Modulating Single-Molecule Magnetic Behavior of a Dinuclear Erbium

Dec 15, 2016 - Magnetic studies reveal that complex 1 shows a fast relaxation process with negligible energy barrier and 2 exhibits a field-induced SM...
2 downloads 9 Views 2MB Size
Download PDF
Article pubs.acs.org/IC

Modulating Single-Molecule Magnetic Behavior of a Dinuclear Erbium(III) Complex by Solvent Exchange Jing-Yuan Ge,† Long Cui,† Jing Li,† Fei Yu,† You Song,† Yi-Quan Zhang,*,‡ Jing-Lin Zuo,*,† and Mohamedally Kurmoo§ †

State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210023, 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 § Institut de Chimie de Strasbourg, Université de Strasbourg, CNRS-UMR 7177, 4 Rue Blaise Pascal, 67008 Cedex Strasbourg, France S Supporting Information *

ABSTRACT: [Er2(thd)4Pc]·2C6H6 (1) (Hthd = 2,2,6,6-tetramethylheptanedione), obtained as green crystals from the reaction of [Er(thd)3]·2H2O with lithium phthalocyanine, Li2Pc, is a stable dinuclear complex with two ErIII centers. Its lattice benzene solvent can be exchanged by soaking the crystals in dichloromethane to give [Er2(thd)4Pc]·2CH2Cl2 (2). The magnetic susceptibility data suggest different coupling interactions for the two complexes. While 1 exhibits fast relaxation and an estimated energy barrier of Ea = 2.6 cm−1 under 600 Oe dc field, the single-molecule magnet behavior of 2 is field-induced and the energy barrier is higher at 34.3 cm−1. Ab initio calculations were performed to understand the nature of the coupling interaction between two ErIII ions bridged by the phthalocyanine and the origin of different magnetic behavior. Importantly, the single-molecule magnetic properties can be reversibly tuned through the exchange of solvent molecules, confirmed by further measurements on the reverse solvated complexes 1-re and 2-re. This subtle control of relaxation by lattice solvents is rarely observed in single-molecule magnets, especially for ErIII-based complexes.

■

INTRODUCTION

Recently, a few dysprosium-SMMs studies concerning the solvent effect have been reported, in which the most common method is solvation/desolvation.7c,8 However, they often lose the single crystal form after desolvation, which has hampered further studies of magnetostructural relations.6c,8a Zhang and co-workers reported a porous lanthanide framework where guest solvent exchange results in different dipole−dipole interactions to switch the effective magnetic relaxation barrier.9 While the highly porous structures can accommodate a wide variety of guest molecules with the stability of the framework and little disturbance of the metallic coordination, 0D SMMs without stable 3D frameworks are likely to collapse after solvent exchange. Therefore, the extended study of magnetic modulation on 4f-SMMs through different solvent exchange is still a challenge.10 In this contribution, we report the solvent-sensitive ErIIISMM, in which the exchange of lattice solvents can be achieved through a single-crystal-to-single-crystal (SCSC) transformation, leading to significant changes in magnetic properties. Ab

Single-molecule magnets (SMMs) have attracted considerable research efforts because of their unique energy barrier and potential applications in high-density storage devices and nanoscale electronics.1 Following the discovery of singlemolecule magnetism in [TbPc2]−,2 there have been a growing number of lanthanide SMMs as well as single-ion magnets (SIMs) that have been designed because of their large groundstate spin and large intrinsic magnetic anisotropy.3 As we know, the magnetic relaxation behavior of 4f-SMMs is very sensitive to the coordination mode of the single metal ion.4 In addition, the intrinsic barrier of 4f-SMMs is affected by several factors such as the inherent features of the lanthanide ion, its magnetic anisotropy, and its magnetic exchange interactions.5 This specialty makes it possible to control their magnetic behaviors through an external stimulus, such as light, pressure, temperature, counterions, and solvents. In some molecular magnets based on transition metal complexes, their magnetic properties are tunable by external physical and chemical effects.6 Tunable magnetism is helpful for understanding the magnetostructural correlation; however, it is rarely studied for 4f-SMMs.7 © XXXX American Chemical Society

Received: September 17, 2016

A

DOI: 10.1021/acs.inorgchem.6b02243 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

non-hydrogen atoms were refined with anisotropic thermal parameters, and hydrogen atoms of the organic ligands and the hydroxide anion were calculated theoretically onto the specific atoms and refined isotropically with fixed thermal factors. More details for the crystal data, data collection parameters, and refinement statistics of complexes 1, 2, and 1-re are given in Table 1. Relevant interatomic bond distances and bond angles are listed in Table S1. CCDC reference numbers: 1494900 (1), 1494901 (2), 1494902 (1-re).

initio calculations demonstrate that this effect is possibly related to the coupling interactions and the subtle structural differences.

■

EXPERIMENTAL SECTION

Materials and Physical Measurements. All chemicals and solvents were obtained and used directly from commercial sources. Li2Pc was purchased from TCI P1049, and Er(thd)3·2H2O was prepared according to the published literature.11 Complex 1 was prepared following a reported procedure with a slight modification.12 Samples for infrared (IR) studies were prepared as KBr pellets, and spectra were obtained in the 400−4000 cm−1 range using a Vector22 Bruker spectrophotometer. Thermogravimetric analyses (TGA) were performed on a SETARAM LABSYS evo TGA instrument. Elemental analyses were performed on an Elementar Vario MICRO analyzer. Xray diffraction (XRD) patterns were obtained on a D8 ADVANCE Xray powder diffractometer (XRPD) with Cu Kα radiation (λ = 1.5405 Å). Magnetic susceptibility measurements for polycrystalline samples were performed on a Quantum Design SQUID vibrating sample magnetometer (VSM) in the temperature range from 2 to 300 K for direct current (dc) applied fields ranging from 0 to 70 kOe. Alternating current (ac) susceptibilities were obtained using an oscillating ac field of 2 Oe and in the frequency range 1−999 Hz. All magnetic data were corrected for the sample holder, the eicosane, and the diamagnetic contribution of the sample.13 Synthesis of [Er2(thd)4Pc]·2C6H6 (1). A mixture of Li2Pc (53 mg, 0.1 mmol) and Er(thd)3·2H2O (151 mg, 0.2 mmol) in anhydrous tetrahydrofuran (10 mL) was stirred for 6 h at 80 °C and monitored by thin-layer chromatography (TLC). After removal of the solvent, the resulting solid and benzene (18 mL) were sealed in a 25 mL glass tube. The mixture was heated at 80 °C for 8 h under autogenous pressure and then cooled to room temperature at a rate of 10 °C/h. Green crystals were isolated from the tube. Yield: 50%. Anal. Calcd (%) for C88H104N8O8Er2: C 60.87, H 6.04, N 6.45. Found: C, 60.59, H, 6.11, N 6.64. IR (KBr pellet cm−1): 3406 (br), 2962 (m), 1653 (w), 1594 (w), 1579 (m), 1553 (m), 1505 (s), 1402 (m), 1360 (m), 1330 (m), 1285 (w), 1222 (w), 1143 (w), 1114 (m), 1070 (m), 886 (w), 796 (w), 734 (vs), 677 (w). Synthesis of [Er2(thd)4Pc]·2CH2Cl2 (2). The single crystals of 1 were immersed in dichloromethane solution under ambient conditions. Every 6 h the solution was replaced with fresh CH2Cl2. After 24 h, the dichloromethane had replaced the benzene molecules in 1 and complex 2 was obtained. The result was successfully checked by single-crystal X-ray diffraction. Anal. Calcd (%) for C78H96Cl4N8O8Er2: C 53.53, H 5.53, N 6.40. Found: C, 53.83, H, 5.61, N 6.61. IR (KBr pellet cm−1): 3409 (br), 2963 (m), 1652 (w), 1595 (w), 1579 (m), 1552 (m), 1504 (vs), 1400 (m), 1360 (m), 1330 (m), 1284 (w), 1223 (w), 1142 (w), 1114 (m), 1069 (m), 885 (w), 795 (w), 734 (s), 677 (w). Syntheses of 1-re and 2-re. 1-re can be recovered by soaking crystals of 2 in benzene for 24 h. The solution was replaced with fresh benzene after 12 h. The result was checked by single-crystal X-ray diffraction. Anal. Calcd (%) for C88H104N8O8Er2: C 60.87, H 6.04, N 6.45. Found: C, 60.61, H, 5.97, N 6.66. The procedure of 2-re was similar to the synthesis of 2 except that 1-re was used in place of 1. The result was evidenced by elemental analyses (C, 53.77, H, 5.50, N 6.58) and magnetic susceptibility comparison with the data of the assynthesized 2. X-ray Crystallography. The crystal structure data were collected on a Bruker Smart Apex II CCD-based diffractometer (Mo Kα radiation, λ = 0.710 73 Å). The raw frame data were integrated into SHELX-format reflection files and corrected for Lorentz and polarization effects using SAINT.14 Corrections for incident and diffracted beam absorption effects were applied using SADABS supplied by Bruker.15 None of the crystals showed evidence of crystal decay during data collection. All structures were solved and refined against F2 by the full-matrix least-squares using the SHELXL-97 program.16 The positions of the metal atoms and their first coordination spheres were located from direct method E-maps. All

Table 1. Crystal Data and Structure Refinement for 1, 2, and 1-re empirical formula fw temp (K) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) ρcalc (g/cm3) GOF on F2 R1a/wR2b [I > 2σ(I)] R1/wR2 [all data] a

1 (Er2-C6H6)

2 (Er2-CH2Cl2)

1-re (Er2-C6H6)

C88H104N8O8Er2

C78H96Cl4N8O8Er2

C88H104N8O8Er2

1736.31 123(2) monoclinic C2/m 19.122(1) 17.948(1) 14.670(1) 90 126.689(1) 90 4037.4(2) 1.428 1.072 0.0467/0.1202

1749.94 123(2) monoclinic C2/m 19.255(4) 17.807(4) 14.734(3) 90 127.849(4) 90 3989.1(2) 1.457 1.088 0.0552/0.1413

1736.31 123(2) monoclinic C2/m 19.155(2) 17.934(2) 14.721(2) 90 126.622(3) 90 4058.7(9) 1.421 1.075 0.0571/0.1461

0.0491/0.1227

0.0625/0.1475

0.0607/0.1495

R1 = ∑∥Fo| − |Fc∥/∑|Fo|. bwR2 = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]0.5.

Ab Initio Calculations for Complexes 1 and 2. There is only one type of structure for complexes 1 and 2, and the two ErIII ions in each of them are centrosymmetric. Thus, we need to calculate only one ErIII fragment for each of them. Complete-active-space selfconsistent field (CASSCF) calculations on individual ErIII fragments of the model structure (see Figure S17 for the model structure of complex 1; the other complexes have a similar structure) extracted from complexes 1 and 2 on the basis of X-ray determined geometry have been carried out with the MOLCAS 8.0 program package.17 During the calculations, the other ErIII ion for each complex was replaced by diamagnetic LuIII. The basis sets for all atoms are atomic natural orbitals from the MOLCAS ANO-RCC library: ANO-RCCVTZP for ErIII 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. The active electrons in seven active spaces include all f electrons (CAS (11 in 7) for complexes 1 and 2 in the CASSCF calculation). To exclude all doubts, we calculated all the roots in the active space. We have mixed the maximum number of spin-free states that were possible with our hardware (all from 35 quadruplets and all from 112 doublets for two ErIII fragments).

■

RESULTS AND DISCUSSION Crystal Structure Description. As shown in Figure 1, complex 2 was afforded through immersing the crystals of 1 in dichloromethane at room temperature. Single-crystal diffraction data analyses reveal that 1 and 2 feature similar dinuclear units with different guest solvents in the crystal lattices. Both 1 and 2 crystallize in the monoclinic C2/m space group, containing two ErIII centers, one double deprotonated Pc ligand, and four thd’s. Each ErIII ion lies in an octacoordinated {ErN4O4} sphere B

DOI: 10.1021/acs.inorgchem.6b02243 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 1. Dinuclear structure of 1. Top view (left) and side view (right). Hydrogen atoms and uncoordinated solvents are omitted for clarity.

composed of four N-donors from one Pc ligand and four Odonors from two bidentate thd anions (Figure 1). The Er−N distances range from 2.579 to 2.607 Å in 1 and from 2.586 to 2.609 Å in 2. Meanwhile, the Er−O distances are 2.219 and 2.225 Å in 1 and 2.223 and 2.227 Å in 2. SHAPE 2.1 software was used to evaluate the exact geometry of the ErIII ion, indicating that both 1 and 2 belong to approximate square antiprism (D4d) symmetry (Table S2). Each ErIII ion is unevenly spaced between the outer thd anions and inner Pc ligand with distances of 1.061 Å (1.058 Å) from the mean plane (named plane O4) of four O atoms of the outer thd and 1.725 Å (1.728 Å) from the mean plane (named plane N4) of four N atoms of the inner Pc ligand in 1 (2). The two planes are almost parallel with the dihedral angle of 0.113° (0.079°) in 1 (2) (Table S3). The intramolecular Er···Er distances are ∼3.451 and ∼3.456 Å in 1 and 2, respectively. In the solid state, these dinuclear units stack regularly in a ··· AAA··· fashion. For 1, neighboring dinuclear units are separated by benzene molecules with the shortest Er2···Er2 separation of 12.324 Å. Benzene molecules are connected to the dimer through one weak C−H···π interaction with a H···π distance of 3.425 Å (Figure S1). In the case of 2 the neutral molecules are separated by dichloromethane guests, leading to a nearest Er2··· Er2 distance of 12.222 Å (Figure S2). One weak C−H···Cl nonclassical hydrogen bond exists between the solvent and dinuclear unit with a H···Cl distance of 2.787 Å. Both separations in 1 and 2 are greater than 10 Å, suggesting weak magnetic exchange interactions between neighboring dinuclear units.9 Thermogravimetric and X-ray Powder Diffraction Analyses. XRPD patterns indicate that the obtained samples are in pure phase, as they match well those calculated using the single-crystal X-ray diffraction data (Figure S3). TGA of 1 and 2 were carried out from 30 to 800 °C in flowing N2 at a heating rate of 10 °C/min. The weight losses of 9.16% (at 125 °C for 1) and 9.87% (at 80 °C for 2) are assigned to the removal of two benzene molecules (calculated 9.01%) and two dichloromethane molecules (calculated 9.71%), respectively. The weight loss occurring around 350 °C is accompanied by the decomposition of organic ligands (Figure S4). Static Magnetic Properties. Direct current magnetic susceptibility data for 1 and 2 were collected under an applied field of 1 kOe from 2 to 300 K on freshly prepared samples (Figure 2). The room-temperature χMT values of 23.01 and 22.81 cm3 K mol−1 for 1 and 2 are in good agreement with the value of two isolated ErIII (22.96 cm3 K mol−1; 4I15/2, J = 15/2, g = 6/5) ions. Upon lowering the temperature, χMT decreases gradually to 50 and 30 K, reaching minima of 21.84 and 21.10

Figure 2. Temperature dependence of χMT for 1 and 2 in a 1 kOe field. The solid lines correspond to the calculated magnetic susceptibilities with the intermolecular interaction zJ′ of −0.01 and 0.03 cm−1 for 1 and 2, respectively. Inset: Field-dependent magnetizations for 1 (left) and 2 (right).

cm3 K mol−1 for 1 and 2, respectively. A similar behavior for diluted samples was observed, suggesting a progressive depopulation of the excited Stark levels (Figure S5).18 On further cooling, a sharp increase in χMT is observed, reaching 29.32 cm3 K mol−1 at 2 K for 2, which is much smaller than the value of 33.43 cm3 K mol−1 in 1. At very low temperature, the increase of χMT indicates that the intramolecular ferromagnetic interactions between the ErIII ions overwhelm the thermal depopulation of the excited states of the ErIII ions.19 The isothermal magnetization increases steeply with the magnetic field, reaching maximum values of 9.82 and 9.58 Nβ at 1.8 K for 1 and 2 (Figure 2). The lack of saturation as well as the nonsuperimposition of isotemperature lines in the M vs H/T plot suggests the presence of significant magnetic anisotropy in these compounds (Figure 3). The field-dependent magnetization also exhibits typical paramagnet behavior with significant magnetic anisotropy.20 Ab initio calculations confirm the strong axial anisotropy of the ground states in 1 and 2 with large gz values (17.727 for 1 and 17.751 for 2, see below). Dynamic Magnetic Properties. The alternating current magnetic susceptibilities of 1 and 2 under Hac = 2 Oe were performed to check for any SMM behavior. For 1, the temperature-dependent out-of-phase signal (χ″) was observed; however, the peaks in the χ″ ac susceptibility do not appear even at a low temperature of 1.8 K and high frequency of 999 Hz (Figures S6, S7). On cooling, a rapid increase in χ″ signal suggests the presence of an activated fast relaxation process, usually seen in ErIII-based complexes.1b,19a Fitting to ln(χ″/χ′) = ln(ωτ0) + Ea/kBT21 allows us to evaluate the energy barrier Ea of 3.1 K (2.1 cm−1) (Figure S8). Under a 600 Oe dc field, the curves of χ″ vs T show similar trends to those at zero dc field without peaks (Figures 4 and S10), and the estimated Ea is 3.8 K (2.6 cm−1) (Figure S11). When a much stronger field (2000 Oe) was introduced, the maximum of χ″ (999 Hz) appear at 2.2 K only (Figure S10). The relaxation time (τ), obtained from the χ″ peaks, obeys the Arrhenius law [τ = τ0 exp(Ea/kBT)] (Figure S11). The energy barrier Ea and pre-exponential factor τ0 are 6.3 K (4.4 cm−1) and 7.29 × 10−6 s, respectively. The χ″ signal at low temperature is probably the intrinsic character of 1.22 C

DOI: 10.1021/acs.inorgchem.6b02243 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 3. Experimental M vs HT−1 plots at different temperatures for complexes 1 (left) and 2 (right).

Figure 4. Frequency dependence of the in-phase (χ′) and out-of-phase (χ″) ac susceptibilities under 600 Oe dc field for 1.

Figure 5. Frequency dependence of the in-phase (χ′) and out-of-phase (χ″) ac susceptibilities under 600 Oe dc field for 2.

Figure 6. Left: Cole−Cole plots for 2 under a 600 Oe dc field. The solid lines represent the fit to the Debye model at the indicated temperatures. Right: ln τ vs T−1 plot for 2; the solid line represents the best fits to the Arrhenius law.

susceptibilities can be used to calculated the parameter φ = (ΔTp/Tp)/Δ(log v) = 0.27, which lies in the range 0.1−0.3, as expected for superparamagnetic behavior.9 The Cole−Cole plots formed a symmetrically semicircular shape (Figure 6), and the generalized single relaxation process Debye model23 allows us to extract the parameter α = 0.14−0.03 for temperatures between 1.8 and 4.8 K (Table S4), revealing the narrow distribution of the relaxation process.24 The resulting relaxation times (τ) were plotted as a function of T−1, as shown in Figure 7. Fitting high-temperature data to the Arrhenius equation

For 2, also no obvious temperature-dependent χ″ peaks were detected under zero dc field (Figures S6, S7), indicating a fast relaxation process similar to that observed for 1. However, this relaxation rate is field dependent since the application of a dc field induces χ″ to exhibit a maximum (Figure S6). Under an optimal dc field (600 Oe), the frequency-dependent χ″ signals exhibit a gradual sweep toward the low-frequency region as the temperature is lowered to 1.8 K (Figure 5), indicating slow relaxation of the magnetization, typical of field-induced SMM behavior. The peak temperatures of the in-phase ac D

DOI: 10.1021/acs.inorgchem.6b02243 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 7. Temperature dependence of χMT (left) and frequency-dependent ac susceptibilities at 1.8 K for 1-re and comparison with the data of assynthesized 1.

affords the reasonable parameters Ea = 49.4 K (34.3 cm−1) and τ0 = 1.62 × 10−9 s. To further understand the relaxation behavior, the data were also fitted with τ−1 = AH2T + CTn + τ0 exp(Ea/kBT) (the three terms represent the direct, Raman, and Orbach processes, respectively) (Figure S13).7b In order to avoid overparametrization, parameter Ea was fixed with a value extracted from the linear fitting to the Arrhenius law in the higher temperature region. The satisfied parameters are A = 6.01 × 10−4 s−2 Oe−2, C = 1.88 s−1 K−5,19 n = 5.19, and τ0 = 2.55 × 10−9 s. Furthermore, if we consider the direct and Raman processes for τ without the Orbach process, the phenomenon does not follow the relationship τ−1 = AH2T + CTn reasonably (Figure S13), also suggesting the existence of a thermally activated relaxation in 2.7b,18a Reversible Magnetic Modulation. The dynamics of the magnetization reveal significant differences in 1 and 2, indicating the dominance of differing relaxation mechanisms depending on the guest solvents. As shown in Scheme S1, complex 1 can be reobtained when soaking 2 in benzene solvent for 1 day (named 1-re for clarity). This SCSC transformation is fully reversible, as determined by both X-ray crystal structure analyses and elemental analyses (Table 1 and Table S1). If the reversible solvent exchange should result in regular change of the magnetic property, it would be useful for magnetic modulations and potential sensing applications. The direct current magnetic susceptibility of 1-re was collected under an applied field of 1 kOe from 2 to 300 K (Figure 7). The room-temperature χMT value is 23.19 cm3 K mol−1. On cooling, χMT decreases gradually to 45 K, reaching a minimum of 22.17 cm3 K mol−1, and then increases sharply to a maximum of 32.76 cm3 K mol−1 at 2 K. The dc magnetic susceptibilities of 1-re are consistent with the data of the assynthesized 1. The ac magnetic susceptibility also shows expected changes following solvent exchange. Complex 1-re exhibits a fast relaxation behavior without no obvious χ″ peak under a 600 Oe dc field even at very low temperature (1.8 K). In the second exchange cycle, complex 2-re was afforded through immersing the crystal of 1-re in dichloromethane. Unfortunately, the crystal data of 2-re could not be obtained due to the significant loss of crystallinity after two solvent exchange cycles. Direct current magnetic susceptibility shows the room-temperature χMT value for 2-re is 22.96 cm3 K mol−1, and χMT decreases gradually to a minimum of 21.45 cm3 K mol−1 at 30 K. At 2 K, χMT reaches 28.79 cm3 K mol−1, which is much smaller than the value of 32.76 cm3 K mol−1 in 1-re (Figure S14). Under a 600 Oe dc field, the slow magnetic relaxation of 2-re was recovered perfectly and the χ″ peak occurs around 63 Hz at 1.8 K, which well overlaps with that in 2 (Figures S14, S15). The Arrhenius law shows that the thermal

barrier Ea and the pre-exponential factor τ0 are 43.8 K (30.4 cm−1) and 6.79 × 10−9 s, respectively, which are close to the values for 2. Cole−Cole plots also show a regularly semicircular shape with a small α value (Figure S16 and Table S5). On the basis of the single-crystal structures and the magnetic data, undoubtedly, the magnetic properties can be modulated reversibly through exchange of guest solvent in this system. Ab Initio Calculations. In order to further elucidate the strikingly difference in magnetic properties of 1 and 2, CASSCF calculations on individual ErIII fragments on the basis of X-raydetermined geometries have been carried out with the MOLCAS 8.017 and SINGLE_ANISO25 programs. The lowest spin−orbit energies and the corresponding g tensors of complexes 1 and 2 are shown in Table S6. Table S6 indicates that the ground Kramers doublet is more axial for the CH2Cl2 analogue (2) than for the C6H6 analogue (1). The calculated gz values of the ErIII fragments in their ground states are both close to 18, and those of gx and gy values are close to zero, which shows that the ErIII−ErIII exchange interactions for 1 and 2 can be approximately regarded as the Ising type. Thus, Lines’ model26 is appropriate to fit the exchange parameters for complexes 1 and 2.27 To investigate the nature of the magnetic interactions, the magnetic susceptibilities of 1 and 2 were simulated with the program POLY_ANISO25 using the exchange parameters from Table 2. Table 2. Fitted Exchange Coupling Constants Jexch, the Calculated Dipolar Interactions Jdipolar, and the Total J (cm−1) between ErIII Ions of 1 and 2 1

2

Jexch

Jdipolar

J

Jexch

Jdipolar

J

−0.27

6.60

6.33

−4.59

6.62

2.03

All parameters in Table 2 were calculated with respect to the pseudospin S̃ = 1/2 of the ErIII ions. The total magnetic interactions (J) within Er2 dinuclear units of 1 and 2 include exchange interactions (Jexch) and dipolar interactions (Jdipolar). The dipolar interactions are calculated using the ab initio results for the g tensors in the ground state of ErIII fragments, and the exchange parameters were derived from the simulation of χMT vs T plots. As shown in Figure 2, the fits are close to the experimental data.28 In both complexes, the Jexch parameters are negative and they have the opposite signs for the Jdipolar values. The dipolar interactions between two ErIII ions are stronger than the exchange ones. The total interaction constant (J = Jexch + Jdipolar) for 1 is 6.33 cm−1, while it is 2.03 cm−1 for 2. In addition, the best fitting gives zJ′ values of −0.01 and 0.03 cm−1 E

DOI: 10.1021/acs.inorgchem.6b02243 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 8. Ab initio magnetic easy axis of the ground states of 1 (left) and 2 (right).

mediating the communication with the other ErIII ion of the dinuclear molecule. Thus, we think that the π-conjugated Pc ligand, bridging two ErIII ions by four N atoms, plays an important role in the exchange coupling between ErIII ions. In addition, complex 2 is closer to the ideal D4d symmetry than 1. The calculated SAPR-8 parameters are 0.968 and 0.938 for 1 and 2, respectively. Herein, the larger the calculated SAPR-8 parameters, the greater the deviation from an ideal D4d symmetry. Compared to the ideal SAPR-8 configuration, different deviations can be observed, which may finally result in different values of the effective energy barriers. These inferences were substantiated by structural analysis for 1-re. In 1-re, the SAPR-8 parameter and dihedral angle between the benzene ring and the adjacent pyrrole ring are 0.964 and 1.5°, respectively. Both values are close to those for complex 1 and distinct from those of complex 2. Subtle structure changes can recover well through reversible single-crystal transformation. Furthermore, different types of weak interactions (C−H···π stacking) and 2 (C−H···Cl hydrogen bonds) may also influence the magnetic properties of 1. The subtle structural differences caused by guest solvents lead to disparate coupling interactions to give rise to dramatically different magnetic relaxations. To the best of our knowledge, this is the first ErIIISMM example in which the relaxation rates can be tuned through the exchange of lattice solvent molecules.

for 1 and 2, respectively, suggesting very weak intermolecular interactions. Furthermore, the main magnetic axes on two ErIII of 1 or 2 are indicated in Figure 8, where main anisotropy axes of the ErIII ions are parallel to each other owing to the centrosymmetric positions of the metal centers in both complexes. Ab initio calculations also predict quite small exchange energies for the first excited Kramers doublet on ErIII over the ground one (Table S7). The calculated exchange state for complex 1 is 3.2 cm−1, and this is a consistent value compared to the experimental energy barrier of 2.1 cm−1 under zero dc field (Figure S8). Under 600 Oe field, the energy barrier for 1 (2.6 cm−1, Figure S11) increases slightly compared with it under zero field. In the same way, the experimental energy barrier of 1.0 cm−1 for 2 (Figure S9) under zero dc field is close to the calculated exchange states (1.1 cm−1). Nevertheless, under 600 Oe dc field, complex 2 shows a slow magnetic relaxation for a wide range of frequencies, and the experimental barrier of 34.3 cm−1 is much higher than the calculated one (see reason below). Sources of the Magnetic Variations. Ab initio calculations give almost the same Jdipolar values of 6.60 cm−1 for 1 and 6.62 cm−1 for 2 (Table 2), so the effect of dipolar interactions may not be crucial in this system. However, we note that the coupling constants J of 1 (6.33 cm−1) and 2 (2.03 cm−1) are quite different. For SMMs, coupling interactions are closely related to magnetic behaviors, as observed in several 4f-based SMMs.29,30 Since the J value in 2 is smaller than in 1, under an external dc field, the main contribution to the energy barrier of blockage of magnetization in 2 might come from individual ErIII ions.3c This difference in coupling interactions is most likely related to subtle structural change.30b Because different temperatures were used to collect crystal data and ac magnetic susceptibilities, a simply analysis of some relevant structural parameters was obtained (Tables S2 and S3). From a structural view, the planarity of the benzopyrrole ring of the Pc ligand in 1 is unlike 2, with the dihedral angle between the benzene ring and the adjacent pyrrole ring of 1.4° and 0.6° for 1 and 2, respectively. According to a recent report by Candini et al.,31 the coupling interaction between two ErIII ions probably happens through a multistep process: the f-electrons hybridize with the 5d orbitals of the ErIII ion, which in turn act as a bridge to the delocalized π-type states in the Pc ligand, ultimately

■

CONCLUSION

In conclusion, a guest exchange reaction between benzene and dichloromethane was performed in a SCSC mode, and complexes [Er2(thd)4Pc]·2C6H6 (1) and [Er2(thd)4Pc]· 2CH2Cl2 (2) were obtained. Magnetic susceptibility measurements reveal that the two complexes show drastically different relaxation behaviors. The source of this magnetic variation is probably related to disparate coupling interactions and subtle structural differences, as confirmed by ab initio calculations. The structural parameters and magnetic properties are sensitive to lattice solvents in this system, which can be reversibly tuned through solvent exchange. This work offers a new example for tuning SMM behavior, and the foregoing results are meaningful to understand the magnetostructural correlation for ErIIISMMs. F

DOI: 10.1021/acs.inorgchem.6b02243 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

■

ligand field dominated single-molecule magnets of a series of indolederivative β-diketone mononuclear Dy(III) complexes. Dalton Trans. 2016, 45, 9148−9157. (c) Wu, J.; Jung, J.; Zhang, P.; Zhang, H.; Tang, J.; Le Guennic, B. Cis-trans isomerism modulates the magnetic relaxation of dysprosium single-molecule magnets. Chem. Sci. 2016, 7, 3632−3639. (d) Grindell, R.; Vieru, V.; Pugh, T.; Chibotaru, L. F.; Layfield, R. A. Magnetic frustration in a hexaazatrinaphthylenebridged trimetallic dysprosium single-molecule magnet. Dalton Trans. 2016, 45, 16556−16560. (5) (a) Rinehart, J. D.; Long, J. R. Exploiting single-ion anisotropy in the design of f-element single-molecule magnets. Chem. Sci. 2011, 2, 2078−2085. (b) Liu, J.; Chen, Y. C.; Liu, J. L.; Vieru, V.; Ungur, L.; Jia, J. H.; Chibotaru, L. F.; Lan, Y.; Wernsdorfer, W.; Gao, S.; Chen, X. M.; Tong, M. L. A Stable Pentagonal-Bipyramidal Dy(III) Single-Ion Magnet with a Record Magnetization Reversal Barrier over 1000 K. J. Am. Chem. Soc. 2016, 138, 5441−5450. (c) Jiang, Y.; Holmberg, R. J.; Habib, F.; Ungur, L.; Korobkov, I.; Chibotaru, L. F.; Murugesu, M. Probing the structural and magnetic properties of a new family of centrosymmetric dinuclear lanthanide complexes. RSC Adv. 2016, 6, 56668−56673. (d) Chen, Y. C.; Liu, J. L.; Ungur, L.; Liu, J.; Li, Q. W.; Wang, L. F.; Ni, Z. P.; Chibotaru, L. F.; Chen, X. M.; Tong, M. L. Symmetry-Supported Magnetic Blocking at 20 K in Pentagonal Bipyramidal Dy(III) Single-Ion Magnets. J. Am. Chem. Soc. 2016, 138, 2829−2837. (e) Gupta, S. K.; Rajeshkumar, T.; Rajaraman, G.; Murugavel, R. An unprecedented zero field neodymium(III) single-ion magnet based on a phosphonic diamide. Chem. Commun. 2016, 52, 7168−7171. (6) (a) Hasegawa, Y.; Sakamoto, R.; Takahashi, K.; Nishihara, H. Bis[(E)-2, 6-bis (1H-pyrazol-1-yl)-4-styrylpyridine] iron(II) Complex: Relationship between Thermal Spin Crossover and Crystal Solvent. Inorg. Chem. 2013, 52, 1658−1665. (b) Herold, C. F.; Shylin, S. I.; Rentschler, E. Solvent-dependent SCO Behavior of Dinuclear Iron(II) Complexes with a 1, 3, 4-Thiadiazole Bridging Ligand. Inorg. Chem. 2016, 55, 6414−6419. (c) Pinkowicz, D.; Southerland, H. I.; Avendaño, C.; Prosvirin, A.; Sanders, C.; Wernsdorfer, W.; Pedersen, K. S.; Dreiser, J.; Clerac, R.; Nehrkorn, J.; Simeoni, G. G.; Schnegg, A.; Holldack, K.; Dunbar, K. R. Cyanide Single-Molecule Magnets Exhibiting Solvent Dependent Reversible “On” and “Off” Exchange Bias Behavior. J. Am. Chem. Soc. 2015, 137, 14406−14422. (d) Castellano, M.; Ferrando-Soria, J.; Pardo, E.; Julve, M.; Lloret, F.; Mathonière, C.; Pasán, J.; Ruiz-Pérez, C.; Cañadillas-Delgado, L.; Ruiz-García, R.; Cano, J. Photoswitching of the antiferromagnetic coupling in an oxamato-based dicopper(II) anthracenophane. Chem. Commun. 2011, 47, 11035−11037. (7) (a) Tanaka, D.; Inose, T.; Tanaka, H.; Lee, S.; Ishikawa, N.; Ogawa, T. Proton-induced switching of the single molecule magnetic properties of a porphyrin based TbIII double-decker complex. Chem. Commun. 2012, 48, 7796−7798. (b) Wang, L. F.; Qiu, J. Z.; Liu, J. L.; Chen, Y. C.; Jia, J. H.; Jover, J.; Ruiz, E.; Tong, M. L. Modulation of single-molecule magnet behavior via photochemical [2 + 2] cycloaddition. Chem. Commun. 2015, 51, 15358−15361. (c) Zhang, S.; Ke, H.; Sun, L.; Li, X.; Shi, Q.; Xie, G.; Wei, Q.; Yang, D.; Wang, W.; Chen, S. Magnetization Dynamics Changes of Dysprosium(III) SingleIon Magnets Associated with Guest Molecules. Inorg. Chem. 2016, 55, 3865−3871. (d) Li, J.; Wei, R.-M.; Pu, T.-C.; Cao, F.; Yang, L.; Han, Y.; Zhang, Y.-Q.; Zuo, J.-L.; Song, Y. Tuning Quantum Tunnelling of Magnetization through 3d-4f Magnetic Interaction: an Alternative Approach for Manipulating Single-molecule Magnetism. Inorg. Chem. Front. 2016, DOI: 10.1039/C6QI00407E. (e) Ganivet, C. R.; Ballesteros, B.; Torre, G.; 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 TbIII Bis(phthalocyaninate). Chem. - Eur. J. 2013, 19, 1457−1465. (8) (a) Ren, M.; Bao, S. S.; Hoshino, N.; Akutagawa, T.; Wang, B.; Ding, Y. C.; Wei, S.; Zheng, L. M. Solvent Responsive Magnetic Dynamics of a Dinuclear Dysprosium Single-Molecule Magnet. Chem. - Eur. J. 2013, 19, 9619−9628. (b) Song, Y. M.; Luo, F.; Luo, M. B.; Liao, Z. W.; Sun, G. M.; Tian, X. Z.; Zhu, Y.; Yuan, Z. J.; Liu, S. J.; Xu, W. Y.; Feng, X. F. The application of single-crystal-to-single-crystal

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02243. Selected bond lengths and angles, XRPD patterns, TGA curves, and magnetic characterizations for 1, 2, and 1-re (PDF) X-ray crystallographic files for 1, 2, and 1-re (CIF)

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail (J.-L. Zuo): [email protected]. *E-mail (Y.-Q. Zhang): [email protected]. ORCID

Jing-Lin Zuo: 0000-0003-1219-8926 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the Major State Basic Research Development Program (2013CB922101), the National Natural Science Foundation of China (21631006 and 91433113), and the Natural Science Foundation of Jiangsu Province of China (BK20130054 and BK20151542). M.K. is supported by the CNRS-France.

■

REFERENCES

(1) (a) Liu, K.; Zhang, X.; Meng, X.; Shi, W.; Cheng, P.; Powell, A. K. Constraining the coordination geometries of lanthanide centers and magnetic building blocks in frameworks: a new strategy for molecular nanomagnets. Chem. Soc. Rev. 2016, 45, 2423−2439. (b) Woodruff, D. N.; Winpenny, R. E.; Layfield, R. A. Lanthanide single-molecule magnets. Chem. Rev. 2013, 113, 5110−5148. (c) Vincent, R.; Klyatskaya, S.; Ruben, M.; Wernsdorfer, W.; Balestro, F. Electronic read-out of a single nuclear spin using a molecular spin transistor. Nature 2012, 488, 357−360. (d) Gatteschi, D.; Sessoli, R.; Villain, J. Molecular Nano-magnets; Oxford University Press: Oxford, 2006. (e) Rinehart, J. D.; Fang, M.; Evans, W. J.; Long, J. R. A N23‑ RadicalBridged Terbium Complex Exhibiting Magnetic Hysteresis at 14 K. J. Am. Chem. Soc. 2011, 133, 14236−14239. (f) Pugh, T.; Tuna, F.; Ungur, L.; Collison, D.; McInnes, E. J.L.; Chibotaru, L. F.; Layfield, R. A. Influencing the properties of dysprosium single-molecule magnets with phosphorus donor ligands. Nat. Commun. 2015, 6, 7492−7499. (2) Ishikawa, N.; Sugita, M.; Ishikawa, T.; Koshihara, S. Y.; Kaizu, Y. Lanthanide double-decker complexes functioning as magnets at the single-molecular level. J. Am. Chem. Soc. 2003, 125, 8694−8695. (3) (a) Blagg, R. J.; Muryn, C. A.; McInnes, E. J.; Tuna, F.; Winpenny, R. E. Single pyramid magnets: Dy5 pyramids with slow magnetic relaxation to 40 K. Angew. Chem., Int. Ed. 2011, 50, 6530− 6533. (b) Guo, Y. N.; Xu, G. F.; Wernsdorfer, W.; Ungur, L.; Guo, Y.; Tang, J.; Zhang, H. J.; Chibotaru, L. F.; Powell, A. K. Strong Axiality and Ising Exchange Interaction Suppress Zero-Field Tunneling of Magnetization of an Asymmetric Dy2 Single-Molecule Magnet. J. Am. Chem. Soc. 2011, 133, 11948−11951. (c) Lin, P.; Burchell, T. J.; Ungur, L.; Chibotaru, L. F.; Wernsdorfer, W.; Murugesu, M. A Polynuclear Lanthanide Single-Molecule Magnet with a Record Anisotropic Barrier. Angew. Chem., Int. Ed. 2009, 48, 9489−9492. (d) Pugh, T.; Chilton, N. F.; Layfield, R. A. A Low-Symmetry Dysprosium Metallocene Single-Molecule Magnet with a High Anisotropy Barrier. Angew. Chem. 2016, 128, 11248−11251. (4) (a) Katoh, K.; Breedlove, B. K.; Yamashita, M. Symmetry of octacoordination environment has a substantial influence on dinuclear TbIII triple-decker single-molecule magnets. Chem. Sci. 2016, 7, 4329− 4340. (b) Dong, Y.; Yan, P.; Zou, X.; Yao, X.; Hou, G.; Li, G. Auxiliary G

DOI: 10.1021/acs.inorgchem.6b02243 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry transformation towards adjustable SMM properties. Chem. Commun. 2012, 48, 1006−1008. (c) Liu, J. L.; Chen, Y. C.; Zheng, Y. Z.; Lin, W. Q.; Ungur, L.; Wernsdorfer, W.; Chibotaru, L. F.; Tong, M. L. Switching the anisotropy barrier of a single-ion magnet by symmetry change from quasi-D5h to quasi-Oh. Chem. Sci. 2013, 4, 3310−3316. (d) Ren, M.; Pinkowicz, D.; Yoon, M.; Kim, K.; Zheng, L. M.; Breedlove, B. K.; Yamashita, M. Dy(III) Single-Ion Magnet Showing Extreme Sensitivity to (De)hydration. Inorg. Chem. 2013, 52, 8342− 8348. (9) Zhang, X.; Vieru, V.; Feng, X.; Liu, J. L.; Zhang, Z.; Na, B.; Shi, W.; Wang, B. W.; Powell, A. K.; Chibotaru, L. F.; Gao, S.; Cheng, P.; Long, J. R. Influence of Guest Exchange on the Magnetization Dynamics of Dilanthanide Single-Molecule-Magnet Nodes within a Metal−Organic Framework. Angew. Chem., Int. Ed. 2015, 54, 9861− 9865. (10) Sun, W. B.; Yan, B.; Jia, L. H.; Wang, B. W.; Yang, Q.; Cheng, X.; Li, H. F.; Chen, P.; Wang, Z. M.; Gao, S. Dinuclear dysprosium SMMs bridged by a neutral bipyrimidine ligand: two crystal systems that depend on different lattice solvents lead to a distinct slow relaxation behavior. Dalton Trans. 2016, 45, 8790−8794. (11) Eisentraut, K. J.; Sievers, R. E.; Coucouvanis, D.; Fackler, J. P. Volatile Rare-Earth Chelates of 2,2,6,6-Tetramethylheptane-3,5-Dione. Inorg. Synth. 2007, 11, 94−98. (12) Sugimoto, H.; Higashi, T.; Maeda, A.; Mori, M.; Masuda, H.; Taga, T. Preparation and X-Ray Crystal Structure (for Ln = Sm) of (μPhthalocyaninato)bis[di(2,2,6,6= tetramethylheptane-3,5-dionato)LnIII] (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Y). J. Chem. Soc., Chem. Commun. 1983, 1234−1235. (13) Boudreaux, E. A.; Mulay, L. N. Theory and Application of Molecular Paramagnetism; John Wiley & Sons: New York, 1976; p 491. (14) SAINT-Plus, version 6.02; Bruker Analytical X-ray System: Madison, WI, 1999. (15) Sheldrick, G. M. SADABS an empirical absorption correction program; Bruker Analytical X-ray Systems: Madison, WI, 1996. (16) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, A64, 112−122. (17) Karlström, G.; Lindh, R.; Malmqvist, P. -Å.; Roos, B. O.; Ryde, U.; Veryazov, V.; Widmark, P.-O.; Cossi, M.; Schimmelpfennig, B.; Neogrady, P.; Seijo, L. MOLCAS: a program package for computational chemistry. Comput. Mater. Sci. 2003, 28, 222−239. (18) (a) Katoh, K.; Horii, Y.; Yasuda, N.; Wernsdorfer, W.; Toriumi, K.; Breedlove, B. K.; Yamashita, M. Multiple-decker phthalocyaninato dinuclear lanthanoid(III) single-molecule magnets with dual-magnetic relaxation processes. Dalton Trans. 2012, 41, 13582−13600. (b) Yu, W.; Schramm, F.; Moreno Pineda, E.; Lan, Y.; Fuhr, O.; Chen, J.; Isshiki, H.; Wernsdorfer, W.; Wulfhekel, W.; Ruben, M. Singlemolecule magnet behavior in 2,2′-bipyrimidine-bridged dilanthanide complexes. Beilstein J. Nanotechnol. 2016, 7, 126−137. (19) (a) Gorczynski, A.; Kubicki, M.; Pinkowicz, D.; Pelka, R.; Patroniak, V.; Podgajny, R. The first example of erbium triple-stranded helicates displaying SMM behavior. Dalton Trans. 2015, 44, 16833− 16839. (b) Ge, J. Y.; Xie, J. Z.; Zhao, Z. Y.; Ru, J.; Song, Y.; Zuo, J. L. Thiacalix[4]arene-supported heterodinuclear NiII−LnIII complexes: slow magnetic relaxation behavior in the dysprosium analogue. RSC Adv. 2016, 6, 1143−1150. (20) Le Roy, J. J.; Ungur, L.; Korobkov, I.; Chibotaru, L. F.; Murugesu, M. Coupling Strategies to Enhance Single-Molecule Magnet Properties of Erbium-Cyclooctatetraenyl Complexes. J. Am. Chem. Soc. 2014, 136, 8003−8010. (21) (a) Bartolomé, J.; Filoti, G.; Kuncser, V.; Schinteie, G.; Mereacre, V.; Anson, C. E.; Powell, A. K.; Prodius, D.; Turta, C. Magnetostructural correlations in the tetranuclear series of {Fe3LnO2} butterfly core clusters: Magnetic and Mössbauer spectroscopic study. Phys. Rev. B: Condens. Matter Mater. Phys. 2009, 80, 014430. (b) Langley, S. K.; Moubaraki, B.; Murray, K. S. Magnetic Properties of Hexanuclear Lanthanide(III) Clusters Incorporating a Central μ6Carbonate Ligand Derived from Atmospheric CO2 Fixation. Inorg. Chem. 2012, 51, 3947−3949.

(22) Mondal, K. C.; Kostakis, G. E.; Lan, Y.; Wernsdorfer, W.; Anson, C. E.; Powell, A. K. Defect-Dicubane Ni2Ln2 (Ln= Dy, Tb) Single Molecule Magnets. Inorg. Chem. 2011, 50, 11604−11611. (23) (a) Katoh, K.; Kajiwara, T.; Nakano, M.; Nakazawa, Y.; Wernsdorfer, W.; Ishikawa, N.; Breedlove, B. K.; Yamashita, M. Magnetic Relaxation of Single-Molecule Magnets in an External Magnetic Field: An Ising Dimer of a Terbium(III)-Phthalocyaninate Triple-Decker Complex. Chem. - Eur. J. 2011, 17, 117−122. (b) Cole, K. S.; Cole, R. H. Dispersion and absorption in dielectrics I. Alternating current characteristics. J. Chem. Phys. 1941, 9, 341−351. (24) Li, J.; Han, Y.; Cao, F.; Wei, R.-M.; Zhang, Y.-Q.; Song, Y. Two field-induced slow magnetic relaxation processes in a mononuclear Co(II) complex with a distorted octahedral geometry. Dalton Trans. 2016, 45, 9279−9284. (25) (a) Chibotaru, L. F.; Ungur, L.; Soncini, A. The Origin of Nonmagnetic Kramers Doublets in the Ground State of Dysprosium Triangles: Evidence for a Toroidal Magnetic Moment. Angew. Chem., Int. Ed. 2008, 47, 4126−4129. (b) Ungur, L.; Van den Heuvel, W.; Chibotaru, L. F. Ab initio investigation of the non-collinear magnetic structure and the lowest magnetic excitations in dysprosium triangles. New J. Chem. 2009, 33, 1224−1230. (26) Lines, M. E. Orbital Angular Momentum in the Theory of Paramagnetic Clusters. J. Chem. Phys. 1971, 55, 2977−2984. (27) Chibotaru, L. F.; Ungur, L.; Aronica, C.; Elmoll, H.; Pilet, G.; Luneau, D. Structure, Magnetism, and Theoretical Study of a MixedValence CoII3CoIII4 Heptanuclear Wheel: Lack of SMM Behavior despite Negative Magnetic Anisotropy. J. Am. Chem. Soc. 2008, 130, 12445−12455. (28) Langley, S. K.; Wielechowski, D. P.; Vieru, V.; Chilton, N. F.; Moubaraki, B.; Abrahams, B. F.; Chibotaru, L. F.; Murray, K. S. A {CrIII2DyIII2} Single-Molecule Magnet: Enhancing the Blocking Temperature through 3d Magnetic Exchange. Angew. Chem., Int. Ed. 2013, 52, 12014−12019. (29) (a) Liddle, S. T.; Slageren, J. Improving f-element single molecule magnets. Chem. Soc. Rev. 2015, 44, 6655−6669. (b) Huang, W.; Le Roy, J. J.; Khan, S. I.; Ungur, L.; Murugesu, M.; Diaconescu, P. L. Tetraanionic Biphenyl Lanthanide Complexes as Single-Molecule Magnets. Inorg. Chem. 2015, 54, 2374−2382. (c) Pugh, T.; Vieru, V.; Chibotaru, L. F.; Layfield, R. A. Magneto-structural correlations in arsenic- and selenium-ligated dysprosium single-molecule magnets. Chem. Sci. 2016, 7, 2128−2137. (30) (a) 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. (b) Ida, Y.; Ghosh, S.; Ghosh, A.; Nojiri, H.; Ishida, T. Strong Ferromagnetic Exchange Interactions in Hinge-like Dy(O2Cu)2 Complexes Involving Double Oxygen Bridges. Inorg. Chem. 2015, 54, 9543−9555. (31) Candini, A.; Klar, D.; Marocchi, S.; Corradini, V.; Biagi, R.; De Renzi, V.; del Pennino, U.; Troiani, F.; Bellini, V.; Klyatskaya, S.; Ruben, M.; Kummer, K.; Brookes, N. B.; Huang, H.; Soncini, A.; Wende, H.; Affronte, M. Spin-communication channels between Ln(III) bis-phthalocyanines molecular nanomagnets and a magnetic substrate. Sci. Rep. 2016, 6, 21740.

H

DOI: 10.1021/acs.inorgchem.6b02243 Inorg. Chem. XXXX, XXX, XXX−XXX