Distinct magnetic dynamic behavior for two polymorphs of the same Dy(iii) complex

Article abstract of DOI:10.1039/c1cc11659b

Two polymorphs of the same Dy(iii) complex show distinct slow magnetic relaxation behaviors due to the different local environments of Dy(iii) in the crystal. This work represents the first example where the magnetic dynamic property of neutral rare earth complexes could be tuned by growing polymorphic crystals without changing the ligand.

Full text of DOI:10.1039/c1cc11659b

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COMMUNICATION
Distinct magnetic dynamic behavior for two polymorphs of the same
Dy(III) complexw
Dong-Ping Li,z Xiao-Peng Zhang, Tian-Wei Wang, Bin-Bin Ma, Cheng-Hui Li,* Yi-Zhi Li
and Xiao-Zeng You*
Received 23rd March 2011, Accepted 27th April 2011
DOI: 10.1039/c1cc11659b
9
Two polymorphs of the same Dy(III) complex show distinct slow
magnetic relaxation behaviors due to the different local environ-
ments of Dy(III) in the crystal. This work represents the first
example where the magnetic dynamic property of neutral rare
earth complexes could be tuned by growing polymorphic crystals
without changing the ligand.
energy barrier for magnetization reversal. Carretta et al.
ꢀ
revealed that matrix arrangements around [Pc
2
Tb] can also
appreciably alter the splitting of the crystal field levels, and
hence, the spin dynamics. Recently, Long et al. demonstrated
that the slow magnetic relaxation behavior of trigonal
II
pyramidal Fe compounds can be finely adjusted by changing
7
the substituent of the ligand.
d
Due to the potential applications in molecule-based informa-
1
tion storage, quantum computing and molecular spintronics,
In this study, we obtained two polymorphic forms of Dy(III)
complexes with diamine and b-diketone ligands. Although the
polymorphic crystals contain the same molecule, they show
quite different magnetic dynamic behaviors due to the different
local environments of Dy(III). This work represents the first
example where the magnetic dynamic behaviors of neutral rare
earth complexes could be tuned by growing polymorphic
crystals without changing the ligand.
single-molecule magnets (SMMs), which exhibit magnetic
hysteresis and slow magnetic relaxation at low temperature,
have seen a rapid growth in research over the past two
2
,3
decades. The superparamagnetic behavior observed in these
complexes stems from a negative axial magnetic anisotropy
(
D) acting on high-spin (S) ground states, which generates a
2
thermal barrier (Ueff = |D|S ) to spin inversion.
The complex [Dy(NTA)
3
L] (Scheme 1) was prepared by the
ꢁ2H
according to the literature method. The two polymorphic
forms 1a and 1b of [Dy(NTA) L] were obtained by using
Recently, constructing SMMs using a single ion has been
4
demonstrated to be possible in lanthanide complexes, actinide
reaction of the chiral diamine ligand with Dy(NTA)
3
2
O
10
5
6
complexes and also in high spin iron complexes. In these
single-ion magnets (SIM), the magnetic anisotropy required
for observing slow relaxation of the magnetization arises from
the interaction between a single metal ion and its ligand field
3
different solvents during synthesis (see ESIw for details).y In
both 1a and 1b, the molecule contains an eight-coordinated
Dy(III) ion, bonded to six oxygen atoms from three b-diketonate
anions and two nitrogen atoms from the diamine ligand. The
(
LF) which creates a strong preferential orientation of the
5
magnetic moment. Theoretical and experimental studies
a
˚
Dy–O bond lengths of 1a range from 2.288(3) to 2.433(3) A,
˚
while the two Dy–N bond lengths are 2.496(4) and 2.502(4) A,
have demonstrated that the LF splitting of the (2J + 1)-fold
III
ground state of the Ln ion can stabilize sublevels with a large
7
respectively (Table S1, ESIw). According to Continuous Shape
Measure Analysis (Table S2, ESIw) the coordination geometry
of the Dy(III) ion in 1a can be described as a distorted bicapped
triangular prism (BTP-8) (Fig. 1, left). There are eight
independent molecules in a unit cell of 1a (Fig. S1, ESIw).
|
M | value, thus achieving an easy axis of the magnetization.
J
Interestingly, the spin dynamic can be modified by the
careful adjustment of the ligand field around the metal center.
8
Ishikawa et al. showed that longitudinal contraction of the
˚
coordination sphere of bis(phthalocyaninato)terbium anion
ꢀ
The shortest Dy–Dy distance in the crystal structure is 8.929 A.
{
[Pc
2
Tb] } by a redox process can significantly increase the
State Key Laboratory of Coordination Chemistry, School of
Chemistry and Chemical Engineering, Nanjing National Laboratory of
Microstructures, Nanjing University, Nanjing 210093, P. R. China.
E-mail: chli@nju.edu.cn; youxz@nju.edu.cn; Fax: +86-25-83314502;
Tel: +86-25-83592969
w Electronic supplementary information (ESI) available: Experimental
details and additional characterization data. CCDC 783990 and
783991. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c1cc11659b
z Present address: Department of Chemistry, Nanchang University,
9
99 Xuefu Avenue, Nanchang 330031, P. R. China.
Scheme 1 Structure of complex 1.
This journal is c The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 6867–6869 6867

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Fig. 1 The coordination environments of complex 1a (left) and 1b (right).
˚
In 1b, the average Dy–O bond distance (2.318 A) is shorter
˚
while the average Dy–N bond distance (2.541 A) is longer than
those in 1a (Table S2, ESIw), resulting in the coordination
geometry of 1b being more like a distorted dodecahedron
(
Fig. 1, right). In contrast to 1a, there are only two inde-
pendent molecules in the unit cell of 1b (Fig. S2, ESIw). p–p
interactions were observed in complex 1b between different
0
00
m
Fig. 3 In-phase ðw Þ and out-of-phase ðw Þ dynamic magnetic
˚
m
naphthyl groups of b-diketonate anions (3.569 A), or the
susceptibilities measured in a 3 Oe ac magnetic field with a 2 kOe
naphthyl groups and phenyl groups in diamine ligands
˚
dc-field for 1a (a and b) and 1b (c and d).
(
3.215 A) (Fig. S3, ESIw). The shortest Dy–Dy distance in
˚
the crystal structure is 9.729 A. No solvent molecules were
found in the lattice of both polymorphs.
The magnetization of 1a reaches a maximum value of 5.26 Nb
above 65 kOe at 1.8 K (Fig. S8, ESIw), lower than the
The (1R,2R)-1,2-diphenylethane-1,2-diamine ligands are
racemated in 1a and 1b. Therefore, both R- and S-diamine
ligands are observed in the unit cell (Fig. S1 and S2, ESIw).
The powder X-ray diffraction patterns for 1a and 1b are
displayed in Fig. S4–S6 (ESIw). The diffraction peaks of the
experimental and simulated patterns match well in key posi-
tions, indicating the phase purities of compounds 1a and 1b.
No ferroelectric and second harmonic generation (SHG) effect
was observed for 1a and 1b, which is consistent with their non-
polar structures. The temperature dependence of the dielectric
constant shows that there is no phase transition between 5–350 K.
Sensitive calorimetric study indicates that 1a has a higher
melting point than 1b (Fig. S7, ESIw).
theoretical value (g
J
ꢂ J = 4/3 ꢂ 15/2 = 10 Nb), indicating
4g,h
a much smaller effective spin in 1a.
The ac magnetic measurements reveal that 1a shows the
typical features associated with the slow magnetic relaxation
0
00
(
Fig. S9, ESIw). The in-phase ðw Þ and out-of-phase ðw Þ
m
m
signals show obvious frequency dependence at low tempera-
ture, but no peak was observed. In order to further investigate
the dynamic properties of the slow magnetic relaxation and
obtain quantitative information of an effective energy barrier
for 1a, a stronger field of 2 kOe was applied in ac measure-
1
3,14
ments to quench the quantum tunneling.
As shown in
Fig. 3a and b, strong frequency dependence in both the
in-phase and out-of-phase signals was observed. Upon cooling,
0
w shows a maximum and begins to decrease in the 2.5–8.0 K
m
range at a frequency of 1–1500 Hz. The w also shows a set of
frequency dependent peaks at 2.5 K (10 Hz)–6.5 K (1500 Hz)
Magnetic measurement (1.8–300 K under 100 Oe of external
ꢀ1
field) revealed that the w
M
T value of 1a is 13.36 emu K mol
0
0
at room temperature, which slowly decreased to
ꢀ
m
1
1.75 emu K mol at 5 K upon cooling, and then slightly
1
0
0
ꢀ1
and then decreases at lower temperatures. The w peaks were
determined by Lorentz peak function fitting in 2000 Oe to
increased to 12.02 emu K mol at 1.8 K (Fig. 2). The decrease
m
upon cooling at high temperature is associated with the
1
thermal depopulation of Stark levels, while the unusual
1
estimate the magnetization–relaxation parameters with the
Arrhenius law [t(T) = t
meters (R = 0.999) afford a barrier height (U /K ) of 30.3 K
0
exp(Deff/k
B
T)]. The best fitting para-
small upturn observed at the low temperature may be due to
1
the weak intermolecular dipolar interactions. The experi-
2
eff
B
ꢀ
6
with t
range of those previously reported for SMMs and SCMs.
0
= 4.5 ꢂ 10 s (inset of Fig. 4). These values are in the
4f,15
mental data above 50 K obey the Curie–Weiss law with a
ꢀ
1
Curie constant C = 13.61 emu K mol , which is close to the
3
expected value of a paramagnetic Dy ion (J = 15/2, g = 4/3,
+
The existence of slow relaxation in 1a was also supported by
the dynamic studies of magnetic properties in the Cole–Cole
plot. At a fixed temperature of 5 K in a 2 kOe dc field, a
ꢀ
1
C = 14.17 emu K mol ), and a Weiss constant Y = ꢀ3.26 K.
0
00
semicircle wm vs. w diagram from 1 Hz to 1500 Hz was
m
observed (Fig. 4). The fit of the data to a general Debye model
gave a = 0.08, indicating the distribution of a single relaxation
process in 1a (a = 0 for an infinitely narrow distribution of
relaxation time). The variable-frequency ac susceptibility data
collected at multiple temperatures from 1 Hz to 1500 Hz
provide a = 0.12, 0.04, 0.06 at 1.8, 5 and 7 K with Hdc = 0 Oe;
and a = 0.07 at 7 K with Hdc = 2 kOe (Fig. S10, ESIw).
Owing to the encapsulation of the Dy(III) ion by the NTA
and diamine ligands, complex 1a is an isolated mononuclear
complex without strong interaction between Dy(III) ions.
Therefore, the slow magnetic relaxation showed by 1a should
be considered as a single-ion property.
Fig. 2 Variable-temperature magnetic susceptibility data for 1a and
M
1b (& for 1a, J for 1b) (H = 100 Oe), w T: left; w
Mꢀ
1
: right). The red
line represents the best fitting to Curie–Weiss law above 50 K.
6
868 Chem. Commun., 2011, 47, 6867–6869
This journal is c The Royal Society of Chemistry 2011

View Article Online
3
˚
b = 77.666(3), g = 87.0151, V = 2534.3(7) A , Z = 2, m =
ꢀ1
1
.560 mm , reflections collected/unique 13 573/9963, Rint = 0.0214,
= 0.0579, wR = 0.1248 for [I 4 2s(I)], R = 0.0786, wR
.1298 for all data. CCDC 783991.
R
0
1
2
1
2
=
1
(a) M. Yamanouchi, D. Chiba, F. Matsukura and H. Ohno,
Nature, 2004, 428, 539; (b) M. N. Leuenberger and D. Loss,
Nature, 2001, 410, 789; (c) P. C. E. Stamp and A. Gaita-Arino,
J. Mater. Chem., 2009, 19, 1718; (d) M. Manoli, A. Collins,
S. Parsons, A. Candini, M. Evangelisti and E. K. Brechin,
J. Am. Chem. Soc., 2008, 130, 11129.
2
(a) R. Sessoli, D. Gatteschi, A. Caneschi and M. A. Novak,
Nature, 1993, 365, 141; (b) D. E. Freedman, D. M. Jenkins,
A. T. Iavarone and J. R. Long, J. Am. Chem. Soc., 2008, 130,
2884; (c) L. F. Jones, A. Prescimone, M. Evangelisti and
E. K. Brechin, Chem. Commun., 2009, 2023; (d) G. Karotsis,
S. J. Teat, W. Wernsdorfer, S. Piligkos, S. J. Dalgarno and
E. K. Brechin, Angew. Chem., Int. Ed., 2009, 48, 8285.
Fig. 4 Cole–Cole diagram at 5 K in a 2 kOe dc field for 1a. The solid
line represents the best fitting with a Debye model. Inset: relaxation-
time fitting to the Arrhenius law in the 10–1500 Hz interval for 1a.
In contrast to 1a, the w
M
T value of 1b gradually
ꢀ
1
decreases from 13.13 emu K mol at room temperature to
3 (a) M. Atanasov, P. Comba, S. Hausberg and B. Martin, Coord.
Chem. Rev., 2009, 253, 2306; (b) M. Sorai, M. Nakano and
Y. Miyazaki, Chem. Rev., 2006, 106, 976.
4 (a) N. Ishikawa, M. Sugita, T. Okubo, N. Tanaka, T. Iino and
Y. Kaizu, Inorg. Chem., 2003, 42, 2440; (b) N. Ishikawa, M. Sugita,
T. Ishikawa, S. Y. Koshihara and Y. Kaizu, J. Am. Chem. Soc.,
ꢀ1
7
.29 emu K mol at 1.8 K (Fig. 2). The Curie–Weiss law fit
ꢀ1
gave C = 13.47 emu K mol and Y = ꢀ7.92 K. Saturation
of magnetization does not reach for 1b above 65 kOe at 1.8 K.
0
00
m
The w and w signals of dynamic magnetic susceptibility of 1b
m
2
003, 125, 8694; (c) N. Ishikawa, M. Sugita and W. Wernsdorfer,
J. Am. Chem. Soc., 2005, 127, 3650; (d) M. A. AlDamen,
J. M. Clemente-Juan, E. Coronado, C. Martı-Gastaldo and
A. Gaita-Arino, J. Am. Chem. Soc., 2008, 130, 8874;
e) M. A. AlDamen, S. Cardona-Serra, J. M. Clemente-Juan,
E. Coronado, A. Gaita-Arino, C. Martı-Gastaldo, F. Luis and
are invariant upon changing the frequency at zero field
(
Fig. S11, ESIw). By applying a 2 kOe dc field, 1b shows
´
0
00
m
ˇ
frequency dependent w and w signals (Fig. 3c and d), but no
m
(
Cole–Cole plot can be obtained due to the poor discriminability
of the signals. These data indicate that 1b may also show single-
ion magnet behavior but at significantly lower temperature.
The distinct magnetic behavior of 1a and 1b can be attrib-
uted to the different local environments of the Dy(III) ion.
According to the single crystal X-ray diffraction study and
Continuous Shape Measure Analysis, the local ligand-field
symmetry of the Dy(III) ion is close to C2v in 1a and close to
D2d in 1b. The different local ligand-field symmetry of the
Dy(III) ion results in different anisotropy and then different
magnetic dynamic behaviors. Moreover, configuration inter-
actions between ground state and low lying excited states in
different symmetry may result in different spin ground states.
In conclusion, two polymorphic forms of Dy(III) complexes
were prepared. The two polymorphs show quite different
slow magnetic dynamic behaviors due to the different local
environments of the Dy(III) ion. The difference may arise from
the different crystal field effect and configuration interaction in
different symmetry. However, more efforts are needed to
understand the mechanism of polymorph formation and
the relation between the structure and magnetic dynamic
behaviors for rare earth complexes.
ˇ
´
O. Montero, Inorg. Chem., 2009, 48, 3467; (f) D. P. Li,
T. W. Wang, C. H. Li, D. S. Liu, Y. Z. Li and X. Z. You, Chem.
Commun., 2010, 46, 2929; (g) Y. Wang, X. L. Li, T. W. Wang,
Y. Song and X. Z. You, Inorg. Chem., 2010, 49, 969;
(
h) S.-D. Jiang, B.-W. Wang, G. Su, Z.-M. Wang and S. Gao,
Angew. Chem., Int. Ed., 2010, 49, 7448; (i) S.-D. Jiang,
B.-W. Wang, H.-L. Sun, Z.-M. Wang and S. Gao, J. Am. Chem.
Soc., 2011, 133, 4730–4733.
(a) J. D. Rinehart and J. R. Long, J. Am. Chem. Soc., 2009, 131,
12558; (b) J. D. Rinehart, K. R. Meihaus and J. R. Long, J. Am.
Chem. Soc., 2010, 132, 7572.
D. E. Freedman, W. H. Harman, T. D. Harris, G. J. Long,
C. J. Chang and J. R. Long, J. Am. Chem. Soc., 2010, 132, 1224.
(a) N. Ishikawa, J. Phys. Chem. A, 2003, 107, 5831;
(b) N. Ishikawa, M. Sugita, T. Ishikawa, S. Y. Koshihara and
Y. Kaizu, J. Phys. Chem. B, 2004, 108, 11265; (c) N. Ishikawa,
M. Sugita and W. Wernsdorfer, Angew. Chem., Int. Ed., 2005, 44,
5
6
7
2
931; (d) W. H. Harman, T. D. Harris, D. E. Freedman, H. Fong,
A. Chang, J. D. Rinehart, A. Ozarowski, M. T. Sougrati,
F. Grandjean, G. J. Long, J. R. Long and C. J. Chang, J. Am.
Chem. Soc., 2010, 132, 18115.
S. Takamatsu, T. Ishikawa, S. Koshihara and N. Ishikawa, Inorg.
Chem., 2007, 46, 7250.
F. Branzoli, P. Carretta, M. Filibian, G. Zoppellaro, M. J. Graf,
J. R. Galan-Mascaros, O. Fuhr, S. Brink and M. Ruben, J. Am.
Chem. Soc., 2009, 131, 4387.
0 L. Melby, N. Rose, E. Abramson and J. C. Caris, J. Am. Chem.
Soc., 1964, 86, 5117.
8
9
1
This work was supported by National Natural Science
Foundation of China (91022031, 21021062), and the National
Basic Research Program of China (2007CB925100,
11 G. F. Xu, Q. L. Wang, P. Gamez, Y. Ma, R. Cle
S. P. Yan, P. Cheng and D. Z. Liao, Chem. Commun., 2010, 46,
506.
2 (a) R. L. Carlin, Magnetochemistry, Springer, Berlin, 1986;
b) K. Bernot, J. Luzon, L. Bogani, M. Etienne, C. Sangregorio,
´
rac, J. k. Tang,
1
2
011CB808704 and 2011CB933300). We thank Prof.
1
Dong-Shan Zhou and Dr Xin-Yi Wang for their kind help
and suggestions.
(
M. Shanmugam, A. Caneschi, R. Sessoli and D. Gatteschi, J. Am.
Chem. Soc., 2009, 131, 5573.
1
3 L. Thomas, F. Lionti, R. Ballou, D. Gatteschi, R. Sessoli and
B. Barbara, Nature, 1996, 383, 145.
Notes and references
y Crystal data for 1a (C56
monoclinic, space group C2/c, a = 35.754(5), b = 10.8207(15),
H
40
F
9
N
2
O
6
Dy): M = 1170.40 g mol,
14 (a) C. J. Milios, A. Vinslava, W. Wernsdorfer, S. Moggach,
S. Parsons, S. P. Perlepes, G. Christou and E. K. Brechin,
J. Am. Chem. Soc., 2007, 129, 2754; (b) D. Yoshihara,
S. Karasawa and N. Koga, J. Am. Chem. Soc., 2008, 130, 10460.
15 (a) G. Poneti, K. Bernot, L. Bogani, A. Caneschi, R. Sessoli,
W. Wernsdorfer and D. Gatteschi, Chem. Commun., 2007, 1807;
(b) S. Kanegawa, S. Karasawa, M. Maeyama, M. Nakano and
N. Koga, J. Am. Chem. Soc., 2008, 130, 3079.
3
˚
˚
c = 27.295(4) A, b = 105.515(3)1, V = 10175(2) A , Z = 8, m =
ꢀ1
1
.554 mm , reflections collected/unique 26 280/9963, Rint = 0.0316,
= 0.0511, wR = 0.1186 for [I 4 2s(I)], R = 0.0706, wR
.1269 for all data. CCDC 783990. Crystal data for 1b
R
0
1
2
1
2
=
ꢀ
(C H F N O Dy): M = 1170.40 g mol, triclinic, space group P1,
56 40 9 2 6
˚
a = 9.7289(16), b = 13.557(3), c = 20.495(3) A, a = 73.683,
This journal is c The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 6867–6869 6869