- Email: [email protected]
New assembly of transition metal complexes based on [GeW9O34]10− building blocks: Syntheses, crystal structures and magnetic properties
Inorganic Chemistry Communications 13 (2010) 372–375
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
New assembly of transition metal complexes based on [GeW9O34]10 building blocks: Syntheses, crystal structures and magnetic properties Ning Jiang, Fengyan Li, Lin Xu *, Yungao Li, Jianmei 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 22 October 2009 Accepted 28 December 2009 Available online 4 January 2010 Keywords: Polyoxometalate Polyoxotungstogermanate Sandwich Magnetic property
a b s t r a c t Two new polyoxotungstates Na3H(C3H5N2)4[{Cu(C3N2H4)2}2Cu4(H2O)2(GeW9O34)2]27H2O (1) and Na10H8[Mn6Ge3W24O94(H2O)2]37H2O (2) have been synthesized in aqueous solution. The polyoxoanion frameworks of the two compounds are built on the lacunary Keggin-type polyanion [GeW9O34]10. The structure of compound 1 is a Weakley-type species capped by two [Cu(C3N2H4)2]2+ units through four bridging oxygen atoms on two opposite W4O4 faces. Compound 2 is a banana-shaped polyoxometalate consisting of two tri-Mn substituted [Mn3GeW9O34]4 Keggin units and a hexavacant bridging cluster [GeW6O26]12. The magnetic investigations demonstrate the presence of both antiferromagnetic and ferromagnetic exchange interactions for 1 and weak antiferromagnetic interactions for 2. Ó 2009 Elsevier B.V. All rights reserved.
Polyoxometalates (POMs), which are composed of edge and corner-shared {MO6} octahedra with early-transition metal ions in high oxidation states (e.g. WVI, MoVI), exhibit potential applications in many diverse areas, including magnetism, catalysis, medicine and materials sciences [1]. In virtue of a great family of POM building blocks, significant effort has gone into creating rational assemblies to obtain new compounds with desired functional properties. The lacunary POM, acting as multidentate ligands, is one of the basic fragments for constructing plenty of impressing and fascinating large structures. Within the class of polyoxoanions, those species especially the sandwich-type complexes based on trivacant Keggin fragments attract much attention. In 1973, Weakley reported the first tetra-CoII substituted inorganic sandwich-type POM [Co4(H2O)2(B-a-PW9O34)2]10 [2]. So far, a number of such sandwich-type polyoxotungstates consisting of two B-a[XW9O34]n (X = PV, AsV, SiIV, GeIV) ligands and a rhomb like fourtransition metal (M) tetragon have been reported [3–12]. Further, Weakley-type species are used as the building blocks to construct their derivatives decorated by transition–metal complexes [13,14]. Moreover, the banana-shaped polyoxoanion, a doublesandwich structure built on B-a-[XW9O34]n, was reported firstly by Coronado et al. for the cobalt(II)-containing tungstophosphate [Co7(H2O)2(OH)2P2W25O94]16 and then several compounds exhibiting similar structure have been synthesized [15–19]. In the reported examples, the trivacant Keggin POMs act as good candidates to incorporate metal centers into novel inorganic aggregates. Therefore, the exploration for new type of coordination compounds * Corresponding author. Fax: +86 431 85099668. E-mail address: [email protected] (L. Xu). 1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2009.12.025
on the base of trivacant Keggin POMs becomes one target of considerable significance in synthetic chemistry and the material science. Herein, we report two new compounds, Na3H(C3H5N2)4[{Cu(C3N2H4)2}2Cu4(H2O)2(GeW9O34)2]27H2O (1) and Na10H8[Mn6Ge3W24O94(H2O)2]37H2O (2), based on trivacant Keggin POM [GeW9O34]10 building blocks. In compound 1, the Weakley-type species is capped by two [Cu(C3N2H4)2]2+ units through four bridging oxygen atoms on two opposite W4O4 faces. To the best of our knowledge, this is the first case of the copper(II)–imidazole fragment coordinated with four bridging oxygen atoms from sandwich-type polyoxotungstogermanates. Compound 2 is a bananashaped POM consisting of two tri-Mn substituted [MnII2MnIIIGeW9O34]3 Keggin units and a hexavacant bridging cluster [GeW6O26]12. Such POM containing two types of lacunary polyoxotungstogermanates units was only reported by Yang et al. [19]. The magnetic property measurements were also made to well characterize these two new complexes. The magnetic investigations demonstrate the presence of both antiferromagnetic and ferromagnetic exchange interactions for 1 and weak antiferromagnetic interactions for 2. Compound 1 and 2 were synthesized by the reaction of Na2WO4, GeO2, CuCl22H2O or Mn(CH3COO)24H2O in the presence of imidazole by a conventional solution method [20]. Notably, the pH is very important for the formation of 1 and 2. Although imidazole does not appear in the crystal structure of compound 2, the addition of imidazole can well facilitate the reaction of Mn ion with the polyanions so as to obtain the crystal product with good quality. From our observation of controlled experiments, without the imidazole into the reaction solution, the product is floccular solid instead of crystal.
N. Jiang et al. / Inorganic Chemistry Communications 13 (2010) 372–375
The polyanion of 1 consists of two capping [Cu(C3N2H4)2]2+ subunits and two lacunary B-a-[GeW9O34] Keggin moieties linked via a rhomb like Cu4O16 group (Fig. 1a) [21], which is similar to that of {Mn(phen)}2Mn4(H2O)2(GeW9O34)2]8 reported by Niu et al. [13]. Two [Cu(C3N2H4)2]2+ fragments are capped on the ‘‘shoulder” positions through four bridging oxygen atoms on two opposite W4O4
373
faces. Cu3 coordinated by two nitrogen atoms from two imidazole ligands connect with four bridging oxygen atoms from the B-aGeW9 unit, exhibiting distorted octahedral geometry in the form {CuN2O4} (Fig. 1c). The central core [Cu4(l4-O)2(l3-O)4(l2O)8(H2O)2] in the anion for 1 where the aqua molecule is bound terminally at the Cu2 to yield a Cu4 rhomb consisting of four
Fig. 1. (a) Crystal structure of the [{Cu(C3N2H4)2}2Cu4(H2O)2(GeW9O34)2]8 polyanion in 1. Plum octahedra, {WO6}; sky blue tetrahedra, {GeO4}. (b) Structure of Cu4 tetragon. (c) Coordination environment of Cu in capping [Cu(C3N2H4)2]2+ subunits. # = 1x, 1y, 2z.
Fig. 2. (a) Crystal structure of the [Mn6Ge3W24O94(H2O)2]18 polyanion in 2. Plum octahedra, {WO6}; sky blue tetrahedra, {GeO4}; yellow ball, MnII; orange ball, MnIII. (b) Structure of Mn6 unit.
374
N. Jiang et al. / Inorganic Chemistry Communications 13 (2010) 372–375
distorted CuO6 octahedra (Fig. 1a and b). The Cu ions site at the neighboring corner of the rhomb with Cu Cu average distance of 3.182(2) Å. Two Cu ions site at the short diagonal with Cu1 Cu1# distance of 3.055(3) Å and the other two Cu ions site at the long diagonal with Cu2 Cu2# distance of 5.587(2) Å. The polyanion of 2 is formed by the condensation of two tri-Mn substituted B-a-½MnII2 MnIII GeW9 O34 3 Keggin units and a hexavacant bridging cluster [GeW6O26] (Fig. 2a) [22]. The Keggin subunit is composed of the trivacant [GeW9O34]10 germanotungstate ligand and three edge-sharing MnO6 octahedra. Bond valence sum (BVS) calculations [23] indicate that four manganese centers exhibit a 2+ oxidation state and two manganese centers exhibit a 3+ oxidation state (Table S1 in Supporting information). Two trinuclear manganese clusters are crystallographically independent (Fig. 2b). This complex can be compared to the reported bananashaped POMs [15–19]. The magnetic susceptibilities of 1 and 2 have been measured on a crystalline sample under a field of 1000 Oe in the temperature range of 2–300 K. Fig. 3 shows the temperature dependence of
vm and vmT of 1. The value of vmT for 1 decreases from 2.75 cm3 mol1 K at 300 K to a minimum of 2.01 cm3 mol1 K at 36 K and then increases to 2.44 cm3 mol1 K at 2 K. The vmT values at 300 K (2.75 cm3 mol1 K corresponding to 4.69 lB) are close to the sum of contributions for six Cu2+ ions (4.75 lB, g = 2.24). The vmT values at 36 K (2.01 cm3 mol1 K corresponding to 4 lB) are close to values expected for four separated Cu2+ ions (3.88 lB, g = 2.24). Such behavior is characteristic of the presence of both antiferromagnetic and ferromagnetic exchange interactions, which might be attributed to the existence of spin frustration at low temperature. The 1/vm versus T plot for 1 could be fit with Curie–Weiss equation from 100 to 300 K, getting C = 3.15 cm3 mol1 K and h = 44.2 K. The negative Weiss constant indicates the existence of antiferromagnetic interaction between the nearest magnetic centers (Fig. S7, see Supporting information). 0 The central core Cu8þ 4 requires three exchange parameters (J, J , and J00 ), which represent the isotropic interactions along the sides, short diagonal, and long diagonal of the rhomb. The magnetic
Fig. 3. Plots of vm and vmT vs. T for 1. The numbering scheme for the spin Hamiltonian for three exchange interactions (J–J0 0 ) and the analyzing results are shown in the inset.
Fig. 4. Plots of vm and vmT vs. T for 2. The numbering scheme for the spin Hamiltonian for two exchange interaction (J and J0 ) and the analyzing results are shown in the inset.
N. Jiang et al. / Inorganic Chemistry Communications 13 (2010) 372–375
susceptibility data of 1 were analyzed using Eq. (3) (see Supporting information). A satisfying description of the experimental data over the whole temperature range (Fig. 3) is obtained with the following set of parameters: J = 0.49 cm1, J0 = 37.4 cm1, J00 = 0.68 cm1 and g = 2.24. Fig. 4 shows the temperature dependence of vm and vmT of 2. The value of vmT for 2 decreases from 25.6 cm3 mol1 K at 300 K to 6.29 cm3 mol1 K at 2 K. The vmT values at 300 K (25.6 cm3 mol1 K corresponding to 14.3 lB) are close to the sum of spin-only (g = 2) contributions for four Mn2+ ions and two Mn3+ ions (13.7 lB). Such behavior demonstrates the presence of antiferromagnetic exchange interactions in trinuclear Mn clusters. The 1/vm versus T plot for 2 could be fit with Curie–Weiss equation from 7 to 300 K, getting C = 26.6 cm3 mol1 K and h = 17.1 K. The negative Weiss constant suggests that overall antiferromagnetic interactions exist in 2 (Fig. S8, see Supporting information). The central core MnII2 MnIII requires two exchange parameter J and J0 (Fig. 4). The magnetic susceptibility data of MnII2 MnIII were analyzed using Eq. (7) (see Supporting information). A satisfying description of the experimental data over the whole temperature range is obtained with the following set of parameters: J = 0.071 cm1, J0 = 1.03 cm1 and g = 1.99. In summary, two new sandwich-type polyoxometalates Na3H(C3H5N2)4{[Cu(C3N2H4)2]2[Cu4(H2O)2(GeW9O34)2]}27H2O and Na10H8[Mn6Ge3W24O94(H2O)2]37H2O have been obtained. The successful synthesis of 1 demonstrates the possibility of copper(II)– imidazole fragment coordinated with four bridging oxygen atoms from sandwich-type polyoxotungstogermanates with conventional solution method. Compound 2 proves that two types of lacunary polyoxotungstogermanates can be also stabilized under conventional solution conditions. Based on the ligand of lacunary POM, the assembly of different transition metal ions may generate more novel solid state compounds with potential magnetic properties. Such work is ongoing in our laboratory. Acknowledgments This work was financially supported by the Natural Science Foundation of China (Grant Nos. 20671017 and 20731002) and the Program for Changjiang Scholars and Innovative Research Team in University, and the Science Foundation for Young Teachers of Northeast Normal University (No. 20090403). Appendix A. Supplementary material CCDC 749940 and 421070 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2009.12.025. References [1] (a) C. Hill (Ed.), Chem. Rev., Polyoxometalates (1998); (b) M.T. Pope, A. Müller (Eds.), Polyoxometalate Chemistry: from Topology via Self-assembly to Applications, Kluwer Academic Publishers, Dordrecht, The Netherlands, 2001.
375
[2] T.J.R. Weakley, H.T. Evans, J.S. Showell, G.F. Tourné, C.M. Tourné, J. Chem. Soc. Chem. Commun. (1973) 139. [3] H.T. Evans, G.F. Tourné, C.M. Tourné, T.J.R. Weakley, J. Chem. Soc., Dalton Trans. (1986) 2699. [4] C.J. Gómez-García, E. Coronado, J. Borrás-Almenar, Inorg. Chem. 31 (1992) 1667. [5] J.M. Clemente-Juan, H. Andres, J.J. Borrás-Alamenar, E. Coronado, H.U. Güdel, M. Aebersold, G. Kearly, H. Büttner, M. Zollinker, J. Am. Chem. Soc. 121 (1999) 10021. [6] H. Andres, J.M. Clemente-Juan, M. Aebersold, H.U. Güdel, E. Coronado, H. Büttner, G. Kearly, J. Melero, R. Burriel, J. Am. Chem. Soc. 121 (1999) 10028. [7] J.M. Clemente-Juan, E. Coronado, J.R. Galán-Mascarós, C.J. Gómez-García, Inorg. Chem. 38 (1999) 55. [8] U. Kortz, S. Isber, M.H. Dickman, D. Ravot, Inorg. Chem. 39 (2000) 2915. [9] L.H. Bi, R.D. Huang, J. Peng, E.B. Wang, Y.H. Wang, C.W. Hu, J. Chem. Soc., Dalton Trans. (2001) 121. [10] U. Kortz, S. Nellutla, A.C. Stowe, N.S. Dalal, J. van Tol, B.S. Bassil, Inorg. Chem. 43 (2004) 144. [11] U. Kortz, S. Nellutla, A.C. Stowe, N.S. Dalal, U. Rauwald, W. Danquah, D. Ravot, Inorg. Chem. 43 (2004) 2308. [12] T. Yamase, H. Abe, E. Ishikawa, H. Nojiri, Y. Ohshima, Inorg. Chem. 48 (2009) 138. [13] J.P. Wang, P.T. Ma, Y. Shen, J.Y. Niu, Crystal. Growth & Design 8 (2008) 3130. [14] G.W. Wang, Y. Chen, Y.C. Zou, Y. Wang, H.T. Wang, K.C. Li, X.B. Cui, S.Y. Shi, J.Q. Xu, Inorg. Chem. Commun. 12 (2009) 646. [15] I.M. Mbomekalle, B. Keita, M. Nierlich, U. Kortz, P. Berthet, L. Nadjo, Inorg. Chem. 42 (2003) 5143. [16] J.J. Borras-Almenar, J.M. Clemente-Juan, M. Clemente-Leon, E. Coronado, J.R. Galan- Mascaros, C.J. Gomez-Garcia, in: M.T. Pope, A. Müller (Eds.), Polyoxometalate Chemistry: From Topology Via Self-Assembly to Applications, Kluwer, Dordrecht, The Netherlands, 2001, p. 231. [17] M.D. Ritorto, T.M. Anderson, W.A. Neiwert, C.L. Hill, Inorg. Chem. 43 (2004) 44. [18] J.D. Compain, P. Mialane, A. Dolbecq, I.M. Mbomekallé, J. Marrot, F. Sécheresse, E. Rivière, G. Rogez, W. Wernsdorfer, Angew. Chem., Int. Ed. 48 (2009) 3077. [19] B. Li, J.W. Zhao, S.T. Zheng, G.Y. Yang, Inorg. Chem. Commun. 12 (2009) 69. [20] All starting materials and chemicals were used without further purification: Synthesis of 1: Na2WO4 (1.32 g), GeO2 (0.0464 g), 0.5 ml 6 M HCl were dissolved in 20 ml H2O and stirred for 1 h to get solution A. CuCl22H2O (0.68 g), imidazole (1.1 g) were dissolved in 10 ml H2O and stirred for 1 h to get solution B, which was added into solution A in small portions with magnetic stirring. The pH of the mixture was adjusted to 4.3 by addition of 6 M HCl and stirred at 90 °C for 2 h. A blue–green precipitate was removed by filtration, and green crystals (0.23 g) suitable for X-ray analysis were obtained after the filtrate was kept for one week at room temperature. The yield was 15% based on W. IR: 3444 (s), 3141 (w), 2831 (w), 1620 (s), 1580 (s), 1541 (s), 1509 (s), 1421 (s), 1328 (m), 1262 (m), 1174 (m), 1072 (s), 947 (s), 888 (s), 772 (s), 695 (s), 500 (w), 457 (m). Elemental analyses calcd. (%): W 54.56, Cu 6.29, Ge 2.40, Na 1.14, C 4.75, O 25.59, N 3.70, H 1.57. Found: W 54.37, Cu 6.48, Ge 2.45, Na 1.11, C 4.72, O 25.53, N 3.73, H 1.61.Synthesis of 2: Na2WO4 (1.65 g), GeO2 (0.0523 g), 1 ml 6 M HCl were dissolved in 20 ml H2O and stirred until the solution became homogeneous. Mn(CH3COO)24H2O (0.123 g) dissolved in 5 ml H2O and imidazole (0.035 g) dissolved in 5 ml H2O were added with stirring (pH 7.3–7.6). The solution was heated at 90 °C for 1 h and then filtered. Brown crystals (0.208 g) suitable for X-ray analysis were obtained after the filtrate was kept for two days at room temperature. The yield was 12% based on W. IR: 941 (s), 875 (s), 770 (s), 697 (s), 509 (w), 458 (m). Elemental analyses calcd. (%): W 59.59, Mn 4.45, Ge 2.94, Na 3.11, O 28.74, H 1.17. Found: W 59.33, Mn 4.57, Ge 2.85, Na 3.19, O 28.81, H 1.25. [21] Crystal data and structure refinements for 1: Mr = 6064.85 g mol1, green blocks, triclinic, space group, P1 , a = 12.618 Å, b = 13.349 Å, c = 18.985 Å, a = 94.24°, b = 103.63°, c = 116.53°, V = 2720.8 Å3, Z = 1, R1 = 0.0463, wR2 = 0.1189. Crystal data were measured on a Bruker Apex CCD diffractometer using MoKa radiation (k = 0.71073 Å) at 293(2) K. [22] Crystal data and structure refinements for 2: Mr = 7404.40 g mol1, brown blocks, monoclinic, space group, P2/c, a = 17.8335(14) Å, b = 22.3430(18) Å, c = 35.817(3) Å, a = 90.00°, b = 93.5550(10)°, c = 90.00°, V = 14244(2) Å3, Z = 2, R1 = 0.0562, wR2 = 0.1485. Crystal data were measured on a Bruker Apex CCD diffractometer using MoKa radiation (k = 0.71073 Å) at 296(2) K. Further details of the structure determination are available on request from the ICSD Team, FIZ Karlsruhe, Hermann–von-Helmholtz–Platz 1, D-76344 Eggenstein– Leopoldshafen. [23] I.D. Brown, D. Altermatt, Acta Crystallogr. B41 (1985) 244.
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
New assembly of transition metal complexes based on [GeW9O34]10 building blocks: Syntheses, crystal structures and magnetic properties Ning Jiang, Fengyan Li, Lin Xu *, Yungao Li, Jianmei 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 22 October 2009 Accepted 28 December 2009 Available online 4 January 2010 Keywords: Polyoxometalate Polyoxotungstogermanate Sandwich Magnetic property
a b s t r a c t Two new polyoxotungstates Na3H(C3H5N2)4[{Cu(C3N2H4)2}2Cu4(H2O)2(GeW9O34)2]27H2O (1) and Na10H8[Mn6Ge3W24O94(H2O)2]37H2O (2) have been synthesized in aqueous solution. The polyoxoanion frameworks of the two compounds are built on the lacunary Keggin-type polyanion [GeW9O34]10. The structure of compound 1 is a Weakley-type species capped by two [Cu(C3N2H4)2]2+ units through four bridging oxygen atoms on two opposite W4O4 faces. Compound 2 is a banana-shaped polyoxometalate consisting of two tri-Mn substituted [Mn3GeW9O34]4 Keggin units and a hexavacant bridging cluster [GeW6O26]12. The magnetic investigations demonstrate the presence of both antiferromagnetic and ferromagnetic exchange interactions for 1 and weak antiferromagnetic interactions for 2. Ó 2009 Elsevier B.V. All rights reserved.
Polyoxometalates (POMs), which are composed of edge and corner-shared {MO6} octahedra with early-transition metal ions in high oxidation states (e.g. WVI, MoVI), exhibit potential applications in many diverse areas, including magnetism, catalysis, medicine and materials sciences [1]. In virtue of a great family of POM building blocks, significant effort has gone into creating rational assemblies to obtain new compounds with desired functional properties. The lacunary POM, acting as multidentate ligands, is one of the basic fragments for constructing plenty of impressing and fascinating large structures. Within the class of polyoxoanions, those species especially the sandwich-type complexes based on trivacant Keggin fragments attract much attention. In 1973, Weakley reported the first tetra-CoII substituted inorganic sandwich-type POM [Co4(H2O)2(B-a-PW9O34)2]10 [2]. So far, a number of such sandwich-type polyoxotungstates consisting of two B-a[XW9O34]n (X = PV, AsV, SiIV, GeIV) ligands and a rhomb like fourtransition metal (M) tetragon have been reported [3–12]. Further, Weakley-type species are used as the building blocks to construct their derivatives decorated by transition–metal complexes [13,14]. Moreover, the banana-shaped polyoxoanion, a doublesandwich structure built on B-a-[XW9O34]n, was reported firstly by Coronado et al. for the cobalt(II)-containing tungstophosphate [Co7(H2O)2(OH)2P2W25O94]16 and then several compounds exhibiting similar structure have been synthesized [15–19]. In the reported examples, the trivacant Keggin POMs act as good candidates to incorporate metal centers into novel inorganic aggregates. Therefore, the exploration for new type of coordination compounds * Corresponding author. Fax: +86 431 85099668. E-mail address: [email protected] (L. Xu). 1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2009.12.025
on the base of trivacant Keggin POMs becomes one target of considerable significance in synthetic chemistry and the material science. Herein, we report two new compounds, Na3H(C3H5N2)4[{Cu(C3N2H4)2}2Cu4(H2O)2(GeW9O34)2]27H2O (1) and Na10H8[Mn6Ge3W24O94(H2O)2]37H2O (2), based on trivacant Keggin POM [GeW9O34]10 building blocks. In compound 1, the Weakley-type species is capped by two [Cu(C3N2H4)2]2+ units through four bridging oxygen atoms on two opposite W4O4 faces. To the best of our knowledge, this is the first case of the copper(II)–imidazole fragment coordinated with four bridging oxygen atoms from sandwich-type polyoxotungstogermanates. Compound 2 is a bananashaped POM consisting of two tri-Mn substituted [MnII2MnIIIGeW9O34]3 Keggin units and a hexavacant bridging cluster [GeW6O26]12. Such POM containing two types of lacunary polyoxotungstogermanates units was only reported by Yang et al. [19]. The magnetic property measurements were also made to well characterize these two new complexes. The magnetic investigations demonstrate the presence of both antiferromagnetic and ferromagnetic exchange interactions for 1 and weak antiferromagnetic interactions for 2. Compound 1 and 2 were synthesized by the reaction of Na2WO4, GeO2, CuCl22H2O or Mn(CH3COO)24H2O in the presence of imidazole by a conventional solution method [20]. Notably, the pH is very important for the formation of 1 and 2. Although imidazole does not appear in the crystal structure of compound 2, the addition of imidazole can well facilitate the reaction of Mn ion with the polyanions so as to obtain the crystal product with good quality. From our observation of controlled experiments, without the imidazole into the reaction solution, the product is floccular solid instead of crystal.
N. Jiang et al. / Inorganic Chemistry Communications 13 (2010) 372–375
The polyanion of 1 consists of two capping [Cu(C3N2H4)2]2+ subunits and two lacunary B-a-[GeW9O34] Keggin moieties linked via a rhomb like Cu4O16 group (Fig. 1a) [21], which is similar to that of {Mn(phen)}2Mn4(H2O)2(GeW9O34)2]8 reported by Niu et al. [13]. Two [Cu(C3N2H4)2]2+ fragments are capped on the ‘‘shoulder” positions through four bridging oxygen atoms on two opposite W4O4
373
faces. Cu3 coordinated by two nitrogen atoms from two imidazole ligands connect with four bridging oxygen atoms from the B-aGeW9 unit, exhibiting distorted octahedral geometry in the form {CuN2O4} (Fig. 1c). The central core [Cu4(l4-O)2(l3-O)4(l2O)8(H2O)2] in the anion for 1 where the aqua molecule is bound terminally at the Cu2 to yield a Cu4 rhomb consisting of four
Fig. 1. (a) Crystal structure of the [{Cu(C3N2H4)2}2Cu4(H2O)2(GeW9O34)2]8 polyanion in 1. Plum octahedra, {WO6}; sky blue tetrahedra, {GeO4}. (b) Structure of Cu4 tetragon. (c) Coordination environment of Cu in capping [Cu(C3N2H4)2]2+ subunits. # = 1x, 1y, 2z.
Fig. 2. (a) Crystal structure of the [Mn6Ge3W24O94(H2O)2]18 polyanion in 2. Plum octahedra, {WO6}; sky blue tetrahedra, {GeO4}; yellow ball, MnII; orange ball, MnIII. (b) Structure of Mn6 unit.
374
N. Jiang et al. / Inorganic Chemistry Communications 13 (2010) 372–375
distorted CuO6 octahedra (Fig. 1a and b). The Cu ions site at the neighboring corner of the rhomb with Cu Cu average distance of 3.182(2) Å. Two Cu ions site at the short diagonal with Cu1 Cu1# distance of 3.055(3) Å and the other two Cu ions site at the long diagonal with Cu2 Cu2# distance of 5.587(2) Å. The polyanion of 2 is formed by the condensation of two tri-Mn substituted B-a-½MnII2 MnIII GeW9 O34 3 Keggin units and a hexavacant bridging cluster [GeW6O26] (Fig. 2a) [22]. The Keggin subunit is composed of the trivacant [GeW9O34]10 germanotungstate ligand and three edge-sharing MnO6 octahedra. Bond valence sum (BVS) calculations [23] indicate that four manganese centers exhibit a 2+ oxidation state and two manganese centers exhibit a 3+ oxidation state (Table S1 in Supporting information). Two trinuclear manganese clusters are crystallographically independent (Fig. 2b). This complex can be compared to the reported bananashaped POMs [15–19]. The magnetic susceptibilities of 1 and 2 have been measured on a crystalline sample under a field of 1000 Oe in the temperature range of 2–300 K. Fig. 3 shows the temperature dependence of
vm and vmT of 1. The value of vmT for 1 decreases from 2.75 cm3 mol1 K at 300 K to a minimum of 2.01 cm3 mol1 K at 36 K and then increases to 2.44 cm3 mol1 K at 2 K. The vmT values at 300 K (2.75 cm3 mol1 K corresponding to 4.69 lB) are close to the sum of contributions for six Cu2+ ions (4.75 lB, g = 2.24). The vmT values at 36 K (2.01 cm3 mol1 K corresponding to 4 lB) are close to values expected for four separated Cu2+ ions (3.88 lB, g = 2.24). Such behavior is characteristic of the presence of both antiferromagnetic and ferromagnetic exchange interactions, which might be attributed to the existence of spin frustration at low temperature. The 1/vm versus T plot for 1 could be fit with Curie–Weiss equation from 100 to 300 K, getting C = 3.15 cm3 mol1 K and h = 44.2 K. The negative Weiss constant indicates the existence of antiferromagnetic interaction between the nearest magnetic centers (Fig. S7, see Supporting information). 0 The central core Cu8þ 4 requires three exchange parameters (J, J , and J00 ), which represent the isotropic interactions along the sides, short diagonal, and long diagonal of the rhomb. The magnetic
Fig. 3. Plots of vm and vmT vs. T for 1. The numbering scheme for the spin Hamiltonian for three exchange interactions (J–J0 0 ) and the analyzing results are shown in the inset.
Fig. 4. Plots of vm and vmT vs. T for 2. The numbering scheme for the spin Hamiltonian for two exchange interaction (J and J0 ) and the analyzing results are shown in the inset.
N. Jiang et al. / Inorganic Chemistry Communications 13 (2010) 372–375
susceptibility data of 1 were analyzed using Eq. (3) (see Supporting information). A satisfying description of the experimental data over the whole temperature range (Fig. 3) is obtained with the following set of parameters: J = 0.49 cm1, J0 = 37.4 cm1, J00 = 0.68 cm1 and g = 2.24. Fig. 4 shows the temperature dependence of vm and vmT of 2. The value of vmT for 2 decreases from 25.6 cm3 mol1 K at 300 K to 6.29 cm3 mol1 K at 2 K. The vmT values at 300 K (25.6 cm3 mol1 K corresponding to 14.3 lB) are close to the sum of spin-only (g = 2) contributions for four Mn2+ ions and two Mn3+ ions (13.7 lB). Such behavior demonstrates the presence of antiferromagnetic exchange interactions in trinuclear Mn clusters. The 1/vm versus T plot for 2 could be fit with Curie–Weiss equation from 7 to 300 K, getting C = 26.6 cm3 mol1 K and h = 17.1 K. The negative Weiss constant suggests that overall antiferromagnetic interactions exist in 2 (Fig. S8, see Supporting information). The central core MnII2 MnIII requires two exchange parameter J and J0 (Fig. 4). The magnetic susceptibility data of MnII2 MnIII were analyzed using Eq. (7) (see Supporting information). A satisfying description of the experimental data over the whole temperature range is obtained with the following set of parameters: J = 0.071 cm1, J0 = 1.03 cm1 and g = 1.99. In summary, two new sandwich-type polyoxometalates Na3H(C3H5N2)4{[Cu(C3N2H4)2]2[Cu4(H2O)2(GeW9O34)2]}27H2O and Na10H8[Mn6Ge3W24O94(H2O)2]37H2O have been obtained. The successful synthesis of 1 demonstrates the possibility of copper(II)– imidazole fragment coordinated with four bridging oxygen atoms from sandwich-type polyoxotungstogermanates with conventional solution method. Compound 2 proves that two types of lacunary polyoxotungstogermanates can be also stabilized under conventional solution conditions. Based on the ligand of lacunary POM, the assembly of different transition metal ions may generate more novel solid state compounds with potential magnetic properties. Such work is ongoing in our laboratory. Acknowledgments This work was financially supported by the Natural Science Foundation of China (Grant Nos. 20671017 and 20731002) and the Program for Changjiang Scholars and Innovative Research Team in University, and the Science Foundation for Young Teachers of Northeast Normal University (No. 20090403). Appendix A. Supplementary material CCDC 749940 and 421070 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2009.12.025. References [1] (a) C. Hill (Ed.), Chem. Rev., Polyoxometalates (1998); (b) M.T. Pope, A. Müller (Eds.), Polyoxometalate Chemistry: from Topology via Self-assembly to Applications, Kluwer Academic Publishers, Dordrecht, The Netherlands, 2001.
375
[2] T.J.R. Weakley, H.T. Evans, J.S. Showell, G.F. Tourné, C.M. Tourné, J. Chem. Soc. Chem. Commun. (1973) 139. [3] H.T. Evans, G.F. Tourné, C.M. Tourné, T.J.R. Weakley, J. Chem. Soc., Dalton Trans. (1986) 2699. [4] C.J. Gómez-García, E. Coronado, J. Borrás-Almenar, Inorg. Chem. 31 (1992) 1667. [5] J.M. Clemente-Juan, H. Andres, J.J. Borrás-Alamenar, E. Coronado, H.U. Güdel, M. Aebersold, G. Kearly, H. Büttner, M. Zollinker, J. Am. Chem. Soc. 121 (1999) 10021. [6] H. Andres, J.M. Clemente-Juan, M. Aebersold, H.U. Güdel, E. Coronado, H. Büttner, G. Kearly, J. Melero, R. Burriel, J. Am. Chem. Soc. 121 (1999) 10028. [7] J.M. Clemente-Juan, E. Coronado, J.R. Galán-Mascarós, C.J. Gómez-García, Inorg. Chem. 38 (1999) 55. [8] U. Kortz, S. Isber, M.H. Dickman, D. Ravot, Inorg. Chem. 39 (2000) 2915. [9] L.H. Bi, R.D. Huang, J. Peng, E.B. Wang, Y.H. Wang, C.W. Hu, J. Chem. Soc., Dalton Trans. (2001) 121. [10] U. Kortz, S. Nellutla, A.C. Stowe, N.S. Dalal, J. van Tol, B.S. Bassil, Inorg. Chem. 43 (2004) 144. [11] U. Kortz, S. Nellutla, A.C. Stowe, N.S. Dalal, U. Rauwald, W. Danquah, D. Ravot, Inorg. Chem. 43 (2004) 2308. [12] T. Yamase, H. Abe, E. Ishikawa, H. Nojiri, Y. Ohshima, Inorg. Chem. 48 (2009) 138. [13] J.P. Wang, P.T. Ma, Y. Shen, J.Y. Niu, Crystal. Growth & Design 8 (2008) 3130. [14] G.W. Wang, Y. Chen, Y.C. Zou, Y. Wang, H.T. Wang, K.C. Li, X.B. Cui, S.Y. Shi, J.Q. Xu, Inorg. Chem. Commun. 12 (2009) 646. [15] I.M. Mbomekalle, B. Keita, M. Nierlich, U. Kortz, P. Berthet, L. Nadjo, Inorg. Chem. 42 (2003) 5143. [16] J.J. Borras-Almenar, J.M. Clemente-Juan, M. Clemente-Leon, E. Coronado, J.R. Galan- Mascaros, C.J. Gomez-Garcia, in: M.T. Pope, A. Müller (Eds.), Polyoxometalate Chemistry: From Topology Via Self-Assembly to Applications, Kluwer, Dordrecht, The Netherlands, 2001, p. 231. [17] M.D. Ritorto, T.M. Anderson, W.A. Neiwert, C.L. Hill, Inorg. Chem. 43 (2004) 44. [18] J.D. Compain, P. Mialane, A. Dolbecq, I.M. Mbomekallé, J. Marrot, F. Sécheresse, E. Rivière, G. Rogez, W. Wernsdorfer, Angew. Chem., Int. Ed. 48 (2009) 3077. [19] B. Li, J.W. Zhao, S.T. Zheng, G.Y. Yang, Inorg. Chem. Commun. 12 (2009) 69. [20] All starting materials and chemicals were used without further purification: Synthesis of 1: Na2WO4 (1.32 g), GeO2 (0.0464 g), 0.5 ml 6 M HCl were dissolved in 20 ml H2O and stirred for 1 h to get solution A. CuCl22H2O (0.68 g), imidazole (1.1 g) were dissolved in 10 ml H2O and stirred for 1 h to get solution B, which was added into solution A in small portions with magnetic stirring. The pH of the mixture was adjusted to 4.3 by addition of 6 M HCl and stirred at 90 °C for 2 h. A blue–green precipitate was removed by filtration, and green crystals (0.23 g) suitable for X-ray analysis were obtained after the filtrate was kept for one week at room temperature. The yield was 15% based on W. IR: 3444 (s), 3141 (w), 2831 (w), 1620 (s), 1580 (s), 1541 (s), 1509 (s), 1421 (s), 1328 (m), 1262 (m), 1174 (m), 1072 (s), 947 (s), 888 (s), 772 (s), 695 (s), 500 (w), 457 (m). Elemental analyses calcd. (%): W 54.56, Cu 6.29, Ge 2.40, Na 1.14, C 4.75, O 25.59, N 3.70, H 1.57. Found: W 54.37, Cu 6.48, Ge 2.45, Na 1.11, C 4.72, O 25.53, N 3.73, H 1.61.Synthesis of 2: Na2WO4 (1.65 g), GeO2 (0.0523 g), 1 ml 6 M HCl were dissolved in 20 ml H2O and stirred until the solution became homogeneous. Mn(CH3COO)24H2O (0.123 g) dissolved in 5 ml H2O and imidazole (0.035 g) dissolved in 5 ml H2O were added with stirring (pH 7.3–7.6). The solution was heated at 90 °C for 1 h and then filtered. Brown crystals (0.208 g) suitable for X-ray analysis were obtained after the filtrate was kept for two days at room temperature. The yield was 12% based on W. IR: 941 (s), 875 (s), 770 (s), 697 (s), 509 (w), 458 (m). Elemental analyses calcd. (%): W 59.59, Mn 4.45, Ge 2.94, Na 3.11, O 28.74, H 1.17. Found: W 59.33, Mn 4.57, Ge 2.85, Na 3.19, O 28.81, H 1.25. [21] Crystal data and structure refinements for 1: Mr = 6064.85 g mol1, green blocks, triclinic, space group, P1 , a = 12.618 Å, b = 13.349 Å, c = 18.985 Å, a = 94.24°, b = 103.63°, c = 116.53°, V = 2720.8 Å3, Z = 1, R1 = 0.0463, wR2 = 0.1189. Crystal data were measured on a Bruker Apex CCD diffractometer using MoKa radiation (k = 0.71073 Å) at 293(2) K. [22] Crystal data and structure refinements for 2: Mr = 7404.40 g mol1, brown blocks, monoclinic, space group, P2/c, a = 17.8335(14) Å, b = 22.3430(18) Å, c = 35.817(3) Å, a = 90.00°, b = 93.5550(10)°, c = 90.00°, V = 14244(2) Å3, Z = 2, R1 = 0.0562, wR2 = 0.1485. Crystal data were measured on a Bruker Apex CCD diffractometer using MoKa radiation (k = 0.71073 Å) at 296(2) K. Further details of the structure determination are available on request from the ICSD Team, FIZ Karlsruhe, Hermann–von-Helmholtz–Platz 1, D-76344 Eggenstein– Leopoldshafen. [23] I.D. Brown, D. Altermatt, Acta Crystallogr. B41 (1985) 244.