- Email: [email protected]
TMC hybrid with AgI⋯AgI interactions
Inorganic Chemistry Communications 11 (2008) 765–768
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis and characterization of the highest connected 3D a-metatungstate POM/TMC hybrid with AgI AgI interactions Chun-Jing Zhang, Ya-Guang Chen *, Hai-Jun Pang, Dong-Mei Shi, Mi-Xia Hu, Jia Li Key Laboratory of Polyoxometalates Science of Ministry of Education, College of Chemistry, Northeast Normal University, Changchun 130024, PR China
a r t i c l e
i n f o
Article history: Received 23 January 2008 Accepted 26 March 2008 Available online 1 April 2008 Keywords: a-Metatungstate polyoxometalate Conventional synthesis Silver Luminescence
a b s t r a c t A novel 3D hybrid based on transition metal complexes (TMCs) modified a-metatungstate polyoxometalate (POMs), Na4[Ag6L4][H2W12O40] 12H2O (1) (L = nicotinate), has been conventionally synthesized and characterized by elemental analysis, IR, UV, TG and single-crystal X-ray diffraction. Each of the W12 clusters is surrounded by 10 Ag centers, which represents the highest connected number of the ametatungstate POMs to date. Additionally, compound 1 is stable in air and shows photoluminescence at room temperature. Ó 2008 Elsevier B.V. All rights reserved.
The design and synthesis of organic–inorganic hybrid materials through crystal engineering have become a significant area of research for chemists because of their intriguing variety of architectures and topologies, and potential applications in photochemistry, catalysis, medicine, electrical conductivity, material science and magnetism [1–4]. In this field, a brand-new advance is the design and construction of various intriguing molecular frameworks based on high-connected POMs [5], because many of their intriguing structural chemistry and potential applications are directly related to their surface characteristics. To date, thanks to the work of Zubieta [6], Wang [5,7], Cronin [8] and others [9], many highdimensional and high-connected POM-based hybrids have been successfully synthesized. All these compounds featured sufficient charge density on the POM anion surface atoms to coordinate TMCs, and it is believed that the surface activation is achieved by reducing the metal centers or by replacing high-oxidation metal(s) by other lower-valence metal(s). Compared with other classical POMs, such as Keggin, WellsDawson, Anderson and Lindqvist type anions, examples based on a-metatungstate POMs as building blocks to construct highdimensional and high-connected POM-based hybrids are still less, although the a-metatungstate POM anion surface atoms have sufficient charge density. Known examples include 0D [{Cu(phen)2}4{H2W12O40}][{Cu(phen)2}2{H2W12O40}] 3H2O with a cationic cluster of four connecting sites and an anionic bimetallic polyoxoanion [10], 1D chainlike [Cu(enMe)2(H2O)][{Cu(enMe)2}{Cu(enMe)2(H2O)W12O40(H2)}] nH2O with three connecting sites * Corresponding author. E-mail address: [email protected] (Y.-G. Chen). 1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.03.029
[11]. However, no higher dimensional POMs/TMCs hybrids based on a-metatungstate POMs have been reported hitherto. So it will be of great interest to construct high-dimensional and high-connected TMCs modified a-metatungstate POMs. Note that the sufficient charge density on the a-metatungstate POM anion surface atoms make covalent graft of POM ease, and its 36 surface oxygen atoms also offers many smart potential sites to link more TMC units. Such as, a novel 3D purely inorganic framework of [Ag(CH3CN)4] {[Ag(CH3CN)2]4[H3W12O40]} has been reported by Cronin et al., in which each [H3W12O40]5 clusters are surrounded by eight {Ag2}2+ bridges [12]. This example gives us the hint that ametatungstate POMs may be a judicious choice to construct highdimensional and high-connected organic–inorganic hybrids. Additionally, soft d10Ag+ ion is often used as a metallic synthon, mainly due to its high affinity to N and O donors, and its flexible coordination number and geometry, as well as the argentophilic Ag Ag interactions; and nicotinate, as multidentate ligand, is considered as the appropriate functional groups because of their flexible coordination modes and adjustive steric hindrance which induce metal ions with flexible coordination spheres (such as Ag+) to form TMCs with diversified characterizations. On the basis of the above considerations, herein, we have chosen a-metatungstate POMs, Ag+ ions, and nicotinate molecules as building blocks to construct the high-dimensional and high-connected TMCs modified a-metatungstate POMs derivatives. Luckily, we obtained such compound, Na4[Ag6L4][H2W12O40] 12H2O. Furthermore, luminescent properties of compound 1 have been studied in the solid state at room temperature. Compound 1 was synthesized by the reaction of (NH4)6 [H2W12O40] 3H2O, AgNO3 and L in the ratio of 4:4:1 (initial pH
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4.07, final pH 3.63, 80 °C, and heated for 1 h) in aqueous solution. The filtrate was kept for one week at ambient conditions, and then wheat block crystals of 1 were isolated in about 46% yield (based on Ag) [13]. Single-crystal X-ray diffraction analysis [14] reveals that compound 1 is constructed from one [H2W12O40]6 (W12) clusters, six Ag+ ions, four L ligands, two Na+ ions and 12 water molecules, as shown in Fig. 1 left. Each W12 cluster is made up of twelve WO6 octahedra which are arranged in four edge-shared {W3O13} triplets, as usually observed in the Keggin type anions [10–12,15–17]. However, its central heteroatom in tetrahedral environment is replaced by two protons, which results in the higher charge density on the W12 clusters surface. The most fascinating structure feature is that each of the W12 clusters is surrounded by 10 Ag centers and represents the highest connected number of the a-metatungstate POMs to date (Fig. 1 right). Another remarkable aspect of 1 is that there are two crystallization-independent L ligands and three crystallographically unique silver atoms. L ligands adopt two different bridging modes (Scheme 1): one mode is a coordinating pyridyl group and a l2(g1, g1)-carboxylato bridge; and the other mode adopts a coordinating pyridyl group and a l4(g2, g2)-carboxylato bridge. The three silver atoms have different coordination environments: threecoordinated Ag1 and Ag3, and two-coordinated Ag2. The Ag1 atom is defined by two O atoms of two L molecules, and O1W molecule. The distances are 2.21(17) Å (Ag1–O18), 2.22(16) Å (Ag1–O19), and 2.56(3) Å (Ag1–O1W). Additionally, the proximity of the fourth oxygen atom (O24) from the W12 with Ag1 atom (Ag1– O24 = 2.89(26) Å), which is shorter than the sum of the Van der Waals radii of Ag and O (3.20 Å) [18], implies long binding and leads to the formation of distorted tetrahedral coordination geometry around Ag1 center. The ‘‘plane-shape” coordination fastion of Ag2 atom is completed by two N atoms of two L molecules [Ag2– N1 = 2.15(2) Å and Ag2–N2 = 2.14(2) Å] and two long-range coordinative bonds to the two remaining oxygens of two adjacent W12 clusters (Ag2–O25: 2.96(20) Å, Ag2–O250 : 2.95(20) Å). The Ag3 atom is defined by two O atoms of two L molecules and one O atom of W12 cluster with the bond lengths of 2.20(19) Å, 2.18(18) Å, and 2.45(18) Å for Ag3–O16, Ag3–O17, and Ag3–O26, respectively. Furthermore, the Ag3 atom forms long-range coordinative bonds to the two remaining oxygens of other W12 and the third L molecular (Ag3–O170 = 2.85(20) Å and Ag3–O24 = 2.95(30) Å). The rich bridging modes of L ligands and coordination geometries of Ag atoms together are in favor of the formation of high-connected a-metatungstate POMs. Interestingly, there are argentophilic {Ag2}2+ dimers constructed by Ag1 and Ag3 (2.823(3) Å is shorter than the sum of the Van der Waals radii of two silver atoms (3.44 Å)), which are also linked by four oxygen atoms (O16, O17, O18, and O19) into {Ag2L2} subunits. And the {Ag2L2} subunits further form
Scheme 1. The coordination modes of L ligands in 1.
fAgðAg2 L2 Þgnþ n cation chain via Ag2 atoms. Furthermore, two adjacent fAgðAg2 L2 Þgnþ n cation chains connect each other through the bond (Ag3–O17) leading to the 1D ladderlike chain (Fig. 2). Besides the interactions of Ag3–O17, less-favorable head-to-head p p interactions (the shortest interplane distance is 3.40 Å) of pyridine rings further strengthen the stabilization of the laddlelike chains. Along the given direction as shown in Fig. 3, each W12 cluster as connector links six Ag+ cations from the neighbor fAgðAg2 L2 Þgnþ n cation chains, resulting in 2D networks. Additionally, W12 POMs further connect additional four Ag+ cations from adjacent 2D layers via Ag1–O24 and Ag3–O24 bands to form a complicated 3D framework in a parallel staggering mode (Fig. S1). The crystal structure of 1 is further strengthened by two crystallization-independent sodium atoms. The average Na–O bond lengths are 2.611 Å for Na1 and 2.488 Å for Na2. The UV spectra of free (NH4)6[H2W12O40] 3H2O and the compound 1 are displayed in Fig. S2. The UV electronic spectrum of 1 shows two bands (k = 220 nm and k = 260 nm) assigned to pp(Od) ? dp*(W) transitions in the W@O bonds and dp–pp–dp transitions between the energetic levels of the W–O–W tricentric bonds, respectively, which are similar to those (k = 217 nm and k = 260 nm) in free (NH4)6[H2W12O40] 3H2O. There is also another weak band (k = 269 nm) ascribed to 4dr* ? 5pr transition originating from close Ag Ag interactions in compound 1 [12,19]. The luminescent properties of compound 1 and free ligand were investigated in the solid state at room temperature (Fig. 4). A blue-fluorescent emission maximum at 467 nm was observed for 1 upon excitation at 270 nm. While the free L ligand displays two emission bands at 397 nm and 468 nm when excited at 254 nm. The band (397 nm) is quenched due to the crystallographic co-planar fashion of the two pyridyl rings
Fig. 1. Left: ORTEP drawing of the basic crystallographic unit in 1. All the hydrogen atoms and sodium molecules have been omitted for clarity. Right: The view of connection details of W12 clusters.
C.-J. Zhang et al. / Inorganic Chemistry Communications 11 (2008) 765–768
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Fig. 2. The diagram of fAg2ðAg2 L2 Þg2nþ laddlelike chain. n
Fig. 3. View of the 2D structure constructed by W12 clusters and fAgðAg2 L2 Þgnþ n .
The TG curve of 1 (see Fig. S3) exhibits two weight-loss steps in the range of 49–500 °C attributed to the loss of coordinated water molecules and decomposition of L. The total weight-loss (16.2%) is consistent with the calculated value (16.4%). In summary, a 3D 10 Ag–L units modified a-metatungstate POMs hybrid containing AgI AgI interactions was successfully obtained which possesses the highest coordination number of the ametatungstate POMs to date. The profuse structure of compound 1 indicates that the high-dimensional assembly of high-connected POM–TMCs hybrid depends on a synergic effect of polyoxoanion clusters, metal ion and coordination geometries. The work provides a good example of reasonable design and controllable assembly of POM-based hybrid.
Acknowledgements
Fig. 4. Solid-state emission spectrum of L and 1 at room temperature.
coordinated to Ag2 (N2–Ag2–N1: 174.2(9)°) in compound 1, which induces the enhancement of p conjugation involving the Ag center [20] and the other band (468 nm) in the same region as that of compound 1, is obvious enhancement attributed to an internal heavy metal effect. The contrast between the emission spectrum of 1 and L leads us to draw the conclusion that compound 1 is attributable to the ligand-centered emission, but closely associated with the local environments around metal ion and internal heavy metal effect.
This work was supported by Analysis and Testing Foundation of the Northeast Normal University and Zhong-Min Shu group for single-crystal X-ray diffraction. Supporting material CCDC 666897 of compound 1 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data containing UV, TG, and structural figures associated with this article can be found, in the online version, at doi:10.1016/ j.inoche.2008.03.029.
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C.-J. Zhang et al. / Inorganic Chemistry Communications 11 (2008) 765–768
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M.E. Davis, Nature 417 (2002) 813. N. Ding, D.Y. Chung, M.G. Kanatzidis, Chem. Commun. (2004) 1170. W.H. Casey, B.L. Phillips, Geochim. Cosmochim. Acta 65 (2001) 705. A.V. Besserguenev, M.H. Dickman, M.T. Pope, Inorg. Chem. 40 (2001) 2582. H.Y. An, D.R. Xiao, E.B. Wang, Y.G. Li, Z.M. Su, L. Xu, Angew. Chem., Int. Ed. 45 (2006) 904. P.J. Hagrman, J. Zubieta, Inorg. Chem. 40 (2001) 2800. F. Qi, Y.G. Li, C. Qin, E.B. Wang, H. Jin, D.R. Xiao, X.L. Wang, S. Chang, Inorg. Chem. 46 (2007) 3217. (a) C. Streb, C. Ritchie, D.L. Long, P. Kögerler, L. Cronin, Angew. Chem., Int. Ed. 46 (2007) 7579; (b) T. Akutagawa, D. Endo, H. Imai, S.I. Noro, L. Cronin, T. Nakamura, Inorg. Chem. 45 (2006) 8628; (c) H. Abbas, A.L. Pickering, D.L. Long, L. Cronin, Chem. Eur. J. 11 (2005) 1071; (d) D.L. Long, P. Kögerler, L. Cronin, Angew. Chem., Int. Ed. 43 (2004) 1817; (e) D.L. Long, P. Kögerler, L.J. Farrugia, L. Cronin, Angew. Chem., Int. Ed. 42 (2003) 4180. (a) Y.P. Ren, X.J. Kong, X.Y. Hu, M. Sun, L.S. Long, Inorg. Chem. 45 (2006) 4016; (b) J.Y. Niu, P.T. Ma, H.Y. Niu, J. Li, J.W. Zhao, Y. Song, J.P. Wang, Chem. Eur. J. 13 (2007) 8739. R.N. Devi, E. Burkholder, J. Zubieta, Inorg. Chim. Acta 348 (2003) 150. B.Z. Lin, Z. Li, L.W. He, L. Bai, X.F. Huang, Y.L. Chen, Inorg. Chem. Commun. 10 (2007) 600. C. Streb, C. Ritchie, D.L. Long, P. Kögerler, L. Cronin, Angew. Chem., Int. Ed. 46 (2007) 7579.
[13] Elem. anal. Found: W, 51.37; Na, 2.18; Ag, 15.02; C, 6.75; N, 1.28 (%). Calcd: W, 51.43; Na, 2.14; Ag, 15.10; C, 6.71; N, 1.31 (%). FTIR data (cm1): 3665.79(s), 3292(s), 1656.65(s), 1643.75(s), 1633.66(s), 1596.28(s), 1569.29(m), 1557.49(m), 1404.43(w), 936.55(vs), 882.98(vs), 762.13(vs), 669.19(m), 418.42(m). [14] Crystal data for Na4Ag6C24H42N4O60W12 (1): Mr = 4292.02, Triclinic, space a = 12.023(5) Å, b = 12.507(5) Å, c = 14.242(5) Å, a = 73.777(5)°, group P 1, b = 66.229(5)°, c = 83.641(5)°, V = 1881.9(13) Å3, Z = 1, Dc = 3.764 g/cm3, 0.982 6 h 6 25.75°, F(0 0 0) = 1882, T = 295(2) K, Rint = 0.0278. Structure solution and refinement based on 7212 independent reflections with [I > 2r(I)] and 467 parameters gave R1 and wR2 were 0.0748 and 0.1889, respectively and S = 1.068. X-ray diffraction data were collected on a SMART CCD diffractometer with graphite monochromated Mo Ka radiation at room temperature. The structure was solved by Direct Methods and refined by full-matrix least-squares on F2 with the SHELXL-97 program package. [15] M.T. Pope, Heteropoly and Isopoly Oxometalates, Springer, New York, 1983. [16] L. Lisnard, A. Dolbecq, P. Mialane, J. Marrot, F. Sécheresse, Inorg. Chim. Acta 357 (2004) 845. [17] J.H. Son, Y.U. Kwon, Inorg. Chim. Acta 358 (2005) 310. [18] J.E. Huheey, Inorganic Chemistry, Principles of Structure and Reactivity, second ed., Harper & Row, New York, 1978. [19] C.M. Che, M.C. Tse, M.C.W. Chan, K.K. Cheung, D.L. Phillips, K.H. Leung, J. Am. Chem. Soc. 122 (2000) 2464. [20] L.X. Xie, M.L. Wei, C.Y. Duan, Q.Z. Sun, Q.J. Meng, Inorg. Chim. Acta 360 (2007) 2541.
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis and characterization of the highest connected 3D a-metatungstate POM/TMC hybrid with AgI AgI interactions Chun-Jing Zhang, Ya-Guang Chen *, Hai-Jun Pang, Dong-Mei Shi, Mi-Xia Hu, Jia Li Key Laboratory of Polyoxometalates Science of Ministry of Education, College of Chemistry, Northeast Normal University, Changchun 130024, PR China
a r t i c l e
i n f o
Article history: Received 23 January 2008 Accepted 26 March 2008 Available online 1 April 2008 Keywords: a-Metatungstate polyoxometalate Conventional synthesis Silver Luminescence
a b s t r a c t A novel 3D hybrid based on transition metal complexes (TMCs) modified a-metatungstate polyoxometalate (POMs), Na4[Ag6L4][H2W12O40] 12H2O (1) (L = nicotinate), has been conventionally synthesized and characterized by elemental analysis, IR, UV, TG and single-crystal X-ray diffraction. Each of the W12 clusters is surrounded by 10 Ag centers, which represents the highest connected number of the ametatungstate POMs to date. Additionally, compound 1 is stable in air and shows photoluminescence at room temperature. Ó 2008 Elsevier B.V. All rights reserved.
The design and synthesis of organic–inorganic hybrid materials through crystal engineering have become a significant area of research for chemists because of their intriguing variety of architectures and topologies, and potential applications in photochemistry, catalysis, medicine, electrical conductivity, material science and magnetism [1–4]. In this field, a brand-new advance is the design and construction of various intriguing molecular frameworks based on high-connected POMs [5], because many of their intriguing structural chemistry and potential applications are directly related to their surface characteristics. To date, thanks to the work of Zubieta [6], Wang [5,7], Cronin [8] and others [9], many highdimensional and high-connected POM-based hybrids have been successfully synthesized. All these compounds featured sufficient charge density on the POM anion surface atoms to coordinate TMCs, and it is believed that the surface activation is achieved by reducing the metal centers or by replacing high-oxidation metal(s) by other lower-valence metal(s). Compared with other classical POMs, such as Keggin, WellsDawson, Anderson and Lindqvist type anions, examples based on a-metatungstate POMs as building blocks to construct highdimensional and high-connected POM-based hybrids are still less, although the a-metatungstate POM anion surface atoms have sufficient charge density. Known examples include 0D [{Cu(phen)2}4{H2W12O40}][{Cu(phen)2}2{H2W12O40}] 3H2O with a cationic cluster of four connecting sites and an anionic bimetallic polyoxoanion [10], 1D chainlike [Cu(enMe)2(H2O)][{Cu(enMe)2}{Cu(enMe)2(H2O)W12O40(H2)}] nH2O with three connecting sites * Corresponding author. E-mail address: [email protected] (Y.-G. Chen). 1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.03.029
[11]. However, no higher dimensional POMs/TMCs hybrids based on a-metatungstate POMs have been reported hitherto. So it will be of great interest to construct high-dimensional and high-connected TMCs modified a-metatungstate POMs. Note that the sufficient charge density on the a-metatungstate POM anion surface atoms make covalent graft of POM ease, and its 36 surface oxygen atoms also offers many smart potential sites to link more TMC units. Such as, a novel 3D purely inorganic framework of [Ag(CH3CN)4] {[Ag(CH3CN)2]4[H3W12O40]} has been reported by Cronin et al., in which each [H3W12O40]5 clusters are surrounded by eight {Ag2}2+ bridges [12]. This example gives us the hint that ametatungstate POMs may be a judicious choice to construct highdimensional and high-connected organic–inorganic hybrids. Additionally, soft d10Ag+ ion is often used as a metallic synthon, mainly due to its high affinity to N and O donors, and its flexible coordination number and geometry, as well as the argentophilic Ag Ag interactions; and nicotinate, as multidentate ligand, is considered as the appropriate functional groups because of their flexible coordination modes and adjustive steric hindrance which induce metal ions with flexible coordination spheres (such as Ag+) to form TMCs with diversified characterizations. On the basis of the above considerations, herein, we have chosen a-metatungstate POMs, Ag+ ions, and nicotinate molecules as building blocks to construct the high-dimensional and high-connected TMCs modified a-metatungstate POMs derivatives. Luckily, we obtained such compound, Na4[Ag6L4][H2W12O40] 12H2O. Furthermore, luminescent properties of compound 1 have been studied in the solid state at room temperature. Compound 1 was synthesized by the reaction of (NH4)6 [H2W12O40] 3H2O, AgNO3 and L in the ratio of 4:4:1 (initial pH
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C.-J. Zhang et al. / Inorganic Chemistry Communications 11 (2008) 765–768
4.07, final pH 3.63, 80 °C, and heated for 1 h) in aqueous solution. The filtrate was kept for one week at ambient conditions, and then wheat block crystals of 1 were isolated in about 46% yield (based on Ag) [13]. Single-crystal X-ray diffraction analysis [14] reveals that compound 1 is constructed from one [H2W12O40]6 (W12) clusters, six Ag+ ions, four L ligands, two Na+ ions and 12 water molecules, as shown in Fig. 1 left. Each W12 cluster is made up of twelve WO6 octahedra which are arranged in four edge-shared {W3O13} triplets, as usually observed in the Keggin type anions [10–12,15–17]. However, its central heteroatom in tetrahedral environment is replaced by two protons, which results in the higher charge density on the W12 clusters surface. The most fascinating structure feature is that each of the W12 clusters is surrounded by 10 Ag centers and represents the highest connected number of the a-metatungstate POMs to date (Fig. 1 right). Another remarkable aspect of 1 is that there are two crystallization-independent L ligands and three crystallographically unique silver atoms. L ligands adopt two different bridging modes (Scheme 1): one mode is a coordinating pyridyl group and a l2(g1, g1)-carboxylato bridge; and the other mode adopts a coordinating pyridyl group and a l4(g2, g2)-carboxylato bridge. The three silver atoms have different coordination environments: threecoordinated Ag1 and Ag3, and two-coordinated Ag2. The Ag1 atom is defined by two O atoms of two L molecules, and O1W molecule. The distances are 2.21(17) Å (Ag1–O18), 2.22(16) Å (Ag1–O19), and 2.56(3) Å (Ag1–O1W). Additionally, the proximity of the fourth oxygen atom (O24) from the W12 with Ag1 atom (Ag1– O24 = 2.89(26) Å), which is shorter than the sum of the Van der Waals radii of Ag and O (3.20 Å) [18], implies long binding and leads to the formation of distorted tetrahedral coordination geometry around Ag1 center. The ‘‘plane-shape” coordination fastion of Ag2 atom is completed by two N atoms of two L molecules [Ag2– N1 = 2.15(2) Å and Ag2–N2 = 2.14(2) Å] and two long-range coordinative bonds to the two remaining oxygens of two adjacent W12 clusters (Ag2–O25: 2.96(20) Å, Ag2–O250 : 2.95(20) Å). The Ag3 atom is defined by two O atoms of two L molecules and one O atom of W12 cluster with the bond lengths of 2.20(19) Å, 2.18(18) Å, and 2.45(18) Å for Ag3–O16, Ag3–O17, and Ag3–O26, respectively. Furthermore, the Ag3 atom forms long-range coordinative bonds to the two remaining oxygens of other W12 and the third L molecular (Ag3–O170 = 2.85(20) Å and Ag3–O24 = 2.95(30) Å). The rich bridging modes of L ligands and coordination geometries of Ag atoms together are in favor of the formation of high-connected a-metatungstate POMs. Interestingly, there are argentophilic {Ag2}2+ dimers constructed by Ag1 and Ag3 (2.823(3) Å is shorter than the sum of the Van der Waals radii of two silver atoms (3.44 Å)), which are also linked by four oxygen atoms (O16, O17, O18, and O19) into {Ag2L2} subunits. And the {Ag2L2} subunits further form
Scheme 1. The coordination modes of L ligands in 1.
fAgðAg2 L2 Þgnþ n cation chain via Ag2 atoms. Furthermore, two adjacent fAgðAg2 L2 Þgnþ n cation chains connect each other through the bond (Ag3–O17) leading to the 1D ladderlike chain (Fig. 2). Besides the interactions of Ag3–O17, less-favorable head-to-head p p interactions (the shortest interplane distance is 3.40 Å) of pyridine rings further strengthen the stabilization of the laddlelike chains. Along the given direction as shown in Fig. 3, each W12 cluster as connector links six Ag+ cations from the neighbor fAgðAg2 L2 Þgnþ n cation chains, resulting in 2D networks. Additionally, W12 POMs further connect additional four Ag+ cations from adjacent 2D layers via Ag1–O24 and Ag3–O24 bands to form a complicated 3D framework in a parallel staggering mode (Fig. S1). The crystal structure of 1 is further strengthened by two crystallization-independent sodium atoms. The average Na–O bond lengths are 2.611 Å for Na1 and 2.488 Å for Na2. The UV spectra of free (NH4)6[H2W12O40] 3H2O and the compound 1 are displayed in Fig. S2. The UV electronic spectrum of 1 shows two bands (k = 220 nm and k = 260 nm) assigned to pp(Od) ? dp*(W) transitions in the W@O bonds and dp–pp–dp transitions between the energetic levels of the W–O–W tricentric bonds, respectively, which are similar to those (k = 217 nm and k = 260 nm) in free (NH4)6[H2W12O40] 3H2O. There is also another weak band (k = 269 nm) ascribed to 4dr* ? 5pr transition originating from close Ag Ag interactions in compound 1 [12,19]. The luminescent properties of compound 1 and free ligand were investigated in the solid state at room temperature (Fig. 4). A blue-fluorescent emission maximum at 467 nm was observed for 1 upon excitation at 270 nm. While the free L ligand displays two emission bands at 397 nm and 468 nm when excited at 254 nm. The band (397 nm) is quenched due to the crystallographic co-planar fashion of the two pyridyl rings
Fig. 1. Left: ORTEP drawing of the basic crystallographic unit in 1. All the hydrogen atoms and sodium molecules have been omitted for clarity. Right: The view of connection details of W12 clusters.
C.-J. Zhang et al. / Inorganic Chemistry Communications 11 (2008) 765–768
767
Fig. 2. The diagram of fAg2ðAg2 L2 Þg2nþ laddlelike chain. n
Fig. 3. View of the 2D structure constructed by W12 clusters and fAgðAg2 L2 Þgnþ n .
The TG curve of 1 (see Fig. S3) exhibits two weight-loss steps in the range of 49–500 °C attributed to the loss of coordinated water molecules and decomposition of L. The total weight-loss (16.2%) is consistent with the calculated value (16.4%). In summary, a 3D 10 Ag–L units modified a-metatungstate POMs hybrid containing AgI AgI interactions was successfully obtained which possesses the highest coordination number of the ametatungstate POMs to date. The profuse structure of compound 1 indicates that the high-dimensional assembly of high-connected POM–TMCs hybrid depends on a synergic effect of polyoxoanion clusters, metal ion and coordination geometries. The work provides a good example of reasonable design and controllable assembly of POM-based hybrid.
Acknowledgements
Fig. 4. Solid-state emission spectrum of L and 1 at room temperature.
coordinated to Ag2 (N2–Ag2–N1: 174.2(9)°) in compound 1, which induces the enhancement of p conjugation involving the Ag center [20] and the other band (468 nm) in the same region as that of compound 1, is obvious enhancement attributed to an internal heavy metal effect. The contrast between the emission spectrum of 1 and L leads us to draw the conclusion that compound 1 is attributable to the ligand-centered emission, but closely associated with the local environments around metal ion and internal heavy metal effect.
This work was supported by Analysis and Testing Foundation of the Northeast Normal University and Zhong-Min Shu group for single-crystal X-ray diffraction. Supporting material CCDC 666897 of compound 1 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data containing UV, TG, and structural figures associated with this article can be found, in the online version, at doi:10.1016/ j.inoche.2008.03.029.
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References [1] [2] [3] [4] [5] [6] [7] [8]
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[13] Elem. anal. Found: W, 51.37; Na, 2.18; Ag, 15.02; C, 6.75; N, 1.28 (%). Calcd: W, 51.43; Na, 2.14; Ag, 15.10; C, 6.71; N, 1.31 (%). FTIR data (cm1): 3665.79(s), 3292(s), 1656.65(s), 1643.75(s), 1633.66(s), 1596.28(s), 1569.29(m), 1557.49(m), 1404.43(w), 936.55(vs), 882.98(vs), 762.13(vs), 669.19(m), 418.42(m). [14] Crystal data for Na4Ag6C24H42N4O60W12 (1): Mr = 4292.02, Triclinic, space a = 12.023(5) Å, b = 12.507(5) Å, c = 14.242(5) Å, a = 73.777(5)°, group P 1, b = 66.229(5)°, c = 83.641(5)°, V = 1881.9(13) Å3, Z = 1, Dc = 3.764 g/cm3, 0.982 6 h 6 25.75°, F(0 0 0) = 1882, T = 295(2) K, Rint = 0.0278. Structure solution and refinement based on 7212 independent reflections with [I > 2r(I)] and 467 parameters gave R1 and wR2 were 0.0748 and 0.1889, respectively and S = 1.068. X-ray diffraction data were collected on a SMART CCD diffractometer with graphite monochromated Mo Ka radiation at room temperature. The structure was solved by Direct Methods and refined by full-matrix least-squares on F2 with the SHELXL-97 program package. [15] M.T. Pope, Heteropoly and Isopoly Oxometalates, Springer, New York, 1983. [16] L. Lisnard, A. Dolbecq, P. Mialane, J. Marrot, F. Sécheresse, Inorg. Chim. Acta 357 (2004) 845. [17] J.H. Son, Y.U. Kwon, Inorg. Chim. Acta 358 (2005) 310. [18] J.E. Huheey, Inorganic Chemistry, Principles of Structure and Reactivity, second ed., Harper & Row, New York, 1978. [19] C.M. Che, M.C. Tse, M.C.W. Chan, K.K. Cheung, D.L. Phillips, K.H. Leung, J. Am. Chem. Soc. 122 (2000) 2464. [20] L.X. Xie, M.L. Wei, C.Y. Duan, Q.Z. Sun, Q.J. Meng, Inorg. Chim. Acta 360 (2007) 2541.