Modulating the Electronic Structures of Dual-Atom Catalysts via Coordination Environment Engineering for Boosting CO2 Electroreduction.

Dual-atom catalysts (DACs) have emerged as efficient electrocatalysts for CO2 reduction owing to the synergistic effect between the binary metal sites. However, rationally modulating the electronic structure of DACs to optimize the catalytic performance remains a great challenge. Herein, we report the electronic structure modulation of three Ni2 DACs (namely, Ni2 -N7 , Ni2 -N5 C2 and Ni2 -N3 C4 ) by the regulation of the coordination environments around the dual-atom Ni2 centres. As a result, Ni2 -N3 C4 exhibits significantly improved electrocatalytic activity for CO2 reduction, not only better than the corresponding single-atom Ni catalyst (Ni-N2 C2 ), but also higher than Ni2 -N7 and Ni2 -N5 C2 DACs. Density functional theory (DFT) calculations revealed that the high electrocatalytic activity of Ni2 -N3 C4 for CO2 reduction could be attributed to the electronic structure modulation to the Ni centre and the resulted proper binding energies to COOH* and CO* intermediates.

Incorporation of Chromophores into Metal-Organic Frameworks for Boosting CO2 Conversion.

The exploitation of highly stable and active catalysts for the conversion of CO2 into valuable fuels is desirable but is a great challenge. Herein, we report that the incorporation of chromophores into metal-organic frameworks (MOFs) could afford robust catalysts for efficient CO2 conversion. Specifically, a porous Nd(III) MOF (Nd-TTCA; TTCA3- = triphenylene-2,6,10-tricarboxylate) was constructed by incorporating one-dimensional Nd(CO2)n chains and TTCA3- ligands, which exhibits a very high stability, retaining its framework not only in the air at 300 °C for 2 h but also in boiling aqueous solutions at pH 1-12 for 7 days. More importantly, Nd-TTCA has achieved a 5-fold improvement in photocatalytic activity for reducing CO2 to HCOOH and a 10-fold improvement in catalytic activity for the cycloaddition of CO2 into cyclic carbonate in comparison to those of H3TTCA itself. This work gives a new strategy to design efficient artificial crystalline catalysts for CO2 conversion.

π-π stacking interactions: Non-negligible forces for stabilizing porous supramolecular frameworks.

Revealing the contribution of π-π stacking interactions in supramolecular assembly is important for understanding the intrinsic nature of molecular assembly fundamentally. However, because they are much weaker than covalent bonds, π-π stacking interactions are usually ignored in the construction of porous materials. Obtaining stable porous materials that are only dependent on π-π stacking interactions, despite being very challenging, could address this concern. Here, we present a porous supramolecular framework (π-1) stabilized only by intermolecular π-π stacking interactions. π-1 shows good thermal and chemical stability not only in various organic solvents but also in aqueous solution in a broad pH range. Furthermore, featuring one-dimensional channels with dangling thiolate groups, π-1 exhibits excellent Hg2+ removal performance, with adsorption capacity as high as 786.67 mg g-1 and an adsorption ratio as high as 99.998%. In addition, π-1 also shows high adsorption selectivity to Hg2+ in the presence of a series of interfering ions.

Facile Exfoliation of 3D Pillared Metal-Organic Frameworks (MOFs) to Produce MOF Nanosheets with Functionalized Surfaces.

The production of two-dimensional (2D) ultrathin metal-organic framework (MOF) nanosheets with functionalized surfaces is significant for extending their applications. To date, no protocol has been developed yet to solve this problem. Herein, we report a facile, mild, and efficient method to produce 2D monolayer MOF nanosheets with hydrophobic surfaces from layer-pillared 3D MOFs. This approach is based on the replacement of weaker coordinating pillar ligands with stronger coordinating capping ligands with the assistance of a high concentration gradient of the latter. Utilizing this method, the replacement of the 4,4'-bipyridine (bpy) pillars in two cadmium-based layer-pillared MOFs with alkylpyridine derivatives has been achieved, producing 2D MOF nanosheets with monolayer thickness and double-sided hydrophobic surfaces. The resulting hydrophobic 2D MOF nanosheets exhibit good performance for the separation of oil and water.

A Lanthanum Carboxylate Framework with Exceptional Stability and Highly Selective Adsorption of Gas and Liquid.

The development of porous metal-organic frameworks that can retain structural integrity under harsh physical and chemical conditions is essential from the perspective of their use in adsorption, catalysis, and sensors. Herein, a lanthanum carboxylate framework was found to exhibit exceptional stability, not only robust in boiling aqueous solutions at pH 2-12 and in boiling common organic solvents over 24 h but also stable upon ball milling for 1 h. Furthermore, this framework displayed highly selective separation for CO2 over N2 ( Sads = 940), as well as size-dependent selective adsorption behavior of water and alcohols.

Photochromism, photoluminescence modulation and selective recognition of small molecules of two highly stable dynamic metal-organic frameworks.

Two highly stable dynamic metal-organic frameworks exhibit photochromism, tunable photoluminescence, and selective detection of oxygen, which can be recognised by the naked eye through color changes. Furthermore, they also display selective recognition of benzyl alcohol and halogenated solvents, respectively.

Two cobalt(II) supramolecular isomers based on N,N'-bis(pyridin-3-yl)oxalamide induced by the molecular orientation of lattice DMF molecules.

Supramolecular isomerism for coordination networks refers to the existence of different architectures having the same building blocks and identical stoichiometries. For a given building block, different arrangements can lead to the formation of a series of supramolecular isomers. Two one-dimensional Co(II) coordination polymers based on N,N'-bis(pyridin-3-yl)oxalamide (BPO), both catena-poly[[[dichloridocobalt(II)]-bis[µ-N,N'-bis(pyridin-3-yl)oxalamide-κ(2)N:N']] dimethylformamide disolvate], {[CoCl2(C12H10N4O2)2]·2C3H7NO}n, have been assembled by the solvothermal method. Single-crystal X-ray diffraction analyses reveal that the two compounds are supramolecular isomers, the isomerism being induced by the orientation of the dimethylformamide (DMF) molecules in the crystal lattice.

Uncovering the Role of Metal Catalysis in Tetrazole Formation by an In Situ Cycloaddition Reaction: An Experimental Approach.

Using an experimental approach, the role of metal catalysis has been investigated in the in situ cycloaddition reaction of nitrile with azide to form tetrazoles. It has been shown that metal catalysis serves to activate the cyano group in the nitrile reagent by a coordinative interaction.

A two-dimensional copper(II) coordination polymer based on 2-propyl-1H-imidazole-4,5-dicarboxylic acid.

Single-crystal X-ray diffraction analysis of poly[bis(µ2-5-carboxy-2-propyl-1H-imidazole-4-carboxylato-κ(3)N(3),O(4):O(5))copper(II)], [Cu(C8H9N2O4)2)]n, indicates that one carboxylic acid group of the 2-propyl-1H-imidazole-4,5-dicarboxylic acid (H3PDI) ligand is deprotonated. The resulting H2PDI(-) anion, acting as a bridge, connects the Cu(II) cations to form a two-dimensional (4,4)-connected layer. Adjacent layers are further linked through interlayer hydrogen-bond interactions, resulting in a three-dimensional supramolecular structure.

A rare (3,4,5)-connected metal-organic framework featuring an unprecedented 1D + 2D → 3D self-interpenetrated array and an O-atom lined pore surface: structure and controlled drug release.

A rare (3,4,5)-connected self-interpenetrated metal-organic framework with an O-atom lined pore surface has been constructed from Zn(II) and H4L (H4L = 5,5'-(1,3,6,8-tetraoxobenzo[lmn][3,8]phenanthroline-2,7(1H,3H,6H,8H)diyl)-diisophthalic acid), which features an unprecedented 1D + 2D → 3D self-interpenetrated array and shows good controlled drug release properties.

A microporous hydrogen-bonded organic framework: exceptional stability and highly selective adsorption of gas and liquid.

An extremely stable hydrogen-bonded organic framework, HOF-8, was fabricated. HOF-8 is not only thermally stable but also stable in water and common organic solvents. More interestingly, desolvated HOF-8 exhibits high CO2 adsorption as well as highly selective CO2 and C6H6 adsorption at ambient temperature.

Tetra-aqua-bis-(tetra-zolido-κN)magnesium.

In the crystal structure of the title compound, [Mg(CHN(4))(2)(H(2)O)(4)], the Mg(II) atom is six-coordinated by two N atoms from two tetra-zolide anions and four O atoms from four coordinated water mol-ecules in a slightly distorted octa-hedral geometry. The Mg atom is located on centres of inversion whereas the tetra-zolide anion and the water mol-ecules occupy general positions. The crystal packing is stabilized by intermolecular O-H⋯N hydrogen bonding between the tetra-zolide anions and the coordinated water mol-ecules.

Bis(µ-5-carboxyl-atotetra-zolido)bis-[aqua-(2,2'-bipyrid-yl)cadmium(II)].

In the title dinuclear Cd(II) complex, [Cd(2)(C(2)N(4)O(2))(2)(C(10)H(8)N(2))(2)(H(2)O)(2)], each Cd atom is in a slightly distorted octa-hedral coordination by two N atoms and one O atom of two 1H-tetra-zole-5-carboxyl-ate (TZC) ligands, two N atoms of a 2,2'-bipyridyl ligand and one water O atom. The TZC ligand acts in a tridentate N,O-chelating N-bridging mode to two symmetry-equivalent Cd(II) atoms. The complex reveals mol-ecular C(i) symmetry. Extensive O-H⋯O hydrogen bonding plays an important role in the crystal packing.

Aqua-(hippurato)bis-(1,10-phenanthroline)cobalt(II) nitrate monohydrate.

In the title compound, [Co(C(9)H(8)NO(3))(C(12)H(8)N(2))(2)(H(2)O)]NO(3)·H(2)O, the Co(II) atom is six-coordinated by a carboxylate O atom of the hippurate (Hc) anion, a water O atom and four N atoms from two 1,10-phenanthroline ligands in a distorted octa-hedral geometry. The uncoordinated O atom of the hippuric acid anion is involved in an intra-molecular hydrogen bond to the coordinated water mol-ecule. The crystal packing is stabilized by inter-molecular O-H⋯O hydrogen bonds involving the Hc anions, the coordinated water mol-ecule, the nitrate anion and the uncoordinated water mol-ecule.

Tetra-µ-benzoato-κO:O'-bis-[(benzoic acid-κO)nickel(II)].

The title compound, [Ni(2)(C(7)H(5)O(2))(4)(C(7)H(6)O(2))(2)], is composed of two Ni(II) ions, four bridging benzoate anions and two η(1)-benzoic acid mol-ecules. The [Ni(2)(PhCOO)(4)] unit adopts a typical paddle-wheel conformation. The center between the two Ni(II) atoms represents a crystallographic center of inversion. In addition, each Ni(II) ion also coordinates to one O atom from a benzoic acid mol-ecule. The crystal packing is realised by inter-molecular hydrogen-bonding inter-actions and π-π stacking inter-actions, with a centroid-centroid distance of 3.921 (1) Å.

Naphthalene-1,4,5,8-tetra-carboxylic acid 1,8-anhydride-4,4'-bipyridine (1/1).

The title compound, C(14)H(6)O(7)·C(10)H(8)N(2), has been hydro-thermally synthesized. Structural ananlysis indicates that the crystals are produced by cocrystallization of naphthalene-1,4,5,8-tetra-carboxylic acid 1,8-anhydride and 4,4'-bipyridine (bpy) mol-ecules. The crystal packing is stabilized by inter-molecular O-H⋯N and C-H⋯O hydrogen bonds and π-π stacking inter-actions [centroid-centroid distances = 3.5846 (9) Å].

1-(2',4'-Difluoro-biphenyl-4-yl)ethanone.

In the crystal structure of the title compound, C(14)H(10)F(2)O, the dihedral angles between the benzene rings in the two crystallographically independent mol-ecules are 46.9 (2) and 47.6 (2)°. The mol-ecules are linked into dimers by C-H⋯F inter-actions and these dimers are further stacked into columns along the b axis by π-π inter-actions between the benzene rings [centroid-centroid distance = 3.8221 Å; the dihedral angle between the planes of these rings is 4.87 (2)°]. In addition, C-F⋯π interactions also contribute to the crystal packing (C⋯centroid distance = 3.5919 Å).

Diaqua-bis(8-chloro-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetra-hydro-7H-purinato-κN)copper(II) dihydrate.

The title mononuclear copper(II) complex, [Cu(C(7)H(6)ClN(4)O(2))(2)(H(2)O)(2)]·2H(2)O, based on 8-chloro-theophylline (HCt), has the Cu atom at a center of symmetry in a slightly distorted trans square-planar geometry coordinated by two N atoms of two deprotonated HCt ligands and two O atoms of water mol-ecules. The crystal packing is stabilized by hydrogen bonds involving deprotonated HCt ligands, coordinated water mol-ecules and uncoordinated solvent water mol-ecules.

Bis(2-amino-pyridine-κN)bis-(benzoato-κO)cobalt(II).

In the title compound, [Co(C(7)H(5)O(2))(2)(C(5)H(6)N(2))(2)], the Co(II) atom is hexa-coordinated by four O atoms from two benzoate anions, and two N atoms from two 2-amino-pyridine mol-ecules, resulting in a distorted octa-hedral geometry. Both benzoate anions act as bidentate ligands and both 2-amino-pyridine mol-ecules are coordinated to the metal through their pyridyl N atoms. The crystal packing is stabilized by inter-molecular N-H⋯O hydrogen bonds, C-H⋯π, and π-π stacking inter-actions involving benzoate anions and 2-amino-pyridine mol-ecules.