Communication pubs.acs.org/IC
Electrochemical Synthesis and Magnetic Properties of [Cu9W6]: The Ultimate Member of the Quindecanuclear Octacyanometallate-Based Transition-Metal Cluster? Zaichao Zhang,†,‡ Yong Liu,‡ Rong-Min Wei,† Zhen-Huan Sheng,‡ Peng Wang,† and You Song*,† †
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China ‡ Jiangsu Key Laboratory for the Chemistry of Low-Dimensional Materials, School of Chemistry and Chemical Engineering, Huaiyin Normal University, Huai’an 223300, China S Supporting Information *
The main reason lies in that the CuII ion is always located in the center of an elongated octahedral environment with strong Jahn−Teller distortion. However, to form a [M′9M6] cluster, the center M′ ion must own a nearly perfect octahedral coordination environment. Thus, the [Cu9M6] cluster is hardly obtained using the routine method of synthesis. In our previous work,2a a large cluster, [Cu13W7], was prepared. All of the coordination environments of CuII ions are Jahn−Teller-distorted, leading to a defected body-centered-cubic [Cu9M5] structure rather than [Cu9M6]. Moreover, most of the center metal ions in [M(CN)8]n− were reduced from +5 to +4 and became diamagnetic.2a Factually, although rare, the CuII ions violating the Jahn−Teller theorem have been found6 when some special chelated ligands, such as ethylenediamine, were applied. Hence, a conclusion can be made that the [Cu9M6] cluster is able to be obtained by kinetic control in the preparation. Up to now, the electrochemical synthesis may be the best method to control the competition between kinetic and thermodynamic products. This method can not only intercept and capture the kinetic product but also control the valences of the center metal ions in [M(CN)8]n−.5g This work still employed Me3tacn (1,4,7trimethyl-1,4,7-triazacyclononane) as the blocking ligand. Me3tacn is a tridentate ligand rather than a bidentate ligand with a solvent molecule in reported [M′9M6] clusters, which can just match the residual coordinate sites of Cu during formation of the [Cu 9 W 6 ] cluster core. This design was aimed at strengthening the stability of the cluster. Furthermore, electrochemical control was introduced, which enabled us to obtain the first octacyanometallate-based [Cu9M6] cluster, [Cu{Cu(Me3tacn)}8{W(CN)8}6]·5CH3OH·31H2O (1). This complex may complete the [M′9M6] family of octacyanometallate-based transition-metal clusters. Herein, we report the synthesis, structure, and magnetic properties of complex 1. Complex 1 was synthesized according to the previously reported method in our work.2a By contrast, a constant potential (0.20 V) was applied to preventing [WV(CN)8]3− reduction (see the synthesis in the Supporting Information, SI). The crystals of 1 are unstable in solution. When the potential was interrupted, the crystals would gradually change into blue spongelike precipitate within 24 h. In a lot of synthesis using
ABSTRACT: [Cu9W6], synthesized by the electrochemical method, may be the ultimate member of the quindecanuclear octacyanometallate-based transitionmetal cluster. Its single-crystal structure and magnetic properties were characterized.
A
s spin carriers and good candidates for mediating magnetic exchange interaction, octacyanometallates [M(CN)8]n− (M = Mo, W, and Nb) have been intensively studied in the past few decades.1−5 Different from hexacyanometallates [M(CN)6]n−, exhibiting a regular octahedron, [M(CN)8]n− usually shows three known spatial configurations, which results in the formation of complexes with versatile structures when they coordinate to transition-metal ions. Additionally, the centers of [M(CN)8]n− are second- or third-row transition-metal ions. The heavy-atom effect can strengthen the coordinate bonds of M− CN and weaken the coordination ability of the N atoms as well. Meanwhile, the NC−M−CN bonding angle (about 144°, smaller than 180°) makes [M(CN)8]n− extend its coordination along a spherical surface, easily forming ball-like complexes even if without a blocking ligand, while [M(CN)6]n− tends to form polymers along the plane, as shown in Scheme 1. Therefore, in all Scheme 1. Extending the Direction of [M(CN)6]n− and [M(CN)8]n− as Building Blocks Coordinating to Other Metal Ions along the Plane and Sphere
octacyanometallate-based complexes, the widely reported ones are zero-dimensional,1,2 among which the most fascinating systems are the [M′9M6] clusters (M′ is first-row transition-metal ions) with a body-centered six-capped cube.1 To date, almost all of the [M′9M6] clusters with bivalent M′, including MnII, FeII, CoII, and NiII, have been obtained except CuII (CrII and VII are too vivacious to be controlled in reaction). © XXXX American Chemical Society
Received: August 12, 2015
A
DOI: 10.1021/acs.inorgchem.5b01852 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry octacyanometallate and different blocking ligands, [M′9M6] was always obtained, which suggests that [M′9M6] is stabilized by thermodynamic process. However, for CuII ion, the typical cluster [M′9M6] has not be achieved by far. It is believed that [Cu9M6] is not the thermodynamic product due to the Jahn− Teller distortion of CuII. In the electrochemical synthesis, [Cu9M6] formed as a preferential product and then would change into spongelike precipitation over time, indicating that this reaction can instantly produce the [Cu9M6] cluster and be controlled by a kinetic process. X-ray crystallographic analysis (in the SI) shows that complex 1 crystallized in a monoclinic group, P21/n, which contains a neutral cluster molecule [Cu{Cu(Me3tacn)}8{W(CN)8}6] and messy guest molecules (about 5 methanol and 31 water) in the lattice (the bond lengths and angles in Table S1, SI). As shown in Figure 1, the cluster has a construction similar to those of other
Figure 2. Temperature dependence of magnetic susceptibilities. The solid lines are the fitted result using PHI software.
gCu = 2), suggesting the ferromagnetic coupling between the CuII and WV ions with gCu > 2. Along with the cooling process, χMT continuously increases to a maximum of 30.39 cm3 K mol−1 at 8 K and then sharply decreases to 23.17 cm3 K mol−1 at 1.8 K. This behavior indicates that the coupling between CuII and WV ions is ferromagnetic in complex 1. The χMT maximum corresponds to the value 31.875 cm3 K mol−1, with the ferromagnetic coupling ground-state spin S = 15/2. Further evidence is provided by variable-field magnetization (M) data from 0 to 70 kOe at 1.8 K (Figure 3). In the range of 0−10 kOe, magnetization rapidly
Figure 1. Cluster structure [Cu{Cu(Me3tacn)}8{W(CN)8}6] in complex 1 (symmetrical code i: 1 − x, 2 − y, −z).
octacyanometallate-based transition-metal clusters with a sixcapped body-centered-cubic motif,1 in which eight CuII ions occupy the apical positions and a CuII ion lies in the cubic center, with each face of the cube capped by an octacyanometallate. All CuII ions are six-coordinated with a distorted octahedral environment. The octahedral geometries of eight CuII ions (Cu2 to Cu5) at the acmes show very large distortion due to the Jahn−Teller effect. The CuII ion at the body center (Cu1) is restricted by the coordination environment without Jahn−Teller distortion. It is demonstrated that the coordination geometry of Cu1 is the key factor in constructing complex 1, referring to the formation of eicosanuclear cluster [Cu13W7].2a All octacyanometallates take a dodecahedral configuration (Table S2, SI). Summarizing the reported [M′9M6] clusters, we can roughly divide them into three groups based on their different lattice types, P, C, and R, respectively. In these structures, the cubes with the P lattice show slightly less distortion than the others (see the edge lengths of the cubes in Table S3, SI). Accordingly, the structure of complex 1 is closer to that of [Ni9W6] reported by Hong et al., including the bond types and the configurations of octacyanometallates.1d,e The magnetic properties of complex 1 were measured on a Quantum Design MPMS-XL7 SQUID magnetometer. The variable-temperature susceptibilities are illustrated in Figure 2 in the forms of χM and χMT−T. At room temperature, the χMT value is 6.60 cm3 K mol−1, which is higher than 5.63 cm3 K mol−1 of nine spin-only CuII and six spin-only WV ions (SCu = SW = 1/2 and
Figure 3. Magnetization data over the field range 0−70 kOe at 1.8 K for 1. The red and blue lines are the Brillouin function for the system with S = 15/2 and S = 1/2 when g = 2.12.
increases with the applied field. Above 20 kOe, the increase rate slows and magnetization quickly reaches saturation until a maximum value of 15.8 NμB in 70 kOe. The ferromagnetic coupling between the CuII and WV ions make the spins easily magnetized, so the magnetization sharply increases in low fields. Brillouin function fitting shows that magnetization of complex 1 is much higher than the paramagnetic value of 15 of the noninteracting S = 1/2 system with g = 2.12 in the range of 0−70 kOe and slightly lower than that in the system with S = 15/2 and g = 2.12, strongly supporting the result of ferromagnetic coupling between ions and proving that the ground-state spin is 15/2. For estimation of the coupling constant between the CuII and V W ions, calculations were attempted by applying the PHI program7 with Hamiltonian Ĥ = −2J1∑16ŜCu(center)ŜW − ̂ ̂ 2J2∑24 1 SCu(apical)SW· However, the program could not carry out the calculation because of too many parameters. When only one coupling constant, namely, J = J1 = J2, is taken into account with the mean-field correction zj′, the best result gave J = 11.66, zj′ = −0.0039 cm−1, and g = 2.08. Regarding this cluster, we performed an alternating-current (ac) magnetic measurement (Figure S3, SI), but no signal was observed in the variable-temperature ac susceptibility. The plots B
DOI: 10.1021/acs.inorgchem.5b01852 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry
(2) Other clusters: (a) Wang, J.; Zhang, Z.-C.; Wang, H.-S.; Kang, L.C.; Zhou, H.-B.; Song, Y.; You, X.-Z. Inorg. Chem. 2010, 49, 3101−3103. (b) Wang, Z.-X.; Li, X.-L.; Wang, T.-W.; Li, Y.-Z.; Ohkoshi, S.; Hashimoto, K.; Song, Y.; You, X.-Z. Inorg. Chem. 2007, 46, 10990− 10995. (c) Herrera, J. M.; Marvaud, V.; Verdaguer, M.; Marrot, J.; Kalisz, M.; Mathonière, C. Angew. Chem., Int. Ed. 2004, 43, 5468−5471. (d) Pradhan, R.; Desplanches, C.; Guionneau, P.; Sutter, J.-P. Inorg. Chem. 2003, 42, 6607−6609. (e) Chorazy, S.; Podgajny, R.; Nogaś, W.; Buda, S.; Nitek, W.; Mlynarski, J.; Rams, M.; Kozieł, M.; Gałązka, E. J.; Vieru, V.; Chibotaru, L. F.; Sieklucka, B. Inorg. Chem. 2015, 54, 5784− 5794. (3) Selected 1D: (a) Podgajny, R.; Pełka, R.; Desplanches, C.; Ducasse, L.; Nitek, W.; Korzeniak, T.; Stefańczyk, O.; Rams, M.; Sieklucka, B.; Verdaguer, M. Inorg. Chem. 2011, 50, 3213−3222. (b) Yoon, J. H.; Lee, J. W.; Ryu, D. W.; Choi, S. Y.; Yoon, S. W.; Suh, B. J.; Koh, E. K.; Kim, H. C.; Hong, C. S. Inorg. Chem. 2011, 50, 11306−11308. (c) Visinescu, D.; Madalan, A. M.; Andruh, M.; Duhayon, C.; Sutter, J.-P.; Ungur, L.; Van den Heuvel, W.; Chibotaru, L. F. Chem. - Eur. J. 2009, 15, 11808−11814. (d) Prins, F.; Pasca, E.; de Jongh, L. J.; Kooijman, H.; Spek, A. L.; Tanase, S. Angew. Chem., Int. Ed. 2007, 46, 6081−6084. (4) Selected 2D: (a) Lim, J. H.; You, Y. S.; Yoo, H. S.; Yoon, J. H.; Kim, J. I.; Koh, E. K.; Hong, C. S. Inorg. Chem. 2007, 46, 10578−10586. (b) Li, D.; Zheng, L.; Wang, X.; Huang, J.; Gao, S.; Tang, W. Chem. Mater. 2003, 15, 2094−2098. (c) Ohkoshi, S.; Arimoto, Y.; Hozumi, T.; Seino, H.; Mizobe, Y.; Hashimoto, K. Chem. Commun. 2003, 2772−2773. (d) Hozumi, T.; Ohkoshi, S.; Arimoto, Y.; Seino, H.; Mizobe, Y.; Hashimoto, K. J. Phys. Chem. B 2003, 107, 11571−11574. (e) Arimoto, Y.; Ohkoshi, S.; Zhong, Z. J.; Seino, H.; Mizobe, Y.; Hashimoto, K. J. Am. Chem. Soc. 2003, 125, 9240−9241. (f) Podgajny, R.; Korzeniak, T.; Balanda, M.; Wasiutynski, T.; Errington, W.; Kemp, T. J.; Alcock, N. W.; Sieklucka, B. Chem. Commun. 2002, 1138−1139. (5) Selected 3D: (a) Ohkoshi, S.; Imoto, K.; Tsunobuchi, Y.; Takano, S.; Tokoro, H. Nat. Chem. 2011, 3, 564−569. (b) Pinkowicz, D.; Podgajny, R.; Gaweł, B.; Nitek, W.; Łasocha, W.; Oszajca, M.; Czapla, M.; Makarewicz, M.; Bałanda, M.; Sieklucka, B. Angew. Chem., Int. Ed. 2011, 50, 3973−3977. (c) Wang, T.-W.; Wang, J.; Ohkoshi, S.; Song, Y.; You, X.-Z. Inorg. Chem. 2010, 49, 7756−7763. (d) Wang, Y.; Wang, T.W.; Xiao, H.-P.; Li, Y.-Z.; Song, Y.; You, X.-Z. Chem. - Eur. J. 2009, 15, 7648−7655. (e) Ohkoshi, S.; Tsunobuchi, Y.; Takahashi, H.; Hozumi, T.; Shiro, M.; Hashimoto, K. J. Am. Chem. Soc. 2007, 129, 3084−3085. (f) Wang, Z.-X.; Shen, X.-F.; Wang, J.; Zhang, P.; Li, Y.-Z.; Nfor, E. N.; Song, Y.; Ohkoshi, S.; Hashimoto, K.; You, X.-Z. Angew. Chem., Int. Ed. 2006, 45, 3287−3291. (g) Hozumi, T.; Hashimoto, K.; Ohkoshi, S. J. Am. Chem. Soc. 2005, 127, 3864−3869. (h) Song, Y.; Ohkoshi, S.; Arimoto, Y.; Seino, H.; Mizobe, Y.; Hashimoto, K. Inorg. Chem. 2003, 42, 1848−1856. (i) Herrera, J. M.; Bleuzen, A.; Dromzée, Y.; Julve, M.; Lloret, F.; Verdaguer, M. Inorg. Chem. 2003, 42, 7052−7059. (6) (a) Cullen, D. L.; Lingafelter, E. C. Inorg. Chem. 1970, 9, 1858− 1864. (b) Smeets, S.; Parois, P.; Bürgi, H.-B.; Lutz, M. Acta Crystallogr., Sect. B: Struct. Sci. 2011, 67, 53−62. (7) Chilton, N. F.; Anderson, R. P.; Turner, L. D.; Soncini, A.; Murray, K. S. J. Comput. Chem. 2013, 34, 1164−1175. (8) Shores, M. P.; Sokol, J. J.; Long, J. R. J. Am. Chem. Soc. 2002, 124, 2279−2292.
of reduced magnetization M vs H/T of 1 (Figure S4, SI) show the slight separation of isofield lines, making it clear that the cluster molecule of 1 possesses very small magnetic anisotropy in the ground state. The ANISOFIT package8 fits these data to give g = 2.12, D = −0.100, and E = 0.0103 cm−1. Thus, a small calculated reversal barrier of U = S2|D| = 5.6 cm−1 was obtained, which is the reason why complex 1 cannot show single-molecule-magnet (SMM) properties above 1.8 K because of the high molecular symmetry of the [Cu9M6] cluster. In conclusion, we used electrochemical synthesis and obtained the first octacyanotungstate-based [Cu9W6] cluster, which may be the ultimate member of the quindecanuclear octacyanometallate-based transition-metal cluster. The magnetic investigation shows that all spins are ferromagnetically coupled. However, the high molecular symmetry of the cluster makes it possess very small magnetic anisotropy and not behave as an SMM above 1.8 K.
■
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b01852. Experimental details, crystallographic analysis, physical measurements, and structural description (PDF) Crystallographic data in CIF format (CIF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the Major State Basic Research Development Program (Grant 2013CB922102), National Natural Science Foundation of China (Grant 21171089), Natural Science Foundation of Jiangsu Province of China (Grant BK20130054), and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institution.
■
REFERENCES
(1) Typical [M′9M6] clusters: (a) Chorazy, S.; Podgajny, R.; Nogas, W.; Nitek, W.; Koziel, M.; Rams, M.; Juszynska-Gala̧zka, E.; Zukrowski, J.; Kapusta, C.; Nakabayashi, K.; Fujimoto, T.; Ohkoshi, S.; Sieklucka, B. Chem. Commun. 2014, 50, 3484−3487. (b) Hilfiger, M. G.; Zhao, H.; Prosvirin, A.; Wernsdorfer, W.; Dunbar, K. R. Dalton Trans. 2009, 5155−5163. (c) Ma, S.-L.; Ren, S.; Ma, Y.; Liao, D.-Z.; Yan, S.-P. Struct. Chem. 2009, 20, 161−167. (d) Lim, J. H.; Yoo, H. S.; Yoon, J. H.; Koh, E. K.; Kim, H. C.; Hong, C. S. Polyhedron 2008, 27, 299−303. (e) Lim, J. H.; Yoon, J. H.; Kim, H. C.; Hong, C. S. Angew. Chem., Int. Ed. 2006, 45, 7424−7426. (f) Song, Y.; Zhang, P.; Ren, X.-M.; Shen, X.-F.; Li, Y.-Z.; You, X.-Z. J. Am. Chem. Soc. 2005, 127, 3708−3709. (g) Bonadio, F.; Gross, M.; Stoeckli-Evans, H.; Decurtins, S. Inorg. Chem. 2002, 41, 5891−5896. (h) Larionova, J.; Gross, M.; Pilkington, M.; Andres, H.; Stoeckli-Evans, H.; Güdel, H. U.; Decurtins, S. Angew. Chem., Int. Ed. 2000, 39, 1605−1609. (i) Zhong, Z. J.; Seino, H.; Mizobe, Y.; Hidai, M.; Fujishima, A.; Ohkoshi, S.; Hashimoto, K. J. Am. Chem. Soc. 2000, 122, 2952−2953. (j) Chorazy, S.; Podgajny, R.; Nakabayashi, K.; Stanek, J.; Rams, M.; Sieklucka, B.; Ohkoshi, S. Angew. Chem., Int. Ed. 2015, 54, 5093−5097. (k) Chorazy, S.; Reczyński, M.; Podgajny, R.; Nogaś, W.; Buda, S.; Rams, M.; Nitek, W.; Nowicka, B.; Mlynarski, J.; Ohkoshi, S.; Sieklucka, B. Cryst. Growth Des. 2015, 15, 3573−3581. C
DOI: 10.1021/acs.inorgchem.5b01852 Inorg. Chem. XXXX, XXX, XXX−XXX
