A family of thiophene-based metal–organic frameworks (MOFs), [Zn(L)(BBI)·(H2O)2] (1) (BBI = 1,1′-(1,4-butanediyl)bis(imidazole)) and [Cd(L)(TPOM)0.75]·xS (2) (TPOM = tetrakis(4-pyridyloxy-methylene) methane, S represents noncoordinated solvent molecules) was constructed by employing a new linear thiophene-functionalized dicarboxylic acid (benzo-(1,2;4,5)-bis(thiophene-2′-carboxylic acid, H2L) to assemble with d10 ions in the presence of a flexible ancillary ligand under solvothermal conditions, which exhibit diverse structures. Most strikingly, both compounds 1 and 2 could be efficient luminescent sensory materials that are highly selective and sensitive to environmental contaminants, especially for Hg(II), Cu(II), Cr(VI), and salicylaldehyde, and yet remain unaffected by other molecules that may coexit. Furthermore, this is the first report on MOF-based sensors capable of recyclable detection of Hg(II), Cr(VI), and salicylaldehyde so far. The luminescent sensing mechanism was studied in detail as well. In addition, compound 2 is one of the rare examples of high-performance MOFs trapping 2,4-dichlorophenol from the wasted methanol solution.Keywords: luminescence sensing; MOFs; pesticide removal; sensing mechanism; thiophene-functionalized dicarboxylate;

The reaction of tricarboxytriphenyl amine (H3TCA) with CdII and auxiliary ligand 4,4′-bis(1-imidazolyl)biphenyl (bimb) afforded [Cd3(TCA)2(bimb)·(DMA)6]n (1) containing a two-fold interpenetrating three-dimensional microporous framework. Compound 1 showed remarkable adsorption enthalpies for CO2 and H2 and good H2/N2 selectivity at low temperature. Moreover, activated 1 showed a highly selective adsorption towards CO2 over N2 and CH4 under ambient conditions. Interestingly, compound 1 selectively removed methyl orange (MO) over methylene blue (MB) from contaminated water with good recyclability, and possessed the second highest adsorption capacity for MO among the MOFs reported to date. Remarkably, complex 1 showed strong guest-dependent luminescence behavior.

Three metal–organic frameworks (MOFs) [M2(d-cam)2(bimb)2]n·3.5nH2O (M = Mn for 1, Co for 2) and [Cd8(d-cam)8(bimb)4]n (3) (d-H2cam = d-camphor acid, bimb = 4,4′-bis(1-imidazolyl)biphenyl), solvothermally synthesized, exhibit structural diversity. The charming aspect of these frameworks is that compound 3 is the very first MOF-based sensor for quantitatively detecting three different types of analytes (metal ions, aromatic molecules, and pesticides). And also, both compounds 2 and 3 show rapid uptake and ready regeneration for methyl orange (MO) and can selectively bind MO over methylene blue (MB) with high MO/MB separation ratio.Keywords: dyes separation; luminescence quenching; metal−organic frameworks; quantitative detecting

Two amino-decorated metal–organic frameworks have been constructed, which are the rare examples of MOF-based fluorescent probes targeting environmentally relevant guest species, such as Hg (II) and Cr (VI) ions in aqueous solution, with high selectivity and sensitivity. The possible sensing mechanism is also discussed.

Solvothermal reactions of 5-(4-pyridyl)-isophthalic acid (H2pbdc) and transition-metal centers (Ni2+/Co2+/Zn2+) in the presence (or absence) of N-auxiliary 4,4′-bis(1-imidazolyl)biphenyl (bimb) ligand produce [Ni2(pbdc)2(μ2-H2O)(H2O)2·(DMA)2.7]n (DMA = N,N′-dimethylacetamide, 1), [Ni12(pbdc)12(μ2-H2O)6(py)2(H2O)8(DMA)2·(H2O)5·(DMA)9]n (2), [Co2(pbdc)2(bimb)2·(bimb)0.5·(H2O)4·(DMF)0.25]n (3) and [Zn(pbdc)(bimb)·(H2O)]n (4), which exhibit structural diversity. Both compounds 1 and 2 display a uninodal 8-connected 3D tsi net, but feature different crystal systems and space groups from each other. Compound 3 adopts a 2-fold interpenetrating binodal (3,5)-connected 3D hms net and compound 4 features a rare 2-fold interpenetrating binodal (3,4)-connected 3D fsx architecture. In particular, activated 3 shows high-efficiency for the selective sorption of small molecules, including CO2 over N2 and CH4, H2 over N2, as well as alcohols from water. More importantly, 4 represents the first report on a MOF as a promising luminescent probe for detecting pesticides, and also the very first example for detecting both pesticides and solvent molecules simultaneously.

A Cd(II)–MOF [Cd(L)(DMF)] (1) (H2L = 5-(4-pyridyl)-isophthalic acid) featuring high thermal and chemical stability has been solvothermally synthesized and characterized. Complex 1 is a robust multifunctional three-dimensional (3D) microporous framework possessing an unusual (4,5)-connected topological net. Activated 1 shows high-efficiency for the selective capture of CO2 over N2 and CH4 under ambient conditions, which ranks it among MOFs with the highest selectivity. In addition, desolvated 1 exhibits good separation ratios of H2 over N2 at lower temperature, as well as alcohols from water. In particular, desolvated 1 demonstrates significantly higher adsorption enthalpies for CO2 and CH4 gas molecules, which are in the range of the highest Qst values reported to date. Furthermore, complex 1 displays visible photoluminescence in the solid state under UV irradiation.

A three-dimensional microporous framework, Zn(II)–MOF [Zn(HPyImDC)(DMA)]n (1) (H3PyImDC = 2-(pyridine-4-yl)-1H-4,5-imidazoledicarboxylic, DMA = N,N′-dimethylacetamide), with open metal sites and small-sized pores, exhibits excellent selective capture of CO2 over N2 and CH4 at 273 K, as well as alcohols from water. The excellent CO2 adsorption selectivity of 1 allows its potential use in the capture of CO2 from industrial flue gas or the removal of CO2 from natural gas. More interestingly, compound 1 represents the rare case of porous materials separating propanol isomers, which may be caused by the relative flexibility of the linear n-propanol considering that both n-propanol and i-propanol have similar kinetic diameters.

Two three-dimensional microporous compounds, Cu6(BTTC)4(H2O)6·xS (1) and [(CH3)2NH2]3[(Cu4Cl)3(BTTC)8]·yS (2, H3BTTC = benzo-(1,2;3,4;5,6)-tris (thiophene-2′-carboxylic acid), S represents noncoordinated solvent molecules), have been solvothermally synthesized and characterized, both of which are based upon truncated octahedron subunits and contain uniform nanosized cavities but exhibit different topological frameworks. Complex 1 demonstrates high adsorption enthalpies for H2 and CO2 gas molecules, stemming principally from the presence of the exposed metal Cu(II) sites on the pore surface. In particular, activated complex 1 shows high efficiency for the separation of energy-correlated molecules, including CO2 over N2 and CH4 under ambient conditions.

Solvothermal reactions of 2,5-thiophenedicarboxylate (H2tdc) and N-auxiliary ligands in the presence of cobalt(II), zinc(II) and cadmium(II) salts have given rise to seven new metal–organic frameworks, namely, [Co2(tdc)2(bpp)2(H2O)·(H2O)]n (bpp = 1,3-bis(4-pyridyl)propane) (1), [Cd(tdc)(bpp)(H2O)·(H2O)2]n (2), [Zn2(tdc)2(bbi)2·(H2O)2]n (bbi = 1,1′-(1,4-butanediyl)bis(imidazole)) (3), [Co4(tdc)3(bimb)4(H2O)5·(tdc)·(DMF)·(H2O)2]n (bimb = 4,4′-bis(1-imidazolyl)biphenyl) (4), [Zn4(O)(tdc)3(bimb)4·(H2O)5.25·(CH3OH)]n (5), [Cd4(tdc)4(bimb)6·(H2O)2·(CH3OH)2·(DMF)4] (6) and [Co2(tdc)2(tib)2·(H2tdc)·(DMF)2] (tib = 1,3,5-tris(1-imidazolyl)benzene) (7), which exhibit structural diversity. Compounds 1–3 display 3D 2-fold interpenetrating 8-connected tsi net, 2D 4-connected sql net, and 3D 5-fold interpenetrating 4-connected dia net, respectively; while compound 4 features an extremely rare 3D 7-connected hxg-d cationic net and compound 5 adopts a 3D trinodal (4,4,6)-connected net with a new topology structure. For compounds 6 and 7, the topology in the structures were determined as 3D 3-fold interpenetrating 5-connected bnn net and 3D 2-fold interpenetrating binodal (3,5)-connected net, respectively. In the solid state, complexes 1, 4 and 5 exhibit nonlinear optical properties, and complex 5 has also been evaluated as a promising visible-light-driven photocatalyst for degradation of organic pollutants. The magnetic investigation of complexes 1 and 4 shows that there exists spin-canted antiferromagnetism for 1, whereas strong antiferromagnetic interaction and/or the depopulation of the higher energy Kramers doublets of the Co(II) centers are dominant in 4.

Solvothermal reactions of 2-amino-1,4-benzene dicarboxylic acid (NH2bdcH2) and N-auxiliary ligands in the presence of manganese(II), zinc(II) and cobalt(II) salts have given rise to four new metal–organic frameworks, namely, [Mn5(NH2bdc)5(bimb)5·(H2O)0.5]n (bimb = 4,4′-bis(1-imidazolyl)biphenyl) (1), [Zn(NH2bdc)(bix)·(DMF)2]n (bix = 1,4-bis(imidazol-1-ylmethyl)benzene) (2), [Co(NH2bdc)(bix)·(DMF)·(CH3CH2OH)]n (3) and [Co(NH2bdc)(bpp)]n (4) (bpp = 1,3-bis(4-pyridyl)propane). Single-crystal X-ray diffraction analyses revealed that MOF 1 displays 5-fold interpenetrating 4-connected dia 3D net; MOFs 2 and 3 are isomorphic, which possess 3-fold interpenetrating dia 3D nets; MOF 4 exhibits 4-connected sql 2D net. Noncentrosymmetric structures and multifunctionality in 1–3 are established by varying ligands and metal centers. In the solid state, polar MOFs 1–3 exhibit nonlinear-optic (NLO) and MOF 1 demonstrates typical ferroelectric behaviour with a remnant electric polarization (Pr) of 1.2 μC cm−2 and an electric coercive field (Ec) of 0.35 kV cm−1. In addition, MOF 2 could be a potential luminescent probe for detecting nitrobenzene or 2-nitrotoluene via fluorescence enhancement and has been evaluated as a promising visible-light-driven photocatalyst for degradation of organic pollutants.

Two microporous cadmium(II) metal–organic frameworks, [Cd(cptpy)(Ac)(H2O)·(DMA)(H2O)]n (1) and [Cd(cptpy)2·(DMF)2]n (2) (Hcptpy = 4-(4-carboxyphenyl)-2,2′:4′,4″-terpyridine, DMA = N,N-dimethylacetamide, DMF = dimethylformamide) have been solvothermally synthesized under different reaction conditions. Complex 1 is a double-interpenetrating 3D network, while 2 is a noninterpenetrating (3,5)-connected 2D framework. The dehydrated forms of compounds 1 and 2 exhibit selective adsorption of CO2 over N2 and H2O over CH3OH. In addition, the adsorption value of CO2 for 2 is higher than that of 1. The contents of uncoordinated pyridine nitrogen (Lewis basic sites) per formula unit of 1 and 2 are 2.16 and 4.36%, respectively. Obviously, the grafting of more uncoordinated pyridine nitrogen into compound 2 could enhance adsorption of the acidic CO2 molecule. Notably, both 1 and 2 display strong photoluminescence. The nature of electronic transitions for complex 1 in the photoluminescent process was investigated by means of time-dependent density functional theory (TDDFT) calculations and molecular orbital analyses, which collaborates that the luminescent property is ligand-based.

Five new metal–organic frameworks [M(btec)0.5(bimb)]n (1) (M = Co (1), Ni (2), Cu (3), Zn (4)) and [Cd(btec)0.5(bimb)0.5]n (5), were obtained by reactions of the conjugated 1,2,4,5-benzenetetracarboxylic acid (H4btec) and 4,4′-bis(1-imidazolyl)biphenyl (bimb) with corresponding metal salts under hydrothermal conditions, respectively. MOFs 1-5 show different structures and topologies: compounds 1 and 4 are isomorphic, which possess typical PtS 3D nets; compound 2, 3 and 5 exhibit 2D layer structure, NbO 3D network and (4,6)-connected 3D binodal topology, respectively. Notably, compounds 1, 2, and 5 represent the rare example of MOFs-based visible-light-driven photocatalysts and show good stability toward photocatalysis. Furthermore, compound 5 is photocatalytically more active than 1 and 2 because of the relatively narrower band gap calculated from LMCT transitions. In addition, the formation rate of •OH radicals on compound 5/H2O interface via photocatalytic reactions is much higher than that of 1 and 2, implying that the formation rate of •OH radicals during photocatalysis is in agreement with photocatalytic activity and the formation rate of •OH radicals is an important factor influencing photocatalytic performance.

The treatment of Cd(II) ion with the sodium salt of H2atc (H2atc = 2-aminoterephthalic acid) in aqueous solution facilely yields crystal nanorods of metal–organic framework at room temperature. The nanocrystal metal–organic framework (NMOF) of [Cd(atc)(H2O)2]n (NMOF 1) has been realized for the straightforward and highly sensitive sensing of nitroaromatic compounds in ethanol solution by the fluorescence quenching and fluorescence titration experiments.Nanocrystal metal–organic framework 1 (NMOF 1) has an very high density arranged with lengths of 4–6 μm, and the superstructures are built from one dimensional (1D) nanorods with thicknesses of 20–40 nm and widths of 80–100 nm. The maximum fluorescence intensities of the ethanol solution of NMOF 1 nanorods with different analytes show that NMOF 1 has an ability for sensing nitroaromatic compounds efficiently.

The treatment of Ln(NO3)3·6H2O (Ln = La, Ce, Eu, Gd, Dy) with 1,3,5-benzenetricarboxylic acid (H3BTC) in a water–ethanol solution facilely yields crystal nanorods of rare earth metal–organic frameworks (MOFs) at room temperature. Electron micrographs show that the nanorods are 50–200 nm in width, 50–100 nm in thickness and 1–2 μm in length. All the crystal nanorods have the same Ln(BTC)(H2O)6 structure as identified by power X-ray diffraction, elemental analysis, thermogravimetric and Fourier transform infrared analysis. The optical properties of all the compounds are recorded; and, the nanoscale MOFs (NMOFs) with Eu3+ and Dy3+ show excellent photoluminescence.

Six new metal–organic frameworks [Cu(obba)(bimb)·(obbaH2)]n (1), [Cu(obba)(bimb)]n (2), [Zn2(obba)2(bimb)2(DMF)2(H2O)3.5]n (3), [Ni3(2,2′,4,4′-bptcH)2(bimb)2(H2O)2·(H2O)2]n (4), [Ni2(bimb)3(H2O)6·(aobtc)·(DMF)2·(H2O)2]n (5) and [Cd(3,3′,4,4′-bptcH2)(H2O)·(bimb)]n (6), were obtained by reactions of 4,4′-bis(1-imidazolyl)biphenyl (bimb) and multi-carboxylic acids of 4,4′-oxybis(benzoic acid) (obbaH2), 2,2′,4,4′-biphenyltetracarboxylate acid (2,2′,4,4′-bptcH4), azoxybenzene-3,3′,5,5′-tetracarboxylic acid (aobtcH4), and 3,3′,4,4′-biphenyltetracarboxylate acid (3,3′,4,4′-bptcH4) with corresponding metal salts under hydro/solvothermal conditions, respectively. Complexes 1–3 have entangled structures with different topologies: 1 is a 3-fold interpenetrating NbO three-dimensional (3D) network; 2 is a 3-fold interpenetrating dmp 3D net; 3 is a 6-fold interpenetrating dia 3D chiral net containing rare 1D helical chains with the same handedness. Complex 4 is an uninodal 6-connected network with a Schäfli symbol of (486483) based on the trinuclear Ni(II) subunits, while complexes 5 and 6 are 1D chains. Interestingly, compound 6 represents the rare example of MOFs that exhibit high photocatalytic activity for dye degradation under visible light and shows good stability towards photocatalysis. Complexes 3 and 6 exhibit intense blue emissions in the solid state at room temperature whereas 3 appears to be a good candidate of novel hybrid inorganic–organic NLO material.

Three metal-organic frameworks based on the connectivity co-effect between rigid aromatic dicarboxylic acids and flexible linear linkers have been synthesized and characterized. [Cd(3-NO2-bdc)(bbi)]n (1) and [Co(3-NO2-bdc)(bbi)]n (2) (3-NO2-bdcH2 = 3-nitro-1,2-benzenedicarboxylic acid, bbi = 1,1′-(1,4-butanediyl)bis(imidazole)) are isostructural, which exhibit two-dimensional (2D) layer frameworks; [Co(3,5-pdc)(bbi)·2H2O]n (3) (3,5-pdcH2 = pyridine-3,5-dicarboxylic acid) has 2D 6-connected network with a Schäfli symbol of (344653). In addition, compounds 1 and 2 exhibit good photocatalytic activities under visible irradiation, and their different photocatalytic activities have also been analyzed based on the diffuse-reflectance UV/Vis spectra.Metal-organic frameworks 1 and 2, derived of rigid aromatic dicarboxylic acid and flexible linear linkers, are isostructural, which possess two-dimensional layer frameworks and exhibit good photocatalytic activities under visible irradiation. Different photocatalytic activities have been analyzed based on the diffuse-reflectance UV/Vis spectra.Research Highlights► Three metal-organic frameworks based on the connectivity co-effect between rigid aromatic dicarboxylic acids and flexible linear linkers have been synthesized. ► Compounds 1 and 2 exhibit good photocatalytic activities under visible irradiation. ► Different photocatalytic activities for 1 and 2 have been analyzed based on the diffuse-reflectance UV/Vis spectra.

A new conjugated metal−organic framework based on 2,2′,4,4′-biphenyltetracarboxylic acid with a uninodal five-connected hexagonal boron nitride net (bnn) was synthesized, which represented the first example of metal−organic frameworks capable of adsorbing a trace level of organophosphate pestcide for efficient detection via stripping voltammetric analysis. A detection limit of 0.006 μg·mL−1 was obtained with the calculation based on a signal−noise ratio equal to 3.

Hydrothermal and solution reactions of pyridine-2,6-dicarboxylic acid N-oxide (2,6-PDCO) and BaCl2·2H2O yield two metal–organic frameworks; namely [Ba(2,6-PDCO)]n (1) and [Ba(2,6-PDCO)·H2O]n (2), respectively. Single-crystal X-ray analyses reveal that compound 1 is a dense framework whereas compound 2 is a porous one, though both compounds have an infinite two-dimensional (2D) layer structure. Compounds 1 and 2 are the first examples of pyridine dicarboxylic acid N-oxide introduced into the alkaline earth metal–organic framework.

Six metal−organic coordination polymers, [Cu(bdc)(bimb)]n (H2bdc = 1,4-benzenedicarboxylate; bimb = 4,4′-bis(1-imidazolyl)biphenyl) (1), [Cu3(btc)2(bimb)2·(H2O)3]n (H3btc = 1,3,5-benzenetricarboxylate) (2), [M3(btc)2(bimb)2·(H2O)4]n (M = Mn for 3, Co for 4, Cd for 5), and [Cd(btcH)(bimb)]n (6) were obtained under hydrothermal conditions and characterized structurally. The networks exhibit a variety of topologies: compound 1 exhibits a triply interpenetrating three-dimensional (3D) framework with a distorted primitive cubic (α-Po) single net; compounds 2−5 are isomorphic, which possess a trinodal 4-connected 3D framework; compound 6 has a two-dimensional (3,4)-connected framework. In addition, the thermal stabilities for 1−6 and the photoluminescence properties for 5 and 6 were examined. An anionic organic dye X3B was selected as a model pollutant in aqueous media to evaluate the photocatalytic effectiveness of isostructural compounds 3 and 4, and the results indicated compounds 3 and 4 represent rare examples of coordination polymers that exhibit high photocatalytic activity for dye degradation under UV light and show good stability toward photocatalysis. The difference in catalytic activity between 3 and 4 arises from the discrepancy in central metal ions of the two compounds.

Three new metal–organic coordination polymers, [Cd3(5-NO2-bdc)2(5-NO2-bdcH)2(bpyo)2]n (1), [Mn(5-NO2-bdc)(bbim)]n (2) and {[Gd(5-NO2-bdc)(5-NO2-bdcH)](bpyo)0.5·2H2O}n (3) (5-NO2-bdcH2 = 5-nitro-1,3-benzenedicarboxylic acid; bpyo = 4,4′-bipyridine-N,N′-dioxide; bbim = 1,1′-(1,4-butanediyl)bis(benzimidazole)), were obtained under hydrothermal conditions and characterized structurally. The networks exhibit a variety of topologies and coordination modes at the metal centers. Complex 1 exhibits NaCl-type topology and contains the centrosymmetric trinuclear cluster SBU [Cd3(COO)4O2]. Complex 2 adopts CsCl-type topology based on bimetallic cores and is the first example of compounds containing a cis bbim bridge. Moreover, complex 3 possesses a 3D supramolecular framework by stronger contacts between 2D layers and non-rigid bpyo bridges. The thermal stabilities of 1–3, the photoluminescence properties of 1 as well as the photocatalytic performance of 3 were also examined, and the results indicated that 1 seems to be a good candidate for novel hybrid inorganic–organic photoactive materials, especially, compound 3 represents the rare example of coordination polymers with a 4f metal ion that exhibit good photocatalytic activity for dye degradation under UV light.

Two 1D inorganic–organic hybrid frameworks, namely, [Zn(5-NO2-bdc)(MIM)3·H2O]n(1) and [Cd(MIM)2Br2]n(2) (5-NO2-bdcH2 = 5-nitro-1,3-benzenedicarboxylic acid, MIM = N-methyl imidazole) were synthesized via ionothermal reactions with ionic liquid 1-ethyl-3-methylimidazolium bromide ([EMIM]Br) as solvent and template. Both compounds have been characterized by elemental analyses, spectroscopic analyses, thermogravimetric analysis (TGA) and the single crystal diffraction. The zinc(II) center in compound 1 is a slightly distorted five-coordinate trigonal bipyramid, 5-NO2-bdc2− anions and MIM moieties effectively bridge Zn centers to result in 1D zigzag chains. While Cd(II) center in compound 2 is in an octahedral coordination environment, and two μ2-bridge bromine link two [Cd(MIM)2] moieties to form a 1D chain structure. In addition, complex 2 exhibits strong fluorescent emission in the solid state at room temperature.

Two novel inorganic–organic hybrid frameworks of [Co(2,5-pydc)(4,4′-bipyo)0.5(H2O)3 · 3H2O]n (1) and [Cu1.5Gd(2,5-pydc)3(2,2′-bipyo)(H2O)4 · 2H2O]n (2) (2,5-pydc = pyridine-2,5-dicarboxylic acid; 4,4′-bipyo = 4,4′-bipyridine-N,N′-dioxide; 2,2′-bipyo = 2,2′-bipyridine-N,N′-dioxide) were prepared. Both compounds have been characterized by the elemental analyses, IR spectra, TG analysis and the single crystal diffraction. The salient structural feature for both compounds 1 and 2 is that the 1D chain and the mononuclear fragment are connected by strong hydrogen bond interactions to form 2D structure.

A three-dimensional microporous framework, Zn(II)–MOF [Zn(HPyImDC)(DMA)]n (1) (H3PyImDC = 2-(pyridine-4-yl)-1H-4,5-imidazoledicarboxylic, DMA = N,N′-dimethylacetamide), with open metal sites and small-sized pores, exhibits excellent selective capture of CO2 over N2 and CH4 at 273 K, as well as alcohols from water. The excellent CO2 adsorption selectivity of 1 allows its potential use in the capture of CO2 from industrial flue gas or the removal of CO2 from natural gas. More interestingly, compound 1 represents the rare case of porous materials separating propanol isomers, which may be caused by the relative flexibility of the linear n-propanol considering that both n-propanol and i-propanol have similar kinetic diameters.

A Cd(II)–MOF [Cd(L)(DMF)] (1) (H2L = 5-(4-pyridyl)-isophthalic acid) featuring high thermal and chemical stability has been solvothermally synthesized and characterized. Complex 1 is a robust multifunctional three-dimensional (3D) microporous framework possessing an unusual (4,5)-connected topological net. Activated 1 shows high-efficiency for the selective capture of CO2 over N2 and CH4 under ambient conditions, which ranks it among MOFs with the highest selectivity. In addition, desolvated 1 exhibits good separation ratios of H2 over N2 at lower temperature, as well as alcohols from water. In particular, desolvated 1 demonstrates significantly higher adsorption enthalpies for CO2 and CH4 gas molecules, which are in the range of the highest Qst values reported to date. Furthermore, complex 1 displays visible photoluminescence in the solid state under UV irradiation.

Solvothermal reactions of 2,5-thiophenedicarboxylate (H2tdc) and N-auxiliary ligands in the presence of cobalt(II), zinc(II) and cadmium(II) salts have given rise to seven new metal–organic frameworks, namely, [Co2(tdc)2(bpp)2(H2O)·(H2O)]n (bpp = 1,3-bis(4-pyridyl)propane) (1), [Cd(tdc)(bpp)(H2O)·(H2O)2]n (2), [Zn2(tdc)2(bbi)2·(H2O)2]n (bbi = 1,1′-(1,4-butanediyl)bis(imidazole)) (3), [Co4(tdc)3(bimb)4(H2O)5·(tdc)·(DMF)·(H2O)2]n (bimb = 4,4′-bis(1-imidazolyl)biphenyl) (4), [Zn4(O)(tdc)3(bimb)4·(H2O)5.25·(CH3OH)]n (5), [Cd4(tdc)4(bimb)6·(H2O)2·(CH3OH)2·(DMF)4] (6) and [Co2(tdc)2(tib)2·(H2tdc)·(DMF)2] (tib = 1,3,5-tris(1-imidazolyl)benzene) (7), which exhibit structural diversity. Compounds 1–3 display 3D 2-fold interpenetrating 8-connected tsi net, 2D 4-connected sql net, and 3D 5-fold interpenetrating 4-connected dia net, respectively; while compound 4 features an extremely rare 3D 7-connected hxg-d cationic net and compound 5 adopts a 3D trinodal (4,4,6)-connected net with a new topology structure. For compounds 6 and 7, the topology in the structures were determined as 3D 3-fold interpenetrating 5-connected bnn net and 3D 2-fold interpenetrating binodal (3,5)-connected net, respectively. In the solid state, complexes 1, 4 and 5 exhibit nonlinear optical properties, and complex 5 has also been evaluated as a promising visible-light-driven photocatalyst for degradation of organic pollutants. The magnetic investigation of complexes 1 and 4 shows that there exists spin-canted antiferromagnetism for 1, whereas strong antiferromagnetic interaction and/or the depopulation of the higher energy Kramers doublets of the Co(II) centers are dominant in 4.

Six new metal–organic frameworks [Cu(obba)(bimb)·(obbaH2)]n (1), [Cu(obba)(bimb)]n (2), [Zn2(obba)2(bimb)2(DMF)2(H2O)3.5]n (3), [Ni3(2,2′,4,4′-bptcH)2(bimb)2(H2O)2·(H2O)2]n (4), [Ni2(bimb)3(H2O)6·(aobtc)·(DMF)2·(H2O)2]n (5) and [Cd(3,3′,4,4′-bptcH2)(H2O)·(bimb)]n (6), were obtained by reactions of 4,4′-bis(1-imidazolyl)biphenyl (bimb) and multi-carboxylic acids of 4,4′-oxybis(benzoic acid) (obbaH2), 2,2′,4,4′-biphenyltetracarboxylate acid (2,2′,4,4′-bptcH4), azoxybenzene-3,3′,5,5′-tetracarboxylic acid (aobtcH4), and 3,3′,4,4′-biphenyltetracarboxylate acid (3,3′,4,4′-bptcH4) with corresponding metal salts under hydro/solvothermal conditions, respectively. Complexes 1–3 have entangled structures with different topologies: 1 is a 3-fold interpenetrating NbO three-dimensional (3D) network; 2 is a 3-fold interpenetrating dmp 3D net; 3 is a 6-fold interpenetrating dia 3D chiral net containing rare 1D helical chains with the same handedness. Complex 4 is an uninodal 6-connected network with a Schäfli symbol of (486483) based on the trinuclear Ni(II) subunits, while complexes 5 and 6 are 1D chains. Interestingly, compound 6 represents the rare example of MOFs that exhibit high photocatalytic activity for dye degradation under visible light and shows good stability towards photocatalysis. Complexes 3 and 6 exhibit intense blue emissions in the solid state at room temperature whereas 3 appears to be a good candidate of novel hybrid inorganic–organic NLO material.

Solvothermal reactions of 5-(4-pyridyl)-isophthalic acid (H2pbdc) and transition-metal centers (Ni2+/Co2+/Zn2+) in the presence (or absence) of N-auxiliary 4,4′-bis(1-imidazolyl)biphenyl (bimb) ligand produce [Ni2(pbdc)2(μ2-H2O)(H2O)2·(DMA)2.7]n (DMA = N,N′-dimethylacetamide, 1), [Ni12(pbdc)12(μ2-H2O)6(py)2(H2O)8(DMA)2·(H2O)5·(DMA)9]n (2), [Co2(pbdc)2(bimb)2·(bimb)0.5·(H2O)4·(DMF)0.25]n (3) and [Zn(pbdc)(bimb)·(H2O)]n (4), which exhibit structural diversity. Both compounds 1 and 2 display a uninodal 8-connected 3D tsi net, but feature different crystal systems and space groups from each other. Compound 3 adopts a 2-fold interpenetrating binodal (3,5)-connected 3D hms net and compound 4 features a rare 2-fold interpenetrating binodal (3,4)-connected 3D fsx architecture. In particular, activated 3 shows high-efficiency for the selective sorption of small molecules, including CO2 over N2 and CH4, H2 over N2, as well as alcohols from water. More importantly, 4 represents the first report on a MOF as a promising luminescent probe for detecting pesticides, and also the very first example for detecting both pesticides and solvent molecules simultaneously.

Solvothermal reactions of 2-amino-1,4-benzene dicarboxylic acid (NH2bdcH2) and N-auxiliary ligands in the presence of manganese(II), zinc(II) and cobalt(II) salts have given rise to four new metal–organic frameworks, namely, [Mn5(NH2bdc)5(bimb)5·(H2O)0.5]n (bimb = 4,4′-bis(1-imidazolyl)biphenyl) (1), [Zn(NH2bdc)(bix)·(DMF)2]n (bix = 1,4-bis(imidazol-1-ylmethyl)benzene) (2), [Co(NH2bdc)(bix)·(DMF)·(CH3CH2OH)]n (3) and [Co(NH2bdc)(bpp)]n (4) (bpp = 1,3-bis(4-pyridyl)propane). Single-crystal X-ray diffraction analyses revealed that MOF 1 displays 5-fold interpenetrating 4-connected dia 3D net; MOFs 2 and 3 are isomorphic, which possess 3-fold interpenetrating dia 3D nets; MOF 4 exhibits 4-connected sql 2D net. Noncentrosymmetric structures and multifunctionality in 1–3 are established by varying ligands and metal centers. In the solid state, polar MOFs 1–3 exhibit nonlinear-optic (NLO) and MOF 1 demonstrates typical ferroelectric behaviour with a remnant electric polarization (Pr) of 1.2 μC cm−2 and an electric coercive field (Ec) of 0.35 kV cm−1. In addition, MOF 2 could be a potential luminescent probe for detecting nitrobenzene or 2-nitrotoluene via fluorescence enhancement and has been evaluated as a promising visible-light-driven photocatalyst for degradation of organic pollutants.