Hexameric Water Clusters Research Articles

Crystal structure of [Rh2(μ-OAc)2(μ-HNOCCF3)2(theophylline)2]·6H2O. Metal bonding to theophylline at the unexpected N(9) site due to the crystal packing effect and a review on intra-molecular interligand interactions affecting metal bonding properties of theophylline

• Crystal structure of a dinuclear Rh 2+ complex of theophylline was determined. • The Rh‒Rh core is occupied at either axial-side by theophylline ligands through N9. • Metal bonding not to expected N7 but to N9 is due to the crystal packing effect. • A discrete, cyclic hexameric water cluster intercalates between theophylline rings. • Metal binding sites of theophylline are reviewed in terms of interligand interaction. Reaction of theophylline with [Rh 2 (μ-OAc) 2 (μ-HNOCCF 3 ) 2 ] gave [Rh 2 (μ-OAc) 2 (μ-HNOCCF 3 ) 2 (theophylline) 2 ]·6H 2 O ( 1 ), whose crystal structure was determined by single-crystal X-ray diffraction. The dirhodium core, where the two different acetato and acetamidato ligands bridging the Rh‒Rh bond are in a trans configuration, is occupied at either axial-side by two theophylline ligands through N(9) with the formation of two kinds of intra-molecular interligand C−H (theophylline)···O hydrogen bonds, one being a bifurcated hydrogen bond between the C(3)-methyl hydrogen as a donor and the acetato and amidato oxygens as acceptors and the other between the C(8) hydrogen and the acetato oxygen. In the crystal lattice, a discrete, hydrogen-bonding, cyclic hexameric water cluster with the flattened chair conformation is sandwiched between theophylline bases, providing the first water hexagon that intercalates between aromatic rings. The participation of the acetamidato NH group in the formation of a hydrogen bond with a water molecule belonging to the water hexagon that governs the crystal packing makes it impossible for the acetamidato ligand to form an intra-molecular hydrogen bond with O(6), causing the failure of the metal bonding to theophylline through N(7). A critical review on metal bonding properties of theophylline observed in so far reported crystal structures is given, emphasizing the significance of intra-molecular interligand interactions (H-bonding, electrostatic repulsion, and steric constraint) as a factor that could affect metal binding sites/modes of theophylline.

A novel three-dimensional tetranuclear CoII coordination polymer with water hexamers based on the V-shaped tetracarboxylate ligand 4-(2,4-dicarboxylatophenoxy)phthalate.

A new coordination polymer (CP), namely, poly[[diaquatris[μ2-1,4-bis(1H-imidazol-1-yl)benzene]bis[μ6-4-(2,4-dicarboxylatophenoxy)phthalato]tetracobalt(II)] hexahydrate], {[Co4(C16H6O9)2(C12H10N4)3(H2O)2]·6H2O}n, has been synthesized by solvothermal reaction. The CP was fully characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and powder and single-crystal X-ray diffraction. It presents a three-dimensional (3D) structure based on tetranuclear CoII secondary building units (SBUs) with a tfz-d net and point symbol (43)2(46·618·84). The 4-(2,4-dicarboxyphenoxy)phthalic acid (H4dcppa) ligands are completely deprotonated and link {Co4(COO)4}4- SBUs into two-dimensional (2D) layers. Furthermore, adjacent layers are connected by 1,4-bis(1H-imidazol-1-yl)benzene (bib) ligands, giving rise to a 3D supramolecular architecture. Interestingly, there are numerous elliptical cavities in the CP where isolated unique discrete hexameric water clusters have been observed. The results of thermogravimetric and magnetic analyses are described in detail.

High-Level VSCF/VCI Calculations Decode the Vibrational Spectrum of the Aqueous Proton

The hydrated excess proton is a common species in aqueous chemistry, which complexes with water in a variety of structures. The infrared spectrum of the aqueous proton is particularly sensitive to this array of structures, which manifests as continuous IR absorption from 1000 to 3000 cm-1 known as the "proton continuum". Because of the extreme breadth of the continuum and strong anharmonicity of the involved vibrational modes, this spectrum has eluded straightforward interpretation and simulation. Using protonated water hexamer clusters from reactive molecular dynamics trajectories, and focusing on their central H+(H2O)2 structures' spectral contribution, we reproduce the linear IR spectrum of the aqueous proton with a high-level local monomer quantum method and highly accurate many-body potential energy surface. The accuracy of this approach is first verified in the vibrational spectra of the two isomers of the protonated water hexamer in the gas phase. We then apply this approach to 800 H+(H2O)6 clusters, also written as [H+(H2O)2](H2O)4, drawn from multistate empirical valence bond simulations of the bulk liquid to calculate the infrared spectrum of the aqueous proton complex. Incorporation of anharmonic effects to the vibrational potential and quantum mechanical treatment of the proton produces a better agreement to the infrared spectrum compared to that of the double-harmonic approximation. We assess the correlation of the proton stretching mode with different atomistic coordinates, finding the best correlation with ⟨ROH⟩, the expectation value of the proton-oxygen distance ROH. We also decompose the IR spectrum based on normal mode vibrations and ⟨ROH⟩ to provide insight on how different frequency regions in the continuum report on different configurations, vibrational modes, and mode couplings.

Water Vapor Single-Gas Selectivity via Flexibility of Three Potential Materials for Autonomous Indoor Humidity Control

Two new isostructural porous supramolecular materials {[Cu2(amp)4Cl][M(C2O4)3]·6H2O}n (amp = 2-aminomethylpyridine), designated as II and III for M = Cr(III) and M = Fe(III) respectively, have been synthesized by a self-assembly process of two ionic complexes [Cu2(amp)4Cl]3+ and [M(C2O4)3]3–, M = Fe(III) and Cr(III). They build heterometallic hydrogen-bonded-, oxalato- and chlorido-bridged zigzag chains with interchain hydrogen bonds and π–π interactions. This results in supramolecular potentially porous architectures exhibiting large channels filled with hexameric water clusters. Their activated phases, II′ and III′, can readsorb the water molecules to regenerate the initial materials which are stable for many water adsorption and desorption cycles like that of their homologous catena-{[(Co(amp)3][Cr(C2O4)3]·6H2O} (I′). The three materials I′, II′, and III′ exhibit water adsorption and desorption isotherms having a sigmoidal shape and resulting in the combination of a type I(b) profile followed by an S-s...

Isostructural series of [{Al(H2O)6}{Ln(pda)3}].10H2O: Synthesis, structure and photoluminescence

A new series of six isostructural molecular solids of the composition [{Al(H2O)6}{Ln(pda)3}].10H2O where Ln = Sm, Eu, Gd, Tb, Dy and Yb have been synthesized and structurally characterised. All the solids are built of three major building blocks: the lanthanide dipicolinate anion, {Ln(pda)3}3−, the counter cation, {Al(H2O)6}3+ and a hexameric water cluster in chair form. The cations and the anions supramolecularly aggregate forming a 2D H-bonded sheet; the sheets are further stabilised through hexameric water clusters in chair form and water molecules. The crystals containing Sm, Eu, Tb and Dy showed characteristic emission of lanthanide ions.

Spectral characterization, crystal structures and biological activities of iminodiacetate ternary complexes

The ternary complexes with stoichiometry [M(imda)(bipy)]·6H2O (M = Cu) and [M(imda)(bipy)(H2O)]·4H2O (M = Ni, Co and Mn) where H2imda = iminodiacetic acid and bipy = 2,2′-bipyridine, are prepared and characterized to exploit as novel antimicrobial agents and SOD mimics. The chemical structures were elucidated by IR, FAB-Mass, 1H, 13C NMR, EPR and spectral techniques. Single crystal X-ray and spectral studies of the complexes (1) and (2) have confirmed a square pyramidal geometry around Cu(II) ion while a saturated six coordinate (distorted octahedral) geometry around the Ni(II), Co(II) and Mn(II) ions due to the additional coordination from water. A supramolecular network is formed by extensive H-bonding in complex (1). The supramolecular assembly in complex (1) is additionally consolidated via the existence of unusual cyclic hexameric water clusters. The antimicrobial activities for the present complexes have been examined against Escherichia coli (K-12), Bacillus subtilis (MTC-121), Staphylococcus aureus (IOASA-22), Salmonella typhymurium (MTCC-98), Candida albicans, Aspergillus fumigatus and Penicillium marneffei. The superoxide dismutase (SOD) activity of the Cu(II) complex (1) is also assessed employing nitrobluetetrazolium (NBT) assay.

Ground and excited states of naphthalene–water (naphtha–W6) clusters: a computational study

An MP2 and DFT study of the structures of naphthalene–water hexamer clusters has been performed for both the prism and cage forms of the cluster.

Guest Exchange Reactions in Isostructural 3D Porous Coordination Polymers of Ni(II), Co(II), and Mn(II)

A series of isostructural compounds, {[Ni2(DBIBA)3]·(BF4)·6H2O}n (1), {[Ni2(DBIBA)3]·(ClO4)·3H2O}n (2), {[Ni2(DBIBA)3]·(NO3)·3H2O}n (3), {[Ni2(DBIBA)3]·Cl·C2H5OH}n (4) {[Co2(DBIBA)3]·(ClO4)·3H2O}n (5), {[Co2(DBIBA)3]·Cl·3C2H5OH}n (7), {[Co2(DBIBA)3]·Cl·3DMF}n (8), {[Co2(DBIBA)3]·Cl·3CH3COCH3·7H2O}n (9), and {[Mn2(DBIBA)3]·Cl·3DMF·3H2O}n (10), have been afforded via anion and solvent exchanges of previously reported coordination polymers {[Ni2(DBIBA)3]·Cl·18H2O}n, {[Co2(DBIBA)3]·Cl·9H2O}n, and {[Mn2(DBIBA)3]·Cl·3H2O}n (DBIBA = 5-di(1H-benzo[d]imidazol-1-yl)benzoate). Anion-exchanged compounds including {[Co2(DBIBA)3]·(NO3)·3H2O}n (6) have also been synthesized under solvothermal conditions by employing metal salts and the corresponding acid hydrolysis of the cyanide functional group of 5-di(1H-benzo[d]imidazol-1-yl) benzonitrile (DBIBN). These structures are obtained with retaining crystallinity, and only insignificant changes are observed in bond lengths and bond angles involving the metal ion. However, noncovalent supramolecular interactions (anion−π, π–π, and hydrogen bonding) are utterly affected or changed. Interestingly, in complex 9, the chloride ion moves from the node of the parent complex to the center of the cavity, where it is surrounded by a hexameric water cluster revealing strong H-bonding, which is very rare to be seen. Exchange of solvent molecules leaves the size of the voids unaltered, but anion exchanges are accompanied by shrinking of the voids, except in the case of NO3– exchange, where there is no change in volume. All are isoreticular structures with a binodal 4,6-connected stp net topology. These compounds have been characterized by single-crystal X-ray crystallography, IR spectroscopy, TGA, PXRD, and elemental analysis.

Synthesis, structure and DFT study of a chelidamic acid based Cu coordination polymer: On the importance of π–π interactions and hexameric water clusters

One-dimensional coordination polymer, i.e., {(Hampy)[Cu(chel)(H2O)]⋅2H2O}n (1, ampy=2-amino-6-methylpyridine, H3chel=chelidamic acid), has been synthesized and characterized by elemental analysis, IR spectroscopy, solution studies and X-ray single-crystal diffraction. In the monomeric unit of compound 1 the metal center exhibits a distorted square–pyramidal coordination sphere. The Cu(II) ion is coordinated to chelidamic acid and water. These monomers are interlinked generating a 1D polymer by means of the para hydroxyl group of the ligand. Protonated 2-amino-6-methylpyridine rings act as counter cations. The crystal lattice is aggregated through intermolecular interactions, such as electrostatic attraction, N–H⋯O, O–H⋯O and C–H⋯O hydrogen bonding and aromatic π stacking interactions. Hydrogen bond interactions between the water molecules led to formation of six-membered rings with chair conformation. These assemblies are described and analyzed by means of density functional theory (DFT) calculations since they play an important role in the construction of three-dimensional supramolecular frameworks.

Encapsulated discrete octameric water cluster, 1D water tape, and 3D water aggregate network in diverse MOFs based on bisimidazolium ligands

Four new metal–organic frameworks, [Zn(2-mBIM)2(SO3CF3)2·(H2O)4] (1), [Zn(BMIE)(1,4-BDC)]·(H2O)3 (2), [Cd(BIM)2(OH)(H2O)2(PF6)]·(H2O)4 (3), and [Cd(PA-BIM)2 (ClO4)2]·11.33H2O (4) (2-mBIM=bis(2-methylimidazol-1-yl)methane, BMIE=1,2-bis[1-(2-methylimidazole)-diethoxy]ethane, BIM=bis(imidazol-1-yl)methane, and PA-BIM=1,1-bis [(2-phenylazo)imidazol-1-yl]methane) have been prepared and structurally characterized. Complex 1 exhibits an infinite 1D cationic beaded-chain structure, which encapsulated discrete octameric water clusters that are comprised of a chair-like hexameric water cluster with two extra water molecules dangling on two diagonal vertices of the chair. Complex 2 forms a 1D infinite zigzag metal–organic chain structure with a 1D T4(0)A(4) water tape. Complexes 3 show a 2D grid-like sheet structure with the 1D water tape T4(0)A(0)2(0) motif. Complex 4 is a porous 3D MOF with tetrahedron-coordinated Cd(II) centers and trans-conformation PA-BIM ligands. These holes are occupied by a fascinating three-dimensional water clathrate network, which consists of cage-shaped structural tetradecameric water cluster (H2O)14 units and six independent bridged water molecules. The results suggest that the bisimidazolium ligands and anions play crucial roles in the formation of the different host structures and different guest water aggregations. Additionally, the thermal stabilities and photoluminescence spectra of the complexes have been discussed.

First-principles energetics of water clusters and ice: A many-body analysis

Standard forms of density-functional theory (DFT) have good predictive power for many materials, but are not yet fully satisfactory for cluster, solid, and liquid forms of water. Recent work has stressed the importance of DFT errors in describing dispersion, but we note that errors in other parts of the energy may also contribute. We obtain information about the nature of DFT errors by using a many-body separation of the total energy into its 1-body, 2-body, and beyond-2-body components to analyze the deficiencies of the popular PBE and BLYP approximations for the energetics of water clusters and ice structures. The errors of these approximations are computed by using accurate benchmark energies from the coupled-cluster technique of molecular quantum chemistry and from quantum Monte Carlo calculations. The systems studied are isomers of the water hexamer cluster, the crystal structures Ih, II, XV, and VIII of ice, and two clusters extracted from ice VIII. For the binding energies of these systems, we use the machine-learning technique of Gaussian Approximation Potentials to correct successively for 1-body and 2-body errors of the DFT approximations. We find that even after correction for these errors, substantial beyond-2-body errors remain. The characteristics of the 2-body and beyond-2-body errors of PBE are completely different from those of BLYP, but the errors of both approximations disfavor the close approach of non-hydrogen-bonded monomers. We note the possible relevance of our findings to the understanding of liquid water.

A one-dimensional coordination polymer with a three-dimensional supramolecular framework:catena-poly[[[(3,4,7,8-tetramethyl-1,10-phenanthroline)cadmium(II)]-μ3-4,4′-sulfonyldibenzoato] trihydrate

In the title mixed-ligand metal-organic polymeric compound, {[Cd(C14H8O6S)(C16H16N2)]·3H2O}n, the asymmetric unit contains a crystallographically unique Cd(II) atom, one doubly deprotonated 4,4'-sulfonyldibenzoic acid (H2SDBA) ligand, one 3,4,7,8-tetramethyl-1,10-phenanthroline (TMPHEN) molecule and three solvent water molecules. Each Cd(II) centre is six-coordinated by two O atoms from a chelating carboxylate group of a SDBA(2-) ligand, two O atoms from monodentate carboxylate groups of two different SDBA(2-) ligands and two N atoms from a chelating TMPHEN ligand. There are two coordination patterns for the carboxylate groups of the SDBA(2-) ligand, with one in a μ1-η(1):η(1) chelating mode and the other in a μ2-η(1):η(1) bis-monodentate mode. Single-crystal X-ray diffraction analysis revealed that the title compound is a one-dimensional double-chain polymer containing 28-membered rings based on the [Cd2(CO2)2] rhomboid subunit. More interestingly, a chair-shaped water hexamer cluster is observed in the compound.

PH modulated assembly in the mixed-ligand system Cd(ii)–dpstc–phen: structural diversity and luminescent properties

Hydrothermal reaction of cadmium salt, 3,3′,4,4′-diphenylsulfonetetracarboxylic acid (H4dpstc) and 1,10-phenanthroline (phen) under different pH conditions have afforded four novel supramolecular complexes, in which the pH value of the reaction solution plays a crucial structure-directing role. [Cd(H2dpstc)(phen)]n (1) formed in a neutral reaction environment exhibits a 1D infinite chain structure containing partially deprotonated H2dpstc2− as the H-bond donors and acceptors. Whereas [Cd2(dpstc)(phen)2]n·4.5nH2O (2), [Cd2(dpstc)(phen)2]n·nH2O (3) and [Cd2(dpstc)(phen)4(H2O)2]·6H2O (4) contain fully deprotonated dpstc4− ligands due to the alkaline reaction conditions. Complex 2 possesses a unique 2D layered structure with 1D channels. The most striking feature of 2 is that its 2D holed (4,4)-water-net is constructed from hexameric water clusters and two types of dimeric water clusters. Surprisingly, the water net and the metal–organic skeleton are interpenetrated to form a fascinating 3D metal–organic–water supramolecular architecture. A further increase of the pH value leads to another 2D layered framework of 3 containing dumbbell-shaped rings as subunits. Reaction at a strongly alkaline solution leads to a discrete molecule of 4. Meanwhile solid-state properties such as thermal stability and the photoluminescence properties at room temperature for these complexes have also been systematically investigated.

Performance of Non-Local and Atom-Pairwise Dispersion Corrections to DFT for Structural Parameters of Molecules with Noncovalent Interactions.

The nonlocal, electron density dependent dispersion correction of Vydrov and Van Voorhis (Vydrov, O. A.; Van Voorhis, T. J. Chem. Phys.2010, 133, 244103), termed VV10 or DFT-NL, has been implemented for structural optimizations of molecules. It is tested in combination with the four (hybrid)GGA density functionals TPSS, TPSS0, B3LYP, and revPBE38 for inter- and intramolecular noncovalent interactions (NCI) and compared to results from atom-pairwise dispersion corrected DFT-D3. The methods are applied to a wide range of different problems, namely the S22 and S66 test sets, large transition metal complexes, water hexamer clusters, hexahelicene, and four other difficult cases of intramolecular NCI. Critical interatomic distances are computed remarkably accurately by both dispersion corrections compared to theoretical or experimental reference data and inter- and intramolecular interactions are treated on equal footing. The methods can be recommended as reliable and robust tools for geometry optimizations of large systems in which long-range dispersion forces are crucial.

An unusual axial–axial combination of alternating cyclic rings in the chair conformations of hexameric water and chlorine-water clusters

An alternating hexameric water (H 2 O) 6 cluster and a chlorine-water cluster [Cl 2 (H 2 O) 4 ] 2- in the chair forms combine axially to each other to form a 1D chain [{Cl 2 (H 2 O) 6 } 2− ] n in complex [FeL 2 ]Cl·(H 2 O) 3 (L = 2-[(2-methylaminoethylimino)-methyl]-phenol)]. The water molecules display extensive H-bonding interactions with monomeric iron–organic units to form a hydrogen-bonded 2D supramolecular assembly. A 1D water-chloro anionic layer [{Cl 2 (H 2 O) 6 } 2− ] n in which alternating chair conformations of hexameric cyclic water clusters (H 2 O) 6 and chlorinated water clusters [Cl 2 (H 2 O) 4 ] 2– are connected axially which is unprecedented as presumed to be energetically unfavourable. ► Synthetic, structural and spectral study of the complex [FeL 2 ]Cl•(H 2 O) 3 . ► An unusual water-chloro anionic chain, [{Cl 2 (H 2 O) 6 } 2− ] n is stabilized. ► The chain contains alternating (H 2 O) 6 and [Cl 2 (H 2 O) 4 ] 2– in chair conformations. ► Two alternating chair conformations are connected axially.

Supramolecular assembled of hexameric water clusters into a 1D chain containing (H2O)6 and [(H2O)4O2] stabilized by hydrogen bonding in a copper complex

BackgroundVarious water clusters including hexamers, heptamers, octamers, decamers and 1D or 2D infinite water chains in a number of organic and inorganic-organic hybrid hosts, have been reported.Results{[Cu(pydc)(amp)].3H2O}n has been hydrothermally synthesized and characterized by elemental analysis and by IR spectroscopy. A wide range of hydrogen bonds (of the O-H...O, N-H...O and N-H...N type) are present in the crystal structure. Hydrogen bond interactions between the co-crystallized water molecules led to formation of six-membered rings with chair conformation.ConclusionIn {[Cu(pydc)(amp)].3H2O}n, there are three uncoordinated water molecules. Thermal methods confirm number of co-crystallized water molecules in polymer. Hydrogen bond interactions between the co-crystallized water molecules led to the formation of a six-membered ring with the chair conformation. These rings are part of a 1D chain containing six-membered O6 rings, which are alternately made from (H2O)6 and [(H2O)4O2] rings. [(H2O)4O2] rings are also in chair conformation.

Isomeric phenylenediacetates as modular tectons for a series of ZnII/CdII coordination polymers incorporating flexible bis(imidazole) co-ligands

This work presents a systematic investigation of the reactions of phenylenediacetate isomers with ZnII/CdII salts in the presence of different flexible bis(imidazole) co-ligands. Seven new coordination polymers, namely, {Zn(o-pda)(biim-3)}n (1), {[Cd(o-pda) (biim-5)]·H2O}n (2), {[Zn(m-pda) (biim-4)]·3H2O}n (3), {Cd(m-pda)(biim-6)0.5(H2O)}n (4), {[Cd(p-pda) (biim-3)]·H2O}n (5), {Zn(p-pda) (biim-4)}n (6), and {[Cd(p-pda)(biim-6)]·H2O}n (7) [o/m/p-pda = 1,2/1,3/1,4-phenylenediacetate acid, biim-3 = 1,1′-(1,3-propanedidyl)bis-(imidazole), biim-4 = 1,1′-(1,4- butanedidyl)bis-(imidazole), biim-5 = 1,1′-(1,5-pentanedidyl)bis-(imidazole), biim-6 = 1,1′-(1,6- hexanedidyl)bis-(imidazole)], have been synthesized and characterized by elemental analysis, IR, TG, single crystal X-ray structural determination and powder X-ray diffraction. Complex 1 shows an uncommon 1D achiral chain structure, which contains the right-handed and left-handed helical chains decorated with two zigzag arms. Complexes 2, 3, and 5 display the similar 2D undulating sql layer structures. Interestingly, in 3, the 1D water tape T4(2)6(2), which contains the hexameric water cluster (H2O)6 with a chair-like conformation, assembles these 2D layers to form a 3D framework. In 5, the 2D adjacent hetero-helical layers stack in an –ABĀ– pattern to generate a 3D mesomeric framework. Complex 4 manifests a 2D (3,4)-connected V2O5-type network. Differently from 1–5, complex 6 features a 3D 5-fold interpenetrated dia network, and complex 7 exhibits a 3D (3,5)-connected (42·6)(42·65·83)-fsc framework. A structural comparison of these polymers suggests that different dispositions of the carboxyl sites, diversiform configurations and binding fashions of phenylenediacetate isomers play important roles in the construction of resulting architectures for 1–7, which can also be well regulated by different flexible bis-(imidazole) co-ligands. Moreover, solid-state properties such as thermal stabilities and luminescent properties of 1–7 were also investigated.

Implementation of Dynamical Nucleation Theory Effective Fragment Potentials Method for Modeling Aerosol Chemistry

In this work, the dynamical nucleation theory (DNT) model using the ab initio based effective fragment potential (EFP) is implemented for evaluating the evaporation rate constant and molecular properties of molecular clusters. Predicting the nucleation rates of aerosol particles in different chemical environments is a key step toward understanding the dynamics of complex aerosol chemistry. Therefore, molecular scale models of nanoclusters are required to understand the macroscopic nucleation process. On the basis of variational transition state theory, DNT provides an efficient approach to predict nucleation kinetics. While most DNT Monte Carlo simulations use analytic potentials to model critical sized clusters, or use ab initio potentials to model very small clusters, the DNTEFP Monte Carlo method presented here can treat up to critical sized clusters using the effective fragment potential (EFP), a rigorous nonempirical intermolecular model potential based on ab initio electronic structure theory calculations, improvable in a systematic manner. The DNTEFP method is applied to study the evaporation rates, energetics, and structure factors of multicomponent clusters containing water and isoprene. The most probable topology of the transition state characterizing the evaporation of one water molecule from a water hexamer at 243 K is predicted to be a conformer that contains six hydrogen bonds, with a topology that corresponds to two water molecules stacked on top of a quadrangular (H(2)O)(4) cluster. For the water hexamer in the presence of isoprene, an increase in the cluster size and a 3-fold increase in the evaporation rate are predicted relative to the reaction in which one water molecule evaporates from a water hexamer cluster.

Tapes of water hexamer clusters in the interlayer space of a 2D MOF: Structural, spectroscopic and computational insight of the confined water

The synthesis, crystal structure and characterization of [Er 2(C 4H 4O 4) 3(H 2O) 4]·6H 2O, with particular emphasis on the structural details and the vibrational behavior of the highly organized sub-net of water are reported. X-ray structural analysis reveals that the hybrid framework, which can be classified as belonging to the I 0O 2 type, acts as a host of an infinite tape of six-membered water rings with distorted chair conformation. The water network extends between the hybrid layers helping the close packing and the stabilization of the structure through H-bond interactions, with further development of the supramolecular tridimensional structure. The self-assembly of the hydration water molecules is conditioned by the hybrid host, forcing them to adopt a less stable conformation when compared with hexagonal ice. The vibrational spectra of partially and completely dehydrated samples as well as of partially isotopic diluted ones have been obtained and analyzed. In order to guide the assignment of the vibrational spectra a theoretical calculation was performed at the B3LYP/6-31G ∗∗ level for a model consisting of three water clusters.

Metal–organic framework (MOF) of [Co(II)(1,4-benzenedicarboxylate)2 (pyridine)2(water)2]: Coexistence of water cyclic hexamers through carboxylate oxygens

A metal–organic framework of [Co(II)(1,4-benzenedicarboxylate)2(pyridine)2(water)2] has been synthesized and characterized by IR spectra, TGA and single crystal X-ray diffraction analysis. Discrete cyclic hexameric water clusters through carboxylate oxygens and pyridine molecules are trapped inside a two-dimensional coordination channel. Discrete cyclic hexameric water clusters and pyridine molecules are trapped inside a two-dimensional coordination polymer. Thermal analysis shows that the oxygen atom of water is strongly incorporated as a part of this cluster. ► A Co(II) coordinated polymer, has been synthesized under hydrothermal condition. ► The 3D supramolecular structure is formed by π–π interaction and H O H hydrogen bondings. ► The water cluster plays important role to make 3D supramolecular. ► Thermal analysis shows that the oxygen atom of water is strongly incorporated as a part of this cluster.