He-Gen Zheng

Solvatochromic Behavior of a Nanotubular Metal−Organic Framework for Sensing Small Molecules

A nanotubular metal-organic framework (MOF), {[(WS(4)Cu(4))I(2)(dptz)(3)]·DMF}(n) (dptz = 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine, DMF = N,N-dimethylformamide) for sensing small solvent molecules is presented. When accommodating different solvent molecules as guests, the resulting inclusion compounds exhibit different colors depending on the solvent guests, and more interestingly, the band gaps of these solvent-included complexes are in linear correlation with the polarity of the guest solvents. The solvent molecules can be sensed by the changes of UV-vis spectra of the corresponding inclusion compounds, showing a new way of signal transduction as a new kind of sensor. The sensing by such a MOF occurs within the channel-containing material rather than on the external surface.

A microporous metal–organic framework with FeS2 topology based on [Zn6(μ6-O)] cluster for reversible sensing of small molecules

The first luminescent metal-organic framework (MOF) with [Zn(6)(μ(6)-O)] cluster has been synthesized and realized for reversible sensing of small molecules.

Syntheses, structures, photoluminescence and magnetic properties of five compounds with 1,3,5-benzenetricarboxylate acid and imidazole ligands

Five new coordination compounds, namely [Zn(Hbtc)(1,3-bix)(H2O)]n (1), {Zn2(µ-O)(btc)(timp)]·3(H2O)}n (2), {[Zn3(4,4′-bibp)2(btc)2(H2O)2]·4(H2O)}n (3), {[Ni3(4,4′-bibp)2(btc)2(H2O)2]·3(H2O)}n (4), {[Cu3(4,4′-bibp)2(btc)2(H2O)]·2(H2O)}n (5), where 1,3 - bix = 1- (3 - (1H -inidazol - 1 − yl)methyl)benzyl)-1H-imidazole, timp = 1- (3,5-di (1H-imidazol-1-yl)phenyl)-1H-imidazole, 4,4′-bibp = 4,4′-bisimidazolylbiphenyl, and btc = 1,3,5-benzenetricarboxylate anion, were synthesized under hydrothermal conditions. In compound 1, both 1,3-bix ligand and btc anion act as bidentate bridging ligands, and connect the zinc cations into a one-dimensional chain. In compound 2, timp and btc anions as tridentate ligands coordinate to zinc cations to form a three-dimensional 3,6-connected network. Compounds 3–5 have similar structures, 4,4′-bibp and btc anions act as bidentate and tetradentate ligands, respectively, and coordinate to metal cations to form a three dimensional 4,4-connected network. The luminescence properties for 1–3 and magnetic properties for 4–5 are also discussed in detail.

Two Lanthanide Metal–Organic Frameworks as Remarkably Selective and Sensitive Bifunctional Luminescence Sensor for Metal Ions and Small Organic Molecules

Two lanthanide metal-organic frameworks (Ln-MOFs) with similar structures have been synthesized through objective synthesis. The two compounds are both 2-fold interpenetrating 3D frameworks. Topological analyses reveal that complexes 1 and 2 are 6-connected pcu net. In addition, both structures were embedded in uncoordinated nitrogen atoms. As the uncoordinated pyridine groups can be used as functional groups, we tested their sensing ability toward metal ions and small organic molecules. To our delight, fluorescence measurements show the two complexes can selectively and sensitively detect for Fe3+ ion and nitromethane, which suggests that the two Ln-MOFs are promising bifunctional luminescence sensor materials with sensing metal ions and small organic molecules.

Solvothermal synthesis, structures and physical properties of four new complexes constructed from multi-variant tricarboxylate ligand and pyridyl-based ligands

Solvothermal reactions of partially or wholly deprotonated biphenyl-3,4′,5-tricarboxylate (H3L) with nitrates of cadmium, manganese and cobalt, in the presence or absence of auxiliary 4,4′-bipyridine (bipy) and 1-(3,5-di(1H-imidazol-1-yl)phenyl)-1H-imidazole (timp) ligands in H2O–DMF, produce four new complexes, namely, {[Cd3(L)2(H2O)9]·(H2O)5}n (1), {[Cd2(HL)2(timp)(H2O)4]·(H2O)4}n (2), {Mn(HL)(bipy)0.5(H2O)}n (3), {Co(HL)(bipy)0.5(H2O)}n (4). Their structures have been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, IR spectra, and thermogravimetric analysis. Complex 1 possesses a three-dimensional (3D) framework composed of two-dimensional (2D) T-shaped molecular bilayer motifs polycatenated with each other. In complex 2, multicarboxylate ligands and timp ligands link Cd centers to generate one-dimensional (1D) ladder structures which are further connected by π–π interactions to form a 3D supramolecular structure. Complexes 3 and 4 are isostructural and possess 2D networks. Magnetic susceptibility measurements indicate that complexes 3 and 4 exhibit ferromagnetic coupling between adjacent Mn(II) ions and Co(II) ions. The photoluminescent properties of 1 and 2 have been studied in the solid state at room temperature.

A second-order nonlinear optical material with a hydrated homochiral helix obtained via spontaneous symmetric breaking crystallization from an achiral ligand.

A unique supramolecular helix assisted by solvent molecules (water and DMF) is obtained from an achiral flexible V-shaped ligand, and spontaneous symmetry breaking occurs in crystallization. Notably, the compound displays strong second-harmonic generation (SHG) response.

Syntheses, structures, photoluminescence and magnetic properties of four new metal–organic frameworks based on imidazole ligands and aromatic polycarboxylate acids

Four metal–organic coordination polymers, {[Cu2(4,4′-bibp)2(NO2)3)]·(NO2)(H2O)}n (1), [Cd(bdc)(4,4′-bibp)]n (2), {[Co2(bdc)2(4,4′-bibp)3(H2O)2]·(H2O)2}n (3), [Zn(Hbtc)(1,4-bix)]n (4) (4,4′-bibp = 4,4′-bis(1-imidazolyl)biphenyl; 1,4-bix = 1,4-bis((1H-imidazol-1-yl)methyl)benzene; H2bdc = 1,4-benzenedicarboxylate; H3btc = 1,3,5-benzenetricarboxylate) were obtained under hydrothermal conditions and characterized structurally. X-Ray diffraction analysis reveals that the four complexes exhibit new frameworks due to diverse coordination conformations. In copper compound 1, with mixed-valence copper(II)–copper(I), rigid linear 4,4′-bibp ligands connect two adjacent layers and the whole structure is a three-dimensional 6,6-connected network. In cadmium compound 2, 4,4′-bibp and bdc anions as bidentate ligands coordinate to cadmium cations to form a three-dimensional 4,4-connected network with a 3-fold interpenetrating framework. In cobalt compound 3, 4,4′-bibp and bdc anions also act as bidentate ligands, and coordinate to cobalt cations to form a three-dimensional 4,6-connected network. Zinc compound 4 shows that both the 1,4-bix ligand and btc anions act as bidentate bridging ligands, and connect the zinc cations to give a 2D polycatenated array structure. The magnetic properties for copper compound 1 and luminescent properties for cadmium compound 2 and zinc compound 4 are also discussed in detail.

Metal–Organic Frameworks Constructed from Versatile [WS4Cux]x−2 Units: Micropores in Highly Interpenetrated Systems

Five metal-organic frameworks (MOFs) formed by [WS(4)Cu(x)](x-2) secondary building units (SBUs) and multi-pyridyl ligands are presented. The [WS(4)Cu(x)](x-2) SBUs function as network vertexes showing various geometries and connectivities. Compound 1 contains one-dimensional channels formed in fourfold interpenetrating diamondoid networks with a hexanuclear [WS(4)Cu(5)](3+) unit as SBU, which shows square-pyramidal geometry and acts as a tetrahedral node. Compound 2 contains brick-wall-like layer also with a hexanuclear [WS(4)Cu(5)](3+) unit as SBU. The [WS(4)Cu(5)](3+) unit in 2 is a new type of [WS(4)Cu(x)](x-2) cluster unit in which the five Cu(+) ions are in one plane with the W atom, forming a planar unit. Compound 3 shows a nanotubular structure with a pentanuclear [WS(4)Cu(4)](2+) unit as SBU, which is saddle-shaped and acts as a tetrahedral node. Compound 4 contains large cages formed between two interpenetrated (10,3)-a networks also with a pentanuclear [WS(4)Cu(4)](2+) unit acting as a triangular node. The [WS(4)Cu(4)](2+) unit in 4 is isomeric to that in 3 and first observed in a MOF. Compound 5 contains zigzag chains with a tetrahedral [WS(4)Cu(3)](+) unit as SBU, which acts as a V-shaped connector. The influence of synthesis conditions including temperature, ligand, anions of Cu(I) salts, and the ratio of [NH(4)](2)WS(4) to Cu(I) salt on the formation of these [WS(4)Cu(x)](x-2)-based MOFs were also studied. Porous MOF 3 is stable upon removal and exchange of the solvent guests, and when accommodating different solvent molecules, it exhibits specific colors depending on the polarity of incorporated solvent, that is, it shows a rare solvatochromic effect and has interesting prospects in sensing applications.

Syntheses, structures, photoluminescence, and magnetic properties of phenanthrene-based carboxylic acid coordination polymers

Four new coordination complexes, M2(Htmopa)4(H2O)4 (M = Zn2+ (1), Mn2+ (2), (M(Htmopa)2(H2O)2)n (M = Ni2+ (3), Co2+ (4)), have been synthesized by the hydrothermal reaction of Htmopa (Htmopa = 2,3,6,7-tetramethoxyphenanthrene-9-carboxylic acid) with different transition metals at a suitable temperature. Single-crystal determinations revealed that 1 and 2 are isostructural and possess a dinuclear subunit, each connected into 3D networks by hydrogen bonds and C-H...pi interactions. 3 and 4 are also isostructural: the metal ions are bridged through water molecules and carboxylate oxygen atoms to form 1D wavelike double chains, and these double chains are further extended to a 3D network via hydrogen bonds and C-H...pi interactions. The photoluminescent properties of the free Htmopa ligand and its complexes have been studied in the solid state at room temperature. Both Htmopa and 1 exhibit strong blue emissions. Magnetic susceptibility measurements indicate that 2 and 3 exhibit antiferromagnetic coupling, whereas 4 shows a ferromagnetic coupling and exhibits a single-ion behavior of the Co II ion at a higher temperature range.

Novel MOF‐Derived Co@N‐C Bifunctional Catalysts for Highly Efficient Zn–Air Batteries and Water Splitting

Metal-organic frameworks (MOFs) and MOF-derived materials have recently attracted considerable interest as alternatives to noble-metal electrocatalysts. Herein, the rational design and synthesis of a new class of Co@N-C materials (C-MOF-C2-T) from a pair of enantiotopic chiral 3D MOFs by pyrolysis at temperature T is reported. The newly developed C-MOF-C2-900 with a unique 3D hierarchical rodlike structure, consisting of homogeneously distributed cobalt nanoparticles encapsulated by partially graphitized N-doped carbon rings along the rod length, exhibits higher electrocatalytic activities for oxygen reduction and oxygen evolution reactions (ORR and OER) than that of commercial Pt/C and RuO2 , respectively. Primary Zn-air batteries based on C-MOF-900 for the oxygen reduction reaction (ORR) operated at a discharge potential of 1.30 V with a specific capacity of 741 mA h gZn-1 under 10 mA cm-2 . Rechargeable Zn-air batteries based on C-MOF-C2-900 as an ORR and OER bifunctional catalyst exhibit initial charge and discharge potentials at 1.81 and 1.28 V (2 mA cm-2 ), along with an excellent cycling stability with no increase in polarization even after 120 h - outperform their counterparts based on noble-metal-based air electrodes. The resultant rechargeable Zn-air batteries are used to efficiently power electrochemical water-splitting systems, demonstrating promising potential as integrated green energy systems for practical applications.