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Magnetic relaxation in two 1D Tb-nitronyl nitroxide complexes
Accepted Manuscript Magnetic relaxation in two 1D Tb-nitronyl nitroxide complexes Feng-Ping Xiao, Peng Hu, Xiang-Ying Hao, Jiang-Fei Cao, Li-Li Zhu PII: DOI: Reference:
S0020-1693(17)30999-4 https://doi.org/10.1016/j.ica.2017.11.026 ICA 17996
To appear in:
Inorganica Chimica Acta
Received Date: Revised Date: Accepted Date:
27 June 2017 16 October 2017 14 November 2017
Please cite this article as: F-P. Xiao, P. Hu, X-Y. Hao, J-F. Cao, L-L. Zhu, Magnetic relaxation in two 1D Tb-nitronyl nitroxide complexes, Inorganica Chimica Acta (2017), doi: https://doi.org/10.1016/j.ica.2017.11.026
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Magnetic relaxation in two 1D Tb-nitronyl nitroxide complexes Feng-Ping Xiao a, Peng Hu a,*, Xiang-Ying Hao a, Jiang-Fei Cao a, Li-Li Zhu b,* [a] Environmental and Chemical Engineering College, Zhaoqing University, Zhaoqing 526061, P. R. China [b] College of Chemistry and Materials Science, Huaibei Normal University, Huaibei 235000, P. R. China * Corresponding author. E-mail: Peng Hu [email protected] ; Li-Li Zhu [email protected]
Abstract: Reaction of the nitronyl nitroxide radical NIT-CH3 and NIT-C3H5 with Tb(hfac)3 affords two one-dimensional lanthanide–nitronyl nitroxide compounds: [TbIII(hfac)3(NIT-CH3)]n (1), and [TbIII(hfac)3(NIT-C3H5)]n (2) (NIT-CH3 = 2,4,4,5,5-pentamethylimidazolyl-1-oxyl-3-oxide; NIT-C3H5 = 2-cyclopropyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). Single crystal X-ray crystallographic analysis reveals that these two compounds are one-dimensional chains built up by Tb(hfac)3 units bridged by radicals through their NO groups. Magnetic studies show that both Tb complexes exhibits frequency-dependent out-of-phase signals. Keywords: Nitronyl nitroxide radical; Lanthanide; Single-molecule magnets; Crystal structure
Introduction Owning to their potential applications such as in high-density information storage and quantum spintronic devices, a lot of attention has been paid to the design and construction of one-dimensional single-chain magnets (SCMs) [1–4]. SCMs are characterized as slow magnetization relaxation caused by the association of large ground state spin (ST) value with a significant uniaxial (Ising-like) magnetic anisotropy (D), which leads to a significant energy barrier to magnetization reversal (U) [5–7]. Such one-dimensional compounds can be observed magnetic hysteresis arising from slow dynamics of the magnetization of pure one-dimensional structures rather than 3D magnetic ordering [8–10]. To show SCM behavior, one-dimensional compounds need to have two main premises: strong uniaxial magnetic anisotropy and negligible magnetic interactions between the adjacent chains [1]. Studies show that lanthanide(III) ions, with significant magnetic anisotropy from the large and unquenched orbital angular momentum, are good candidates for the construction of SCMs. However, the intrinsic drawback for lanthanide(III) ions is the naturally accompanying quantum tunneling from the hyperfine couplings and dipolar spin–spin interactions of lanthanide ions, which always lowers the effective relaxation energy barrier and induces the loss of remnant magnetization [11]. Fortunately, exchange interactions which generally exist 1
in molecular paramagnetic species have been proved to be an effective method to mitigate quantum-tunneling relaxation and then might increase the effective relaxation energy barrier processes [11-15]. The challenge of using this approach in lanthanide based SCMs is that the limited radial extension of the 4f orbital always induces weak exchange interactions. In 2011 Long research group indicated that the N23－ radical ligands can effectively transfer the magnetic interactions between lanthanide ions. This strong exchange coupling between anisotropic metal and radical ligand generally leads to SCMs with high relaxation energy barrier [14]. Nitronyl nitroxides are excellent bridging ligands to construct one-dimensional systems because they possess two identical N–O coordination groups, which can be coordinated with two different metal ions and contribute to complexes with 1D structures [16-19]. Moreover, stable radical ligands can transfer the effective magnetic interactions. Therefore, nitronyl nitoxide radicals are appealing ligands for constructing SCMs. As well known, the first reported single-chain magnet is Co(II)-nitronyl nitoxide chain [1]. Recently, SCM behavior has been observed in some nitronyl nitroxide-Co(II) /Ln(III) one-dimensional compounds, and some of them show a relatively high energy barrier [20-32]. It's worth noting that these reported SCMs are based on aromatic group substituted nitronyl nitroxides [16,17,25-32]. Therefore, in order to further explore the relationship between the magnetic properties and substitution of the radical ligands, we decided to employ two aliphatic group substituted nitronyl nitroxides (NIT-CH3 and NIT-C3H5) to construct new one-dimensional lanthanide–radical compounds. Herein, we report two one-dimensional complexes [TbIII(hfac)3(NIT-CH3)]n (1) and [TbIII(hfac)3(NIT-C3H5)]n (2). Magnetic studies show that both complexes exhibit slow magnetic relaxation. F O
N
N
O
F
F O
N
N
O
F
F
O
NIT-C3H5
NIT-CH3
F
O
hfac
Scheme 1. Molecule structure of NIT-CH3, NIT-C3H5 and hfac.
Experimental Section Materials and physical measurements All the starting chemicals were bought from Aldrich and used without further purification. The radical ligands NIT-CH3 and NIT-C3H5 were prepared according to literature methods [33]. Elemental analyses (C, H, N) were determined by Perkin–Elmer 240 elemental analyzer. The infrared spectra were recorded from KBr pellets in the range 4000–400 cm–1 with a Bruker Tensor 27 IR spectrometer. The magnetic measurements were carried out with MPMSXL–7 SQUID magnetometer. Diamagnetic corrections were made with Pascal’s constants for all the constituent 2
atoms. Synthesis of [Tb(hfac)3(NIT-CH3)]n (1) A solution of Tb(hfac)3·2H2O (0.0814 g 0.1 mmol) in 30 mL dry boiling n-heptane was heated to reflux for about 1.5 h. Then the solution was cooled to 60 oC, a solution of NIT-CH3 (0.0171 g 0.1 mmol) in 2 mL of CH2Cl2 was added. The resulting solution was stirred for 1 min and cooled to room temperature. After about two days, red crystals suitable for single-crystal X-ray analysis were collected, yield 51% Anal. Calc. for C23H18F18N2O8Tb (951.29): C 29.04, H 1.91, N 2.94 %; found: C 29.38, H 1.96, N 2.89 %. FT-IR (KBr): 1653 (s), 1617 (s) 1559 (s), 1532 (s), 1258 (s) 1206 (s), 1147 (s), 801 (m), 662 (m) cm–1. Synthesis of [Tb(hfac)3(NIT-C3H5)]n (2) Tb(hfac)3·2H2O (0.0814g 0.1 mmol) was added to 25 mL n-heptane and heated to reflux for 2 h. The solution was subsequently cooled to 70 ℃, then a solution of NIT-C3H5 (0.0197g 0.1 mmo) in CH2Cl2 (3 mL) was added and stirred for 5 min. The resulting solution was then cooled to room temperature. After a few days, red crystals suitable for single-crystal X-ray analysis were obtained with 41 % yield. Analysis C25H20F18N2O8Tb (977.35): calcd. C 30.72, H 2.06, N 2.87 %; found C 30.94, H 2.01, N 2.78 %. FT-IR (KBr): 1653 (s), 1501 (s), 1258 (s), 1202 (s), 1145 (s), 801 (m), 660 (m) cm–1. X-ray crystal structure determinations X-ray single-crystal diffraction data for two complexes were collected using a Bruker APEX-II CCD diffractometer at 173 K equipped with graphite-monochromated Mo/Kα radiation (λ = 0.71073 Å). The structures were solved by direct methods by using the program SHELXS-97 and refined by full-matrix least-squares methods on F2 with the use of the SHELXL-97 program package [34]. Anisotropic thermal parameters were assigned to all non-hydrogen atoms. The hydrogen atoms were set in calculated positions and refined as riding atoms with a common fixed isotropic thermal parameter. Disordered C and F atoms were observed for all compounds. The restraints of SPLIT, DELU and ISOR were applied to keep the disordered molecules reasonable. Pertinent crystallographic data and structure refinement parameters for all four complexes were listed in Table 1 and 2. Table 1. Crystallographic data for complexes 1 and 2. 1
2
Formula
C23H18TbF18N2O8
C25H20TbF18N2O8
Mr
951.31
977.35
Crystal system
Monoclinic
Monoclinic
Space group
P21/n
P21/c
a /Å
10.788(2)
10.853(3)
b /Å
16.128(4)
17.169(4)
c /Å
19.234(4)
18.365(4)
3
β ,deg
93.605(3)
97.804(3)
3339.7(13)
3390.3(14)
4
4
1.892
1.915
Tmin and Tmax
0.746 1.000
0.780 1.000
θmin, θmax deg
1.65 , 25.01
1.63 , 25.01
Reflections collected
29802
38223
Unique reflns/ Rint
5833/ 0.0441
8071/0.0534
GOF (F )
1.016
1.022
R1/wR2 (I > 2σ(I))
0.0334/0.0845
0.0324/0.0671
R1/wR2 (all data)
0.0360/ 0.0867
0.0400/0.0703
3
V /Å Z
Dcalcd /g cm
-3
2
Results and discussion Structural descriptions As shown in Figure 1, complex 1 crystallizes in P21/n space group with a monoclinic crystal system. The [Tb(hfac)3] units are connected by NIT-CH3 to form a one-dimensional infinite Tb(III)–NIT-CH3 chain. There is only one crystallographically independent Tb(hfac)3(NIT-CH3) moiety in the asymmetric unit. The nitroxide ligands which connect to the same Tb(III) are trans and the angles of Orad–Tb–Orad are found to be 134.72°. The Tb–O(radical) bond lengths are 2.357 Å and 2.373 Å, respectively. The Tb–O(hfac) distances are in the range of 2.331–2.369 Å . The nearest intrachain Tb···Tb distances are found to be 8.129 Å. The packing arrangement of 1 is shown in Figure 2. The shortest interchain Tb···Tb contacts in 1 are 9.909 Å. To the best of our knowledge, this is the nearest interchain Tb–Tb distance among the reported Tb-nitronyl nitroxide radical 1D chain compounds.
Figure 1. One-dimensional chain structure of complex 1 with the atom-labeling scheme. All hydrogen and fluorine atoms have been omitted for clarity.
4
Figure 2. Packing arrangement of the chains of 1. All hydrogen and fluorine atoms have been omitted for clarity.
The structure of complex 2 is shown in Figure 3. Similar to complex 1, complex 2 crystallizes in P21/c space group with only one crystallographically independent Tb(hfac)3(NIT-C3H5) moiety is observed in the asymmetric unit. The [Tb(hfac)3] units are connected by NIT-C3H5 to form a one-dimensional infinite Tb(III)–NIT-C3H5 chain. The nitroxide ligands which connect to the same Tb(III) are trans and the angles of Orad–Tb–Orad are found to be 136.88°. The Tb–O(hfac) distances are in the range of 2.315–2.355 Å . The nearest intrachain Tb···Tb distances are found to be 8.646 Å. The shortest interchain Tb···Tb contact in complex 2 are 10.753 Å ( Figure 4).
Figure 3. One-dimensional chain structure of complex 2 with the atom-labeling scheme. All hydrogen and fluorine atoms have been omitted for clarity.
Figure 4. Packing arrangement of the chains of complex 2. All hydrogen and fluorine atoms have been omitted for clarity.
5
Table 2. Selected bond distances (nm) and angles (o) for 1 and 2. 1 Tb(1)-O(3)
2.331(3)
Tb(1)-O(2)
2.357(3)
O(2)-N(2)
1.286(4)
Tb(1)-O(4)
2.340(3)
Tb(1)-O(5)
2.361(3)
O(1)-N(1)
1.282(4)
Tb(1)-O(7)
2.344(3)
Tb(1)-O(8)
2.369(3)
Tb(1)-O(6)
2.347(3)
Tb(1)-O(1)#1
2.373(3)
O(3)-Tb(1)-O(4)
74.67(11)
O(4)-Tb(1)-O(6)
137.66(10)
O(7)-Tb(1)-O(2)
148.68(10)
O(3)-Tb(1)-O(7)
137.84(10)
O(7)-Tb(1)-O(6)
85.36(11)
O(6)-Tb(1)-O(2)
73.07(10)
O(4)-Tb(1)-O(7)
115.05(10)
O(3)-Tb(1)-O(2)
73.16(10)
O(3)-Tb(1)-O(5)
75.44(11)
O(3)-Tb(1)-O(6)
115.74(11)
O(4)-Tb(1)-O(2)
71.48(10)
O(4)-Tb(1)-O(5)
145.77(10)
2 Tb(1)-O(7)
2.364(2)
Tb(1)-O(6)
2.334(2)
N(2)-O(8)
1.292(3)
Tb(1)-O(4)
2.318(2)
Tb(1)-O(5)
2.349(2)
N(1)-O(7)
1.289(3)
Tb(1)-O(2)
2.321(2)
Tb(1)-O(3)
2.354(2)
Tb(1)-O(1)
2.357(2)
Tb(1)-O(8)
2.337(2)
O(8)-Tb(1)-O(3)
73.12(9
O(8)-Tb(1)-O(5)
72.49(9)
C(7)-O(1)-Tb(1)
134.6(2)
O(4)-Tb(1)-O(7)
89.29(9)
O(4)-Tb(1)-O(6)
146.50(8)
O(4)-Tb(1)-O(5)
74.22(8)
O(4)-Tb(1)-O(2)
138.44(8)
O(2)-Tb(1)-O(6)
74.82(8)
O(2)-Tb(1)-O(5)
146.67(8)
O(6)-Tb(1)-O(5)
73.63(8)
O(4)-Tb(1)-O(3)
72.19(8)
O(2)-Tb(1)-O(3)
74.44(8)
Symmetry transformations used to generate equivalent atoms for 1: #1 -x+1/2,y-1/2,-z+1/2 #2 -x+1/2,y+1/2,-z+1/2 and for 2: #1 -x+1,y-1/2,-z-1/2 #2 -x+1,y+1/2,-z-1/2.
To estimate the degree of distortion of complexes 1 and 2, we also carried out the calculations of the shape factor S based on the crystal data based on Equation (1):
Where m is the number of edges (m = 18 in this work), δi is the observed angle between normals of adjacent faces (dihedral angle) along the i edge of the experimental polyhedron δ, and θi is the dihedral angle of the corresponding ideal polytopal shape θ. While the value S (δ, θ) is a measure of structural similarity to an ideal polytopal shape. The estimated S values of complexes 1 and 2 are summarized in Tables S1 and S2. For complex 1, the S values are S(D2d) =13.7°, S(C2v) = 13.6°, S(D4d) = 4.1°. Based on the minimum value of S, the coordination geometry of complex 2 is square antiprism (D4d) as shown in Figure 5. However, for complex 1, the S value are S(D2d) =7.7°, S(C2v) = 12.8°, S(D4d) = 8.1° indicates that the coordination geometry of complex 2 is trigonal dodecahedron (D2d) (Figure 5) [35].
6
Figure 5. The coordination polyhedron of 1 (right) and 2 (left).
Magnetic properties To study the static magnetic properties of both complexes, variable-temperature magnetic susceptibilities were measured from 300 K to 2 K in an applied field of 1 kOe. The MT vs.T plots for complex 1 are shown in Figure 6. At 300 K, the MT value is 11.99 cm3 K mol–1, which close to the theoretical value of 12.20 cm3 K mol−1 (an uncoupled Tb(III) ion (Tb(III): 7F6 , g = 3/2, C = 11.82 cm3 K mol−1) plus one organic radical (S = 1/2, 0.375 cm3 K mol−1)). While lowing the temperature, the χMT value of complex 1 gradually increases to 27.33 cm3 K mol−1 at 2 K. This increase of χMT suggests ferromagnetic interactions dominate in the chains.
Figure 6. Temperature dependence of MT for complex 1.
Figure 7. Field dependence of magnetization of 1 at 2.0 K.
7
The field dependence of magnetization of complex 1 has been determined at 2 K in the range of 0–70 kOe (Figure 7). Increasing the applied field, M value reaches up to 5.50 Nβ at 70 kOe. No saturation values were observed, indicating the presence of a magnetic anisotropy and/or low-lying excited states in the system. To investigate the dynamics of the magnetization, alternating current (ac) susceptibility measurements for complex 1 were carried out in low temperature regime under a zero dc field. As depicted in Figure 8, complex 1 only shows week frequency dependent out-of-phase signals which may due to the existence of a fast quantum tunneling relaxation of the magnetization (QTM). Thus, ac measurements were performed under external dc field of 1000 Oe to suppress the possible fast quantum tunneling relaxation. The frequency dependent out-of-phase signals of complex 1 still do not exhibit any maximum at 1400 Hz. Therefore, we are unable to determine the energy barrier Ueff and 0 via the conventional Arrhenius plot method as no maxima in " were observed. Bartolome ´et al employed an alternative method which is to assume that there is only one characteristic relaxation process of the Debye type, with one energy barrier and one time constant [36]. According to this assumption, one obtains Equation (2): ln(χ"/χ') = ln(ω0) + Ea/kBT From this equation, we can extract the estimated activation energy and the characteristic time by fitting the experimental data of ac susceptibility in 1000 Oe dc field for complex 1 (Figure 9). The best fit yielded Ueff ≈ 9.41(6) K and 0 ≈ 9.06 ×10–6 s.
Figure 8. Temperature dependence of the in-phase and out-of-phase components of ac susceptibility for 1 in zero dc field (above) and 1000 Oe dc field (below).
8
Figure 9. Natural logarithm of the ratio of " to ′vs. 1/T for complex 1 (1000 Oe dc field). The solid line represents the fitting results.
Figure 10. Temperature dependence of MT for complex 2.
Figure 11. Field dependence of magnetization of 2 at 2.0 K.
9
Figure 12. Temperature dependence of the in-phase and out-of-phase components of ac susceptibility for 2 in zero dc field(above) and 1000 Oe dc field(below).
Figure 13. Natural logarithm of the ratio of " to ′vs. 1/T for complex 2 (zero dc field). The solid line represents the fitting results.
For complex 2 (Figure 10), at 300 K the MT value is 12.35 cm3 K mol−1 (theoretical value is 12.20 cm3 K mol−1). The MT value keeps almost constant until 50 K, below which it continuously decreases to reach a value of 1.22 cm3 K mol−1 at 2.0 K. Furthermore, the field dependency of magnetization in the 0−70 kOe field range for complex 2 have been determined at 2.0 K (Figure 11). Upon increasing in the applied field, M reaches to 5.64 Nβ at 70 kOe, which does not reach the saturation values, indicating the presence of a magnetic anisotropy and/or low-lying excited states in the system. 10
In order to investigate spin dynamic magnetic behaviors of complex 2, ac magnetic susceptibility measurements were carried out in the temperature range of at different frequencies under a zero-external field. The frequency dependent out-of-phase signals are observed below 5 K, but no peak maximum is found above 2 K (Figure 12). This behavior may result from a fast quantum tunneling relaxation of the magnetization (QTM). Thus, ac measurements were performed under a external dc field of 1000 Oe. The frequency dependent in-phase signals show a peak maximum at high frequencies. However, the out-of-phase signals of complex 2 still do not exhibit any maximum at 1400 Hz (Figure 12). Therefore, we employed the same method as complex 1. By fitting the experimental data of ac susceptibility in 0 Oe dc field for complex 2, the best fit yielded Ueff ≈ 7.03(4) K and 0 ≈ 8.08×10–7 (Figure 13). Table 3. Structural and magnetic data for Tb- nitronyl nitroxide radical 1D chain compounds. Substitue Compound
nt (R)
[Tb(hfac)3NITPhOPh]n
S
[Tb(hfac)3NIT3BrPhO
Ref
interchain
Energy
Relaxation
Tb–Tb
barrier [K]
time 0 [S]
11.37
Ueff
= 45
9.62×10−9
17
10.89
Ueff
= 77.2
1.91×10-9
27
11.24
Ueff = 58.75
2.25×10-7
29
11.34
Ueff = 56.06
9.69×10-10
30
10.75
Ueff
≈ 9.41
~9.06×10–6
9.91
Ueff
≈ 7.03
~8.08×10–7
distance[Å]
O
[Tb(hfac)3NIT2Thien]n
Neareast
S
Me]n Br
O
[Tb(hfac)3 (NITPh2OEt)]n
[Tb(hfac)3(NIT-C3H5)]
O
n
[Tb(hfac)3(NIT-CH3)]n
this work
this work
As shown in Table 3, compare to those reported SCMs which base on aromatic group substituted nitronyl nitroxides, the Ueff values of complexes 1 and 2 are much 11
lower. This phenomenon might be caused by two reasons. Firstly, due to the π-π conjugate, aromatic groups are donating electron groups, therefore aromatic group substituted nitronyl nitroxides can transfer the magnetic interactions more effectively due to their high electron density. Secondly, on account of the relative small size of methyl group and cyclopropyl group, the interchain distance of complexes 1 and 2 are relative short. According to previous studies of SCMs need to avoid magnetic interactions between the adjacent chains [1,16,17], short interchain distance would impose negative influence on value of Ueff.
Conclusion In this paper, we have successfully obtained two novel one-dimensional Tb-radical complexes base on aliphatic group substituted nitronyl nitroxides. The X-ray analyses reveal that complex 1 shows the nearest interchain Tb···Tb distance among the reported Tb-nitronyl nitroxide radical 1D chain compounds. Magnetic studies reveal that slow magnetic relaxation was observed in both complexes.
Acknowledgments This work was funded by Guangdong college students' innovative project ( No. 201610580046); The science and technology innovation project of Zhaoqing (No. 201624030906); Huaibei science and technology research program (No.20140219); The National Science Foundation of Anhui Educational Bureau (No. KJ2016B010).
Supporting Information CCDC 1548424 (for 1) and 1548547(for 2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Observed dihedral angles dihedral angles of idealized angles and the calculated S values for complexes 1 and 2.
References [1] A. Caneschi, D. Gatteschi, N. Lalioti, C. Sangregorio, R. Sessoli, G. Venturi, A. Vindigni, A. Rettori, M. G. Pini, M. A. Novak, Angew. Chem. Int. Ed. 40 (2001) 1760. [2] R. Clérac, H. Miyasaka, M. Yamashita, C. Coulon, J. Am. Chem. Soc. 124 (2002) 12837. [3] L. Bogani, A. Vindigni, R. Sessoli, D. Gatteschi, J. Mater. Chem. 18 (2008) 4750. [4] a)Y.-C. Chen, J.-L. Liu, L. Ungur, J. Liu, Q.-W. Li, L.-F. Wang, Z.-P. Ni, L. F. Chibotaru, X.-M. Chen, M.-L. Tong, J. Am. Chem. Soc. 138 (2016) 2829; b) Y.-S. Ding, N. F. Chilton, R. E. P. Winpenny, Y.-Z. Zheng, Angew. Chem. Int. Ed. 55 (2016) 1. [5] W. Wernsdorfer, R. Sessoli, Science 284 (1999) 133. [6] L. Ungur, L. F. Chibotaru, Phys. Chem. Chem. Phys. 13 (2011) 20086. [7] N. F. Chilton, C. A. P. Goodwin, D. P. Mills, R. E. P. Winpenny, Chem. Commun. 51(2015) 101. [8] D. Gatteschi, R. Sessoli, Angew. Chem., Int. Ed. 42 (2003) 268.
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[9] L. Bogani, W. Wernsdorfer, Nat. Mater. 7 (2008) 179. [10] F. Troiani, M. Affronte, Chem. Soc. Rev. 40 (2011) 3119. [11] J. D. Rinehart, M. Fang, W. J. Evans, J. R. Long, Nat. Chem. 3 (2011) 538. [12] Y. N. Guo, G. F. Xu, W. Wernsdorfer, L. Ungur, Y. Guo, J. Tang, H. J. Zhang, L. F. Chibotaru, A. K. Powell, J. Am. Chem. Soc. 133 (2011) 11948. [13] W. Wernsdorfer, N. Aliaga-Alcalde, D. N. Hendrickson, G. Christou, Nature 416 (2002) 406. [14] J. D. Rinehart, M. Fang, W. J. Evans, J. R. Long, J. Am. Chem. Soc. 133 (2011) 14236. [15] J.-J. Wang, M. Zhu, C. Li, J.-Q. Zhang, L.-C. Li, Eur. J. Inorg. Chem. 2015 (2015) 1368. [16] L. Bogani, C. Sangregorio, R. Sessoli, D. Gatteschi, Angew. Chem. Int. Ed. 44 (2005) 5817. [17] K. Bernot, L. Bogani, A. Caneschi, D. Gatteschi, R. Sessoli, J. Am. Chem. Soc. 128 (2006) 7947. [18] N. Ishii, Y. Okamura, S. Chiba, T. Nogami, T. Ishida, J. Am. Chem. Soc. 130 (2008) 24. [19] K. Bernot, L. Bogani, R. Sessoli, D. Gatteschi, Inorg. Chim. Acta. 360 (2007) 3807. [20] X.-F. Wang, Y.-G. Li, P. Hu, J.-J. Wang, L.-C. Li, Dalton Trans. 44 (2015) 4560. [21] M. G. F.Vaz, R. A. A.Cassaro, H. Akpinar, J. A.Schlueter, P.-M. Lahti, M.-A. Novak, Chem.Eur. J. 20 (2014) 5460. [22] R. A. A. Cassaro, S. G. Reis, T. S. Araujo, P. M.Lahti, M. A. Novak, M. G. Vaz, Inorg. Chem. 54 (2015) 9381. [23] P. Hu, C. Zhang, Y. Gao, Y. Li, Y. Ma, L. Li, D. Liao, Inorg. Chim. Acta. 398 (2013) 136. [24] H.-X. Tian, X.-F. Wang, X.-L. Mei, R.-N. Liu, M. Zhu, C.-M. Zhang, L.-C. Li, D.-Z. Liao, Y. Ma, Eur. J. Inorg. Chem. (2013) 1320. [25] T. Han, W. Shi, Z. Niu, B. Na, P. Cheng, Chem-Eur. J. 19 (2013) 994. [26] A. Datcu, N. Roques, V. Jubera, D. Maspoch, X. Fontrodona, K. Wurst, I. Imaz, G. Mouchaham, J.-P. Sutter, C. Rovira, J. Veciana, Chem. Eur. J. 18 (2012) 152. [27] R.-N. Liu, Y. Ma, P.-P. Yang, X.-Y. Song, G.-F. Xu, J.- K. Tang, L.-C. Li, D.-Z. Liao, S.-P. Yan, Dalton Trans. 39 (2010) 3321. [28] P. Hu, X.-F. Ma, Y. Wang, Q.-L. Wang, L.-C. Li, D.-Z. Liao, Dalton Trans. 43 (2014) 2234. [29] R.-N. Liu, C.-M. Zhang, X.-L. Mei, P. Hu, H.-X. Tian, L.- C.Li, D.-Z. Liao, J.-P. Sutter, New J. Chem. 36 (2012) 2088. [30] C. Li, J. Sun, M. Yang, G. Sun, J. Guo, Y. Ma, L. Li. Cryst. Growth Des. 16 (2016) 7155. [31] D. Shao, L. Shi, S.-L. Zhang, X.-H. Zhao, D.-Q. Wu, X.-Q. We, X.-Y. Wang, Cryst. Eng. Comm, 18 (2016) 4150. [32] B. Yao, Z. Guo, X. Zhang, Y. Ma, Z. Yang, Q. Wang, L. Li, P. Cheng, Cryst. Growth Des. 17 (2017) 95. [33] E. F. Ullman, J. H. Osiecki, D. G. B. Boocock, R. Darcy, J. Am. Chem. Soc. 94(1972) 7049. [34] a) G. M. Sheldrick, SHELXS 97, Program for the Solution of Crystal Structures, University of Gçttingen, Germany, 1997; b) G. M. Sheldrick, SHELXL 97, Program for the Refinement of Crystal Structures, University of Gçttingen, Germany, 1997. [35] J. Xu, E. Radkov, M. Ziegler and K. N. Raymond, Inorg. Chem. 39 (2000) 4156. [36] J. Bartolome ´, G. Filoti, V. Kuncser, G. Schinteie, V. Mereacre, C. E. Anson, A. K. Powell, D. Prodius and C. Turta, Phys. Rev. B: Condens. Matter Mater. Phys. 80 (2009) 014430.
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Highlights 1. Two one-dimensional novel lanthanide-radical complexes. 2. Slow magnetic relaxations were observed for both complexes.
14
Graphical abstract Magnetic relaxation in two 1D Tb-nitronyl nitroxide complexes Peng Hu a, Feng-Ping Xiao a,*, Xiang-Ying Hao a, Jiang-Fei Cao a, Li-Li Zhu b,*
Two one-dimensional lanthanide–nitronyl nitroxide compounds have been successfully prepared. The magnetic studies reveal that slow magnetic relaxations were observed for both two Tb complexes.
15
S0020-1693(17)30999-4 https://doi.org/10.1016/j.ica.2017.11.026 ICA 17996
To appear in:
Inorganica Chimica Acta
Received Date: Revised Date: Accepted Date:
27 June 2017 16 October 2017 14 November 2017
Please cite this article as: F-P. Xiao, P. Hu, X-Y. Hao, J-F. Cao, L-L. Zhu, Magnetic relaxation in two 1D Tb-nitronyl nitroxide complexes, Inorganica Chimica Acta (2017), doi: https://doi.org/10.1016/j.ica.2017.11.026
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Magnetic relaxation in two 1D Tb-nitronyl nitroxide complexes Feng-Ping Xiao a, Peng Hu a,*, Xiang-Ying Hao a, Jiang-Fei Cao a, Li-Li Zhu b,* [a] Environmental and Chemical Engineering College, Zhaoqing University, Zhaoqing 526061, P. R. China [b] College of Chemistry and Materials Science, Huaibei Normal University, Huaibei 235000, P. R. China * Corresponding author. E-mail: Peng Hu [email protected] ; Li-Li Zhu [email protected]
Abstract: Reaction of the nitronyl nitroxide radical NIT-CH3 and NIT-C3H5 with Tb(hfac)3 affords two one-dimensional lanthanide–nitronyl nitroxide compounds: [TbIII(hfac)3(NIT-CH3)]n (1), and [TbIII(hfac)3(NIT-C3H5)]n (2) (NIT-CH3 = 2,4,4,5,5-pentamethylimidazolyl-1-oxyl-3-oxide; NIT-C3H5 = 2-cyclopropyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). Single crystal X-ray crystallographic analysis reveals that these two compounds are one-dimensional chains built up by Tb(hfac)3 units bridged by radicals through their NO groups. Magnetic studies show that both Tb complexes exhibits frequency-dependent out-of-phase signals. Keywords: Nitronyl nitroxide radical; Lanthanide; Single-molecule magnets; Crystal structure
Introduction Owning to their potential applications such as in high-density information storage and quantum spintronic devices, a lot of attention has been paid to the design and construction of one-dimensional single-chain magnets (SCMs) [1–4]. SCMs are characterized as slow magnetization relaxation caused by the association of large ground state spin (ST) value with a significant uniaxial (Ising-like) magnetic anisotropy (D), which leads to a significant energy barrier to magnetization reversal (U) [5–7]. Such one-dimensional compounds can be observed magnetic hysteresis arising from slow dynamics of the magnetization of pure one-dimensional structures rather than 3D magnetic ordering [8–10]. To show SCM behavior, one-dimensional compounds need to have two main premises: strong uniaxial magnetic anisotropy and negligible magnetic interactions between the adjacent chains [1]. Studies show that lanthanide(III) ions, with significant magnetic anisotropy from the large and unquenched orbital angular momentum, are good candidates for the construction of SCMs. However, the intrinsic drawback for lanthanide(III) ions is the naturally accompanying quantum tunneling from the hyperfine couplings and dipolar spin–spin interactions of lanthanide ions, which always lowers the effective relaxation energy barrier and induces the loss of remnant magnetization [11]. Fortunately, exchange interactions which generally exist 1
in molecular paramagnetic species have been proved to be an effective method to mitigate quantum-tunneling relaxation and then might increase the effective relaxation energy barrier processes [11-15]. The challenge of using this approach in lanthanide based SCMs is that the limited radial extension of the 4f orbital always induces weak exchange interactions. In 2011 Long research group indicated that the N23－ radical ligands can effectively transfer the magnetic interactions between lanthanide ions. This strong exchange coupling between anisotropic metal and radical ligand generally leads to SCMs with high relaxation energy barrier [14]. Nitronyl nitroxides are excellent bridging ligands to construct one-dimensional systems because they possess two identical N–O coordination groups, which can be coordinated with two different metal ions and contribute to complexes with 1D structures [16-19]. Moreover, stable radical ligands can transfer the effective magnetic interactions. Therefore, nitronyl nitoxide radicals are appealing ligands for constructing SCMs. As well known, the first reported single-chain magnet is Co(II)-nitronyl nitoxide chain [1]. Recently, SCM behavior has been observed in some nitronyl nitroxide-Co(II) /Ln(III) one-dimensional compounds, and some of them show a relatively high energy barrier [20-32]. It's worth noting that these reported SCMs are based on aromatic group substituted nitronyl nitroxides [16,17,25-32]. Therefore, in order to further explore the relationship between the magnetic properties and substitution of the radical ligands, we decided to employ two aliphatic group substituted nitronyl nitroxides (NIT-CH3 and NIT-C3H5) to construct new one-dimensional lanthanide–radical compounds. Herein, we report two one-dimensional complexes [TbIII(hfac)3(NIT-CH3)]n (1) and [TbIII(hfac)3(NIT-C3H5)]n (2). Magnetic studies show that both complexes exhibit slow magnetic relaxation. F O
N
N
O
F
F O
N
N
O
F
F
O
NIT-C3H5
NIT-CH3
F
O
hfac
Scheme 1. Molecule structure of NIT-CH3, NIT-C3H5 and hfac.
Experimental Section Materials and physical measurements All the starting chemicals were bought from Aldrich and used without further purification. The radical ligands NIT-CH3 and NIT-C3H5 were prepared according to literature methods [33]. Elemental analyses (C, H, N) were determined by Perkin–Elmer 240 elemental analyzer. The infrared spectra were recorded from KBr pellets in the range 4000–400 cm–1 with a Bruker Tensor 27 IR spectrometer. The magnetic measurements were carried out with MPMSXL–7 SQUID magnetometer. Diamagnetic corrections were made with Pascal’s constants for all the constituent 2
atoms. Synthesis of [Tb(hfac)3(NIT-CH3)]n (1) A solution of Tb(hfac)3·2H2O (0.0814 g 0.1 mmol) in 30 mL dry boiling n-heptane was heated to reflux for about 1.5 h. Then the solution was cooled to 60 oC, a solution of NIT-CH3 (0.0171 g 0.1 mmol) in 2 mL of CH2Cl2 was added. The resulting solution was stirred for 1 min and cooled to room temperature. After about two days, red crystals suitable for single-crystal X-ray analysis were collected, yield 51% Anal. Calc. for C23H18F18N2O8Tb (951.29): C 29.04, H 1.91, N 2.94 %; found: C 29.38, H 1.96, N 2.89 %. FT-IR (KBr): 1653 (s), 1617 (s) 1559 (s), 1532 (s), 1258 (s) 1206 (s), 1147 (s), 801 (m), 662 (m) cm–1. Synthesis of [Tb(hfac)3(NIT-C3H5)]n (2) Tb(hfac)3·2H2O (0.0814g 0.1 mmol) was added to 25 mL n-heptane and heated to reflux for 2 h. The solution was subsequently cooled to 70 ℃, then a solution of NIT-C3H5 (0.0197g 0.1 mmo) in CH2Cl2 (3 mL) was added and stirred for 5 min. The resulting solution was then cooled to room temperature. After a few days, red crystals suitable for single-crystal X-ray analysis were obtained with 41 % yield. Analysis C25H20F18N2O8Tb (977.35): calcd. C 30.72, H 2.06, N 2.87 %; found C 30.94, H 2.01, N 2.78 %. FT-IR (KBr): 1653 (s), 1501 (s), 1258 (s), 1202 (s), 1145 (s), 801 (m), 660 (m) cm–1. X-ray crystal structure determinations X-ray single-crystal diffraction data for two complexes were collected using a Bruker APEX-II CCD diffractometer at 173 K equipped with graphite-monochromated Mo/Kα radiation (λ = 0.71073 Å). The structures were solved by direct methods by using the program SHELXS-97 and refined by full-matrix least-squares methods on F2 with the use of the SHELXL-97 program package [34]. Anisotropic thermal parameters were assigned to all non-hydrogen atoms. The hydrogen atoms were set in calculated positions and refined as riding atoms with a common fixed isotropic thermal parameter. Disordered C and F atoms were observed for all compounds. The restraints of SPLIT, DELU and ISOR were applied to keep the disordered molecules reasonable. Pertinent crystallographic data and structure refinement parameters for all four complexes were listed in Table 1 and 2. Table 1. Crystallographic data for complexes 1 and 2. 1
2
Formula
C23H18TbF18N2O8
C25H20TbF18N2O8
Mr
951.31
977.35
Crystal system
Monoclinic
Monoclinic
Space group
P21/n
P21/c
a /Å
10.788(2)
10.853(3)
b /Å
16.128(4)
17.169(4)
c /Å
19.234(4)
18.365(4)
3
β ,deg
93.605(3)
97.804(3)
3339.7(13)
3390.3(14)
4
4
1.892
1.915
Tmin and Tmax
0.746 1.000
0.780 1.000
θmin, θmax deg
1.65 , 25.01
1.63 , 25.01
Reflections collected
29802
38223
Unique reflns/ Rint
5833/ 0.0441
8071/0.0534
GOF (F )
1.016
1.022
R1/wR2 (I > 2σ(I))
0.0334/0.0845
0.0324/0.0671
R1/wR2 (all data)
0.0360/ 0.0867
0.0400/0.0703
3
V /Å Z
Dcalcd /g cm
-3
2
Results and discussion Structural descriptions As shown in Figure 1, complex 1 crystallizes in P21/n space group with a monoclinic crystal system. The [Tb(hfac)3] units are connected by NIT-CH3 to form a one-dimensional infinite Tb(III)–NIT-CH3 chain. There is only one crystallographically independent Tb(hfac)3(NIT-CH3) moiety in the asymmetric unit. The nitroxide ligands which connect to the same Tb(III) are trans and the angles of Orad–Tb–Orad are found to be 134.72°. The Tb–O(radical) bond lengths are 2.357 Å and 2.373 Å, respectively. The Tb–O(hfac) distances are in the range of 2.331–2.369 Å . The nearest intrachain Tb···Tb distances are found to be 8.129 Å. The packing arrangement of 1 is shown in Figure 2. The shortest interchain Tb···Tb contacts in 1 are 9.909 Å. To the best of our knowledge, this is the nearest interchain Tb–Tb distance among the reported Tb-nitronyl nitroxide radical 1D chain compounds.
Figure 1. One-dimensional chain structure of complex 1 with the atom-labeling scheme. All hydrogen and fluorine atoms have been omitted for clarity.
4
Figure 2. Packing arrangement of the chains of 1. All hydrogen and fluorine atoms have been omitted for clarity.
The structure of complex 2 is shown in Figure 3. Similar to complex 1, complex 2 crystallizes in P21/c space group with only one crystallographically independent Tb(hfac)3(NIT-C3H5) moiety is observed in the asymmetric unit. The [Tb(hfac)3] units are connected by NIT-C3H5 to form a one-dimensional infinite Tb(III)–NIT-C3H5 chain. The nitroxide ligands which connect to the same Tb(III) are trans and the angles of Orad–Tb–Orad are found to be 136.88°. The Tb–O(hfac) distances are in the range of 2.315–2.355 Å . The nearest intrachain Tb···Tb distances are found to be 8.646 Å. The shortest interchain Tb···Tb contact in complex 2 are 10.753 Å ( Figure 4).
Figure 3. One-dimensional chain structure of complex 2 with the atom-labeling scheme. All hydrogen and fluorine atoms have been omitted for clarity.
Figure 4. Packing arrangement of the chains of complex 2. All hydrogen and fluorine atoms have been omitted for clarity.
5
Table 2. Selected bond distances (nm) and angles (o) for 1 and 2. 1 Tb(1)-O(3)
2.331(3)
Tb(1)-O(2)
2.357(3)
O(2)-N(2)
1.286(4)
Tb(1)-O(4)
2.340(3)
Tb(1)-O(5)
2.361(3)
O(1)-N(1)
1.282(4)
Tb(1)-O(7)
2.344(3)
Tb(1)-O(8)
2.369(3)
Tb(1)-O(6)
2.347(3)
Tb(1)-O(1)#1
2.373(3)
O(3)-Tb(1)-O(4)
74.67(11)
O(4)-Tb(1)-O(6)
137.66(10)
O(7)-Tb(1)-O(2)
148.68(10)
O(3)-Tb(1)-O(7)
137.84(10)
O(7)-Tb(1)-O(6)
85.36(11)
O(6)-Tb(1)-O(2)
73.07(10)
O(4)-Tb(1)-O(7)
115.05(10)
O(3)-Tb(1)-O(2)
73.16(10)
O(3)-Tb(1)-O(5)
75.44(11)
O(3)-Tb(1)-O(6)
115.74(11)
O(4)-Tb(1)-O(2)
71.48(10)
O(4)-Tb(1)-O(5)
145.77(10)
2 Tb(1)-O(7)
2.364(2)
Tb(1)-O(6)
2.334(2)
N(2)-O(8)
1.292(3)
Tb(1)-O(4)
2.318(2)
Tb(1)-O(5)
2.349(2)
N(1)-O(7)
1.289(3)
Tb(1)-O(2)
2.321(2)
Tb(1)-O(3)
2.354(2)
Tb(1)-O(1)
2.357(2)
Tb(1)-O(8)
2.337(2)
O(8)-Tb(1)-O(3)
73.12(9
O(8)-Tb(1)-O(5)
72.49(9)
C(7)-O(1)-Tb(1)
134.6(2)
O(4)-Tb(1)-O(7)
89.29(9)
O(4)-Tb(1)-O(6)
146.50(8)
O(4)-Tb(1)-O(5)
74.22(8)
O(4)-Tb(1)-O(2)
138.44(8)
O(2)-Tb(1)-O(6)
74.82(8)
O(2)-Tb(1)-O(5)
146.67(8)
O(6)-Tb(1)-O(5)
73.63(8)
O(4)-Tb(1)-O(3)
72.19(8)
O(2)-Tb(1)-O(3)
74.44(8)
Symmetry transformations used to generate equivalent atoms for 1: #1 -x+1/2,y-1/2,-z+1/2 #2 -x+1/2,y+1/2,-z+1/2 and for 2: #1 -x+1,y-1/2,-z-1/2 #2 -x+1,y+1/2,-z-1/2.
To estimate the degree of distortion of complexes 1 and 2, we also carried out the calculations of the shape factor S based on the crystal data based on Equation (1):
Where m is the number of edges (m = 18 in this work), δi is the observed angle between normals of adjacent faces (dihedral angle) along the i edge of the experimental polyhedron δ, and θi is the dihedral angle of the corresponding ideal polytopal shape θ. While the value S (δ, θ) is a measure of structural similarity to an ideal polytopal shape. The estimated S values of complexes 1 and 2 are summarized in Tables S1 and S2. For complex 1, the S values are S(D2d) =13.7°, S(C2v) = 13.6°, S(D4d) = 4.1°. Based on the minimum value of S, the coordination geometry of complex 2 is square antiprism (D4d) as shown in Figure 5. However, for complex 1, the S value are S(D2d) =7.7°, S(C2v) = 12.8°, S(D4d) = 8.1° indicates that the coordination geometry of complex 2 is trigonal dodecahedron (D2d) (Figure 5) [35].
6
Figure 5. The coordination polyhedron of 1 (right) and 2 (left).
Magnetic properties To study the static magnetic properties of both complexes, variable-temperature magnetic susceptibilities were measured from 300 K to 2 K in an applied field of 1 kOe. The MT vs.T plots for complex 1 are shown in Figure 6. At 300 K, the MT value is 11.99 cm3 K mol–1, which close to the theoretical value of 12.20 cm3 K mol−1 (an uncoupled Tb(III) ion (Tb(III): 7F6 , g = 3/2, C = 11.82 cm3 K mol−1) plus one organic radical (S = 1/2, 0.375 cm3 K mol−1)). While lowing the temperature, the χMT value of complex 1 gradually increases to 27.33 cm3 K mol−1 at 2 K. This increase of χMT suggests ferromagnetic interactions dominate in the chains.
Figure 6. Temperature dependence of MT for complex 1.
Figure 7. Field dependence of magnetization of 1 at 2.0 K.
7
The field dependence of magnetization of complex 1 has been determined at 2 K in the range of 0–70 kOe (Figure 7). Increasing the applied field, M value reaches up to 5.50 Nβ at 70 kOe. No saturation values were observed, indicating the presence of a magnetic anisotropy and/or low-lying excited states in the system. To investigate the dynamics of the magnetization, alternating current (ac) susceptibility measurements for complex 1 were carried out in low temperature regime under a zero dc field. As depicted in Figure 8, complex 1 only shows week frequency dependent out-of-phase signals which may due to the existence of a fast quantum tunneling relaxation of the magnetization (QTM). Thus, ac measurements were performed under external dc field of 1000 Oe to suppress the possible fast quantum tunneling relaxation. The frequency dependent out-of-phase signals of complex 1 still do not exhibit any maximum at 1400 Hz. Therefore, we are unable to determine the energy barrier Ueff and 0 via the conventional Arrhenius plot method as no maxima in " were observed. Bartolome ´et al employed an alternative method which is to assume that there is only one characteristic relaxation process of the Debye type, with one energy barrier and one time constant [36]. According to this assumption, one obtains Equation (2): ln(χ"/χ') = ln(ω0) + Ea/kBT From this equation, we can extract the estimated activation energy and the characteristic time by fitting the experimental data of ac susceptibility in 1000 Oe dc field for complex 1 (Figure 9). The best fit yielded Ueff ≈ 9.41(6) K and 0 ≈ 9.06 ×10–6 s.
Figure 8. Temperature dependence of the in-phase and out-of-phase components of ac susceptibility for 1 in zero dc field (above) and 1000 Oe dc field (below).
8
Figure 9. Natural logarithm of the ratio of " to ′vs. 1/T for complex 1 (1000 Oe dc field). The solid line represents the fitting results.
Figure 10. Temperature dependence of MT for complex 2.
Figure 11. Field dependence of magnetization of 2 at 2.0 K.
9
Figure 12. Temperature dependence of the in-phase and out-of-phase components of ac susceptibility for 2 in zero dc field(above) and 1000 Oe dc field(below).
Figure 13. Natural logarithm of the ratio of " to ′vs. 1/T for complex 2 (zero dc field). The solid line represents the fitting results.
For complex 2 (Figure 10), at 300 K the MT value is 12.35 cm3 K mol−1 (theoretical value is 12.20 cm3 K mol−1). The MT value keeps almost constant until 50 K, below which it continuously decreases to reach a value of 1.22 cm3 K mol−1 at 2.0 K. Furthermore, the field dependency of magnetization in the 0−70 kOe field range for complex 2 have been determined at 2.0 K (Figure 11). Upon increasing in the applied field, M reaches to 5.64 Nβ at 70 kOe, which does not reach the saturation values, indicating the presence of a magnetic anisotropy and/or low-lying excited states in the system. 10
In order to investigate spin dynamic magnetic behaviors of complex 2, ac magnetic susceptibility measurements were carried out in the temperature range of at different frequencies under a zero-external field. The frequency dependent out-of-phase signals are observed below 5 K, but no peak maximum is found above 2 K (Figure 12). This behavior may result from a fast quantum tunneling relaxation of the magnetization (QTM). Thus, ac measurements were performed under a external dc field of 1000 Oe. The frequency dependent in-phase signals show a peak maximum at high frequencies. However, the out-of-phase signals of complex 2 still do not exhibit any maximum at 1400 Hz (Figure 12). Therefore, we employed the same method as complex 1. By fitting the experimental data of ac susceptibility in 0 Oe dc field for complex 2, the best fit yielded Ueff ≈ 7.03(4) K and 0 ≈ 8.08×10–7 (Figure 13). Table 3. Structural and magnetic data for Tb- nitronyl nitroxide radical 1D chain compounds. Substitue Compound
nt (R)
[Tb(hfac)3NITPhOPh]n
S
[Tb(hfac)3NIT3BrPhO
Ref
interchain
Energy
Relaxation
Tb–Tb
barrier [K]
time 0 [S]
11.37
Ueff
= 45
9.62×10−9
17
10.89
Ueff
= 77.2
1.91×10-9
27
11.24
Ueff = 58.75
2.25×10-7
29
11.34
Ueff = 56.06
9.69×10-10
30
10.75
Ueff
≈ 9.41
~9.06×10–6
9.91
Ueff
≈ 7.03
~8.08×10–7
distance[Å]
O
[Tb(hfac)3NIT2Thien]n
Neareast
S
Me]n Br
O
[Tb(hfac)3 (NITPh2OEt)]n
[Tb(hfac)3(NIT-C3H5)]
O
n
[Tb(hfac)3(NIT-CH3)]n
this work
this work
As shown in Table 3, compare to those reported SCMs which base on aromatic group substituted nitronyl nitroxides, the Ueff values of complexes 1 and 2 are much 11
lower. This phenomenon might be caused by two reasons. Firstly, due to the π-π conjugate, aromatic groups are donating electron groups, therefore aromatic group substituted nitronyl nitroxides can transfer the magnetic interactions more effectively due to their high electron density. Secondly, on account of the relative small size of methyl group and cyclopropyl group, the interchain distance of complexes 1 and 2 are relative short. According to previous studies of SCMs need to avoid magnetic interactions between the adjacent chains [1,16,17], short interchain distance would impose negative influence on value of Ueff.
Conclusion In this paper, we have successfully obtained two novel one-dimensional Tb-radical complexes base on aliphatic group substituted nitronyl nitroxides. The X-ray analyses reveal that complex 1 shows the nearest interchain Tb···Tb distance among the reported Tb-nitronyl nitroxide radical 1D chain compounds. Magnetic studies reveal that slow magnetic relaxation was observed in both complexes.
Acknowledgments This work was funded by Guangdong college students' innovative project ( No. 201610580046); The science and technology innovation project of Zhaoqing (No. 201624030906); Huaibei science and technology research program (No.20140219); The National Science Foundation of Anhui Educational Bureau (No. KJ2016B010).
Supporting Information CCDC 1548424 (for 1) and 1548547(for 2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Observed dihedral angles dihedral angles of idealized angles and the calculated S values for complexes 1 and 2.
References [1] A. Caneschi, D. Gatteschi, N. Lalioti, C. Sangregorio, R. Sessoli, G. Venturi, A. Vindigni, A. Rettori, M. G. Pini, M. A. Novak, Angew. Chem. Int. Ed. 40 (2001) 1760. [2] R. Clérac, H. Miyasaka, M. Yamashita, C. Coulon, J. Am. Chem. Soc. 124 (2002) 12837. [3] L. Bogani, A. Vindigni, R. Sessoli, D. Gatteschi, J. Mater. Chem. 18 (2008) 4750. [4] a)Y.-C. Chen, J.-L. Liu, L. Ungur, J. Liu, Q.-W. Li, L.-F. Wang, Z.-P. Ni, L. F. Chibotaru, X.-M. Chen, M.-L. Tong, J. Am. Chem. Soc. 138 (2016) 2829; b) Y.-S. Ding, N. F. Chilton, R. E. P. Winpenny, Y.-Z. Zheng, Angew. Chem. Int. Ed. 55 (2016) 1. [5] W. Wernsdorfer, R. Sessoli, Science 284 (1999) 133. [6] L. Ungur, L. F. Chibotaru, Phys. Chem. Chem. Phys. 13 (2011) 20086. [7] N. F. Chilton, C. A. P. Goodwin, D. P. Mills, R. E. P. Winpenny, Chem. Commun. 51(2015) 101. [8] D. Gatteschi, R. Sessoli, Angew. Chem., Int. Ed. 42 (2003) 268.
12
[9] L. Bogani, W. Wernsdorfer, Nat. Mater. 7 (2008) 179. [10] F. Troiani, M. Affronte, Chem. Soc. Rev. 40 (2011) 3119. [11] J. D. Rinehart, M. Fang, W. J. Evans, J. R. Long, Nat. Chem. 3 (2011) 538. [12] Y. N. Guo, G. F. Xu, W. Wernsdorfer, L. Ungur, Y. Guo, J. Tang, H. J. Zhang, L. F. Chibotaru, A. K. Powell, J. Am. Chem. Soc. 133 (2011) 11948. [13] W. Wernsdorfer, N. Aliaga-Alcalde, D. N. Hendrickson, G. Christou, Nature 416 (2002) 406. [14] J. D. Rinehart, M. Fang, W. J. Evans, J. R. Long, J. Am. Chem. Soc. 133 (2011) 14236. [15] J.-J. Wang, M. Zhu, C. Li, J.-Q. Zhang, L.-C. Li, Eur. J. Inorg. Chem. 2015 (2015) 1368. [16] L. Bogani, C. Sangregorio, R. Sessoli, D. Gatteschi, Angew. Chem. Int. Ed. 44 (2005) 5817. [17] K. Bernot, L. Bogani, A. Caneschi, D. Gatteschi, R. Sessoli, J. Am. Chem. Soc. 128 (2006) 7947. [18] N. Ishii, Y. Okamura, S. Chiba, T. Nogami, T. Ishida, J. Am. Chem. Soc. 130 (2008) 24. [19] K. Bernot, L. Bogani, R. Sessoli, D. Gatteschi, Inorg. Chim. Acta. 360 (2007) 3807. [20] X.-F. Wang, Y.-G. Li, P. Hu, J.-J. Wang, L.-C. Li, Dalton Trans. 44 (2015) 4560. [21] M. G. F.Vaz, R. A. A.Cassaro, H. Akpinar, J. A.Schlueter, P.-M. Lahti, M.-A. Novak, Chem.Eur. J. 20 (2014) 5460. [22] R. A. A. Cassaro, S. G. Reis, T. S. Araujo, P. M.Lahti, M. A. Novak, M. G. Vaz, Inorg. Chem. 54 (2015) 9381. [23] P. Hu, C. Zhang, Y. Gao, Y. Li, Y. Ma, L. Li, D. Liao, Inorg. Chim. Acta. 398 (2013) 136. [24] H.-X. Tian, X.-F. Wang, X.-L. Mei, R.-N. Liu, M. Zhu, C.-M. Zhang, L.-C. Li, D.-Z. Liao, Y. Ma, Eur. J. Inorg. Chem. (2013) 1320. [25] T. Han, W. Shi, Z. Niu, B. Na, P. Cheng, Chem-Eur. J. 19 (2013) 994. [26] A. Datcu, N. Roques, V. Jubera, D. Maspoch, X. Fontrodona, K. Wurst, I. Imaz, G. Mouchaham, J.-P. Sutter, C. Rovira, J. Veciana, Chem. Eur. J. 18 (2012) 152. [27] R.-N. Liu, Y. Ma, P.-P. Yang, X.-Y. Song, G.-F. Xu, J.- K. Tang, L.-C. Li, D.-Z. Liao, S.-P. Yan, Dalton Trans. 39 (2010) 3321. [28] P. Hu, X.-F. Ma, Y. Wang, Q.-L. Wang, L.-C. Li, D.-Z. Liao, Dalton Trans. 43 (2014) 2234. [29] R.-N. Liu, C.-M. Zhang, X.-L. Mei, P. Hu, H.-X. Tian, L.- C.Li, D.-Z. Liao, J.-P. Sutter, New J. Chem. 36 (2012) 2088. [30] C. Li, J. Sun, M. Yang, G. Sun, J. Guo, Y. Ma, L. Li. Cryst. Growth Des. 16 (2016) 7155. [31] D. Shao, L. Shi, S.-L. Zhang, X.-H. Zhao, D.-Q. Wu, X.-Q. We, X.-Y. Wang, Cryst. Eng. Comm, 18 (2016) 4150. [32] B. Yao, Z. Guo, X. Zhang, Y. Ma, Z. Yang, Q. Wang, L. Li, P. Cheng, Cryst. Growth Des. 17 (2017) 95. [33] E. F. Ullman, J. H. Osiecki, D. G. B. Boocock, R. Darcy, J. Am. Chem. Soc. 94(1972) 7049. [34] a) G. M. Sheldrick, SHELXS 97, Program for the Solution of Crystal Structures, University of Gçttingen, Germany, 1997; b) G. M. Sheldrick, SHELXL 97, Program for the Refinement of Crystal Structures, University of Gçttingen, Germany, 1997. [35] J. Xu, E. Radkov, M. Ziegler and K. N. Raymond, Inorg. Chem. 39 (2000) 4156. [36] J. Bartolome ´, G. Filoti, V. Kuncser, G. Schinteie, V. Mereacre, C. E. Anson, A. K. Powell, D. Prodius and C. Turta, Phys. Rev. B: Condens. Matter Mater. Phys. 80 (2009) 014430.
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Highlights 1. Two one-dimensional novel lanthanide-radical complexes. 2. Slow magnetic relaxations were observed for both complexes.
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Graphical abstract Magnetic relaxation in two 1D Tb-nitronyl nitroxide complexes Peng Hu a, Feng-Ping Xiao a,*, Xiang-Ying Hao a, Jiang-Fei Cao a, Li-Li Zhu b,*
Two one-dimensional lanthanide–nitronyl nitroxide compounds have been successfully prepared. The magnetic studies reveal that slow magnetic relaxations were observed for both two Tb complexes.
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