Magnetic Relaxation Dynamics of a Centrosymmetric Dy2 Single

Article pubs.acs.org/IC

Magnetic Relaxation Dynamics of a Centrosymmetric Dy2 SingleMolecule Magnet Triggered by Magnetic-Site Dilution and External Magnetic Field Hui-Ming Dong,†,‡ Hai-Yan Li,‡ Yi-Quan Zhang,*,§ En-Cui Yang,*,‡ and Xiao-Jun Zhao*,†,‡ †

Department of Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, Nankai University, Tianjin 300071, People’s Republic of China ‡ College of Chemistry, Key Laboratory of Inorganic−Organic Hybrid Functional Material Chemistry, Ministry of Education, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Tianjin Normal University, Tianjin 300387, People’s Republic of China § Jiangsu Key Laboratory for NSLSCS, School of Physical Science and Technology, Nanjing Normal University, Nanjing 210023, People’s Republic of China S Supporting Information *

ABSTRACT: A centrosymmetric Dy2 single-molecule magnet (SMM) and its doped diamagnetic yttrium analogues, Dy0.19Y1.81 and Dy0.10Y1.90, were solvothermally synthesized to investigate the effects of intramolecular exchange coupling and quantum tunneling of magnetization (QTM) on the magnetic relaxation dynamics. Constructed from two hula-hoop-like DyIII ions and a pair of phenoxido groups, the antiferromagnetically coupled Dy2 exhibits a thermal-activated zero-field effective energy barrier (Ueff) of 277.7 K and negligible hysteresis loop at 2.0 K. The doping of a diamagnetic YIII matrix with 90.5% and 95.0% molar ratios reveals the single-ion origin of the Orbach channel, increases the relaxation time by partially quenching the QTM process, and induces an open hysteresis loop until 5.0 K. In contrast, an optimal dc field of 1.0 kOe improves the barrier height up to 290.1 K through complete elimination of the QTM and delays the relaxation time of the direct relaxation pathway. More interestingly, the collaborative dual effects of magnetic-site dilution and external magnetic field make the effective energy barrier and relaxation time increase 8.1% and 49 times, respectively. Thus, the overall magnetization dynamics of the Dy2 system systematically elaborate the inherent interplay of the QTM and Orbach processes on the effective energy barrier, highlighting the vital role of the relaxation time on the coercive hysteresis loop.

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K,6,7 respectively. However, it is still rare to observe coercive hysteresis loops at high temperatures, although high Ueff values have been achieved in several magnetically isolated systems by a coordination symmetry approach.8−10 The quick quantum tunneling of the magnetization (QTM) that caused by dipolar interaction, transverse anisotropy, and/or hyperfine interaction can significantly decrease the thermally activated barrier height and manipulate the relaxation time of the temperaturedependent relaxation pathway. Therefore, it is necessary to

INTRODUCTION

Single-molecule magnets (SMMs) with large effective energy barrier (Ueff) and high blocking temperature (TB) have recently attracted unprecedented interest due to their intriguing applications in quantum information processing, molecular spintronics, and ultrahigh-density information storage.1−3 Owing to strong single-ion anisotropy, fine-tuning ligand-field effects, and small but important superexchange interactions, dysprosium(III)-based SMMs (Dy-SMMs) with various nuclearities and topologies have made rapid progress toward the enhancement of the magnetic performance.4−11 The Ueff and TB values have been greatly improved up to 1815 and 20 © 2017 American Chemical Society

Received: December 24, 2016 Published: April 28, 2017 5611

DOI: 10.1021/acs.inorgchem.6b03089 Inorg. Chem. 2017, 56, 5611−5622

Article

Inorganic Chemistry Table 1. Crystal and Structure Refinement Data for Dy2, Y2, and Two Magnetic-Site Diluted Samples empirical formula fw cryst size (mm) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z, Dc (g cm−3) h/k/l F(000) μ (mm−1) no. of collected/unique rflns Rint no. of data/restraints/params R1,a wR2b (I > 2σ(I)) R1, wR2 (all data) GOF on F2 Δρmax, Δρmin (e Å−3) a

Dy2

Dy0.19Y1.81

Dy0.10Y1.90

Y2

C50H40Dy2N10O24 1489.92 0.22 × 0.21 × 0.17 triclinic P1̅ 9.614(5) 10.347(5) 13.541(6) 92.851(11) 102.116(12) 90.169(12) 1315.2(11) 1, 1.881 −12, 8/−11, 12/−12, 16 734 2.918 8570/5413 0.0884 5413/0/388 0.0995, 0.2332 0.1176, 0.2461 1.039 4.717, − 5.097

C50H40Dy0.19Y1.81N10O24 1356.72 0.22 × 0.21 × 0.18 triclinic P1̅ 9.599(8) 10.419(10) 13.609(12) 86.90(2) 78.20(2) 89.57(2) 1330(2) 1, 1.693 −10, 12/−12, 13/−17, 15 685 2.327 8795/5505 0.0836 5505/0/388 0.0771, 0.1282 0.1585, 0.1456 1.010 0.616, − 0.802

C50H40Dy0.10Y1.90N10O24 1350.10 0.22 × 0.21 × 0.18 triclinic P1̅ 9.597(9) 10.416(10) 13.600(12) 86.89(2) 78.20(2) 89.58(2) 1329(2) 1, 1.687 −10, 12/−13, 13 /−17, 15 683 2.302 9622/6252 0.0865 6252/0/388 0.0763, 0.1237 0.1852, 0.1553 1.006 0.551, − 1.004

C50H40Y2N10O24 1342.74 0.25 × 0.22 × 0.20 triclinic P1̅ 9.491(5) 10.348(5) 13.383(6) 86.609(4) 78.902(4) 89.881(4) 1287.6(11) 1, 1.732 −11, 9/−12, 12/−15, 15 680 3.895 8481/4590 0.0576 4590/0/391 0.0413, 0.0898 0.0518, 0.0957 0.995 1.16, − 0.55

R1 = ∑(||Fo| − |Fc||)/∑|Fo|. bwR2 = [∑w(|Fo|2 − |Fc|2)2/∑w(Fo2)2]1/2.

the well-resolved temperature-/frequency-dependent ac responses of the Dy2 provide good opportunities to investigate the effects of the intradimer exchange coupling and quantum tunneling on the magnetic dynamics. Herein, structure, magnetization dynamics, and theoretical computations were reported to correlate the energy barrier for magnetization reversal with hysteresis loop temperature.

fully explore the magnetization dynamics of the SMMs to properly elucidate the magnetostructural relationships of the Dy-SMMs. The magnetic-site dilution strategy is considered to be one of the most powerful methods to deeply understand the origin of the slow relaxations.12−23 Because a dysprosium(III) ion in a diluted sample can retain its coordination environment, the dipolar spin−spin interactions and intermetallic exchange coupling that always facilitate the tunneling process can be weakened by modulating the concentration of the diamagnetic dopant ions. To date, the magnetization dynamics of some typical Dy-SMMs have been subsequently studied by replacing the dysprosium(III) site by diamagnetic YIII and/or less anisotropic YbIII ions. These Dy-SMMs include discrete monometallic Dy,5,13,14 asymmetric and symmetric binuclear Dy2,15−17 polymetallic Dy4, and Dy5 entities.18 All of these investigations highlight the significant effects of intramolecular superexchange interactions on the anisotropy energy barrier, revealing the origin of thermally activated slow relaxations.16,24,25 To continue the research on magnetic dynamics, herein, a new centrosymmetric Dy 2 SMM was constructed by solvothermal self-assembly of 2-hydroxyimino-N′-[(2-hydroxy3-methoxyphenyl)methylidene]propanohydrazone (H3L), mnitrobenzoic acid (Hnb), and DyIII ion. The trifunctional vanillin−hydrazone−oxime ligand can play effective bridging roles during the constructions of both transition-metal- and lanthanide-based SMMs.26 By expanded bridging coordination of the oxime group, hydrazone, and phenolic oxygen atoms, a great variety of reaction-condition-dependent products ranging from mononuclear to dinuclear, tetranuclear, and hexanuclear motifs have been successively obtained.26 The H2L-based Dy2 SMM with two antiferromagnetically coupled DyIII ions displays a relatively high Ueff value of 277.7 K under zero dc field and with a negligible hysteresis loop. More interestingly,

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EXPERIMENTAL SECTION

Materials and Instruments. All raw materials were commercially purchased from either Acros or Tianjin Chemical Reagent Factory and used as received without further purification. H3L was prepared by a slightly modified method.27 Elemental analyses for C, H, and N were carried out with a CE-440 (Leeman Laboratories) analyzer. Fourier transform (FT) IR spectra (KBr pellets) were taken on an Avatar-370 (Nicolet) spectrometer in the range 4000−400 cm−1. Powder X-ray diffraction (PXRD) patterns were obtained from a Bruker D8 ADVANCE diffractometer at 40 kV and 40 mA for Cu Kα radiation (λ = 1.5406 Å), with a scan speed of 0.1 s/step and a step size of 0.01° in 2θ. The simulated PXRD patterns were calculated using singlecrystal X-ray diffraction data and processed by the free Mercury v1.4 program provided by the Cambridge Crystallographic Data Center. Magnetic susceptibilities were acquired on Quantum Design (SQUID) MPMS-XL-7 magnetometers with crystalline samples, in which the phase purity of the samples was determined by PXRD experiments. The diamagnetic corrections were calculated using Pascal’s constants, and an experimental correction for the sample holder was also applied. Synthesis of [Dy2(nb)4(H2L)2] (Dy2). Dy(NO3)2·6H2O (91.4 mg, 0.2 mmol), Hnb (33.4 mg, 0.2 mmol), H3L (51.2 mg, 0.2 mmol), and triethylamine (20.2 mg, 0.2 mmol) were dissolved in a mixed CH3CN/CH3OH solution (10.0 mL, v/v 1/1). The resulting mixture was then sealed in a Parr Teflon-lined stainless steel vessel (23.0 mL) and heated at 80 °C for 12 h under autogenous pressure. After the mixture was cooled to room temperature at a rate of 1.2 °C h−1, yellow block-shaped crystals suitable for X-ray analysis were obtained directly, washed with cold methanol, and dried in air. Yield: 50% based on Hnb. Anal. Calcd for C50H40Dy2N10O24: C, 40.31; H, 2.71; N, 9.40. Found: C, 40.33; H, 2.69; N, 9.41. FT-IR (KBr pellet, cm−1): 3387 (br), 1598 5612


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Inorganic Chemistry

tensors, local magnetic axis, coupling constant Jdipole for magnetic dipole−dipole interaction, and so on). Then, the exchange interaction between the magnetic centers was considered within the Lines model. 34 The exchange Hamiltonian operator is Ĥ exch = −JexchŜDy1ŜDy1A, and Ŝ = 1/2 is the ground pseudospin on the dysprosium(III) site. The Lines model is effective and has been used widely in the research field of f-element SMMs.35

(s), 1532(s), 1458 (s), 1438 (s), 1407 (s), 1377 (s),1350 (s), 1306 (w), 1276 (w), 1246 (w), 1222 (m), 1165 (w), 1064 (m), 950 (w), 896 (w), 849 (w), 785 (w), 719 (m), 651 (w), 581 (w), 522 (w), 423 (w). Synthesis of [Y2(nb)4(H2L)2] (Y2). Yellow block-shaped crystals of Y2 were generated by adopting procedures similar to those for Dy2 except that Dy(NO3)2·6H2O was replaced by Y(NO3)2·6H2O (76.6 mg, 0.2 mmol). Yield: 50% based on Hnb. Anal. Calcd for C50H40Y2N10O24: C, 44.73; H, 3.00; N, 10.43. Found: C, 44.71; H, 3.02; N, 10.42. FT-IR (KBr pellet, cm−1): 3354 (br), 1599 (s), 1533 (s), 1456 (s), 1437 (s), 1405 (s), 1374 (s), 1348 (s), 1305 (w), 1274 (w), 1245 (w), 1220 (m), 1163 (w), 1062 (m), 948 (w), 895 (w), 846 (w), 784 (w), 718 (m), 650 (w), 578 (w), 519 (w), 422 (w). Syntheses of [Dy 0.19 Y 1.81 (nb) 4 (H 2 L) 2 ] (Dy 0.19 Y 1.81 ) and [Dy0.10Y1.90(nb)4(H2L)2] (Dy0.10Y1.90). Two magnetic-site diluted samples with different doping levels were respectively obtained with the same procedures as for Dy2 except that Dy(NO3)2·6H2O was replaced by a mixture of Dy(NO3)2·6H2O and Y(NO3)2·6H2O in molar ratios of 1:9 for Dy0.19Y1.81 and 1:19 for Dy0.10Y1.90. Anal. Calcd for C50H40Dy0.19Y1.81N10O24: C, 44.26; H, 2.97; N, 10.32. Found: C, 44.29; H, 3.01; N, 10.36. Calcd for C50H40Dy0.10Y1.90N10O24: C, 44.48; H, 2.99; N, 10.37. Found: C, 44.46; H, 2.96; N, 10.41. The dysprosium(III) and yttrium(III) contents in the final crystalline products were 9.64% and 90.36% as well as 4.99% and 95.01% determined by energy dispersive spectroscope (EDS) of field-emission scanning electron microscope (Table S1 in the Supporting Information). X-ray Single-Crystal Data Collection and Structure Determination. Diffraction intensities of Dy2, Dy0.19Y1.81, and Dy0.10Y1.90 were collected on a Bruker APEX-II QUAZAR diffractometer equipped with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) by using the φ−ω scan technique at 296 K. For Y2, measurements were carried out on a SuperNova, Dual, Cu at zero, AtlasS2 diffractometer equipped with mirror-monochromated Cu Kα radiation (λ = 1.54184 Å) at 150 K. There was no evidence of crystal decay during data collection. Semiempirical multiscan absorption corrections were applied by SADABS (for Dy2, Dy0.19Y1.81, and Dy0.10Y1.90) and SCALE3 ABSPACK (for Y2).28,29 The programs SAINT (for Dy2, Dy0.19Y1.81, and Dy0.10Y1.90) and CrysAlisPro (for Y2) were used for integration of the diffraction profiles.30,31 The structures were solved by direct methods and refined with the fullmatrix least-squares technique using the SHELXS-97 and SHELXL-97 programs (for Dy2, Dy0.19Y1.81, and Dy0.10Y1.90) and the ShelXT and ShelXL software (for Y2).32 The non-H atoms were located by difference Fourier maps and subjected to anisotropic refinement. Hydrogen atoms were added according to theoretical models. A summary of crystallographic data for the four complexes is given in Table 1. Ab Initio Computations. Complete-active-space self-consistent field (CASSCF) calculations were carried out for the centrosymmetric Dy2 molecule with the MOLCAS 8.0 program package.33 The initial geometry for theoretical calculations was extracted from the singlecrystal X-ray structural determinations. During the calculation, one DyIII ion was kept in the experimentally determined position and the other was replaced by a diamagnetic LuIII ion. The basis sets for all atoms are atomic natural orbitals from the MOLCAS ANO-RCC library: ANO-RCC-VTZP for DyIII ion; VTZ for close O and N; VDZ for distant atoms. The calculations employed the second order Douglas−Kroll−Hess Hamiltonian, where scalar relativistic contractions were taken into account in the basis set, and the spin−orbit couplings were handled separately in the restricted active space state interaction (RASSI-SO) procedure. For the fragment of the dysprosium(III) ion, active electrons in 7 active spaces include all f electrons (CAS(9 in 7)) in the CASSCF calculation. We have mixed the maximum number of spin-free state which was possible with our hardware (all from 21 sextets, 128 from 224 quadruplets, 130 from 490 doublets for the DyIII fragment). Two steps were performed to obtain the intermetallic exchange interaction of Dy2 sample. First, the dysprosium(III) fragment was calculated using the CASSCF method to obtain the corresponding magnetic properties (spin−orbit energy, g

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RESULTS AND DISCUSSION Syntheses, IR Spectra, and PXRD Patterns. Lanthanidebased metal complexes constructed from different rare-earthmetal ions are generally isomorphous. This is one of the fundamentally prerequisite conditions for the magnetic dynamics investigation by magnetic-site dilution methods. Indeed, Dy2 and Y2 with anisotropic DyIII and diamagnetic YIII ions were crystallographically isostructural and were solvothermally generated in satisfactory yields. Single crystals of Dy0.19Y1.81 and Dy0.10Y1.90 were successfully obtained, in which the final contents of the DyIII ion were almost consistent with the values of 10% and 5.0% employed in the synthesis. Structural consistency and phase purity of the bulky crystalline samples of Dy2, Dy0.19Y1.81, Dy0.10Y1.90, and Y2 have been further evidenced by the well-matched experimental and computer-simulated PXRD patterns (Figure S1 in the Supporting Information). In the IR spectra, the strong and broad band located at 3370 ± 17 cm−1 should be ascribed to the stretching vibrations of O−H and/or N−H belonging to oximate and hydrazone moieties of the H2L− ligand. The absence of a strong absorption at 1675 cm−1 indicates the deprotonation of the Hnb ligand. Intense bands at 1599 ± 1, 1533 ± 1, and 1457 ± 1 cm−1 are associated with the stretching vibrations of CO and CN groups from carboxylate of the nb− and hydrazone of the H2L− ligand. Weak and moderate absorptions at 1164 ± 1 and 1063 ± 1 cm−1 result from the characteristic stretching vibrations of N−Nhydrazone and N− Ooximate groups.27 Crystal Structures. All four complexes (Dy2, Dy0.19Y1.81, Dy0.10Y1.90, and Y2) are crystallographically isostructural, and they all crystallize in the triclinic P1̅ space group with Z = 1 in each asymmetric unit (Table 1). It should be mentioned that the slightly different ionic radii of DyIII and YIII ions make the unit cell volume and Ln−O/Ln−N bond lengths of Dy0.19Y1.81 and Dy0.10Y1.90 between those of the concentrated Dy2 and Y2 entities (Table 1 and Table S2 in the Supporting Information). Due to their analogous motif, only the crystal structure of Dy2 is described herein as representative. As shown in Figure 1a, Dy2 possesses a centrosymmetric dinuclear structure with two octacoordinate DyIII ions aggregated by a pair of phenoxido groups from two H2L− ligands. The asymmetric unit contains one DyIII ion, one monodeprotonated H2L−, and two monodeprotonated nb− anions in terminally monodentate and bidentate chelating modes. The DyIII site is surrounded by one N and seven O atoms. The N and four O donors are from one H2L−, and the remaining three O atoms belong to the carboxylate groups of two nb− ligands. The coordination geometry of the DyIII ion was evaluated by continuous shape measurements via the SHAPE software.36 The calculated results reveal that the geometry of DyIII is closer to a biaugmented trigonal prism with a CShM value of 2.214 (Figure 1b and Table S3 in the Supporting Information). The eight-coordinate DyIII site can also be described as a hula-hoop-like coordination geometry with the cyclic ring defined by N1, O3, O1A, O2A, and O2 atoms from two H2L− anions (Figure 1b). One 5613


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Inorganic Chemistry

dinuclear entity (Figure 1a) with intramolecular DyIII···DyIII separation and Dy−O−Dy angle (∠DyODy) of 3.6997(13) Å and 105.245(20)°, respectively. The dihedral angle of the central Dy2O2 unit (θDyOODy) is 180.00°, which is consistent with most of the known phenoxido-bridged dinuclear dysprosium SMMs (Table 2). Furthermore, the summarized geometric parameters of all the known phenoxido-bridged Dy2 complexes indicate that three variables, rDy−O, rDy···Dy, and ∠DyODy, are more important than θDyOODy, which can significantly control the exchange coupling of two adjacent DyIII ions (Table 2).37−39,41 The individual Dy2 molecules are periodically arranged through weak intermolecular N−H···O hydrogen-bonding interactions between the hydrazone moiety of H2L− and the carboxylate group of the nb− ligand, leading to a one-dimensional supramolecular array with the nearest intermolecular DyIII···DyIII separation of 7.2432(35) Å responsible for negligible intermolecular magnetic interactions (Figure S3 and Table S4 in the Supporting Information). Dc Magnetization. Variable-temperature (300−2.0 K) direct current (dc) magnetic susceptibilities were measured on the polycrystalline samples of Dy2, Dy0.19Y1.81, and Dy0.10Y1.90 under 1.0 kOe. As shown in Figure 2a, the χMT value for each Dy2 molecule is 28.00 cm3 K mol−1 at 300 K, close to the expected value (28.34 cm3 K mol−1) for two magnetically uncoupled DyIII ions in a free-ion approximation (6H15/2 and g = 4/3). Upon cooling, the χMT product exhibits a gradual decrease between 300 and 100 K and a more rapid decrease below 50.0 K, reaching a minimum value of 4.80 cm3 K mol−1 at 2.0 K. The rapid decrease in χMT product below 50.0 K is attributed to the thermal depopulation of the excited Stark sublevels of the dysprosium(III) ion and the intramolecular antiferromagnetic interactions.5 To quantitatively describe the strength of the intermetallic exchange interaction, a suitable magnetic model was considered by checking the anisotropy of the dysprosium(III) ion. Ab initio CASSCF calculations reveal that the anisotropy axis of the DyIII ion in the ground Kramers doublets of Dy2 goes almost along the Dy1−O7 vector (Figure 1c), and the angle of the anisotropy axis with the shortest Dy1−O7 bond is about 5o. The gz tensor of the dysprosium(III) ion in the ground state of Dy2 sample is 19.827 as calculated by CASSCF methods, which is obviously greater than those of the gx and gy components (gx = 0.004 and gy = 0.005). Therefore, the intramolecular DyIII···DyIII exchange interaction can be approximately regarded as an Ising type. The Lines model can be used to evaluate the exchange coupling constant (Jexch) between the two centrosymmetric DyIII ions.34,35 A least-squares fitting of the experimental magnetic susceptibility to the exchange Hamiltonian operator through the fit procedure affords Jexch = −2.75 ± 0.78 cm−1, Jdipolar = −3.12 ± 0.56 cm−1, and Jtotal = −5.87 ± 0.95 cm−1, in which the total coupling constant Jtotal is the sum of dipolar (Jdipolar) and exchange (Jexch) interactions. Obviously, the magnetic dipolar interaction in the Dy2 sample is approximately comparable with that of the exchange contribution. Careful comparisons of the bridging structural parameters of these analogous {Dy2O2} cores (Table 2) reveal that the type (ferromagnetic coupling vs antiferromagnetic interaction) and strength (−8.38 < J < 0.52) of the intramolecular exchange coupling are highly sensitive to the DyIII···DyIII and Dy−O distances as well as the ∠DyODy angle, rather than the dihedral angle of the {Dy2O2} units. Slight variations in these values can essentially regulate the overlap extent of the magnetic orbitals of the dysprosium(III) ions, which can sometimes reverse the antiferromagnetic

Figure 1. (a) Centrosymmetric dinuclear structure for Dy2 (hydrogen atoms omitted for clarity; symmetry code A 1 − x, 1 − y, 1 − z). (b) Local coordination polyhedron of the DyIII ion. (c) CASSCF computed orientation of the magnetic axis for the ground Kramers doublet of Dy2.

monodentate (O7) and one bidentate chelating carboxylate (O5 and O6) from two unique nb− anions are above and below the hula-hoop ring, completing the coordination sphere of the eight-coordinate DyIII ion. The axial Dy1−O7 distance (2.229(9) Å) is the shortest among all the Dy−O and Dy−N bonds (2.229(9)−2.470(9) Å, Table S2). The angle between the Dy1−O7 vector and the least-squares cyclic plane is 73°. Previous investigations demonstrated that the hula-hoop configuration favors persisting axiality of the DyIII ion37−40 and is expected to significantly affect the intramolecular magnetic dipole−dipole interactions. The H2L− anion with a deprotonated phenolic hydroxy group in Dy2 provides its four donors (Omethoxy, Ophenoxido, Nhydrazone, and Ohydrazone) to aggregate two DyIII ions through a μ2-η1:η2:η1:η1 coordination mode (Figure S2 in the Supporting Information). Two centrosymmetric DyIII ions are bridged by a pair of μOphenoxido atoms from two separate H2L− ligands, generating a 5614


38

9, N2O7 9, NO8 8, NO7 9, NO8 9, N2O7 8, N2O6 8, N2O6 8, N2O6

[Dy2(μ2-anthc)4(anthc)2(L5)2]45

[Dy2(H3L6)2(PhCOO)4]·4H2O55

[Dy2(dbm)4(OQ)2(CH3OH)2]56

[Dy2(H2L7)2(μ-piv)2(piv)2]·2CHCl357


[Dy2(bfac)4(L9)2]·C7H1658

[Dy2(tfac)4(L10)2]58

[Dy2(hfac)4(L11)2]58

8, N2O6

[Dy2(H2O)2(ovph)2(NO3)2]40

9, N2O7

8, N3O5

[Dy2(valdien)2(NO3)2]47


8, NO7

[Dy2(CH3OH)2(HL2)2(PhCOO)2]39

8, NO7

6, O3Cl3

[Dy2(Mq)4Cl6](EtOH)252

[Dy2(hmi)2(NO3)2(MeOH)2]54

8, N2O6; 7, N2O3Cl2

[Dy2(ovph)2Cl2(MeOH)3]•MeCN37

8, NO7

8, N2O6; 7, N2O3Cl2

[Dy2(HL1)2Cl2(H2O)3]·2H2O·MeCN46

[Dy2(L3)2(C2H5OH)2(NO3)2]•0.5C5H5N53

8, NO7

8, N2O6

CN, donors

[Dy2(nb)4(H2L)2]this work

[Dy2(a’povh)2(OAc)2(DMF)2]

complex

5615

dodecahedral

dodecahedral

dodecahedral

monocapped square antiprism

monocapped squareantiprism

square antiprism

tricapped trigonal prism



dodecahedral

dodecahedral

dodecahedral

dodecahedral

dodecahedral

octahedral

hula-hoop pentagonal bipyramidal

hula-hoop pentagonal bipyramidal

biaugmented trigonal prism

dodecahedral

confign 2.314(4) 2.398(4) 2.287(9) 2.368(1) 2.342(8) 2.366(7) 2.351(8) 2.359(7) 2.322(3) 2.340(3) 2.334(3) 2.335(3) 2.300(3) 2.361(3) 2.261(1) 2.295(2) 2.317(7) 2.334(7) 2.319(4) 2.348(4) 2.314(5) 2.339(6) 2.317(5) 2.330(5) 2.311(3) 2.371(3) 2.294(2) 2.669(2) 2.287(3) 2.606(3) 2.341(1) 2.421(1) 2.361(2) 2.368(3) 2.305(3) 2.337(3) 2.296(2) 2.635(2) 2.303(3) 2.401(3) 2.326(7) 2.417(6) 2.289(2)

rDy−O (Å)

3.7633

3.8800

3.8326

3.9224

3.633

3.908

3.695

3.9176

3.9490

3.750

3.8024

3.8258

3.768

3.769

3.836

3.8644

3.9557

3.6997

3.6768

rDy···Dy (Å)

Table 2. Structural and Magnetic Parameters for the Reported Phenoxido-Bridged Dy2 Complexes

107.57

110.1

108.88

105.18

103.02

111.45

101.78

106.20

105.18

106.41

109.9

109.5

110.12

108.22

111.67

110.80

112.3

111.5

114.6

105.25

102.62

∠DyODy (deg)

180.00

179.84

180.00

180.00

180.00

180.00

180.00

180.00

180.00

180.00

169.48

180.00

180.00

180.00

180.00

173.74

177.97

180.00

180.00

θDyOODy (deg)

AF

AF

AF

F/−0.75, 2.67

AF

AF

AF

F/−1.25, 3.21

F/−0.50, 2.78

F

F

6.77

19.83

25.65

8.96 35.51 31.6

40.01

42.7

49.4

51.2

56

66.7

69

76

AF/−0.21, −5.25 F

94

102.4

198

150

F

AF

F/0.52, 5.36

103

204

277.7

AF/−2.75 ± 0.78, −3.12 ± 0.56 F

322.1

Ueff (K)

AF/−8.38, −2.65

magnetic interaction/Jexch, Jdipolar (cm−1)

Inorganic Chemistry Article


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Inorganic Chemistry

2.375(2)

complex

Table 2. continued

CN, donors

confign

rDy−O (Å)

rDy···Dy (Å)

∠DyODy (deg)

θDyOODy (deg)

magnetic interaction/Jexch, Jdipolar (cm−1)

Ueff (K)

coupling to ferromagnetic interaction with different coupling constants. In addition to the geometry distortion, the electronic structure of the donors tuned by the ligand field should be considered during the discussions on the magnetic dipolar interactions. The χMT products for the diluted samples of Dy0.19Y1.81 and Dy0.10Y1.90 are 2.675 and 1.408 cm3 K mol−1 at 300 K, compatible with those of a free dysprosium(III) ion multiplied by the doping ratio (14.17 × 2 × 9.5% = 2.692 cm3 K mol−1 and 14.17 × 2 × 5.0% = 1.417 cm3 K mol−1). With a lowering of the temperature, they slowly decrease to 2.111 (for Dy0.19Y1.81) and 1.186 cm3 K mol−1 (for Dy0.10Y1.90) at 2.0 K, implying that the intramolecular antiferromagnetic interaction is seriously destroyed by the doping of the diamagnetic YIII matrix. On the other hand, the intramolecular antiferromagnetic coupling of the Dy2 entity can also be evidenced by the appearance of a peak at 3.5 K on the plot of χM versus T (Figure 2a, inset).38 However, no apparent peak is observed on the plots of χM versus T for the two diluted samples due to the absence of the intradimer antiferromagnetic interactions. The isothermal magnetization of Dy2, plotted as M versus H (Figure 2b), measured at 2.0 K shows a relatively rapid increase at fields lower than 20.0 kOe and a very slow linear increase to reach a value of 13.33 Nβ at the maximum applied field of 70 kOe. Dy0.19Y1.81 and Dy0.10Y1.90 exhibit an M−H trend similar to that of Dy2 at H < 20 kOe. The magnetizations of the diluted systems are almost saturated (1.10 and 0.53 Nβ for Dy0.19Y1.81 and Dy0.10Y1.90) once the magnetic field exceeds 20 kOe, hinting at the absence of negligible intramolecular magnetic interactions. The magnetizations of Dy2, Dy0.19Y1.81, and Dy0.10Y1.90 at 70 kOe are far from the theoretically saturated values (20.0, 3.8, and 2.0 Nβ) anticipated for their respective magnetically independent DyIII ions with an S = 5/2 ground state. The difference is due to the fact that depopulation of the Stark levels of the DyIII 6H15/2 ground state under the ligand field perturbation produces a much smaller effective spin. Magnetization Dynamics. To explore the effects of the intramolecular magnetic interaction and QTM on the magnetic dynamics, ac susceptibility measurements for Dy2, Dy0.19Y1.81, and Dy0.10Y1.90 were respectively carried out in the temperature range of 2.0−17.5 K under different external magnetic fields (0, 500, 1000, and 1500 Oe). In the absence of a dc field, both the in-phase (χ′) and out-of-phase (χ″) signals of the ac susceptibility of Dy2 feature strong frequency-dependent phenomena (Figure 3 and Figure S4 in the Supporting Information), suggesting slow magnetic relaxation behavior typical for SMM properties. Above 4.0 K, the peak maximum of the χ″ component exhibits a gradual shift toward the lowfrequency region as the temperature is decreased. The peak maxima of the χ″ signal are respectively found at 4.0 and 17.0 K for oscillating fields of 1.2 and 1380 Hz (Figure 3), suggesting that a thermally activated Orbach process of Dy2 predominates between 4.0 and 17.0 K. The strong temperature-dependent ac responses probably originate from the large magnetic anisotropy of the DyIII ion achieved by the designed axial ligand field. Below 3.0 K, the χ″ signals reach an almost constant value of 1.0 Hz, indicative of the tunnelling relaxation process of the magnetization. These temperature-involved ac responses reveal a crossover from a thermally activated Orbach mechanism that is predominant at high temperature to a QTM process operating mainly at low temperature. Cole−Cole plots of χ″ versus χ′ show an evolution from asymmetric arcs to semicircular profiles between 4.0 and 17.5 K 5616


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Figure 2. (a) Temperature dependence of χMT and χM (inset) under 1.0 kOe for Dy2, Dy0.19Y1.81, and Dy0.10Y1.90. (b) Field-dependent magnetizations for Dy2, Dy0.19Y1.81, and Dy0.10Y1.90 measured at 2.0 K.

Figure 3. Frequency dependence of χ″ of the ac susceptibility (left) and plots of ln τ versus 1/T for Dy2, Dy0.19Y1.81, and Dy0.10Y1.90 measured under zero dc field (right; black solid line is the best fitting to the multiple relaxation process; blue, purple, and green solid lines represent the best fitting to the Arrhenius law, QTM, and Roman relaxation processes, respectively).

pathways) and/or calculated from ln τ = 2πf (for the QTM channel).

(Figure S5 in the Supporting Information). These curves obey a generalized Debye model well, affording magnetizationrelaxation time (τ) and distribution of relaxation times (α).42 The α values vary within a range of 0.08−0.12 (Table S5 in the Supporting Information), indicating that the relaxation occurs through a single process between 4.0 and 17.5 K. Magnetic dynamics related to the magnetization reversal in real systems are much more complicated and are highly temperature dependent due to the spin−lattice interactions.43 Acting as one of significant parameters involved in the magnetization dynamics, the relaxation time (τ) of the multiple relaxation process is made up of Orbach (τ0−1 exp(−Ueff/kBT)), Roman (CTn), direct (ATm), and quantum tunneling (τQTM) pathways (eq 1),44 which can be extracted from the fitting of the frequency-dependent data (for temperature-dependent

τ −1 = τQTM −1 + AT m + CT n + τ0−1 exp( −Ueff /kBT ) (1)

The plot of ln τ versus 1/T of Dy2 exhibits linear dependence above 14.0 K and exponential dependence between 13.0 and 8.0 K and then starts to be temperature independent below 3.0 K (Figure 3). The characters of the relaxation times originate from typical transitions from the thermally activated Orbach pathway to the Roman channel and to a quantum tunneling process. Neglecting the direct relaxation process under zero dc field, fitting of the ln τ versus 1/T curve to eq 1 over the entire temperature range yields the parameters τQTM = 0.16 s, C = 6.51 × 10−4 s−1 K−5,11 n = 5.11, and Ueff/k = 277.7 K with τ0 = 5617


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Inorganic Chemistry 1.05 × 10−11 s. Notably, the considerations of both the acoustic and optical phonons in magnetic dynamics cause the obtained n value deviation from the rational value of the Kramers ion (n = 9). The experimental Ueff/k for the thermally activated Orbach process of Dy2 is comparable with the energy separation (329.5 K) between the ground and first excited states calculated by the ab initio CASSCF method (Table S6 in the Supporting Information). Moreover, it is also consistent with most of the Dy2 SMMs aggregated by carboxylato,45 alkoxido,37,38,46 sulfur,9 hydroxyl,14 and phenoxido mediators.41,47 Comparisons of these barrier heights of the known dinuclear dysprosium molecules with hula-hoop-like DyIII configurations reveal that the transverse magnetic anisotropy becomes a more important factor directing the energy barrier in comparison to the gz value and exchange coupling strength and types.38,45,47 The transverse magnetic anisotropy is closely associated with the distortions of the hula-hoop-like DyIII configuration. The τ0 value of the Dy2 molecule is comparable with those of the known SMMs (10−6−10−11 s). The relaxation time for the QTM pathway is 160 ms below 3.0 K, which is too short to induce an open hysteresis loop even down to 2.0 K (Figure 4).

comparison with that of Dy2, the Ueff/k values of Dy0.19Y1.81 and Dy0.10Y1.90 are increased by 3.8 and 7.3 K, meaning that the thermally activated Orbach process of Dy2 arises primarily from the single-ion anisotropy.16 Thus, the contribution of the exchange interaction to Ueff is negligible for the present Dy2 system, which is quite different from the case in previous investigations.11,20,21,41,47 Since the barrier height depends only on the single molecule, the fits of the relaxation time for the two diluted systems were performed again by fixing the parameters of the Orbach process (Ueff/k = 277.7 K and τ0 = 1.05 × 10−11 s).48,49 The resulting values are τQTM = 0.31 s, C = 1.13 × 10−3 s−1 K−4.91, and n = 4.91 for Dy0.19Y1.81 as well as τQTM = 0.51 s, C = 9.72 × 10−4 s−1K−4.95, and n = 4.95 for Dy0.10Y1.90. It can be seen that the relaxation time of the diluted sample for the QTM pathway is almost 3 times longer than that of the parent Dy2, which is enhanced from 160 ms (for Dy2) to 310 ms (for Dy0.19Y1.81) and 510 ms (for Dy0.10Y1.90). Such a long relaxation time is significantly crucial for information storage applications. More importantly, the delayed relaxation times make Dy0.19Y1.81 and Dy0.10Y1.90 show butterfly-shaped hysteresis loops at 2.0 K (Figure 4), which can persist to 5.0 K (Figure S8 in the Supporting Information). Field-cooled (FC) and zero-field-cooled (ZFC) magnetic susceptibilities also display divergences at 3.9 and 4.2 K for Dy0.19Y1.81 and Dy0.10Y1.90 (Figure S9 in the Supporting Information) indicative of the magnetization blocking. At the decreasing temperature and an increasing field sweep rate, the diluted systems display widening steps of butterfly-shaped loops consistent with other reported SMMs arising from the occurrence of QTM.5 The coercive fields of Dy0.19Y1.81 and Dy0.10Y1.90 samples are 70 and 210 Oe at a sweep rate of 200 Oe s−1 and 2.0 K. When the field sweep rate varied from 700 to 50 Oe s−1, the coercive field of Dy0.10Y1.90 decreased from 230 to 190 Oe (Figure S10 in the Supporting Information). An external dc field can be applied to prevent the spin relaxation through a tunnelling process, enabling an observation of a slow relaxation process through the real thermally activated energy barrier. Consequently, the ac susceptibility of Dy2 was recorded by varying the dc fields from 0 to 3.0 kOe to search for an optimum dc field. With an increase in the external magnetic fields from 0 to 1500 Oe, the temperature regime of the QTM pathway become more and more narrow, and temperature-dependent direct relaxation between the nondegenerate ±mJ levels is slowly activated (Figure S11 in the Supporting Information). Once the external magnetic field is stronger than 1000 Oe, almost no temperature-independent χ″ signals were detected, revealing that the QTM channel vanished completely. Obviously, the field-dependent ac measurements of Dy2 reveal the conversion of the relaxation mechanism from QTM to direct relaxation at low temperature. Treatment of the ln τ versus 1/T curve with eq 1 led to τQTM = 0.23 s, A = 0.34 s−1 K−1, m = 1, C = 4.72 × 10−4 s−1 K−5.26, n = 5.26, and Ueff/k = 283.6 K with τ0 = 7.43 × 10−12 s under 500 Oe dc field. Under 1500 Oe dc field, these corresponding values are A = 1.35 s−1 K−1, m = 1, C = 8.09 × 10−5 s−1 K−5.99, n = 5.99, and Ueff/k = 292.1 K with τ0 = 5.09 × 10−12 s by ignoring the QTM process. The relaxation time of Dy2 under 1.0 kOe is the longest among all the fields examined (Figure S12 in the Supporting Information). Thus, a 1.0 kOe dc field was the optimized field to suppress the QTM of Dy2. As shown in Figure 5, both the χ′ and χ″ signals also show clear maxima under 1.0 kOe dc field, which shift to lower frequency with a decrease in temperature down to 2.0 K. Differently, the

Figure 4. Hysteresis loops for Dy2, Dy0.19Y1.81, and Dy0.10Y1.90 normalized to the saturated magnetization measured at a sweep rate of 200 Oe s−1 and 2.0 K.

Magnetic relaxations of Dy0.19Y1.81 and Dy0.10Y1.90 are quite different from those of the pure Dy2 molecule, although they both display apparent frequency- and temperature-dependent ac signals below 17.5 K (Figure 3). The peak maxima of the χ″ signals at a given temperature shift to lower frequency in comparison to those of Dy2. In particular, the peaks for the QTM channel become widened and incomplete, suggesting that the quantum tunneling in the doped sample is suppressed but not completely quenched by the doping level used herein due to the weakened dipole spin−spin interactions. Cole−Cole curves of the two magnetic-dilution samples between 4.0 and 17.5 K show arcs more asymmetric than those of Dy2 (Figures S6 and S7 in the Supporting Information). The distribution of relaxation times, 0.08 < α < 0.60 for Dy0.19Y1.81 and 0.12 < α < 0.57 for Dy0.10Y1.90 (Tables S7 and S8 in the Supporting Information), suggests the coexistence of multiple relaxation processes due to the weakened intramolecular exchange interactions. These phenomena make the plots of ln τ versus 1/T have less curvature, and the best least-squares fits to eq 1 give rise to τQTM = 0.31 s, C = 5.75 × 10−4 s−1 K−5.23, n = 5.23, and Ueff/k = 281.5 K with τ0 = 1.15 × 10−11 s for Dy0.19Y1.81 as well as τQTM = 0.48 s, C = 4.06 × 10−4 s−1K−5.36, n = 5.36, and Ueff/k = 285.0 K with τ0 = 1.07 × 10−11 s for Dy0.10Y1.90. In 5618


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Figure 5. Frequency dependence of χ″ of the ac susceptibility (left) and plots of ln τ versus 1/T for Dy2 and Dy0.10Y1.90 measured under 1.0 kOe dc field (right; black solid line corresponds to the best fitting to the multiple relaxation process; blue, orange, and green solid lines represent the best fitting to the Arrhenius law, direct, and Roman relaxation processes, respectively).

temperature-independent χ″ signals cannot be observed, revealing that the QTM pathway was absent under the optimized field. The disappearance of the tunneling regime can also be evidenced from the temperature-dependent ln τ versus 1/T curve over the temperature determined (Figure 5 and Figure S13 and Table S9 in the Supporting Information). Fitting of the ln τ versus 1/T curve to eq 1 was carried out by taking into account the direct relaxation (ATm) and ignoring the QTM terms, which led to A = 1.34 s−1 K−1, m = 1, C = 9.91 × 10−5 s−1 K−5.89, n = 5.89, and Ueff/k = 290.1 K with τ0 = 5.44 × 10−12 s. Additionally, the relaxation time of Dy2 at 2.0 K is 350 ms under 1.0 kOe field, almost 2 times longer than that under zero dc field. Under the same conditions, fitting of the ln τ versus 1/T curve of Dy0.10Y1.90 to eq 1 resulted in A = 0.061 s−1 K−1, m = 1, C = 2.41 × 10−5 s−1 K−6.31, n = 6.31, and Ueff/k = 300.2 K with τ0 = 5.83 × 10−12 s. Remarkably, the relaxation time for the direct pathway of Dy0.10Y1.90 at 2.0 K is greatly enhanced by about 17 times in comparison to that under zero dc field (8.00 vs 0.48 s), quantitatively demonstrating the more essential role of the external field in comparison to that of magnetic-site dilution on the relaxation time. The relaxation time of the pure Dy2 sample at 2.0 K (0.35 s) for the dominant direct relaxation pathway is enhanced about 23 times in comparison to that of the diluted Dy0.10Y1.90 sample (8.0 s) under 1.0 kOe, which is due to the spin-phonon bottleneck effect controlled significantly by the change in concentration of paramagnetic ions.50,51

thermally activated Orbach relaxation originates from the single-ion anisotropy of the Dy2, confirmed by the doping of the diamagnetic YIII matrix. The relaxation times of the QTM processes of the diluted samples were extended by 1.9 and 3.2 times in comparison to that of pure Dy2, and the opening temperature of the hysteresis loop is up to 5.0 K. An optimal external field can increase the barrier height by 12.4 K due to the full suppression of the QTM. More surprisingly, the dual effects of magnetic-site dilution and external optimum field make the effective energy barrier and relaxation time increase respectively to 300.2 K and 8.0 s, suggesting a synergetic enhancement on the magnetism performance of the Dy2 SMM. Thus, the detailed magnetic dynamics of the phenoxido-bridged Dy2 system enable a deep understanding of the relaxation mechanism.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b03089. Selected bond lengths and angles, hydrogen-bonding parameters, one-dimensional supramolecular array, PXRD patterns, and Cole−Cole plots and fitting results for Dy2, Dy0.19Y1.81, and Dy0.10Y1.90 under zero and optimum fields (PDF)

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CONCLUSIONS A phenoxido-bridged centrosymmetric Dy2 SMM with hulahoop-shaped DyIII configuration was solvothermally obtained by a simple mixed-ligand strategy. The Dy2 molecule exhibits an effective spin-reversal energy barrier of 277.7 K and insignificant hysteresis loop above 2.0 K. The relaxation dynamics of the Dy2 was fully elucidated by both magneticsite dilution and application of an optimal external field. The

Accession Codes

CCDC 1505999−1506002 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. 5619


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(7) Ding, Y.-S.; Chilton, N. F.; Winpenny, R. E. P.; Zheng, Y.-Z. On Approaching the Limit of Molecular Magnetic Anisotropy: A NearPerfect Pentagonal Bipyramidal Dysprosium(III) Single-Molecule Magnet. Angew. Chem., Int. Ed. 2016, 55, 16071−16074. (8) Rinehart, J. D.; Fang, M.; Evans, W. J.; Long, J. R. Strong Exchange and Magnetic Blocking in N23−-Radical-Bridged Lanthanide Complexes. Nat. Chem. 2011, 3, 538−542. (9) Tuna, F.; Smith, C. A.; Bodensteiner, M.; Ungur, L.; Chibotaru, L. F.; McInnes, E. J. L.; Winpenny, R. E. P.; Collison, D.; Layfield, R. A. A High Anisotropy Barrier in a Sulfur-Bridged Organodysprosium Single-Molecule Magnet. Angew. Chem., Int. Ed. 2012, 51, 6976−6980. (10) Ganivet, C. R.; Ballesteros, B.; Torre, G. D. L.; Clemente-Juan, J. M.; Coronado, E.; Torres, T. Influence of Peripheral Substitution on the Magnetic Behavior of Single-Ion Magnets Based on Homo- and Heteroleptic TbIIIBis(phthalocyaninate). Chem. - Eur. J. 2013, 19, 1457−1465. (11) Moreno Pineda, E.; Chilton, N. F.; Marx, R.; Dörfel, M.; Sells, D. O.; Neugebauer, P.; Jiang, S.-D.; Collison, D.; Slageren, J. V.; Mclnnes, E. J. L.; Winpenny, R. E. P. Direct Measurement of Dysprosium(III)-Dysprosium(III) Interactions in a Single-Molecule Magnet. Nat. Commun. 2014, 5, 5243−5249. (12) Bhunia, A.; Gamer, M. T.; Ungur, L.; Chibotaru, L. F.; Powell, A. K.; Lan, Y.; Roesky, P. W.; Menges, F.; Riehn, C.; NiednerSchatteburg, G. From a Dy(III) Single Molecule Magnet (SMM) to a Ferromagnetic [Mn(II)Dy(III)Mn(II)] Trinuclear Complex. Inorg. Chem. 2012, 51, 9589−9597. (13) Meihaus, K. R.; Rinehart, J. D.; Long, J. R. Dilution-Induced Slow Magnetic Relaxation and Anomalous Hysteresis in Trigonal Prismatic Dysprosium(III) and Uranium(III) Complexes. Inorg. Chem. 2011, 50, 8484−8489. (14) (a) Jiang, S.-D.; Wang, B.-W.; Sun, H.-L.; Wang, Z.-M.; Gao, S. An Organometallic Single-Ion Magnet. J. Am. Chem. Soc. 2011, 133, 4730−4733. (b) Jiang, S.-D.; Wang, B.-W.; Su, G.; Wang, Z.-M.; Gao, S. A Mononuclear Dysprosium Complex Featuring Single-MoleculeMagnet Behavior. Angew. Chem., Int. Ed. 2010, 49, 7448−7451. (15) Leng, J. D.; Liu, J. L.; Zheng, Y. Z.; Ungur, L.; Chibotaru, L. F.; Guo, F. S.; Tong, M. L. Relaxations in Heterolanthanide Dinuclear Single-Molecule Magnets. Chem. Commun. 2013, 49, 158−160. (16) Habib, F.; Lin, P. H.; Long, J.; Korobkov, I.; Wernsdorfer, W.; Murugesu, M. The Use of Magnetic Dilution to Elucidate the Slow Magnetic Relaxation Effects of a Dy2 Single-Molecule Magnet. J. Am. Chem. Soc. 2011, 133, 8830−8833. (17) Chow, C. Y.; Bolvin, H.; Campbell, V. E.; Guillot, R.; Kampf, J. W.; Wernsdorfer, W.; Gendron, F.; Autschbach, J.; Pecoraro, V. L.; Mallah, T. Assessing the Exchange Coupling in Binuclear Lanthanide(III) Complexes and the Slow Relaxation of the Magnetization in the Antiferromagnetically Coupled Dy2 Derivative. Chem. Sci. 2015, 6, 4148−4159. (18) Blagg, R. J.; Ungur, L.; Tuna, F.; Speak, J.; Comar, P.; Collison, D.; Wernsdorfer, W.; Mclnnes, E. J. L.; Chibotaru, L. F.; Winpenny, R. E. P. Magnetic Relaxation Pathways in Lanthanide Single-Molecule Magnets. Nat. Chem. 2013, 5, 673. (19) Dickie, C. M.; Nippe, M. Magnetization Dynamics of a Heterometallic Dy-Isocarbonyl Complex. Inorg. Chem. Front. 2016, 3, 97−103. (20) Liu, J.; Chen, Y. C.; Lai, J. J.; Wu, Z. H.; Wang, L. F.; Li, Q. W.; Huang, G. Z.; Jia, J. H.; Tong, M. L. Evolution of Slow Magnetic Relaxation: from Diamagnetic Matrix Y(OH)CO3 to Dy0.06Y0.94(OH)CO3 with High Spin-Reversal Barrier and Blocking Temperature. Inorg. Chem. 2016, 55, 3145−3150. (21) Li, L. L.; Liu, S.; Li, H.; Shi, W.; Cheng, P. Influence of External Magnetic Field and Magnetic-Site Dilution on the Magnetic Dynamics of a One-Dimensional Tb(III)-Radical Complex. Chem. Commun. 2015, 51, 10933−10936. (22) Jia, L.; Chen, Q.; Meng, Y. S.; Sun, H. L.; Gao, S. Elucidation of Slow Magnetic Relaxation in a Ferromagnetic 1D Dysprosium Chain through Magnetic Dilution. Chem. Commun. 2014, 50, 6052−6055. (23) Blagg, R. J.; Ungur, L.; Tuna, F.; Speak, J.; Comar, P.; Collison, D.; Wernsdorfer, W.; McInnes, E. J. L.; Chibotaru, L. F.; Winpenny, R.

AUTHOR INFORMATION

Corresponding Authors

*E-mail for Y.-Q.Z.: [email protected]. *E-mail for E.-C.Y.: [email protected]. *E-mail for X.-J.Z.: [email protected]. ORCID

Xiao-Jun Zhao: 0000-0002-6371-9528 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We appreciate the financial funds from the 973 Program (2014CB845601), the NSFC (Grants 21371134, 21571140, and 21531005), and the Natural Science Foundation of Jiangsu Province of China (BK20151542).

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ABBREVIATIONS CN,coordination number; θDyOODy,dihedral angle of the Dy2O2 unit; H2a′povh,N′-[amino(pyrimidin-2-yl)methylene]-o-vanilloyl hydrazine; H3L1,3-hydroxy-N′-(2-hydroxybenzylidene)picolinohydrazide; H2ovph,pyridine-2-carboxylic acid [(2-hydroxy-3-meth-oxyphenyl)methylene]hydrazide; Mq,8-hydroxy2-methylquinoline; H3 L2,3-(2-hydroxybenzylideneamino)propane-1,2-diol; H2valdien,N1,N3-bis(3-methoxysalicylidene)diethylenetriamine; H2 ovph,o-vanillinpicolinoylhydrazone; H 2 L3,2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}naphthalen-1-ol; H 2 hmi,(2-hydroxy-3-methoxyphenyl)methylene (isonicotino)hydrazine; anthc,9-anthracenecarboxylate; L4,2,2′-bipyridyl; anthc,9-anthracenecarboxylate; L5,10phenanthroline; H4L6,1,5-bis(2-hydroxy-3methoxybenzylidene)carbonohydrazide; dbm,dibenzoylmethanate; OQ,8-quinolinolate; H3L7,2,2′-(2-hydroxy-3-methoxy-5methylbenzylazanediyl)diethanol; piv,pivalic acid; anthc,9anthracenecarboxylate; L8,4,7-dimethyl-1,10-phenanthroline; L9,2-[[(4-fluorophenyl)imino]methyl]-8-hydroxyquinoline; bfac,benzoyltrifluoroacetone; L10,2-[[(4-fluorophenyl)imino]; tfac,trifluoroacetylacetonate; L11,2-[[(4-fluorophenyl)imino]; hfac,hexafluoroacetylacetonate

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REFERENCES

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Inorganic Chemistry

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Inorganic Chemistry (53) Zhang, J.; Zhang, H. F.; Chen, Y. M.; Zhang, X. F.; Li, Y. H.; Liu, W.; Dong, Y. P. A series of dinuclear lanthanide complexes with slow magnetic relaxation for Dy2 and Ho2. Dalton Trans. 2016, 45, 16463−16470. (54) Lin, P. H.; Burchell, T. J.; Clérac, R.; Murugesu, M. Dinuclear Dysprosium(III) Single-Molecule Magnets with a Large Anisotropic Barrier. Angew. Chem., Int. Ed. 2008, 47, 8848−8851. (55) Ke, H. S.; Zhang, S.; Li, X.; Wei, Q.; Xie, G.; Wang, W. Y.; Chen, S. P. A Dy2 single-molecule magnet with benzoate anions and phenol-O−bridging groups. Dalton Trans. 2015, 44, 21025−21031. (56) Shen, H. Y.; Wang, W. M.; Gao, H. L.; Cui, J. Z. Near-infrared luminescence and SMM behaviors of a family of dinuclear lanthanide 8-quinolinolate complexes. RSC Adv. 2016, 6, 34165−34174. (57) Bag, P.; Rastogi, C. K.; Biswas, S.; Sivakumar, S.; Mereacre, V.; Chandrasekhar, V. Homodinuclear lanthanide {Ln2} (Ln = Gd, Tb, Dy, Eu) complexes prepared from an o-vanillin based ligand: luminescence and single-molecule magnetism behavior. Dalton Trans. 2015, 44, 4328−4340. (58) Wang, W. M.; Zhang, H. X.; Wang, S. Y.; Shen, H. Y.; Gao, H. L.; Cui, J. Z.; Zhao, B. Ligand Field Affected Single-Molecule Magnet Behavior of Lanthanide(III) Dinuclear Complexes with an 8Hydroxyquinoline Schiff Base Derivative as Bridging Ligand. Inorg. Chem. 2015, 54, 10610−10622.

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Magnetic Relaxation Dynamics of a Centrosymmetric Dy2 Single

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