 5.6 nm. The polymer exhibits intense emission bands in visible region upon excitation at 390 nm. The polymer is thermally robust and undergoes thermal decomposition in well-defined steps.

Two Novel Cationic Frameworks Based on Cadmium(II) Vinylphosphonate with 4,4′-Bipyridine as Coligand

The reaction of cadmium nitrate and vinylphosphonic acid (H2L) with 4,4′-bipyridine (bipy) as coligand led to two novel cadmium(II) vinylphosphonates, namely, [Cd4(L)3(NO3)(bipy)4(H2O)3]·(NO3)·3(H2O) (1) and [Cd3(HL)3(L)(bipy)3(H2O)4]·(NO3)·3.5(H2O) (2). Both compounds feature a cationic framework which encloses charge-balanced nitrate anions as well as guest water molecules. They represent the first examples of metal-organic frameworks based on mixed bridging ligands that contain a low-carbon-number alkylphosphonate. Notably, the cationic framework of 2 manifests an unprecedented (4,5)-connected net topology with point symbol of (42·6·83)·(43·65·82)2. Two novel cationic frameworks based on cadmium(II) vinylphosphonate with 4,4′-bipyridine as coligand are reported here.

Side-chain-modulated supramolecular assembly between CuX2 (X = Cl, Br) and quasi-planar π-conjugated organic synthons of 1, 3, 5-tris(2-alkylthiolpyrimidinyl)benzene: Crystal structures and conductive properties

A class of π-conjugated organic synthons, namely 1, 3, 5-tris(2-alkylthiolpyrimidinyl)benzene (TMPB: alkyl=Me; TEPB: alkyl=Et; TPPB: alkyl=n-Pr) was designed and prepared, which only differ in the length of linear side chain. It was found that these organic synthons can keep a quasi-planar conformation even coordinated to metal ions due to intramolecular C–H⋯N hydrogen bonds. Assembly of these organic synthons with CuX2 (X=Cl, Br) generated four coordination polymers: [(TPPB)CuCl2]n (1), {[(TMPB)CuCl2]·H2O}n (2), [(TPPB)CuBr2]n (3), [(TEPB)CuBr2]n (4), among which 1–3 exhibit one-dimensional coordination ribbon structure and 4 shows a two-dimensional wave-like coordination network. Although 1–3 exhibit similar assembly hierarchy going from 1-D ribbon through 2-D supramolecular layer to 3-D supramolecular architecture, the side-chain-effect can be clearly seen which modulates intra-chain or inter-chain Cu⋯Cu distance; inter-chain C–H⋯S supramolecular interactions and even the co-existence of guest water molecules. The room-temperature direct-current (dc) conductivity of 1–4 is measured about 9.6×10−12Scm−1, 2.9×10−9Scm−1, 2.6×10−12Scm−1 and 5.7×10−11Scm−1, respectively, wherein the highest electronic conduction of 2 is assumed to be pertinent to the existence of unique inter-chain C–H⋯S interactions. Furthermore, the complex impedance technique reveals that 2 exhibits a alternate-current (ac) conductivity of 4.3×10−6Scm−1 at room temperature, which almost decreases linearly with the rising temperature. The higher ac conductivity of 2 against its dc conductivity is assumed to be largely contributed by proton-conduction as the matter of fact that there exist in 2 guest water molecules and water-molecule-associated O–H⋯Cl hydrogen bonding network. The unusual temperature-dependent ac conductivity of 2 is possibly due to the temperature-sensitive O–H⋯Cl hydrogen bonding network, which is responsible for proton transporting.

A dynamic metal–organic supramolecular host based on weak π-stacking interactions incorporating 2D water-chloride-methanolic supramolecular sheet

Herein, we report the formation of a unique water-chloride-methanol 2D supramolecular network within the hydrophobic interlayer cavities of a novel flexible metal–organic supramolecular host (MOSH) framework formed by π-induced self-assembly of the monomeric metal–organic complex [Pr(1,10-phen)2(H2O)5]Cl3(H2O)(CH3OH) (1,10-phen=1,10-phenanthroline) (complex 1). Single crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD) and spectroscopic techniques are used to characterize the complex. The structural analysis reveals that in this MOSH the discrete metal–organic moieties are connected by π⋯π interactions to form 2D metal–organic supramolecular sheet structures. The guest water and methanol molecules together with counter chloride anions stabilize in the MOSH framework through hydrogen bonding interactions between the 2D metal–organic supramolecular layers. The hydrogen bonding interactions among the coordinated water and guest species form a unique 2D supramolecular water-chloride-methanol sheet structure. Upon removal of guest water and methanol molecules by heat treatment the supramolecular framework gets shrunk but retains the crystallinity while upon re-absorption of water molecules it undergoes structural change with expansion of effective guest accessible void space. The flexibility of the supramolecular framework and the mechanism of thermally induced phase transformation in the MOSH are examined by PXRD study. The photoluminescence property of the complex 1 and the crystalline complex obtained after rehydration has been thoroughly investigated. The theoretical analysis has been performed to resolve the issue of stability of the 2D supramolecular water-chloride-methanol sheet in the MOSH framework and it has been found that for complex 1 the stabilization energy of the [(H2O)6-(CH3OH)-Cl3]n3− is 1949.427Kcal mol−1.

Dissociation mechanism of gas hydrates (I, II, H) of alkane molecules: a comparative molecular dynamics simulation

Employing NPT molecular dynamics method with consistent valence force field, the dissociation processes of sI, sII and sH gas hydrates are simulated at different temperatures and at a constant pressure of 100 MPa. The dissociation mechanisms of gas hydrates are revealed by analysing the structural snapshots, radial distribution functions and diffusion coefficients at different temperatures. As temperature increases, the diffusion rates of water molecules and guest molecules increase; thus the clathrate skeleton formed by water molecules with hydrogen bonds distorts and breaks down; meanwhile the guest molecules encapsulated in the water cavities are released. The size of guest molecules affects the dissociation behaviour of gas hydrate. In addition, the dissociation behaviour also relies on the structural phase of gas hydrates.

Structural Diversity of MOFs Constructed by Tricarboxylate Ligand

Considerable progress has been made in the construction of metal-organic frameworks (MOFs) recently[1]. Due to the close relationship between the structures of MOFs and their properties, tuning structures by rational design through the judicious choice of metal ions, bridging organic ligands and reaction conditions becomes very attractive[2]. Three-dimensional pillar-layer architecture of [Co3L2(bpe)4]·2DMF·2(H2O)] (complex 1, Fig 1a), honeycomb-like channels of [Zn2L(OH)(bpe)]·5.5(H2O)] (complex 2,Fig 1b), and chain-like structure of [Zn2(HL)2(bpy)2(H2O)])2]·(bpy)·6(H2O)] (complex 3, Fig 1c) (HL3>=5-(4-carboxybenzoylamino-isophthalic acid), bpe = 1,2-bis(4-pyridyl)ethane and bpy = 4,4'-bipyridine and) have been synthesized and characterized by single X-ray crystallography(Figure 1). Complex 1 features a three-dimensional (3D) pillar-layer architecture generated from bpe-pillared M-L3-layers. Complex 2 is a 3D structure with 4- and 6-coordinated Zn2+in the centrosymmetric tetranuclear Zn4(µ3OH)2(COO)6(bpe)4SBU. Complex 3 is 2D structure. The [Zn(HL)(bpy)(H2O)] chains are connected each other by hydrogen bonding, with free bpy and guest water molecules accommodated in.

Formation of intercalation compound of kaolinite–glycine via displacing guest water by glycine

The kaolinite–glycine intercalation compound was successfully formed by displacing intercalated guest water molecules in kaolinite hydrate as a precursor. The microstructure of the compound was characterized by X-ray diffraction, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscope. Results show that glycine can only be intercalated into hydrated kaolinite to form glycine–kaolinite by utilizing water molecules as a transition phase. The intercalated glycine molecules were squeezed partially into the ditrigonal holes in the silicate layer, resulting in the interlayer distance of kaolinite reaching 1.03nm. The proper intercalation temperature range was between 20°C and 80°C. An intercalation time of 24h or above was necessary to ensure the complete formation of kaolinite–glycine. The highest intercalation degree of about 84% appeared when the system was reacted at the temperature of 80°C for 48h. There were two activation energies for the intercalation of glycine into kaolinite, one being 21kJ/mol within the temperature range of 20–65°C and the other 5.8kJ/mol between 65°C and 80°C. The intercalation degree (N) and intercalation velocity (v) of as a function of intercalation time (t) can be empirically expressed as N=−79.35e−t/14.8+80.1 and v=5.37e−t/14.8, respectively.

Topotactic structural conversion and hydration-dependent thermal expansion in robust LnMIII(CN)6·nH2O and flexible ALnFeII(CN)6·nH2O frameworks (A = Li, Na, K; Ln = La–Lu, Y; M = Co, Fe; 0 ≤ n ≤ 5)

The structures of the AxLnM(CN)6·nH2O (A = Li, Na, K; Ln = La–Lu, Y; M = Co, Fe; x = 0, 1; 0 ≤ n ≤ 5) cyanide frameworks, their thermal expansion behaviour, and their transformations upon dehydration are explored using X-ray and neutron single crystal diffraction and X-ray powder diffraction. Modification from positive to negative thermal expansion in the LnCo(CN)6·nH2O phases is achieved by removal of the guest water molecules. Most notable is the unprecedented flexibility demonstrated by the “coiling” of KLnFe(CN)6·nH2O frameworks upon their dehydration, wherein the lanthanoid coordination geometry reversibly converts from a 9-coordinate tri-capped trigonal prism to a 6-coordinate octahedron via a single-crystal-to-single-crystal process, accompanied by a large (14–16%) decrease in unit cell volume.

Synthesis, supramolecular assemblies and luminescence of nickel(II) complexes based on a series of N-(2-pyridylmethyl) amino acid derivatives

N-(2-Pyridylmethyl)-l-alanine (l-Hpana), and N-(2-pyridylmethyl)-aspartic acid (l-H2pasp) have been solvothermally prepared and structurally characterized by X-ray single-crystal diffraction. Complexes 1 and 2 crystallize in the monoclinic P21/c and orthorhombic C2221 space groups, respectively, due to the dissimilar ligand features (chirality of l-Hpana). They show similar mononuclear coordination structures with two kinds of five-member chelating rings, which are assembled into 2D supramolecular networks through multiple N–H⋯O and O–H⋯O interactions. For complex 3, the formation of a Ni–O bond between Ni(II) and the side-chain carboxylate lead to a left-handed helical coordination polymer with helical water chains inclusion. The most striking feature is that the helical hydrogen-bonding motif represents rare hydrated hydronium aggregation that formed by strong interactions between hydronium ions and guest water molecules. This helical aggregate is further stabilized by multiple hydrogen bonds with other lattice water molecules and chloride counteranions. The thermal and luminescent properties of these complexes have also been investigated.

Studies of the structural and magnetic properties of an unsymmetrical ligand 1,2,4-benzenetricarboxylic acid based chiral 3-D trinickel coordination polymer as an alkali base-influenced hydrothermal reaction product

The reaction of 1,2,4-benzenetricarboxylic acid (H3btc), as a ligand, under pH-controlled hydrothermal conditions with nickel salts leads to the formation of a coordination polymer of {CsNi3(OH)(H2O)3[C6H3(CO2)3]2·3H2O}n (1). The subunit of compound 1 contains a hydroxide- and carboxylate-bridged trinickel clusters that are linked by an unsymmetrical organic carboxylate spacer to form a chiral three-dimensional anionic framework, in which cesium cations and guest water molecules are located in one-dimensional channels. The presence of a hydroxide ion serves both as a deprotonation agent and a cation source during the hydrothermal reaction, thus permitting the extent of deprotonation of the unsymmetrical ligand H3btc to be controlled, which is essential for the successful formation of compound 1. The magnetic properties of compound 1 were analyzed. Both dc and ac magnetic susceptibility as well as reduced magnetization measurements confirmed the spin-frustration nature of 1.

An ultrastable, flexible POM-based coordination polymer with redox properties

A new porous coordination polymer (1) has been prepared under hydrothermal conditions. The flexible framework of1shows dynamic behavior accompanied with the removal/adsorption of guest water molecules. Remarkably, crystals of1can remain intact even in 8 mol L−1hydrochloric acid, dilute NaOH solution (pH = 12) and boiling water.

Net charge changes in the calculation of relative ligand-binding free energies via classical atomistic molecular dynamics simulation.

The calculation of binding free energies of charged species to a target molecule is a frequently encountered problem in molecular dynamics studies of (bio-)chemical thermodynamics. Many important endogenous receptor-binding molecules, enzyme substrates, or drug molecules have a nonzero net charge. Absolute binding free energies, as well as binding free energies relative to another molecule with a different net charge will be affected by artifacts due to the used effective electrostatic interaction function and associated parameters (e.g., size of the computational box). In the present study, charging contributions to binding free energies of small oligoatomic ions to a series of model host cavities functionalized with different chemical groups are calculated with classical atomistic molecular dynamics simulation. Electrostatic interactions are treated using a lattice-summation scheme or a cutoff-truncation scheme with Barker–Watts reaction-field correction, and the simulations are conducted in boxes of different edge lengths. It is illustrated that the charging free energies of the guest molecules in water and in the host strongly depend on the applied methodology and that neglect of correction terms for the artifacts introduced by the finite size of the simulated system and the use of an effective electrostatic interaction function considerably impairs the thermodynamic interpretation of guest-host interactions. Application of correction terms for the various artifacts yields consistent results for the charging contribution to binding free energies and is thus a prerequisite for the valid interpretation or prediction of experimental data via molecular dynamics simulation. Analysis and correction of electrostatic artifacts according to the scheme proposed in the present study should therefore be considered an integral part of careful free-energy calculation studies if changes in the net charge are involved. © 2013 The Authors Journal of Computational Chemistry Published by Wiley Periodicals, Inc.

An unusual μ-1,2,3-squarato-bridged two dimensional coordination polymer: Crystal structure, thermal, photoluminescence and magnetic studies

A new 2D coordination polymer, {[NiII(squarate)(2,2′-bipy)(H2O)]·H2O}n, [squarate=3,4-dihydroxycyclobut-3-ene-1,2-dionate, 2,2′-bipy=2,2′-bipyridine], has been synthesized by using multi-oxygen donor squaric acid ligand and characterized by single crystal X-ray crystallographic and various spectroscopic studies. The structural analysis has revealed that the complex crystallizes in orthorhombic Pbca space group and it has 3D supramolecular structure. Within the complex, the squarato-dianion exhibits unusual μ-1,2,3 bridging mode with Ni(II) ions and 2D coordination sheets are formed through bridging the metal ions by squarato-anions. The 2D coordination sheets are packed along crystallographic b-axis and the 2,2′-bipyridyl (blocking ligand) moieties are hanging in the interlamellar spaces between the 2D coordination sheets. These 2D coordination sheets are further bridged by supramolecular π⋯π interactions using 2,2′-bipyridyl ligands leading to the formation of 3D supramolecular framework which acts as a metal–organic supramolecular host (MOSH). During formation of 3D supramolecular structure, 1D supramolecular channels are formed along the crystallographic c-axis. The guest water molecules get stability within such supramolecular channels through hydrogen bonding interactions with free oxygen atoms of bridging squarate ions. The thermal study indicates that the complex decomposes in three steps. The variable temperature magnetic measurements suggest that the complex is antiferromagnetic in nature. The complex exhibits solid-state photoluminescence spectra at room temperature due to π–π∗/n–π∗ transition of the squarate and 2,2′-bipyridine ligands. The present study points to the squarato-bridged metal complexes as unique model system to carry out the study on different bridging modes exhibited by the ligand.

Synthesis, crystal structure and spectroscopic studies of a cobalt(III) Schiff base complex and its use as a heterogeneous catalyst for the oxidation reaction under mild condition

A new Schiff base oriented Co(III) complex, (CoL)Cl4H2O (L=Schiff base), has been synthesized by careful design of the Schiff base ligand thorough oxidation of Co(II) to Co(III) during the reaction process. The complex has been characterized by single-crystal X-ray structure analysis and various spectral analyses. Structure analysis reveals that this monomeric complex crystallizes in triclinic P−1 space group. Supramolecular hydrogen bonding interactions among the guest water molecules and counter anion chloride leads to the formation of 1D water-chloride chain. A polymer anchored heterogeneous cobalt complex has been synthesized, characterized by various physicochemical techniques and successfully used for the oxidation of alkenes and sulfides using H2O2 as oxygen source. The influence of the various reaction parameters has been studied. The heterogeneous cobalt complex can be reused seven times without any significant loss in its catalytic activity.

Syntheses, structures, and host-guest interactions of 2-D grid-type cyanide-bridged compounds [Zn(L)(H2O)2][M(CN)4]·3H2O (L = N,N′-bis(4-pyridylformamide)-1,4-benzene; M = Ni, Pd or Pt)

Self-assembly of Zn2+, the pillar ligand N,N′-bis(4-pyridylformamide)-1,4-benzene, and [M(CN)4]2− (M = Ni, Pd, or Pt) formed three compounds [Zn(L)(H2O)2][M(CN)4]·3H2O (1–3). Single-crystal X-ray diffraction (XRD) analysis reveals that 1–3 are isostructural and consist of cyanide-bridged 2-D grid-type layers built of [Zn(L)(H2O)2]2+ chains cross-linked by [M(CN)4]2− units. Thermogravimetric and powder XRD analyses indicate that 1 has a high thermal stability and exhibits reversibility for desorption/resorption of water guest molecules.

Dielectric Properties of One-dimensional Water Clusters Confined in the Porous Crystal, [Co3(2,4-pydc)2(µ3-OH)2]·9H2O (2,4-pydc: pyridine-2,4-dicarboxylate)

Abstract The dielectric properties of the one-dimensional (1D) water clusters confined in the porous crystal, [Co3(2,4-pydc)2(µ3-OH)2]·9H2O, were examined. The dielectric constant (ε′) decreased abruptly below 200 K, where the first-order phase transition occurred. The results of molecular dynamics simulations suggested freezing of the molecular motion of the guest water molecules, forming 1D water clusters at 200 K. ε′ (10 kHz) increased sharply above 300 K and became as high as 500 at 383 K. The hysteresis loop observed at 340 K indicated the antiferroelectric state of the guest water system.

Synthesis and characterization of polymorphs of photoluminescent Eu(III)-(2,5-furandicarboxylic acid, oxalic acid) MOFs

A novel metal organic framework (MOF) formulated as [Eu(H2O)2(fdc)(ox)0.5·(H2O)]n (1, fdc2−=2,5-furandicarboxylate, ox2−=oxalate), was hydrothermally synthesized via in situ ox2− generation from the partial decomposition of the fdc2− ligand. This material crystallizes in the monoclinic space group C2/c, unit cell parameters of 1: a=16.7570(10), b=10.5708(7), c=13.5348(14) Å, β=116.917(2)° (Z=8), and exhibits a three-dimensional (3D)-porous framework, with guest water molecules residing in the channel linking all other ligands (H2O, ox2−and fdc2−) via hydrogen bonding interactions. Compound 2 is a polymorph of 1 crystallizing in monoclinic P21/c space group. The photoluminescence properties of 1 and 2 were studied at room temperature. The spectra show the typical Eu3+ red emission and the differences observed reflects the slightly different structures of these polymorphs.

Synthesis and structure of a one- and a three-dimensional material constructed from molybdenum phosphates and macrocyclic metal complexes

Two new polyoxometalate-based materials, [CuL]2[H2Mo5P2O23]·2H2O·2CH3CN (1) and [NiL]2[H2Mo5P2O23]·10H2O (2) (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraaza-cyclotetradecane), have been isolated from the reactions of [CuL](ClO4)2 and [NiL](ClO4)2 with (NH4)6Mo7O24, respectively, and structurally characterized. Single-crystal X-ray diffraction analysis of 1 showed that clusters of [H2Mo5P2O23]4− bridge [CuL]2+ to form 1-D chains, with O–HO and N–HO hydrogen bonding interactions forming a 3-D framework. The structure of 2 showed a 3-D network structure constructed from [H2Mo5P2O23]4− clusters bridging [NiL]2+, generating 1-D channels occupied by guest water molecules.