Hai Fu

An Ionothermal Synthetic Approach to Porous Polyoxometalate‐Based Metal–Organic Frameworks

Porous materials with regular, bulky, accessible cages and channels have aroused great research interest owing to their potential applications in gas storage, separation, ionexchange, and heterogeneous catalysis. 2] Polyoxometalates (POMs), as a unique class of metal oxide clusters, constitute promising building units for targeting multifunctional materials because of their nanosize, adjustable compositions, abundant topologies, and their oxygen-rich surface with strong coordination abilities. 4] Despite the unparalleled success in the preparation of microporous/mesoporous compounds by covalently linking simple metal ions and organic ligands, attempts to prepare porous POM-based metal– organic frameworks have met with only limited success. Therefore, the synthesis of such frameworks is one of the most challenging issues in synthetic chemistry. Normally, porous materials are prepared by conventional solution synthesis and hydroor solvothermal synthesis. Solvents of these systems have been largely restricted to water and traditional organic solvents, such as methanol, acetonitrile, and acetone. It is undeniable that these solvents have some intrinsic disadvantages: for example, regarding synthesis, their lower boiling points have limited the use of higher temperatures out of safety concerns; furthermore, from the environmental perspective, volatile organic solvents have caused serious health and environmental problems. Therefore, it is very necessary to explore a more effective and environmentally friendly synthetic method to overcome these existing shortcomings. Ionic liquids (ILs), composed of cations and anions, have gained attention owing to their low melting points, high ionic conductivity, non-volatility, nonflammability, high polarity, low toxicity, zero vapor pressure, and relatively low viscosity. Therefore, they may be environmentally friendly alternatives to the traditional solvents. Ionothermal synthesis, with the use of an IL as solvent and structural directing agent, has already been comprehensively discussed in several detailed reviews, and has been successfully applied in the synthesis of zeolites or microporous solids. The remarkable work of Pakhomova and others have also proved the feasibility of such ionothermal methods for preparation of non-porous POM-based materials. Inspired by these recent developments, we present herein the extension of the ionothermal method to the realm of POM-based porous frameworks and demonstrate its capacity to produce such crystalline solids. To our knowledge, no reliable design of POM-based porous materials from this approach has yet been reported to date. In planning the synthesis, we chose a readily available ionic liquid, 1-ethyl-3-methylimidazolium bromide ([Emim]Br) as solvent, the weak coordinating ability of which can facilitate the self-assembly of the polyoxoanions. Meanwhile, to surmount the major obstacle in construction of POM-based solids with extra-large pores, bulky tetrabutylammonium bromide was used. On one hand, it could increase the aperture when it acts as a counterion filling in the cavity; on the other hand, subsequent ion exchange of it with smaller cations would recover the porosity effectively. Indeed, by slightly varying the experimental conditions, three porous POM-based 3D structures have been obtained based on the above design strategy: (TBA)2[Cu (BBTZ)2(xMo8O26)] (x = b for 1, x = a for 2 and 3) (TBA = tetrabutylammonium cation, BBTZ = 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene). Single-crystal X-ray diffraction analysis reveals that the octamolybdate anion in 1 adopts the structural feature of the b-isomer, which consists of eight edge-shared MoO6 octahedra. Each [b-Mo8O26] 4 unit is covalently linked to two [CuBBTZ4] fragments through terminal oxo groups of octahedral Mo sites with Cu O distances of 2.302(4) and 2.302(4) . Each Cu cation adopts an octahedral geometry, defined by four N atoms from four BBTZ organic ligands (Cu1 N5 2.022(5), Cu1 N6 2.036(5)), and two O atoms from the [b-Mo8O26] 4 unit. The BBTZ ligands coordinated to the Cu center adopt a U-type configuration, and thus the CuBBTZ4 fragment has a windmill-type configuration with the four included angles between the four BBTZ ligands coordinated to the Cu centers of 908 (Supporting Information, Figure S1). The Cu centers of the windmills are extended to a 3D covalent net through the [b-Mo8O26] 4 units and the BBTZ ligands. The structure of 1 is very open, and contains three-directional channel systems. These channels intersect with each other and run along three different directions: 1.20 1.20 nm along the [100] direction, and 1.20 1.37 nm along the [011] and [0 11] directions, as shown in Figure 1a. From the topological view, the 3D architecture of 1 can be [*] Dr. H. Fu, Prof. C. Qin, Prof. Y. Lu, Dr. Z.-M. Zhang, Prof. Y.-G. Li, Prof. Z.-M. Su, Dr. W.-L. Li, Prof. E.-B. Wang Key Laboratory of Polyoxometalate Science of Ministry of Education Department of Chemistry, Northeast Normal University Changchun, Jilin 130024 (China) E-mail: qinc703@nenu.edu.cn wangeb889@nenu.edu.cn

Controllable self-assembly of four new metal–organic frameworks based on different phosphomolybdate clusters by altering the molar ratio of H3PO4 and Na2MoO4

By adjusting the molar ratio of the reactants H3PO4 and Na2MoO4, four new metal–organic frameworks, namely, CoH(bix)4[PMoVI8VV4O40(VIVO)2] (1), (H2bix)2(NaHP2Mo5O23)·2H2O (2), H2(bix)4[Cd(H2O)4][Cd(HPO4)4(H2PO4)4(MoO2)12 (OH)6]·10H2O (3) and (H2en)3(Co3P4Mo4O28) (4) (bix = 1,4-bis(imidazol-1-ylmethyl)benzene, en = 1,2-ethylenediamine), have been hydrothermally prepared and characterized by elemental analyses, IR spectroscopy, TG analyses, and single-crystal X-ray diffraction. Compound 1 consists of straight chains based on pseudo-Keggin [PMoVI8VV4O40(VIVO)2]3−polyanions and [CoH(bix)4]3+ complex fragments, which are further connected into a three-dimensional (3D) open framework by hydrogen bonding interactions between polyanions and organic bix ligands . Compound 2 shows 3D supramolecular networks constructed from weak interactions between free biprotonated bix, water and oxygen atoms of polyanions [P2Mo5O23]6−. In compound 3, [Cd(HPO4)4(H2PO4)4(MoO2)12(OH)6]4−polyanions are linked by [Cd(H2O)4]2+ cations to build one-dimensional (1D) chains. Then weak interactions between free bix ligands, water and oxygen atoms of the polyanions extend these 1D chains to 3D supramolecular frameworks. Compound 4 exhibits open-framework structures. Interestingly, it also shows 1D left and right-handed helical chains and 2D (6,3)-layers. The molar ratio of the reactants H3PO4 and Na2MoO4 influence the transformation of the phosphomolybdate clusters in compounds 1–4. The electrochemistry and photocatalysis properties of these compounds have also been investigated in this paper.

Controllable self-assembly of two novel metal–organic frameworks based on different tetradentate in situ ligands

Two novel metal–organic frameworks (MOFs) based on different tetradentate in situ ligands, CuI3(L1)2(L2)[PMoVI8VV4O40(VIVO)2]·2H2O (1) and [CuI2Cl2(L3)] (2) (L1 = 1,4-bis(imidazol-1-ylmethyl)benzene, L2 = 1,2,4,5-tetra(4-pyridyl)-benzene L3 = a-1-hydroxy-e,e,e,e-1,2,4,5-tetra(4-pyridyl)cyclohexane) have been rationally hydrothermally synthesized and characterized by elemental analyses, IR spectroscopy, TG analyses, and single-crystal X-ray diffraction, respectively. Here, compound 1 represents the first example that dehydrogenative coupling has been employed to yield a novel tetradentate coplanar dye molecule in POM-based MOFs. It also exhibits unique 3D MOFs with two topologies (4284)(4283101)(86)2 and (4383)(4284)(446289)(4106183) due to different definitions of nodes. Compound 2 shows a two-fold diagonal/diagonal inclined interpenetration based on CuI ions and in situ synthesized ligands L3. Interestingly, reaction conditions play important roles in the domination of in situ ligands (L2 and L3) from the same precursor bpp (bpp = 1,3-bis(4-pyridyl)propane). Additionally, electrochemical and photocatalysis properties of compound 1 have also been minutely investigated.

Expansion of sodalite-type metal–organic frameworks with heterometallic metal–oxo cluster and its cation exchange property

The sodalite-type metal–organic framework constructed from heterometallic alkali metal/V secondary building units with large internal cavity was firstly obtained. The organic amine cations within the channels can be replaced by transition metal ions through a cation exchange process, and subsequent gas adsorption measurements confirm the permanent porosity.

One polyoxometalate-based hybrid 3-D network: synthesis, structure, photo- and electro-catalytic properties

A new polyoxometalate-based inorganic–organic hybrid material, H5Ag(Bbi)1.5(Bbi)2[P2W18O62] (1) (Bbi = 1,1-(1,4-butanediyl)-bis(imidazole)), has been hydrothermally synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, IR spectroscopy, and thermogravimetric analysis. In 1, adjacent [P2W18O62]6− (short for P2W18) anions are connected through Ag by equatorially positioned terminal oxygen atoms to generate a 1-D chain. Adjacent chains were further connected through Ag and two-coordinated Bbi ligands into a (6, 3)-layer, which are extended to 3-D supermolecule nets through H bonds. The photo- and electro-catalytic properties of 1 have been studied.