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A newly constructed hexanuclear cadmium metal–organic framework (MOF) exhibits a highly selective and sensitive fluorescence‐quenching response toward Fe 3+ ions, which is attributable to the coaction of absorption competition and an energy‐transfer mechanism.

Dynamic metal-organic frameworks (MOFs) that respond to external stimuli have recently attracted great attention. However, the subtle control of dynamic processes as well as the illustration of the underlying mechanism, which is crucial for the targeted construction and modulation purpose, is extremely challenging. Herein, we report the achievement of simultaneous kinetic and thermodynamic modulation of the structure transformation processes of a family of cobalt(II)-organic frameworks, through the rational combination of coligand replacement, solvent molecule substitution, and ligand-based solid solution strategies. On the basis of the systematic investigation of the structural transformation behaviors, the underlying response mechanism and principles for modulation were illustrated. It is expected that this work can provide valuable hints for the study and further development of dynamic materials.

Three new mixed-ligand divalent coordination polymers (CPs) {[Zn3(L)(1,4-bdc)3]·2DMF}n (1), {[Zn2(L)(2,6-ndc)2]·3DMF}n (2) and {[Cd2(L)3(2,6-ndc)2]}n (3) [L = 9,10-di(pyridine-4-yl)anthracene, 1,4-H2bdc = 1,4-benzenedicarboxylic acid, 2,6-H2ndc = 2,6-naphthalenedicarboxylic acid] have been prepared and well characterized by elemental analyses, infrared spectroscopy, single-crystal X-ray diffraction techniques, powder X-ray diffraction patterns and thermogravimetric analyses. The crystal structure analyses of coordination polymers (CPs) reveal that all the complexes 1–3 have the three-dimensional (3D) coordination networks. The structure of 1 can be simplified as a sqc3 3D 8-connected framework with the point symbol of (424·64). Particularly, in the presence of the linear 2,6-H2ndc auxiliary ligand, a double-deck interpenetrating pcu 3D network of 2 is assembled by 6-connecting framework with the point symbol of (412·63). Complex 3 exhibits a ttd 3D 5-connected net with a point symbol of (46·64). Further, the solid-state luminescent properties of the complexes 1–3 were measured and studied at room temperature.

In order to elucidate the effect of the structure on stability and gas adsorption performance, three porous Zn(II) metal–organic frameworks, NKU-106, NKU-107, and NKU-108, have been constructed. NKU-106 and NKU-107 assembled from acylamide functionalized tetracarboxylate ligand exhibit low stability and thereby poor gas adsorption ability. However, when one isophthalate moiety of the tetracarboxylate ligand is replaced with a pyrazole group, and the resulting NKU-108 shows improved thermal and chemical stability as well as good adsorption capacities with respect to CO2 and C2 hydrocarbons. This result demonstrates that coordination group optimization is an effective strategy to improve the stability and gas adsorption properties of metal–organic frameworks (MOFs) and thus provides very valuable information for future design and synthesis of porous MOFs for practical application.

A new coordination compound [Mg(L)(H 2 O) 5 ∙H 2 O] (NKU-109, H 2 L = 5-(4 H -1,2,4-triazol-4-yl)benzene-1,3-dicarboxylic acid) was solvothermally synthesized, featuring a supramolecular hydrogen-bonding network. A good proton conductivity of 5.87 × 10 −4 S/cm was recorded at 70 °C and a relative humidity of 75% in alternating current (AC) impedance experiment, which sheds a new light on the design of proton conduction materials based on coordination compounds.

In this paper, two 3D anionic metal–organic frameworks, [(CH3CH2)2NH2]·[Zn(BTC)1/3(PyC)]·1/2CH3CN·2H2O (NKU-102) and [(CH3CH2)2NH2]·[Zn2(BTC) (PyC)]·1.5H2O·DEF (NKU-103), were constructed from the same reaction system at different temperature. Though both are of anionic framework, NKU-102 possesses a sealed 3D framework based on octahedral cage and shows negligible adsorption capacity of organic dyes, whereas NKU-103 features an open triangular microchannel surrounded by two types of helical chains, and thus exhibits outstanding size-selective adsorption toward small cationic organic dyes.

The new functional ligand 5-(1H-pyrazole-4-carboxamido)isophthalic acid (H3L) reacts with CoSO4·7H2O to form a new three-dimensional metal–organic framework, [Co4(HL2−)4(DMF)2(H2O)2]n·solvent (1) with a new (3,6)-connected topology. 1 exhibits one-dimensional polar channels with approximate dimensions of 6.0 × 8.0 A2 decorated with accessible functional sites. These sites contribute to enhanced CO2 uptake (103.2 cm3 g−1 at 273 K and 1 bar) and CO2/CH4 selectivity (7.25 for CO2/CH4 = 50 : 50; 8.59 for CO2/CH4 = 5 : 95) at 298 K and 1 bar. DFT calculations were also performed to elucidate the binding sites. These results suggest that complex 1 is an attractive candidate for CO2 adsorption and separation.

Water instability is a crucial limiting factor in the practical application of most fluorescent metal-organic frameworks (MOFs). Here, by introducing a fascinating double-helical structure generated through dense stacking of organic ligands, a water-stable fluorescence MOF has been synthesized, namely, [Cd2(tib)2(bda)2]·(solvent)n (1) [tib =1,3,5-tris(1-imidazolyl) benzene; H2bda = 2,2'-biphenyl dicarboxylic acid]. This helical structure helps to enhance the stability of 1 against common organic solvents and water, even acid/base aqueous solutions with a pH value ranging from 3 to 11. Furthermore, this material can be a potential fluorescent sensor for ketones.

A series of porous pillar-layer frameworks have been prepared with 1,3,5-tris(p-imidazolylphenyl)benzene (tipb) as the main ligand and dicarboxylic acids as coligands. Our studies have demonstrated that tipb is prone to form a 63 layer with targeted metal ions, which could be utilized to construct pillar-layer frameworks. The structure and porous properties of the resulting metal–organic frameworks could be tuned by modifying the size, geometry, and functional groups of the coligands (pillars). Moreover, gas adsorption measurements revealed that both complexes 1 and 2 exhibit selective adsorption of H2 over N2 for the pore-size effect.

Metal–organic frameworks (MOFs) are typically built by assembly of metal centres and organic linkers, and have emerged as promising crystalline materials in a variety of fields. However, the stability of MOFs is a key limitation for their practical applications. Herein, we report a novel Sr 2+ -MOF [Sr 4 (Tdada) 2 (H 2 O) 3 (DMF) 2 ] (denoted as NKU- 105 , NKU = Nankai University; H 4 Tdada = 5,5'-((thiophene-2,5-dicar bonyl)bis(azanediyl))diisophthalic acid; DMF = N,N -dimethylformamide) featuring an open square channel of about 6 Å along the c -axis. Notably, NKU- 105 exhibits much outstanding chemical stability against common organic solvents, boiling water, acids and bases, relative to most MOF materials. Furthermore, NKU- 105 is an environment-friendly luminescent material with a bright cyan emission. This article is part of the themed issue ‘Coordination polymers and metal–organic frameworks: materials by design’.

This communication reports a novel metal–organic framework exhibiting an excellent performance in adsorbing small toxic cationic herbicides, i.e. methyl viologen and diquat, with large adsorption capacities and ultratrace residue levels. To the best of our knowledge, this is the first example of high-performance MOFs trapping toxic cationic herbicides.

The conversion from a [2 + 2] nested double-helical column, {[Mn2(ptptp)(suc)(H2O)2]·1.5H2O}n (1), to a cationic spiral staircase, {[Mn2(ptptp)(suc)0.5(H2O)3]·Br·0.5H2O}n (2), has been achieved through ionic liquid anion stimulations under solvothermal conditions. The conversion does not change the antiferromagnetic interactions.