Poly[diaqua­di-μ 4-citrato-trizinc(II)]

The title compound, [Zn3(C6H5O7)2(H2O)2]n, is a polymer in which the repeating unit contains three zinc atoms, two hepta-dentate Hcit ligands (Hcit = citric acid trianion) and two coordinated water mol­ecules, only half of which are independent due to one of the metal atoms lying on a centre of symmetry. The two independent cations both exhibit an octa­hedral geometry, but the way in which they are coordinate are different; while the Zn atom in a general position is bound to three Hcit ligands and one water mol­ecule, the one at the centre of symmetry is coordinated by six O atoms from two symmetry-related Hcit ligands through the (protonated) hydroxyl and carboxyl­ate groups. The three carboxyl­ate groups coordinate to the Zn centres in three different ways, viz. chelating, bridging and a mixture of both, in an unusual coordination mode for citrate. The result is a two-dimensional structure parallel to (010), built up by a square-grid motif. Intermolecular O—H⋯O hydrogen bonds are present in the crystal structur

catena-Poly[[[bis­(thio­cyanato-κN)zinc(II)]-μ-1,2-bis­{[2-(2-pyrid­yl)-1H-imidazol-1-yl]meth­yl}benzene] 0.28-hydrate]

The title one-dimensional coordination polymer, {[Zn(NCS)2(C24H20N6)2]·0.28H2O}n, was obtained by the reaction of Zn(OAc)2·2H2O, KSCN and 1,2-bis­{[2-(2-pyrid­yl)-1H-imid­azol-1-yl]meth­yl}benzene (hereafter L). The ZnII ion shows a distorted octa­hedral coordination geometry and is coordin­ated by two N atoms from two SCN− anions and four N atoms from two organic ligands. The L ligands act as bridging bis-chelating ligands with cis coordination modes at the ZnII ion. One-dimensional coordination polymers are arranged into layers by π–π stacking inter­actions between the imidazole rings of adjacent chains, with an inter­planar distance of 3.46 (1) Å and centroid–centroid distances of 3.8775 (16) Å. One of the thio­cyanate ligands is disordered over two positions with an occupancy factor of 0.564 (3) for the major component. The partially occupied water mol­ecule forms an O—H⋯S hydrogen bond with the disordered thio­cyanate group

Poly[bis­(N,N-dimethyl­formamide)tris­(μ4-trans-stilbene-4,4′-dicarboxyl­ato)­tricadmium(II)]: a two-dimensional network with an unusual 36 topology

In the title compound, [Cd3(C16H10O4)3(C3H7NO)2]n or [Cd3(SDA)3(DMF)2]n (H2SDA is trans-stilbene-4,4′-dicarboxylic acid and DMF is dimethyl­formamide), the linear dicarboxylate ligand forms a two-dimensionally layered metal–organic network with the relatively uncommon 36 topology. The structure reveals trinuclear secondary building units and has an octa­hedral geometry at a central metal ion (occupying a symmetry site) and tetra­hedral geometries at two surrounding symmetrically equivalent metal ions lying on a threefold axis. The six-connected planar trinuclear CdII centers, Cd3(O2CR)6, play a role as potential nodes in generation of the relatively uncommon 36 topology. The coordinated DMF unit is disordered around the threefold axis

Poly[diaqua­bis(μ2-azido-κ2 N 1:N 1)bis­(μ3-1-oxoisonicotinato-κ3 O:O′:O′′)dicadmium(II)]

In the title compound, [Cd2(C6H4NO3)2(N3)2(H2O)2]n, one CdII atom is located on an inversion center and is coordinated by four O atoms from four bridging 1-oxoisonicotinate ligands and two N atoms of two bridging azide ligands in a slightly distorted octa­hedral geometry. The other CdII atom, also lying on an inversion center, is coordinated by four O atoms from two bridging 1-oxoisonicotinate ligands and two water mol­ecules and two N atoms of two bridging azide ligands in a slightly distorted octa­hedral geometry. The Cd atoms are connected via the 1-oxoisonicotinate and azide ligands into a two-dimensional coordination network. The crystal structure involves O—H⋯N and O—H⋯O hydrogen bonds

Methyl 4-(trimethyl­silylethyn­yl)benzoate

The title compound, C13H16O2Si, was synthesized as a precursor for ethynylarene derivatives and crystallized from hexane. In the crystal structure, mol­ecules are linked by weak C—H⋯O hydrogen bonds to form chains that pack in layers in a herringbone fashion

Coordination polymers undergoing spin crossover and reversible ligand exchange in the solid

Here we report the synthesis and characterisation of a polymer made up of a system of parallel 2-D grids of Fe(II) ions linked by [Au(CN)2]– bridges and its transformation into a new system of three interpenetrated 3-D coordination open frameworks with the NbO topology. Reversibility of this crystal-to-crystal transformation is evidenced by X-ray crystallographic data and from their spin crossover properties.Real Cabezos, Jose Antonio, [email protected]

Understanding hysteresis in carbon dioxide sorption in porous metal-organic frameworks

Two new isostructural microporous coordination frameworks [Mn3(Hpdc)2­(pdc)2] (1) and [Mg3(Hpdc)2­(pdc)2] (2) (pdc2– = pyridine-2,4-dicarboxylate) showing primitive cubic (pcu) topology have been prepared and characterized. The pore aperture of the channels is too narrow for the efficient adsorption of N2; however, both compounds demonstrate substantially higher uptake of CO2 (119.9 mL·g–1 for 1 and 102.5 mL·g–1 for 2 at 195 K, 1 bar). Despite of their structural similarities, 2 shows a typical reversible type I isotherm for adsorption/desorption of CO2, while 1 features a two-step adsorption process with a very broad hysteresis between the adsorption and desorption curves. This behavior can be explained by a combination of density functional theory calculations, sorption, and X-ray diffraction analysis and gives insights into the further development of new sorbents showing adsorption/desorption hysteresis

Hydrogen storage in metal-organic and covalent-organic frameworks by spillover

Covalent-organic framework COF-1 and metal-organic frameworks HKUST-1 and MIL-101 were synthesized and studied for hydrogen storage at 77 and 298 K. Although MIL-101 had the largest surface area and pore volume among the three materials, HKUST-1 had the highest uptake (2.28 wt %) at 77 K. However, the H 2 storage capacity at 298 K and high pressure correlated with the surface area and pore volume. The H 2 storage in the COF and MOF materials assisted by hydrogen spillover, measured at 298 K up to a pressure of 10 MPa, have been examined for correlations with their structural and surface features for the first time. By using our simple technique to build carbon bridges, the hydrogen uptakes at 298 K were enhanced significantly by a factor of 2.6–3.2. The net uptake by spillover was correlated to the heat of adsorption through the Langmuir constant. Results on water vapor adsorption at 298 K indicated that COF-1 was unstable in moist air, while HKUST-1 and MIL-101 were stable. The results suggested that MIL-101 could be a promising material for hydrogen storage because of its high heat of adsorption for spiltover hydrogen, large surface area and pore volume, and stability upon H 2 O adsorption. © 2007 American Institute of Chemical Engineers AIChE J, 2008Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57505/1/11362_ftp.pd

Halochromic coordination polymers based on a triarylmethane dye for reversible detection of acids

Chromeazurol B (Na2HL) is a pH-sensitive (halochromic) dye based on a hydroxytriarylmethane core and two carboxylate functional groups, which makes it suitable for the synthesis of coordination polymers. Two new coordination polymers [NaZn4(H2O)3(L)3]·3THF·3H2O (1) and [Zn3(H2O)3(μ2- OH2)(μ3-OH)(HL)2(H2L)]·2THF·3H2O (2) incorporating Chromeazurol B linkers have been prepared and characterised. The structure of 1 comprises pentanuclear heterometallic {Zn4Na} nodes linked by six L3– anions to give a layered structure with a honeycomb topology. 2 crystallizes as a double-chain ribbon (ladder) structure with two types of metal node: a mononuclear Zn(II) cation and tetranuclear {Zn(II)}4 cluster. Chromeazurol B anions link each tetranuclear cluster to four individual Zn(II) cations and each Zn(II) cation with four tetranuclear clusters. Both compounds show pH-sensitivity in water solution which can be observed visually, giving the first example of a halochromic coordination polymer. The halochromic properties of 1 towards HCl vapors were systematically investigated. As-synthesized violet-grey 1 reversibly changes color from orange to pink in the presence of vapors of 2M and 7M HCl, respectively. The coordination of the Chromeazurol B anion at each color stage was examined by diffuse reflectance spectroscopy and FT-IR measurements. The remarkable stability of 1 to acid and the observed reversible and reproducible color changes provide a new design for multifunctional sensor materials

Enhancement of CO2 Uptake and Selectivity in a Metal-Organic Framework by the Incorporation of Thiophene Functionality

The complex [Zn2(tdc)2dabco] (H2tdc = thiophene-2,5-dicarboxylic acid; dabco = 1,4-diazabicyclooctane) shows a remarkable increase in carbon dioxide (CO2) uptake and CO2/dinitrogen (N2) selectivity compared to the nonthiophene analogue [Zn2(bdc)2dabco] (H2bdc = benzene-1,4-dicarboxylic acid; terephthalic acid). CO2 adsorption at 1 bar for [Zn2(tdc)2dabco] is 67.4 cm3·g–1 (13.2 wt %) at 298 K and 153 cm3·g–1 (30.0 wt %) at 273 K. For [Zn2(bdc)2dabco], the equivalent values are 46 cm3·g–1 (9.0 wt %) and 122 cm3·g–1 (23.9 wt %), respectively. The isosteric heat of adsorption for CO2 in [Zn2(tdc)2dabco] at zero coverage is low (23.65 kJ·mol–1), ensuring facile regeneration of the porous material. Enhancement by the thiophene group on the separation of CO2/N2 gas mixtures has been confirmed by both ideal adsorbate solution theory calculations and dynamic breakthrough experiments. The preferred binding sites of adsorbed CO2 in [Zn2(tdc)2dabco] have been unambiguously determined by in situ single-crystal diffraction studies on CO2-loaded [Zn2(tdc)2dabco], coupled with quantum-chemical calculations. These studies unveil the role of the thiophene moieties in the specific CO2 binding via an induced dipole interaction between CO2 and the sulfur center, confirming that an enhanced CO2 capacity in [Zn2(tdc)2dabco] is achieved without the presence of open metal sites. The experimental data and theoretical insight suggest a viable strategy for improvement of the adsorption properties of already known materials through the incorporation of sulfur-based heterocycles within their porous structures