formate coordination framework exhibits weak

View Online / Journal Homepage / Table of Contents for this issue

ChemComm

Dynamic Article Links

Cite this: Chem. Commun., 2012, 48, 6568–6570 www.rsc.org/chemcomm

COMMUNICATION

A unique substituted Co(II)-formate coordination framework exhibits weak ferromagnetic single-chain-magnet like behaviorw

Downloaded by Tianjin University on 23 June 2012 Published on 09 May 2012 on http://pubs.rsc.org | doi:10.1039/C2CC31204B

Jiong-Peng Zhao,ab Qian Yang,a Zhong-Yi Liu,c Ran Zhao,a Bo-Wen Hu,a Miao Du,c Ze Changa and Xian-He Bu*a Received 17th February 2012, Accepted 9th May 2012 DOI: 10.1039/c2cc31204b A magnetic isolated chain-based substituted cobalt–formate framework was obtained with isonicotine as a spacer. In the chain, canted antiferromagnetic interactions exist in between the CoII ions, and slow magnetic relaxation is detected at low temperature. For the block effects of the isonicotine ligands, the complex could be considered as a peculiar example of a weak ferromagnetic single-chain-magnet. The investigation of single-chain magnets (SCMs) is one of the most active topics in current molecular magnetism since they may afford extended correlation lengths of magnetization at relatively higher temperatures compared with the pioneer super paramagnet single-molecule magnets (SMMs).1 The development of SCMs has taken advantage of molecule-based materials, where some peculiar properties or even multi-functions could be achieved and modified at the molecular level.2 To obtain SCMs, strong uniaxial Ising-type anisotropy and high ratio between the intrachain and interchain magnetic interactions are the two basic requirements.3 Notably, most known SCMs are ferromagnetic or ferrimagnetic chains built by anisotropic metal centers,4 and the recent detection of SCMs behavior in weak ferromagnetic chain systems for their non-collinearity of anisotropic axes brings new inspiration in this domain.5 However, SCMs with weak ferromagnetism are really rare and only a few examples have been reported so far.4,5 To design and assemble weak ferromagnetic SCMs, ligands that can bridge two or more metal ions without center of symmetry are preferred, as the resulting conformation will satisfy the requirement of non-collinear arrangement of spins.6 As the smallest carboxylate, the formate anion can bridge metal centers in diverse fashions and weak ferromagnetism is frequently observed in metal–formate.7 However, a long range magnetic order is often triggered by the strong interactions a

Department of Chemistry and TKL of Metal and Molecule-Based Material Chemistry, Nankai University, Tianjin 300071, China. E-mail: [email protected]; Fax: +86 22-23502458 b School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, China c College of Chemistry, TKL of Structure and Performance for Functional Molecules, Tianjin Normal University, Tianjin 300387, China w Electronic supplementary information (ESI) available: Tables S1 and S2 and Fig. S1–S11. CCDC 837840. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2cc31204b

6568

Chem. Commun., 2012, 48, 6568–6570

transmitted by formate or the dipole–dipole effect between the sub-layers or chains in metal–formate. Thus, it is a challenge to obtain metal–formate with real one-dimensional (1D) chain character from the viewpoint of magnetism.8 In this context, introducing a second ligand as the spacer may be feasible to properly meet the requirement of the isolation of magnetic chains. However, the goal is difficult to achieve for both synthetic and magnetic controls. In this work, we present a substituted cobalt–formate coordination framework [Co8(OMe)6(HCO2)4(isonic)6H2O]n (1) in the presence of isonicotine (isonic).z The three-dimensional (3D) framework of 1 contains 1D chains constructed by both dimeric and tetrahedral CoII clusters with rare syn,syn,anti,anti-coordinated formate anions as the linkers. Remarkably, magnetic investigations indicate the coexistence of spin competition, spin canting, and slow magnetic relaxation in this new material, which can be considered as a unique paradigm of weak ferromagnetic SCMs. Single-crystal X-ray diffraction analysisy reveals that in 1 the asymmetric unit has one OMe anion and one isonic moiety at a general position, and there is also one isonic anion, two formate and one OMe anions which are all half contained lying on a mirror plane, such that the lone water of crystallization is at a site with 2/m symmetry. There are two crystallographic independent octahedral coordinated CoII ions (Co1 and Co2, Fig. 1a). Co1 and Co2 are all in a slightly compressed octahedral geometry with O1, O3 and O2, O7 at the apical positions (see selected bond lengths and angles in Table S1, ESIw). A dinuclear unit was formed by m2-OMe, syn,syn-carboxylate and syn,syn-formate anions and two Co1 ions, while a tetrahedral cluster unit was constructed by four m3-OMe anions, and two syn,syn-formate. Besides constructing Co2 and Co4 clusters, the formate ligands also play a role in bridging these dinuclear/tetrahedral units in anti,anti exhibiting an infrequent syn,syn,anti,anti coordination mode.9 One isonic anion takes the m3-mode to link three CoII ions Co1, Co2 and Co1E using all its heteroatoms, while the other bridges the same type of CoII centers Co1 and Co1D using the carboxylate with a disordered uncoordinated pyridine ring. As a result, an eight-membered metal nest ring was formed by the linkage of formate, carboxylate and OMe anions (see Fig. 1b) and such rings are further extended into a 1D chain via sharing the tetrahedral clusters (see Fig. 2a). In each ring, the CoII ions This journal is

c

The Royal Society of Chemistry 2012

View Online


Fig. 3 Plot of wmT vs. T at 0.2 T of 1 (inset: plot of the reduced magnetization at 2 K). Fig. 1 (a) The coordination and linkage modes of metals and ligands in 1. Symmetry code: A: y 1, x + 1, z + 3/2; B: y + 3/2, x + 3/2, z + 3/2; C: y 1/2, x + 1/2, z + 3/2; D: x, y, z + 2; E: y + 1, x + 1, z + 3/2; F: x + 1, y + 2, z. (b) The ring like structure in 1 (C in cyan, O in red, N in blue, Co in pink, polyhedron of Co2 in green and Co1 in yellow).

Fig. 2 (a) Polyhedron view of the chain in 1. (b) The predigesting arrangement of CoII ions in the 1D chain and mainly antiferromagnetic interactions (blue) in the chains.

are located in two different planes with a dihedral angle of 18.091 (Fig. S1, ESIw), however the axes of the neighbouring CoII octahedrons tilt towards each other both in and out of the planes. Further, the rings in the 1D chain are alternated in two orientations (see Fig. 2). Thus, the CoII centers in 1 are arranged in four different planes in the 1D motif, and the axis parallel CoII octahedrons could be found in interval rings. Furthermore, the chains are linked by the m3-isonic ligands to construct a 3D coordination framework with water filling 1D channels (see Fig. S2, ESIw). From the viewpoint of network topology, the m3-isonic anion, dimeric and tetranuclear clusters can be considered as the 3-, 6-, and 8-connected nodes, respectively. Then the whole framework could be simplified as a new 3-nodal (3,6,8)-connected network with the Schla¨fli symbol of (3.6.7)4(32.4.52.64.74.82)2 (34.42.54.614.74).10 Magnetic measurements were carried out on a crystalline sample of 1, the phase purity of which was confirmed by XRPD (see Fig. S3, ESIw). At 300 K, the wmT value is 3.4 cm3 K mol1, which is higher than the value for a spin-only case (1.87 cm3 K mol1, S = 3/2), as expected for an orbital contribution. As the temperature is lowered, the wmT value decreases smoothly until at ca. 20 K then the wmT curve rises abruptly to a maximum at 4 K before dropping. The decrease of the wmT plot upon cooling at high temperature is attributed to spin–orbit coupling effects and possible antiferromagnetic interactions (Fig. 3).11 Fitting the data above 100 K by the Curie–Weiss law gives C = 4.1 cm3 K mol1 and y = 52.5 K (see Fig. S4, ESIw) suggesting strong magnetic interactions between the metal ions. On the other hand, the increase in wmT at low temperature indicates ferrimagnetism or spin-canting. This journal is

c


Taking account of both the numerous magnetic exchange pathways present within the chains and the adjacent coordinated octahedrons of the anisotropic CoII ions that tilt towards each other, spin canting is probable (Fig. 2b; Fig. S5 and Table S2, ESIw).4b,12 The canted antiferromagnetism of 1 was confirmed by the field dependence of magnetization at 2 K (see Fig. 3, inset), which shows an abrupt increase to above 0.3 Nb of magnetization below 1300 Oe and then increases linearly to 0.68 Nb at 50 kOe without achieving saturation. The magnetic interactions conducted by the isonic anion between the CoII ions in neighboring chains is very weak,8b and 1 has a 1D character (Fig. S6, ESIw). It is worth noting that spin competition exists in the tetrahedron for triangle arrangement of antiferromagnetic interactions. And the so-called frustration index, f E |y|/Tb = 18 (Tb is the block temperature defined by the divaricated temperature of the ZFC and FC magnetization which is owing to a frozen magnetized effect3,6b,13 (Fig. S7, ESIw)) suggests the strong competition in 1.14 The larger f value also reflects very weak magnetic interactions between the 1D chains in 1. To further understand the magnetism of 1, ac dynamic susceptibility measurements were performed at an oscillating 3.0 Oe applied field in the 10–1202 Hz interval. Both in-phase (wm 0 ) and out-of-phase (wm00 ) signals show a peak at low temperatures and obvious frequency dependence (see Fig. 4) is observed. The wm00 curves reach their maximum between 2.1 K (10 Hz) and 3.0 K (1202 Hz). That precluded the significant 3D ordering and suggested the neglectable interchains interactions. The peak temperatures of wm00 extracted from these data can be fitted well by the Arrhenius plot, showing clearly the occurrence of crossover between two different activated regimes at T* = 2.6 K and giving the characteristic relaxation time, t0 of 8.1 1012 s and 8.0 108 s, for high and low temperature regimes with two

Fig. 4 ac plots for 1 between 2 K and 6 K at different frequencies. Inset: magnetization relaxation time (t) vs. T 1 for 1 (solid line represents the best fit to the Arrhenius law).

Chem. Commun., 2012, 48, 6568–6570

6569


View Online

corresponding energy barriers, Dt1/kB = 49.4 K and Dt2/kB = 26.0 K, respectively (Fig. 4, inset), which is similar to the observed finite-size effect halving the Glauber activation barrier in 1.15 However the comparison of the difference of energy gap (Dt1 Dt2 = 23 K) with the energy gap obtained by the linear analysis of ln(wmT) vs. 1/T (Fig. S8, ESIw) is not appropriate. Actually in the case of non-collinear 1D antiferromagnets the only experimentally accessible correlation is that of the noncompensated component of the magnetization, and the commonly employed linear analysis of ln(wmT) vs. 1/T leads to a large error in the estimation of the exchange contribution to the barrier in canted AF chains.4a,16 In addition, the frequency shift parameter, F = DTp/[TpD(log f)] = 0.14, is in an excellent agreement with that expected for superparamagnetic behavior and the presence of glassiness can be discarded.17 The frequency dependence of ac susceptibilities at 2.0 K, 2.5 K, 3.0 K results in a semicircular Cole–Cole plotting of wm00 vs. wm 0 (Fig. S9 and S10, ESIw). The least-squares fitting of the data suggests a distribution of single relaxation processes with the a parameters of 0.33, 0.39, 0.32 and t of 2 102 s, 1 103 s, 1 104 s.3 The order of magnitude of relaxation times is consistent with that obtained by the Arrhenius law. A hysteresis loop is clearly observed at 2.0 K without the coercive field, and at 0.5 K a more distinct magnetization hysteresis loop is observed with a remanent magnetization of 0.16 Nb and a coercive field of 2100 Oe (Fig. S11, ESIw). In summary, a unique substituted 3D CoII–formate framework has been designed and prepared, in which the 1D magnetic chain is built from the alternating linkage of dinuclear and tetrahedral CoII units. Dominating antiferromagnetic interactions are observed between the CoII centers. However, spin canting is presented at low temperature accompanied by spin competition. Of further significance, SCMs like behavior is also found due to the strong anisotropy of canting in the chains and neglectable interchain couplings that will prevent the triggering of 3D ordering. The magnetic character of 1 is quite remarkable for the incorporation of spin canting and superparamagnetic behavior, which represents a new example of superparamagnetism based on the canted ferromagnetic chains. The synthetic strategy used in this work will be further extended for obtaining more molecule-based magnetic materials with tunable structures and desired properties. This work was supported by the NNSF of China (21031002 and 21101114), the 973 Program of China (2012CB821700), the Natural Science Fund of Tianjin, China (10JCZDJC22100), the Tianjin Municipal Education Commission (No. 20100502) and the Fundamental Research Funds for the Central Universities.

Notes and references z Synthesis of 1: a mixture of Co(HCO2)24H2O (1.5 mmol), isonicotinic acid (0.75 mmol), and MeOH (10 mL) was sealed in a Teflonlined autoclave, heated to 140 1C, and kept for 48 h. Then, the reaction vessel was cooled to room temperature in 12 h. A red crystalline product was collected as a mixture of 1 with ca. 20% yield based on isonicotinic acid. Anal. calcd for C46H48Co8N6O27 (1): C, 34.78; H, 3.05; N, 5.29%; found: C, 34.54; H, 3.12; N, 5.55%. y Crystal data for 1: C46H48Co8N6O27, Mr = 1588.34, tetragonal, space group: P42/mbc, a = b = 19.244(3) A˚, c = 16.406(3) A˚, V = 6076.1(1) A˚3, Z = 4, rcalcd = 1.736 g cm3, l = 0.71073 A˚,

6570

Chem. Commun., 2012, 48, 6568–6570

m(Mo Ka) = 2.214 mm1, F(000) = 3192, GOF = 1.352, T = 293 K, R1 = 0.0872, wR2 = 0.1693 [I > 2s(I)]. CCDC 837840. 1 (a) A. Caneschi, D. Gatteschi, N. Lalioti, C. Sangregorio, R. Sessoli, A. Venturi, A. Vindigni, A. Rettori, M. G. Pini and M. A. Novak, Angew. Chem., Int. Ed., 2001, 40, 1760; (b) R. Cle´rac, H. Miyasaka, M. Yamashita and C. Coulon, J. Am. Chem. Soc., 2002, 124, 12837. 2 (a) D. Maspoch, D. Ruiz-Molina, K. Wurst, N. Domingo, M. Cavallini, F. Biscarini, J. Tejada, C. Rovira and J. Veciana, Nat. Mater., 2003, 2, 190; (b) J. Lu, D. R. Turner, L. P. Harding, L. T. Byrne, M. V. Baker and S. R. Batten, J. Am. Chem. Soc., 2009, 131, 10372. 3 E. Coronado, J. R. Galań-Mascaro´s and C. Martı´ -Gastaldo, J. Am. Chem. Soc., 2008, 130, 14987. 4 (a) M. Ding, B.-W. Wang, Z.-M. Wang, J.-L. Zhang, O. Fuhr, D. Fenske and S. Gao, Chem.–Eur. J., 2011, 18, 915; (b) D.-F. Wong, Z.-M. Wang and S. Gao, Chem. Soc. Rev., 2011, 40, 3157 and references cited therein. 5 For example: (a) Z.-M. Sun, A. V. Prosvirin, H.-H. Zhao, J.-G. Mao and K. R. Dunbar, J. Appl. Phys., 2005, 97, 10B305; (b) A. V. Palii, S. M. Ostrovsky, S. I. Klokishner, O. S. Reu, Z.-M. Sun, A. V. Prosvirin, H.-H. Zhao, J.-G. Mao and K. R. Dunbar, J. Phys. Chem. A, 2006, 110, 14003; (c) A. V. Palii, O. S. Reu, S. M. Ostrovsky, S. I. Klokishner, B. S. Tsukerblat, Z.-M. Sun, J.-G. Mao, A. V. Prosvirin, H.-H. Zhao and K. R. Dunbar, J. Am. Chem. Soc., 2008, 130, 14729; (d) L. Bogani, C. Sangregorio, R. Sessoli and D. Gatteschi, Angew. Chem., Int. Ed., 2005, 44, 5817. 6 (a) Y.-L. Bai, J. Tao, W. Wernsdorfer, O. Sato, R.-B. Huang and L.-S. Zheng, J. Am. Chem. Soc., 2006, 128, 16428; (b) H.-B. Xu, B.-W. Wang, F. Pan, Z.-M. Wang and S. Gao, Angew. Chem., Int. Ed., 2007, 46, 7388; (c) X.-T. Liu, X.-Y. Wang, W.-X. Zhang, P. Cui and S. Gao, Adv. Mater., 2006, 18, 2852; (d) W. Ouellette, A. V. Prosvirin, K. Whitenack, K. R. Dunbar and J. Zubieta, Angew. Chem., Int. Ed., 2009, 48, 2140. 7 (a) Z.-M. Wang, B. Zhang, H. Fujiwara, H. Kobayashi and M. Kurmoo, Chem. Commun., 2004, 416; (b) Z.-M. Wang, B. Zhang, T. Otsuka, K. Inoue, H. Kobayashi and M. Kurmoo, Dalton Trans., 2004, 2209. 8 (a) Y.-Z. Zheng, M.-L. Tong, W.-X. Zhang and X.-M. Chen, Angew. Chem., Int. Ed., 2006, 45, 6310; (b) J.-P. Zhao, B.-W. Hu, X.-F. Zhang, Q. Yang, M. S. E. Fallah, J. Ribas and X.-H. Bu, Inorg. Chem., 2010, 49, 11325. 9 G. Wu, R. Cle´rac, W. Wernsdorfer, S.-L. Qiu, C. E. Anson, I. J. Hewitt and A. K. Powell, Eur. J. Inorg. Chem., 2006, 1927. 10 (a) Reticular Chemistry Structure Resource (RCSR), http://rcsr. anu.edu.au; (b) Euclidean Patterns in Non-Euclidean Tilings (EPINET), http://epinet.anu.edu.au; (c) V. A. Blatov, A. P. Shevchenko, TOPOS 4.0, Samara State University, Russia. 11 F. Lloret, M. Julve, J. Cano, R. R. Ruiz-Garcı´ a and E. Pardo, Inorg. Chim. Acta, 2008, 361, 3432. 12 (a) K. C. Mondal, G. E. Kostakis, Y. Lan, C. E. Anson and A. K. Powell, Inorg. Chem., 2009, 48, 9205; (b) Z.-M. Wang, B. Zhang, M. Kurmoo, M. A. Green, H. Fujiwara, T. Otsuka and H. Kobayashi, Inorg. Chem., 2005, 44, 1230. 13 (a) D. Wu, D. Guo, Y. Song, W. Huang, C. Duan, Q. Meng and O. Sato, Inorg. Chem., 2009, 48, 854; (b) X.-B. Li, J.-Y. Zhang, Y.-Q. Wang, Y. Song and E.-Q. Gao, Chem.–Eur. J., 2011, 17, 13883. 14 J. E. Greedan, J. Mater. Chem., 2001, 11, 37. 15 (a) C. Coulon, R. Cle´rac, L. Lecren, W. Wernsdorfer and H. Miyasaka, Phys. Rev. B, 2004, 69, 132408; (b) L. Bogani, A. Caneschi, M. Fedi, D. Gatteschi, M. Massi, M. A. Novak, M. G. Pini, A. Rettori, R. Sessoli and A. Vindigni, Phys. Rev. Lett., 2004, 92, 207204; (c) L. Bogani, R. Sessoli, M. G. Pini, A. Rettori, M. A. Novak, P. Rosa, M. Massi, M. E. Fedi, L. Giuntini, A. Caneschi and D. Gatteschil, Phys. Rev. B, 2005, 72, 064406; (d) C. Coulon, H. Miyasaka and R. Cle´rac, Struct. Bonding, 2006, 122, 163. 16 K. Bernot, J. Luzon, R. Sessoli, A. Vindigni, J. Thion, S. Richeter, D. Leclercq, J. Larionova and A. Lee, J. Am. Chem. Soc., 2008, 130, 1619. 17 A. H. Morrish, The Physical Principles of Magnetism, Wiley, New York, 1966.

This journal is

c
