Assembly of Polyoxometalate-Based Hybrids with Different Helical

Article pubs.acs.org/crystal

Assembly of Polyoxometalate-Based Hybrids with Different Helical Channels upon Subtle Ligand Variation Meng-Ting Li,†,‡ Jing-Quan Sha,*,†,‡ Xi-Ming Zong,‡ Jing-Wen Sun,† Peng-Fei Yan,*,† Liang Li,‡ and Xiao-Ning Yang‡ †

School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, People’s Republic of China School of Pharmacy, Jiamusi University, Jiamusi, 154007, People’s Republic of China

‡

S Supporting Information *

ABSTRACT: Self-assembly of multiple components into well-defined and predictable structures remains one of the foremost challenges in chemistry. Here, upon subtle ligand variation, we reported on the assembly of three new polyoxometalate-based organic−inorganic hybrid compounds with different helical channel, [Ag3(H2pyttz-I)2][PMo12O40] (1), [Ag6(H2pyttz-II)4][CoW12O40]·2H2O (2), and [Ag7(Hpyttz-II)3(H2pyttz-II)][GeW12O40]·7H2O (3) (H2pyttz-I/II = 4-/ 3-pyrid-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, POM = polyoxometalates). X-ray diffraction analysis shows that compound 1 is constructed by “butterfly-like” Ag5(H2pyttz-I)2 subunits and POMs clusters, which are assembled into close helical channels impregnated with the components selves. Both compounds 2 and 3 are constructed by “paddle-wheel like” Ag4(H2pyttz-II)4 motifs and POMs clusters, which bring into being the larger helical channels (10.5% and 12.5% of the cell volume, respectively). Note that the only difference in compounds 2 and 3 is that the former contains 1D metal−organic chain structure, and the latter contains 2D metal−organic layer structure. In addition, the photocatalytic degradation of RhB by these compounds was also investigated.

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INTRODUCTION Assembly of crystalline materials with periodic nanoscale channels and/or porous has captivated the attention of many investigators due to their elegant structures as well as their excellent ability to encapsulate guest molecules, such as stabilization, catalysis, storage, and separation of chemical matter.1 Recently, the rational design and synthesis of metal− organic frameworks (MOFs) crystalline solids have been widely studied,2 which shows that MOFs allow the defined spatial arrangement of the components and the formation of a diverse range of three-dimensional structures with unique functions. In particular, MOFs with porous and helix have made them feasible for performing a variety of chemical reactions such as gas storage, gas separation, heterogeneous catalysts, etc.3 Polyoxometalates (POMs), as anionic nanosized metal oxygen clusters, are suitable inorganic building blocks to form functional crystalline solids4 because of their discrete structures and notable acid/base, redox, and photochemical properties, and so on.5 In the aspect, a remarkable branch of MOF chemistry is the synthesis of POMs-based metal−organic frameworks (POMOFs) with helices or channels. The representative work was reported by Mizuno and co-workers, who have synthesized a series of POMs-based nanostructured ionic crystals with hydrophobic channels.6 Wang et al. have described two new enantiomerically pure 3D POM-based frameworks with helical feature and channel.7 Henceforth, many POMOFs containing helices or channels have been reported one after another.8 Summarizing the reported © 2014 American Chemical Society

compounds, we found that, in most cases, POMs as templates insert into the channels of POMOFs, but POMs as building units of channels are few reported. The synthesis progress about POMOFs with porous and helix feature has been made on the practical manipulation by our groups.9 By elaborative studies on those POMOFs with porous and helix structure, we find that syntheses of POMsbased frameworks with periodic nanoscale channels are very difficult, because the intersecting channels, which frequently occur in zeolites, are often unstable upon loss of solvent as a result of framework instability associated with high porosity.10 More importantly, although POMs as a building unit participate in the construction of channels, all of the previous working outcomes (Figure 1) are not perfect; more specifically, POMs and organic−metal complexes occupy the channels, which results in the narrowing of channel or even disappearance. The results have deviated from our original intention, the assembly of larger channel frameworks. So the synthesis of POMOFs with larger helical channel is an attractive but challenging topic. On the basis of the previous work and comprehensive consideration, and to avoid building molecules occupying the channel and to expand the size of channel, we rely on the suitably designed structure and coordination mode of organic molecules as a general strategy for the preparation of target Received: January 9, 2014 Revised: April 8, 2014 Published: April 16, 2014 2794

dx.doi.org/10.1021/cg500045q | Cryst. Growth Des. 2014, 14, 2794−2802

Crystal Growth & Design

Article

Figure 1. Representation of the assembly of helical channels in POMOF systems.

Scheme 1. Schematic Representations of the Ligands H2pyttz-I and H2pyttz-II

Figure 2. Ball/stick representation of the molecular structure unit of compounds 1−3. P, orange; Mo, dark green; Co, green; W, gray; Ge, cyan; O, red; Ag, purple; N, blue; C, light gray. All of the hydrogen atoms have been omitted for clarity.

construction of channel. In this Article, three new POMOFs with different helical channel, [Ag3(H2pyttz-I)2][PMo12O40] (1), [Ag 6 (H 2 pyttz-II) 4 ][H 2 CoW 12 O 40 ]·2H 2 O (2), and [Ag7(Hpyttz-II)3(H2pyttz-II)][GeW12O40]·7H2O (3), have been obtained. The influence of organic ligand on the structure is discussed. The successful isolation of three new compounds demonstrates a feasible assemble process upon the synergistic reaction of Keggin POMs, Ag ions, and pyttz ligands, especially the subtle structure of pyttz ligands.

compounds. In this work, we select 3-(pyrid-3-yl)-5-(1H-1,2,4triazol-3-yl)-1,2,4-triazolyl (hereafter noted H2pyttz-I) and 3(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl (hereafter noted H2pyttz-II) (Scheme 1) to connect with POMs clusters and silver atoms, because of the following considerations: (1) The multiple N-donor atoms and radial coordination style of the triazolyl rings provide controllable coordinated modes through tuning the reaction condition. (2) The H2pyttz ligand contains a pyridyl ring, which may extend the coordinated length of two triazolyl rings (about 5.5 Å) into a more suitable length (8.5−9.5 Å) for marrying the POMs (∼10 Å). This character is positive for the formation of POMOFs with larger helical channel and POMs as a building unit participating in the

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RESULTS AND DISCUSSION The single-crystal X-ray diffraction analysis shows that compound 1 crystallizes in the monoclinic space group C2/c 2795



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Figure 3. The coordination mode of POM cluster, Ag cation, and H2ppytz ligands: (a) #1, −0.5 + x, −0.5 + y, z; #2, −1 + x, y, z; (b) #1, x, y, −1 + z; #2, 1 − x, 1 − y, 1 − z; #3, 1 + x, y, z; #4, −x, 1 − y, −z; #5, 1 − x, 1 − y, −z; #6, 1 − x, 2 − y, 1 − z; (c) #1, x, 1 + y, z; #2, 1 − x, 1 − y, 2 − z; #3, 1 − x, 2 − y, 1 − z; #4, 1 − x, 2 − y, 2 − z; #5, x, y, 1 + z; #6, 1 − x, 1 − y, 1 − z; #7, −1 + x, −1 + y, z.

Figure 4. Combined ball-and-stick representation of the left-handed helical chain (top) and right-handed helical chain (bottom) of 1. All of the hydrogens and part of the triazole ring and pyridine ring have been omitted for clarity.

and exhibits a fascinating 3D network with close helical channels impregnated with the selves. Compounds 2 and 3 crystallize in the triclinic space group P1̅ and exhibit a surprising 3D network with helical channels than those of compound 1.

For a single net, the asymmetric unit of compound 1 is composed of a [PMo12O40]3− polyanion (abbreviate as {PMo12}), two independent Ag+ cations and one-half each of two Ag+ cations, and two independent H2ppytz-I ligands (Figure 2a). The coordination modes of {PMo12} cluster, Ag 2796



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Figure 5. (a) Combined ball/stick representation of the 1D helical channel. (b) Combined polyhedral/ball-and-stick representation of the 2D helical channel layer. (c) 3D supramolecular net along a axis of 1. All of the hydrogen has been omitted for clarity.

Figure 6. Combined space-filling and topological representations of (a) left- and right-handed helical chain. (b) The 1D helical channel. (c) 2D helical channel layer. (d) Schematic representations of 3D supramolecular net along a axis of 1. POMs, blue and green; Ag, purple; N, medium blue; C, light blue. All of the hydrogen has been omitted for clarity.

Ag1, Ag2, Ag2#1, Ag4, Ag4#1 (named as subunit B) (Supporting Information Figure S1). An interesting structural feature is that each subunit A (or subunit B) as a chelating ligand node (named as node A or B) coordinates with adjacent {PMo12} clusters forming the left-handed (or right-handed) helical chain (Figures 4 and 6a). Both left- and right-handed helical chains with a pitch of 10.385 Å are linked together via the bonds between Ag+ cations and bridging oxygen atoms (2.543 Å for Ag4−O1 and 2.639 Å for Ag2−O9), as shown in Supporting Information Figure S2. The left- and right-handed helical chains are then perfectly enclosed by sharing {PMo12} clusters forming the channels (Figures 5a and 6b). Furthermore, a 2D layer is formed by the assembly of these helical channels via sharing “butterfly-like” Ag5(H2ppytz)2 subunits, where each helical channel is connected with two adjacent ones along the a axis (Figures 5b and Figure 6c). As a consequence, these helical channel layers extended into a single

cation, and H2ppytz-I ligands are illustrated in Figure 3a. The basic structural unit of compound 2 contains one-half of [CoW12O40]6− polyanion (abbreviated as {CoW12}), three independent Ag+ cations, one H2ppytz-II ligand, one H2ppytz-II ligand, and lattice water molecules (Figure 2b), and their coordination modes are illustrated in Figure 3b. The basic structural unit of compound 3 contains one-half of [GeW12O40]4− polyanion (abbreviated as {GeW12}), four independent Ag+ cations, two H2ppytz-II ligands, and four lattice water molecules (Figure 2c), and their coordination modes are illustrated in Figure 3c. The bond lengths of Ag−O and Ag−N are in the range of 2.543−2.790 and 2.075−2.614 Å, respectively. The bond lengths and angles of these polyanions are in the normal range. In compound 1, two H2ppytz-I ligands link five Ag+ cations forming two kinds of “butterfly-like” Ag5(H2ppytz-I)2 subunits, Ag2#1, Ag2#2, Ag3, Ag4, Ag4#3 (named as subunit A) and 2797



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Figure 7. Combined space-filling, ball/stick, and topological representations of left- and right-handed helical chain of 2. All of the hydrogen, water atoms, and unnecessary triazole rings and pyridine rings have been omitted for clarity.

3D supramolecular net by intermolecular forces (O30···O37 = 2.810 Å, O32···O32 = 2.844 Å, O32···N1 = 2.855 Å). It is regrettable that these helical channels are mainly filled by each building block, leaving only small cavities (0.4% of the cell volume calculated by PLATON) (Figures 5c and 6d). To interlink the helical channel motifs into a larger porosity array, a V-shaped ligand H2ppytz-II, whose coordination chemistry has been investigated in our work, was used instead of H2ppytz-I. As expected, a larger helical channel 3D network occupied by water molecules in compound 2 was isolated. Four H2pyttz-II ligands link with four silver atoms forming a “paddlewheel like” Ag4(H2ppytz-II)4 motif (Supporting Information Figure S3, left). Each Ag4(H2ppytz-II)4 motif as a six-connected node connects with six adjacent {CoW12} POMs (Supporting Information Figure S2, right), which further expand into a 3D structure. Note that each {CoW12 } cluster links one Ag4(H2ppytz-II)4 motif (abbreviated as Node) forming a building fragment via Ag1 or Ag3 atom, which further connects with Ag2 atoms resulting in the formation of left- and righthanded helical chains (Node-Ag2-POMs-Node-Ag2-POMs, in Figure 7). Although these helical chains are composed of the same components, the different helical directions are obtained due to the symmetric coordination of Ag4(H2ppytz-II)4 unit with Ag2 centers. Similar to compound 1, the left- and righthanded helical chains are enclosed through sharing {CoW12} clusters into a larger channel (Figure 8a). As a consequence, a single 3D framework with larger helical channels contains large cavities (10.5% of the cell volume calculated by PLATON), which are occupied by the guest water molecules (Figure 8b). Surprisingly, a further investigation reveals that the structural character of compound 3 is similar to that of 2, a 3D network with larger helical channels. In 3, the composed modes of helical chains (Node-Ag-POMs-Node-Ag-POMs) and channels are the same as that in compound 2. However, different from 2, there is a bidentate coordinated Ag+ center (Ag3) in compound 3 (Figure 3c), which leads to the slight difference in the connected nodes. Both compounds 2 and 3 contain the Ag4(H2ppytz-II)4 motifs as connected nodes, but the difference is that the Ag4(H2ppytz-II)4 motifs in 2 are connected with four Ag2+ ions to obtain a 1D coordination chain, and the Ag4(H2ppytz-II)4 motifs in 3 are linked together by six Ag+ centers (four Ag2+ ions and two Ag3+ ions) to obtain the 2D coordination layer (Figure 9). As a consequence, a single 3D

Figure 8. (a) Combined space-filling, ball, stick, and topological representations of the larger helical channel. (b) Combined ball/stick and topological representation of the 3D framework with open helical channels along the c axis of 2. All of the hydrogen and water atoms have been omitted for clarity.

framework with larger helical channels contains large cavities (12.5% of the cell volume calculated by PLATON) to host the guest water molecules (Supporting Information Figure S3). Influence of Organic Ligand on the Structure of the Compounds. It is obvious that the organic ligand H2pyttz plays a significant role in determining the structure of the resultant compounds. Compound 1 was synthesized by using H2ppytz-I ligand, and 2 and 3 by using H2ppytz-II ligand. During the investigation of network shown in Figure 10, we find that the channels in compound 1 are mainly filled by building blocks due to Ag5(H2ppytz-I)2 subunits with a diameter of 8.4 Å (atom-to-atom separation), which is too small to hold Keggin-type POMs clusters (about 10 Å diameters) into large cavities. In the case of compounds 2 and 3, the diameters of the Ag4(H2ppytz-II)4 motifs (17.6 Å for 2 and 18.1 Å for 3) are larger than that of Ag5(H2ppytz-I)2 subunits, which affords a key role to form helical channel with larger window. It should be deduced that the proper coordination modes of organic ligands are the underlying reason for the formation of targeted structures, which is attributed to the choosing of optimized coordination sites of 2798



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Figure 9. Combined ball/stick and schematic representation of the Ag4(H2ppytz-II)4 motif connected with four Ag2+ ions of 2 (left) and Ag4(H2ppytz-II)4 motif connected with six Ag+ centers (four Ag2+ ions and two Ag3+ ions) of 3 (right).

The IR spectra of compounds 1, 2, and 3 are shown in Supporting Information Figure S5. Characteristic bands at 1062, 945, and 782 cm−1 for 1 are attributed to ν (P−O), ν (MoO), and ν (Mo−O−Mo) vibrations, 940, 864, and 744 cm−1 for 2 are attributed to ν (WO), ν (W−O−W), and ν (Co−O) vibrations, and 956, 877, and 771 cm−1 for 3 are attributed to ν (WO), ν (Ge−O), and ν (W−O−W) vibrations, respectively. Bands in the regions of 1639−1299 cm−1 for 1 are attributed to the H2pyttz-I ligand, while 1608− 1273 cm−1 for 2 and 1613−1295 cm−1 for 3 are attributed to the H2pyttz-II ligand. Photocatalysis Properties. To investigate the photocatalytic activities of these new compounds as catalyst, the photodecomposition of Rhodamine-B (RhB) is evaluated under UV light irradiation through a typical process: 50 mg of the compounds was mixed together with 100 mL of 1.0 × 10−5 mol/L (C0) RhB solution in a beaker by ultrasonic dispersion for 10 min. The mixture was stirred for 0.5 h until it reached the surface-adsorption equilibrium on the particles of the title compound. The mixture then was stirred continuously under ultraviolet (UV) irradiation from a 125 W high pressure Hg lamp. At 10, 20, 40, 60, 90, 120, 180, 240, 300, and 360 min, 3 mL of the sample was taken out of the beaker, respectively, followed by several centrifugations to remove the title compounds, and a clear solution was obtained for UV−vis analysis. The photodegradation of RhB assisted by compounds 1−3 is shown in Figure 11. For comparison, insoluble (NBu4)3[PMo12O40], (NBu4)6[CoW12O40], and (NBu4)4[GeW12O40] were also employed in the same catalytic experiments. When compounds 1 and 3 are used, the absorption maximum of the degraded solution with irradiation time exhibits hypsochromic shifts to some extent concomitantly with the cleavage of the conjugated structure, which results from the formation and decomposition of a series of Ndeethylation of RhB during irradiation, N,N,N′-triethyl thodamine (TER, 539 nm) and N,N′-diethyl rhodamine (DER, 522

Figure 10. Representations of the strategy for the larger channel and the coordination mode of each building block.

H2pyttz ligands themselves. This result indicates that the controllable and designable coordination modes of H2pyttz ligand greatly prompt the POMs as a building unit participating in the construction of helical channel. XRPD Pattern and IR Spectra. The XRPD pattern for 1 and 2 is presented in Supporting Information Figure S4. The diffraction peaks of both simulated and experimental patterns match well, thus indicating that the phase purity of the compounds is good. The difference in reflection intensities between the simulated and the experimental patterns is due to the different orientation of the crystals in the powder samples. 2799



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Figure 11. UV−vis adsorption changes observed for RhB solutions as a function of UV light irradiation time: (a) in the presence of (NBu4)3[PMo12O40] and compound 1 as catalyst, and time dependence and pictures of RhB concentration over compound 1 and (NBu4)3[PMo12O40]. (b) In the presence of (NBu4)6[CoW12O40] and compound 2 as catalyst, and time dependence and pictures of RhB concentration over compound 2 and (NBu4)6[CoW12O40]. (c) In the presence of (NBu4)4[GeW12O40] and compound 3 as catalyst, and time dependence and pictures of RhB concentration over compound 3 and (NBu4)4[GeW12O40].

nm).11 After irradiation of the compounds for 360 min, the photocatalytic decomposition rates, defined as 1 − C/C0, are 74.5% for 1, 8.2% for 2, 93.9% for 3, 55.8% for (NBu4)3[PMo12O40], 15.5% for (NBu4)6[CoW12O40], and 75.4% for (NBu4)4[GeW12O40], respectively. It is worth noting that both (NBu4)6[CoW12O40] and compound 2 show barely no capability of photocatalytic activities. When compounds 1 and 3 are used, the absorption peak of the dye undergoes a fairly large decrease, and the hypsochromic shifts of the absorption band are considerably insignificant. It is presumed that the cleavage of the whole chromophore structure of RhB occurs preferentially over the surface of compounds 1 and 3, which illustrates that the formation of POM-based compound could improve the photocatalytic performance of the POMs. The enhanced photocatalytic property may have arisen from the Ag-pyttz complex subunits, which may act as photosensitizer under UV light, promoting transition of electrons to

POMs. The result indicates that compounds 1 and 3 may be a potential photocatalyst to decompose some organic dye.

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CONCLUSION

In summary, three Keggin polyoxometalate-based organic− inorganic hybrid compounds with different helical channels have been synthesized, and their unique structure, porosity, and photocatalytic properties were characterized and studied. The successful syntheses of compounds 1−3 demonstrate that the controllable and designable coordination modes of organic ligand can greatly prompt the construction of POMOFs with different structures including the helical channel structures. Because of the wide availability of various organic ligands including N-, O-donor ligand, the use of the controllable coordination mode of ligand as a general strategy in coassembly can lead to a new generation of hybrid multifunctional porous materials. The work provides not only novel examples of 2800



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Table 1. Crystallographic Data and Structural Refinements for Compounds 1−3 compound formula fw T (K) space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (g cm−3) μ (mm−1) F(000) final R1,a wR2b [I > 2σ(I)] final R1,a wR2b (all data) GOF on F2 a

1

2

3

C18H14Ag3N14O40Mo12P 2572.23 293(2) C2/c 10.385(5) 32.060(5) 31.248(5) 90 96.776(5) 90 10 331(5) 8 3.303 4.064 9568.0 0.0245, 0.0513 0.0314, 0.0537 1.056

C36H32Ag6N28O42W12Co 4435.08 293(2) P1̅ 11.830(5) 12.709(5) 14.789(5) 105.033(5) 99.809(5) 115.518(5) 1833.6(12) 1 4.017 20.621 1971.0 0.1022, 0.2434 0.1811, 0.2915 1.038

C36H39Ag7N28O47W12Ge 4649.65 293(2) P1̅ 12.387(5) 13.140(5) 14.969(5) 104.870(5) 99.856(5) 116.097(5) 1998.3(13) 1 3.835 19.335 2049.0 0.0713, 0.1410 0.0801, 0.1451 1.203

R1 = ∑||F0| − |Fc||/∑|F0|. bwR2 = {∑[w(F02 − Fc2)2]/∑[w(F02)2]}1/2. over a period of 16 h. Yellow block crystals of 3 were filtered, washed with water, and dried at room temperature (22% yield based on Ag). Anal. Calcd for C36H39Ag7N28O47W12Ge (4649.65): C, 9.33; H, 0.43; N, 8.47; Ag, 16.31. Found: C, 9.29; H, 0.84; N, 8.43; Ag, 16.24. IR (KBr, cm−1): 1631(w), 1455(w), 1295(w), 956(s), 871(s), 771(s). X-ray Crystallography. Crystal data for compounds 1, 2, and 3 were collected on a Bruker SMART-CCD diffractometer with Mo Kα monochromatic radiation (λ = 0.71073 Å) at 293 K. The structures were solved by the directed methods and refined by full matrix leastsquares on F2 using the SHELXTL crystallographic software package.12 All of the non-hydrogen atoms were refined anisotropically. The positions of hydrogen atoms on carbon atoms were calculated theoretically. During the refinement, the command “ISOR” was used to restrain the non-H atoms with ADP and NPD problems, which led to relative high restraint values: 197 for compound 2, 108 for compound 3; O1, O3, O6, O7, O8, O9, O12, O13, O15, O16, O18, O20, O21, O22, C2, C4, C5, C6, C8, C11, C12, C16, C18, N1, N4, N7, N10, N11, and N12 in compound 2; O1, O2, O3, O4, O5, O6, O7, O15, O18, O20, O21, O22, N11, C15, and C17 in compound 3. Additionally, restraint command “SIMU” was used to average the thermal parameters of atoms with the same environments for compounds 2 and 3. It refined atoms C10, C11, and N1 in compound 2, O3, O15, and O20 in compound 3. Finally, restraint command “DELU” was used to average the thermal parameters of atoms with similar environments for compound 2. It refined atoms C1 and C2, N14 and C6 in compound 2. The positions of hydrogen atoms were calculated theoretically. The crystal data and structure refinements of compounds 1, 2, and 3 are summarized in Table 1. Selected bond lengths and angles for compounds 1, 2, and 3 are listed in Supporting Information Tables S1−S3, respectively. CCDC reference numbers: 960751 for 1, 960752 for 2, and 960753 for 3.

POMOFs with helical channels, but also a new strategy for the oriented assembly of different channels.

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MATERIALS AND METHODS

All reagents were purchased commercially and used without further purification. The ligands (H2pyttz-I and H2pyttz- II) were purchased from Jinan Henghua Sci. & Tec. Co., Ltd. Elemental analyses (C, H, N, and Ag) were performed on a Perkin Elmer 2400 CHN Elemental Analyzer and on a Leaman inductively coupled plasma (ICP) spectrometer. The IR spectra were obtained on an Alpha Centaurt FT/IR spectrometer with KBr pellet in the 400−4000 cm−1 region. The XRPD patterns were obtained with a Rigaku D/max 2500 V PC diffractometer with Cu Kα radiation; the scanning rate is 4 deg/s, with 2θ ranging from 5° to 40°. UV−vis absorption spectra were recorded on a 756 CRT UV−vis spectrophotometer. Synthesis of [Ag3(Hpyttz-I)4][PMo12O40] (1). A mixture of H3PMo12O40 (300 mg), AgNO3 (150 mg), H2pyttz-I (40 mg), and H2O (10 mL) was stirred for 1 h in air. The pH was then adjusted to 1.97 with 1 M HCl, and the mixture was transferred to an 18 mL Teflon-lined reactor. After 6 days’ heating at 180 °C, the reactor was slowly cooled to room temperature over a period of 16 h. Yellow block crystals of 1 were filtered, washed with water, and dried at room temperature (35% yield based on Ag). Anal. Calcd for C18H14Ag3N14O40Mo12P (2572.23): C, 8.41; H, 0.38; N, 7.63; Ag, 12.6. Found: C, 8.4; H, 0.54; N, 7.6; Ag, 12.58. IR (KBr, cm−1): 1639(m), 1514(w), 1299(m), 1062(s), 945(s), 782(s). Synthesis of [Ag6(H2pyttz-II)4][CoW12O40]·2H2O (2). A mixture of K6CoW12O40 (300 mg), AgNO3 (150 mg), H2pyttz (50 mg), NH4VO3 (36 mg), and H2O (10 mL) was stirred for 1 h in air. The pH was then adjusted to 1.86 with 1 M HCl, and the mixture was transferred to an 18 mL Teflon-lined reactor. After 6 days’ heating at 170 °C, the reactor was slowly cooled to room temperature over a period of 16 h. Blue block crystals of 2 were filtered, washed with water, and dried at room temperature (25% yield based on Ag). Anal. Calcd for C36H32Ag6N28O42W12Co (4441.06): C, 9.72; H, 0.72; N, 8.82; Ag, 14.59. Found: C, 9.65; H, 0.8; N, 8.75; Ag, 14.46. IR (KBr, cm−1): 1608(w), 1473(w), 1273(w), 940(s), 864(s), 744(s). Synthesis of [Ag7(Hpyttz-II)3(H2pyttz-II)][GeW12O40]·7H2O (3). A mixture of H4GeW12O40 (300 mg), AgNO3 (150 mg), H2pyttz (50 mg), NH4VO3 (36 mg), and H2O (10 mL) was stirred for 1 h in air. The pH was then adjusted to 2.3 with 1 M HCl, and the mixture was transferred to an 18 mL Teflon-lined reactor. After 6 days’ heating at 170 °C, the reactor was slowly cooled to room temperature

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ASSOCIATED CONTENT

S Supporting Information *

Tables of selected bond lengths (Å), bond angles (deg), figures, IR, and XRPD for compounds. This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data and CCDC can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac. uk/data_request/cif. 2801



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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is financially supported by the National Natural Science Foundation (Grant nos. 21271089), the Natural Science Foundation (no. B201214), the training program for New Century Excellent Talents in Universities (1253-NCET022) and the Postdoctoral Foundation of Heilongjiang Province.

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