Owing to the potential applications in catalysis, analytical chemistry, ion exchange, magnetism, biological chemistry and medicine, tremendous effort has been dedicated to exploring polyoxometalate (POM) chemistry. Chiral POM-based materials are particularly attractive due to the combination of the advantage of POMs with the importance of chirality. Nearly 100 chiral POM-based compounds were reported, which were mainly used as asymmetric catalysts, molecular recognition and nonlinear optical materials. In addition, the chirality within POM systems has attracted the attention of theoretical chemists and research was carried out to explore the origin of chirality by density functional theoretical methods. In this review, we summarize the developments of chiral POM-based materials, including their synthetic strategies, calculations on the origin of chirality and the relevant applications.Graphical abstractChiral POM-based materials are particularly attractive due to the combination of the advantage of POMs with the importance of chirality. In this review, we summarize the developments of chiral POM-based materials, including their synthetic strategies, the calculations on the origin of chirality and the relevant applications.Highlights► We review the synthesis strategies and recent results of chiral polyoxometalates (POMs). ► Theoretical calculations on the origin of chirality within chiral POMs were discussed. ► The applications of chiral POMs in asymmetric catalysis, molecular recognition and NLO materials were summarized. ► The challenges of preparation and applications of chiral POMs were discussed.

Two S-containing MOFs, interpenetrating IFMC-27 and non-interpenetrating IFMC-28, were synthesized by altering solvent size. The nanoporous IFMC-28 reveals high selective adsorption for Cu2+ ions and has been applied as a chromatographic column for separating transition metal ions for the first time.

Here, we synthesize a novel polyoxometalate-based crystalline tubular inorganic–organic compound, Mn[Zn(im)]2{[Na(H2O)]2[Mn(H2O)2][Zn(im)2][P4Mo6O31H6]2}·8H2O (IFMC-100) (im and IFMC correspond to imidazole and Institute of Functional Material Chemistry, respectively). Au-anchored tubular microreactor, Au@IFMC-100, has been prepared by simple immersion of IFMC-100 in an ethanol solution of HAuCl4 without any extra reducing agents, photochemical and electrochemical auxiliaries. Furthermore, IFMC-100 and Au@IFMC-100 have been employed as catalysts for the reduction of K3Fe(CN)6 and 4-nitrophenol with NaBH4 in aqueous solution, respectively. The results indicate the as-prepared Au@IFMC-100 microtubes exhibit enhanced catalytic performance in redox catalysis.

A novel zeolite-like metal–organic framework (ZMOF) with sodalite topology, [Zn(HL)]·DMA (IFMC-1, L = 4,5-di(1H-tetrazol-5-yl)-2H-1,2,3-triazole and IFMC = Institute of Functional Material Chemistry), was solvothermally synthesized based on an N-rich aromatic ligand without a NH2 group. It exhibits high CO2 uptake and selective CO2/N2 adsorption capacity. For the first time, we investigated the influence of a large number of uncoordinated nitrogen atoms from aromatic rings for CO2 adsorption in ZMOFs. This result reveals that the high percentage of open N-donor sites leads to the high uptake capacity for CO2, even in the absence of any NH2 groups and open metal sites. In addition, it also exhibits efficient drug delivery capacity.

Five heterometallic luminescent crystalline materials with the metalloligand, [Zn(HL)EuxTby(H2O)2][ZnBr4]·H2O (x = 1, y = 0, IFMC-21; x = 0.75, y = 0.25, IFMC-22; x = 0.5, y = 0.5, IFMC-23; x = 0.25, y = 0.75, IFMC-24; x = 0, y = 1, IFMC-25; H4L = 4,4′,4′′,4′′′-(2,2′,2′′,2′′′-(ethane-1,2-diylbis(azanetriyl))tetrakis(methylene)-tetrakis-(1H-benzo[d]imidazole-2,1-diyl))tetrakis(methylene)-tetrabenzoic acid; IFMC = Institute of Functional Material Chemistry), were prepared by the combination of hydrothermal and ionothermal methods for the first time. IFMC-21–25 can be obtained by introducing the desired Eu(III) and Tb(III) in the initial experiments. In these crystalline materials, the metalloligand Zn(HL) was connected by bi-lanthanide cores leading to a 2D sheet-structure and [ZnBr4]2− ions were distributed in the interspaces of the sheet. The luminescent properties of IFMC-21 to 25 were investigated and the results reveal that they exhibit characteristic Eu(III) and Tb(III) ion emissions, and the intensities of red and green arising from Eu(III) and Tb(III) emissions are shifted correspondingly by tuning the ratios of Eu(III):Tb(III).

Three metal–organic frameworks (MOFs) comprising micropore, mesocage and nanotube structures have been prepared based on the same ligands and binuclear zinc secondary building units. We have successfully achieved flexible modulation of pore size from micropore to mesopore in a binary system by adjusting the reactant ratio. With the merit of a nanoscale channel, IFMC-8 can be applied as the host material for encapsulating Alq3 chromophores to exhibit tunable luminescence. The fluorescence emission of composite material Alq3@IFMC-8 has changed from green to blue. More importantly, the inclusion of IFMC-8 effectively prolonged the excited-state lifetime of Alq3 in ethanol. To the best of our knowledge, it is the first time that a MOF was studied as the host material for modulating the fluorescence properties of Alq3 chromophores.

A 3D eight-connected redox-active polyoxometalate (POM)-based crystalline material, IFMC-101, has been synthesized based on reduced {P4Mo6O31H6}-based tetrameric clusters. IFMC-101 was used as a reducing agent and stabilizer to prepare Au and Pt nanoparticles (NPs) by auto-redox reactions without extra reduction assistance. For the first time, we have demonstrated a new strategy to prepare noble metal NP-loaded POM-based crystalline catalysts. These crystalline catalysts were employed toward the reduction of 4-nitrophenol by NaBH4 and the efficiency of the Au NP-loaded material, Au@IFMC-101, was nearly 9 times higher than that of the POM-based crystalline material, IFMC-101. This result reveals that Au@IFMC-101 exhibits enhanced activity owing to the synergistic catalysis of noble metal NPs and crystalline POM components.

A novel non-interpenetrating metal–organic framework IFMC-15 was successfully constructed based on octahedral cage-like building units and its outstanding performance in reversible adsorption of iodine was investigated.

The first 3D uninodal eight-connected {P4Mo6O31H6}-based pure inorganic framework linked by transition metal ions has been synthesized and its electrochemical behavior and diffuse reflectance UV-Vis spectrum were investigated.

Here, we report two novel POM-based MOFs: a nano-caged hybrid compound [Ni2(BIMB)2(MoVI4MoV2O19)] (1), whose cages are based on [Mo6O19]4− units and a [Mo6O19]2−-templated framework [Zn4(BIMB)4(PO4)2(Mo6O19)]·2H2O (2) (BIMB = 1,4-bis(1-imidazolyl)benzene). According to topological analysis, the first is a 3D (4,6)-connected self-penetrating framework with polycatenanes motif. In contrast, the second metal–organic framework has no interpenetration for the templated [Mo6O19]2− occupying the cavity. The UV-vis absorption spectrum of 1 was investigated to prove the existence of MoV atoms and the typical peak at 577 nm can be attributed to MoV → MoVI charge transfer. Furthermore, the diffuse reflectivity spectrum shows that its band gap can be assessed as 3.06 eV, which can be regarded as a wide gap semiconductor. Additionally, cyclic voltammogram of compound 1 shows two redox peaks in the range of 0–800 mV in H2SO4 aqueous solution.

With the bottom-up design principle, we use metal-ions to bridge the predesigned tectons (1 [(H2L1)2(Mo8O26)]·4H2O and 3 [(H2L2)(L2)0.5(Mo8O26)0.5]·H2O) so that two higher dimensional γ-octamolybdate based inorganic–organic hybrid compounds 2 [CuI2(L1)3(Mo8O26)0.5] and 4 [Ni(L2)2(HL2)2(Mo8O26)]·4H2O are successfully obtained.

A new 3D chiral metal–organic framework [Co2(BTT)(OH)(H2O)5]·5CH3OH·6DMA (1) has been synthesized using an achiral tritopic bridging ligand, 1,3,5-tris(2H-tetrazol-5-yl)benzene (H3BTT). 1 possesses a (10,3)-a net containing large helical channels of 17.43 Å and exhibits a high solvent-accessible volume (calculated 79%). The N2 adsorption and magnetic properties for 1 have been examined.

Three organic–inorganic hybrid compounds have been designed and synthesized based on different vanadate chains, Zn(II) ions and flexible ligands at different pH values under hydrothermal conditions, namely, [Zn2(bbi)2(V3O9)(OH)]·H2O (1), [Zn2(bbi)2(V4O12)] (2), and [Zn(bbi)(V2O6)] (3), where bbi is 1,1′-(1,4-butanediyl)bis(imidazole). In 1, helical chains [(V3O9)3−]∞ were connected by [Zn2(OH)]3+ dimers giving rise to a 2D chiral layer which was further bridged via bbi ligands to construct a 3D POM-based chiral framework. There are two opposite helical chains [(V4O12)4−]∞ in 2. The [(V4O12)4−]∞ chains with the same chirality were connected each other by Zn2 cations to generate a 2D chiral layer, respectively. The adjacent chiral layers were linked by Zn1 ions to generate a 3D non-centrosymmetric framework with large channel encased by bbi. Similarly, the [(V2O6)2−]∞ chains with the same chirality in 3 were connected by zinc atoms to form a 2D chiral layer which was further linked through bbi to generate a 3D centrosymmetric network. Compounds 2 and 3 are supramolecular isomers. With adjusting the pH value of reaction mixture, we have achieved three new hybrids crystallized from chiral, non-centrosymmetric to centrosymmetric space group.

With BIMB ligand, we have successfully obtained and characterized three novel entangled inorganic–organic hybrid compounds by choosing different metal ions, that is, [Ni(BIMB)2(γ-Mo8O26)0.5]·3H2O (1), [Zn(BIMB)2(γ-Mo8O26)0.5] (2), and [Cu3(BIMB)4(H2O)(δ-Mo8O26)Cl2]·3H2O (3) (where BIMB=1,4-bis(1-imidazolyl)benzene). Compound 1 is a 2-fold interpenetration 4-connected 3D framework with the short Schläfli symbol of (4×64×8)2(42×62×82), in which octamolybdate anion shows γ-isomer; 2 exhibits a (5,6)-connected 3D self-penetrating topological motif with the short Schläfli symbol of (4×57×62)2(42×511×72), and 3 shows a (4,6)-connected self-penetrating 3D framework with the short Schläfli symbol of (42·52·6·7) (44·5·69·8) (54·62) whose octamolybdate has δ-isomer. In addition, the optical band gaps of these three compounds have been measured, which are 2.98 eV for 1, 3.42 eV for 2, and 2.88 eV for 3. Moreover, 2 has photoluminescent property, which can be attributed to ligand-to-metal charge-transfer (LMCT) band.Graphical abstractWith BIMB ligand, we have obtained and characterized three novel POM-based entangled hybrid compounds. Compound 1 is a 2-fold interpenetration 3D framework; 2 and 3 exhibit self-penetrating 3D polycatenated frameworks.Highlights► Three novel octamolybdate-based entanglement frameworks successfully obtained by choosing the rigid ligand 1,4-bis(1-imidazolyl)benzene and different metal ions. Compound 1 is a 2-fold interpenetration 4-connected 3D framework; 2 exhibits a (5,6)-connected 3D self-penetrating topological net, and 3 shows a (4,6)-connected self-penetrating 3D framework. ► In compounds 1 and 2, the octamolybdate anions show the γ-isomer, while in 3 the octamolybdate anion is a δ-isomer. ► Optical band gap of these three compounds have been investigated and the results show that they are all wide gap semiconductors, which are 2.98 eV for 1, 3.42 eV for 2, and 2.88 eV for 3.

With the bottom-up design principle, we use metal-ions to bridge the predesigned tectons (1 [(H2L1)2(Mo8O26)]·4H2O and 3 [(H2L2)(L2)0.5(Mo8O26)0.5]·H2O) so that two higher dimensional γ-octamolybdate based inorganic–organic hybrid compounds 2 [CuI2(L1)3(Mo8O26)0.5] and 4 [Ni(L2)2(HL2)2(Mo8O26)]·4H2O are successfully obtained.

A novel non-interpenetrating metal–organic framework IFMC-15 was successfully constructed based on octahedral cage-like building units and its outstanding performance in reversible adsorption of iodine was investigated.

A 3D eight-connected redox-active polyoxometalate (POM)-based crystalline material, IFMC-101, has been synthesized based on reduced {P4Mo6O31H6}-based tetrameric clusters. IFMC-101 was used as a reducing agent and stabilizer to prepare Au and Pt nanoparticles (NPs) by auto-redox reactions without extra reduction assistance. For the first time, we have demonstrated a new strategy to prepare noble metal NP-loaded POM-based crystalline catalysts. These crystalline catalysts were employed toward the reduction of 4-nitrophenol by NaBH4 and the efficiency of the Au NP-loaded material, Au@IFMC-101, was nearly 9 times higher than that of the POM-based crystalline material, IFMC-101. This result reveals that Au@IFMC-101 exhibits enhanced activity owing to the synergistic catalysis of noble metal NPs and crystalline POM components.

Two S-containing MOFs, interpenetrating IFMC-27 and non-interpenetrating IFMC-28, were synthesized by altering solvent size. The nanoporous IFMC-28 reveals high selective adsorption for Cu2+ ions and has been applied as a chromatographic column for separating transition metal ions for the first time.

Five heterometallic luminescent crystalline materials with the metalloligand, [Zn(HL)EuxTby(H2O)2][ZnBr4]·H2O (x = 1, y = 0, IFMC-21; x = 0.75, y = 0.25, IFMC-22; x = 0.5, y = 0.5, IFMC-23; x = 0.25, y = 0.75, IFMC-24; x = 0, y = 1, IFMC-25; H4L = 4,4′,4′′,4′′′-(2,2′,2′′,2′′′-(ethane-1,2-diylbis(azanetriyl))tetrakis(methylene)-tetrakis-(1H-benzo[d]imidazole-2,1-diyl))tetrakis(methylene)-tetrabenzoic acid; IFMC = Institute of Functional Material Chemistry), were prepared by the combination of hydrothermal and ionothermal methods for the first time. IFMC-21–25 can be obtained by introducing the desired Eu(III) and Tb(III) in the initial experiments. In these crystalline materials, the metalloligand Zn(HL) was connected by bi-lanthanide cores leading to a 2D sheet-structure and [ZnBr4]2− ions were distributed in the interspaces of the sheet. The luminescent properties of IFMC-21 to 25 were investigated and the results reveal that they exhibit characteristic Eu(III) and Tb(III) ion emissions, and the intensities of red and green arising from Eu(III) and Tb(III) emissions are shifted correspondingly by tuning the ratios of Eu(III):Tb(III).

The first 3D uninodal eight-connected {P4Mo6O31H6}-based pure inorganic framework linked by transition metal ions has been synthesized and its electrochemical behavior and diffuse reflectance UV-Vis spectrum were investigated.

A novel zeolite-like metal–organic framework (ZMOF) with sodalite topology, [Zn(HL)]·DMA (IFMC-1, L = 4,5-di(1H-tetrazol-5-yl)-2H-1,2,3-triazole and IFMC = Institute of Functional Material Chemistry), was solvothermally synthesized based on an N-rich aromatic ligand without a NH2 group. It exhibits high CO2 uptake and selective CO2/N2 adsorption capacity. For the first time, we investigated the influence of a large number of uncoordinated nitrogen atoms from aromatic rings for CO2 adsorption in ZMOFs. This result reveals that the high percentage of open N-donor sites leads to the high uptake capacity for CO2, even in the absence of any NH2 groups and open metal sites. In addition, it also exhibits efficient drug delivery capacity.

Here, we synthesize a novel polyoxometalate-based crystalline tubular inorganic–organic compound, Mn[Zn(im)]2{[Na(H2O)]2[Mn(H2O)2][Zn(im)2][P4Mo6O31H6]2}·8H2O (IFMC-100) (im and IFMC correspond to imidazole and Institute of Functional Material Chemistry, respectively). Au-anchored tubular microreactor, Au@IFMC-100, has been prepared by simple immersion of IFMC-100 in an ethanol solution of HAuCl4 without any extra reducing agents, photochemical and electrochemical auxiliaries. Furthermore, IFMC-100 and Au@IFMC-100 have been employed as catalysts for the reduction of K3Fe(CN)6 and 4-nitrophenol with NaBH4 in aqueous solution, respectively. The results indicate the as-prepared Au@IFMC-100 microtubes exhibit enhanced catalytic performance in redox catalysis.

Three metal–organic frameworks (MOFs) comprising micropore, mesocage and nanotube structures have been prepared based on the same ligands and binuclear zinc secondary building units. We have successfully achieved flexible modulation of pore size from micropore to mesopore in a binary system by adjusting the reactant ratio. With the merit of a nanoscale channel, IFMC-8 can be applied as the host material for encapsulating Alq3 chromophores to exhibit tunable luminescence. The fluorescence emission of composite material Alq3@IFMC-8 has changed from green to blue. More importantly, the inclusion of IFMC-8 effectively prolonged the excited-state lifetime of Alq3 in ethanol. To the best of our knowledge, it is the first time that a MOF was studied as the host material for modulating the fluorescence properties of Alq3 chromophores.