Yuehong Wen

Effect of Functionalized Groups on Gas‐Adsorption Properties: Syntheses of Functionalized Microporous Metal–Organic Frameworks and Their High Gas‐Storage Capacity

The microporous metal-organic framework (MMOF) Zn4O(L1)2⋅9 DMF⋅9 H2O (1-H) and its functionalized derivatives Zn4O(L1-CH3)2⋅9 DMF⋅9 H2O (2-CH3) and Zn4O(L1-Cl)2⋅9 DMF⋅9 H2O (3-Cl) have been synthesized and characterized (H3L1=4-[N,N-bis(4-methylbenzoic acid)amino]benzoic acid, H3L1-CH3=4-[N,N-bis(4-methylbenzoic acid)amino]-2-methylbenzoic acid, H3L1-Cl=4-[N,N-bis(4-methylbenzoic acid)amino]-2-chlorobenzoic acid). Single-crystal X-ray diffraction analyses confirmed that the two functionalized MMOFs are isostructural to their parent MMOF, and are twofold interpenetrated three-dimensional (3D) microporous frameworks. All of the samples possess enduring porosity with Langmuir surface areas over 1950 cm(2) g(-1). Their pore volumes and surface areas decrease in the order 1-H>2-CH3 >3-Cl. Gas-adsorption studies show that the H2 uptakes of these samples are among the highest of the MMOFs (2.37 wt% for 3-Cl at 77 K and 1 bar), although their structures are interpenetrating. Furthermore, this work reveals that the adsorbate-adsorbent interaction plays a more important role in the gas-adsorption properties of these samples at low pressure, whereas the effects of the pore volumes and surface areas dominate the gas-adsorption properties at high pressure.

A Luminescent Metal–Organic Framework Thermometer with Intrinsic Dual Emission from Organic Lumophores

A new mixed-ligand metal-organic framework (MOF), ZnATZ-BTB, has been constructed as a luminescent ratiometric thermometer by making use of the intrinsic dual emission at cryogenic temperatures. Its twofold interpenetrated network promotes the Dexter energy transfer (DET) between the mixed organic lumophores. The temperature-dependent luminescent behavior arises from the thermal equilibrium between two separated excited states coupled by DET, which is confirmed by Boltzmann distribution fitting. The small excited-state energy gap allows ZnATZ-BTB to measure and visualize cryogenic temperatures (30-130 K) with significantly high relative sensitivity (up to 5.29% K(-1) at 30 K). Moreover, it is the first example of a ratiometric MOF thermometer the dual emitting sources of which are widely applicable mixed organic ligands, opening up new opportunities for designing such devices.

A series of d10 coordination polymers constructed with a rigid tripodal imidazole ligand and varied polycarboxylates: syntheses, structures and luminescence properties

Five novel Zn(II)/Cd(II) coordination polymers, [Zn2(tib)(L1)(μ2-OH)(HCOO)·2H2O]n (1), [Cd2(tib)2(L1)(NO3)2·2H2O·4DMF]n (2), [Cd2(tib)2(L2)(NO3)2·2H2O·4DMF]n (3), [Cd(tib)(L3)·H2O·2DMF]n (4) and [Cd3(tib)4(L4)·5/2NO3·1/2OH·3DMF]n (5) (tib = 1,3,5-tris(1-imidazolyl)benzene, H2L1 = terephthalic acid, H2L2 = isophthalic acid, H2L3 = 1,4-naphthalenedicarboxylic acid, H3L4 = (1α,3α,5α)-1,3,5-cyclohexanetricarboxylic acid, DMF = N,N-dimethylformamide), have been synthesized under solvothermal conditions. In compound 1, two-dimensional (2D) Zn-tib layers are pillared by L1 to afford a (3,5)-connected three-dimensional (3D) framework with topology (63)(69·8). Compound 2 displays a 2D + 2D → 2D interpenetrated bi-layer array based on a 2D (3,4) network. Compound 3 is characterized as an infinite one-dimensional (1D) chain structure, which is further extended into a 3D supramolecular architecture via weak π⋯π stacking interactions. Compound 4 possesses a 3D 2-fold interpenetrated architecture with the Schlafli symbol (42·65·83)(42·6). Compound 5 features a fascinating petal shaped (3,5)-connected network with a (42·6·84·103)3(42·6)3(83)2 topology which until now has never been documented. In this series of compounds, the diversity of the structures is tuned by the coordination geometries of the metal ions and the nature of the varied co-ligands. Furthermore, the luminescence properties of compounds 1–5 at room temperature have also been studied in detail.

Effect of anions on the self-assembly of two Cd–organic frameworks: syntheses, structural diversity and photoluminescence properties

By employing a rigid tripodal ligand 1,3,5-tris(1-imidazolyl)benzene (tib) to assemble with two different Cd(II) salts, we have obtained two distinct cationic metal–organic frameworks, [Cd(tib)2·2NO3·4DMF]n (1) and [Cd(tib)2·2ClO4·4DMF]n (2) (DMF = N,N-dimethylformamide). The compounds were structurally characterized by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD), and thermogravimetric analyses (TGA). Both compounds 1 and 2 are constructed based on 2D square lattice (sql) nets, through ligand-to-axial (L–A), pillared by triangular tib ligands, resulting in two diverse 3D pillar-layered architectures. Compound 1 features a cationic framework with a (3,6)-connected rtl topology and has rhomboid channels; while for 2, the 2D layers repeat in an ⋯ABAB⋯ staggered stacking mode pillared by tib ligands, resulting in a different cationic framework from 1 with a pyr net. The results demonstrate that counterions NO3− and ClO4− play an important role in the fabrication of structures of 1 and 2. Furthermore, the photoluminescence of compounds 1 and 2 have been investigated in the solid state at ambient temperature.

From Pair Quadruple- to Single-Stranded Helices to Lines in a Mixed Ligand System via Adjusting the N-Substituent of l-Glu

Utilizing the mixed-ligand strategy, a novel fourfold-interpenetrated 3D homochiral metal-organic framework (1) with rare pair quadruple-stranded helices was assembled from bpee (1,2-bis(4-pyridyl)ethylene) and NCG (N-carbamyl-l-glutamate). Changing the carbamyl substituent of NCG with benzoyl group (NBzG: N-benzoyl-l-glutamate), a non-interpenetrated 3D homochiral coordination polymer (2) composed of alternate right-handed and left-handed single helix was obtained. When p-tolylsulfonyl substituent was used instead, an interesting homochiral linear structure (3) was formed from mixed-ligand bpee and NTsG (N-p-tolylsulfonyl-l-glutamate), with all individual NTsG being lined up orderly. The steric hindrance of N-substituent of l-glu has a tremendous impact on the construction of these diverse frameworks. Complexes 1-3 display second harmonic generation (SHG) efficiencies, which are approximately 0.32, 0.45, and 0.55 times as much as that of KDP powder.

1D to 3D and Chiral to Noncentrosymmetric Metal–Organic Complexes Controlled by the Amount of DEF Solvent: Photoluminescent and NLO Properties

A mixture of 2D and 1D metal-organic complexes, [ZnL(H2O)2·G1·DEF·2H2O]n (1a: G1 = naphthalene-2,7-disulfonate; DEF = N,N-diethylformamide) and [ZnL(H2O)3·G1·DEF·2H2O]n (2), has been prepared from a hydrogenated Schiff base L and Zn(II) in a DEF-contained solvent system under mild conditions. The yields of 1a and 2 are equivalent; however, they can be tuned by varying the amount of DEF solvent. Increasing the use of DEF tends to form pure 1a, while decreasing it generates 2. Without DEF, another novel 3D four-connected CdSO4 (cds) framework [ZnL(H2O)2·G1·2H2O]n (3) composed of alternated right-handed and left-handed helical chains has been constructed. The amount of DEF solvent has a significant impact on the diverse coordination architectures of 1-3, which is rare in the preparation of metal-organic complexes. The photoluminescence of complexes 1-3 along with naphthalene-2,7-disulfonate has been investigated in the solid state. The luminescent emission of G1 was enhanced greatly after being confined into metal-organic networks. In addition, complexes 1-3 display second-harmonic generation efficiencies, which are approximately 0.58, 0.42, 0.32, and 0.52 times as much as that of potassium dihydrogen phosphate.

Lanthanide coordination polymers assembled from triazine-based flexible polycarboxylate ligands and their luminescent properties

Two flexible triazine-based polycarboxylate ligands, 1,3,5-triazine-2-iminodiacetic acid-4,6-bis(L-alanine) (H4L1) and 1,3,5-triazine-2-iminodiacetic acid-4,6-biglycine (H4L2), have been designed and used to construct a series of luminescent lanthanide coordination polymers {[Ln(HL1)](H2O)5}n (Ln = 1, Tb; 2, Eu; 3, Gd) and {[Ln(HL2)(H2O)](H2O)2}n (Ln = 4, Tb; 5, Eu; 6, Gd). The complexes were structurally authenticated by single-crystal X-ray diffraction, revealing that isostructural complexes 1–3, derived from H4L1, possess a 2-D framework with the monoclinic space group C2/c, whereas isostructural complexes 4–6, based on H4L2, exhibit a 2-D layer structure with the monoclinic space group P2(1)/c. Solid-state photoluminescence properties of the complexes were investigated. Complexes 1 and 2 exhibit remarkable green and red luminescence emissions with high quantum yields up to 67% and 68%, respectively, and millisecond-level lifetimes. Nevertheless, complexes 4 and 5 feature weak quantum yields (9.9% for 4; and 30% for 5).

Two cationic metal–organic frameworks featuring different cage-to-cage connections: syntheses, crystal structures, photoluminescence and gas sorption properties

Solvothermal reactions of a neutral rigid tripodal ligand, 1,3,5-tris(1-imidazolyl)benzene (tib), with Zn(NO3)2·6H2O and Zn(ClO4)2·6H2O produced two metal–organic frameworks, [Zn3(tib)4·6NO3·6H2O·3DMA]n (1) and [Zn2(tib)3·4ClO4·6H2O·6DMA]n (2) (DMA = N,N-dimethylacetamide), respectively, which feature different cage-to-cage connections. Both compounds 1 and 2 exhibit 3D cationic frameworks with charge-balancing extraframework anions. Interestingly, the counterions NO3− and ClO4− play an important role in the fabrication of structures of 1 and 2. Compound 1 shows 2-fold interpenetration while 2 gives a non-interpenetrated 3D porous framework. Adjacent M6L4 octahedral cages in compound 1 are further linked via vertex sharing to construct a 3D framework. For compound 2, neighboring octahedral cages connect with each other through sharing four metal ions which are in the equatorial plane to generate a 2D layer. Furthermore, the 2D layers are linked by other layers via sharing the other two metal ions which are in the axial position, finally forming a 3D supramolecular framework. The photoluminescence of compounds 1 and 2 has been investigated in the solid state. Gas sorption measurements were conducted on the activated 1, showing a H2 uptake of 1.2 wt% at 77 K and 1 bar with high initial adsorption enthalpy of 8.4 kJ mol−1.

Strategies to construct homochiral metal–organic frameworks: ligands selection and practical techniques

The booming development of homochiral metal–organic frameworks (HMOFs) since the start of the 21st century has attracted considerable attention from the scientific community. With the features inherited from MOFs, HMOFs have great potential for application in gas storage, separation, sensing, catalysis, ferroelectric materials and nonlinear optics. Moreover, they show incomparable potential in enantioseparation and asymmetric catalysis, which are emergent technologies in modern chemical engineering. In this highlight, we summarize the classical ways to construct HMOFs based on the selection of ligands, as well as the practical techniques utilized. Moreover, the merits and demerits of each method are discussed along with the predictability of homochirality.

Effect of anions on the self-assembly of Zn(II) with a hydrogenated Schiff base ligand: structural diversity and photoluminescent properties

A flexible tetradentate ligand, 1,2-bis(4′-pyridylmethylamino)ethane (L), has been used for assembly with different Zn(II) salts. Six complexes with diverse structures from zero- to two-dimensional array have been prepared under mild conditions. Complexes (Zn2LCl4·2H2O)2 (1) and (Zn2LBr4·H2O)2 (2) form novel discrete M4L2 square metallacycles, which are further linked by Cl (or Br)⋯H hydrogen bonds and weak intermolecular interactions to result in 3D frameworks. Complex [ZnL(SCN)2·2H2O]n (3) is a one-dimensional hinged chain. Different chains are stacked in a staggered pattern by the π–π interactions. Complex (ZnLCl2·2H2O)n (4) displays an infinite one-dimensional hinged chain too, but its 3D supramolecular structure is formed by the intrachain and interchain hydrogen bonds. Both complexes [ZnL(H2O)2·2ClO4·4H2O]n (5) and [ZnLAc(H2O)·Ac·2H2O]n (6) exhibit 2D networks. Structural analyses of complexes 1–6 suggest that anions Cl−, Br−, SCN−, ClO4−, and Ac− play an important role in the formation of those complexes with hydrogenated Schiff base L. Furthermore, the photoluminescence of complexes 1–6 have also been investigated in the solid state.