OrganicâInorganic Hybrids Constructed from Mixed-Valence

Article pubs.acs.org/crystal

Organic−Inorganic Hybrids Constructed from Mixed-Valence Multinuclear Copper Complexes and Templated by Keggin Polyoxometalates Ming-guan Liu, Peng-peng Zhang, Jun Peng,* Hua-xin Meng, Xiang Wang, Min Zhu, Dan-dan Wang, Cui-li Meng, and Kundawlet Alimaje Key Laboratory of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, P. R. China S Supporting Information *

ABSTRACT: Five organic−inorganic hybrids containing mixed−valence multinuclear copper complexes and Keggin polyoxometalates, [CuI5CuII3(ptz)8(H2O)][HSiW12O40] (1), [CuI10CuII2(ptz)8(Cl)3][PW12O40] (2), [CuI2CuII4(ptz)6(OH)(H2O)2][PW12O40]·2H2O (3), C u I 2 C u I I 5 ( p t z ) 6 ( O H ) 2 S i W 1 2 O 4 0· 6 H 2 O ( 4 ) , a n d [CuI2CuII5(ptz)6][PMoV3MoVI9O40]·8H2O (5) (ptz = 5-(2pyridyl)-tetrazole), were hydrothermally synthesized and structurally characterized. Compound 1 exhibits a threedimensional (3D) network that features unprecedented double chains consisting of tetranuclear Cu clusters. Compound 2 displays a 3D network that has unusual Cl-centered hexanuclear Cu clusters and Cl-bridged tetranuclear Cu units. Compound 3 shows a 3D supramolecular network extended by two-dimensional (2D) grid-like sheets which are composed of mixed-valence multinuclear copper chains and PW12 polyanions. Isostructural compounds 4 and 5 exhibit a 3D network consisting of 2D ladder-like copper−ptz layers and SiW12 (PMo12 in 5) polyanions. The roles of copper ions with different oxidation states and ptz ligands with different coordination modes in the construction of the copper−ptz frameworks are discussed. Their electrochemical properties were investigated as well.

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INTRODUCTION Metal−organic frameworks (MOFs) have been paid intensive attention in recent years because of their applications in catalysis, sorption, electrical conductivity, magnetism, and photochemistry.1−3 Multinuclear clusters are a kind of significant building subunit in the crystal engineering of MOFs, as they have a larger size and multiple coordination sites, which is in favor of forming high-connected and highdimensional MOFs.4 Many multinuclear clusters have been successfully synthesized, such as manganese, iron, copper, nickel, and silver clusters.5−8 Among the transition metals, copper is a good candidate for assembly of multinuclear clusters due to its easily changeable oxidation state and flexible coordination modes.9,10 Another important role in the construction of multinuclear clusters is a multidentate organic ligand,11 which can connect more than one metal to increase the nuclearity of the complex and expand the dimension of MOFs. Among the numerous multidentate ligands, the rigid ligand 5-(2-pyridyl)-1H-tetrazole (Hptz) looks particularly attractive. Hptz has five potential N-coordination sites. The adjacently four N atoms of tetrazolyl and the one N atom of pyridyl are readily available to coordinate to metal ions for the construction of multinuclear clusters with bridging and/or chelating fashion. The Hptz ligand usually deprotonates to ptz © 2011 American Chemical Society

with a negative charge when it coordinates to metal ions. Scheme 1 summarizes main coordination types of ptz ligand. Scheme 1. The Main Coordination Types of ptz Ligand

Polyoxometalates (POMs), one kind of multiple functional metal oxide cluster, have often been employed as inorganic building blocks for constructing various MOFs with open Received: September 27, 2011 Revised: December 15, 2011 Published: December 20, 2011 1273

dx.doi.org/10.1021/cg2012809 | Cryst. Growth Des. 2012, 12, 1273−1281

Crystal Growth & Design

Article

Table 1. Crystal Data and Structure Refinements for Compounds 1−5 1 formula Fw T (K) crystal system space group a (Å) b (Å) c (Å) α (o ) β (o) γ (o) V (Å3) Z Dc (g·cm−3) μ (mm−1) F(000) final R1a, wR2b [I > 2σ(I)] final R1a, wR2b (all data) GOF on F2 a

C48H35Cu8N40O41SiW12 4570.57 293(2) triclinic P1̅ 14.294(3) 14.856(3) 23.109(4) 92.787(2) 91.568(2) 109.889(2) 4604.0(16) 2 3.295 16.839 4124.0 R1 = 0.0843, wR2 = 0.1977 R1 = 0.1760, wR2 = 0.2395 1.162

2 C48H32Cu12Cl3N40O40PW12 4914.98 293(2) monoclinic C2 24.001(12) 17.455(18) 11.676(3) 90.000(13) 105.096(14) 90.000(13) 4722.7(13) 2 3.456 17.382 4444 R1 = 0.0471, wR2 = 0.1411 R1 = 0.0600, wR2 = 0.1544 1.049

3 C36H35Cu6N30O45PW12 4224.15 293(2) triclinic P1̅ 11.3850(4) 12.3920(4) 15.0540(3) 99.216(2) 95.468(2) 110.979(3) 1930.45(11) 1 3.626 19.538 1887.0 R1 = 0.0437, wR2 = 0.1353 R1 = 0.0555, wR2 = 0.1395 1.002

R1 = ∑||Fo| − |Fc||/∑|Fo|. bwR2 = {∑[w(Fo2−Fc2)2]/∑[w(Fo2)2]}1/2.

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frameworks and nanochannels due to their large nanosizes, controllable shapes, high electronic density, and oxo-rich surfaces.12,13 A number of POM-based MOFs have been reported to date. However, reports on POM-based MOFs containing multinuclear clusters, especially the high-dimensional mixed-valence frameworks, are seldom. To the best of our knowledge, only three compounds based on [MoxOy]n− polyanions with Hptz as an organic linker were reported: [C u 2 (ptz)( H 2 O)( μ 2 -O )(M o 4 O 1 3 )] · H 2 O , 1 4 [ A g 4 (2pttz)2Mo4O13],15 and [Mn(ptz)Mo2O7].16 Compared with [MoxOy]n− polyanions, the Keggin polyanions have a larger volume and a higher negative charge; therefore, the Keggintype POMs may provide more coordination numbers and stronger coordination ability in constructing high-dimensional network. On the basis of the aforementioned points, in this work we chose a system of Keggin POMs, Cu and Hptz to construct POM-based MOFs containing multinuclear Cu clusters, and five new compounds were obtained: [CuI5CuII3(ptz)8(H2O)][HSiW12O40] (1), [CuI10CuII2(ptz)8(Cl)3][PW12O40] (2), [Cu I 2 Cu I I 4 (ptz) 6 (OH)(H 2 O) 2 ][PW 1 2 O 4 0 ]·2H 2 O (3), Cu I 2Cu I I 5( p t z )6 (O H) 2S iW 12O 40·6 H2O ( 4) , and [CuI2CuII5(ptz)6][PMoV3MoVI9O40]·8H2O (5) (ptz = 5-(2pyridyl)-tetrazole) (ptz = 5-(2-pyridyl)-tetrazole). Compounds 1 and 2 show a three-dimensional (3D) POM-templated Cu− ptz framework, which features unprecedented multinuclear Cu double chains in 1 and Cl-centered hexanuclear Cu clusters and Cl-bridged tetranuclear Cu units in 2. Compound 3 exhibits a 2D grid-like sheet which is composed of mixed-valence multinuclear copper chains and PW12 polyanions. Compounds 4 and 5 are isostructural, in which polyanions connect neighboring Cu−ptz layers to form a 3D POM-templated Cu−ptz framework. To the best of our knowledge, Compounds 1−5 represent the first mixed-valence Cu−ptz frameworks based on Keggin POMs.

4 C36H38Cu7N30O48SiW12 4337.85 296(2) triclinic P1̅ 11.9372(10) 13.8906(11) 14.1593(11) 99.5940(11) 91.4080(10) 111.3580(9) 2146.7(3) 1 3.345 17.811 1939.0 R1 = 0.0663, wR2 = 0.1675 R1 = 0.0842, wR2 = 0.1851 1.103

5 C36H40Cu7N30O48PMo12 3287.93 293(2) triclinic P1̅ 11.841(2) 13.837(3) 14.269(3) 99.426(3) 91.965(3) 110.705(2) 2146.6(7) 1 2.531 3.505 1556.0 R1 = 0.0654, wR2 = 0.1958 R1 = 0.0831, wR2 = 0.2134 1.016

EXPERIMENTAL SECTION

Materials and General Methods. All reagents were purchased commercially and used without further purification. Elemental analyses (C, H, and N) were performed on a Perkin-Elmer 2400 CHN elemental analyzer. The IR spectra were obtained on an Alpha Centaurt FT/IR spectrometer with KBr pellet in the 400−4000 cm−1 region. X-ray photoelectron spectroscopy (XPS) analyses were performed on a VG ESCALAB MK II spectrometer with an MgKα (1253.6 eV) achromatic X-ray source. The vacuum inside the analysis chamber was maintained at 6.2 × 10−6 Pa during analysis. The thermal gravimetric analyses (TGA) were carried out in flowing N2 on a Perkin-Elmer DTA 1700 differential thermal analyzer with a rate of 10.00 °C/min. Cyclic voltammograms were obtained with a CHI 660 electrochemical workstation at room temperature. Platinum gauze was used as a counter electrode and Ag/AgCl electrode was referenced. Chemically bulk-modified carbon paste electrode (CPE) was used as the working electrode. Synthesis of [CuI5CuII3(ptz)8(H2O)][HSiW12O40] (1). A mixture solution of H4[SiW12O40]·14H2O (0.30 g, 0.10 mmol), Cu(CH3COO)2 (0.24 g, 1.32 mmol), Hptz (0.04 g, 0.28 mmol), and H2O (8.00 mL) was stirred for 1 h at room temperature. The pH was adjusted to 4.8 with 1.0 mol·L−1 HCl, and then the suspension was transferred to a Teflon-lined reactor and kept under autogenous pressure at 170 °C for 3 days. Brown block crystals were filtered and washed with distilled water (yield 61% based on W). C48H35Cu8N40O41SiW12 (4570.57): Calc: C, 12.60%; H, 0.77%; N, 12.25%; Found: C, 12.73%; H, 0.75%; N, 12.29%. Synthesis of [CuI10CuII2(ptz)8(Cl)3][PW12O40] (2). The synthetic procedure was the same as that of compound 1, except that H4[SiW12O40]·14H2O was replaced by H3[PW12O40]·12H2O and the pH was adjusted to 4.2. Dark red block crystals were filtered and washed with distilled water (yield 49% based on W). C48H32Cu12Cl3N40O40PW12 (4914.98): Calc: C, 11.72%; H, 0.65%; N, 11.39%; Found: C, 11.86%; H, 0.81%; N, 11.27%. Synthesis of [CuI2CuII4(ptz)6(OH)(H2O)2][PW12O40]·2H2O (3). The synthetic procedure was the same as that of compound 2, except that the pH was adjusted by 1.0 mol·L−1 CH3COOH rather than HCl. Blue block crystals were filtered and washed with distilled water (yield 48% based on W). C36H33Cu6N30O45PW12 (4224.15): Calc: C, 10.23%; H, 0.78%; N, 9.94%; Found: C, 10.26%; H, 0.88%; N, 9.89%. 1274



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Synthesis of CuI2CuII5(ptz)6(OH)2SiW12O40·6H2O (4). The synthetic procedure was the same as that of compound 1, except for the following changes: Hptz (0.03 g, 0.21 mmol), pH 4.6; temperature 120 °C. Yellow-green block crystals were filtered and washed with distilled water (yield 53% based on W). C36H38Cu7N30O48SiW12 (4337.85): Calc: C, 9.96%; H, 0.88%; N, 9.68%; Found: C, 9.98%; H, 0.72%; N, 9.83%. Synthesis of [CuI2CuII5(ptz)6][PMoV3MoVI9O40]·8H2O (5). The synthetic procedure was similar to that of compound 4, except that H4[SiW12O40]·14H2O was replaced by H3[PMo12O40]·14H2O. Deep blue block crystals were filtered and washed with distilled water (yield 58% based on Mo). C36H37Cu7N30O48PMo12 (3284.93): Calc: C, 13.15%; H, 1.13%; N, 12.79%; Found: C, 12.88%; H, 1.18%; N, 12.62%. Preparations of 1−, 2−, 3−, 4−, and 5−CPEs. The compound 1 modified carbon paste electrode (1−CPE) was fabricated as follows: 90 mg of graphite powder and 8 mg of 1 were mixed and ground together by agate mortar and pestle to achieve a uniform mixture, and then 0.6 mL of nujol was added with stirring. The homogenized mixture was packed into a glass tube with a 1.2 mm inner diameter, and the tube surface was wiped with paper. Electrical contact was established with a copper rod through the back of the electrode. In a similar manner, 2−, 3−, 4−, 5−CPEs were made with compounds 2, 3, 4, and 5. X-ray Crystallographic Study. X-ray diffraction analysis data for compounds 1−5 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 direct methods and refined on F2 by full-matrix least-squares methods using the SHELXTL package.17 All the non-hydrogen atoms were refined anisotropically. Crystallographic data for the structures have been deposited with Cambridge Crystallographic Data Center with CCDC numbers: 833085 for 1, 843117 for 2, 833086 for 3, 833083 for 4, and 833084 for 5. Crystallographic data and structural determination for them are given in Table 1. Selected bond lengths and angles of compounds 1−5 are listed in Table S1 (Supporting Information).

the compounds (Figure S1, Supporting Information). The CuI ions exhibit common coordination modes of triangle and tetrahedral geometries, rather than the linear 2-fold coordination mode found in the complex [Cu(py)2]4[MoV2MoVI10O36(SO4)].20 Crystal Structure of Compound 1. Crystal structure analysis reveals that compound 1 consists of two half SiW12 polyanions, nine CuI/II ions, eight ptz ligands, and one water molecule (Figure 1a). All the W atoms are in the +VI oxidation state,

Figure 1. View of the (a) asymmetric unit of 1. (b) Tetranuclear Cu (Cu4) cluster. (c) Mixed-valence multinuclear copper double chain. Hydrogen atoms are omitted for clarity.

three Cu atoms (Cu1, Cu3, and Cu5) are in the +II oxidation state, and the other six (Cu2, Cu4 Cu6, Cu7, Cu8, and Cu9) are in the +I oxidation state. The SiW12 polyanions coordinate to two Cu ions (Cu1 and Cu3) in a bidentate coordination mode. The Cu−O distances are 2.331(18) and 2.44(2) Å, respectively. The nine crystallographically independent Cu centers show four kinds of coordination geometries: (i) a tetragonal pyramid mode for penta-coordinated Cu1, Cu3, and Cu5, achieved by four nitrogen atoms from two ptz ligands and one oxygen atom from the SiW12 polyanion or water molecule; (ii) a seesawshaped geometry for tetra-coordinated Cu2 and Cu7, which are coordinated by four nitrogen atoms from two ptz ligands; (iii) a planar fashion for tetra-coordinated Cu6 and Cu8, accomplished by four nitrogen atoms from two ptz ligands; (iv) a triangle geometry for tricoordinated Cu4 and Cu9, achieved by three nitrogen atoms from three ptz ligands. The bond lengths and angles around the Cu ions are in the ranges of 1.90(2)− 2.14(3) Å (Cu−N), 2.331(18)−2.44(2) Å (Cu−O), 79.7(10)− 180.000(14)° (N−Cu−N), and 85.2(9)−110.1(9)° (N−Cu− O). The coordination fashion of the eight ptz ligands can be divided into three kinds: μ1,2,4, μ1,2,5, and μ1,2,4,5. For the charge balance, a proton is added to the polyoxoanion. In compound 1, two interesting structural features exist: (i) tetranuclear Cu (Cu4) clusters formed through the connection of Cu2, Cu9 (or Cu4, Cu7) with μ1,2,5- and μ1,2,4,5-ptz ligands (Figure 1b); (ii) the mixed-valence multinuclear copper double chain constructed by the Cu4 clusters, Cu1−ptz and Cu3−ptz segments (Figure 1c). The double chains are linked to give a 2D grid-like sheet via the connections of Cu6−ptz and Cu8− ptz segments (Figure 2a). Further, the sheets are linked by Cu5−ptz segments to form a 3D Cu−ptz framework. SiW12 polyanions acting as bidentate ligands connect to the Cu−ptz framework. To simplify this network, schematic structure is shown in Figure 2b. It is clearly seen in Figure 2b (and Figure

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RESULTS AND DISCUSSION Synthesis. Compounds 1−5 were obtained in the reaction system of Keggin-type POM/Cu/Hptz under hydrothermal conditions. During the synthetic processes, some factors which might influence the assembly results of the POM/Cu/Hptz system were studied. Compounds 2 and 3 were synthesized from the same starting materials under identical reaction conditions, except for using different inorganic acids (HCl in 2 and CH3COOH in 3) to adjust the pH. As a result, Cl atoms are united in the crystal structure of compound 2, leading to the structural differences compared to that of compound 3. The synthetic conditions for isostructural compounds 4 and 5 are the same, except for using different Keggin-type POMs as building blocks, suggesting that small differences in the shape, size, and charge of the polyanions SiW12 and PMo12 do not affect on the assembly results of the POM/Cu/Hptz system. In addition, the generation of CuI ions should be attributed to the redox reaction of CuII ions and N-containing ligands (ptz in this paper) which occasionally occurs under the hydrothermal conditions.10 Description of the Crystal Structures. All the Keggin polyanions exhibit a classical α-Keggin configuration: the central atoms Si (P) are disordered surrounded by a cube of eight oxygen atoms with each oxygen site half occupied; the bond lengths and bond angles both are in the normal ranges.18 The formulas of the five compounds are given according to integrated results of the crystal structure analyses, XPS spectra, bond valence sum (BVS),19 coordination mode of Cu (Tables S2 and S3; Figure S2, Supporting Information), and color of 1275



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Figure 2. (a) Combined stick/ball representation of the 2D sheet structure in compound 1; (b) schematic view of the 3D network of compound 1 (Cu ions, blue; Cu4 cluster, green).

coordinated by four nitrogen atoms (Cu5−N, 1.90(6)− 2.04(8) Å) from two ptz ligands and two oxygen atoms (Cu5−O, 2.55(10)−2.60(10) Å) from two PW12. Cu6 coordinates with three nitrogen atoms (Cu6−N, 1.99(17)− 2.20(7) Å) from two ptz ligands and one Cl atom (Cu6−Cl1, 2.15(6) Å) in a distorted seesaw-shaped fashion. Additionally, Cu1 and Cu6 are disordered with the farthest distance of 2.86 Å, indicating a Cu−Cu metal bond.21 The ptz ligands in the structure show three kinds of coordination modes: μ1,2,3,4, μ1,2,4,5, and μ1,2,3,4,5. In compound 2, three motifs exist: Cu5−ptz segments; Clbridged tetranuclear Cu (Cu4) units; Cl-centered hexanuclear Cu (Cu6) clusters (Figure S4a, Supporting Information). The Cu5−ptz segments act as linkages, connecting the Cu6 clusters to generate a 2D grid-like layer (Figure 4a). The adjacent layers

S3, Supporting Information) that two kinds of channels (A and B) exist, accommodating SiW12 polyanions. The coordinated water molecules of Cu5 point toward the inside in channel A whereas they point toward the outside in channel B. Channels A and B are arranged alternately to form a POM-templated mixed-valence MOFs containing Cu4 clusters. Crystal Structure of Compound 2. Crystal structure analysis reveals that compound 2 is constructed from 1 [PW12O40]3− (PW12) polyanion, 12 CuI/II ions, 8 ptz ligands, and 3 chlorine anions (Figure 3). All the W atoms are in the +VI oxidation

Figure 3. Stick/polyhedral view of the asymmetric unit of 2. Hydrogen atoms are omitted for clarity.

state, 2 Cu5 atoms are in the +II oxidation state, and 10 Cu atoms (two Cu1, two Cu2, two Cu3, two Cu4, and two Cu6) are in the +I oxidation state. Cu1 is coordinated by two nitrogen atoms (Cu1−N, 1.83(6)−2.04(7) Å) from two ptz ligands and one Cl atom (Cu1−Cl1, 2.24(5) Å) in a triangle coordination mode. Cu2 and Cu4 are coordinated by two nitrogen atoms (Cu2(4)−N, 1.85(4)−1.98(4) Å) from two ptz ligands, one Cl atom (Cu2(4)−Cl2, 2.36(5)−2.44(5) Å) and one oxygen atom (Cu2(4)−O, 2.46(10)−2.78(10) Å) from one PW12 in a triangular pyramid mode. Cu3 adopts a seesaw-type coordinate fashion through four nitrogen atoms (Cu3−N, 1.93(13)− 2.32(3) Å) from three ptz ligands. Cu5 is octahedrally

Figure 4. (a) Combined stick/ball representation of the grid-like layer in compound 2; (b and c) schematic view of the 3D framework (Cu ions, blue; Cu4 cluster, yellow; Cu6 cluster, green).

are further connected through two Cu4 units, leading to a 3D Cu−ptz framework. Consideration of the Cu6 clusters as nodes and Cu5−ptz and Cu4 units as linkers, the Cu−ptz framework can be symbolized as a net with pcu topologic (Figure 4b; Figure S4b, Supporting Information). As shown in Figure 4c, PW12 polyanions acting as templates are enclosed in channels 1276



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and one μ2-OH anion. Two kinds of ptz ligands exist in the μ1,2,3 and μ1,2,3,5 coordination modes in the structure. The six Cu centers can also be divided into two kinds of segments according to their roles in the construction of the 2D sheet of compound 3: tetranuclear Cu (Cu4) clusters constructed from Cu1, Cu2, and μ1,2,3-, μ1,2,3,5-ptz ligands; Cu3 groups constructed from two Cu3 atoms and one μ2-OH. Each Cu4 cluster is connected to a mixed-valence multinuclear copper chain via two Cu3 groups, and then the neighboring chains are linked by polyanion PW12 which acts as a bidentate inorganic linker covalently bonding to two Cu2 atoms to form a 2D grid-like sheet (Figure 6a). Along the a direction, the sheet shows a “ribbon-like” motif. The adjacent “ribbon” stack parallelly through π···π interactions with the shortest distance of 3.35 Å resulting in a supramolecular network with supramolecular channels, in which the PW12 reside (Figure 6b). Crystal Structure of Compounds 4 and 5. Crystal structure analysis reveals that compounds 4 and 5 are isostructural. Two Cu1 are in the +I oxidation state and five Cu (two Cu2, two Cu4, and one Cu3) are in the +II oxidation state; All the W atoms are in the +VI oxidation state for compound 4, while 3 out of 12 Mo atoms are in the +V oxidation state for compound 5. Here only the structure of 4 is discussed. Compound 4 contains one [SiW12O40]4− (SiW12) polyanion, seven CuI/II ions, six ptz ligands, two μ2-OH anions, and six water molecules (Figure 7). The seven Cu centers are in four

and meanwhile connect to the copper−ptz framework as octadentate ligands. Besides, to the best of our knowledge, the Cl-centered hexanuclear Cu cluster is rarely observed in the POM-based MOFs. Crystal Structure of Compound 3. In the asymmetric structural unit of 3, there exist one [PW12O40]3− (PW12) polyanion, six CuI/II ions, six ptz ligands, one μ2-OH anion, and four water molecules (Figure 5). All the W atoms are in the +VI

Figure 5. Stick/polyhedral view of the asymmetric unit of 3. Hydrogen atoms and crystal water molecules are omitted for clarity.

oxidation state, four Cu (two Cu1 and two Cu2) atoms are in the +II oxidation state and two Cu3 are in the +I oxidation state. Cu1 coordinates with four nitrogen atoms (Cu1−N, 1.989(11)−2.077(11) Å) from three ptz ligands and one water molecule (Cu(1)−OW1, 2.184(9) Å) and shows a tetragonal pyramid coordination mode. Cu2 exhibits an octahedral fashion by coordinating with five nitrogen atoms (Cu2−N, 1.972(11)−2.387(11) Å) from three ptz molecules and one oxygen atom (Cu2−O21, 2.388(10) Å) from PW12. Cu3 exhibits a “T-type” coordinated mode by two nitrogen atoms (Cu3−N, 1.966(14)−1.984(13) Å) from two ptz ligands

Figure 7. Stick/polyhedral view of the asymmetric unit of compound 4. Hydrogen atoms and crystal water molecules are omitted for clarity.

kinds of coordination environments: Cu1 in a distorted triangular pyramid achieved by three nitrogen atoms (Cu1−

Figure 6. Combined stick/polyhedral representation of (a) the grid-like sheet in compound 3; (b) the supramolecular network with supramolecular channels. 1277



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Figure 8. Combined stick/polyhedral representation of (a) the grid-like layer in compound 4; (b) the 3D network with supramolecular channels.

Figure 9. Schematic view of the roles of CuI/CuII ions and ptz ligands with different coordination modes in the construction of copper−ptz frameworks of compounds 1−5.

are constructed by Cu/Hptz complex segments, except for the differences in oxidation states of copper ions and coordination modes of ptz ligands. For clarity, the roles of CuI/CuII ions and ptz ligands with different coordination modes in the construction of copper−ptz frameworks are schematically summarized in Figure 9. In compounds 1 and 2, the multinuclear Cu clusters (Cu4 in 1, Cu6 and Cu4 in 2) are all composed of CuI ions. Furthermore, these multinuclear Cu clusters are linked through μ1,2,4,5-, μ1,2,4-, and μ1,2,5-ptz/Cu segments in 1, and μ1,2,4,5-ptz/Cu segments in 2, to form a 3D framework, respectively. In compound 3, the multinuclear Cu clusters (Cu4) are composed of CuII ions, which are linked through Cu3 segments, resulting in a 1D chain. In compounds 4 and 5, the multinuclear Cu clusters (Cu6) are composed of CuI and CuII ions, which are linked through μ1,2,4,5-ptz/Cu segments, resulting in a 2D grid-like sheet. We therefore deduce that the valences of copper and the binding modes of ptz ligands might affect significantly the dimensionality of the copper−ptz frameworks. FT-IR and XPS Spectra. The IR spectra of compounds 1−5 are shown in Figure S5. In the spectra, the characteristic bands at 919, 973, 876, and 785 cm−1 for 1, 918, 972, 875, and 785 cm−1 for 4 are attributed to ν(Si−O), ν(W−Od), ν(W−Ob− W), and ν(W−Oc−W), respectively. The characteristic bands at 1079, 980, 896, and 801 cm−1 for 2, 1079, 980, 894, and 800 cm−1 for 3, are attributed to ν(P−O), ν(W−Od), ν(W−Ob− W), and ν(W−Oc−W), respectively. The absorption bands at 1064, 961, 871, and 782 cm−1 for 5 are attributed to ν(P−O), ν(Mo−Od), ν(Mo−Ob−Mo), and ν(Mo−Oc−Mo). Furthermore, a series of characteristic bands in the regions of 1170− 1617 cm−1 for 1−5 are attributed to the ptz ligands. The XPS spectra of compounds 1−5 (Figure S6, Supporting Information) give the peaks at 935.0, 954.2, 944.1, and 962.8

N, 1.925(16)−2.051(16) Å) from three ptz ligands and one oxygen atom (Cu1−O17, 2.438(19) Å) of the SiW12 polyanion; Cu2 in a tetragonal pyramid achieved by four nitrogen atoms (Cu2−N, 1.971(15)−2.253(19) Å) from three ptz ligands and one hydroxyl anion (Cu2−OW2, 1.941(19) Å); Cu3 in an octahedron achieved by four nitrogen atoms (Cu3−N, 1.974(17)−2.035(17) Å) from two ptz ligands and two water molecules (Cu3−OW1, 2.566(19) Å); Cu4 in a distorted octahedron achieved by four nitrogen atoms (Cu4−N, 1.953(16)−2.373(18) Å) from three ptz ligands, one oxygen atom (Cu4−O5, 2.454(19) Å) from the SiW12 polyanion, and one hydroxyl anion (Cu4−OW2, 1.982(19) Å). The ptz ligands adopt three kinds of coordination modes: μ1,2,3,4, μ1,2,4,5, and μ1,2,3,4,5. In compound 4, two μ1,2,3,4- and two μ1,2,3,4,5-ptz ligands bridge six copper ions to form a nearly flat hexanuclear Cu (Cu6) cluster. These Cu6 clusters are extended through the μ3N atoms to a mixed-valence multinuclear copper chain undulating along the c direction, which is structurally analogous to the complex [Cu2(ptz)(H2O)(μ2-O)(Mo4O13)]·H2O.14 Further, the neighboring chains are connected by Cu3−ptz segments through Cu2 and Cu4 to form a 2D copper−ptz layer, and the layers are parallel to each other (Figure 8a). The SiW12 polyanions insert into the 1D supramolecular channels composed of ladder-like copper−ptz layers along the c direction and covalently connect the neighboring copper−ptz layers in a tetradentate-coordination fashion, resulting in a 3D architecture. In other words, the SiW12 polyanion acts as a template, directing the extension of the framework (Figure 8b). The Roles of Copper Ions with Different Oxidation States and ptz Ligands with Different Coordination Modes in the Construction of the copper−ptz Frameworks. In compounds 1−5, all the metal−organic frameworks 1278



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Figure 10. The cyclic voltammograms of the 3−, 4−, and 5−CPE in 1 M H2SO4 at different scan rates. (From inner to outer: 40, 50, 60, 70, 80, 90, 100, 110, 120, and 130 mV·s−1 for 3; 40, 80, 120, 160, 200, 240, 280, 320, 360, and 400 mV·s−1 for 4; 150, 200, 250, 300, 350, and 400 mV·s−1 for 5.)

range of +450 to −700 mV for 3−CPE, there are three pairs of redox peaks (II−II′, III−III′, IV−IV′) with the peak potentials E1/2 = (Epc + Epa)/2 of −103, −339, and −542 mV. Redox peaks II−II′ and III−III′ correspond to two consecutive one electron processes of W, while IV−IV′ corresponds to a twoelectron process, and one irreversible redox peak (I) at 190 mV (scan rate: 100 mV·s−1), assigned to the oxidation of the Cu(I).23 In the potential range of +500 to −750 mV for 4− CPE, there are two reversible redox peaks (II−II′, III−III′) with the half-wave potentials E1/2 = (Epc + Epa)/2 at −353 and −512 mV, respectively (scan rate: 160 mV·s−1), which correspond to two consecutive two-electron processes of W.24 There is also an irreversible anodic peak (I) which should be assigned to the oxidation of the Cu(I).25 In the potential range of +600 to −130 mV for 5−CPE, three pairs of reversible redox peaks (I− I′, II−II′, III−III′) are observed and the corresponding E1/2 values are +424, +268, and +36 mV (scan rate: 300 mV·s−1), respectively. These redox peaks can be ascribed to three consecutive two-electron processes of Mo centers.26 However, the oxidation peak of copper centers is not observed in the scan range of +600 and −130 mV. This phenomenon was also observed in the previous report.27 Furthermore, when the scan rates varied from 40 to 130 mV·s−1 for 3−CPE, 40 to 400 mV·s−1 for 4−CPE, and 150 to 400 mV·s−1 for 5−CPE, the peak potentials change gradually: the cathodic peak potentials shift to the negative direction and the corresponding anodic peak potentials to the positive direction with increasing scan rates.

eV for 1, 935.0, 955.1, 943.5, and 962.9 eV for 2, 934.5, 954.3, 943.2, and 962.3 eV for 3, 935.4, 954.7, 942.8, and 963.1 eV for 4, and 935.3, 954.6, 943.2, and 963.2 eV for 5, attributed to CuII ions. The peaks at 932.1 and 952.3 eV for 1, 932.2 and 952.4 eV for 2, 932.6 and 951.8 eV for 3, 932.6 and 952.4 eV for 4, 932.7 and 952.3 eV for 5 are attributed to CuI ions. Two peaks, at 35.3 and 37.4 eV for 1, 35.3 and 37.5 eV for 2, 35.2 and 37.3 eV for 3, 35.2 and 37.2 eV for 4, are ascribed to WVI(4f7/2) and WVI(4f5/2) ions. The four overlapped peaks at 231.7 and 232.6 eV, 234.8 and 235.8 eV for 5 are ascribed to MoV(3d5/2), MoVI(3d5/2), MoV(3d3/2), and MoVI(3d5/2) ions, respectively.22 These results are conform to the BVS and coordination environments of copper in the crystal structures. Thermal Analyses. The thermal stabilities of compounds 1−5 were investigated under a N2 atmosphere with a heating rate of 10 °C·min−1 from 30 to 800 °C. The TG curves (Figure S7, Supporting Information) of 1, 3−5 exhibit a two-step weight loss process: the weight loss of 0.47% (calc. 0.39%) for 1, 2.38% (calc. 2.13%) for 3, 3.76% (calc. 3.32%) for 4 and 4.52% (calc. 4.38%) for 5 below 300 °C correspond to the release of water molecules and the hydroxyl anions. After 300 °C, the weight loss steps can be ascribed as the loss of ptz ligands and decomposition of POMs, 25.73% (calc. 25.56%) for 1, 20.95% (calc. 20.74%) for 3, 20.63% (calc. 20.19%) for 4 and 27.12% (calc. 26.67%) for 5, respectively. For the anhydrous complex 2, the TG curve shows a one-step weight loss of 26.36% (calc. 25.93%) in the range of 30−700 °C, ascribed to the removal of Cl, decomposition of ptz ligands and POMs. Cyclic Voltammetry. Compounds 1−5 are insoluble in water and common organic solvent, so the bulk-modified CPE becomes an optimal choice to investigate the electrochemical behaviors. The electrochemical behaviors of 1−CPE and 4− CPE are similar; 2−CPE and 3−CPE are also analogous. Thus, 3−, 4− and 5−CPE have been taken as examples to study their electrochemical properties. The electrochemical behaviors were studied in 1 M H2SO4 solution (Figure 10). In the potential

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CONCLUSION In this paper, by utilizing copper with various coordination spheres and Hptz with multiple coordination modes, five POMtemplated mixed-valence MOFs containing multinuclear Cu clusters were synthesized by adjusting hydrothermal conditions. Compounds 1 and 4 were obtained from the same reaction 1279



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(8) (a) Guo, Y. Q.; Yang, B. P.; Song, J. L.; Mao, J. G. Cryst. Growth Des. 2008, 8, 600−605. (b) Biswas, S.; Tonigold, M.; Volkmer, D. Z. Anorg. Allg. Chem. 2008, 634, 2532−2538. (9) (a) Hathaway, B. J.; Billing, D. E. Coord. Chem. Rev. 1970, 5, 143andreferences citedtherein. (b) Hathaway, B. J. Struct. Bonding (Berlin) 1984, 57, 55. (c) Palaniandavar, M.; Butcher, R. J.; Addison, A. W. Inorg. Chem. 1996, 35, 467−471. (10) (a) Lei, C.; Mao, J. G.; Sun, Y. Q.; Song, J. L. Inorg. Chem. 2004, 43, 1964−1968. (b) Shi, Z. Y.; Gu, X. J.; Peng, J.; Yu, X.; Wang, E. B. Eur. J. Inorg. Chem. 2006, 385−388. (c) Zhang, X. M.; Tong, M. L.; Chen, X. M. Angew. Chem., Int. Ed. 2002, 114, 1071. (d) Liu, C. M.; Zhang, D. Q.; Zhu, D. B. Cryst. Growth Des. 2005, 5, 1639−1642. (11) (a) Zhang, Z. M.; Qi, Y. F.; Qin, C.; Li, Y. G.; Wang, E. B.; Wang, X. L.; Su, Z. M.; Xu, L. Inorg. Chem. 2007, 46, 8162−8169. (b) Wang, W. G.; Zhou, A. J.; Zhang, W. X.; Tong, M. L.; Chen, X. M.; Nakano, M.; Beedle, C. C.; Hendrickson, D. N. J. Am. Chem. Soc. 2007, 129, 1014−1015. (c) Li, J. T.; Tao, J.; Huang, R. B.; Zheng, L. S.; Yuen, T.; Lin, C. L.; Varughese, P.; Li, J. Inorg. Chem. 2005, 44, 4448−4450. (12) (a) Hill, C. L. Chem. ReV. 1998, 98, 1. (b) Long, D. L.; Burkholder, E.; Cronin, L. Chem. Soc. ReV. 2007, 36, 105−121. (c) Han, Q. X.; Ma, P. T.; Zhao, J. W.; Wang, Z. L.; Yang, W. H.; Guo, P. H.; Wang, J. P.; Niu, J. Y. Cryst. Growth Des. 2011, 11, 436−444. (d) Botar, B.; Kő gerler, P.; Hill, C. L. Inorg. Chem. 2007, 46, 5398− 5403. (13) (a) Bareyt, S.; Piligkos, S; Hasenknopf, B.; Gouzerh, P.; Lacôte, E.; Thorimbert, S.; Malacria, M. J. Am. Chem. Soc. 2005, 127, 6788− 6794. (b) Sun, C. Y.; Liu, S. X.; Liang, D. D.; Shao, K. Z.; Ren, Y. H.; Su, Z. M. J. Am. Chem. Soc. 2009, 131, 1883−1888. (c) Li, Y. G.; Dai, L. M.; Wang, Y. H.; Wang, X. L.; Wang, E. B.; Su, Z. M.; Xu, L. Chem. Commun. 2007, 2593−2595. (d) Dai, L. M.; You, W. S.; Li, Y. G.; Wang, E. B.; Huang, C. Y. Chem. Commun. 2009, 2721−2723. (e) Ma, F. J.; Liu, S. X.; Sun, C. Y.; Liang, D. D.; Ren, G. J.; Wei, F.; Chen, Y. G.; Su, Z. M. J. Am. Chem. Soc. 2011, 133, 4178−4181. (14) Wu, X. Y.; Dong, P.; Yu, R. M; Zhang, Q. K.; Kuang, X. F.; Chen, S. C.; Lin, Q. P.; Lu, C. Z. CrystEngComm 2011, 13, 3686− 3688. (15) Yang, M. X.; Chen, L. J.; Lin, S.; Chen, X. H.; Huang, H. Dalton Trans. 2011, 40, 1866−1872. (16) Dong, P.; Zhang, Q. K.; Wang, F.; Chen, S. C.; Wu, X. Y.; Zhao, Z. G.; Lu, C. Z. Cryst. Growth Des. 2010, 10, 3218−3221. (17) (a) Sheldrick, G. M. SHELX-97, Program for Crystal Structure Refinement; University of Göttingen: Germany, 1997. (b) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Solution; University of Göttingen: Germany, 1997. (18) (a) Evans, H. T.; Pope, M. T. Inorg. Chem. 1984, 23, 501−504. (b) Maguerès, P. L.; Ouahab, L.; Golhen, S.; Grandjean, D.; Peňa, O.; Jegaden, J. C.; Gomez-Garcia, C. J.; Delhab, P. Inorg. Chem. 1994, 33, 5180−5187. (c) Chen, J.; Sha, J. Q.; Peng, J.; Shi, Z. Y.; Dong, B. X.; Tian, A. X. J. Mol. Struct. 2007, 846, 128−133. (19) Brown, I. D.; Altermatt, D. Acta Crystallogr. B. 1985, 41, 244. (20) Yang, W. B.; Lu, C. Z.; Zhuang, H. H. J. Chem. Soc., Dalton Trans. 2002, 2879−2884. (21) (a) Tian, A. X.; Han, Z. G.; Peng, J.; Ying, J.; Sha, J. Q.; Dong, B. X.; Zhai, J. L.; Liu, H. S. Inorg. Chim. Acta 2008, 361, 1332−1338. (b) Wang, J. P.; Ren, Q.; Zhao, J. W.; Niu, J. Y. Inorg. Chem. Commun. 2006, 9, 1281−1285. (c) Goforth, A. M.; Gerth, K.; Smith, M. D.; Shotwell, S.; Bunz, U. H. F.; Loye, H. C. Solid State Sci. 2005, 7, 1083− 1095. (d) Ellena, J.; Kremer, E.; Facchin, G.; Baran, E. J.; Nascimento, O. R.; Costa-Filho, A. J.; Torre, M. H. Polyhedron 2007, 26, 3277− 3285. (22) (a) Sun, X. F.; You, W. S.; Cheng, H. W.; Zhang, F.; Meng, B. F.; Zhang, L. C. Inorg. Chim. Acta 2011, 373, 137−141. (b) Yang, H. X.; Lin, J. X.; Chen, J. T.; Zhu, X. D.; Gao, S. Y.; Cao, R. Cryst. Growth Des. 2008, 8, 2623−2625. (c) Shi, S. Y.; Zou, Y. C.; Cui, X. B.; Xu, J. N.; Wang, Y.; Wang, G. W.; Yang, G. D.; Xu, J. Q.; Wang, T. G.; Gao, Z. M. CrystEngComm 2010, 12, 2122−2128. (d) Hou, G. F.; Bi, L. H.; Li, B.; Wu, L. X. Inorg. Chem. 2010, 49, 6474−6483. (e) Zhao, J. W.; Song, Y. P.; Ma, P. T.; Wang, J. P.; Niu, J. Y. J. Solid State Chem. 2009,

system of SiW12/Cu/Hptz, but with different pH, reaction temperature, and amount of Hptz; compounds 2 and 3 were obtained from the same reaction system of PW12/Cu/Hptz but with different inorganic acids; compounds 4 and 5 were obtained from the same reaction system of Cu/Hptz, but with different Keggin-type POMs. The structural analyses reveal that these alternations might or not influence the assembly results of the POM/Cu/Hptz system. The different valences of copper and the binding modes of ptz ligands might affect significantly the dimensionality of the copper−ptz frameworks, whereas different Keggin-type POMs seem not to influence their structures. Compounds 1−5 are featured with the MOFs composed of mixed-valence multinuclear copper−ptz segments, which have been seldom reported until now. This work provides informative examples for constructing mixed-valence MOFs based on multinuclear metal clusters and POMs.

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ASSOCIATED CONTENT

S Supporting Information *

Optical micrographs of compounds 1−5; table of selected bond lengths and angles and IR, XPS, TG, BVS data for compounds 1−5; additional structural figures of compounds 1 and 2; coordination number and mode of Cu in compounds 1−5. This information is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +86-431-85099667. E-mail: [email protected].

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ACKNOWLEDGMENTS

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REFERENCES

This work is financially supported by the National Natural Science Foundation of China (21071029), the Program for Changjiang Scholars and Innovative Research Team in University.

(1) (a) Férey, G.; Serre, C. Chem. Soc. Rev. 2009, 38, 1380−1399. (b) O’Keeffe, M. Chem. Soc. Rev. 2009, 38, 1215−1217. (2) (a) Yuan, D. Q.; Zhao, D.; Sun, D. F.; Zhou, H. C. Angew. Chem., Int. Ed. 2010, 122, 5485−5489. (b) Zheng, S. T.; Bu, J. T.; Li, Y. F.; Wu, T.; Zuo, F.; Feng, P. Y.; Bu, X. H. J. Am. Chem. Soc. 2010, 132, 17062−17064. (3) (a) Perman, J. A.; Dubois, K.; Nouar, F.; Zoccali, S.; Wojtas, L.; Eddaoudi, M.; Larsen, R. W.; Zaworotko, M. J. Cryst. Growth Des. 2009, 9, 5021−5023. (b) Ma, S. Q.; Zhou, H. C. Chem. Commun. 2010, 46, 44−53. (c) Horner, M. J.; Holman, K. T.; Ward, M. D. J. Am. Chem. Soc. 2007, 129, 14640−14660. (4) Chun, H.; Kim, D.; Dybtsev, D. N.; Kim, K. Angew. Chem., Int. Ed. 2004, 116, 989. (5) (a) Fang, X. K.; Luban, M. Chem. Commun. 2011, 47, 3066− 3068. (b) Collison, D.; McInnes, E. J. L.; Brechin, E. K. Eur. J. Inorg. Chem. 2006, 2725−2733. (c) Zhang, Z. M.; Li, Y. G.; Yao, S.; Wang, E. B.; Wang, Y. H.; Clérac, R. Angew. Chem., Int. Ed. 2009, 121, 1609− 1612. (6) (a) Karotsis, G.; Kennedy, S.; Dalgarno, S. J.; Brechin, E. K. Chem. Commun. 2010, 46, 3884−3886. (b) Zhang, S. Y.; Zhen, L. N.; Xu, B.; Inglis, R.; Li, K.; Chen, W. Q.; Zhang, Y.; Konidaris, K. F.; Perlepes, S. P.; Brechin, E. K.; Li, Y. H. Dalton Trans. 2010, 39, 3563− 3571. (7) (a) Fielden, J.; Long, D. L.; Slawin, A. M. Z.; Kö1gerler, P.; Cronin, L. Inorg. Chem. 2007, 46, 9090−9097. (b) Pyykkö, P. Chem. Rev. 1997, 97, 597−636. 1280



Article

182, 1798−1805. (f) Yu, F.; Zheng, P. Q.; Long, Y. X.; Ren, Y. P.; Kong, X. J.; Long, L. S.; Yuan, Y. Z.; Huang, R. B.; Zheng, L. S. Eur. J. Inorg. Chem. 2010, 4526−4531. (23) Tian, A. X.; Ying, J.; Peng, J.; Sha, J. Q.; Su, Z. M.; Pang, H. J.; Zhang, P. P.; Chen, Y.; Zhu, M.; Shen, Y. Cryst. Growth Des. 2010, 10, 1104−1110. (24) (a) Sadakane, M.; Steckhan, E. Chem. Rev. 1998, 98, 219−237. (b) Zhang, P. P.; Peng, J.; Pang, H. J.; Chen, Y.; Zhu, M.; Wang, D. D.; Liu, M. G.; Wang, Y. H. Solid State Sci. 2010, 12, 1585−1592. (25) Sha, J. Q.; Peng, J.; Tian, A. X.; Liu, H. S.; Chen, J.; Zhang, P. P.; Su, Z. M. Cryst. Growth Des. 2007, 7, 2535−2541. (26) (a) Wang, X. L.; Bi, Y. F.; Chen, B. K.; Lin, H. Y.; Liu, G. C. Inorg. Chem. 2008, 47, 2442−2448. (b) Wang, P.; Wang, X. P.; Jing, X. Y.; Zhu, G. Y. Anal. Chim. Acta 2000, 424, 51. (27) Wang, X. L.; Qin, C.; Wang, E. B.; Su, Z. M.; Li, Y. G.; Xu, L. Angew. Chem., Int. Ed. 2006, 118, 7571−7574.

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