A 3D Heterometallic Coordination Polymer Constructed by Trimeric

Jan 11, 2016 - ... Constructed by Trimeric {NiDy2} Single-Molecule Magnet Units ... School of Chemistry and Chemical Engineering, Hunan University of ...
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A 3D Heterometallic Coordination Polymer Constructed by Trimeric {NiDy2} Single-Molecule Magnet Units Shaowei Zhang,†,§ Han Li,† Eryue Duan,† Zongsu Han,† Leilei Li,† Jinkui Tang,∥ Wei Shi,*,†,‡ and Peng Cheng*,†,‡ †

Department of Chemistry, Key Laboratory of Advanced Energy Materials Chemistry (MOE), Nankai University, Tianjin 300071, P. R. China ‡ Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, P. R. China § Key Laboratory of Theoretical Organic Chemistry and Functional Molecule of the Ministry of Education, School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, P. R. China ∥ State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, P. R. China S Supporting Information *

ABSTRACT: The solvothermal reaction of DyCl3·6H2O, Ni(NO3)2·6H2O, and H4abtc ligands (H4abtc = 3,3′,5,5′-azobenzene-tetracarboxylic acid) in the mixed DMF/H2O solvents (DMF = N,N-dimethylformamide) produced a three-dimensional (3D) NiII−DyIII heterometallic coordination polymer (HCP) formulated as {[NH2(CH3)2]2[NiDy2(HCOO)2(abtc)2]}n (1). In 1, DyIII and NiII ions interconnect through carboxylic O donors of abtc4− ligands to generate a linear trimer “Hourglass”-type {NiDy2} cluster, and the adjacent trinuclear {NiDy2} units are bridged by HCOO− groups to give a 1D “ladder” chain, which is further bridged by abtc4− ligands to form a new topology and named as “zsw3”. Alternating-current magnetic susceptibility results indicate that 1 exhibits frequency-dependent out-of-phase signals with two relaxation processes, which suggests that it shows single-molecule magnet (SMM) behavior and represents the first example by using an SMM cluster as the building block to create a 3D Ni−Ln HCP, to the best of our knowledge. The energy barriers for 1 under a 1000 Oe applied direct current magnetic field are estimated from Arrhenius plots to be 40 and 42 K at higher and lower frequencies, respectively. Additionally, the crystalline structure of 1 could be stable to at least 310 °C, supported by thermogravimetric analyses and in situ variable-temperature powder X-ray diffraction patterns.

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INTRODUCTION Single-molecule magnets (SMMs) displaying slow relaxation of magnetization due to the intrinsic energy barrier (Ueff) to magnetization inversion are mainly discrete magnetic molecules with the potentialities for high-density information storage, quantum processing, and spintronics devices.1 Much effort has been devoted to this area to improve their magnetic characteristics, and numerous SMMs have been documented1 since the pioneering work on the first SMM of dodeca-nuclear {Mn12} in 1993.2 In 2002, Wernsdorfer and co-workers prepared a supramolecular SMM dimer in which antiferromagnetic interactions between the two components resulted in quantum behavior distinct from that of the individual SMMs.3 Two years later, Clérac et al. isolated the first example of magnetic material in which an SMM complex has been applied to design a 3D ordered magnet.4 Their results expand new perspectives on the design of magnetic materials by introducing SMM clusters as secondary building units (SBUs) to construct multidimensional architectures because multidimensional networks of magnetically coupled SMMs could produce interesting © XXXX American Chemical Society

magnetic behavior induced by the intrinsic properties carried by these magnetic SBUs (such as quantum effects, Ising-type anisotropy, high spin state).5 One of the possible approaches is to use SMMs as magnetic SBUs and assemble them by choosing suitable linkers with the aid of coordination chemistry. However, the strategy that controlled association of SMM SBUs into coordination networks is an intellectual challenge because the inherent magnetic properties of the SMM precursors could be changed in the formation of targeted coordination polymers (CPs). Although lots of discrete SMMs with large anisotropy barriers have been successively obtained in the past decade, including transition-metal (TM)-based SMMs,6 lanthanide (Ln)-based SMMs,7 as well as mixed d−f heterometallic SMMs,8 the exploration of multidimensional CPs based on SMM SBUs is very limited to date.9,10 Furthermore, most previous reports of multidimensional CPs based on SMM SBUs are employing cyanide- or oxalate-bearing Received: October 15, 2015

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DOI: 10.1021/acs.inorgchem.5b02378 Inorg. Chem. XXXX, XXX, XXX−XXX

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165 °C for 72 h, and then cooled to the room temperature over a period of 48 h. Yellow rodlike crystals were collected. Yield: ca. 68% (based on H4abtc). The final formula was determined by combination of elemental analyses, TGA result, and X-ray single-crystal diffraction data. Elemental analyses calcd. (%) for C38H30N6O20NiDy2: C 35.81, H 2.37, N 6.59. Found: C 35.68, H 2.51, N 6.48. X-ray Crystallography. Crystallographic experiment for 1 was carried out on an Oxford SuperNova diffractometer with a graphite monochromatic Mo Kα radiation (λ = 0.71073 Å) at 130 K. Routine Lorentz polarization and empirical absorption corrections were applied. All the structures were solved by direct methods and refined by full-matrix least-squares methods on F2 with the SHELXTL-97 program package.16 Anisotropic thermal parameters were assigned to all non-hydrogen atoms. Positions of H atoms attached to C and N atoms were geometrically added. The HCOO− groups and H4abtc ligands were disorder and geometrically restrained. The occupancy of the N2 atom of the H4abtc ligand is 0.5, resulting into the alerts “short non-bonding inter D···A contacts” in the CheckCIF reports. The final formula was generated by the combination of element analyses and TG analyses, as well as single-crystal data. The crystallographic parameters and structural refinements of 1 are presented in Table 1. CCDC 1043681 is for 1. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac. uk/data_request/cif.

mononuclear precursors such as [M III (CN) 6 ] 3− or [MIII(C2O4)3]3− (M = Cr, Fe) as metalloligands toward different valent metal ions.9 On the other hand, multidimensional CPs have provoked fascinating interests because their structures can be easily adjusted by employing different metal ions and organic linkers, which subsequently produces promising applications in catalysis, gas storage and separation, chemical recognition, and molecular magnets.11 Metal centers and organic likers are the two most important components of CPs, which can be specifically designed and adjusted, and consequently provide the possible approach to construct SMM-based multifunctional CPs, such as dynamic porous magnets, luminescent porous magnets, and magnetic sensing materials.9,12 Our strategy in this area is based on combining metal clusters or metal-oxo chains and suitable organic linkers to construct multidimensional CPs with interesting magnetic properties.13 By this approach, we have obtained a dynamic porous CP featuring binuclear Dy2 SMM units as nodes,13a an unusual 3D homospin Néel N-type ferrimagnet CP,13b and a 3D waterbridged homospin CoII-single-chain magnetic CP,13c as well as some other multidimensional CPs based on SMM SBUs.13d−f In addition, inspired by our previous work on the investigation of the 3,3′,5,5′-azobenzene-tetracarboxylic acid (H4abtc) ligand, in which the H4abtc ligand presents abundant coordination modes with both TM and Ln ions to produce multidimensional CPs, we isolated a series of TM-containing CPs,14a as well as the first example of Ln-CP with the H4abtc ligand.14b We expected that the H4abtc ligand should be able to combine simultaneously with both TM and Ln ions and form multidimensional TM−Ln HCPs with fascinating architectures and properties if the reaction conditions permit. In this contribution, we presented a highly thermally stable 3D NiII−DyIII HCP with a new “zsw3”-type topology constructed from “Hourglass”-type trimer {NiDy2} SMM clusters and H4abtc ligands formulated as {[NH2(CH3)2]2[NiDy2(HCOO)2(abtc)2]}n (1), which represents the first 3D Ni−Ln-CP based on SMM SBUs, to the best of our knowledge. Furthermore, 1 demonstrates remarkable thermal stability and the crystalline structure can be stable to at least 310 °C, evidenced by the in situ variable-temperature PXRD patterns and TG analyses.

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Table 1. Crystallographic Data and Structure Refinements for 1 1 C38H30N6O20NiDy2 1274.39 129.9(3) orthorhombic Ibam 12.3451(4) 23.7349(7) 13.1709(4) 4171.8(2) 4 0.10 × 0.06 × 0.04 2.029 4.084 0.0752 −15 ≤ h ≤ 9 −15 ≤ k ≤ 28 −15 ≤ l ≤ 14 5547 1915 225 1.138 0.0519, 0.0597 0.1151, 0.1192

formula Mr (g mol−1) T (K) cryst syst space group a (Å) b (Å) c (Å) V (Å3) Z cryst size (mm3) Dc (g cm−3) μ (mm−1) Rint limiting indices

EXPERIMENTAL SECTION

reflns collected indep reflns params GOF on F2 R1a, wR2b [I > 2σ(I)] R1a, wR2b [all data]

General Methods and Materials. H4abtc was synthesized according to the modified literature process.15 Other chemical materials were purchased and utilized directly. C, N, and H analyses results were harvested from a PerkinElmer 2400-II CHNS/O analyzer. Thermogravimetric (TG) analyses between 25 and 800 °C were obtained from a Labsys NETZSCH TG 209 Setaram apparatus under a N2 atmosphere with the heating rate of 10 °C·min−1. PXRD spectra were recorded on a Rigaku Ultima IV instrument using Cu Kα radiation (λ = 1.54056 Å), in the range 2θ = 3−60° with the scan speed of 10° min−1. The in situ variable-temperature PXRD patterns were measured on the Pt sample platform under the N2 atmosphere from 25 to 400 °C with the heating rate of 10 °C min−1, and in the range 2θ = 3−60° with a scan speed of 5° min−1. Magnetic data were from a Quantum Design SQUID VSM magnetometer. Diamagnetic corrections were handled with the combination of Pascal’s constants and the sample holder. Preparation of {[NH2(CH3)2]2[NiDy2(HCOO)2(abtc)2]}n (1). A mixture of DyCl3·6H2O (0.0565 g, 0.15 mmol), Ni(NO3)2·6H2O (0.0291 g, 0.10 mmol), H4abtc (0.0358 g, 0.10 mmol), 1 mol·L−1 LiOH (100 μL), HNO3 (100 μL), DMF (2 mL), and H2O (2 mL) was sealed in a 25 mL Telfon-lined stainless steel autoclave and placed at

R 1 = ∑||F o | − |F c ||/∑|F o |. ∑[w(Fo2)2]}1/2. a

b

wR 2 = {∑[w(F o 2 − F c 2 ) 2 ]/

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RESULTS AND DISCUSSION Structural Descriptions. The observed PXRD pattern for 1 is in good accordance with the simulated PXRD patterns based on the single-crystal data, suggesting high phase purity for 1 (Figure S1 in the SI). Reaction of DyCl3·6H2O, Ni(NO3)2·6H2O, H4abtc, LiOH, and HNO3 in the mixed solvent of DMF/H2O produces yellow rodlike crystals of 1 in 68% yield. X-ray single-crystal diffraction analysis implies that 1 crystallizes in the orthorhombic space B

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180.000(4)°. The distances for Dy1III···Ni1II and Dy1III··· Dy1AIII are 3.755 and 7.510 Å, respectively. Adjacent trinuclear {NiDy2} units are connected by HCOO− groups to generate a 1D “ladder” chain with the shortest DyIII···DyIII distance of 6.742 Å (Figure 1d). Adjacent “ladders” are further linked by abtc4− ligands to give the 3D architecture (Figure 1e). Topologically,19 each trinuclear {NiDy2} unit serves as a 10connected node, while the abtc4− ligand acts as the linker, and the 3D framework of 1 can be depicted as a (4,4,10)-connected topology with the point symbol of {32·42·52}{34·412·58·621}{45· 6} (Figure 1f and Figure S2 in the SI). It is a new topology and named as “zsw3”.19 TG Analyses and in Situ Variable-Temperature PXRD. The thermal stability of 1 was evaluated by using the crystalline sample under the N2 atmosphere from 25 to 800 °C, and the thermogravimetric (TG) curve of 1 demonstrates that the skeleton is stable to at least 310 °C (Figure 2). In order to

group Ibam. The complex is anionic, with the [NH2(CH3)2]+ counterions in the crystal lattice, which is in situ decomposed from DMF molecules under solvothermal conditions, as well as the HCOO− groups.17 Each asymmetric unit comprises two DyIII ions, one NiII ion, two abtc4−ligands, two HCOO− groups, and two protonated [NH2(CH3)2]+ ions (Figure 1a). The NiII

Figure 2. TG curve of 1 on crystalline sample in the range of 25−800 °C in a N2 atmosphere. Inset: the in situ variable-temperature PXRD pattern for 1, measured on a Pt sample platform in the range of 25− 400 °C under the N2 atmosphere.

further confirm the stability of 1, the in situ variabletemperature PXRD pattern was carried out on a Pt sample platform from 25 to 400 °C (Figure 2, inset). The corresponding PXRD patterns declare that the crystalline structure of 1 remains unchanged until 310 °C, which further demonstrates the high thermal stability of 1. The high thermal stability of 1 may be mainly because of the rigid H4abtc ligand, possessing a longer organic backbone with four carboxyl groups, which could be liable to be partially or completely deprotonated to display different metal−oxygen coordination modes to enhance the thermal stability and entire rigidity of the frameworks. Magnetic Properties. Variable-temperature magnetic susceptibility measurement of 1 was measured in the range of 1.8−300 K at 1000 Oe direct-current (dc) field. The χMT value is 29.61 cm3·K·mol−1 at ambient temperature, which corresponds to the expected value of 29.34 cm3·K·mol−1 for two free DyIII ions (14.17 cm3·K·mol−1, 6H15/2, g = 4/3) and one independent NiII ion (1.0 cm3·K·mol−1, S = 1, g = 2). As the temperature decreases, χMT gradually decreases to ca. 100 K, then further drops sharply to a minimum value of 24.99 cm3·K· mol−1 at 1.8 K (Figure S3 in the SI), which could be ascribed to a combination of the depopulation of the MJ sublevels and

Figure 1. (a) Ball-and-stick representation of the asymmetric unit of 1. The coordination environments for Dy1 (b) and Ni1 (c) ions, respectively. (d) The 1D “ladder” chain. (e) The 3D framework of 1. (f) The schematic view of the (4,4,10)-connected net for “zsw3”-type topology exhibited by 1. H and protonated [NH2(CH3)2]+ ions are omitted for clarity.

ion locates in an inversion center with the position occupation of 0.25; thus, there is only one crystallographically independent DyIII ion with the position occupation of 0.50. The free program SHAPE 2.018 analyses indicate that the most ideal coordination geometry of the nine-coordinated DyIII ion (Cs) is muffin (Figure 1b and Table S1 in the SI), which is defined by seven O atoms from abtc4− ligands, and two O atoms from HCOO− groups with Dy−O distances of 2.212(3)−2.617(3) Å (2.416 Å on average). The six-coordinated NiII ion adopts octahedron (Oh) geometry with six O atoms from abtc4− ligands with Ni−O distances of 1.976(3)−2.221(2) Å (2.139 Å on average) (Figure 1c and Table S2 in the SI). Through carboxylic O atoms of abtc4− ligands, the Dy1 ion, Ni1 ion, and symmetry-operated Dy1A ion (A = 1 − x, 1 − y, z) are associated together to create a linear trimer “Hourglass”-type {NiDy2} cluster with a Dy1III−Ni1II−Dy1AIII angle of C

DOI: 10.1021/acs.inorgchem.5b02378 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry possible magnetic interactions between the metal ions.20 However, it is difficult to evaluate the coupling interactions of DyIII···NiII and DyIII···DyIII in 1, because the DyIII ion has inherently intricate magnetic characteristics, including the presence of magnetic anisotropy and spin−orbit coupling.1c The field-dependent magnetization data (M) of 1 was carried out at 2 K in the range 0−70 kOe (Figure S4 in the SI), exhibiting a dramatic increase below 10 kG, and then gradually enhance with increasing H to the maximum value of 11.75 μB at 70 kOe and 2 K, obviously smaller than the theoretical value of 22 μB for two free DyIII ions and one NiII ion, which suggests the presence of magnetic anisotropy and/or the population of low-lying excited states.21 To explore the dynamics of magnetization, the alternatingcurrent (ac) magnetic susceptibilities for 1 are collected at zero dc fields (Figure S5 in the SI). The out-of-phase (χM″) component of the susceptibility exhibits frequency dependence below ca. 6 K, associated with SMM behavior. Unfortunately, no peak maxima of the χM″ value is detected in the temperature region, which could be ascribed to the presence of fast quantum tunnelling effect (QTM).1c It is well-known that an external dc field (Hext) could effectively restrain the QTM; therefore, the ac susceptibility measurements are recorded at 2.0 K with Hext = 0−2000 Oe. Relaxation times are extracted from the obtained data, and the results suggest that an external field of 1000 Oe could suppress QTM efficiently (Figure S6 in the SI). The frequency dependences can be observed obviously in both inphase (χM′) and out-of-phase (χM″) components of the susceptibilities (Figure S7 in the SI and Figure 3a). Obviously and differing from the phenomena observed in most previously documented Ni−Ln-containing complexes,24 two well-resolved peak maxima in χM″ are observed below 3.0 K. The Cole−Cole plots exhibited two convoluted semicircular plots and reflected two relaxation processes, especially for 1.9− 3.0 K, which can be well-fitted to the generalized Debye model including two relaxation pathways (Figure 3b).22 Fitting the two relaxation processes in 1.9−11.0 K gives α1 and α2 values covering the ranges of 0.56−0.06 and 7.5 × 10−23 to 5.9 × 10−30, respectively (Table S3 in the SI). However, the corresponding plots of ln(τ) vs T−1 display obvious deviations from linearity (Figure 4), further demonstrating the multistep processes that occur for relaxation of the magnetizations. To acquire the relaxation energy barrier and pre-exponential factor, the best fitting based on the Arrhenius law21 [−ln(2πf) = ln(τ0) − (Ueff/kTp)] gives the energy barrier Ueff = 36 K with the pre-exponential factor τ0 = 3.2 × 10−6 s for the peak observed at higher frequencies (Figure S8a in the SI), and the energy barrier Ueff = 38 K with the pre-exponential factor τ0 = 6.2 × 10−6 s for the peak observed at lower frequencies (Figure S8b in the SI), respectively. In order to quantificationally evaluate the respective effects of the other possible relaxation mechanisms, that is, QTM, Raman and direct processes, eq 123 was employed to fit the overall range of temperature-dependent relaxation. τ −1 = τQ−1 + AT m + CT n + τ0−1 exp( −Ueff /kBT )

Figure 3. (a) Temperature dependence of χM″ measured at different temperatures for 1 in 1000 Oe dc field. (b) The Cole−Cole plots of 1 in 1000 Oe dc field. The solid lines are the best fits.

= 0.00941 s, C = 0.307, n = 4, the effective energy barrier Ueff = 40 K, and the pre-exponential factor τ0 = 3.2 × 10−6 s (Figure 4a). For the peak observed at lower frequencies, the successful fitting over the temperature range was gained considering the combination of direct, Raman, and Orbach processes with the best-fit parameters are as follows: A = 1.124, m = 1, C = 0.0393, n = 4, the effective energy barrier Ueff = 42 K, and the preexponential factor τ0 = 4.7 × 10−6 s (Figure 4b). All of the above magnetic parameters clearly indicate that the {NiDy2} SMM cluster has been successfully brought in 1, and the Ueff value of 1 is the second largest among all known Ni−Lncontaining SMMs,24,25 only smaller than one recent example of the discrete trinuclear {NiDy2} compound reported by Tang et al.25a However, previous reports of Ni−Ln-based SMMs are mainly discrete clusters; the 3D complex based on SMM SBUs has not been documented to date (Table S4 in the SI), to the best of our knowledge. Although there are dozens of Ni−Ln-based SMMs that have been reported, only two examples of analogous {NiLn2} cluster based SMMs have been documented, namely, {[Dy(hfac)3]2[Ni(bpca)2]}·CHCl3 (A) (Hhfac = 1,1,1,5,5,5-hexafluoroacetylacetonate and Hbpca = bis(2-pyridylcarbonyl)amine),24b and [Dy2Ni(C7H5O2)8]·(C7H6O2)2 (B) (C7H6O2 = salicylaldehyde).25a In the absence of an external field, χM″ signals are almost undetectable for A, whereas, at an applied field of 1000 Oe, ac susceptibilities exhibit a thermally activated dynamic behavior

(1)

In eq 1, the first, second, third, and last terms represent the temperature dependence of QTM, direct, Raman, and Orbach processes, respectively. For the peak observed at higher frequencies, an excellent fitting among the temperature range of 1.9−11.0 K was obtained by combining QTM, Raman, and Orbach processes with the best-fit parameters are as follows: τQ D

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more, 1 represents the first 3D Ni−Ln-HCP based on SMM SBUs. This work illustrates a useful strategy to prepare a highly stable multidimensional CP based on SMM SBUs, which not only enriches the structural and topological variety of CPs but also promises to make new avenues for the development of 3d−4f mixed multidimensional CPs based on SMM SBUs.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02378. PXRD patterns and magnetic and crystallographic data for 1 (PDF) Crystallographic data for 1 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (P.C.). *E-mail: [email protected]. Fax: (+86) 22-23502458 (W.S.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the MOST (“973 program” 2012CB821702), the NSFC (21331003, 91422302, 21421001), the MOE (IRT-13022, 13R30), and 111 project (B12015).

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REFERENCES

(1) (a) Rinehart, J. D.; Long, J. R. Chem. Sci. 2011, 2, 2078−2085. (b) Woodruff, D. N.; Winpenny, R. E. P.; Layfield, R. A. Chem. Rev. 2013, 113, 5110−5148. (c) Liu, K.; Shi, W.; Cheng, P. Coord. Chem. Rev. 2015, 289−290, 74−122. (d) Ungur, L.; Lin, S.-Y.; Tang, J.; Chibotaru, L. F. Chem. Soc. Rev. 2014, 43, 6894−6905. (2) (a) Sessoli, R.; Gatteschi, D.; Caneschi, A.; Novak, M. A. Nature 1993, 365, 141−143. (b) Sessoli, R.; Tsai, H. L.; Schake, A. R.; Wang, S.; Vincent, J. B.; Folting, K.; Gatteschi, D.; Christou, G.; Hendrickson, D. N. J. Am. Chem. Soc. 1993, 115, 1804−1816. (3) Wernsdorfer, W.; Aliaga-Alcalde, N.; Hendrickson, D. N.; Christou, G. Nature 2002, 416, 406−409. (4) Miyasaka, H.; Nakata, K.; Sugiura, K.-i.; Yamashita, M.; Clérac, R. Angew. Chem., Int. Ed. 2004, 43, 707−711. (5) (a) Jeon, I.-R.; Clerac, R. Dalton Trans. 2012, 41, 9569−9586. (b) Miyasaka, H.; Nakata, K.; Lecren, L.; Coulon, C.; Nakazawa, Y.; Fujisaki, T.; Sugiura, K.-i.; Yamashita, M.; Clérac, R. J. Am. Chem. Soc. 2006, 128, 3770−3783. (6) For example, see: (a) Milios, C. J.; Vinslava, A.; Wernsdorfer, W.; Moggach, S.; Parsons, S.; Perlepes, S. P.; Christou, G.; Brechin, E. K. J. Am. Chem. Soc. 2007, 129, 2754−2755. (b) Zadrozny, J. M.; Xiao, D. J.; Atanasov, M.; Long, G. J.; Grandjean, F.; Neese, F.; Long, J. R. Nat. Chem. 2013, 5, 577−581. (7) For example, see: (a) Ishikawa, N.; Sugita, M.; Ishikawa, T.; Koshihara, S.-y.; Kaizu, Y. J. Am. Chem. Soc. 2003, 125, 8694−8695. (b) Blagg, R. J.; Ungur, L.; Tuna, F.; Speak, J.; Comar, P.; Collison, D.; Wernsdorfer, W.; McInnes, E. J. L.; Chibotaru, L. F.; Winpenny, R. E. P. Nat. Chem. 2013, 5, 673−678. (8) For example, see: (a) Liu, J.-L.; Wu, J.-Y.; Chen, Y.-C.; Mereacre, V.; Powell, A. K.; Ungur, L.; Chibotaru, L. F.; Chen, X.-M.; Tong, M.L. Angew. Chem., Int. Ed. 2014, 53, 12966−12970. (b) Mougel, V.; Chatelain, L.; Pécaut, J.; Caciuffo, R.; Colineau, E.; Griveau, J.-C.; Mazzanti, M. Nat. Chem. 2012, 4, 1011−1017. (9) (a) Liu, T.; Zheng, H.; Kang, S.; Shiota, Y.; Hayami, S.; Mito, M.; Sato, O.; Yoshizawa, K.; Kanegawa, S.; Duan, C. Nat. Commun. 2013, 4, 2826. (b) Grancha, T.; Ferrando-Soria, J.; Castellano, M.; Julve, M.;

Figure 4. Plots of ln(τ) vs T−1 for 1 under 1000 Oe dc field and 1.9− 11.0 K: (a) for the peak observed at higher frequencies, (b) for the peak observed at lower frequencies. The red lines are the best fits. Inset: Plots of ln(τ) vs ln(T−1) for 1; the negative n values are the slopes of the lines.

with the energy barrier of 4.9 K and τ0 of 1.3 × 10−6 s. For B, ac susceptibilities show dual relaxation processes under 1500 Oe external applied field with the energy barrier of 12.2/55.2 K and τ0 of 1.34 × 10−5/5.21 × 10−8 s for low- and high-temperature dynamics of the magnetization, respectively. It is worth emphasizing that the two relaxation pathways may be derived from the single ion behavior of individual DyIII ions at the higher temperature and the weak coupling between DyIII and NiII ions at the lower temperature;1c,8a,21,25 however, the precise origin of the relaxations cannot be determined at present. We attempted to replace the NiII ion by ZnII or CdII ions to further explore the origin of magnetic relaxation. In spite of our efforts, we have not yet prepared the isostructural analogues, which may be ascribed to that the different metal ions prefer to crystallize in different crystal systems for this type of complex.

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CONCLUSIONS In conclusion, we depicted a highly thermally stable 3D NiII− DyIII HCP with a new “zsw3”-type topology built by trimer {NiDy2} SMM SBUs and H4abtc ligands, which presents excellent thermal stability, and the crystalline structure can be stable to at least 310 °C, supported by the results of TG analyses and variable-temperature PXRD patterns. FurtherE

DOI: 10.1021/acs.inorgchem.5b02378 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.5b02378 Inorg. Chem. XXXX, XXX, XXX−XXX