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Article

Six-Coordinate Ln(III) Complexes with Various Coordination Geometries Showing Distinct Magnetic Properties

1
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
*
Author to whom correspondence should be addressed.
Inorganics 2018, 6(1), 16; https://doi.org/10.3390/inorganics6010016
Submission received: 29 November 2017 / Revised: 14 January 2018 / Accepted: 15 January 2018 / Published: 18 January 2018
(This article belongs to the Special Issue Single-Molecule Magnets)

Abstract

:
The syntheses, structural characterization, and magnetic properties of three lanthanide complexes with formulas [Ln(L1)3] (Ln = Dy (1Dy); Er (1Er)); and [Dy(L2)2] (2Dy) were reported. Complexes 1Dy and 1Er are isostructural with the metal ion in distorted trigonal-prismatic coordination geometry, but exhibit distinct magnetic properties due to the different shapes of electron density for DyIII (oblate) and ErIII (prolate) ions. Complex 1Dy shows obvious SMM behavior under a zero direct current (dc) field with an effective energy barrier of 31.4 K, while complex 1Er only features SMM behavior under a 400 Oe external field with an effective energy barrier of 23.96 K. In stark contrast, complex 2Dy with the octahedral geometry only exhibits the frequency dependence of alternating current (ac) susceptibility signals without χ″ peaks under a zero dc field.

Graphical Abstract

1. Introduction

Single-molecule magnets (SMMs), with the individual molecules acting as tiny magnets, are the most appealing candidates to develop memory devices with ultra-high density and spintronic devices [1,2,3,4,5,6]. The realization of those potential applications firstly depends on the high magnetic blocking temperature (TB) and large effective energy barrier (Ueff), which have attracted the interests of chemists, physicists, and theorists [7,8,9]. The effective energy barrier (also called the anisotropy barrier, ∆E) is the potential barrier hampering the reversal of the magnetization. For polynuclear transition metal SMMs, such as Mn12 [10] and Mn4 [11], the anisotropy barrier can be expressed as ∆E = DS2 or D(S2 − 1/4) for integer and half-integer spins, in which D is the axial zero-field splitting parameter and S is the spin of ground state. The magnetic blocking temperature (TB) can refer to the highest temperature at which the M(H) hysteresis loop is observed. It is worth noting that TB strongly depends on the field-sweep rate. Usually, a complex with a high anisotropy barrier will not have a guaranteed high blocking temperature, which may be attributed to the fast quantum tunneling of magnetizations. Up to now, the records of blocking temperature and effective energy barrier have been achieved by the complex {[(Cpttt)2Dy][B(C6F5)4]} (Cpttt = 1,2,4-tri(tertbutyl)cyclopentadienide) [12,13], as reported by the Layfield and Mills groups, with TB = 60 K and Ueff = 1837 K, in which the value of Ueff is higher by more than a factor of 30 than that of the Mn12 [10], the first SMM with Ueff = 61 K. The remarkable SMM properties of {[(Cpttt)2Dy][B(C6F5)4]} should mainly benefit from a perfectly axial crystal field realized by the bis(cyclopentadienyl) ligand, which demonstrates that the coordination environment of lanthanide ions plays a critical role in designing and modifying the SMMs, with the exception of complex N23−–Ln2 [14,15], where strong lanthanide-radical magnetic exchange coupling hinders zero-field fast relaxation pathways, and the asymmetric Dy2(ovph)2 [16,17] with the Ising exchange interaction between DyIII ions, which efficiently suppresses fast QTM [18].
Considering the various coordination geometries and numbers of lanthanide complexes, choosing the particular coordination geometry is of vital importance in order to obtain better SMMs. For DyIII ions with the oblate-shaped electron density, a crystal field in which the ligand electron density is concentrated above and below the equatorial plane is desired to enhance the magnetic anisotropy [19]. Furthermore, this kind of crystal field could lead to a highly efficient dysprosium SIM (single-ion magnet), such as D4d [20,21,22] or D5h [23,24,25]. Moreover, the low-coordinate lanthanide complexes are superior at controlling the coordinated environment and understanding the magneto-structural relationship [26,27,28,29,30].
SIMs with six-coordination geometries are still rare in the previously reported Ln-based complexes, compared with other SIMs with high coordination numbers [31,32]. Recently, Gao and co-workers reported that the complex [(LCO)Dy(N*)2] (LCOH = {N-[(2-MeO)–C6H5]}N = C(Me)CH = C(Me)N(H){N′-[(2-MeO)C6H5]} and HN* = HN(SiMe3)2) with trigonal-prismatic coordination geometry, exhibited a high energy barrier Ueff = 190 K under a zero dc field [33]. It is crucial to note that the magnetic axis is approximately collinear to the direction of [N*]–N, resulted from the strong axial-ligand field improved by the short Dy–N([N*]) bond lengths of 2.296 Å. However, complexes Dy(H2BPzMe2)3 (HPz = pyrazole) [34] and Dy(BcMe)3 ([BcMe] = dihydrobis(methylimidazolyl)borate) [35] both exhibit only field- or dilution-induced slow relaxation of magnetization, in which cases the averaged bond distances of Dy–N and Dy–C are 2.477 and 2.577 Å, respectively. Those cases have demonstrated that the occurrence of SIMs’ properties not only depends on the coordination geometry, but also on the strong axial-ligand field. In contrast, the six-coordinate Ln-based complexes possessing octahedral geometries show no SIM properties under a zero dc field, such as {(H2O)[Ln(NA)2]·H2O}n (H2NA = 5-hydroxynicotinic acid) [28] and [Yb(H3L)2]Cl·5CH3OH·H2O (H3L = tri(((2-hydroxy-3-methoxybenzyl)amino)ethyl)amine) [36], which can be attributed to the fact that the cubic Oh symmetry does not have second-order uniaxial anisotropy parameter B 2 0 [37,38,39].
Herein, we report three six-coordinate lanthanide complexes, [Ln(L1)3] (Ln = Dy (1Dy); Er (1Er)); and [Dy(L2)2] (2Dy), where HL1 = 2-(((2,6-diisopropylphenyl)imino)methyl)-phenol and H2L2 = 6,6′-(2-(dimethylamino)ethylazanediyl)bis(methylene)bis(2,4-di-tert-butylphenol) (Scheme 1). Complexes 1Ln present the distorted trigonal-prismatic coordination geometry, while complex 2Dy shows distorted octahedral coordination geometry. The ac susceptibility data reveal the SIM behavior of 1Dy under a zero dc field, but the field-induced SIM behavior of 1Er. Without exception, complex 2Dy only shows the frequency dependence of ac signals without χ″ peaks under a zero dc field, as reported previously [28,40]. Therefore, this series of complexes sheds light on the magneto-structural correlation of six-coordinate complexes with different geometries. Importantly, complex 1Dy is the second SIM with trigonal-prismatic coordination geometry in the absence of an external field.

2. Results and Discussion

2.1. Crystallography

Single-crystal X-ray diffraction investigation revealed that complexes 1Dy, 1Er (Figure 1), and 2Dy (Figure 2) crystallize in the triclinic P 1 ¯ space group with Z = 2, in which complexes 1Dy and 1Er are isostructural. Herein, the crystal structure of 1Dy is described representatively. Details of the crystallographic data and the structure solution of three complexes are summarized in Table 1. Selected bond distances and angles are listed in Table S1 (see Supplementary Materials). The asymmetric unit of 1Dy contains one DyIII ion with a [N3O3] coordination environment, which comes from three [L1] ligands. The coordination geometry around the DyIII ion is similar to the trigonal-prismatic geometry, which has been proven by the SHAPE 2.1 software [41,42,43], revealing that the DyIII ion is located in a distorted trigonal prism with a deviation of 2.36 from the ideal D3h symmetry (Table S2, Supplementary Materials). The up and down basal planes are constructed by atoms O1, O3, and N3 and O2, N1, and N2, respectively, in which the θ angle between the two planes is 13.12° (Figure S1, Supplementary Materials). The bond distances of Dy–O and Dy–N are in the range of 2.144(3)–2.167(3) Å and 2.446(3)–2.606(3) Å, respectively. The angles of O1–Dy–O2 and O2–Dy–O3 are 142.05° and 132.32°, respectively. The packing arrangement along the c axis (Figure S2, Supplementary Materials) demonstrates that the shortest Dy···Dy distance is 10.88 Å. For complex 1Er, the bond distances of Er–O and Er–N are in the range of 2.123(5)–2.146(5) Å and 2.411(4)–2.567(5) Å, respectively, which are shorter than those of 1Dy. The angles of O1–Er–O2 and O2–Er–O3 are 140.62° and 132.89°, respectively. The θ angle between two planes is 11.56° (Figure S3, Supplementary Materials), and the shortest Er···Er distance is 10.94 Å (Figure S4, Supplementary Materials).
The DyIII ion of complex 2Dy locates in a [N4O2] coordination environment, in which O1 and O2 come from one H2L2 ligand, and O3, O4, N3, and N4 come from a second H2L2 ligand. The six-coordinate DyIII ion is in a distorted octahedral arrangement with a deviation of 1.70 from the ideal Oh symmetry (Table S2, Supplementary Materials). Two phenol O atoms (O3 and O4) are axially coordinated to DyIII with a Dy–O3 distance of 2.275(3) and a Dy–O4 distance of 2.170(3) Å, and O3–Dy–O4 bond angle of 155.23°. The other bond distances of Dy–O are 2.182(3) and 2.208(3) Å, which are longer than those of Dy–O4. The bond distances of Dy–N are 2.515(4) and 2.662(4) Å. Furthermore, the shortest distance of the neighboring DyIII ions is 10.36 Å (Figure S5, Supplementary Materials).

2.2. Magnetic Properties

The variable-temperature magnetic susceptibility data of complexes 1Dy, 1Er, and 2Dy were collected on the polycrystalline samples under an applied magnetic field of 1 kOe. At room temperature, the χMT values (Figure 3) of 1Dy, 1Er, and 2Dy are 13.77, 11.38, and 13.21 cm3·K·mol−1, respectively, which are slightly lower than the expected value for free DyIII (14.17 cm3·K·mol−1) and ErIII (11.48 cm3·K·mol−1) ions. As the temperature decreased, the χMT products decrease slowly down to 2 K, reaching values of 11.60 and 11.15 cm3·K·mol−1 for 1Dy and 2Dy, respectively. For complex 1Er, upon cooling, the χMT products slightly decrease over the range of 300–100 K, followed by an obvious decrease until 2 K with a minimum of 7.99 cm3·K·mol−1. The decrease of χMT values can be attributed to the Stark level splitting of lanthanide ions with large unquenched orbital moment. The field-dependent magnetizations for complexes 1Dy and 2Dy show the same tendency (Figures S6 and S8, Supplementary Materials), as observed in most dysprosium complexes reported [44]. The magnetizations increase rapidly up to a field of 10 kOe, followed by an almost constant rise to 70 kOe, reaching values of 5.57 and 4.91 μB at 1.9 K for 1Dy and 2Dy, respectively. However, a residual slope for complex 1Er (Figure S7, Supplementary Materials) is observed even at high field, and the magnetization finally reaches a value of 5.07 μB at 1.9 K. The non-saturation of the field-dependent magnetizations at high field (70 kOe) for three complexes reveal the presence of magnetic anisotropy caused by the crystal-field effects and/or low-lying excited states.
Alternating current susceptibility measurements were also conducted for three complexes under zero and 400 Oe dc field to further probe the dynamics of magnetization. In the absence of an applied dc field, both in-phase (χ′) and out-of-phase (χ″) ac susceptibilities for complex 1Dy exhibit frequency (Figure 4) and temperature (Figure S9, Supplementary Materials) dependency. However, no maximum peaks of temperature dependence of the out-of-phase (χ″) signal are observed in the range of 1–1488 Hz, which may be caused by the quantum tunneling of the magnetization (QTM), as also indicated by strong temperature-independent peaks below 9 K showed in Figure 4. To evaluate the effective barrier of magnetic relaxation, the relaxation times (τ) were extracted from the plot χ″ versus υ using the Debye model [45]. The τ versus T−1 plot (Figure 5) shows a crossover from a linear increase of thermally activated to a temperature independent regime of QTM, which suggests the presence of more than one relaxation pathway. The plot was fitted using Equation (1), yielding effective energy barriers Ueff of 31.40 K with a τ0 = 3.56 × 10−4 s, where the τ−1QTM, AH2T, CTn, and τ 0 1 exp(−Ueff/kBT) represent quantum tunneling, direct, Raman, and Orbach relaxation processes, respectively. For complex 1Dy, the direct process is excluded since the corresponding contribution is nullified at zero dc field. Other parameters obtained from the fitting are given in Table S3 (see Supplementary Materials).
τ 1 o b s = τ 1 Q T M + A H 2 T + C T n + τ 0 1 exp ( U e f f k B T )
For complex 1Er, no out-of-phase (χ″) signals (Figure S10, Supplementary Materials) were observed above 1.9 K at 997 Hz, which may be attributed to the fast quantum tunneling of the magnetization at zero dc field. The rather different magnetic behaviors of 1Dy and 1Er are correlated with the axial ligand field of trigonal-prismatic coordination geometry, as DyIII is oblate and ErIII is prolate [19]. In order to suppress the QTM process, the ac magnetic susceptibility measurements were also performed under a dc field (Figure S11, Supplementary Materials). The non-zero frequency- and temperature-dependent χ′ and χ″ signals (Figure 4 and Figure S12, Supplementary Materials) were observed at low temperature, indicating the field-induced SMM behavior. The relaxation times (τ) of 1Er were extracted from the plot χ″ versus υ using the Debye model. The τ versus T−1 plot (Figure 5), showing a smooth increase as the temperature was lowered, corroborates that the QTM is suppressed to a certain extent. The plot was fitted using Equation (1), yielding effective energy barriers Ueff of 23.96 K with a τ0 = 5.46 × 10−8 s, and other parameters are listed in Table S3 (see Supplementary Materials). To avoid overparametrization, the direct process is canceled.
The Cole-Cole plots (Figure 6) of 1Dy and 1Er both show an asymmetrical semicircular shape, which can be fitted by the generalized Debye model [45], giving a series of α parameters below 0.11 from 1.9 to 13 K for 1Dy and 0.13 from 1.9 to 3.7 K for 1Er, respectively, which indicates a narrow distribution of the relaxation time for both complexes.
For complex 2Dy, both in-phase (χ′) and out-of-phase (χ″) ac susceptibilities exhibited frequency (Figure 4) and temperature (Figure S13, Supplementary Materials) dependency under a zero dc field, indicative of slow relaxation of magnetization. However, no peaks of χ″ were observed, indicating the presence of fast QTM relaxation.
Compared with 1Ln with trigonal-prismatic geometry, the six-coordinated 2Dy with octahedral geometry demonstrates inferior magnetic properties, verifying that the coordination geometry around lanthanide ions directly affects the SMM performance. The closer the distribution of the ligands to spherical symmetry, such as the environment of cubic symmetry (octahedron, etc.), the smaller the crystal-field (CF) splitting [46]. Therefore, the trigonal prismatic geometry can improve a relatively axial ligand field compared with the octahedron, which means that the six-coordinated lanthanide-based complexes, especially dysprosium complexes, located in trigonal-prismatic geometry are more likely to show SMM behavior in principle, which coincides with our experimental results. In order to further explore the magnetic properties of these two six-coordinate Dy-based complexes, the Magellan program [47] was used to calculate the magnetic anisotropy axes of complex 1Dy (Figure 7). The results reveal that the orientation of the magnetic axis of complex 1Dy is found to be almost collinear to Dy–O2 with an angle of 3.707°. Apparently, the negative charges on the O atoms are much larger than those on the N atoms for 1Dy, where it is more capable of stabilizing the ground doublet. As the ground-state wave function of complex [(LCO)Dy(N*)2] [33] featuring similar trigonal-prismatic coordination geometry around DyIII ion with complex 1Dy shows a dominant MJ = ±15/2 doublet, the magnetic axis orientation might prefer the negative charge dense direction for the DyIII ion with the oblate shaped electron density of <±15/2> doublet. Herein, the calculation was based on an electrostatic model, and a further quantitative evaluation of the anisotropy axis through ab initio calculation is definitely needed.

3. Materials and Methods

All manipulations of air- and moisture-sensitive complexes were performed under a nitrogen atmosphere using standard Schlenk techniques and a glovebox. THF (tetrahydrofuran) and toluene were distilled under nitrogen over sodium and sodium benzophenone. Pentane and hexane were distilled under nitrogen over CaH2 (calcium hydride). Ln(N(SiMe3)2)3 [48], ligand HL1 [49], and ligand H2L2 [50,51] were synthesized according to previously published procedures under ambient conditions. All other starting materials were commercially available and used without further purification. FTIR spectra were obtained using a Nicolet 6700 Flex FTIR spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) equipped with smart iTRTM attenuated total reflectance (ART) sampling accessory in the range from 500 to 4000 cm−1. Elemental analysis for C, N, and H was carried out via a Perkin-Elmer 2400 analyzer (Perkin Elmer, Waltham, MA, USA).
X-ray crystal structure determinations. Single-crystal X-ray data of the title complexes were collected using a Bruker Apex II CCD diffractometer (Bruker, Billerica, MA, USA) equipped with graphite-monochromatized Mo Kα radiation (λ = 0.71073 Å). Data processing was completed using the SAINT processing program (Bruker, Billerica, MA, USA). The structures were solved by direct methods and refined by full-matrix least-squares methods on F2 using SHELXTL-2014 [52,53,54]. All non-hydrogen atoms were determined from the difference Fourier maps and anisotropically refined. Hydrogen atoms were introduced at the calculated positions and refined with fixed geometry with respect to their carrier atoms. Further details may be obtained from the Cambridge Crystallographic Data Centre on quoting the depository numbers 1586924–1586926 (http://www.ccdc.cam.ac.uk).
Magnetic susceptibility measurements were recorded on a Quantum Design MPMS-XL7 SQUID magnetometer (Quantum Design, San Diego, CA, USA) equipped with a 7 T magnet. The variable-temperature magnetization was measured in the temperature range of 1.9–300 K with an external magnetic field of 1000 Oe. The dynamics of the magnetization were investigated in a 3.0 Oe ac oscillating field at different frequencies ranging from 1 to 1500 Hz. Diamagnetic corrections for the complexes were made with the Pascal’s constants [55] for all the constituent atoms as well as the contributions of the sample holder.
Synthesis of [Dy(L1)3] (1Dy). Dy(N(SiMe3)2)3 (0.1 mmol) in 5 mL of toluene was added to a solution of HL1 (0.3 mmol) in 10 mL toluene at room temperature. The solution was stirred at room temperature for 6 h, and then filtered. After removal of toluene under reduced pressure, recrystallization of the residue in hexane at ambient temperature gave 1Dy as yellow crystals after several days. Yield: ~70%. Selected IR (cm−1): 2960 (s), 2926 (m), 1603 (s), 1583 (s), 1536 (s), 1464 (m), 1443 (s), 1381 (m), 1359 (w), 1254 (w), 1200 (w), 1167 (m), 1143 (m), 1106 (w), 921 (m), 851 (m), 792 (m), 750 (m), 739 (m), 593 (w). Anal. Calcd. for [Dy(L1)3] (C57H66DyN3O3, MW = 1003.62): C, 68.15%; H, 6.57%; N, 4.18%. Found: C, 68.21%; H, 6.67%; N, 4.26%.
Synthesis of [Er(L1)3] (1Er). 1Er were synthesized using a procedure similar to that for 1Dy with the replacement of Dy(N(SiMe3)2)3 by Er(N(SiMe3)2)3. Yield: ~70%. Selected IR (cm−1): 2959 (s), 2926 (m), 1603 (s), 1583 (s), 1536 (s), 1464 (m), 1444 (s), 1381 (m), 1360 (w), 1342 (s), 1320 (m), 1254 (w), 1200 (w), 1167 (m), 1143 (m), 1106 (w), 921 (m), 851 (m), 792 (m), 750 (m), 739 (m), 594 (w). Anal. Calcd. for [Er(L1)3] (C57H66ErN3O3, MW = 1008.38): C, 67.83%; H, 6.55%; N, 4.16%. Found: C, 67.72%; H, 6.79%; N, 4.08%.
Synthesis of [Dy(L2)2] (2Dy). A solution of Dy(N(SiMe3)2)3 (0.5 mmol) in pentane was added dropwise to a solution of H2L2 (1 mmol) in pentane at −78 °C. The solution was stirred overnight at room temperature and then filtered. The final filtrate was left unperturbed at room temperature, X-ray quality crystals of 2Dy were obtained after few days. Yield: ~60%. Anal. Calcd. for [Dy(L2)2] (C68H109DyN4O4, MW = 1209.09): C, 67.48%; H, 9.02%; N, 4.63%. Found: C, 67.52%; H, 9.09%; N, 4.59%.

4. Conclusions

In summary, we have synthesized and characterized three Ln-based mononuclear complexes, 1Dy, 1Er, and 2Dy, which show distinct magnetic properties. In complexes 1Dy and 1Er, the trigonal-prismatic coordination geometry provides an axial ligand field, which is in favor of the oblate DyIII ion rather than the prolate ErIII ion; therefore, 1Dy exhibits the better magnetic properties with Ueff = 31.4 K under a zero dc field. 1Er shows field-induced SIM properties with Ueff = 23.96 K under a 400 Oe dc field. Complex 2Dy with the Oh symmetry only displays the frequency dependence of ac signals without χ″ peaks under the zero dc field, indicating the presence of fast QTM relaxation. For six-coordinate dysprosium complexes, the trigonal-prismatic coordination geometry is much more favorable to designing effective SIMs.

Supplementary Materials

The following are available online at www.mdpi.com/2304-6740/6/1/16/s1. Cif and Checkcif files. Table S1: Selected bond distances [Å] and angles [°] for complexes 1Dy, 1Er, and 2Dy. Table S2: Lanthanide geometry analysis by SHAPE software for 1Dy, 1Er, and 2Dy. Table S3: Best-fit parameters for the Arrhenius plots of 1Dy and 1Er. Figure S1: X-ray structures of complexes 1Dy. The green planes represent the coordination planes with labeled dihedral angle (θ). Solvents and hydrogen atoms have been omitted for clarity. Figure S2: Packing diagram of 2 viewed along the c-axis. Figure S3: X-ray structures of complexes 1Er. The green planes represent the coordination planes with labeled dihedral angle (θ). Solvents and hydrogen atoms have been omitted for clarity. Figure S4: Packing diagram of 1Er viewed along the c-axis. Figure S5: Packing diagram of 2Dy viewed along the c-axis. Figure S6: Molar magnetization (M) versus field (H) for complex 1Dy at 1.9, 3.0, and 5.0 K. Figure S7: Molar magnetization (M) versus field (H) for complex 1Er at 1.9, 3.0, and 5.0 K. Figure S8: Molar magnetization (M) versus field (H) for complex 2Dy at 1.9, 3.0, and 5.0 K. Figure S9: Temperature dependent in phase (χ′) and out of phase (χ″) ac susceptibilities for complexes 1Dy at indicated frequencies under a zero dc field. Figure S10: Temperature dependence in phase (χ′) and out of phase (χ″) ac susceptibilities for complexes 1Er under zero dc field. Figure S11: The field dependence of the out-of-phase signals of 1Er and 2Dy on applied dc field strength at 1.9 K and 997 Hz. Figure S12: Temperature dependent in phase (χ′) and out of phase (χ″) ac susceptibilities for complexes 1Er under a 400 Oe dc field. Figure S13: Temperature dependent in phase (χ′) and out of phase (χ″) ac susceptibilities for complexes 2Dy under a zero dc field.
Supplementary File 1

Acknowledgments

We thank the National Natural Science Foundation of China (Grants 21525103, 21331003, and 21521092) for financial support.

Author Contributions

Jinkui Tang designed and supervised the research. Mei Guo carried out the synthesis and characterization studies. Mei Guo and Jinkui Tang wrote the paper.

Conflicts of Interest

The authors declare no conflict of interest.

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Scheme 1. The schematic diagram of ligands HL1 and H2L2.
Scheme 1. The schematic diagram of ligands HL1 and H2L2.
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Figure 1. The molecular structures of complexes 1Dy (left) and 1Er (right). The dashed green lines represent the basal planes. Hydrogen atoms have been omitted for clarity.
Figure 1. The molecular structures of complexes 1Dy (left) and 1Er (right). The dashed green lines represent the basal planes. Hydrogen atoms have been omitted for clarity.
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Figure 2. The molecular structure of complex 2Dy. The dashed green lines represent the equatorial plane. Hydrogen atoms have been omitted for clarity.
Figure 2. The molecular structure of complex 2Dy. The dashed green lines represent the equatorial plane. Hydrogen atoms have been omitted for clarity.
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Figure 3. Plots of the χMT versus T for 1Dy, 1Er and 2Dy in an applied field of 1 kOe.
Figure 3. Plots of the χMT versus T for 1Dy, 1Er and 2Dy in an applied field of 1 kOe.
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Figure 4. Frequency-dependent in-phase χ′ (top) and out-of-phase χ″ (bottom) ac susceptibilities for 1Dy (left), 2Dy (right) under 0 Oe dc field, and 1Er (middle) under 400 Oe dc field.
Figure 4. Frequency-dependent in-phase χ′ (top) and out-of-phase χ″ (bottom) ac susceptibilities for 1Dy (left), 2Dy (right) under 0 Oe dc field, and 1Er (middle) under 400 Oe dc field.
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Figure 5. Plots of τ versus T−1 for 1Dy (left) and 1Er (right), respectively. The red lines correspond to the best fits, and the blue line corresponds to the Orbach process.
Figure 5. Plots of τ versus T−1 for 1Dy (left) and 1Er (right), respectively. The red lines correspond to the best fits, and the blue line corresponds to the Orbach process.
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Figure 6. Cole-Cole plots for 1Dy (left) and 1Er (right) at the indicated temperature; the solid lines correspond to the best fits.
Figure 6. Cole-Cole plots for 1Dy (left) and 1Er (right) at the indicated temperature; the solid lines correspond to the best fits.
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Figure 7. Ground-state magnetic anisotropy of complexes 1Dy. The green lines represent the orientations of the anisotropy axes for DyIII ion (charges for the calculation: Dy + 3; O − 1; other 0), as calculated by the electrostatic model.
Figure 7. Ground-state magnetic anisotropy of complexes 1Dy. The green lines represent the orientations of the anisotropy axes for DyIII ion (charges for the calculation: Dy + 3; O − 1; other 0), as calculated by the electrostatic model.
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Table 1. Crystallographic data and structure refinement details of complexes 1Dy, 1Er, and 2Dy.
Table 1. Crystallographic data and structure refinement details of complexes 1Dy, 1Er, and 2Dy.
1Dy1Er2Dy
FormulaC57H66DyN3O3C57H66ErN3O3C68H109DyN4O4 c
FW, g·mol−11003.621008.381209.09 c
crystal systemTriclinicTriclinicTriclinic
space groupP 1 ¯ P 1 ¯ P 1 ¯
T, K293(2)293(2)293(2)
λ, Å0.710730.710730.71073
a, Å10.8822(15)10.9407(11)13.7983(12)
b, Å11.4229(15)11.4509(11)16.6655(15)
c, Å20.823(3)20.735(2)18.6715(17)
α, °89.735(3)90.066(2)70.7220(10)
β, °88.681(3)91.458(2)77.406(2)
γ, °76.170(2)103.853(2)86.857(2)
V, Å32512.7(6)2521.3(4)3954.7(6)
Z222
reflns collected161001571023959
unique reflns10012968615601
Rint0.03000.06050.0408
GOF on F21.0360.9961.080
R1 a, wR2 b (I ≥ 2σ(I))0.0381, 0.07660.0584, 0.10140.0606, 0.1659
R1, wR2 (all data)0.0476, 0.08220.0956, 0.12120.0878, 0.1857
CCDC number158692415869251586926
a R1 = ∑||Fo| − |Fc||/∑|Fo|; b wR2 = [∑w(Fo2Fc2)2/∑w(Fo2)2]1/2; c The formula and the formula weight of 2Dy do not include the squeezed solvents.

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Guo, M.; Tang, J. Six-Coordinate Ln(III) Complexes with Various Coordination Geometries Showing Distinct Magnetic Properties. Inorganics 2018, 6, 16. https://doi.org/10.3390/inorganics6010016

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Guo M, Tang J. Six-Coordinate Ln(III) Complexes with Various Coordination Geometries Showing Distinct Magnetic Properties. Inorganics. 2018; 6(1):16. https://doi.org/10.3390/inorganics6010016

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Guo, Mei, and Jinkui Tang. 2018. "Six-Coordinate Ln(III) Complexes with Various Coordination Geometries Showing Distinct Magnetic Properties" Inorganics 6, no. 1: 16. https://doi.org/10.3390/inorganics6010016

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