金属取代的多金属化合物KMn4,DyMn4.doc

CREATED USING THE RSC COMMUNICATION TEMPLATE (VER. 3.1) - SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILSARTICLE TYPE/xxxxxx | XXXXXXXXHeterometallic Appended MMnIII4 Cubanes Encapsulated by Lacunary Polytungstate Ligands Hai-Hong Wu,a Shuang Yao,c Zhi-Ming Zhang,*a Yang-Guang Li,a You Song,b* Zhu-Jun Liu,a Xin-Bao Hana and En-Bo Wang*aReceived (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XXDOI: 10.1039/b000000xThis journal is The Royal Society of Chemistry yearJournal Name, year, vol, 0000 | 5The heterometallic appended MMnIII4 (M = Dy3+ and K+) cubanes were firstly trapped by two diamagnetic POM shells, which were robust enough to construct the inorganic crystalline tubular materials. Magnetic study reveals the presence of SMM-like slow magnetic relaxation feature in the heterometallic cluster-containing POM.Design and synthesis of polynuclear metal clusters have been widely studied in the past two decades as their potential application in catalysis, magnetism and biological systems.1-5 In this field, manganese-based clusters have demonstrated promising potentials in the field of molecular magnetism and biological systems in the oxygen-evolving complex (OEC).3-6 Up to now, a series of polynuclear manganese clusters with nuclearities up to 84 have been reported, and the single molecule magnets (SMMs) have been usually found for many manganese cluster-based samples. Polyoxometalates (POMs), as a typical class of metal-oxo clusters with O-enriched surfaces, various structural features and physicochemical versatilities, such as catalysis, optics and medicine, represent an class of useful inorganic polydentate ligands to assemble various transition metal (TM) ions into aggregates.7-10 In the past twenty years, numerous TM4 cubane core-containing POMs have been synthesized by reaction of lacunary diamagnetic POM shells with 3d ions or 3d metal clusters.9-11 These studies have shown that lacunary POMs could be the effective ligands for the synthesis of the magnetically interesting species and the appended cubane model in OEC of PSII. Since 2008, it is known that 3d-metal- _aKey Laboratory of Polyoxometalate Science of Ministry of Education, Faculty of Chemistry, Northeast Normal University, Ren Min Street No. 5268, Changchun, Jilin 130024, (P. R. China); E-mail: (Z.-M. Zhang); (E.-B. Wang)bState Key Laboratory of Coordination Chemistry, Nanjing University, 22 Hankou Road, Nanjing 210093 (P. R. China); E-mail: (Y. Song).cCollege of Chemistry and Environmental Engineering, Changchun University of Science and Technology, Changchun, Jilin 130022, (P. R. China)Electronic Supplementary Information (ESI) available: Supplementary structural Figures of 1 and 2, IR, TG and CIF files. See DOI: 10.1039/b000000x/substituted POMs can behave as SMMs,9,10,11a,12 which have also been found for the Mn4-cubane containing derivatives Mn6W18, Mn4W15 and Mn7W30.9,10 Recently, the number of 4f metal cluster-based SMMs coordinated by organic polydentate ligands or inorganic lacunary POM ligands has grown significantly owing to the 4f metal cations possess rather large and anisotropic magnetic moments.13,14 A recent aspect has focused on the construction of high-spin and anisotropic 3d-4f heterometallic clusters encapsulated by lacunary diamagnetic POM shells. Until now, only a few examples have been reported, 15,16 but none of them exhibits SMM properties. We have attempted to explore the POM-SMMs for a long time, and several dimers Mn2 and Ln-Cu, stabilized by Schiff-base ligands and modulated by Anderson-type POMs, have been obtained with SMM properties.17 In this paper, the appended DyMn4- and KMn4 cubanes sandwiched by two tetravacant diamagnetic POM shells were synthesized, K7Na6DyIIIMn4(3-O)2(2-OH)2(H2O)(CO3)(-SiW8O31)221H2O (1) and K9Na6KMn4(3-O)2(2-OH)2(CO3)(-SiW8O31)222H2O (2), representing the first heterometallic appended cubanes stabilized by pure inorganic POM ligands. Fig. 1. (a), (b) Optical micrographs, and (c) and (d) SEM images of crystalline tubular material of 1.As well known, the redox properties of the Mn2+ ions will gradually increase with increasing the pH value of aqueous solution. Under alkaline conditions, the Mn2+ could be easily oxidized to Mn3+ ions by oxygen. Among the POM species, incorporation of manganese cations in intermediate oxidation Fig. 2. (a), (b) Mixed polyhedral and ball-and-stick representation of DyMn4- and KMn4 clusters sandwiched by two tetravacant POM shells in 1 and 2; (c), (d) ball-and-stick representation of heterometallic appended DyMn4 and KMn4 cubanes.states has received current attention owing to their interesting physicochemical properties, such as 1) these manganese ions possess active redox catalytic activities, which can be used to prepare a series of POM-based catalysts; 2) they have been extensively employed to construct interesting magnetic aggregates, especially the SMMs, attributed to their relatively high spin values (S) and negative single-axis magnetic anisotropy (D). Compound 1 was prepared by reaction of divacant K8-SiW10O38 with Mn2+, Dy3+ and CO32 by the conventional aqueous solution method, and the synthesis of 2 is similar to that of 1, except that K+ was used instead of Dy3+ during the reaction. Under optical microscopy, it is clear to see that the single crystals of 1 formed highly transparent solid show tetragonal tubular (Fig. 1a and 1b). Further examination of the single-crystal microreactors with scanning electron microscopy (SEM) suggests that the inner diameter range from 50 to 140 m, representing the first example of POM-based pure inorganic crystalline tubular materials (Fig. 1c and 1d).18 Single-crystal X-ray structural analysis reveals that compound 1 crystallized in the monoclinic space group P2(1)/c, and 2 crystallized in triclinic space group P-1 (Table S1). Structure analysis indicates that compound 1 comprise a pentanuclear 3d-4f cluster composed of four manganese ions and one Dy3+ cations, which was encapsulated by two tetravacant polytungstate ligands (Fig. 2a). In the sandwich-type polyoxoanion, the tetravacant POM unit -SiW8O31, deriving from the saturated -Keggin structure by removal of four adjacent WO6 octahedra, provides seven oxygen donor atoms that are capable of coordinating with the central pentanuclear DyMn4 cluster, which was further stabilized by one dianion CO32- with two 2-O atoms. In DyMn4 cluster, four +3 valence manganese ions are connected by four 3-O atoms into a Mn4O4 cubane structure (Fig. 2c, s1, s2). Further, a Dy3+ ion was connected by two 2-OH groups with Mn4O4 resulting in a 3d-4f heterometallic appended cubane. To our knowledge, this is the first heterometallic appended cubane encapsulated by two lacunary POM ligands, and it is also the first time that a 3d-4f cluster was sandwiched by two tetravacant polytungstate units -SiW8O31. The structure of polyoxoanion 2 is similar to that of 1 with a heterometallic appended KMnIII4 cubane resides in the central of the sandwich-type polyoxoanion (Fig. 2b). In the KMn4 cluster, four MnIII ions were connected by four 3-O atoms into a Mn4O4 cubane which attached to a K+ ion through two 2-OH groups (Fig. 2d). In the MMn4 (M = Dy3+ and K+) clusters, the coordination geometry of Mn3+ ions is octahedral, the Dy3+ and K+ ions are in the 7 and 8 coordinated environments, respectively. The MnO distances fall into the range of 1.890(7)2.277(7) in 1 and 1.861(13)2.286(12) in 2, which is consistent with the range of length of MnO. The DyO and KO distances are in the range of 2.300(7)2.580(8) and 2.198(14)2.924(15) , respectively. Bond valence calculations confirm that the manganese centers in both compounds 1 and 2 are all in the oxidation state of +3 (Table S2). Interestingly, this structure is reminiscent of the proposed structures for active site CaMn4 core of OEC in PSII.5,6 Several groups have contributed much on the chemistry toward the preparation of inorganic model complexes of the OEC, aiming to improve the understanding of its structure and properties and ultimately to mimic its water oxidation function.5,6,9 In the packing arrangement, all the planes of these anions are parallel with each other (Fig. S3-S6), and all of the polyoxoanions are well separated and charged-balanced by the K+ and Na+ cations. Solvent water molecules resided in the interspaces between the sandwich-type polyoxoanions, and are coordinated with alkali-metal cations or H-bonded to the surface O atoms of the POMs. It is worth mentioning that all of the MMn4 complexes are well wrapped and separated by the SiW8O31 moieties, allowing the magnetic core to be well isolated from a magnetic point of view.Fig. 3. Temperature dependence of magnetic susceptibilitites in the form of MT for 1 and 2.All magnetic measurements were performed on a polycrystalline sample. The dc magnetic susceptibility data of 2 was collected in the temperature range of 1.8300 K at a 100 Oe magnetic field (Fig. 3 and S7). As shown in Fig. 3, the MT products successively and slowly decrease from 11.9 cm3 K mol-1 at 300 K to 9.61 cm3 K mol-1 at 30 K, and then rapidly drop to a value of 6.58 cm3 K mol-1 at 1.8 K. All of these phenomena indicate that the magnetic properties of 2 are dominated by the antiferromagnetic coupling in the cluster. The non-zero value ofSchem 1. The model for fitting the magnetic properties of 2.MT at 1.8 K indicates that the ground state spin is not zero, implying both anti- and ferromagnetic coupling between MnIII ions in this cluster. The field dependence of magnetization (Fig. S8) show the magnetization increase quickly below 10 kOe and slowly above this field with the applied filed. At 70 kOe, the magnetization reaches 9.28 NB but is not saturated, so the ground state spin cannot be determined by M-H plot. It was roughly estimated by fitting the variable-temperature magnetic properties with the model and Hamiltonian as follows:When the mean-field theory was considered as the correction, the best fitting results give g = 2.02, J = -4.44, J1 = -0.69, J2 = 3.92 and zj = -0.05 cm-1 with R = 1 103 (MT)calc-(MT)obs2/(MT)obs2), which deduce the ground state spin to be 4 (Fig. S9 and Appendix). The reduced magnetization (M/NB) vs H/T of 2 (Fig. S10) shows that the isofield lines do not superimpose, indicting significant magnetic anisotropy (zero-field splitting) in the ground state. Fitting by ANISOFIT19 give D = -0.62 and E = 3.5 10-5 cm-1 with g = 1.94, which is in a good agreement with ST = 4. AC susceptibilities for 2 were measured in zero applied static field and with a 5 Oe field oscillating at frequencies between of 1 and 1500 Hz (Fig. S11). No maximum was observed, but the frequency-dependent show the signals below 2.5 K, indicating the slow magnetization relaxation behavior occurring in 2.The magnetic properties of compound 1 are also shown in Fig. 3 and Fig. S12. At room temperature, MT is 26.44 cm3 K mol-1, which is in reasonably good agreement with the expected value of 26.17 cm3 K mol-1 for four MnIII (S = 2) and a noninteracting DyIII ions (DyIII: 6H15/2, S = 5/2, L = 5, g = 4/3), also confirms that the Mn centers are all in the oxidation-state of +3. As the system cooling, MT monotonously decreases and reaches 13.27 cm3 K mol-1 at 1.8 K. This phenomenon may be ascribed to the significant orbital contribution of DyIII ion and the dominant antiferromagnetic coupling between MnIII ions due to the same unit of MnIII4 in 1. For evaluating the coupling nature between DyIII and MnIII ions, an empirical method reported by Kahn et al20 and the treatment of MT = MT (1) - MT (2) has been done as shown in Fig. 3. It is observed that the room-temperature value of MT (1) MT (2) is 14.5 cm3 K mol-1, corresponding to the magnetic contribution of one DyIII ion, and decreases with cooling, but a minimum of 6.59 cm3 K mol-1 is observed at 3 K, and then the products increases to 6.70 cm3 K mol-1 at 1.8 K (Fig. S13). It suggests the antiferromagnetic coupling between MnIII and DyIII ions, because the low-temperature values of MT (1) - MT (2) are much lower than 10.510.83 for that of one DyIII ion.19,21 The increase below 3 K can be attributed to the arrangement of the net spins between MnIII4 and DyIII ion along to the applied field.Fig. 4. Out-of-phase of AC susceptibility for 1 measured in zero dc field and a 5 Oe field oscillating at frequencies between of 1 and 1500 Hz.The field dependence of magnetization shows the similar shape of plot to 2. In low field, the magnetization increases sharply and still keep a quick increase trend above 8 kOe but does not reach a saturation state until 70 kOe (11.66 NB in Fig. S14 in Supporting Information). As the expected anisotropy of DyIII ion, the reduced magnetization (M/NB) vs H/T of 1 (Fig. S15) also show the strongly separated isofield lines. However, the zero-field splitting parameter cannot be estimated due to the orbital contribution of DyIII ion. In the same condition as 2, the AC susceptibilities were measured and showed strongly frequency-dependent signals below 4 K although no peak was observed until 1.8 K (Fig. S16), which indicated the SMM-like slow relaxation of in 1 (Fig. 4). Under a field of 2 kOe the AC data were also collected (Fig. S17), but the magnetic properties were not improved largely, so not further studied in detail.In summary, the MMn4 (M = Dy3+ and K+) paramagnetiic clusters were trapped by two diamagnetic lacunary POM shells, resulting in two heterometallic appended cubanes-containing sandwich-type polytungstates. These are the first heterometallic appended cubanes encapsulated by two lacunary POM ligands, and it is also the first time that the 3d-4f clusters were sandwiched by two tetravacnt polytungstate units -SiW8O31. Magnetic study reveals the presence of SMM-like feature in compound 1. Interestingly, compound 1 is robust enough to construct the single-crystal microreactors. Also, the synthesis of the pure inorganic clusters containing MMn4 heterometallic cores have shown that lacunary POMs might be the effective ligands for the synthesis of the inorganic model complexes of the OEC in PSII. The further study of their water oxidation function is on going in our group now.This work was supported by the National Natural Science Foundation of China (21101022/21171089/91022031).References 1 (a) R. E. P. Winpenny in Comprehensive Coordination Chemistry II, Vol. 7 (Eds.: J. A. McCleverty, T. J. Meyer), Elsevier Pergamon, Amsterdam, 2004, pp. 125; (b) D. Gatteschi, M. Fittipaldi, C. Sangregorio and L. Sorace, Angew. Chem. Int. Ed., 2012, 51, 4792; (c) C.-F. Wang, J.-L. Zuo, B.-M. Bartlett, Y. Song, J. R. Long and X. Z. You, J. Am. Chem. Soc., 2006, 128, 7162. 2 (a) A. Mandel, W. Schmitt, T. G. Womack, R. Bhalla, R. K. Henderson, S. L. Heath and A. K. Powell, Coord. Chem. Rev., 1999, 190, 1067; (b) V. Mereacre, D. Prodius, Y. Lan, C. Turta, C. E. Anson and A. K. Powell, Chem. Eur. J., 2011, 17, 123; (c) T. Liu, Y. J. Zhang, Z. M.Wang and S. Gao, J. Am. Chem. Soc., 2008, 130, 10500; (d) J. Liu, F. Guo, Z. Meng, Y. Zheng, J. Leng, M. Tong, L. Ungur, L. F. Chibotaru, K. J. Heroux and D. N. Hendrickson, Chem. Sci., 2011, 2, 1268.3 (a) A. J. Tasiopoulos, A. Vinslava, W. Wernsdorfer, K. A. Abboud and G. Christou, Angew. Chem. Int. Ed., 2004, 43, 2117; (b) J. B. Peng, Q. C. Zhang, X. J. Kong, Y. Z. Zheng, Y. P. Ren, L. S. Long, R. B. Huang, L. S. Zheng and Z. P. Zheng, J. Am. Chem. Soc., 2012, 134, 3314; (c) Y. Zhang, D. Li, R. Clrac, M. Kalisz, C. Mathonire and S. M. Holmes, Angew. Chem. Int. Ed., 2010, 49, 3752.4 (a) P. Gerbier, N. Domingo, J. Gmez-Segura, D. Ruiz-Molina, D. B. Amabilino, J. Tejada, B. E. Williamson and J. Veciana, J. Mater. Chem., 2004, 14, 2455; (b) Z. M. Zhang, Y. G. Li, S. Yao, E. B. Wang, Y. H. Wang and R. Clrac, Angew. Chem. Int. Ed., 2009, 48, 1581; (c) Z. M. Zhang, S. Yao, Y. G. Li, R. Clrac, Y. Lu, Z. M. Su and E. B. Wang, J. Am. Chem. Soc., 2009, 131, 14600.5 (a) B. Loll, J. Kern, W. Saenger, A. Zouni and J. Biesiadka, Nature, 2005, 438, 1040; (b) Y. Umena, K. Kawakami, J. R. Shen and N. Kamiya, Nature, 2011, 473, 55; (c) J. S. Kanady, E. Y. Tsui, M. W. Day and T. Agapie, Science, 2011, 333, 733; (d) K. N. Ferreira, T. M. Iverson, K. Maghlaoui, A. Barber and S. Iwata, Science, 2004, 303, 1831; (e) J. Yano, J. Kern, K. Sauer, M. J. Latimer, Y. Pushkar, J. Biesiadka, B. Loll, W. Saenger, J. Messinger, A. Zouni and V. K. Yachandra, Science, 2006, 314, 821.6 (a) J. Yano, K. Sauer, Boussac A and V. K. Yachandra, Proc. Natl. Acad. Sci. USA, 2008, 105, 1879; (b) S. Mukherjee, JA. Stull, J. Yano, T. C. Stamatatos, K. Pringouri, T. A. Stich, K. A. Abboud, R. D. Britt, V. K. Yachandra and G. Christou, Proc. Natl. Acad. Sci. USA, 2012, 109, 2257; (c) Z. Huang, Z. Luo, Y. V. Geletii, J. W. Vickers, Q. Yin, D. Wu, Y. Hou, Y. Ding, J. Song, D. G. Musaev, C. L. Hill and T. Lian, J. Am. Chem. Soc., 2011, 133, 2068; (d) A. Sartorel, M. Carraro, G. Scorrano, R. D. Zorzi, S. Geremia, N. D. McDaniel, S. Bernhard and M. Bonchio, J. Am. Chem. Soc., 2008, 130, 5006.7 (a) A. Dolbecq, E. Dumas, C. R. Mayer and P. Mialane, Chem. Rev., 2010, 110, 6009; (b) D.-L. Long, R. Tsunashima and L. Cronin, Angew. Chem. Int. Ed., 2010, 49, 1736; (c) A. Mller and S. Roy, Coord. Chem. Rev., 2003, 245, 153; (d) E. Coronado, C. Gimnez-Saiz, C. J. Gmez-Garca and V. Laukhin, Nature, 2000, 408, 447; (e) E. Coronado, C. Gimnez-Saiz and C. J. Gmez-Garca, Coord. Chem. Rev., 2005, 249, 1776; (f) S. T. Zheng, J. Zhang and G. Y. Yang, Angew. Chem. Int. Ed., 2008, 47, 3909; (g) P. Yin, P. Wu, Z. Xiao, D. Li, E. Bitterlich, J. Zhang, P. Cheng, D.