Monolayer Nanosheets Exfoliated from Cage-Based Cationic Metal-Organic Frameworks.

The rational design and preparation of monolayer metal-organic framework (MOF) nanosheets remain great challenges. Recently, we found that monolayer MOF nanosheets can be facially exfoliated on a large scale from pristine two-dimensional (2D) MOFs with substantially reduced interlaminar interaction. By employing cage-like bicyclocalix[2]arene[2]triazine tri-imidazole as the building block, a family of cationic two-dimensional metal-organic frameworks (2D MOFs) with steric layer were designed and prepared. The single crystal structures have clearly identified that only very weak and sparse distributed C-H···π interaction exists between adjacent layers.On the basis of density functional theory calculation, the interlayer interaction of these cage-based cationic 2D MOFs was estimated to be 1/46th of that of graphite. Due to the extremely weak interaction, these cationic 2D MOFs tend to degenerate into an "amorphous" state after being soaked in other solvents; they can be readily exfoliated into 1.1 nm thick monolayer nanosheets with a high degree of thickness homogeneity, large lateral size, and significantly enlarged surface area. This work has identified that a cage-like molecule is the ideal building block for 2D cationic MOFs and ultrathin nanosheets; It was futher confirmed that weakening the interlaminar interaction is an effective strategy for facilely producing monolayer nanosheets.

Cd-MOF: specific adsorption selectivity for linear alkyne (propyne, 2-butyne and phenylacetylene) molecules.

The selective adsorption of APPT-Cd-MOF 1 for propyne, 2-butyne and phenylacetylene was confirmed by single-crystal analysis. In addition, the selective adsorption performance of Cd-MOF for C3H4/C3H6/C3H8 was investigated. The matching of the functionality and size/shape between porous materials and guest molecules clarified the specific recognition of 1 for linear alkyne molecules.

Pd(0)@UiO-68-AP: chelation-directed bifunctional heterogeneous catalyst for stepwise organic transformations.

A bifunctional heterogeneous catalyst Pd(0)@UiO-68-AP based on a chelation-directed post-synthetic approach is reported. It exhibits typical heterogeneous catalytic behaviour and can promote benzyl alcohol oxidiation-Knoevenagel condensation in a stepwise way.

Cd(ii)-MOF-IM: post-synthesis functionalization of a Cd(ii)-MOF as a triphase transfer catalyst.

A robust and porous Cd(ii)-MOF based on a bent imidazole-bridged ligand was synthesized and post-synthetically functionalized with linear alkyl chains to afford imidazolium salt (IM)-type triphase transfer catalysts for organic transformations. The imidazolium salt decorated Cd(ii)-MOF-IM exhibits typical solid phase transfer catalytic behavior for the azidation and thiolation of bromoalkane between aqueous/organic phases. Moreover, they can be easily recovered and reused under the PTC conditions. Cd(ii)-MOF-IM herein created a versatile family of solid phase transfer catalysts for promoting a broad scope of reactions carried out in a biphasic mixture of two immiscible solvents.

An in situ self-assembled Cu4I4-MOF-based mixed matrix membrane: a highly sensitive and selective naked-eye sensor for gaseous HCl.

The Cu4I4-MOF-based mixed matrix membranes (MMMs) can be readily prepared by one-step in situ self-assembly of a tri-armed oxadiazole-bridged ligand and CuI in polymer binder solution under ambient conditions. The visual and luminescent HCl(g) sensing detecting limits of the resulting Cu4I4-MOF-based MMMs are 3.2 and 1.6 ppb, respectively, and the response time is less than 1 min.

Copper(I) Metal-Organic Framework: Visual Sensor for Detecting Small Polar Aliphatic Volatile Organic Compounds.

A porous Cu(I)-MOF [H2O⊂Cu2(L)2I2; L = 1-benzimidazolyl-3,5-bis(4-pyridyl)benzene], which can be a visual and luminescent sensor for detecting small polar aliphatic volatile organic compounds (VOCs), such as alcohols, ketones, and halocarbons, is reported. The naked-eye and luminescent detection limitations for these VOCs are 5 and 1 ppm, respectively.

Co(II)-MOF: A Highly Efficient Organic Oxidation Catalyst with Open Metal Sites.

A porous Co(II)-MOF (1) was synthesized by the combination of a bent imidazole-bridged ligand and p-phthalic acid (PTA) with Co(OAc)2 under solvothermal conditions. This Co(II)-MOF (1) is able to undergo a reversible MeOH substitution reaction on the Co(II) center via a single-crystal-to-single-crystal process. The desolvated Co(II)-MOF (2) with the open Co(II) sites is very stable (up to 350 °C). Furthermore, 2 is a highly active heterogeneous catalyst for various organic substrates oxidation in the presence of tert-butyl hydroperoxide (TBHP) under milder conditions. The importance of open Co(II) sites in 2 for the organic substrates oxidation is directly evidenced by the single-crystal X-ray diffraction.

Nanoscale UiO-MOF-based luminescent sensors for highly selective detection of cysteine and glutathione and their application in bioimaging.

We report a practical approach, the first of its kind, to construct nanoscale UiO-type metal-organic framework (Mi-UiO-66 and Mi-UiO-67) fluorescent probes for the detection of Cys and GSH. They showed high sensitivity (10(-11) M) and selectivity for Cys and GSH, and their fluorescence imaging of Cys and GSH in living cells was well demonstrated.

Fabrication of Cd(II)-MOF-based ternary photocatalytic composite materials for H2 production via a gel-to-crystal approach.

Cd(II)-MOF-based ternary composite materials of CdS@Cd(II)-MOF@TiO2 were prepared by a unique TiO2 induced gel-to-crystal approach. CdS@Cd(II)-MOF@TiO2 was demonstrated to be a highly active photocatalyst for hydrogen production under visible light based on water photolysis.

p-Benzoquinone adsorption-separation, sensing and its photoinduced transformation within a robust Cd(II)-MOF in a SC-SC fashion.

p-Benzoquinone (Q) adsorption­separation, sensing and its photoinduced transformation within a robust Cd(II)-MOF (1) is reported. All the adsorption, sensing and photochemical reactions are directly performed on the single-crystals of 1.

A Ni(II)-MOF: reversible guest adsorption and heterogeneous catalytic properties for silylcyanation of aromatic aldehydes.

A porous Ni(II)-MOF, which was constructed from a new bent fluorene-bridged ligand and NiCl2 under solvothermal conditions, can reversibly uptake organic solvent molecules and iodine species in a single-crystal-to-single-crystal (SC-SC) fashion. Furthermore, the obtained I2⊂Ni(II)-MOF can be a highly active heterogeneous catalyst to promote solvent-free silylcyanation of aromatic aldehydes under mild conditions.

Visual synchronous exchange of metal nodes and counteranions constituting a cobalt(II) coordination polymer.

A solid-state simultaneous exchange of metal nodes and counteranions based on a cobalt(2+) coordination polymer is reported for the first time. The ion-exchange process is visual, and the structural integrity of the cobalt(2+) coordination polymer is maintained during the ion-exchange process.

Cd(II)-MOF: adsorption, separation, and guest-dependent luminescence for monohalobenzenes.

A series of isostructural 2-fold interpenetrating 2D Cd(II)-MOFs, namely G⊂CdL2(OTs)2 (G = THF (1), PhF (2), PhCl (3), PhBr (4), PhI (5), L = 1,2-bis[(3-(pyridin-4-yl)phenoxy]ethane, and OTs(-) = p-toluenesulfonate anion), have been successfully synthesized from the flexible ethylene glycol ether-bridging ligand L and Cd(OTs)2 in solution. The CdL2(OTs)2 framework contains squarelike nonpolar channels, and the encapsulated guest molecules can be removed by heating (150 °C) to generate a guest-free host framework which is able to reversibly adsorb monohalobenzenes PhX (X = F, Cl, Br, I) in the liquid phase under ambient conditions without loss of framework integrity. Furthermore, it can effectively separate these monohalobenzenes and exhibits a clear affinity for monohalobenzenes according to the following order: PhI > PhBr > PhCl > PhF. In addition, PhX⊂CdL2(OTs)2 exhibits guest-dependent luminescence properties.

A nanoporous Ag(I)-MOF showing unique selective adsorption of benzene among its organic analogues.

A stable porous Ag(I)-MOF with new topology is constructed from AgSbF6 and 3,6-bis[2-(4-oxide-quinoxaline)-yl]-4,5-diaza-3,5-octadiene (L). This compound can be a highly selective porous MOF material to effectively separate benzene from its six-membered cyclic organic analogues such as cyclohexane, cyclohexene and o-, m-, p-xylene under ambient conditions in both vapor and liquid phases.

Oxygen and methanol mediated irreversible coordination polymer structural transformation from a 3D Cu(I)-framework to a 1D Cu(II)-chain.

An interesting irreversible structural transformation visible to the naked-eye occurs when a 3D Cu(I)-polymeric complex Cu2L(NO3)2(DMF)0.4 (1) is suspended in CH3OH in air to produce a 1D-Cu(II) polymeric complex Cu(µ-OCH3)(L)(NO3) (2) (L = 1,2-bis[4-(pyrimidin-4-yl)phenoxy]ethane). The transformation mechanism from 1 to 2 was also investigated.

Three one-dimensional coordination polymers based on 1,1'-bis(pyridin-4-ylmethyl)-2,2'-bi-1H-benzimidazole and HgX2 (X = Cl, Br and I).

A new 2,2'-bi-1H-benzimidazole bridging organic ligand, namely 1,1'-bis(pyridin-4-ylmethyl)-2,2'-bi-1H-benzimidazole, C26H20N6, L or (I), has been synthesized and used to create three new one-dimensional coordination polymers, viz. catena-poly[[dichloridomercury(II)]-µ-1,1'-bis(pyridin-4-ylmethyl)-2,2'-bi-1H-benzimidazole], [HgCl2(C26H20N6)]n, (II), and the bromido, [HgBr2(C26H20N6)]n, (III), and iodido, [HgI2(C26H20N6)]n, (IV), analogues. Free ligand L crystallizes with two symmetry-independent half-molecules in the asymmetric unit and each L molecule resides on a crytallographic inversion centre. In structures (II)-(IV), the L ligand is also positioned on a crystallographic inversion centre, whereas the Hg centre resides on a crystallographic twofold axis. Compound (I) adopts an anti conformation in the solid state and forms a two-dimensional network in the crystallographic bc plane via π-π and C-H...π interactions. The three Hg(II) coordination complexes, (II)-(IV), have one-dimensional zigzag chains composed of L and HgX2 (X = Cl, Br and I), and the Hg(II) centres are in a distorted tetrahedral [HgX2N2] coordination geometry. Complexes (III) and (IV) are isomorphous, whereas complex (II) displays an interesting conformational difference from the others, i.e. a twist in the flexible bridging ligand.

'0'- and '8'-shaped complexes generated from a nano-sized oxadiazole-containing organic ligand with CdI2 and CuI.

A new nano-sized rigid double-armed oxadiazole-bridged organic ligand, 2,5-bis{2-methyl-5-[2-(pyridin-3-yl)ethenyl]phenyl}-1,3,4-oxadiazole, C30H20N4O, L or (I), which adopts a cis conformation in the solid state, has been synthesized and used to create the two novel metallocycle complexes (2,5-bis{2-methyl-5-[2-(pyridin-3-yl-κN)ethenyl]phenyl}-1,3,4-oxadiazole)diiodidocadmium(II) dichloromethane monosolvate, [CdI2(C30H20N4O)]·CH2Cl2, (II), and di-µ-iodido-bis[(2,5-bis{2-methyl-5-[2-(pyridin-3-yl-κN)ethenyl]phenyl}-1,3,4-oxadiazole)copper(I)], [Cu2I2(C30H20N4O)2], (III). Molecules of complex (II) adopts a 20-membered `0'-shaped metallocycle structure with crystallographic mirror symmetry. The discrete units are linked into one-dimensional chains through intermolecular π-π and C-H...π interactions. In (III), the two I atoms and two Cu(I) atoms form a {Cu2(µ-I)2} cluster. One {Cu2(µ-I)2} cluster and two L ligands form two 20-membered monometallic rings in a head-to-head fashion, leading to a discrete centrosymmetric `8'-shaped metallocyclic complex. These metallocycles stack together via two kinds of intermolecular π-π interactions to generate a two-dimensional network in the ac plane. The luminescence properties of (I)-(III) were investigated in the solid state at room temperature and displayed an obvious red shift.

Cu(I)-MOF: naked-eye colorimetric sensor for humidity and formaldehyde in single-crystal-to-single-crystal fashion.

A porous Cu(I)-MOF was constructed from CuI and 1-benzimidazolyl-3,5-bis(4-pyridyl)benzene. This Cu(I)-MOF can be a highly sensitive naked-eye colorimetric sensor to successively detect water and formaldehyde species in a single-crystal-to-single-crystal fashion. Solid-state guest-responsive luminescence is also used to monitor the sensing process.

The coordination chemistry of two symmetric fluorene-based organic ligands with cuprous chloride.

Two novel symmetric fluorene-based ligands, namely, 2,7-bis(1H-imidazol-1-yl)-9,9-dimethyl-9H-fluorene [L1 or (I), C21H18N4] and 2,7-bis(1H-imidazol-1-yl)-9,9-dipropyl-9H-fluorene (L2), have been used to construct the coordination polymers catena-poly[[dichloridodicopper(I)(Cu-Cu)]-µ-2,7-bis(1H-imidazol-1-yl)-9,9-dimethyl-9H-fluorene], [Cu2Cl2(C21H18N4)]n, (II), and catena-poly[[tetra-µ2-chlorido-tetracopper(I)]-bis[µ-2,7-bis(1H-imidazol-1-yl)-9,9-dipropyl-9H-fluorene]], [Cu4Cl4(C25H26N4)2]n, (III). There are three types of C-H···N hydrogen bonds in (I), resulting a two-dimensional network in the ab plane, including a chiral helical chain along the b axis. Compounds (II) and (III) are related one-dimensional polymers. In both, Cu(I) atoms connect the symmetric ligands (L1 or L2) into a one-dimensional chain. In (II), the {[Cu(I)Cl2](-)} unit, acting as a co-anion, adheres to the one-dimensional chain through a weak Cu···Cu interaction. However, in (III), the {[Cu(I)2Cl4](2-)} unit links two different chains into a one-dimensional rope-ladder-type chain. In addition, there are C-H···Cl hydrogen bonds and π-π interactions in the extended structures of (II) and (III), the difference is that the chains in (II) are linked into a two-dimensional network while the chains in (III) are stacked into a three-dimensional framework.

A well-resolved cyclic water tetramer in a dinuclear CuII coordination complex based on 1,2-bis(pyridin-3-yloxy)ethane and capped by pyridine-2,6-dicarboxylic acid.

µ-1,2-Bis(pyridin-3-yloxy)ethane-κ(2)N:N'-bis[aqua(pyridine-2,6-dicarboxylato-κ(3)O(2),N,O(6))copper(II)] tetrahydrate, [Cu2(C7H3NO4)2(C12H12N2O2)(H2O)2]·4H2O, (I), is a C-shaped molecule based on 1,2-bis(pyridin-3-yloxy)ethane (L) and Cu(II) in the presence of pyridine-2,6-dicarboxylic acid (H2pydc). The two five-coordinated Cu(II) centres are chelated by terminal pydc(2-) ligands and bridged by an L spacer. The molecules are arranged in a two-dimensional sheet via 15 O-H...O hydrogen bonds, and C-H...O interactions further bridge neighbouring sheets into a three-dimensional supermolecular architecture. The structure includes a well-resolved cyclic water tetramer, which acts as a subunit to form a larger aggregate. A thermogravimetric analysis of complex (I) was also carried out.