A New Bis(phthalocyaninato) Terbium Single-Ion Magnet with an

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Article Cite This: Inorg. Chem. 2017, 56, 13889-13896

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A New Bis(phthalocyaninato) Terbium Single-Ion Magnet with an Overall Excellent Magnetic Performance Yuxiang Chen,† Fang Ma,‡ Xiaoxiang Chen,§ Bowei Dong,§ Kang Wang,† Shangda Jiang,§ Chiming Wang,† Xin Chen,† Dongdong Qi,*,† Haoling Sun,*,‡ Bingwu Wang,*,§ Song Gao,§ and Jianzhuang Jiang*,† †

Beijing Key Laboratory for Science and Application of Functional Molecular and Crystalline Materials, Department of Chemistry, University of Science and Technology Beijing, Beijing 100083, China ‡ Department of Chemistry and Beijing Key Laboratory of Energy Conversion and Storage Materials, Beijing Normal University, Beijing 100875, China § Beijing National Laboratory of Molecular Science State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China S Supporting Information *

ABSTRACT: Bulky and strong electron-donating dibutylamino groups were incorporated onto the peripheral positions of one of the two phthalocyanine ligands in the bis(phthalocyaninato) terbium complex, resulting in the isolation of heteroleptic double-decker (Pc)Tb{Pc[N(C4H9)2]8} {Pc = phthalocyaninate; Pc[N(C4H9)2]8 = 2,3,9,10,16,17,23,24octakis(dibutylamino)phthalocyaninate} with the nature of an unsymmetrical molecular structure, a square-antiprismatic coordination geometry, an intensified coordination field strength, and the presence of organic radical-f interaction. As a total result of all these factors, this sandwich-type tetrapyrrole lanthanide single-ion magnet (SIM) exhibits an overall enhanced magnetic performance including a high blocking temperature (TB) of 30 K and large effective spin-reversal energy barrier of Ueff = 939 K, rendering it the best sandwich-type tetrapyrrole lanthanide SIM reported thus far.

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SMMs.7 In particular, a recent investigation revealed that incorporation of strong electron-donating peripheral substituents significantly enhances the magnetic performance of bis(phthalocyaninato) lanthanide SMMs in terms of both the blocking temperature and energy barrier.3c,d Despite the efforts paid for the purpose of clarifying the effect(s) of each single factor, understanding of the overall effect of all these factors as a whole in sandwich-type tetrapyrrole lanthanide SMMs still remains unknown. In this regard, designing and synthesizing a special sandwich-type tetrapyrrole lanthanide complex by simultaneously combining all of the clarified optimized factors into one system become necessary. It is noteworthy that studies on single-ion magnets (SIMs), a special sort of SMM encapsulating only one metal spin carrier center, are of special importance toward easily understanding and clarifying the relationship between molecular/electronic structure and magnetic properties. In the present paper, hetetroleptic bis(phthalocyaninato) terbium double-decker complex (Pc)Tb{Pc[N(C4H9)2]8} {Pc[N(C4H9)2]8 = 2,3,9,10,16,17,23,24-octakis(dibutylamino)-

INTRODUCTION Sandwich-type tetrapyrrole lanthanide complexes have been intensively studied in the past few decades,1 resulting in the report of a large number of tetrapyrrole lanthanide-based single-molecule magnets (SMMs),2 some of which exhibit quite good magnetic properties as exemplified by a quite high spinreversal energy barrier.3 Future practical applications of such an important series of lanthanide-based SMMs, however, still suffer from their relatively weak magnetic performance similar to that of other lanthanide- and transition metal-based SMMs.4 Contuining to improve the magnetic behavior of sandwich-type tetrapyrrole lanthanide SMMs has therefore become a longterm task in this field. Conversely, extensive studies have disclosed some structural and electronic effects on the magnetic properties of sandwichtype tetrapyrrole lanthanide SMMs.1a,5 For example, employment of a square-antiprismatic coordination geometry of the lanthanide ion has been revealed to be able to elevate the spinreversal energy barrier of the sandwich-type tetrapyrrole Tb/Dy SMM.6 Unsymmetrical peripheral substitution seems to play the same role despite the lack of any theoretical clarification.3a,b The existence of an organic radical-f interaction could optimize the magnetic behavior of sandwich-type tetrapyrrole lanthanide © 2017 American Chemical Society

Received: August 5, 2017 Published: November 7, 2017 13889

DOI: 10.1021/acs.inorgchem.7b02010 Inorg. Chem. 2017, 56, 13889−13896

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Inorganic Chemistry

Scheme 1. Molecular Structures of Unsymmetrically Substituted Neutral Compound (Pc)Tb{Pc[N(C4H9)2]8} (left) and Reduced Compound [(Pc)Tb{Pc[N(C4H9)2]8}]−·[(C4H9)4N]+ (right)

The two newly prepared double-decker compounds were characterized by a wide range of spectroscopic methods as detailed in the Supporting Information. In particular, a typical characteristic organic radical signal was observed at g = 2.005 in the EPR spectrum of the yttrium analogue (Pc)Y{Pc[N(C4H9)2]8},10 demonstrating the organic radical nature of the neutral double-deckers, Figure S1, ensuring the existence of an organic radical-f interaction in the neutral terbium doubledecker compound. After being reduced to [(Pc)Y{Pc[N(C4H9)2]8}]−·[(C4H9)4N]+, this signal completely disappears. Structural Studies. Single crystals of (Pc)Tb{Pc[N(C4H9)2]8} and [(Pc)Tb{Pc[N(C4H9)2]8}]−·[(C4H9)4N]+ suitable for X-ray diffraction analysis were obtained by diffusing acetonitrile vapor into their tetrahydrofuran solution. The neutral species crystallizes in the monoclinic system, and the space group is C2/c. There is one whole (Pc)Tb{Pc[N(C4H9)2]8} molecule in the asymmetric unit, whereas the reduced double-decker crystallizes in the tetragonal system with the space group P4/n; there is 4-fold symmetry in the [(Pc)Tb{Pc[N(C4H9)2]8}]−·[(C4H9)4N]+ molecule, resulting in one-quarter of the molecule in the asymmetric unit, Table S3. Figure 1 shows the single crytal structure of the neutral species together with the reduced double-decker. The central Tb3+ in the neutral compound is octa-coordinated by the eight isoindole nitrogen atoms of the two phthalocyaninato ligands, resulting in a square-antiprismatic coordination polyhedron for the terbium ion with an average twist angle of 43.71°. Obviously, introducing the bulky dibutylamino groups onto the periphery of one of two phthalocyanine ligands ensures a nearly perfect square-antiprismatic coordination geometry for terbium in the unsymmetrically substituted double-decker. In addition, the terbium ion center in the neutral double-decker molecule lies at 2.410−2.425 and 2.407−2.417 Å from the isoindole nitrogen atoms of the unsubstituted Pc and substituted Pc[N(C4H9)2]8, respectively, which in turn results in a distance of 1.389 Å for the terbium ion to the N4 mean planes of both Pc and Pc[N(C4H9)2]8, leading to a ring-to-ring separation of 2.778 Å, Tables S4 and S5. After adding one electron to the neutral double-decker molecule, the twist angle in the reduced double-decker is decreased to 39.42°, indicating a more deviated square-antiprismatic coordination geometry for the Tb3+ in this compound. In addition, the Tb−N(Pc) and Tb−N{Pc[N(C4H9)2]8} bond lengths in the reduced doubledecker increase to 2.436 and 2.425 Å, respectively, with the ring-to-ring separation also increasing to 2.840 Å.

phthalocyaninate, Pc = phthalocyaninate} was designed and prepared. Incorporation of the strong electron-donating and bulky dibutylamino groups onto the periphery positions of one of the two phthalocyanine ligands endows this double-decker system simultaneously with the combined characteristics of an unsymmetrical molecular structure, a square-antiprismatic coordination geometry, an intensified coordination field strength, and the existence of organic radical-f interactions. As a comprehensive result of all these factors, this sandwichtype tetrapyrrole lanthanide SIM displays enhanced magnetic behavior overall including both high blocking temperature and large energy barrier. At the end of this section, it is noteworthy that significant development has been achieved in both experimental and theoretical studies over SMMs in 2017. In particular, a new lanthanide SIM of [(Cpttt)2Dy][B(C6F5)4] with TB = 60 K was reported.8 In addition, the key role of vibrations in the relaxation of SMMs was also determined.9 These results indicate that studies for SMMs are quickly moving into a new era.

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RESULTS AND DISCUSSION Molecular Design and Synthesis. As mentioned above, employment of square-antiprismatic coordination geometry, unsymmetrical peripheral substitution, introduction of organic radicals, and incorporation of strong electron-donating substituents are able to improve the magnetic properties of sandwich-type tetrapyrrole terbium SIMs by raising either TB and/or Ueff.3,5−7 As a result, in the present case we try to incorporate all these clarified optimized factors simultaneously into one system by introducing the bulky and strong electrondonating dibutylamino groups onto the peripheral positions of one of the two phthalocyanine ligands in the bis(phthalocyaninato) terbium double-decker complex. Treatment of Tb(acac)3·nH2O with H2{Pc[N(C4H9)2]8} in refluxing noctanol afforded the half-sandwich complex Tb{Pc[N(C4H9)2]8}(acac), which further reacted in situ with Li2Pc, giving the target unsymmetrical double-decker complex in neutral form (Pc)Tb{Pc[N(C4H9)2]8} in a yield of 37.9%. The neutral form of double-decker (Pc)Tb{Pc[N(C4H9)2]8} further reacted with [(C4H9)4N]+Br− in THF at room temperature in the presence of hydrazine hydrate, leading to the formation and isolation of the reduced form of double-decker [(Pc)Tb{Pc[N(C4H9)2]8}]−·[(C4H9)4N]+ in a yield of 94.5%, Scheme 1 and Scheme S1. 13890

DOI: 10.1021/acs.inorgchem.7b02010 Inorg. Chem. 2017, 56, 13889−13896

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groups in one of the two phthalocyanine chromophores. Interestingly, the adjacent reduced double-deckers are packed into a one-dimensional supramolecular structure depending on electrostatic interaction between the [(Pc)Tb{Pc[N(C4H9)2]8}]− anion and [(C4H9)4N]+ cation, leading to a relatively shorter intermolecular Tb···Tb distance than that of neutral species, 10.976 Å, which seems still large enough to avoid obvious intermolecular magnetic interaction according to previous investigation results.2b,11 Magnetic Properties. Direct current magnetic measurements were performed on polycrystalline samples to investigate the static magnetic performance of the two compounds at 2− 300 K with an applied field of 1 kOe. As shown in Figure S6, the curves of the magnetic susceptibility for both complexes show obvious temperature-dependent character. The χMT = 12.18 cm3 K mol−1 for the neutral compound at 300 K is consistent with the theoretical value of 12.19 cm3 K mol−1 expected for one Tb3+ [7F6, S = 3, L = 3, g = 3/2] and a radical (S = 1/2), and χMT = 11.47 cm3 K mol−1 for the reduced species recorded at 300 K is consistent with the theoretical value of 11.82 cm3 K mol−1 expected for one terbium ion.12 The χMT value of the neutral double-decker was decreased until 24 K with a minimum value of 10.26 cm3 K mol−1 achieved at 24 K because of the depopulation of excited Stark sublevels,13 which however increased rapidly until 2 K to 11.40 cm3 K mol−1, Figure S6a. As exhibited in Figure S6b, the curve of the magnetic susceptibility for the reduced species is more complicated. When the temperature was lowered, the χMT value of reduced double-decker slightly increased until 150 K (11.70 cm3 K mol−1) and then decreased slowly until 17 K (11.04 cm3 K mol−1), which increased again until 6 K (11.19 cm3 K mol−1) followed by the rapid decrease to the minimum value of 6.03 cm3 K mol−1 at 2 K. In addition, the maximum value of M(H) for the neutral double-decker at 2 K and 50 kOe was 5.55 Nβ, Figure S7a, which obviously deviates from the theoretical magnetization saturation value of 9 Nβ,12 indicating

Figure 1. Single crystal molecular structures of neutral double-decker (a) and reduced double-decker (b) in side (left) and top (right) view with all H and disorder C atoms omitted for clarity {Tb (purple), unsubstituted Pc (blue), Pc[N(C 4H9)2]8 (green), [(C4H9)4N]+ (yellow)}.

The crystal packing diagrams of these two compounds are shown in Figures S4−S5, and the corresponding data are summarized in Table S4. As can be seen, the molecules in the single crystal of neutral species are well separated with the nearest Tb···Tb distance being 12.724 Å due to the steric hindrance effect from the eight peripheral bulky dibutylamino

Figure 2. Temperature dependence of the in-phase (χ′) and out-of-phase (χ″) ac magnetic susceptibility of the neutral double-decker [(a, c) for χ′ and (b, d) for χ″]. 13891

DOI: 10.1021/acs.inorgchem.7b02010 Inorg. Chem. 2017, 56, 13889−13896

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Figure 3. Temperature dependence of the in-phase (χ′) and out-of-phase (χ″) ac magnetic susceptibility of the reduced double-decker [(a, c) for χ′ and (b, d) for χ″].

Figure 4. Comparison in the plots of ln(τ) vs. 1/T for (a) neutral and (b) reduced double-deckers.

10000 Hz) were fitted by Arrhenius law, Figure 4. As can be seen, the existence of a linear relationship between ln(τ) and 1/ T for the neutral double-decker SIM in the high-temperature region results in a barrier energy of Ueff = 939 ± 8 K and τ0 = (1.11 ± 0.21) × 10−13 s. This is surely also true for the reduced double-decker with Ueff = 769 ± 6 K and τ0 = (8.89 ± 0.87) × 10−13 s. The larger energy barrier for the neutral double-decker than that of the reduced counterpart is obviously attributed to the increased magnitude of the ligand-field parameter associated with the shorter ring-to-ring distance in the neutral species.14 In addition, the existence of the organic radical-f interaction in the neutral double-decker certainly also contributes to its higher energy barrier over the reduced one, which is revealed by the best simulation for the EPR spectrum of the neutral double-decker with the exchange interaction parameters of Jx = Jy = 0.586 cm−1 and Jz = 0.18 cm−1, Figure S8. At the end of this section, it is noteworthy that the energy barrier of Ueff = 939 K revealed for the neutral double-decker compound actually represents one of the highest Ueff for sandwich-type tetrapyrrole lanthanide SIMs, Figure S9. In addition, the magnetic hysteresis loops were measured at 2 K for the neutral double-decker under 100, 200, and 500 Oe/s sweep rates of the magnetic field, Figure S13a, reconfirming its SIM nature. Obviously, the hysteresis loop becomes narrower

significant magnetic anisotropy for Tb3+ in this compound associated with the unsymmetrical substitution of the strong electron-donating dibutylamino groups in bis(phthalocyaninato) terbium compound. This is also true for the reduced double-decker species with a maximum value of M(H) at 2 K and 50 kOe amounting to 3.71 Nβ, Figure S7b. The dynamic magnetic properties for the two complexes were studied in a 2.0 Oe ac field (1−999 Hz by SQUID) and 3.0 Oe ac field (1000−10000 Hz by PPMS), Figures 2 and 3. As shown in Figure 2, the neutral double-decker exhibits frequency-dependent character in both χ′ and χ″, revealing its slow magnetic relaxation, which in turn reveals its SIM nature. This is also true for the reduced double-decker analogue, Figure 3. In addition, the χ″ peak at 10000 Hz appearing at Tmax = 50 K for the neutral double-decker is 4 K larger than that of the reduced double-decker (Tmax = 46 K at 10000 Hz), suggesting the larger TB in the neutral double-decker than the reduced one, Figures 2d and 3d. However, the Tmax = 50 K at 10000 Hz for the neutral double-decker is still lower than Tmax = 58 K at 10000 Hz of (Pc)Tb{Pc[O(C6H4)-p-tBu]8},3a the latter representing the highest value among the previously reported sandwich-type tetrapyrrole lanthanide SIMs. Furthermore, according to the thermally activated mechanism, τ = τ0exp(Ueff/kT) and τ = 1/(2πν), the data of the χ″ peaks (1000− 13892

DOI: 10.1021/acs.inorgchem.7b02010 Inorg. Chem. 2017, 56, 13889−13896

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neutral double-decker. In contrast, a typical single-butterflyshaped hysteresis loop was disclosed for the reduced counterpart, which is more clearly revealed by the graphic of ΔM3b vs H at 5 K for both complexes, Figure S14. Nevertheless, it is noteworthy that both samples before and after the magnetic measurements were analyzed by X-ray powder diffraction. As shown in Figure S19, the XRD powder patterns of both samples after the magnetic measurements are consistent with those before the magnetic measurement, indicating the unchanged inner structures of samples before and after measuring the magnetic properties. Dilution Magnetic Studies. To clarify the existence/ inexistence of intermolecular f-f interaction with the nearest Tb···Tb distance in the range of 10.976−12.724 Å in the two SIMs, the diamagnetic yttrium-diluted samples (Pc)Tb 0.13 Y 0.87 {Pc[N(C 4 H 9 ) 2 ] 8 } and [(Pc)Tb 0.11 Y 0.89 {Pc[N(C4H9)2]8}]−·[(C4H9)4N]+ were prepared.10 As shown in Figure S20, the X-ray powder diffraction pattern for (Pc)Tb0.13Y0.87{Pc[N(C4H9)2]8} corresponds well with that of (Pc)Tb{Pc[N(C4H9)2]8}, confirming its same phase purity with the latter sample. This is also true for the reduced species, Figure S21. Different from the pure Tb species, the curves of the magnetic susceptibility for both diluted samples show obvious temperature-dependent character, Figure S6a. The χMT = 2.30 cm3 K mol−1 at 300 K for (Pc)Tb0.13Y0.87{Pc[N(C4H9)2]8} is consistent with the theoretical value of 1.91 cm3 K mol−1 expected for one Tb3+ [7F6, S = 3, L = 3, g = 3/2] (13%) and an organic radical (S = 1/2) (100%). However, comparison of the DC magnetic susceptibility curves indicates the obvious difference between (Pc)Tb0.13Y0.87{Pc[N(C4H9)2]8} and (Pc)Tb{Pc[N(C4H9)2]8}: The χMT value of (Pc)Tb0.13Y0.87{Pc[N(C 4 H 9 ) 2 ] 8 } was decreased slowly upon cooling in a monotonous manner, whereas the χMT value of (Pc)Tb{Pc[N(C4H9)2]8} was decreased until 24 K followed by a rapid increase until 2 K, suggesting the existence of the intermolecular f-f interaction in (Pc)Tb{Pc[N(C4H9)2]8}. This is also true for the reduced species, Figure S6b. In addition, the ac susceptibility measurements (1000− 10000 Hz) were also performed for the diluted samples (Pc)Tb0.13Y0.87{Pc[N(C4H9)2]8} and [(Pc)Tb0.11Y0.89{Pc[N(C4H9)2]8}]−·[(C4H9)4N]+. As displayed in Figure S22, (Pc)Tb0.13Y0.87{Pc[N(C4H9)2]8} exhibits frequency-dependent character in both the in-phase signal (χ′) and out-of-phase signal (χ″), indicating its slow magnetic relaxation, which in turn reveals its intrinsic SIM nature as expected. The χ″ peak at 10000 Hz appears at Tmax = 50 K, which is consistent with that

along with decreasing the sweep rate, which is in line with previously reported SIMs.3c,4a,5b This is surely also true for the reduced species, Figure S13b. For easy comparison with other SIMs reported, measurements over the magnetic hysteresis loops were also carried out under a 200 Oe/s sweep rate of the magnetic field. As shown in the Figure 5 and Figures S15 and

Figure 5. Normalized magnetic hysteresis loops for the (a) neutral double-decker at 2−30 K and (b) reduced double-decker at 2−27 K under 200 Oe/s of the magnetic field.

S16, the hysteresis loops of the neutral species are able to be observed in the range of 2−30 K. This is also true for the reduced species with the hysteresis loops observed in a slightly diminished temperature range from 2 to 27 K, Figure 5 and Figures S17 and S18. It is noteworthy that the value of 30 K revealed here for the neutral compound represents the highest temperature at which the hysteresis loop can be observed for the sandwich-type tetrapyrrole lanthanide SIMs reported thus far, Figure S9. As shown in Figure S14a, at a temperature of 5 K and swept by the magnetic field from +30 to −30 kOe and back again, the magnetization of the neutral double-decker species becomes saturated at field strengths of ±30 kOe with the value of ±4.8 Nβ, respectively. This is also true for the reduced double-decker with the saturated magnetization of ±3.5 Nβ achieved at the field strengths of ±30 kOe, Figure S14b. Quite interestingly, a double-butterfly-shaped instead of the classical single-butterfly-shaped hysteresis loop was revealed for the

Figure 6. Electrostatic potential around the Tb3+ (2 Å radius sphere) caused by the two Pc ligands. 13893

DOI: 10.1021/acs.inorgchem.7b02010 Inorg. Chem. 2017, 56, 13889−13896

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CONCLUSIONS Briefly summarizing above, simultaneous combination of the thus far clarified optimized structural and electronic effects into one system leads to the design and synthesis of an unsymmetrically substituted bis(phthalocyaninato) terbium double-decker complex, which shows the best overall magnetic performance among all the sandwich-type tetrapyrrole lanthanide SIMs. The present result provides not only a useful pathway for the fabrication of sandwich-type tetrapyrrole lanthanide SIMs but also a good platform for the application, even for just proof-of-concept application-driven exploration, due to the combination of good magnetic performance with high stability.

of the corresponding undiluted sample. Furthermore, on the basis of a thermally activated mechanism, the data of the χ″ peaks (1000−10000 Hz) were fitted by Arrhenius law, giving Ueff = 873 ± 10 K and τ0 = (4.30 ± 0.85) × 10−13 s, Figure S23. Obviously, these values are comparable to those found for the undiluted sample (Pc)Tb{Pc[N(C4H9)2]8}, indicating the quite small effect of the intermolecular f-f interaction on the magnetic properties of the neutral double-decker SIM. Nevertheless, it is worth mentioning that observation of the stronger quantum tunneling of magnetization (QTM) for the diluted sample in comparison with the undiluted sample (Pc)Tb{Pc[N(C4H9)2]8} in the temperature below 10 K gives additional support for the existence of the long-range magnetic coupling between Tb3+ ions in the latter species, Figure 2d and Figure S22b. This is also true for the reduced species, Figure 3 and Figure S22. Density Functional Theory (DFT) Calculations. Toward understanding the enhanced magnetic behavior of (Pc)Tb{Pc[N(C4H9)2]8} SIM, DFT calculations were performed for (Pc)Tb{Pc[N(C2H5)2]8} using M06-GD3 for molecular optimization and wave function analysis.15 A mixed basis set, including 6-311+G(d,p)/6-311+G(2df,p) for C/H/N and SDD for Tb, was utilized to calculate the wave function.16 For comparison, the calculation results for Tb(Pc)2 and Tb{Pc[N(C2H5)2]8}2 are also displayed in Figure 6. According to the calculation results, the electrostatic potential around the Tb3+ from both Pc ligands in Tb(Pc)2 is −3.75 au, which increases to −11.59 au for Tb{Pc[N(C2H5)2]8}2, indicating the enhanced coordination field strength around the terbium ion after peripherally incorporating the dialkylamino groups in both phthalocyanine ligands. Introduction of the same dialkylamino groups in an unsymmetrical manner, however, leads to a slightly decreased electrostatic potential from the Pc side, −3.58 au, but a further increased electrostatic potential, −18.05 au, from the Pc[N(C2H5)2]8 side around the Tb3+ in (Pc)Tb{Pc[N(C2H5)2]8}, enlarging the molecular magnetic anisotropy for the Tb3+ spin carrier center. This in turn yields overall enhanced magnetic behavior for the unsymmetrical (Pc)Tb{Pc[N(C2H5)2]8} SIM over that of their symmetric counterparts. Thermogravimetric Analysis (TGA). The thermal gravimetric analysis for the neutral as well as the reduced doubledecker was carried out to reveal its thermal stability. As shown in Figure S24, according to the TGA curve in the single crystals of the neutral double-decker, the solvent tetrahydrofuran and methanol molecules are lost first in the range of 235−261 °C (exptl 4.7%, calcd for 1THF+1CH3OH 4.5%). In the range of 261−428 °C, eight n-C 4 H 9 chains of the peripheral dibutylamino groups are gradually decomposed (exptl 20.7%, calcd 19.8%). Above 428 °C, the rest of the side chains and the framework of the double-decker are decomposed. For the reduced species, the TGA curve shows that the solvent tetrahydrofuran molecule was lost from 200 to 208 °C (exptl 2.9%, calcd for 1THF 2.9%). The decomposition temperature of the eight n-C4H9 chains in this compound spans the range of 210−300 °C. Above 300 °C, the rest of the side chains and the framework of this compound are decomposed. Obviously, the good stability, in combination with the well-defined molecular and electronic structure, and overall excellent SIM property, ensures the future application, even for just a proof-of-concept application-driven study.

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EXPERIMENTAL SECTION

General Procedures. n-Octanol was distilled freshly from sodium under N2. Column chromatography was performed with the indicated eluents on silica gel (200−300 mesh). The complexes Y(acac)3·nH2O, Tb(acac)3·nH2O,17 H2{Pc[N(C4H9)2]8},18 and Li2Pc19 were synthesized according to reported procedures. All the other solvents and reagents were used as received. MALDI-TOF MS was recorded on a Bruker BIFLEX III ultra-highresolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer with α-cyano-4-hydroxycinnamic acid as the matrix. Electronic absorption spectra were carried out on a Hitachi U-2910 spectrophotometer. Elemental analyses were taken on an Elementar Vavio El III. The magnetic measurements were performed on PPMS, SQUIDVSM, SQUID-XL, and magnetometer on polycrystalline samples. EPR measurements were performed on Bruker Elexsys E580 X-band. TGA was performed on a PerkinElmer TG-7 analyzer with a heating rate of 10 °C/min in the range of 25−800 °C under a N2 atmosphere. Crystal data for (Pc)Tb{Pc[N(C4H9)2]8} and [(Pc)Tb{Pc[N(C4H9)2]8}]−·[(C4H9)4N]+ were determined by using Oxford Diffraction Gemini E system at 100 K with Cu Kα radiation λ = 1.5418 Å, and both the structures were solved and refined by SHELXL-97. The crystal structure refinement details are summarized in Table S3. The supplementary crystallographic data of this article could be obtained from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif (the CCDC numbers are 1524821 and 1524822 for the neutral and reduced complexes, respectively). Details of the computation are shown in the Supporting Information. Powder X-ray diffraction (PXRD) data were collected on a Shimadzu XRD-6000 diffractometer using Cu Kα radiation (λ = 1.54056 Å) at room temperature. Synthesis of (Pc)Tb{Pc[N(C4H9)2]8}. A mixture of Tb(acac)3·nH2O (10.5 mg, 0.0206 mmol) and H2{Pc[N(C4H9)2]8} (29.5 mg, 0.0193 mmol) in n-octanol (1.0 mL) was heated to reflux under N2 for 6 h. Then, Li2Pc (12.6 mg 0.0239 mmol) was added, and the mixture was heated to reflux for another 6 h. After cooling to room temperature, the mixture was evaporated under reduced pressure. Then, the residue was chromatographed on a silica gel column using CH2Cl2/CH3OH (150:1) as eluent. Repeated chromatography followed by recrystallization from THF/CH3OH afforded dark-green microcrystals of (Pc)Tb{Pc[N(C4H9)2]8} in a yield of 16.1 mg, 37.9%. MS (MALDI−TOF) m/z: 2202.029 [M + H]+. Elemental analysis (%) calcd for C128H168N24Tb·CH3OH·C4H8O: C 69.27, H 7.87, N 14.58; found: C 69.56, H 7.75, N 14.28. UV−vis (CHCl3) λ/nm (log ε): 330 (5.05), 658 (4.87), 694 (4.97), 926 (3.95), 1258 (3.74), 1434 (4.05), 1534 (3.97). Synthesis of [(Pc)Tb{Pc[N(C4H9)2]8}]−·[(C4H9)4N]+. Hydrazine hydrate (0.1 mL) in CH3OH (2 mL) was added to a solution of (Pc)Tb{Pc[N(C4H9)2]8} (22.3 mg, 0.0101 mmol) in THF (5 mL) at room temperature, and the mixture was stirred under N2 for 1 h. Then, an excess amount of [(C4H9)4N]+Br− was added to the mixture, which was stirred for another 1 h. Then, the mixture was evaporated under reduced pressure, and the residue was recrystallized from THF/ CH3OH, affording a dark green powder of target compound in a yield 13894

DOI: 10.1021/acs.inorgchem.7b02010 Inorg. Chem. 2017, 56, 13889−13896

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Inorganic Chemistry of 23.4 mg, 94.5%. MS (MALDI−TOF) m/z: 2201.155 [M − (C4H9)4N+]−. Elemental analysis calcd (%) for C144H204N25Tb· CH3OH·C4H8O·H2O: C 69.73, H 8.56, N 13.64; found: C 69.62, H 8.82, N 13.45. UV−vis (CHCl3) λ/nm (log ε): 330 (4.95), 649 (5.00), 696 (4.73).

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Acc. Chem. Res. 2009, 42 (1), 79−88. (c) Functional Phthalocyanine Molecular Materials, Structure and Bonding; Jiang, J., Vol. Ed.; Mingos, D. M. P., Series Ed.; Springer: Heidelberg, Germany, 2010. (d) Bian, Y.; Jiang, J. In 50 Years of Structure and Bonding − The Anniversary Vol.; Mingos, D. M. P., Ed.; Springer International Publishing: Berlin Heidelberg, 2015; pp 159−199. (e) Ng, D. K. P.; Jiang, J. Sandwichtype heteroleptic phthalocyaninato and porphyrinato metal complexes. Chem. Soc. Rev. 1997, 26 (6), 433−442. (2) (a) 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 (29), 8694− 8695. (b) Cao, W.; Gao, C.; Zhang, Y.-Q.; Qi, D.; Liu, T.; Wang, K.; Duan, C.; Gao, S.; Jiang, J. Rational enhancement of the energy barrier of bis(tetrapyrrole) dysprosium SMMs via replacing atom of porphyrin core. Chem. Sci. 2015, 6 (10), 5947−5954. (c) Wang, K.; Qi, D.; Wang, H.; Cao, W.; Li, W.; Liu, T.; Duan, C.; Jiang, J. Binuclear Phthalocyanine-Based Sandwich-Type Rare Earth Complexes: Unprecedented Two π-Bridged Biradical-Metal Integrated SMMs. Chem. Eur. J. 2013, 19 (34), 11162−11166. (d) Wang, H.; Qian, K.; Wang, K.; Bian, Y.; Jiang, J.; Gao, S. Sandwich-type tetrakis(phthalocyaninato) dysprosium-cadmium quadruple-decker SMM. Chem. Commun. 2011, 47 (34), 9624−9626. (3) (a) Ganivet, C. R.; Ballesteros, B.; de la Torre, G.; ClementeJuan, 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 (4), 1457−1465. (b) Mannini, M.; Bertani, F.; Tudisco, C.; Malavolti, L.; Poggini, L.; Misztal, K.; Menozzi, D.; Motta, A.; Otero, E.; Ohresser, P.; Sainctavit, P.; Condorelli, G. G.; Dalcanale, E.; Sessoli, R. Magnetic behaviour of TbPc2 single-molecule magnets chemically grafted on silicon surface. Nat. Commun. 2014, 5, 4582. (c) Chen, Y.; Ma, F.; Chen, X.; Dong, B.; Wang, K.; Jiang, S.; Wang, C.; Chen, X.; Qi, D.; Sun, H.; Wang, B.; Gao, S.; Jiang, J. Novel bis(phthalocyaninato) rare earth complexes with the bulky and strong electron-donating dibutylamino groups: synthesis, spectroscopy, and SMM properties. Inorg. Chem. Front. 2017, 4, 1465−1471. (d) Here, the magnetic blocking temperature (TB) is the highest temperature at which an SMM displays hysteresis in plots of magnetization (M) versus magnetic field (H). It is worth noting that the value of TB strongly depends on the sweep rate of the magnetic field. In the present work, the sweep rate of the magnetic field is 200 Oe/s. (4) (a) 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. SymmetrySupported Magnetic Blocking at 20 K in Pentagonal Bipyramidal Dy(III) Single-Ion Magnets. J. Am. Chem. Soc. 2016, 138 (8), 2829− 2837. (b) Yao, X.-N.; Du, J.-Z.; Zhang, Y.-Q.; Leng, X.-B.; Yang, M.W.; Jiang, S.-D.; Wang, Z.-X.; Ouyang, Z.-W.; Deng, L.; Wang, B.-W.; Gao, S. Two-Coordinate Co(II) Imido Complexes as Outstanding Single-Molecule Magnets. J. Am. Chem. Soc. 2017, 139 (1), 373−380. (5) (a) Liu, J. L.; Chen, Y. C.; Guo, F. S.; Tong, M. L. Recent advances in the design of magnetic molecules for use as cryogenic magnetic coolants. Coord. Chem. Rev. 2014, 281, 26−49. (b) Woodruff, D. N.; Winpenny, R. E. P.; Layfield, R. A. Lanthanide single-molecule magnets. Chem. Rev. 2013, 113 (7), 5110−5148. (c) Rinehart, J. D.; Long, J. R. Exploiting single-ion anisotropy in the design of f-element single-molecule magnets. Chem. Sci. 2011, 2 (11), 2078−2085. (6) (a) Wang, H.; Wang, K.; Tao, J.; Jiang, J. Twist angle perturbation on mixed (phthalocyaninato)(porphyrinato) dysprosium(III) double-decker SMMs. Chem. Commun. 2012, 48 (24), 2973− 2975. (b) Kan, J.; Wang, H.; Sun, W.; Cao, W.; Tao, J.; Jiang, J. Sandwich-Type Mixed Tetrapyrrole Rare-Earth Triple-Decker Compounds. Effect of the Coordination Geometry on the Single-MoleculeMagnet Nature. Inorg. Chem. 2013, 52 (15), 8505−8510. (c) Thiele, S.; Balestro, F.; Ballou, R.; Klyatskaya, S.; Ruben, M.; Wernsdorfer, W. Electrically driven nuclear spin resonance in single-molecule magnets. Science 2014, 344 (6188), 1135−1138. (7) (a) Habib, F.; Murugesu, M. Lessons learned from dinuclear lanthanide nano-magnets. Chem. Soc. Rev. 2013, 42 (8), 3278−3288. (b) Demir, S.; Jeon, I.-R.; Long, J. R.; Harris, T. D. Radical ligand-

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b02010. Spectroscopic and magnetic characterization, details of the DFT calculation, synthesis of heteroleptic bis(phthalocyaninato) rare earth(III) double-decker complexes, experimental and simulated isotopic patterns and electronic absorption spectra for neutral and reduced double-deckers, molecular packing in single crystals for neutral and reduced double-deckers, temperature dependence of χMT, the M vs H curves, temperature dependence of the in-phase and out-of-phase ac magnetic susceptibility, the plots of ln(τ) vs 1/T, and the magnetic hysteresis loops (200 Oe/s) for neutral and reduced double-deckers, analytical, mass spectrometric data, and electronic absorption data, crystal data and structure refinements, and relaxation fitting parameters for neutral and reduced double-deckers (PDF) Accession Codes

CCDC 1524821−1524822 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.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: *E-mail: *E-mail: *E-mail:

[email protected]. [email protected]. [email protected]. [email protected].

ORCID

Shangda Jiang: 0000-0003-0204-9601 Haoling Sun: 0000-0002-2112-4331 Bingwu Wang: 0000-0001-8092-5959 Jianzhuang Jiang: 0000-0002-4263-9211 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the National Key Basic Research Program of China (Grant 2013CB933402), Natural Science Foundation of China (Nos. 21290174, 21631003, 21671017, 21301017, and 21401009), Beijing Municipal Commission of Education, and University of Science and Technology Beijing is gratefully acknowledged.

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REFERENCES

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