A tricobalt(II) coordination polymer incorporating in situ generated 5-methyltetrazolate ligands

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Inorganic Chemistry Communications 11 (2008) 572–575 www.elsevier.com/locate/inoche

A tricobalt(II) coordination polymer incorporating in situ generated 5-methyltetrazolate ligands Yang Chen a, You Song b, Yong Zhang a, Jian-Ping Lang a,b,* b

a School of Chemistry and Chemical Engineering, Suzhou University, Suzhou 215123, Jiangsu, People’s Republic of China State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, Jiangsu, People’s Republic of China

Received 5 February 2008; accepted 16 February 2008 Available online 21 February 2008

Abstract A tricobalt(II) coordination polymer {Na0.5[Co3(l4-Mtta)1.5(l2-OAc)3(l3-OAc)(l3-OH)]}n (1) (Mtta = 5-methyl tetrazolate) was prepared from the solvothermal reaction of Co(OAc)2  4H2O with NaN3 in MeCN in the presence of water. Complex 1 was characterized by elemental analysis, IR, and X-ray crystallography. 1 consists of a unprecedented 3D hydrogen-bound supramolecular structure in which a 2D layer with unusual (326272) topology holds the adjacent layers together in a ABAB sequence via unusual O–H  Na pseduo–agostic interactions. Complex 1 displayed the characteristics of a weak antiferromagnetic exchange interactions between Co2+ ions in the system of Co3(Mtta)3 trigonal unit. Ó 2008 Elsevier B.V. All rights reserved. Keywords: Cobalt; 5-Methyltetrazolate; Solvothermal synthesis; Structure; Magnetic properties

In the past decade, design and syntheses of new coordination polymers containing paramagnetic metal ions linked by organic components have received much attention because of their fascinating molecular topologies and outstanding properties for potential applications in magnetic materials [1,2]. These compounds are mainly prepared from routine solution reactions or hydro(solvo)thermal reactions of paramagnetic metal salts with readymade organic ligands [1]. However, employment of in situ metal/ligand reactions has been less explored [3]. Among the in situ reactions, so-called Demko-Sharpless [2 + 3] cycloaddition reaction is the typical one [4]. For example, some tetrazolate ligands could be prepared in situ through [2 + 3] cycloaddition reactions of organicnitriles with azide anion in the presence of metal ions such as Zn2+, Cd2+, Ag+, and Cu+ [5]. However, other transition metal ions such as Co2+ have not been explored yet. Is it possible * Corresponding author. Address: School of Chemistry and Chemical Engineering, Suzhou University, Suzhou 215123, Jiangsu, People’s Republic of China. Tel.: +86 512 65882865; fax: +86 512 65880089. E-mail address: [email protected] (J.-P. Lang).

1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.02.015

for cobalt(II) ions to catalysis such [2 + 3] reactions? If it works, what about their structures and magnetic properties? With these ideas in mind, we chose Co(OAc)2  4H2O and carried out its solvothermal reactions with NaN3 and MeCN in the presence of water and an interesting cobalt(II) coordination polymer {Na0.5[Co3(l4-Mtta)1.5(l2OAc)3(l3-OAc)(l3-OH)]}n (1) (Mtta = 5-methyl tetrazolate) was isolated therefrom. Herein we report its synthesis, structural characterization and magnetic properties. The solvothermal reaction of Co(OAc)2  4H2O with equimolar NaN3 and excess MeCN in the presence of water at 150 °C for 70 h followed by cooling to ambient temperature afforded purple–red hexagonal plates of 1 in 51% yield [6]. The elemental analysis of 1 is consistent with its chemical formula. In the IR spectrum of 1, the absence of the C„N stretching vibration at ca. 2200 cm1 and the appearance of a new stretching vibration of tetrazolate anion at ca. 1400 cm1 are line with the in situ formation of tetrazolate ligand generated by a [2 + 3] cycloaddition reaction of MeCN and N 3 [5a]. In addition, the strong bands at 1568 and 1386 cm1 for 1 are assigned to the C@O asymmetric and symmetric stretching bands of bridging

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acetates. Compound 1 also shows a broad hydroxyl stretching band at 3441 cm1. It is noted that the reaction time, temperature and solvent remarkably affected the yield of 1. Short reaction time (e.g. 1000 min) formed tiny crystals of 1 in a low yield (24%) while long reaction time (e.g. 7000 min) produced cracked crystals of 1 in 45% yield. The yield of 1 became as poor as <1% when the temperature was either elevated above 180 °C or lowered below 120 °C. Without water, the yield of 1 was also low (<1%), which may be due to the low solubility of Co(OAc)2  4H2O and NaN3 in MeCN. Solid 1 is stable towards air and moisture and virtually insoluble in common organic solvents such as DMF and MeCN. The thermogravimetric analysis (TGA) revealed that 1 was stable up to 300 °C. The TGA curve of 1 showed a sharp weight loss of 57.23% in the range of 313–400 °C, which corresponds roughly to the loss of the Mtta ligands, acetate and hydroxyl groups (calculated 57.55%). The decomposition residual species was assumed to be a mixture of 6CoO + 0.5Na2O (42.77% versus calculated 42.45%) according to X-ray fluorescence analysis (see Supplementary Material). 1 crystallizes in the trigonal space group R-3c and the asymmetric unit contains one third of the anion [Co3(l4-Mtta)1.5(l-OAc)3(l3-OAc)(l3-OH)]1/2 and one sixth of Na+ ion [7]. The anion consists of a trigonal [Co3(l3OH)(l3-OAc)] unit that is bridged by l4-Mtta and l-OAc

Fig. 1. Perspective view of Na0.5[Co3(l4-Mtta)1.5(l3-OH)(l3-OAc)(l-OAc)3] of 1, where only one set of the disordered l3-OH and l-OAc is shown. All hydrogen atoms along with methyl groups of the l-OAc ligands are omitted for clarity. Symmetry transformations used to generate equivalent atoms: A, 2  y, 1 + x  y, z; B: 1  x + y, 2  x, z; C: 2/3 + x  y, 4/3  y, 11/6  z; D: 1/3 + y, 1/3 + x, 11/6  z. Co, C, N, O and Na atoms are represented by pink, black, blue, red and green spheres, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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ligands (Fig. 1). There is a C3 axis running through the O1 and C5 and C6 atoms. The local coordination geometry around each Co center can be best described as a distorted octahedron with two N atoms from two l4-Mtta ligands and four O atoms of one l3-OH, one l3-OAc ion, and two l-OAc ions. In each [Co3(l3-OH)(l3-OAc)] unit, one acetate carrying C5 and C6 atoms is disordered over the C3 axis, which makes it an unusual triply-bridging ligand capping over the [Co3(l3-OH)] core with the Co–O (l3˚ . At the center of the [Co3(l3OAc) distance of 2.134(8) A OH)] core is sitting one disordered OH group that works as a triply-bridging ligand to link three Co2+ ions. Such a core was found in [Co3(DBM)3(pz)4(OH)]  2THF (DBM = dibenzoylmethanate; pz = pyrazole) [8]. The ˚ ) is longer than mean Co1–O1(OH) distance (2.113(2) A that of the corresponding ones in [Co3(DBM)3(p˚ ). Each Co  Co contact in z)4(OH)]  2THF (2.033(2) A ˚ the core of 1 is 3.51 A, which is too long to include any metal–metal interaction [9]. Each l-OAc is also disordered over two sites. Pairs of such l-OAc ligands link the Co2+ ions of the neighboring core to form a 2D clover-like network extending along the ab plane (Fig. 2a). The average ˚ ) is shorter than Co–O bond distance for l-OAc (1.960(7) A ˚ ) [10]. the literature values (range from 2.10 to 2.25 A Each Mtta in 1 works as a l4-g1:g1:g1:g1-bridging ligand [5e]. Around each [Co3(l3-OH)(l3-OAc)] unit are three l4Mtta ligands, each of which bridges two Co2+ ions with its two N atoms, thereby forming a [Co3(l4-Mtta)1.5(l3OH)(l3-OAc)] fragment. The mean Co–N bond distance ˚ ) is comparable with that observed in (2.108(3) A {[Co3(IDC)2 (4,40 - bipy)(H2O)4]  2H2O}n (IDC = imidazole 4,5-dicarboxylic acid, Co–NIDC = 2.069(3))[11]. With another two N atoms, each Mtta links a pair of Co2+ ions of the adjacent fragment to form a 2D Mtta–AcO composite layer extending along the ab plane (Fig. 2a). If Co2+ and Mtta are treated as a two-connected node and a four-connected node, respectively, this 2D net adopts an unprecedented (326272) Schla¨fli symbol topology network (Fig. 2b). The distance between two adjacent layers is ˚ . Such a layer further connects with its neighboring 7.069 A ones by the Na  H–O pseduo–agostic interactions ˚ , H–O 0.959 A ˚ , Na  H–O 180°) [12] to (Na  H 2.069 A give a 3D hydrogen-bound supramolecular structure (Fig. 3). The magnetic measurements were performed by using a SQUID magnetometer. Magnetic properties of the crystalline sample1 was measured at an applied field of 2 kOe from 300 to 1.8 K as shown in Fig. 4 in the forms of vMT versus T. At room temperature, vMT is equal to 8.68 emu K mol1, which is much higher than the spin-only value of 5.625 emu K mol1 based on three Co2+ ion (g = 2 and s = 3/2) due to the prominent orbital contribution. Upon lowering the temperature, vMT continuously decreases and reaches 0.62 emu K mol1 at 1.8 K. Above 100 K, the magnetic properties of 1 obey Curie–Weiss law and gives C = 9.57(3) and h = 28.5(6) K. The smaller Weiss

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Fig. 2. (a) View of the 2D anionic network of 1 along the ab plane. Hydrogen atoms and one set of disordered OAc and OH groups are omitted for clarity. (b) 2D layered network with a Schla¨fli symbol (326272). The Mtta ligands are represented by the blue balls. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

coupling in 1. According to the preceding structure description of 1, no appropriate model could be used for fitting the magnetic properties of such a system. So, the treatment method reported by Rueff et al. [14] and the simple phenomenological Eq. (1) [15] can be used here vM T ¼ A expðE1 =kT Þ þ B expðE2 =kT Þ

Fig. 3. Packing diagrams of 1 looking along the a axis. H atoms and AcO groups are omitted for clarity.

Fig. 4. Temperature dependence of magnetic susceptibilities of 1 in the forms of 1/vM and vMT versus T. The solid lines are the fitting results.

constant than 20 K for non-interacting Co2+ ions [13] indicates the additional antiferromagentic coupling between Co2+ ions except the contribution of spin-orbital

ð1Þ

where A + B equals the Curie constant and E1 and E2 represent the ‘‘activation energies” corresponding to the spinorbit coupling and to the magnetic exchange interaction, respectively. The best fitting results give: E1/k = 41(1) K and E2/k = 2.4(1) K with C = 9.55 cm3 K mol1. Thus, the magnetic coupling constants between Co2+ ions are 4.8 K for 1 according to the relationship of vMT / exp(+J/2kT) [2b,16]. This indicates that the weak antiferromagnetic exchange interaction between Co2+ ions with spin-orbital coupling of Co2+ ions dominate the magnetic properties in 1. In summary, the present work demonstrated that a new cobalt(II) coordination polymer 1 was prepared from solvothermal reactions of Co(OAc)2  4H2O with NaN3 in MeCN in the presence of water. The formation of 1 is involved in a [2 + 3] cycloaddition of the azide and acetonitrile. Complex 1 displayed an unprecedented 3D hydrogen-bound structure in which 2D layers with (326272) topology are linked by unusual O–H  Na pseduo–agostic interactions. Investigations of this system are continuing in an effort to examine if other main group metal ions such as Li+, Cs+, Ca2+ could be introduced and, if so, to explore their effects on the topological structures and the magnetic properties of the resulting products. Acknowledgements This work was supported by the NNSF (No. 20525101), the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20050285004), and the State

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Key Laboratory of Coordination Chemistry of Nanjing University, and the Qin-Lan Project of Jiangsu Province in China. The authors also thank the helpful suggestions of Prof. B.F. Abrahams in University of Melbourne and Prof. G.L. Ma in Suzhou University. Appendix A. Supplementary material

[7]

CCDC 674064 contains the supplementary crystallographic data for 1. 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 associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2008.02.015. References [1] (a) X.Y. Wang, L. Wang, Z.M. Wang, S. Gao, J. Am. Chem. Soc. 128 (2006) 674; (b) A. Rodrı´guez, R. Kiveka¨s, E. Colacio, Chem. Commun. (2005) 5228; (c) S.M. Humphrey, P.T. Wood, J. Am. Chem. Soc. 126 (2004) 13236; (d) K.I. Pokhodnya, M. Bonner, J.H. Her, P.W. Stephens, J.S. Miller, J. Am. Chem. Soc. 128 (2006) 15592; (e) N. Yanai, W. Kaneko, K. Yoneda, M. Ohba, S. Kitagawa, J. Am. Chem. Soc. 129 (2007) 3496; (f) M.H. Zeng, B. Wang, X.Y. Wang, W.X. Zhang, X.M. Chen, S. Gao, Inorg. Chem. 45 (2006) 7069; (g) M.P. Shores, E.A. Nytko, B.M. Bartlett, D.G. Nocera, J. Am. Chem. Soc. 127 (2005) 13462; (h) R.H. Wang, E.Q. Gao, M.C. Hong, S. Gao, J.H. Luo, Z.Z. Lin, L. Han, R. Cao, Inorg. Chem. 42 (2003) 5486; (i) H.R. Wen, C.F. Wang, Y.Z. Li, J.L. Zuo, Y. Song, X.Z. You, Inorg. Chem. 45 (2006) 7032. [2] (a) J.S. Miller, M. Drilon (Eds.), Magnetism: Molecules to Materials, vol. 3, Wiley-VCH, Weinheim, 2002; (b) O. Kahn, Molecular Magnetism, VCH, Weinheim, 1993. [3] (a) E.C. Constable, Metals and Ligand Reactivity, VCH, Weinheim, 1996, pp. 245–262; (b) J. Burgess, C.D. Hubbard, Adv. Inorg. Chem. 54 (2003) 71. [4] (a) Z.P. Demko, K.B. Sharpless, J. Org. Chem. 66 (2001) 7945; (b) Z.P. Demko, K.B. Sharpless, Org. Lett. 4 (2002) 2525; (c) F. Himo, Z.P. Demko, L. Noodleman, K.B. Sharpless, J. Am. Chem. Soc. 125 (2003) 9983. [5] (a) X.S. Wang, Y.Z. Tang, X.F. Huang, Z.R. Qu, C.M. Che, P.W. Hong Chan, R.G. Xiong, Inorg. Chem. 44 (2005) 5278; (b) Q. Ye, Y.M. Song, G.X. Wang, K. Chen, D.W. Fu, P.W. Hong Chan, J.S. Zhu, S.D. Huang, R.G. Xiong, J. Am. Chem. Soc. 128 (2006) 6554; (c) Q. Ye, Y.H. Li, Y.M. Song, X.F. Huang, R.G. Xiong, Z.L. Xue, Inorg. Chem. 44 (2005) 3618; (d) X.M. Zhang, Y.F. Zhao, H.S. Wu, S.R. Batten, S.W. Ng, Dalton Trans. (2006) 3170; (e) T. Wu, B.H. Yi, D. Li, Inorg. Chem. 44 (2005) 4130. [6] To a solution containing Co(OAc)2  4H2O (249 mg, 1 mmol) in H2O (2 mL) was added a solution containing NaN3 (65 mg, 1 mmol) in H2O (1 mL) and 5 mL of acentonitrile. The resulting indigo solution was stirred for 5 min, and transferred into a 15-mL Teflon-lined reactor and sealed. The reactor was heated in an oven to 150 °C for 70 h and then cooled to ambient temperature at a rate of 5 °C h1 to

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form purple–red hexagon plates of 1, which were washed with water and dried it in air. Yield: 0.096 g (50.82% based on Co). Anal. Calcd. for C22H35Co6N12NaO18: C, 23.34; H, 3.12; N, 14.85. Found: C, 22.89; H, 3.17; N, 14.69. IR (KBr disc, cm1): 3441 (m), 3006 (w), 2935 (w), 1568 (s), 1522 (m), 1450 (s), 1386 (m), 1344 (m), 1291 (w), 1198 (w), 1129 (w), 1084 (w), 1050 (w), 1023 (w), 719 (w), 676 (w), 656 (w), 620 (w), 530 (w). Crystal data for 1: C22H35N12O18Co6Na, Mr = 1132.19, purple–red crystal (0.45  0.45  0.05 mm), trigonal, space group R3c, ˚ , c = 42.751(9) A ˚ , c = 120.00°, V = 5293.3(15) a = b = 11.9571(17) A ˚ 3, Z = 6, Dc = 2.132 g/cm3, F(0 0 0) = 3408.8 and l = 2.865 mm1. A T = 173(2) K; 15823 reflections collected, 1082 unique (Rint = 0.0395). R1 = 0.0446, wR2 = 0.1111 and S = 1.120 based on 1075 observed reflections with I > 2r(I). Data collections of 1 were performed on a Rigaku Mercury CCD X-ray diffractometer (3 kW, ˚ ). sealed tube), using graphite monochromatic Mo Ka (k = 0.71073 A Diffraction data were collected at x mode with a detector distance of 35 mm to the crystal. Indexing was performed from 6 images, each of which was exposed for 5 s. A total of 720 oscillation images for each were collected in the range 6.18° < 2h < 50.70° for 1. The collected data were reduced by using the program CrystalClear (Rigaku and MSC, Ver. 1.3, 2001), and an absorption correction (multi-scan) was applied, which resulted in transmission factors raging from 0.359 to 0.870 for 1. The reflection data were also corrected for Lorentz and polarization effects. The crystal structures of 1 was solved by direct methods, using SHELXS-97 program and refined on F2 by full-matrix least-squares using SHELXL-97 program. All non-hydrogen atoms were refined anisotropically, and all other hydrogen atoms except H1 on OH ion were placed in geometrically idealized positions (C– ˚ for methyl groups) and constrained to ride on their parent H = 0.98 A atoms with Uiso(H) = 1.5Ueq(C). The O atom of OH ion is disordered over two sites O1/O10 with an occupancy ratio of 0.66/ 0.34. The Uij-values and the direction of thermal ellipsoids of O1, O10 ˚ . The O were restrained to be equal and the O1–H1 was fixed at 0.96 A atoms of l2-CH3COO group are disordered over two sites O2/O20 and O3/O30 with the occupancy ratios of 0.57/0.43. The Na  O20 ˚ , which indicated that there is weak interaction distance is 2.524(11) A + between Na and l2-CH3COO. For l3-CH3COO group, the O atoms are disordered over three sites O4/O4A/O4B with the occupancy ratios of 0.33  2/0.33  2/0.33  2, respectively, and the C5– ˚. C6 bond was fixed at 1.41 A M. Lukasiewicz, Z. Ciunik, J. Mazurek, J. Sobczak, A. Staron´, S. Wolowiec, J.J. Zio´lkowski, Eur. J. Inorg. Chem. (2001) 1575. K. Uehara, S. Hikichi, A. Inagaki, M. Akita, Chem. Eur. J. 11 (2005) 2788. (a) W.D.H. Junior, J.N. Ishley, R.R. Whittle, Inorg. Chem. 21 (1982) 3270; (b) J. Costamagna, F. Caruso, M. Rossi, M. Campos, J. Canales, J. Ramirez, J. Coord. Chem. 54 (2001) 247. Y.L. Wang, D.Q. Yuan, W.H. Bi, X. Li, X.J. Li, F. Li, R. Cao, Cryst. Growth Des. 5 (2005) 1849. D. Braga, F. Grepioni, E. Tedesco, Organometallics 16 (1997) 1846. (a) F.E. Mabbs, D.J. Machin, Magnetism and Transition Metal Complexes, Chapman and Hall, London, 1973; (b) M.E. Lines, J. Chem. Phys. 55 (1971) 2977. (a) J.M. Rueff, N. Masciocchi, P. Rabu, A. Sironi, A. Skoulios, Chem. Eur. J. 8 (2002) 1813; (b) J.M. Rueff, N. Masciocchi, P. Rabu, A. Sironi, A. Skoulios, Eur. J. Inorg. Chem. (2001) 2843. P. Rabu, J.M. Rueff, Z.L. Huang, S. Angelov, J. Souletie, M. Drillon, Polyhedron 20 (2001) 1677. R.L. Carlin, Magnetochemistry, Springer-Verlag, Berlin Heidelbery, 1986.