Exceptional structural phase transition near room temperature in an organic-inorganic hybrid ferroelectric.

An organic-inorganic hybrid ferroelectric, (C6H5CH2CH2NH3)2[HgI4], undergoes an exceptional structural phase transition near room temperature, triggered by a flip of half the organic cations and an order-disorder transition of the inorganic anions, and may be regarded as a displacive-type ferroelectric. This finding provides a new structural phase transition mechanism in molecule-based ferroelectrics.

A 2D flexible cobalt-MOF: reversible solid-state structural transformation, two-step and gate-opening adsorption behaviours, and selective adsorption of C2H2 over CO2 and CH4.

A new 2D flexible cobalt(II) framework (Co-MOF) exhibits a reversible solid-state structural transformation upon guest molecule removal/uptake. After activation, Co-MOF-α with 1D porous channels transformed into Co-MOF-ß (0D voids) accompanied by a shift in metal and carboxylate coordination modes, the rotation of organic linkers and the contraction of interstitial spaces. Gas adsorption experiments reveal that Co-MOF-ß exhibits a two-step CO2 adsorption isotherm and close-to-open (type F-IV) isotherms for C2H2, C2H4 and C2H6 at 195 K. Moreover, it shows typical type I adsorption isotherms for the above gases and the selective uptake of C2H2 over CH4 and CO2 at room temperature.

Shape memory luminescent cellulose/chitosan hydrogel for high sensitive detection of formaldehyde.

Hybrid hydrogels containing biomacromolecules have been widely used in sensors, fluorescent probes, and other fields due to their high biocompatibility and nontoxicity. In this paper, tough hydrogels with interconnected macro-pores have been fabricated by freeze-induced chemical cross-linking of microfibrillated cellulose (MFC) and organic modified chitosan (CS). In this hydrogel materials, three-dimensional networks were formed by abundant hydrogen bonds and chemical cross-linking. Luminescent lanthanide complexes were covalently bonded to the hydrogel networks through coordination of Eu3+ ions with 2, 3-pyridine dicarboxylic acid modified chitosan. The luminescence of hydrogel materials was further improved by the replacement of coordination water with 2-thiophenyltrifluoroacetone (TTA). The prepared hydrogels showed excellent shape memory properties both under water and in air. The stress of the hybrid hydrogel at 80 % strain can reach 159 kPa, which is much higher than that of the traditional microfibrillated cellulose-based hydrogels. The obtained luminescent hybrid hydrogels exhibited an excellent fluorescence detection effect on formaldehyde. The detection limit for formaldehyde is 45.7 ppb, which is much lower than the WHO standard (80 ppb for indoor air). The novel, facile preparing procedure may extend the potential applications of hybrid lanthanide luminescent hydrogel as fluorescence probes for pollution monitoring, especially for formaldehyde and other organic aldehydes.

Poly[bis-[µ2-4,4'-bis-(imidazol-1-ylmeth-yl)biphenyl-κ2 N:N']di-chlorido-nickel(II)].

In the title compound, [NiCl2(C20H18N4)2] n , the Ni2+ cation is situated on an inversion center and is coordinated by two chloride ions and four imidazole N atoms of four different 4,4'-bis-[(1H-imidazol-1-yl)meth-yl]-1,1'-biphenyl (BIMB), forming a slightly distorted octa-hedral geometry. Each BIMB ligand adopts a linear linker to connect Ni2+ ions, forming a two-dimensional layer with an sql network. In the crystal, neighboring layers repeat in an ABAB stacking mode, and weak inter-molecular C-H⋯Cl hydrogen bonds between alternate layers lead to a three-dimensional, twofold inter-penetrated, supra-molecular framework with a pcu topology net.

Water vapour induced reversible switching between a 1-D coordination polymer and a 0-D aqua complex.

[Zn(3-tba)2], 1, a 1-D coordination polymer synthesised as 1 DMA, 1α, transformed to a nonporous form, 1ß, upon activation. 1ß underwent further transformation to the dimeric complex [Zn(3-tba)2(H2O)2], 2, above 40% RH. The reverse transformations, 2 to 1ß and 1ß to 1α, were accomplished by heating and exposure to DMA, respectively, and were single-crystal-to-single-crystal phase changes. Single crystal X-ray diffraction revealed that the second transformation resulted from Zn-carboxylate bond breakage and concomitant coordination of water molecules. Other solvent molecules did not induce a phase change.

Covalent Grafting Terbium Complex to Alginate Hydrogels and Their Application in Fe3+ and pH Sensing.

Biocompatible luminescent hydrogels containing covalently linked terbium complexes with a macrocyclic ligand are prepared by a facile method. The environmentally friendly preparation procedure is carried out at room temperature using water as a solvent. These new hybrid materials can act as luminescent sensors to detect Fe3+ with relative selectivity and high sensitivity. The hydrogels also show pH sensing with a wide range.

Tuning the Gate-Opening Pressure in a Switching pcu Coordination Network, X-pcu-5-Zn, by Pillar-Ligand Substitution.

Coordination networks that reversibly switch between closed and open phases are of topical interest since their stepped isotherms can offer higher working capacities for gas-storage applications than the related rigid porous coordination networks. To be of practical utility, the pressures at which switching occurs, the gate-opening and gate-closing pressures, must lie between the storage and delivery pressures. Here we study the effect of linker substitution to fine-tune gate-opening and gate-closing pressure. Specifically, three variants of a previously reported pcu-topology MOF, X-pcu-5-Zn, have been prepared: X-pcu-6-Zn, 6=1,2-bis(4-pyridyl)ethane (bpe), X-pcu-7-Zn, 7=1,2-bis(4-pyridyl)acetylene (bpa), and X-pcu-8-Zn, 8=4,4'-azopyridine (apy). Each exhibited switching isotherms but at different gate-opening pressures. The N2 , CO2 , C2 H2 , and C2 H4 adsorption isotherms consistently indicated that the most flexible dipyridyl organic linker, 6, afforded lower gate-opening and gate-closing pressures. This simple design principle enables a rational control of the switching behavior in adsorbent materials.

Coordination Network That Reversibly Switches between Two Nonporous Polymorphs and a High Surface Area Porous Phase.

We report a 2-fold interpenetrated primitive cubic (pcu) network X-pcu-5-Zn, [Zn2(DMTDC)2(dpe)] (H2DMTDC = 3,4-dimethylthieno[2,3- b]thiophene-2,5-dicarboxylic acid, dpe = 1,2-di(4-pyridyl)ethylene), that exhibits reversible switching between an as-synthesized "open" phase, X-pcu-5-Zn-α, and two nonporous or "closed" polymorphs, X-pcu-5-Zn-ß and X-pcu-5-Zn-γ. There are two unusual features of X-pcu-5-Zn. The first relates to its sorption properties, which reveal that the α form exhibits high CO2 uptake (ca. 255 cm3/g at 195 K) via reversible closed-to-open switching (type F-IV isotherm) of the type desirable for gas and vapor storage; there are only three other reports of porous materials that combine these two features. Second, we could only isolate the ß form by activation of the CO2 loaded α form and it persists through multiple CO2 adsorption/desorption cycles. We are unaware of a new polymorph having been isolated in such a manner. That the observed phase changes of X-pcu-5-Zn-α occur in single-crystal-to-single-crystal fashion enabled structural characterization of the three forms; γ is a coordination isomer of α and ß, both of which are based upon "paddlewheel" clusters.

Self-catalysed aerobic oxidization of organic linker in porous crystal for on-demand regulation of sorption behaviours.

Control over the structure and property of synthetic materials is crucial for practical applications. Here we report a facile, green and controllable solid-gas reaction strategy for on-demand modification of porous coordination polymer. Copper(I) and a methylene-bridged bis-triazolate ligand are combined to construct a porous crystal consisting of both enzyme-like O2-activation site and oxidizable organic substrate. Thermogravimetry, single-crystal X-ray diffraction, electron paramagnetic resonance and infrared spectroscopy showed that the methylene groups can be oxidized by O2/air even at room temperature via formation of the highly active Cu(II)-O2(˙-) intermediate, to form carbonyl groups with enhance rigidity and polarity, without destroying the copper(I) triazolate framework. Since the oxidation degree or reaction progress can be easily monitored by the change of sample weight, gas sorption property of the crystal can be continuously and drastically (up to 4 orders of magnitude) tuned to give very high and even invertible selectivity for CO2, CH4 and C2H6.

4,4'-{[1,2-Phenyl-enebis(methyl-ene)]bis-(-oxy)}di-benzoic acid di-methyl-formamide disolvate.

In the title solvate, C22H18O6·2C3H7NO, the complete dicarboxylic acid molecule is generated by a crystallographic twofold axis, which bisects the central benzene ring and one N,N-di-methyl-formamide solvent mol-ecule. The dihedral angle between the central and pendant benzene rings is 54.53 (5)° while that between the pendant rings is 45.44 (5)°. In the crystal, the acid molecules are linked to the solvent molecules via O-H⋯O and weak C-H⋯O hydrogen bonds. Further weak C-H⋯O inter-actions link adjacent acid mol-ecules into a three-dimensional network.

Chiral recognition of a 3D chiral nanoporous metal-organic framework.

Some racemates including alcohol, ketone, flavone, phenol, base, and amide racemates etc. were successfully separated by using a 3D chiral nanoporous metal-organic framework (MOF) as a new chiral stationary phase in HPLC. The experimental results show that the chiral MOF possesses excellent recognition ability for various racemates, and indicate that enantioseparation on the chiral MOF column is practicable.

Strong and dynamic CO2 sorption in a flexible porous framework possessing guest chelating claws.

Using a bis-triazolate ligand and tetrahedral Zn(II) ion, we synthesized a flexible porous coordination polymer functionalized with pairs of uncoordinated triazolate N-donors that can be used as guest chelating sites to give very high CO(2) adsorption enthalpy and CO(2)/N(2) selectivity. The dynamic CO(2) sorption behavior could be monitored well by single-crystal X-ray diffraction.

Single-crystal X-ray diffraction and Raman spectroscopy studies of isobaric N2 adsorption in SOD-type metal-organic zeolites.

The two-step N(2) adsorption behaviour of sodalite-type Zn(II) 2-methylimidazolate and 3-methyl-1,2,4-triazolate has been comprehensively and accurately elucidated.

3-Ethyl-1H-1,2,4-triazole-5(4H)-thione.

The mol-ecule of the title compound, C(4)H(7)N(3)S, exists as the thione tautomer in the solid state. The asymmetric unit consits of one mol-ecule in which all atoms are located on a crystallographic mirror plane. In the crystal, adjacent mol-ecules are linked by N-H⋯N and N-H⋯S hydrogen bonds into chains running along the a axis. π-π stacking inter-actions between the triazole rings [centroid-centroid distance = 3.740 (1) Šand inter-planar distance = 3.376 Å] may further stabilize the structure.

Bis(5-phenyl-1H-1,2,4-triazol-3-yl) disulfide dihydrate.

A crystallographic twofold axis passing through the centre of the disulfide linkage in the title compound, C(16)H(12)N(6)S(2)·2H(2)O, results in one-half of the mol-ecule and one uncoordinated water mol-ecule described in the asymmetric unit. In the mol-ecule, the mean planes of the benzene and triazole rings are close to being coplanar and are separated by a dihedral angle of 2.08 (15)°. The triazole rings are twisted by a dihedral angle of 37.67 (6)° from the disulfide linkage. The crystal packing is stabilized by inter-molecular N-H⋯O and O-H⋯N hydrogen bonds with the water mol-ecules, forming a three-dimensional supra-molecular network.

1,4-Bis(5-methyl-1H-1,2,4-triazol-3-yl)benzene tetra-hydrate.

In the title compound, C(12)H(12)N(6)·4H(2)O, the two triazole rings adopt a cis configuration with a crystallographic twofold axis passing through the central benzene group. The benzene and triazole rings are almost coplanar with a dihedral angle of 5.5 (1)°. In the crystal, water mol-ecules are joined together by OW-H⋯OW hydrogen bonds to form a one-dimensional zigzag chain. These water chains are further connected to the organic mol-ecule, forming a three-dimensional network by inter-molecular OW-H⋯N and N-H⋯OW hydrogen bonds. Moreover, π-π stacking inter-actions between triazole rings [centroid-centroid distances = 3.667 (1)-3.731 (1) Å] are observed. One of the water mol-ecules shows one of the H atoms to be disordered over two positions.

Isomeric zinc(II) triazolate frameworks with 3-connected networks: syntheses, structures, and sorption properties.

Two pairs of supramolecular isomers based on ternary zinc(II)/triazolate/X (triazolate = 3,5-dimethyl-1,2,4-triazolate (Hdmtz), X = HCOO(-), F(-)) metal azolate frameworks, namely, [Zn(dmtz)(HCOO)] x H(2)O (MAF-X3, 1a), [Zn(dmtz)(HCOO)] x (1/6Me(2)NH)(1/4H(2)O) (MAF-X4, 1b), [Zn(dmtz)F] (MAF-X5, 2a), and [Zn(dmtz)F] (MAF-X6, 2b), have been synthesized via variations of the reaction conditions. The 3-connected Zn(dmtz) networks in 1a, 1b, 2a, and 2b can be described as rarely observed 4.8(2), 4.12(2), (8,3)-b, and 8(2).10-a, respectively. Besides the mu(3)-dmtz, tetrahedral and trigonal-bipyramidal/square-pyramidal coordination of the Zn ions are accomplished by monodentate formate and mu-F, respectively. While 1a and 2b are nonporous structures, 1b and 2a exhibits 1D nanotubular hydrophilic (d 3.2 A) and hydrophobic (d 3.6 A) channels, respectively. Thermogravimetric analysis shows that the stabilities of 2a and 2b are much better than those of 1a and 1b, which may be ascribed to different coordination numbers of zinc atoms. Moreover, 1b and 2a with different pore properties show selective sorption behavior.

Pentanuclear and heptanuclear helicates by self-assembly of d10 metal ions and a rigid aromatic bis-bidentate chelator.

The self-assembly of Zn(II) and Cd(II) ions with a bis-bidentate ligand 3,5-bis(benzimidazol-2-yl)pyrazole (H 3L) was studied by Electrospray ionization mass spectrometry, (1)H NMR measurements, and single-crystal X-ray diffraction analyses. Reaction of Zn(ClO 4) 2.6H 2O and Cd(ClO 4) 2.6H 2O with H 3L in DMF gave two pentanuclear complexes [(Zn 5(mu 3-O)(H 2L) 6)(ClO 4) 2.DMF.9.5H 2O ( 1) and [Cd 5(mu 3-O)(H 2L) 6](ClO 4)(OH).4.75DMF.0.25EtOH.10.5H 2O ( 2), in which the trigonal-bipyramidal core structures are bridged by mu 3-oxo and pyrazolate rings of the monodeprotonated H 2L. When Na 3PO 4.12H 2O was used in the reaction system of CdBr 2.4H 2O and H 3L, [Cd 5(mu 3-O)(H 2L) 6]Br 2.4.5DMF.6.5H 2O ( 3) and [Cd 7(mu 6-PO 4)(mu-Br) 3(H 2L) 6](HPO 4).DMF.10H 2O ( 4) were isolated. 3 displays the same core structure as that of 2, whereas 4 exhibits a turbinate, heptanuclear core which is bridged by a mu 6-PO 4, three mu-Br, and three pyrazolate rings. All of the pentanuclear and heptanuclear cores are surrounded by three pairs of bis-bidentate H 2L (-) ligands with offset pi-pi stacking, showing propeller-like molecular structures and triple-stand helicates. Electrospray ionization mass spectrometry studies and (1)H NMR measurements demonstrate that the pentanuclear complexes have different stability in the solution, depending on the metal ions and the counteranions. Furthermore, both 1 and 2 emit blue fluorescence with nanosecond luminescent lifetimes in DMF at room temperature.