POM-based inorganic–organic hybrid compounds: synthesis, structures, highly-connected topologies and photodegradation of organic dyes

Abstract

Four new polyoxovanadate-based organic–inorganic hybrid materials [MnV₂(bpp)₂O₆] (1), [Ag₄V₄(bpp)₄O₁₂]·2H₂O (2) and [M₃V₆(bpp)₄O₁₈·4H₂O]·2H₂O [M = Ni (3), Zn (4), bpp = 1,3-bis(4-pyridyl)propane] have been synthesized under hydrothermal conditions through the self-assembly of transition metal salts, bpp ligands and ammonium metavanadate. Single-crystal X-ray diffraction analyses show that 1 possesses a three-dimensional framework, constructed from arrays of {V₄O₁₂} rings covalently linked through metal–organic units, {Mn(C₁₃H₄N₂)₂}. Compound 2 is an eight-connected self-catenated metal–organic framework, based on bimetallic {Ag₄V₄O₁₂} clusters as nodes. Compounds 3 and 4 are isostructural, both of them exhibit an intriguing 6,10-connected network. The structure of 4, as an example, is based on single zinc atoms as six-connected nodes, as well as bimetallic {Zn₂V₆O₁₈} clusters as ten-connected nodes, defining not only a new topology for three-periodic nets but also the first 6,10-connected framework using heterometallic clusters as nodes. Furthermore, the thermal stabilities and photocatalytic activities of 1–4 have been discussed in detail.

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Introduction

Organic–inorganic hybrid materials based on polyoxometalates (POMs) have attracted increasing interest due to their aesthetic architectures, intriguing topologies and potential applications in a variety of fields, such as catalysis, electrochemistry, gas storage, photochemistry, and as magnetic and electromagnetic functional materials.¹ It is well known that polyoxovanadates, containing many V_mO_n^x− subunits rich with oxygen atoms that can coordinate to various metal ions, are suitable inorganic building blocks that can form polyoxovanadate-based hybrid materials.^2–6 As the use of polynuclear metal clusters as building blocks is a promising strategy for the construction of highly connected coordination frameworks, polyoxovanadates are promising building blocks due to their aforementioned advantages.⁷ Up to now, there are a handful of highly connected networks reported based on monometallic or heterometallic clusters.⁸

To date, a lot of N/O-donor organic ligands, including pyridine derivatives,⁹ pyrazine derivatives,¹⁰ imidazole derivatives,¹¹ carboxylic acids¹² and so on have been utilized to coordinate with the vanadium resulting in multiple polyoxovanadate-based hybrid materials. Compared to rigid bidentate 4,4-bipyridyl analogues, bpp ligands are flexible dipyridyl ligands with different conformations, exhibiting lots of different N-to-N distances with respect to the relative orientations of the CH₂ groups and the pyridyl rings. The flexibility and conformational freedom of bpp ligands offer the possibility to meet the requirements of the coordination geometries of different ions in the assembly process and construct charming frameworks with tailored properties and functions.¹³ Therefore, we chose bpp as a bridging ligand to incorporate into the polyoxovanadate framework to produce unusual structures. As a result, four transition metal complex-based polyoxovanadate compounds [MnV₂(bpp)₂O₆] (1), [Ag₄V₄(bpp)₄O₁₂]·2H₂O (2) and [M₃V₆(bpp)₄O₁₈·4H₂O]·2H₂O [M = Ni (3), Zn (4)] were obtained, which display 4,6-, 8- and 6,10-connected topologies with different three-dimensional structures. For the 6,10-connected topology network, it is not only a new topology as a highly connected network but also the first 6,10-connected framework using heterometallic clusters as ten-connected nodes. The thermal stabilities and photocatalytic activities of 1–4 have been investigated.

Experimental section

Materials and methods

All reagents and solvents for the syntheses were purchased from commercial sources and used as received without further purification. Elemental analyses (C, H, and N) were performed on a Perkin-Elmer 240C elemental analyzer. IR spectra were recorded in the range 400–4000 cm⁻¹ on an Alpha Centauri FT/IR spectrophotometer using KBr pellets. PXRD patterns were collected using a Siemens D5005 diffractometer with Cu-Kα (λ = 1.5418 Å) radiation in the range of 3–50° at 293 K. Thermogravimetric analyses (TGA) were conducted on a Perkin-Elmer TG-7 analyzer heated from room temperature to 800 °C under a nitrogen atmosphere at a rate of 10 °C min⁻¹. The UV/Vis absorption spectra were recorded on a Shimadzu UV-2550 spectrophotometer in the wavelength range of 200–800 nm. Inductively coupled plasma (ICP) analyses were conducted on a Leeman Laboratories Prodigy inductively coupled plasma-optical atomic emission spectrometry (ICP-AES) system.

Syntheses of compounds 1–4

Synthesis of [MnV₂(bpp)₂O₆] (1). A mixture of MnCl₂·4H₂O (0.040 g, 0.2 mmol), NH₄VO₃ (0.047 g, 0.4 mmol), bpp (0.030 g, 0.15 mmol) and H₂O (8 mL) was stirred for 30 min at room temperature. Then the mixture was sealed in a 15 mL Teflon reactor at 100 °C for 3 days. After slowly cooling to room temperature, orange block crystals of 1 were filtered and washed with deionized water. Yield: 42% (based on Mn). Anal. calcd for C₂₆H₂₈N₄MnO₆V₂ (649.34): C 48.09, H 4.35, N 8.63, Mn 33.84, V 15.69; found C 48.26, H 4.21, N 8.81, Mn 34.05, V 15.36. IR (KBr pellet, cm⁻¹): 3445 (s), 2930 (s), 1612 (m), 1504 (s), 1425 (s), 923 (w), 825 (w), 725 (w), 632 (w).

Synthesis of [Ag₄V₄(bpp)₄O₁₂]·2H₂O (2). A mixture of AgNO₃ (0.034 g, 0.2 mmol), NH₄VO₃ (0.100 g, 0.8 mmol) and bpp (0.030 g, 0.15 mmol) was dissolved in 8 mL of distilled water at room temperature. Then the pH value of the mixture was adjusted to about 7.0 with 2 mol L⁻¹ NaOH. Then the mixture was stirred for 30 min at room temperature and was sealed in a 15 mL Teflon reactor at 100 °C for 3 days. After slowly cooling to room temperature, colourless block crystals of 2 were filtered and washed with deionized water. Yield: 38% (based on Ag). Anal. calcd for C₅₂H₅₆N₈Ag₄O₁₅V₄ (1668.29): C 37.44, H 3.38, N 6.72, Ag 25.87, V 12.21; found C 37.29, H 3.12, N 6.98, Ag 26.15, V 11.94. IR (KBr pellet, cm⁻¹): 3447 (s), 2931 (s), 1611 (m), 1501 (s), 1426 (s), 915 (s), 805 (m), 663 (s), 519 (w).

Synthesis of [Ni₃V₆(bpp)₄O₁₈·4H₂O]·2H₂O (3). A mixture of NiCl₂·6H₂O (0.050 g, 0.2 mmol), NH₄VO₃ (0.047 g, 0.4 mmol) and bpp (0.030 g, 0.15 mmol) was dissolved in 8 mL of distilled water at room temperature. Then the pH value of the mixture was adjusted to about 3.0 with concentrated HNO₃. Then the mixture was stirred for 30 min at room temperature and was sealed in a 15 mL Teflon reactor at 100 °C for 3 days. After slowly cooling to room temperature, green blocks of crystals 3 were filtered and washed with deionized water. Yield: 65% (based on Ni). Anal. calcd for C₅₂H₆₂N₈Ni₃O₂₄V₆ (1664.87): C 37.52, H 3.75, N 6.73, Ni 10.57, V 18.36; found C 37.39, H 3.52, N 6.58, Ni 10.34, V 17.93. IR (KBr pellet, cm⁻¹): 3444 (s), 2930 (s), 1613 (m), 1493 (s), 1424 (s), 931 (s), 898 (m), 839 (s), 726 (w), 636 (w).

Synthesis of [Zn₃V₆(bpp)₄O₁₈·4H₂O]·2H₂O (4). A mixture of Zn(CH₃COO)₂·2H₂O (0.150 g, 0.7 mmol), NH₄VO₃ (0.047 g, 0.4 mmol), bpp (0.03 g, 0.15 mmol) and H₂O (8 mL) was stirred for 30 min at room temperature. Then the mixture was sealed in a 15 mL Teflon reactor at 100 °C for 3 days. After slowly cooling to room temperature, yellow block crystals of 4 were filtered and washed with deionized water. Yield: 55% (based on Zn). Anal. calcd for C₅₂H₅₆N₈Zn₃O₂₄V₆ (1678.80): C 37.20, H 3.36, N 6.67, Zn 11.68, V 18.20; found C 37.35, H 3.12, N 6.81, Zn 11.32, V 18.47. IR (KBr pellet, cm⁻¹): 3445 (s), 2931 (s), 1613 (w), 1504 (m), 1424 (m), 936 (s), 897 (m), 727 (w), 631 (m).

X-ray crystallography

Single-crystal X-ray diffraction data for 1–4 were collected on a Bruker SMART APEX II CCD diffractometer equipped with a graphite monochromator using Mo-Kα radiation (λ = 0.71073 Å) by using the Φ/ω scan technique at room temperature; there was no evidence of crystal decay during data collection. A multiscan technique was used to perform adsorption corrections. The crystal structures of 1–4 were solved using direct methods and refined using the full-matrix least-squares method on F² with anisotropic thermal parameters for all non-hydrogen atoms using the SHELXL-97 program.¹⁴ Relevant crystal data and structure refinements for 1–4 are listed in Table 1. Selected bond lengths (Å) and angles (°) for 1–4 are given in Table S1.†

Table 1 Crystallographic data for compounds 1–4

Compound	1	2	3	4
a R1 = ∑‖Fo| − |Fc‖/∑|Fo|.b wR2 = |∑w(|Fo|^2 − |Fc|^2)|/∑|w(Fo^2)^2|^1/2.
Chemical formula	C26H28Mn4O6V2	C52H56Ag4N8O15V4	C52H62N8Ni3O24V6	C52H56N8O24V6Zn3
Formula weight	649.34	1668.29	1664.87	1678.80
Crystal system	Tetragonal	Monoclinic	Monoclinic	Monoclinic
Space group	I4(1)/a	P2/n	P2(1)/n	P2(1)/n
a (Å)	21.5654(11)	12.382(3)	13.081(3)	13.1897(16)
b (Å)	21.5654(11)	9.697(2)	16.379(4)	16.438(2)
c (Å)	13.0149(8)	25.365(6)	15.407(4)	15.4725(19)
α (°)	90	90	90	90
β (°)	90	92.003(4)	102.368(5)	102.345(2)
γ (°)	90	90	90	90
V (Å^3)	6052.8(6)	3043.5(13)	3224.4(14)	3277.0(7)
Temperature (K)	293(2)	293(2)	293(2)	293(2)
Z	8	2	2	2
Dcalcd (g cm^−3)	1.425	1.820	1.715	1.701
GOF on F^2	1.061	0.937	1.013	1.020
R1 [I > 2σ(I)]^a	0.0393	0.0665	0.0376	0.0557
wR2 [I > 2σ(I)]^b	0.1089	0.1537	0.0844	0.1431
R1^a (all data)	0.0551	0.1280	0.0632	0.0946
wR2^b (all data)	0.1173	0.1890	0.0968	0.1667
Rint	0.0502	0.0963	0.0460	0.0728

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Results and discussion

Crystal structure of [MnV₂(bpp)₂O₆] (1)

The single-crystal X-ray diffraction analysis of 1 reveals that it crystallizes in the tetragonal group I4(1)/a. As shown in Fig. 1a, the asymmetric unit of 1 consists of a half Mn(II) ion, one bpp ligand and one V cation of a {V₄O₁₂} ring. In the {V₄O₁₂} ring, all four vanadium atoms show a VO₄ tetrahedron coordination configuration, and each vanadium centre is coordinated with three bridging oxygen atoms (O_b) and one terminal oxygen atom (O_t). The V–O_t distance of 1.615(3) Å is slightly shorter than the V–O_b distances of 1.772(3) and 1.651(2) Å. The Mn1 ion is six-coordinated by four nitrogen atoms from four bpp ligands and two oxygen atoms from two adjacent {V₄O₁₂} rings. The Mn–N bond lengths are 2.189(3) and 2.224(3) Å, and the Mn–O bond length is 1.995(2) Å, which are summarized in Table S1.† Furthermore, all of the bpp ligands adopt a trans–gauche conformation.¹⁵

Fig. 1 (a) Mn(II) coordination environments of 1. Symmetry codes: (A) −x + 1, −y + 2, −z; (B) −x + 3/2, −y + 2, z + 1/2; (C) x + 1/4, −y + 5/4, z + 1/4. (b) 2D layer of 1. (c) 3D framework of 1. (d) 3D binodal (4,6)-connected 3D net with a (4⁴·5⁵·6⁶)₂(5⁴·6²) topology of 1. All hydrogen atoms are omitted for clarity.

In 1, the adjacent {V₄O₁₂} rings are linked to Mn ions to form neutral bimetallic oxide layers {Mn₂V₄O₁₂} (Fig. 1b) with channels occupied by bpp ligands which cross-link the {Mn₂V₄O₁₂} motifs to generate a three dimensional framework, as shown in Fig. 1c. In order to simplify the 3D framework of 1, the Mn1 ion is regarded as a six-connected node and the {V₄O₁₂} rings can be considered as four-connected nodes. Thus, 1 exhibits a binodal (4,6)-connected 3D net with a (4⁴·5⁵·6⁶)₂(5⁴·6²) topology when analysed by TOPOS software (Fig. 1d).

Crystal structure of [Ag₄V₄(bpp)₄O₁₂]·2H₂O (2)

2 contains neutral bimetallic {Ag₄V₄O₁₂} clusters as nodes, according to the single-crystal X-ray analysis, which consist of a central {V₄O₁₂}⁴⁻ cluster decorated with four Ag units, as shown in the insert of Fig. 2a. There are two crystallographically independent vanadium atoms in 2, which show a similar distorted tetrahedron to 1.814(7) Å (Fig. 2a). Tetrahedral and planar-trigonal coordination geometries of Ag ions are presented in Fig. 2a. The Ag1 ion is coordinated with two nitrogen atoms from two bpp ligands and two terminal oxygen atoms from one {V₄O₁₂}⁴⁻ anion, constructing a tetrahedral geometry. The Ag2 ion is coordinated with two nitrogen atoms from two bpp ligands and one terminal oxygen atom from one {V₄O₁₂}⁴⁻ anion to form a planar-trigonal geometry. The average Ag–O distance [2.636(3)Å] and Ag–N distance [2.222(8) Å] in the tetrahedron is longer than the corresponding values [2.371(8) Å and 2.145(9) Å] in the trigonal geometry. All of the bpp ligands exhibit a trans–trans conformation with the present N–N distances ranging from 9.718(0) to 10.191(4) Å. Fig. 2b shows that the Ag ions in adjacent {Ag₄V₄O₁₂} clusters have Ag⋯Ag interactions with short silver–silver contacts of 3.0767(19) and 3.2069(18) Å, which are shorter than the sum of the van der Waals radii of the two silver atoms (3.440(0) Å).¹⁶ Every {Ag₄V₄O₁₂} cluster is further connected to its eight nearest neighbours through eight bpp ligands, thus resulting in the three-dimensional framework illustrated in Fig. 2c.

Fig. 2 (a) Ag(I) coordination environments of 2. Symmetry codes: (A) −x, −y + 1, −z + 1; (b) the Ag⋯Ag interactions of adjacent {Ag₄V₄O₁₂} clusters. (c) 3D framework of 2. (d) 3D uninodal 8-connected networks with a 4²⁴·6⁴ topology of 2. All hydrogen atoms are omitted for clarity. The light blue, green, red and dark blue represent silver, vanadium, oxygen and nitrogen atoms, respectively.

From the viewpoint of the topology, each bimetallic {Ag₄V₄O₁₂} cluster is surrounded by eight bridging bpp ligands, further connecting eight {Ag₄V₄O₁₂} clusters with distances of 12.238(2) to 22.853(2) Å, defining an eight-connected node. In this bridging of parallel layers, the catenated four-membered shortest rings are observed at the intersection of the crossing of two-dimensional layers, therefore resulting in a single eight-connected self-catenated network (Fig. 2d). The total Schlafli symbol of this net is (4²⁴·6⁴). It is worth noting that the first self-catenated framework using heterometallic clusters as nodes was [Cu₄(bpp)₄V₄O₁₂]·3H₂O [bpp = 1,3-bis(4-pyridyl)propane] reported in 2007.¹⁷

Crystal structure of [Ni₃V₆(bpp)₄O₁₈·4H₂O]·2H₂O (3)

3 and 4 are isostructural, so the structural description of 3 is given as a representative example. The single-crystal X-ray diffraction analysis reveals that 3 crystallized in the monoclinic space group P2(1)/n. As shown in Fig. 3a, the asymmetric unit of 3 consists of one and a half Ni(II) ions, two bpp ligands and three vanadium atoms. All of the vanadium atoms exhibit a {VO₄} tetrahedron coordination configuration, and each vanadium centre is coordinated with three bridging oxygen atoms (O_b) and one terminal oxygen atom (O_t). The V–O_b distances range from 1.650(2) to 1.809(2) Å and are slightly longer than the values of V–O_t distances of 1.614(2) to 1.650(2) Å. Ni ions are six-coordinated showing an octahedral geometry coordination but different coordination environments. The Ni1 ion is coordinated with two nitrogen atoms from two bpp ligands and four oxygen atoms from two vanadium tetrahedra and two water molecules, while the Ni2 ion is coordinated with four nitrogen atoms from four bpp ligands and two oxygen atoms from two vanadium tetrahedra. The Ni–N bond lengths are in the range of 2.077(2)–2.158(2) Å and the Ni–O distances vary from 2.042(2) to 2.113(3) Å (Table S1†). All of the bpp ligands show trans–gauche conformations with the N–N distances in the range 8.791(9) to 9.267(3) Å.

Fig. 3 (a) Ni(II) and coordination environments of 3. Symmetry codes: (A) −x + 1/2, y − 1/2, −z + 3/2; (B) −x, −y + 1, −z + 1; (C) −x + 1/2, y + 1/2, −z + 3/2; (D) −x + 1, −y + 1, −z + 1; (E) −x + 1/2, y + 1/2, −z + 1/2; (F) x + 1/2, −y + 1/2, z + 1/2. (b) 2D inorganic layer of 3. (c) 3D framework of 3. (d) The binodal (6,10)-connected 3D net with a (3⁴·4⁸·5³)(3⁸·4²⁰·5¹²·6⁵) topology of 3. All hydrogen atoms are omitted for clarity. The light blue, green, red and dark blue represent nickel, vanadium, oxygen and nitrogen atoms, respectively.

In 3, two Ni1 ions and six vanadium atoms are bridged by eight bridging oxygen atoms to generate a bimetallic {Ni₂V₆O₂₀}⁶⁻ clusters. Each {Ni₂V₆O₂₀}⁶⁻ cluster links four neighbours by a V₂–O₉–V₁ bridge to form 2D inorganic layers, given in Fig. 3b. The 2D inorganic layers are further connected by the Ni2 ions through bridging oxygen atoms into a 3D framework (Fig. 3c). From a topological point of view, each {Ni₂V₆O₂₀}⁶⁻ cluster is surrounded by four bpp ligands, four neighbouring {Ni₂V₆O₂₀}⁶⁻ clusters and two Ni1 ions, which defines a bimetallic ten-connected node. Likewise, a Ni2 ion is surrounded by two {Ni₂V₆O₂₀}⁶⁻ clusters and four bpp ligands, thus defining a six-connected node. Therefore, 3 presents a binodal (6,10)-connected 3D net with a point symbol of (4¹³·6²)(4³⁶·6⁹) in which each {Ni₂V₆O₂₀}⁶⁻ cluster is linked to ten nearest-neighbours (eight {Ni₂V₆O₂₀}⁶⁻ clusters and two Ni2 ions) and each Ni2 ion is linked to six nearest-neighbours (two {Ni₂V₆O₂₀}⁶⁻ clusters and four Ni₂ ions) with distances of 6.594–13.882 Å (centre to centre), as shown in Fig. 3d.

To the best of our knowledge, only one (6,10)-connected structure has been reported up to now.¹⁸ The example is [Zn₇(trz)₆(pt)₄(H₂O)₂] (Htrz = 1,2,4-triazole, H₂pt = isophthalic acid) based on binuclear zinc clusters as six-connected nodes and pentanuclear zinc clusters as ten-connected nodes, which is the first binodal (6,10)-connected metal–organic network with the topology of (3⁴·4⁸·5³)(3⁸·4²⁰·5¹²·6⁵).

Thermogravimetric analyses

To study the thermal stabilities of 1–4, the thermogravimetric analyses were carried out under a N₂ atmosphere from room temperature to 1000 °C with a heating rate of 10 °C min⁻¹. 1 shows a single weight loss step (Fig. S2†). The loss step (180–240 °C for 1) corresponds to the decomposition of the bpp ligands and the {V₄O₁₂} clusters. 2–4 exhibit three separate weight loss steps (Fig. S2†). The first weight loss (120–200 °C for 2–4) corresponds to the release of interstitial water molecules (found 3.21% for 2, 6.54% for 3, 6.47% for 4; calcd 4.11% for 2, 5.35% for 3, 6.04% for 4). The second and third weight losses (300–800 °C for 2, 270–800 °C for 3 and 4) are attributed to the decomposition of the bpp ligands and the {Ag₄V₄O₁₂} clusters for 2, and the {M₂V₆O₂₀} cluster for 3 and 4 [M = Ni (3), Zn (4)]. The remaining products should be MO (M = Mn, Ni, Zn), M₂O (M = Ag) and V₂O₅ (found 38.93% for 1, 49.64% for 2, 46.25% for 3, 47.13% for 4; calcd 38.46% for 1, 48.27% for 2, 5.82% for 3, 46.55% for 4).

Photocatalytic activity

It is well known that a wide range of polyoxovanadate-based compounds possess photocatalytic activities.¹⁹ Herein, methylene blue (MB), a typical, difficult-to-degrade dye contaminant molecule present in waste water, was selected to evaluate the photocatalytic effectiveness of 1–4. It is worth noting that 1–4 cannot be dissolved in aqueous solution, thus they are used as heterogeneous catalysts. The photocatalytic reactions were performed as follows: 50 mg of the catalyst (1–4) was dispersed in a 300 mL aqueous solution of MB (10 mg L⁻¹) under stirring in the dark for 30 min in order to rule out the effect of its absorption to the particle surfaces. Then the solution was exposed to UV light (125 W) and kept continuously stirring. Samples of 5 mL were taken out every 15 min for UV measurement. The photodegradation process of MB without any photocatalyst was also performed for comparison.

Fig. 4 and 5 show the photocatalytic results of 1–4 in the MB solution. We can see that the absorption peaks of aqueous MB in the presence of 1–4 dramatically decreased within 90 min under UV irradiation from Fig. 4. It is obvious that 1–4 all show good photocatalytic activity for the degradation of MB. Furthermore, based on the plots of C_t/C₀ versus reaction time (Fig. 5), it can be observed that the photocatalytic activities obviously increase from 25.8% to 79.9, 85.1, 77.4, 69.5% for 1–4, respectively, after 90 min of irradiation. The PXRD patterns of 1–4 simulated from single-crystal X-ray data, as-synthesized and after the photocatalytic reaction, are shown in Fig. S2.† The PXRD results reveal that 1–4 remain unchanged after the photocatalytic reaction, indicating that they are stable photocatalysts. Moreover, because 2 exhibits the highest catalytic activity in the degradation of MB under UV light, it was chosen as a representative catalyst to investigate catalyst lifetime. In our initial experiment, the catalytic activity of 2 was maintained when it was recycled five times (Fig. S5†). According to the related literature,²⁰ the photocatalytic mechanisms may be deduced as follows: during the photocatalytic process, there is an electron transfer from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) which is produced from the POM, induced by UV light. The HOMO strongly needs an electron in order to return to its stable state. Therefore, one electron is abstracted from a H₂O molecule, which is oxygenated into the ˙OH active species. Then the ˙OH radicals could cleave MB effectively to complete the photocatalytic process.

Fig. 4 (a–d) UV/Vis absorption spectra of aqueous MB during the decomposition reaction under UV light irradiation in the presence of 1–4, respectively.

Fig. 5 Plot of C_t/C₀ of MB versus irradiation time under UV light in the presence of 1–4 (1 (▲); 2 (●); 3 (★), 4 (■); experiment in the absence of catalyst (▶)).

Conclusions

Four new polyoxovanadate-based hybrid materials constructed from {V₄O₁₂} clusters, {Ag₄V₄O₁₂} clusters and {M₂V₆O₂₀} clusters have been prepared under hydrothermal conditions, which all exhibit 3D frameworks with different topologies. 3 and 4 show a new complicated 6,10-connected topology. 2 shows good photocatalytic activity and selectivity for the degradation of MB. This work provides useful information for designing and constructing intriguing architectures of high dimensional and highly connected multifunctional polyoxovanadate-based hybrid materials.

Acknowledgements

This work was financially supported by the NSFC of China (no. 21471027, 21171033, 21131001, 21222105), the National Key Basic Research Program of China (no. 2013CB834802), and the Changbai mountain scholars of Jilin Province.

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Footnote

† Electronic supplementary information (ESI) available: The materials, synthesis methods, BVS, XRD, XPS, TGA, ESI-MS, UV-Vis diffuse reflectance spectra. CCDC 1063206–1063209. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5ra09339b

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