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A new Dawson-like tungstoantimonate related to [SbVW18O60(OH)2]9−
Inorganic Chemistry Communications 13 (2010) 1418–1420
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Inorganic Chemistry Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i n o c h e
A new Dawson-like tungstoantimonate related to [SbVW18O60(OH)2]9− Yuan-Yuan Zhang, Shu-Xia Liu ⁎, Chao-Jie Yu, Qun Tang, Da-Dong Liang, Chun-Dan Zhang, Feng-Ji Ma, Shu-Jun Li, Wei Zhang, Rui-Kang Tan Key Laboratory of Polyoxometalate Science of Ministry of Education, College of Chemistry, Northeast Normal University, Changchun, Jilin 130024, China
a r t i c l e
i n f o
Article history: Received 6 April 2010 Accepted 3 August 2010 Available online 10 August 2010 Keywords: Polyoxometalates Tungstoantimonate Dawson-like Synthesis
a b s t r a c t A new tungstoantimonate (NH4)9[SbVW18O60(OH)2]·25H2O (1) has been synthesized under acidic medium conditions and characterized by element analysis, IR, TG, UV, PXRD and single-crystal X-ray diffraction analysis. Compound 1 represents the first example of Sb(V)-containing polyoxometalate with unusual Dawson-like construction. The polyoxoanion incorporates an {SbO6} unit into the center of {W18O54} cluster cage. © 2010 Elsevier B.V. All rights reserved.
Polyoxometalates (POMs), as discrete early transition-metal-oxide clusters, have attracted extensive interest not only because of their intriguing architectures but also in terms of the wide range of topological properties, displaying potential applications in many fields such as catalysis, medicine, materials science, optical and magnetic properties [1]. Much attention has been focused on the designing and synthesizing POMs with novel structures since the first POM was discovered in 1826 by Berzelius [2], but the creation of new POM compounds is still a great challenge. In the field of POM chemistry, Dawson-type compounds are one of the most common families and often represented with the general formula [M18O54 (XO4)2]m−, where X is heteroatom and M is the addendum atom. Furthermore, it is well-known that the {M18} cluster cages are templated by two tetrahedral heteroanions [3]. However, there are four kinds of species possessing {M18} cluster cages embedded in nontetrahedral groups being addressed. The first incorporates only one 3− 3− 4− 2− pyramidal (AsO3− 3 , SbO3 , BiO3 , SnO3 , or TeO3 ) [4–9]; the second ) hetero groups [10]; the third encapencloses ditetrahedral (P2O4− 7 sulates two pyramidal (SO2− 3 ) moiety [11]; and the fourth embeds 5− 6− trigonal–prismatic or octahedron (WO6− 6 , IO6 , or TeO6 ) as templates, the central heteroatoms are all hexa-coordinated, respectively [9,12] (Fig. S1). All the above-mentioned structural types are different from the classical Dawson-type constitution, namely Dawson-like type compounds, which are uncommon in POM chemistry. In the past few decades, many Sb(III)-containing polyoxoanions have been synthesized and structurally characterized [13–17]. On the contrary, relatively few cases of Sb(V)-containing polyoxoanions have
⁎ Corresponding author. Tel./fax: +86 431 85099328. E-mail address: [email protected] (S.-X. Liu). 1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.08.005
been reported [18,19]. Recently, an example of Sb-containing POM with Dawson-like construction has been made and described as the “peanut-like” shaped tungstoantimonate [H2SbIIIW18O60 ]7−, in which the sole Sb is tricoordinated and with a pair of electrons, as well as the occupancy rate is 0.5 [7]. To the best of our knowledge, the γ*-isomer isopolyoxoanion [H4W19O62]6– with Dawson-like structure was first reported in 2006 by Cronin and co-workers [12a]. Then in the following two years, they prepared the first Dawson-like γ*-isomer heteropolyoxoanion [H3W18O56(TeO6)]7– [12b]. The two clusters containing {WO6} and {TeO6} unit as templates inside the {W18} cluster shell, respectively. Herein, we report the expansion of POM compounds with Dawson-like structure formed by {SbO6} moiety as template embedded into a {W18O54} cluster cage. The polyoxotungstates system containing hexa-coordinated antimony has been synthesized under acidic medium conditions, leading to the compound formulated as (NH4)9[SbVW18O60(OH)2]·25H2O (1). It is notable that the title heteropolyoxoanion is the first example of Sb(V)-containing POM with unusual Dawson-like construction, and it is the second Dawsonlike cluster has a γ* conformation, which extended the family of Dawson-like clusters. Compound 1 was easily prepared by a mixture of Na2WO4·2H2O and SbCl5 (molar ratio 4:1) at pH = 2–3 aqueous solution kept at 80 °C for 1 h [20]. SbCl5 is tend to be hydrolyzed in the air and should be quick to be dissolved to concentrated hydrochloric acid. And then we selected common base such as NaOH, KOH, and NH3⋅H2O to adjust the pH until 2–3. When Na+ or K+ was used as cation, we failed to obtain perfect crystals suitable for X-ray diffraction analysis under similar reaction conditions, instead forming amorphous precipitate; only the title compound in the form of NH+ 4 salt is obtained. And it is worth mentioning that the crystallization is very quick, which occurred in 10 minutes. In order to check the phase purity of 1, the powder X-ray
Y.-Y. Zhang et al. / Inorganic Chemistry Communications 13 (2010) 1418–1420
diffraction (PXRD) patterns of 1 was recorded at room temperature (Fig. S8). The peak positions of simulated and experimental patterns of 1 are in agreement with each other, indicating the good phase purity of 1. Single-crystal X-ray structure analysis [21] reveals that the novel compound 1 is crystallizes in the trigonal space group R-3. The structure of the polyoxoanion [SbVW18O60(OH)2]9– (abbreviated as {SbVW18}) is markedly different from [H2SbIIIW18O60]7– (abbreviated as {SbIIIW18}) [6], as shown in Fig. 1. The “peanut-like” shaped polyoxoanion {SbIIIW18} has a pyramidal SbO3 group (average Sb–O distance = 2.00 Å) and the group is disordered over two possible positions in the cluster cage. The Sb–Sb distance is appropriately 2.18 Å apart, the sole Sb with a pair of electrons and the occupancy rate is 0.5. Comparatively, the new polyoxoanion {SbVW18} enclosed pentavalent antimony resulting in a novel structure (Fig. 2). The Sbcentered atom is coordinated via six oxo ligands with Sb–O distance of 2.026 Å and the (Sb)O–W mean distance of 2.297(5) Å. Moreover, there are 60 oxygen atoms in {SbIIIW18} while 62 in {SbVW18}. In {SbIIIW18}, there are six μ4–O oxygen atoms which connected one Sb and three W atoms. Nevertheless, there are eight μ3–O oxygen atoms in {SbVW18}: two of them bridge three W atoms from the capping unit inside the cluster, the other six combine with one Sb and two W atoms. Compound 1 was characterized by bond valence calculations (BVS) [22] to identify the oxidation states of tungsten and antimony atoms, as well as the possible protonated oxygen atoms on polyanion. The BVS clearly show that all the tungsten atoms and antimony atom in 1 exhibit +6 and + 5 oxidation state, respectively. It is also noteworthy that there are two μ3–O (O8) (Fig. S2), both bridges the capping {W3} unit inside the framework, the distance between O8 and W is 2.266 Å, which leads to a calculated valence of the two oxygen atoms is 1.168, respectively, indicating that they are indeed monoprotonated [18b,23]. These result two OH groups inside the {W18} cluster cage and therefore, the charge of the polyanion is − 9, thus the molecular formula is described as [SbVW18O60(OH)2]9−. The BVS values for other terminal or bridging oxygen atoms (ca. 1.541–2.077), indicate there is no additional protonation. The distances between the μ3–O (O8) and neighboring μ2–O or μ3–O is ranging from 2.835 to 3.009 Å, thus we speculate that there may be exist stable hydrogenbonding inside the cluster, enhancing the stability of the framework [SbVW18O60(OH)2]9–. In addition, in the {SbVW18} cluster cage, the D3d symmetric of the {SbO6} unit match the {W18O54} D3d-symmetric of the cluster shell, thus representing a γ*-isomer in the family of Dawson-like clusters. To
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Fig. 2. Polyhedral representation of polyoxoanion [SbVW18O60(OH)2]9–. Color code: Sb bright green; W pale blue; O red.
our knowledge, compound 1 is the second Dawson-like heteropolyoxoanion has a γ* conformation. The γ*-{SbVW18} is slightly different from the reported β*-isomer polyoxoanion [H3W18O56(IO6)]6– [12b], where the orientation of the trigonal {W3O13} caps are interconverted by a 60° rotation (Fig. S3). The IR spectrum of 1 shows a broad peak at 3417 cm–1 and a strong peak at 1615 cm–1 ascribed to the lattice water molecules. It displays four characteristic absorptions below 1000 cm–1 attributed to the Dawson-like structure, the characteristic peaks at 584 cm–1 probably assigned to the absorptions of Sb–O vibrations [19,24]. And the peaks at 3180 and 1412 cm–1 are indicative of the presence of NH+ 4 (Fig. S4). In addition, UV–vis spectrum was performed to investigate the stability of 1 in the aqueous solution [25]. We monitored compound 1 in the pH range of 1–9 and found that it maintained stable in acidic
Fig. 1. Ball-and-stick representation of [SbVW18O60(OH)2]9– (left) and the peanut-shaped anion [H2SbIIIW18O60]7– (right) for comparison. Color code: Sb(V) bright green; Sb(III) tan; W pale blue; O red.
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solution (Fig. S5). Also, UV–vis spectrum of 1 was carried out in distilled water (pH = 6.00) for 40 days, the results revealed that it can stably exist within 40 days (Fig. S6). Thermal gravimetric (TG) analyses of compound 1 was carried out from 25 to 600 °C under a nitrogen atmosphere (Fig. S7). In the TG curve of compound 1, there are two weight loss steps. The first rapid weight loss of 9.68% in the temperature range of 25–156 °C corresponds to the release of 25 lattice H2O molecules and two NH3 molecules. The second weight loss of 2.46% in the temperature range of 156–450 °C is probably the result of release of seven NH3 molecules. After 450 °C, there is no further decomposition of the compound, indicating that the polyanion maintained a stable framework until 600 °C. In summary, a new compound has been successfully synthesized in hot aqueous solution. Compound 1 is the first example of Sb(V)containing POM bearing unusual Dawson-like construction, and it is the second Dawson-like heteropolyoxoanion has a γ* conformation. On account of the stability of title tungstoantimonate in aqueous solution, in further work, we will attempt to link the anion to construct high-dimentional extended structures by employing transition metal or lanthanide metal ions, which is of significance for the development of POM chemistry. Acknowledgements This work was supported by the National Science Foundation of China (Grant Nos. 20871027 and 20973035), the Program for New Century Excellent Talents in University (NCET-07-0169), and the Program for Changjiang Scholars and Innovative Research Team in University. Appendix A. Supplementary material Further details of the crystal structure investigations for 1 could be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein–Leopoldshafen, Germany (fax: (+ 49)7247-808-666; e-mail: crystdata@fiz-karlsruhe.de) on quoting the depository number CSD421580. Supplementary material associated with the article can be found, in the online version, doi:10.1016/j.inoche.2010.08.005. References [1] (a) M.T. Pope, A. Müller, Angew. Chem. Int. Ed Engl. 30 (1991) 34–38; (b) J.T. Rhule, C.L. Hill, D.A. Judd, R.F. Schinazi, Chem. Rev. 98 (1998) 327–358; (c) C.L. Hill (Ed.), Polyoxometalates in Catalysis, J. Mol. Catal. A:Chem., 262, 2007, pp. 1–242; (d) Z.Q. Zhang, R.D. Huang, L.J. Dong, Y.Q. Xu, L.Q. Yu, Z.W. Jiao, C.W. Hu, Inorg. Chim. Acta 362 (2009) 3056–3064; (e) L.J. Zhang, Y.H. Li, Y.S. Zhou, J. Mol. Struct. 969 (2010) 69–74. [2] J. Berzelius, Ann. Phys. 6 (1826) 369–380. [3] (a) X.Y. Zhao, D.D. Liang, S.X. Liu, C.Y. Sun, R.G. Cao, C.Y. Gao, Y.H. Ren, Z.M. Su, Inorg. Chem. 47 (2008) 7133–7138; (b) M. Abbessi, R. Contant, R. Thouvenot, G. Hervé, Inorg. Chem. 30 (1991) 1695–11702; (c) B. Keita, B. Girard, L. Nadjo, R. Contant, J. Canny, M. Richet, J. Electroanal. Chem. 478 (1999) 76–82; (d) B. Dawson, Acta Crystallogr. 6 (1953) 113–126; (e) R. Contant, Inorg. Synth[M] 27 (1990) 104–107. [4] R. Contant, S. Piro-Sellem, J. Canny, R. Thouvenot, C.R.Acad.Sci.Paris, Sér. IIc 3 (2000) 157–161. [5] Y. Jeannin, J.M. Frere, Inorg. Chem. 18 (1979) 3010–3014.
[6] (a) B. Krebs, R. Klein, in: M.T. Pope, A. Müller (Eds.), Polyoxometalates: From Platonic Solids to Anti-Retroviral Activity, Kluwer Academic Publishers, Dordrecht, 1994, pp. 41–57; (b) D.L. Long, C. Streb, Y.F. Song, S. Mitchell, L. Cronin, J. Am. Chem. Soc. 130 (2008) 1830–1832. [7] (a) Y. Ozawa, Y. Sasaki, Chem. Lett. (1987) 923–926; (b) D. Rodewald, Y. Jeannin, C. R. Acad. Sci. Paris Ser. IIc 2 (1999) 63–67. [8] B. Krebs, E. Droste, M. Piepenbrink, G. Vollmer, C.R. Acad, Paris, Sci., Sér. IIc, Chim. 3 (2000) 205–210. [9] J. Yan, D.L. Long, E.F. Wilson, L. Cronin, Angew. Chem. Int. Ed. 48 (2009) 4376–4380. [10] U. Kortz, M.T. Pope, Inorg. Chem. 33 (1994) 5643–5646. [11] D.L. Long, P. Kögerler, L. Cronin, Angew. Chem. Int. Ed. 43 (2004) 1817–1820. [12] (a) D.L. Long, P. Kögerler, L. Cronin, Angew. Chem. Int. Ed. 45 (2006) 4798–4803; (b) D.L. Long, Y.F. Song, E.F. Wilson, P. Kögerler, S.X. Guo, A.M. Bond, J.S.J. Hargreaves, L. Cronin, Angew. Chem. Int. Ed. 47 (2008) 4384–4387. [13] (a) U. Kortz, M.G. Savelieff, B.S. Bassil, M.H. Dickman, Angew. Chem. Int. Ed. 40 (2001) 3384–3386; (b) U. Kortz, M.G. Savelieff, F.Y.A. Ghali, L.M. Khalil, S.A. Maalouf, D.I. Sinno, Angew. Chem. Int. Ed. 41 (2002) 4070–4073. [14] (a) L.J. Zhang, X.L. Zhao, J.Q. Xu, T.G. Wang, J. Chem. Soc., Dalton Trans. (2002) 3275–3276; (b) Y.K. Lu, J.N. Xu, X.B. Cui, J. Jin, S.Y. Shi, J.Q. Xu, Inorg. Chem. Commun. 13 (2010) 46–49. [15] R. Kiebach, C. Näther, W. Bensch, R. Kiebach, Solid State Sci. 8 (2006) 964–970. [16] (a) J.P. Wang, P.T. Ma, J.W. Zhao, J.Y. Niu, Inorg. Chem. Commun. 10 (2007) 523–526; (b) J.P. Wang, P.T. Ma, J. Li, J.Y. Niu, Chem. Lett. 35 (2006) 994–995. [17] (a) W. Zhang, S.X. Liu, P. Sun, C.D. Zhang, F.J. Ma, D. Feng, J. Mol. Struct. 969 (2010) 76–80; (b) W. Zhang, S.X. Liu, D. Feng, C.D. Zhang, P. Sun, F.J. Ma, J. Mol. Struct. 936 (2010) 194–198; (c) S. Yao, Z.M. Zhang, Y.G. Li, E.B. Wang, Inorg. Chem. Commun. 12 (2009) 937–940. [18] (a) A. Ogawa, H. Yamato, U. Lee, H. Ichida, A. Kobayashi, Y. Sasaki, Acta Cryst. C44 (1988) 1879–1881; (b) D. Drewes, G. Vollmer, B. Krebs, Z. Anorg, Allg. Chem. 630 (2004) 2573–2575. [19] (a) G.L. Xue, X.M. Liu, H.S. Xu, H.M. Hu, F. Fu, J.W. Wang, Inorg. Chem. 47 (2008) 2011–2016; (b) Y.Z. Zhen, Q. Shen, L.L. Li, G.L. Xue, H.M. Hu, F. Fu, J.W. Wang, Inorg. Chem. Commun. 11 (2008) 886–888. [20] Synthesis of 1: Na2WO4·2H2O (2.5 g, 7.58 mmol) was dissolved in 25 mL of distilled water and heated to 80 °C. Whilst SbCl5 (0.6 g, 2.00 mmol) was dissolved in 2 mL of 12 M hydrochloric acid and added quickly to the hot solution, the pH was adjusted to 2–3 with NH3·H2O. The reaction mixture was stirred and kept at 80 °C for 1 h. After the solution had cooled to the ambient temperature, a small amount of white precipitate was filtered off, and the filtrate was left to evaporate at room temperature, the well-shaped colorless block crystals which suitable for X-ray diffraction analysis were obtained in 10 minutes. The yield was 10 % (0.2 g). Elemental analysis calcd (%) for N9H88O87SbW18: H 1.73, N 2.56, Sb 2.47, W 65.71; Found: H 1.76, N 2.50, Sb 2.41, W 65.67%. IR (KBr pellet, cm–1) for (1): 3417.28, 3180.09, 3027.74, 2827.28, 1615.60, 1412.66, 1011.30, 944.77, 807.98, 584.91, 485.98 [21] Crystal data for H88N9O87SbW18: M = 5037.59, trigonal, space group R-3, a = 19.8072(9), b = 19.8072(9), c = 16.7059(11) Å, γ = 120°, V = 5676.1 Å3, T = 293 K, Z = 3, μ(Mo Kα) = 27.685 mm–1, F(0 0 0) = 5970, Rint = 0.075, R1= 0.0555 and wR2 = 0.1353. Of 7659 total reflections collected, 2226 were unique [(I N 2σ(I)]. The structure was solved by the direct method and refined by the full-matrix least-squares method on F2 using the SHELXS-97. Anisotropic thermal parameters were used to refine all non-hydrogen atoms except for the part of oxygen atoms. Those hydrogen atoms attached to lattice water molecules were not located. [22] I.D. Brown, D. Altermatt, Acta Crystallogr. B41 (1985) 244–247. [23] (a) S.T. Zheng, J. Zhang, J.M. Clemente-Juan, D.Q. Yuan, G.Y. Yang, Angew. Chem. Int. Ed. 48 (2009) 7176–7179; (b) R. Tsunashima, D.L. Long, H.N. Miras, D. Gabb, C.P. Pradeep, L. Cronin, Angew. Chem. Int. Ed. 49 (2009) 113–116; (c) X.K. Fang, C.L. Hill, Angew. Chem. Int. Ed. 46 (2007) 3877–3880; (d) C.R. Sprangers, J.K. Marmon, D.N. Duncan, Inorg. Chem. 45 (2006) 9268–9630. [24] S.J. Gilliam, J.O. Jensen, A. Banerjee, D. Zeroka, S.J. Kirkby, C.N. Merrowa, Spectrochim, Acta, Part A 60 (2004) 425–434. [25] J.P. Wang, J.W. Zhao, P.T. Ma, J.C. Ma, L.P. Yang, Y. Bai, M.X. Li, J.Y. Niu, Chem. Commun. (2009) 2362–2364.
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Inorganic Chemistry Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i n o c h e
A new Dawson-like tungstoantimonate related to [SbVW18O60(OH)2]9− Yuan-Yuan Zhang, Shu-Xia Liu ⁎, Chao-Jie Yu, Qun Tang, Da-Dong Liang, Chun-Dan Zhang, Feng-Ji Ma, Shu-Jun Li, Wei Zhang, Rui-Kang Tan Key Laboratory of Polyoxometalate Science of Ministry of Education, College of Chemistry, Northeast Normal University, Changchun, Jilin 130024, China
a r t i c l e
i n f o
Article history: Received 6 April 2010 Accepted 3 August 2010 Available online 10 August 2010 Keywords: Polyoxometalates Tungstoantimonate Dawson-like Synthesis
a b s t r a c t A new tungstoantimonate (NH4)9[SbVW18O60(OH)2]·25H2O (1) has been synthesized under acidic medium conditions and characterized by element analysis, IR, TG, UV, PXRD and single-crystal X-ray diffraction analysis. Compound 1 represents the first example of Sb(V)-containing polyoxometalate with unusual Dawson-like construction. The polyoxoanion incorporates an {SbO6} unit into the center of {W18O54} cluster cage. © 2010 Elsevier B.V. All rights reserved.
Polyoxometalates (POMs), as discrete early transition-metal-oxide clusters, have attracted extensive interest not only because of their intriguing architectures but also in terms of the wide range of topological properties, displaying potential applications in many fields such as catalysis, medicine, materials science, optical and magnetic properties [1]. Much attention has been focused on the designing and synthesizing POMs with novel structures since the first POM was discovered in 1826 by Berzelius [2], but the creation of new POM compounds is still a great challenge. In the field of POM chemistry, Dawson-type compounds are one of the most common families and often represented with the general formula [M18O54 (XO4)2]m−, where X is heteroatom and M is the addendum atom. Furthermore, it is well-known that the {M18} cluster cages are templated by two tetrahedral heteroanions [3]. However, there are four kinds of species possessing {M18} cluster cages embedded in nontetrahedral groups being addressed. The first incorporates only one 3− 3− 4− 2− pyramidal (AsO3− 3 , SbO3 , BiO3 , SnO3 , or TeO3 ) [4–9]; the second ) hetero groups [10]; the third encapencloses ditetrahedral (P2O4− 7 sulates two pyramidal (SO2− 3 ) moiety [11]; and the fourth embeds 5− 6− trigonal–prismatic or octahedron (WO6− 6 , IO6 , or TeO6 ) as templates, the central heteroatoms are all hexa-coordinated, respectively [9,12] (Fig. S1). All the above-mentioned structural types are different from the classical Dawson-type constitution, namely Dawson-like type compounds, which are uncommon in POM chemistry. In the past few decades, many Sb(III)-containing polyoxoanions have been synthesized and structurally characterized [13–17]. On the contrary, relatively few cases of Sb(V)-containing polyoxoanions have
⁎ Corresponding author. Tel./fax: +86 431 85099328. E-mail address: [email protected] (S.-X. Liu). 1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.08.005
been reported [18,19]. Recently, an example of Sb-containing POM with Dawson-like construction has been made and described as the “peanut-like” shaped tungstoantimonate [H2SbIIIW18O60 ]7−, in which the sole Sb is tricoordinated and with a pair of electrons, as well as the occupancy rate is 0.5 [7]. To the best of our knowledge, the γ*-isomer isopolyoxoanion [H4W19O62]6– with Dawson-like structure was first reported in 2006 by Cronin and co-workers [12a]. Then in the following two years, they prepared the first Dawson-like γ*-isomer heteropolyoxoanion [H3W18O56(TeO6)]7– [12b]. The two clusters containing {WO6} and {TeO6} unit as templates inside the {W18} cluster shell, respectively. Herein, we report the expansion of POM compounds with Dawson-like structure formed by {SbO6} moiety as template embedded into a {W18O54} cluster cage. The polyoxotungstates system containing hexa-coordinated antimony has been synthesized under acidic medium conditions, leading to the compound formulated as (NH4)9[SbVW18O60(OH)2]·25H2O (1). It is notable that the title heteropolyoxoanion is the first example of Sb(V)-containing POM with unusual Dawson-like construction, and it is the second Dawsonlike cluster has a γ* conformation, which extended the family of Dawson-like clusters. Compound 1 was easily prepared by a mixture of Na2WO4·2H2O and SbCl5 (molar ratio 4:1) at pH = 2–3 aqueous solution kept at 80 °C for 1 h [20]. SbCl5 is tend to be hydrolyzed in the air and should be quick to be dissolved to concentrated hydrochloric acid. And then we selected common base such as NaOH, KOH, and NH3⋅H2O to adjust the pH until 2–3. When Na+ or K+ was used as cation, we failed to obtain perfect crystals suitable for X-ray diffraction analysis under similar reaction conditions, instead forming amorphous precipitate; only the title compound in the form of NH+ 4 salt is obtained. And it is worth mentioning that the crystallization is very quick, which occurred in 10 minutes. In order to check the phase purity of 1, the powder X-ray
Y.-Y. Zhang et al. / Inorganic Chemistry Communications 13 (2010) 1418–1420
diffraction (PXRD) patterns of 1 was recorded at room temperature (Fig. S8). The peak positions of simulated and experimental patterns of 1 are in agreement with each other, indicating the good phase purity of 1. Single-crystal X-ray structure analysis [21] reveals that the novel compound 1 is crystallizes in the trigonal space group R-3. The structure of the polyoxoanion [SbVW18O60(OH)2]9– (abbreviated as {SbVW18}) is markedly different from [H2SbIIIW18O60]7– (abbreviated as {SbIIIW18}) [6], as shown in Fig. 1. The “peanut-like” shaped polyoxoanion {SbIIIW18} has a pyramidal SbO3 group (average Sb–O distance = 2.00 Å) and the group is disordered over two possible positions in the cluster cage. The Sb–Sb distance is appropriately 2.18 Å apart, the sole Sb with a pair of electrons and the occupancy rate is 0.5. Comparatively, the new polyoxoanion {SbVW18} enclosed pentavalent antimony resulting in a novel structure (Fig. 2). The Sbcentered atom is coordinated via six oxo ligands with Sb–O distance of 2.026 Å and the (Sb)O–W mean distance of 2.297(5) Å. Moreover, there are 60 oxygen atoms in {SbIIIW18} while 62 in {SbVW18}. In {SbIIIW18}, there are six μ4–O oxygen atoms which connected one Sb and three W atoms. Nevertheless, there are eight μ3–O oxygen atoms in {SbVW18}: two of them bridge three W atoms from the capping unit inside the cluster, the other six combine with one Sb and two W atoms. Compound 1 was characterized by bond valence calculations (BVS) [22] to identify the oxidation states of tungsten and antimony atoms, as well as the possible protonated oxygen atoms on polyanion. The BVS clearly show that all the tungsten atoms and antimony atom in 1 exhibit +6 and + 5 oxidation state, respectively. It is also noteworthy that there are two μ3–O (O8) (Fig. S2), both bridges the capping {W3} unit inside the framework, the distance between O8 and W is 2.266 Å, which leads to a calculated valence of the two oxygen atoms is 1.168, respectively, indicating that they are indeed monoprotonated [18b,23]. These result two OH groups inside the {W18} cluster cage and therefore, the charge of the polyanion is − 9, thus the molecular formula is described as [SbVW18O60(OH)2]9−. The BVS values for other terminal or bridging oxygen atoms (ca. 1.541–2.077), indicate there is no additional protonation. The distances between the μ3–O (O8) and neighboring μ2–O or μ3–O is ranging from 2.835 to 3.009 Å, thus we speculate that there may be exist stable hydrogenbonding inside the cluster, enhancing the stability of the framework [SbVW18O60(OH)2]9–. In addition, in the {SbVW18} cluster cage, the D3d symmetric of the {SbO6} unit match the {W18O54} D3d-symmetric of the cluster shell, thus representing a γ*-isomer in the family of Dawson-like clusters. To
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Fig. 2. Polyhedral representation of polyoxoanion [SbVW18O60(OH)2]9–. Color code: Sb bright green; W pale blue; O red.
our knowledge, compound 1 is the second Dawson-like heteropolyoxoanion has a γ* conformation. The γ*-{SbVW18} is slightly different from the reported β*-isomer polyoxoanion [H3W18O56(IO6)]6– [12b], where the orientation of the trigonal {W3O13} caps are interconverted by a 60° rotation (Fig. S3). The IR spectrum of 1 shows a broad peak at 3417 cm–1 and a strong peak at 1615 cm–1 ascribed to the lattice water molecules. It displays four characteristic absorptions below 1000 cm–1 attributed to the Dawson-like structure, the characteristic peaks at 584 cm–1 probably assigned to the absorptions of Sb–O vibrations [19,24]. And the peaks at 3180 and 1412 cm–1 are indicative of the presence of NH+ 4 (Fig. S4). In addition, UV–vis spectrum was performed to investigate the stability of 1 in the aqueous solution [25]. We monitored compound 1 in the pH range of 1–9 and found that it maintained stable in acidic
Fig. 1. Ball-and-stick representation of [SbVW18O60(OH)2]9– (left) and the peanut-shaped anion [H2SbIIIW18O60]7– (right) for comparison. Color code: Sb(V) bright green; Sb(III) tan; W pale blue; O red.
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solution (Fig. S5). Also, UV–vis spectrum of 1 was carried out in distilled water (pH = 6.00) for 40 days, the results revealed that it can stably exist within 40 days (Fig. S6). Thermal gravimetric (TG) analyses of compound 1 was carried out from 25 to 600 °C under a nitrogen atmosphere (Fig. S7). In the TG curve of compound 1, there are two weight loss steps. The first rapid weight loss of 9.68% in the temperature range of 25–156 °C corresponds to the release of 25 lattice H2O molecules and two NH3 molecules. The second weight loss of 2.46% in the temperature range of 156–450 °C is probably the result of release of seven NH3 molecules. After 450 °C, there is no further decomposition of the compound, indicating that the polyanion maintained a stable framework until 600 °C. In summary, a new compound has been successfully synthesized in hot aqueous solution. Compound 1 is the first example of Sb(V)containing POM bearing unusual Dawson-like construction, and it is the second Dawson-like heteropolyoxoanion has a γ* conformation. On account of the stability of title tungstoantimonate in aqueous solution, in further work, we will attempt to link the anion to construct high-dimentional extended structures by employing transition metal or lanthanide metal ions, which is of significance for the development of POM chemistry. Acknowledgements This work was supported by the National Science Foundation of China (Grant Nos. 20871027 and 20973035), the Program for New Century Excellent Talents in University (NCET-07-0169), and the Program for Changjiang Scholars and Innovative Research Team in University. Appendix A. Supplementary material Further details of the crystal structure investigations for 1 could be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein–Leopoldshafen, Germany (fax: (+ 49)7247-808-666; e-mail: crystdata@fiz-karlsruhe.de) on quoting the depository number CSD421580. Supplementary material associated with the article can be found, in the online version, doi:10.1016/j.inoche.2010.08.005. References [1] (a) M.T. Pope, A. Müller, Angew. Chem. Int. Ed Engl. 30 (1991) 34–38; (b) J.T. Rhule, C.L. Hill, D.A. Judd, R.F. Schinazi, Chem. Rev. 98 (1998) 327–358; (c) C.L. Hill (Ed.), Polyoxometalates in Catalysis, J. Mol. Catal. A:Chem., 262, 2007, pp. 1–242; (d) Z.Q. Zhang, R.D. Huang, L.J. Dong, Y.Q. Xu, L.Q. Yu, Z.W. Jiao, C.W. Hu, Inorg. Chim. Acta 362 (2009) 3056–3064; (e) L.J. Zhang, Y.H. Li, Y.S. Zhou, J. Mol. Struct. 969 (2010) 69–74. [2] J. Berzelius, Ann. Phys. 6 (1826) 369–380. [3] (a) X.Y. Zhao, D.D. Liang, S.X. Liu, C.Y. Sun, R.G. Cao, C.Y. Gao, Y.H. Ren, Z.M. Su, Inorg. Chem. 47 (2008) 7133–7138; (b) M. Abbessi, R. Contant, R. Thouvenot, G. Hervé, Inorg. Chem. 30 (1991) 1695–11702; (c) B. Keita, B. Girard, L. Nadjo, R. Contant, J. Canny, M. Richet, J. Electroanal. Chem. 478 (1999) 76–82; (d) B. Dawson, Acta Crystallogr. 6 (1953) 113–126; (e) R. Contant, Inorg. Synth[M] 27 (1990) 104–107. [4] R. Contant, S. Piro-Sellem, J. Canny, R. Thouvenot, C.R.Acad.Sci.Paris, Sér. IIc 3 (2000) 157–161. [5] Y. Jeannin, J.M. Frere, Inorg. Chem. 18 (1979) 3010–3014.
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