As a kind of MOFs, cage-based MOFs usually carry large voids and small windows, which are advantageous to the storage of small molecules that remain kinetically trapped inside the cages (confinement effect). By adjusting the size of windows via reticular synthesis, the cage-based MOFs can selectively capture and separate the suitable size molecules. Here, considering angle-directed and face-directed strategies, a novel multicage-based MOF NUM-3 with a new (3,4,5)-connected topology was successfully constructed in the mixed-ligands assembly. In the framework of NUM-3, there exist four different kinds of cages, which exhibit diverse polyhedral configurations. The four kinds of cages in the order ABCDDCBA as the minimum repeat unit form a 1D tortuous channel along the c axis. Based on the structure characteristics that the 1D channel exhibits different inner diameter (from 4.0 to13.0 Å), NUM-3a (actived NUM-3) can capture CO2 over C2H4 and C2H6 by the size selectivity (the empirical kinetic diameters: CO2 < C2H4 < C2H6). In addition, it also exhibits commendable selectivity for CO2 over N2 and CH4.Keywords: angle-directed and face-directed strategies; carbon dioxide capture; mixed-ligands assembly; multicage-based metal−organic framework; tortuous channel;

Based on the same in situ formed ligand, two new MOFs, namely {[Zn2(HL)2]·0.5DMF·H2O}n (1) and {[Cd2(HL)2]·1.5H2O}n (2) (H3L = 5-[(2H-tetrazol-5-yl)amino]isophthalic acid), have been solvothermally synthesized and structurally characterized by elemental analysis, IR, PXRD, and single-crystal X-ray diffraction. During the self-assembly process, the original ligand H2ATBDC (5-(5-amino-1H-tetrazol-1-yl)-1,3-benzenedicarboxylic acid) undergoes the Dimroth rearrangement to form a new ligand H3L, consequently contributing to the construction of the two new MOFs. Structural analysis reveals that both 1 and 2 possess a three-directional intersecting channel system and pts topology. The major structural difference between them is the metal coordination, which displays four- and six-coordinated modes in 1 and 2, respectively, and results in diverse channels and different stabilities. Moreover, the adsorption properties of 1a (i.e., the desolvated 1) have been studied, and the results show that 1a possesses moderate capability of gas sorption for N2, CO2, and CH4 gases, along with high selectivity ratios of 102 and 20 for CO2/N2 (15 : 85) and CO2/CH4 (50 : 50) at 273 K, respectively.

Aluminum ions are harmful to human health and can damage the central nervous system leading to brain cell injury in excessive amounts. Hence, sensing and detection of Al3+ ions are important and require a method with high sensitivity and high selectivity. Here, a metal–organic framework {[Zn2(O-BTC)(4,4′-BPY)0.5(H2O)3]·(H2O)1.5·(DMA)0.5}n (NUM-2) was constructed by ligands 2-hydroxy-benzene-l,3,5-tricarboxylic acid (HO-H3BTC) and 4,4′-bipyridine (4,4′-BPY) based upon chain-shaped secondary building units (SBUs). NUM-2 itself exhibits extremely weak fluorescence emission, however, the luminescence intensity of NUM-2 is enhanced obviously when there are Al3+ ions in ethanol solutions, and the detection limit calculated using 3σ/k could reach 0.10 ppm, indicating that NUM-2 could be used as an efficient turn-on-based fluorescent sensor with high sensitivity and high selectivity for Al3+ ions.

Metal–organic frameworks (MOFs) constructed with metal ions/clusters and organic ligands have emerged as an important family of porous materials for various applications. However, the stability of this class of materials is crucial for their practical applications, which might be improved by varying their chemical composition and/or structurally tuning them. To fabricate MOFs with high stability, several strategies for enhancing the stability of MOFs have been developed, in which the strength of metal–ligand bonds is especially considered: the use of highly charged cations and higher pKa ligands, and varying the chemical functionality of linkers. On the other hand, the regulation of their structural architectures is also investigated: interpenetrated frameworks, multi-walled frameworks, and self-strengthening of the frameworks. In addition, the surface modification can also improve the stability of the materials. In this review, we introduce and summarize these strategies from the viewpoint of structural tuning and component choosing, providing useful instructions for the further design and synthesis of MOFs with high-level stability.

•A porous fluorescence Zn-MOF had been prepared by zwitterionic H3LCl ligand.•The MOF could sense Fe3 + ions with high sensitivity and excellent regeneration.•MOF-based sensors with such high recycle performance have not yet been reported.A new 3D luminescence metal–organic framework with open channels was constructed by the assembling of the zwitterionic H3LCl ligand and Zn(II) ions under solvothermal conditions. The compound exhibits relatively high luminescence selective sensing for Fe3 + ions with surprisingly excellent recyclability, making it a promising candidate for sensing metal ions in practical.A new 3D luminescence metal–organic framework with open channels was constructed by the assembling of the zwitterionic H3LCl ligand and Zn(II) ions under solvothermal conditions. The compound exhibits relatively high luminescence selective sensing for Fe3 + ions with excellent recyclability, making it a promising candidate as a fluorescent probe for Fe3 + ions in the field of detection application.

A microporous luminescent metal-organic framework [Zn4L2(H2O)2]·(H2O)m(DMA)n (1) (H4L=5,5′-((1H-pyrazole-3,5-dicarbonyl) bis(azanediyl))diisophthalic acid, DMA=N,N-dimethylacetamide) was synthesized and characterized by infrared radiation (IR), thermogravimetric analyses (TGA), powder X-ray diffraction spectra (PXRD) and X-ray diffraction. Complex 1 has a three dimensional (3D) framework, which can be simplified as 5,5,5,5-c net with the Schläfi symbol of {43.64.83} {44.65.8}{45.65}2. This luminescent metal-organic framework (MOF) shows selectively sensitive to nitrobenzene and series of nitroaromatic explosives such as 4-nitrotoluene, 1,4-dinitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene, and exhibits well recyclability. So complex 1 could be used to detect nitroaromatic explosives as a selective sensing material.

Isostructural CoII and MnII organic frameworks with anionic frameworks and counterions (Me2NH2)+, namely {[M2Cl2(BTC)4/3]·(Me2NH2)+2·4/3H2O}n (M = Co (1) and Mn (2)), have been constructed by one-pot synthesis. Complexes 1 and 2 take paddle-wheel-like dinuclear metal cluster-based three-dimensional structures. Thermogravimetric analysis and variable-temperature powder X-ray diffraction spectra suggested that 1 displays better thermal stability than 2. Both exhibit relatively high proton conductivities at 65% relative humidity (RH) and room temperature (σ > 2.5 × 10–4 S cm–1); however, complex 1 possesses the better cycling capability and stability with Ea = 0.21 eV under 65% RH.

Two microporous MOFs have been constructed from different metal cluster SBUs. Both of them exhibit highly selective CO2 adsorption capacity over CH4 and N2 owing to their abundant active sites.

Two highly porous metal–organic frameworks are successfully constructed through the assembling of Co/Ni ions and mixed ligands. From the contribution of the uncoordinated tetrazolate N atoms of the ligand the two complexes show high CO2 adsorption capacities, serving as potential CO2 adsorption materials.

The reaction of polydentate ligand Bis-tris propane {(CH2OH)3CNH(CH2)3NHC(CH2OH)3} with Ln(NO3)3·6H2O and Fe3O precursor resulted in the formation of a series of Fe6Ln2 nanoclusters. Magnetic measurements indicate that the Fe6 core exhibits ferrimagnetic behavior, and slow magnetic relaxation was observed in Fe6Dy2 and Fe6Tb2.

An in situ doping strategy was successfully applied to tune the magnetic behaviour and induce fluorescence signal mutation of a spindle heptanuclear zinc cluster-based MOF, by only modifying its structural composition. The CoII-doped ZnII-MTV-M′MOF exhibits canted antiferromagnetism and weaker fluorescence properties.

Two CuII-based MOFs have been constructed by synergistic assembly involving the mixed-ligand synthetic strategy and the solvent effect. Compound 1 is a 3D structure and represents a cds topology, while compound 2 displays a rare structure built by three distinct {Cu4} clusters as SBUs. Moreover, the magnetic properties of 2 have been thoroughly investigated.

Two new metal–drug complexes constructed from non-toxic zinc and theophylline (TPL), an anti-asthmatic active drug, have been introduced into a release system based on matrices of hydroxypropylmethylcellulose (HPMC) and microcrystalline cellulose (MC). The release rate of TPL from the metal–drug complexes could be controlled by the amount of MC added, and the release mechanism changed from anomalous transport to Fickian diffusion.

A 1D polyoxometalate chain has been constructed from a {Mo16Ni16P24} cluster linked by two {NiO6} edge-shared octahedrons. This chained molybdenum nickel phosphate, Na2[Ni(H2O)8][Ni2(H2O)6][(Mo16O32)Ni16(OH)8(H2PO4)4(HPO4)16(PO4)4(H2O)8]·14H2O (1), crystallizes under hydrothermal reaction and in the monoclinic space group C2/m. In the chain of 1, another {NiO8} polyhedron is capsulated in the {Mo16Ni16P24} wheel. Magnetism analysis shows that there are antiferromagnetic interactions in 1.A 1D polyoxometalate chain Na2[Ni(H2O)8][Ni2(H2O)6][(Mo16O32)Ni16(OH)8(H2PO4)4(HPO4)16(PO4)4(H2O)8]·14H2O constructed from a {Mo16Ni16P24} cluster has been synthesized under hydrothermal conditions. The magnetic studies reveal that antiferromagnetic interactions exist in the chain.Highlights► A 1D polyoxometalate chain has been constructed from a {Mo16Ni16P24} cluster. ► In the chain, another {NiO8} polyhedron is capsulated in the {Mo16Ni16P24} wheel. ► The magnetic properties of the reported compound have been investigated.

In our efforts to construct new metal–organic frameworks (MOFs) by template-directing method, a new cadmium oxalate, [Co(NH3)6]2[Cd8(C2O4)11(H2O)4]·8H2O (denoted HNU-1), has been synthesized under hydrothermal condition in the presence of Co(NH3)6Cl3. The crystal structure of HNU-1 was determined by single-crystal X-ray diffraction (monoclinic, C2/c), a = 11.126(2) Å, b = 17.361(4) Å, c = 16.119(3) Å, β = 102.40(3)°, V = 3040.8(10) Å3 and Z = 8. The open framework of HNU-1 contains 12-ring channels and exhibits a 5-connected sqp topological network with dinuclear Cd(II) clusters acting as nodes. The Co(NH3)63+ cations and unusual hydrogen-bonded (H2O)4 clusters are found in the 12-ring channels with an alternative arrangement. It is believed that the (H2O)4 clusters play a co-templating role in the crystallization of HNU-1.A novel metal–organic cadmium oxalate compound has been hydrothermally synthesized. Its open-framework presents a 5-connected sqp topology based on dinuclear Cd cluster, with a unique hydrogen-bonded (H2O)4 cluster and Co(NH3)63+ cations alternately arranged inside the 12-ring channels as co-template.

Three new cobalt complexes, {[Co5(tci)2(bimb)3(µ3-O)2(H2O)2]·3DMF·4H2O}n (1), {[Co3(tci)2(bib)]·2DMF·2H2O}n (2) and {[Co(Htci)(bpea)0.5]·H2O}n (3) (H3tci = tris(2-carboxyethyl)isocyanurate, bimb = 4,4′-bis(imidazol-1-yl)biphenyl, bib = 1,4-bis(imidazol-1-yl)benzene, bpea = 1,2-bis(4-pyridyl)ethane, DMF = N,N′-dimethylformamide), have been successfully synthesized through the assembly of Co(II) ions, H3tci and different N-donor ligands, respectively. All complexes were structurally characterized by single crystal X-ray diffraction, elemental analyses, IR spectra, thermogravimetric (TG) analyses and X-ray powder diffraction (XRPD). Complex 1 exhibits a 3D three-fold parallel interpenetrated 3D → 3D structure with (65·8) CdSO4 topology. Complex 2 is built from [Co3(µ2-Ocarboxyl)2(CO2)4] clusters and linear bib ligands, displaying a two-fold parallel interpenetrated (3,8)-connected (43)2(46·618·84) topology, while complex 3 is a 3D pillar-layered structure involving an infinite -Co-(µ2-Ocarboxyl)(CO2)-Co-chain. The diverse structures of the three complexes indicate that the skeletons of different N-donor ligands play an important role in the assembly of such different frameworks. In addition, magnetic investigation indicates that besides spin-orbit coupling of Co(II) ions, there exist antiferromagnetic exchange interactions in Co5 and Co3 clusters of 1 and 2, respectively.

Two new CoII coordination polymers with a pyridinedicarboxylate ligand, {[Co(L)(H2O)]·H2O}n (1) and [Co3(HCOO)2(L)2(H2O)2]n (2) (H2L = 5-(pyridin-4-yl)isophthalic acid), have been synthesized and structurally characterized by elemental analysis, IR, XRPD, and single-crystal X-ray diffraction. Structure analyses show that complex 1 has a two-dimensional (2D) double-layered structure with a (3,6)-connected kgd topology based on [Co2O2] units, while complex 2 takes a three-dimensional (3D) structure with (3,6)-connected rtl topology network based on linear [Co3(HCOO)2(CO2)4] clusters with triple carboxylate bridges. Magnetic investigation indicates that besides strong spin–orbit coupling of CoII ions, ferromagnetic and weak ferromagnetic exchange interactions between CoII ions in the Co2 and Co3 clusters exist in 1 and 2, respectively. The FC/ZFC magnetization behaviors for both of them suggest the absence of any long-range magnetic ordering.

Two series of lanthanide metal–organic frameworks, [Ln(FDA)(OX)0.5(H2O)2]·(H2O) (1Ln) (Ln = Pr 1, Nd 2, Eu 3, Gd 4, Tb 5), [Ln(FDA)(OX)0.5(H2O)2]·(H2O) (2Ln) (Ln = Sm 6, Tb 7, Dy 8, Ho 9, Yb 10) (OX = oxalate), have been prepared by reacting Ln(NO3)3·6H2O with furan-2,5-dicarboxylic acid (H2FDA) at different temperatures under hydrothermal conditions. All the complexes are characterized by elemental analysis, IR, X-ray powder diffraction, and single-crystal X-ray diffraction. Structure analyses show that 1Ln and 2Ln are supramolecular isomerisms. 1Ln possesses a three-dimensional network with monoclinic space group P21/c, whereas 2Ln exhibits a three-dimensional framework with monoclinic space group C2/c. The distinct architectures of these two series of ten complexes indicated that the reaction temperature plays an important role in the formation of such coordination structures. Meanwhile, the photoluminescent properties of 4, 5, 7, and 8 are also investigated in the solid state at room temperature.

In our efforts to investigate the influence of the backbone of different triazole-based bridging ligands on the structure of their metal complexes, four new coordination polymers, {[Cu(L1)2(H2O)2]Cl2}n (1), [Cu(L2)2Cl2]n (2), [Co(L2)2(SCN)2]n (3), and [Cu(L3)2(NO3)2]n (4), (L1 = 1,2-bis(triazol-1-ylmethyl)benzene, L2 = 1,3-bis(triazol-1-ylmethyl)benzene, L3 = 1,4-bis(triazol-1-ylmethyl)benzene), have been synthesized. All the complexes have been structurally characterized by IR, elemental analysis and single-crystal X-ray diffraction. Structural analyses show that 1 and 4 possess 2D coordination networks with (4,4) topology, and 1 shows a diagonal–diagonal inclined interpenetration. 2 and 3 are isostructural and feature 1D double chain, which further connected by C–H···Cl or π···π weak interactions to form 2D supramolecular frameworks. The results show that the structures of ligands (with different non-coordination backbone spacers) play important roles in the formation of such coordination architectures. Furthermore, EPR (Electron Paramagnetic Resonance) spectra of CuII complexes (1, 2, and 4) have been investigated in the solid state at room temperature.Highlights► The effect of ligands’ structures [o-, m-, p-] has been studied in this work. ► EPR spectra of all CuII complexes have been investigated in detail. ► One rare diagonal–diagonal inclined interpenetration structure had been obtained.

Aiming at exploring the effect of substituting groups of three structurally related ligands, 5,6-diethyl-pyrazine-2,3-dicarboxylic acid (H2L1), 5,6-diphenyl-pyrazine-2,3-dicarboxylic acid (H2L2), and dibenzo[f,h]quinoxaline-2,3-dicarboxylic acid (H2L3), seven new coordination polymers constructed from these three substituted dicarboxylate ligands, {[Zn(L1)(H2O)3]·2H2O}∞ (1), {[Cd2(L2ʹ)4(H2O)]·3H2O}∞ (2), [Zn(L2)(CH3OH)]∞ (3), {[Zn(L2)(H2O)2]·H2O}∞ (4), {[Zn(L2ʹ)]·H2O}∞ (5), [Zn2(L3)(DMF)4]∞(6), [Zn(L3)(2,2ʹ-bipy)(H2O)]∞(7), have been prepared and structurally characterized. 1 is a 1D chain structure in which ZnII ion is six-coordinated with octahedron geometry. 2 is also a 1D chain structure in which there are two crystallographically independent CdII ions in the asymmetric unit and exist transformative L2ʹ ligands in the resulting complex. 3 and 4 both possess 2D layer network with the same (4, 82) topology, while the two complexes take different coordination modes during the forming of the compounds. 5 has a 1D chain structure based on the transformative L2ʹ ligand in which ZnII ion is five-coordinated with bipyramidal geometry. 6 and 7 both have 1D chain structure constructed from L3 ligand. Thereinto, ZnII ion in 6 is five-coordinated by three oxygen atoms from two individual L3 ligands and two oxygen atoms from two DMF molecules. While in 7 there are also five coordination sites occupied by two carboxylate oxygen atoms from two L3 ligands. In addition, the compounds are characterized by elemental analysis, IR spectra. The luminescent properties of the compounds are also discussed and exhibit strong fluorescent emissions in the solid state.Graphical abstractHighlights► Research on the coordination chemistry of related pyrazine-dicarboxylate ligands. ► Seven new ZnII and CdII coordination complexes have been obtained. ► The strong fluorescent properties of seven compounds are discussed.

Two new metal-organic frameworks, {[CuLI]·CHCl3}∞(1) and {[HgL(Br)2]4·2CH2Cl2}∞ (2) have been prepared by reacting CuI and HgBr2 with the new flexible ligand L [L = 2,3-Bis(benzimidazol-1-ylmethyl)quinoxaline]. Both complexes have been characterized by elemental analysis, IR, TGA, XRPD, and single crystal X-ray diffraction determination. In 1, the Cu(I) ion takes tetrahedral coordination geometry, and the flexible ligands bridge dinuclear units (Cu2I2) to form a one dimensional (1D) double chain structure. While in 2, the Hg(II) coordinates to two bromine ions and two nitrogen donors of L to form a 1D coordination polymer. The structure differences of the two complexes mainly depend on the geometry of the metal ions and the influence of anions. The coordination features of the ligand have also been primarily investigated by density functional theory (DFT) calculations. In addition, the fluorescent properties of the complexes and free ligand L have been investigated in the solid state at room temperature.

Four Ag(I) coordination complexes formulated as {[Ag(L1)(ClO4)]}n (1), {[Ag(L1)(NO3)]}n (2), {[Ag(L1)(PF6)]}2 (3) and {[Ag(L2)](ClO4)·CH3OH}n (4), (L1 = 3,6-bis(1-pyrazolyl)pyridazine, L2 = 3,6-bis(3,5-dimethyl-1-pyrazolyl)pyridazine) have been synthesized in the presence of different anions [ClO4− (1) and (4), NO3− (2), PF6− (3)] and structurally characterized by FT-IR spectra, elemental analysis and X-ray diffraction. Studies of X-ray diffraction reveal that complexes 1, 2 and 4 show infinite helical chains, which are the alternate left- and right-handed helical chains. Furthermore, helical chains are arranged to 2D sheet via C–H⋯O (from anion O atoms) hydrogen bonds. As the anion changed to PF6−, a dinuclear molecule is formed in complex 3, further constructing a 2D sheets by C–H⋯F hydrogen bonds. The photoluminescence properties of all the complexes 1–4 have been investigated in the solid state at room temperature.

Two new Silver(I) complexes, {[AgL]·(H2O)2}n (1, HL = acridine-9-carboxylic acid) and {[Ag(L)(4,4′-bipy)]·(H2O)5}n (2), has been synthesized and characterized by elemental analysis, IR, and single-crystal X-ray diffraction analysis. Ag(I) ion in complex 1 is coordinated by L as a bridging ligand with its acridine N donor and bidentate chelating carboxylate group forming a 1D chain. Different from 1, complex 2 adopts a 1D chain structure with 4,4′-bipy as a bridging ligand. In 2, L coordinates to Ag(I) ion as a terminal ligand by its carboxylate group in a bidentate chelating mode similar to that in 1, leaving N donor as a H-bond acceptor. It is worth noting that in 1 C–H⋯Ag weak interactions are observed, and these weak interactions are also elucidated by theoretical investigation of TD-DFT (B3LYP) methods and NBO analysis. Furthermore, the photoluminescence properties of 1 and 2 are also investigated in the solid state at room temperature, and the theoretical calculations of the absorption and emission spectra of 1 were carried out with B3LYP method on the basis of the experimental structure.

An in situ doping strategy was successfully applied to tune the magnetic behaviour and induce fluorescence signal mutation of a spindle heptanuclear zinc cluster-based MOF, by only modifying its structural composition. The CoII-doped ZnII-MTV-M′MOF exhibits canted antiferromagnetism and weaker fluorescence properties.

Two CuII-based MOFs have been constructed by synergistic assembly involving the mixed-ligand synthetic strategy and the solvent effect. Compound 1 is a 3D structure and represents a cds topology, while compound 2 displays a rare structure built by three distinct {Cu4} clusters as SBUs. Moreover, the magnetic properties of 2 have been thoroughly investigated.

A family of Fe12Ln4 clusters based on thiophene-3-carboxylic acid (3-TCA) or 3-methoxybenzoic acid (m-MOBA) were synthesized with a step-by-step strategy, namely [Fe12Ln4(μ4-O)6(μ3-O)4(μ3-OH)4(3-TCA)24] (Ln = La (1), Gd (3) and Dy (4)), {[Fe24Sm8(μ4-O)12(μ3-O)8(μ3-OH)8(3-TCA)46(NO3)2]·4CH3CN} (2), [Fe12La4(μ4-O)6(μ3-O)4(μ3-OH)4(m-MOBA)24] (5) and {[Fe12Sm4(μ4-O)6(μ3-O)4(μ3-OH)4(m-MOBA)24]·4CH3CN} (6). For each of the six complexes, two Fe4O2(OH)2 cubane units “sandwich” four FeIII centers to form Fe12O10(OH)4, and it is further connected to four LnIII ions through six μ4-O2− bridges to obtain a Fe12Ln4 core. Magnetic analyses indicate that 1–6 show different magnetic properties, and 2 and 6 show SMM-like behaviors, due to the differences in lanthanide ions and aromatic monocarboxylate ligands. Note that SmIII-containing 3d–4f clusters exhibiting SMM-like behavior are still rare in the documented cases.

Based on the same in situ formed ligand, two new MOFs, namely {[Zn2(HL)2]·0.5DMF·H2O}n (1) and {[Cd2(HL)2]·1.5H2O}n (2) (H3L = 5-[(2H-tetrazol-5-yl)amino]isophthalic acid), have been solvothermally synthesized and structurally characterized by elemental analysis, IR, PXRD, and single-crystal X-ray diffraction. During the self-assembly process, the original ligand H2ATBDC (5-(5-amino-1H-tetrazol-1-yl)-1,3-benzenedicarboxylic acid) undergoes the Dimroth rearrangement to form a new ligand H3L, consequently contributing to the construction of the two new MOFs. Structural analysis reveals that both 1 and 2 possess a three-directional intersecting channel system and pts topology. The major structural difference between them is the metal coordination, which displays four- and six-coordinated modes in 1 and 2, respectively, and results in diverse channels and different stabilities. Moreover, the adsorption properties of 1a (i.e., the desolvated 1) have been studied, and the results show that 1a possesses moderate capability of gas sorption for N2, CO2, and CH4 gases, along with high selectivity ratios of 102 and 20 for CO2/N2 (15:85) and CO2/CH4 (50:50) at 273 K, respectively.

Aluminum ions are harmful to human health and can damage the central nervous system leading to brain cell injury in excessive amounts. Hence, sensing and detection of Al3+ ions are important and require a method with high sensitivity and high selectivity. Here, a metal–organic framework {[Zn2(O-BTC)(4,4′-BPY)0.5(H2O)3]·(H2O)1.5·(DMA)0.5}n (NUM-2) was constructed by ligands 2-hydroxy-benzene-l,3,5-tricarboxylic acid (HO-H3BTC) and 4,4′-bipyridine (4,4′-BPY) based upon chain-shaped secondary building units (SBUs). NUM-2 itself exhibits extremely weak fluorescence emission, however, the luminescence intensity of NUM-2 is enhanced obviously when there are Al3+ ions in ethanol solutions, and the detection limit calculated using 3σ/k could reach 0.10 ppm, indicating that NUM-2 could be used as an efficient turn-on-based fluorescent sensor with high sensitivity and high selectivity for Al3+ ions.

Metal–organic frameworks (MOFs) constructed with metal ions/clusters and organic ligands have emerged as an important family of porous materials for various applications. However, the stability of this class of materials is crucial for their practical applications, which might be improved by varying their chemical composition and/or structurally tuning them. To fabricate MOFs with high stability, several strategies for enhancing the stability of MOFs have been developed, in which the strength of metal–ligand bonds is especially considered: the use of highly charged cations and higher pKa ligands, and varying the chemical functionality of linkers. On the other hand, the regulation of their structural architectures is also investigated: interpenetrated frameworks, multi-walled frameworks, and self-strengthening of the frameworks. In addition, the surface modification can also improve the stability of the materials. In this review, we introduce and summarize these strategies from the viewpoint of structural tuning and component choosing, providing useful instructions for the further design and synthesis of MOFs with high-level stability.

Two microporous MOFs have been constructed from different metal cluster SBUs. Both of them exhibit highly selective CO2 adsorption capacity over CH4 and N2 owing to their abundant active sites.

Two new CoII coordination polymers with a pyridinedicarboxylate ligand, {[Co(L)(H2O)]·H2O}n (1) and [Co3(HCOO)2(L)2(H2O)2]n (2) (H2L = 5-(pyridin-4-yl)isophthalic acid), have been synthesized and structurally characterized by elemental analysis, IR, XRPD, and single-crystal X-ray diffraction. Structure analyses show that complex 1 has a two-dimensional (2D) double-layered structure with a (3,6)-connected kgd topology based on [Co2O2] units, while complex 2 takes a three-dimensional (3D) structure with (3,6)-connected rtl topology network based on linear [Co3(HCOO)2(CO2)4] clusters with triple carboxylate bridges. Magnetic investigation indicates that besides strong spin–orbit coupling of CoII ions, ferromagnetic and weak ferromagnetic exchange interactions between CoII ions in the Co2 and Co3 clusters exist in 1 and 2, respectively. The FC/ZFC magnetization behaviors for both of them suggest the absence of any long-range magnetic ordering.

Two new metal–drug complexes constructed from non-toxic zinc and theophylline (TPL), an anti-asthmatic active drug, have been introduced into a release system based on matrices of hydroxypropylmethylcellulose (HPMC) and microcrystalline cellulose (MC). The release rate of TPL from the metal–drug complexes could be controlled by the amount of MC added, and the release mechanism changed from anomalous transport to Fickian diffusion.