Lanthanide-organic coordination frameworks showing new 5-connected network topology and 3D ordered array of single-molecular magnet behavior in the Dy case

Article abstract of DOI:10.1021/ic500490x

Five isostructural lanthanide-organic coordination frameworks with a unique 3-D 5-connected (4⁷.6³)(4³.6 ⁵.8²) network, namely, [Ln(phen)(L)]_n (Ln = Dy for 1, Gd for 2, Ho for 3, Er for 4, and Tb for 5), have been prepared based on bridging 5-hydroxyisophthalic acid (H₃L) and chelating 1,10-phenanthroline (phen) coligand. Significantly, the Dy(III) complex 1 is an organized array of single-molecular magnets (SMMs), with frequency-dependent out-of-phase ac susceptibility signals and magnetization hysteresis at 4 K. Further analysis of the magnetic results can reveal that the SMM behavior of 1 should arise from the smaller ferromagnetic interaction between the Dy(III) ions. Complex 1 was also characterized by X-ray absorption spectra, which give the clear X-ray magnetic circular dichroism signal.

Full text of DOI:10.1021/ic500490x

Article
pubs.acs.org/IC
Lanthanide−Organic Coordination Frameworks Showing New
5‑Connected Network Topology and 3D Ordered Array of Single-
Molecular Magnet Behavior in the Dy Case
Min Chen,† E. Carolina Sanudo,‡ Erika Jimenez,§ Shao-Ming Fang,† Chun-Sen Liu,*,† and Miao Du*,∥
́
̃
†Henan Provincial Key Lab of Surface & Interface Science, Zhengzhou University of Light Industry, Zhengzhou 450002, Henan
People’s Republic of China
‡Institut de Nanocien
̀ ̀
cia i Nanotecnologia i Departament de Química Inorganica, Universitat de Barcelona, Diagonal, 647,
08028-Barcelona, Spain
§European Synchrotron Radiation Facility, Beamline ID-08, ESRF, 38000 Grenoble, France
∥College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, MOE Key Laboratory of
Inorganic−Organic Hybrid Functional Material Chemistry, Tianjin Normal University, Tianjin 300387, People’s Republic of China
S
* Supporting Information
ABSTRACT: Five isostructural lanthanide−organic coordination frameworks
with a unique 3-D 5-connected (47.63)(43.65.82) network, namely, [Ln(phen)-
(L)]n (Ln = Dy for 1, Gd for 2, Ho for 3, Er for 4, and Tb for 5), have been
prepared based on bridging 5-hydroxyisophthalic acid (H3L) and chelating
1,10-phenanthroline (phen) coligand. Significantly, the Dy(III) complex 1 is
an organized array of single-molecular magnets (SMMs), with frequency-
dependent out-of-phase ac susceptibility signals and magnetization hysteresis
at 4 K. Further analysis of the magnetic results can reveal that the SMM
behavior of 1 should arise from the smaller ferromagnetic interaction between
the Dy(III) ions. Complex 1 was also characterized by X-ray absorption
spectra, which give the clear X-ray magnetic circular dichroism signal.
from the combination of an appreciable spin ground state (S)
and a negative uniaxial magnetic anisotropy (D),8 producing
the energy barrier U given by the expressions U = S2|D| for
integer and U = (S2 − 1/4)|D| for half-integer spins. At the
beginning of SMMs investigation, many SMMs based on high
nuclearity first-row transition-metal clusters with high-spin
ground states, such as Co24,9 Mn12,10 and Mn25,11 have been
reported. Meanwhile, the strong spin−orbit coupling in certain
lanthanide ions (DyIII and TbIII and so on) results in strong
magnetic anisotropy of their complexes and thus higher
blocking temperatures, compared with those of first-row
transition-metal SMMs. In fact, new synthetic strategies have
been explored to achieve high blocking temperature and high
energy barrier coordination structures. Consequently, the
search for new 3d−4f architectures as well as pure 4f systems
will be of great significance. In most reported lanthanide
SMMs, the magnet-like behavior reveals single-ion relaxation
mechanisms.12 To move the molecular magnet materials
toward practical application, more transparent insights of the
relaxation mechanism are required.
INTRODUCTION
■
The realm of crystal engineering has been flourishing,1 and the
crystal engineering technique has been widely used for the
rational design and controlled synthesis of diverse lanthanide−
organic frameworks (LnOFs) owing to their fascinating
structural topologies.2 Normally, lanthanide ions tend to
coordinate with the O-donor ligands in higher and flexible
coordination numbers (CNs), compared with the d-block
transition-metal (TM) ions. In this regard, carboxylic acids can
generally cater for the oxophilic nature of Ln ions and also,
their ability to take different binding fashions fits well with the
irregular coordination geometries of 4f metals.3 Several
synthetic strategies have been developed to prepare such
crystalline materials with desired structures and properties,
among which the appropriate choice of predesigned organic
bridging ligands and lanthanide ions or clusters is one of the
most effective ways.1,4
Molecular magnets attract much attention for their potential
applications in information storage, molecular electronics, MRI
imaging, among other possible applications.5 In molecular
magnetism, the research on single-molecular magnets (SMMs)
is one of the most hottest areas since the 1990s.6,7 Slow
relaxation of magnetization is the intrinsic characteristic of
SMMs, resulting in each single molecule behaving as a magnet.
This magnet-like behavior below a blocking temperature arises
Furthermore, the fascinating long-lived and narrow emission
bands from near-infrared to visible regions of lanthanide ions
Received: March 3, 2014
© XXXX American Chemical Society
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a
Table 1. Crystallographic Data and Structural Refinement Summary for 1−5
1
2
3
empirical formula
C20H11DyN2O5
521.81
C20H11GdN2O5
516.56
C20H11HoN2O5
524.24
formula weight
crystal system
space group
a/Å
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/n
9.7431(2)
13.9008(3)
12.0310(2)
97.243(2)
1616.44(6)
4
9.7723(6)
13.8718(8)
12.0958(7)
97.200(6)
1626.77(17)
4
9.7320(6)
13.9346(8)
11.9536(8)
97.326(6)
1607.81(17)
2
b/Å
c/Å
β/°
V/Å3
Z
D/g cm−3
μ/mm−1
Rint
2.144
2.109
2.166
4.662
4.116
4.960
0.0301
0.0467
0.0677
GOF
1.033
1.007
1.003
T/K
294(2)
294(2)
294(2)
a
b
R1 /wR2 [I > 2σ(I)]
0.0274/0.0630
4
0.0366/0.090
5
0.0406/0.0831
empirical formula
C20H11ErN2O5
526.57
C20H11TbN2O5
518.23
formula weight
crystal system
space group
a/Å
monoclinic
P21/n
monoclinic
P21/n
9.6993(7)
13.9504(10)
11.9486(8)
97.382(6)
1603.4(2)
2
9.7851(11)
13.9179(16)
12.1056(14)
97.2270(10)
1635.5(3)
4
b/Å
c/Å
β/°
V/Å3
Z
D/g cm−3
μ/mm−1
Rint
2.181
2.105
5.274
4.363
0.0606
0.0217
GOF
1.058
1.051
T/K
294(2)
294(2)
a
b
R1 /wR2 [I > 2σ(I)]
0.0595/0.1476
0.0166/0.0382
a
b
2
R1 = ∑(||Fo| − |Fc||)/∑|Fo|. wR2 = [∑w(|Fo|2 − |Fc|2)2/∑w(Fo )2]1/2
.
on a Bruker D8 Advance diffractometer (Cu−Kα, λ = 1.54056 Å) at
40 kV and 30 mA, by using a Cu-target tube and a graphite
monochromator. The powder samples were prepared by crushing the
crystals, and the intensity data were recorded by continuous scan in a
2θ/θ mode from 5° to 80° with a step size of 0.02° and a scan speed of
2°/min. Simulation of the PXRD spectra was carried out by the single-
crystal data and diffraction-crystal module of the Mercury (Hg)
program. The emission/excitation spectra of the solid samples were
recorded on an F-7000 (Hitachi) spectrophotometer at room
temperature. Magnetic measurements were carried out in the Unitat
make them good candidates for new multifunctional magnetic
and luminescent materials. Though the rational design and
construction of multifunctional materials with two or more
physical properties is still an exciting challenge, the
combination of molecular magnet behavior and luminescent
properties in the same entity for lanthanide−organic coordina-
tion frameworks has come true in a few instances.13 Herein, we
present a series of lanthanide−organic coordination frameworks
[Ln(phen)(L)]n (Ln = Dy for 1, Gd for 2, Ho for 3, Er for 4,
and Tb for 5, phen = 1,10-phenanthroline, and H3L = 5-
hydroxyisophthalic acid), in which complex 1 shows interesting
SMM behavior and luminescent properties. The magnetic
properties of other complexes have also been investigated for
comparison.
̀
de Mesures Magnetiques (Universitat de Barcelona) on polycrystalline
samples (ca. 30 mg) with a Quantum Design SQUID MPMS-XL
magnetometer equipped with a 5 T magnet. Diamagnetic corrections
were calculated using Pascal’s constants, and an experimental
correction for the sample holder was applied.
Preparation of Complexes 1−5. A mixture of Ln2O3 (0.3 mmol,
Ln = Dy for 1, Gd for 2, Ho for 3, Er for 4) or Tb4O7 (0.15 mmol, for
5), H3L (0.3 mmol), phen (0.15 mmol), and H2O (15 mL) was sealed
in a Teflon-lined autoclave (23 mL), heated in an oven at 170 °C for 5
days, and then cooled to room temperature at a rate of 5 °C h−1.
Single crystals of 1−5 suitable for X-ray diffraction were obtained.
For 1: Yield ca. 30%. Anal. Calcd for C20H11DyN2O5: C, 46.03; H,
2.12; N, 5.37%. Found: C, 46.19; H, 2.27; N, 5.51%. IR (cm−1): 3392
(m, br), 2974 (w), 2364 (w), 1617 (s), 1562 (s), 1428 (vs), 1375 (vs),
1315 (s), 1147 (w), 1126 (w), 1096 (w), 1049 (w), 1010 (s), 914 (w),
883 (w), 864 (w), 858 (w), 847 (w), 784 (s), 730 (s), 710 (s), 638
(w), 605 (m), 446 (w).
EXPERIMENTAL SECTION
■
Materials and Physical Measurements. All reagents and
solvents were obtained commercially and used as received. Fourier
transform (FT) IR spectra (KBr pellets) were recorded in the range of
4000−400 cm−1 on a Tensor 27 OPUS (Bruker) FT-IR spectrometer.
Elemental analyses (C, H, and N) were performed on a Vario EL III
elemental analyzer. Thermogravimetric analysis (TGA) experiments
were carried out on a PerkinElmer Diamond SII thermal analyzer in
the temperature range of 25−900 °C at a heating rate of 10 °C/min
under a nitrogen atmosphere with an empty Al2O3 crucible as the
reference. Powder X-ray diffraction (PXRD) patterns were recorded
B
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Figure 1. (a) Local coordination environment of DyIII (symmetry codes for A = −x + 1, −y + 1, −z + 1; B = x − 1/2, −y + 1/2, z − 1/2; C = −x, −y
+ 1, −z + 1; D = −x + 1/2, y + 1/2, −z + 3/2). (b) The 2-D layer constructed by L ligands and DyIII ions running parallel to ac plane. (c) Schematic
representation of the 5-connected (47.63)(43.65.82) topology.
For 2: Yield ca. 25%. Anal. Calcd for C20H11GdN2O5: C, 46.50; H,
2.15; N, 5.42%. Found: C, 46.62; H, 2.29; N, 5.58%. IR (cm−1): 3586
(s), 3401 (m, br), 1612 (s), 1561 (vs), 1428 (vs), 1376 (vs), 1316 (s),
1279 (w), 1147 (w), 1123 (w), 1102 (w), 1010 (m), 987 (w), 908
(w), 883 (w), 848 (m), 821 (w), 786 (s), 732 (w), 725 (w), 711 (m),
637 (w), 601 (m), 448 (m).
For 3: Yield ca. 35%. Anal. Calcd for C20H11HoN2O5: C, 45.82; H,
2.11; N, 5.34%. Found: C, 45.96; H, 2.28; N, 5.49%. IR (cm−1): 3429
(m, br), 1618 (s), 1562 (vs), 1428 (vs), 1376 (vs), 1317 (s), 1147 (w),
1126 (w), 1103 (w), 1010 (m), 915 (w), 883 (w), 849 (m), 784 (s),
730 (m), 710 (m), 639 (w), 605 (w), 580 (w), 447 (w).
For 4: Yield ca. 40%. Anal. Calcd for C20H11ErN2O5: C, 45.62; H,
2.11; N, 5.32%. Found: C, 45.68; H, 2.17; N, 5.47%. IR (cm−1): 3595
(s), 3354 (m, br), 2974 (w), 2360 (w), 1616 (s), 1560 (m), 1383 (m),
1317 (s), 1280 (s), 1147 (w), 1128 (s), 1102 (s), 1050 (w), 1008 (s),
1010 (s), 984 (s), 915 (s), 884 (w), 866 (w), 847 (w), 818 (s), 803
(s), 784 (vs), 726 (vs), 710 (s), 635 (w), 603 (w), 557 (w), 521 (w),
457 (w).
For 5: Yield: ca. 30%. Anal. Calcd for C20H11TbN2O5: C, 46.35; H,
2.14; N, 5.41%. Found: C, 46.51; H, 2.21; N, 5.53%. IR (cm−1): 3736
(w), 3371 (m, br), 2974 (s), 2841 (w), 1923 (w), 1616 (s), 1562 (vs),
1428 (vs), 1376 (vs), 1316 (s), 1123 (w), 1091 (s), 1050 (s), 1010
(m), 910 (w), 883 (w), 846 (m), 784 (s), 708 (m), 636 (w), 603 (w),
447 (w).
X-ray Crystallography. Single-crystal X-ray diffraction data for
complexes 1−5 were collected on a Bruker Apex II CCD
diffractometer at 294(2) K with Mo Kα radiation (λ = 0.71073 Å).
A semiempirical absorption correction was applied using SADABS,
and the program SAINT was used for integration of the diffraction
profiles.14 The structures were solved by direct methods with the
SHELXS program of the SHELXTL package and refined with
SHELXL.15 The non-H atoms were modeled with anisotropic thermal
parameters and refined by full-matrix least-square methods on F2. In
general, C-bound hydrogen atoms were placed geometrically and
refined as riding. Further details for crystallographic data and
refinement conditions are listed in Table 1. Selected bond parameters
are shown in Tables S1−S5 (Supporting Information), respectively.
CCDC-963516 (1), 963515 (2), 963518 (3), 963517 (4), and 963519
(5) contain the supplementary crystallographic data for this paper.
Supporting Information), which are thermally stable up to ca.
500 °C. Upon further heating, pyrolysis of the organic ligands
occurs, which does not stop until the heating ends at 900 °C.
Single-crystal X-ray structural analysis reveals that complexes
1−5 are isostructural (see Table 1, Tables S1−S5, and Figure
S3 in Supporting Information). Thus, only the crystal structure
of 1 will be discussed in detail herein. The asymmetric unit of
[Dy(phen)(L)]n (1) contains one crystallographically inde-
pendent DyIII atom, one L ligand, and one phen ligand. As
depicted in Figure 1a, each DyIII center is seven-coordinated
with a distorted pentagonal-bipyramidal geometry, which is
defined by two N-donor atoms of one phen ligand [Dy−N =
2.544(4) and 2.573(4) Å], four carboxylate oxygen atoms of
four L ligands [Dy−Ocarboxylate = 2.291(3)−2.369(3) Å], and
one hydroxyl oxygen atom of L ligand [Dy−Ohydroxyl = 2.168(3)
Å]. The L ligand adopts a fully deprotonated μ5-bridging
fashion to connect five DyIII centers, through the syn−syn and
syn−anti binding carboxylate groups, as well as the mono-
dentate hydroxyl oxygen atom. Such a fully deprotonated form
for the aromatic hydroxyl/carboxyl ligands have also been
observed in quite a few Ln coordination polymers.2f−h Two
adjacent DyIII atoms are bridged by four carboxylate groups to
form a paddle-wheel motif with a Dy···Dy distance of 4.097(2)
Å. Each ligand links two such paddle-wheel motifs by the
carboxylate groups to result in a left- or right-handed helical
chain parallel to the b axis with the pitch of 13.92 Å. The chains
with opposite chirality are alternately arranged to afford a 2-D
corrugated layer by sharing the paddle-wheel motifs (see Figure
1b). The adjacent layers are further extended by Dy−O5
interactions to construct the final 3-D network (see Figure S4
in Supporting Information).
To fully understand the complicated network structure of 1,
the topological approach is applied to simplify this 3-D
coordination framework. In this approach, when the ligands
and DyIII centers are considered as the network nodes, such
two kinds of 5-connected nodes are connected to form a 3-D 5-
connected network (Figure 1c) with the point symbol of
(47.63)(43.65.82). Significantly, the 5-connected nodes usually
result in a (44.66) or (46.64) topological network, and such a
case observed in 1 represents a new structural paradigm.
Alternatively, each ligand can also be viewed as a 3-connected
node and each paddle-wheel dinuclear DyIII unit as a 6-
connected node, respectively. Thus, the overall framework can
also be described as a (3,6)-connected rtl topology (see Figure
RESULTS AND DISCUSSION
■
Synthesis and Crystal Structures. MOFs 1−5 were
prepared from Ln2O3 (for 1−4) and Tb4O7 (for 5) and the
poly(carboxylic acid) organic ligand 5-hydroxyisophthalic acid
(H3L) in the presence of phen under hydrothermal conditions,
which were characterized by IR spectra and microanalyses. The
phase purity of bulk samples was further confirmed by PXRD
patterns (Figure S1 in Supporting Information). Complexes 1−
5 exhibit similarly high thermal stability (see Figure S2 in
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S5 in Supporting Information) with the point symbol of
(4.62)(42.610.83).16
coupling is always weak, as reflected by the θ values (see Table
S6 in Supporting Information), always below |10| K. This is to
be expected from the detailed analysis of crystal structures
(Figure 1 and Figures S3−S5, Supporting Information). The
shortest Ln···Ln distances within the paddle-wheel dimers are
ca. 4 Å in complexes 1−5, with no monatomic bridge to
enforce a good pathway for the magnetic exchange. The
shortest interdimer Ln···Ln distances are ca. 7.53 Å for 1, 7.58
Å for 2, 7.51 Å for 3, 7.48 Å for 4, and 7.58 Å for 5, respectively.
Furthermore, the donor oxygen groups of the L ligand are
situated in meta with respect to each other in the central
aromatic ring, favoring weak ferromagnetic coupling between
the metal ions.18
Magnetic Studies. Magnetic susceptibility data for [Ln-
(phen)(L)]n (Ln = Dy for 1, Gd for 2, Ho for 3, Er for 4, and
Tb for 5) were collected at an applied field of 0.3 T in the 2−
300 K temperature range and at an additional field on 200 Oe
in 30−2 K. The data are shown in Figure 2 as χT vs T plots.
We then proceeded to study the ac magnetic susceptibility of
this series of complexes, in order to clarify if the magnetic
coupling can lead to long-range magnetic ordering or SMM-
type behavior in these 3-D systems. The results reveal that only
the DyIII complex 1 shows a decrease of the in-phase signal
accompanied by the appearance of an out-of-phase signal
between 40 and 5 K that is frequency-dependent (see Figure
3). Below 5 K, a tail of another out-of-phase signal is observed,
Figure 2. χT vs T plots for [Ln(phen)(L)]n (Ln = Dy for 1, Gd for 2,
Ho for 3, Er for 4, and Tb for 5) at 0.3 T applied field.
The χT products of the different complexes at 300 K have
values of Dy (1) = 14.5 cm3 K mol−1, Gd (2) = 8.4 cm3 K
mol−1, Ho (3) = 13.4 cm3 K mol−1, Er (4) = 12.9 cm3 K mol−1,
and Tb (5) = 12.8 cm3 K mol−1, which agree well with the
expected values for one free LnIII ion with spin−orbit coupling:
DyIII = 14.16 cm3 K mol−1 (6H15/2, S = 5/2, L = 5, J = 15/2, and
gJ = 4/3),17 GdIII = 7.9 cm3 K mol−1 (8S7/2, S = 7/2, L = 0, g =
2.0), HoIII = 14 cm3 K mol−1 (5I8, S = 2, L = 6, J = 8, and gJ = 5/
4), ErIII = 11.81 cm3 K mol−1 (4I15/2, S = 3/2, L = 6, J = 15/2,
and gJ = 6/5), and TbIII = 11.81 cm3 K mol−1 (7F6, S = 3, L = 3,
J = 6, and gJ = 3/2). As can be clearly observed from the χT vs
T plot for the Er complex 4, as the temperature decreases, the
depopulation of the excited Stark sublevels leads to a decrease
in the χT product, whereas, for the Gd complex 2, the χT vs T
plot is nearly constant, only decreasing at temperatures below
25 K, indicating practically uncoupled ions or a weak
antiferromagnetic coupling. For the lanthanide complexes of
Tb (5), Dy (1), and Ho (3), the χT vs T plots indicate the
onset of weak ferromagnetic magnetic coupling below 50 K.
This is confirmed by the Curie−Weiss plots shown in Figure S6
(Supporting Information) and the fitting results of the
susceptibility to the Curie−Weiss law, which are summarized
in Table S6 (Supporting Information). For complexes Gd (2)
to Er (4), as the number of f electrons grows, the Weiss
constant θ goes from small and negative (indicating
antiferromagnetic interactions) to positive, and then small
and negative again for Er (4). However, Tb (5), Dy (1) and Ho
(3) show positive Weiss constant values, which indicate the
prevalence of ferromagnetic coupling. This is unusual for HoIII
dimers, but not unprecedented. For example, Tong et al. have
reported a HoIII dimer with ferromagnetic coupling similar to
that found in 3.21 The coordination geometries of the
lanthanide ions in both cases are similar: Tong’s complex is
between a capped octahedron and a distorted capped trigonal
prism, whereas the complex reported herein is closer to the
capped trigonal prism (see Figure S8 and Table S7 in the
Supporting Information). As usual for the LnIII ions, this
Figure 3. ac magnetic susceptibility with a 4 Oe oscillating field at
various frequencies and no applied dc field for [Dy(phen)(L)]n (1).
The lines are only a guide for the eye.
indicating a faster relaxation process. Analysis of the relaxation
dynamics by using the Arrhenius equation shows that the
process centered at 20 K has a τo = 1.6 × 10−6 s and an effective
barrier of ΔE = 131 K (see Figure 4), with a Mydosh parameter
of 0.29, in agreement with the expected values for an SMM.
The relaxation dynamics were also studied by measuring ac
susceptibility as a function of frequency. The Cole−Cole plot
(see Figure S7, Supporting Information) reveals a distribution
of energy barriers with an α value of 0.03, indicating more than
one possible relaxation pathway for 1.
The value of the pre-exponential parameter indicates that the
relaxation process observed in 1 is not due to long-range order
and is similar to those reported for mononuclear SMMs or
single-ion magnets (SIMs) of DyIII.19 Magnetization hysteresis
D
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but sometimes these are not so clear for lanthanide-based
SMMs.
In transition-metal (TM) complexes, the QTM process will
happen when the applied magnetic field is sufficient to reach a
level crossing between S substates due to the Zeeman effect.
However, for the lanthanide complexes, the level crossing does
not usually occur at the magnetic fields used in the experiment
due to the large energy difference between the lowest and the
second lowest MJ substates. Below 5 K, the out-of-phase
magnetic susceptibility shows the tail of a signal that could be
caused by the fast quantum tunneling typical of lanthanide
complexes, and the frequency dependence of which cannot be
assessed since the maxima are not observed above 2 K.
Application of a dc field of up to 1500 Oe shifts this signal to
lower temperatures but does not make it disappear. The DyIII
example 1 is the only complex to display an out-of-phase signal
in the ac magnetic susceptibility in this work, thus the only one
to be able to retain the magnetization when an applied field is
removed below a blocking temperature and to behave as a
physically ordered array of SMMs. Complex 1 displays
hysteresis of the magnetization up to 4 K. Similarly to what
Figure 4. Arrhenius plot for the ac out-of-phase signal of complex 1
between 5 and 40 K. See text for fitting parameters.
vs field data were collected at 2 and 4 K on a Teflon-coated
pressed pellet of crushed crystalline complex 1. There is a clear
hysteresis loop of the magnetization vs field at 2 and 4 K for 1
(see Figure 5). It is known that the M−H loops of transition-
́
has been reported by Clerac et al. for the 2D arrays of
transition-metal SMMs and 3d−4f SMMs,20 a small ferromag-
netic interaction seems to enhance the SMM property of 1.
When this interaction is stronger as is the case of the Tb
analogue 5, no slow relaxation is observed in the ac magnetic
susceptibility and the SMM property is obliterated.
The Dy(III) complex 1 was also characterized by X-ray
absorption spectra (XAS), measured at ID08 beamline of the
European Synchrotron Radiation Facility (ESRF). The
measurements have been performed at 7 K under 4 T applied
magnetic field, and the field is applied along the beam direction.
The magnetic signal has been extracted from the measurements
in total electron yield mode, and no sample damaging due to
radiation has been observed. Using circular polarized light and
the possibility to change from positive to negative polarization
allows extracting the dichroic signal (XMCD). A series of eight
spectra, changing the polarization, positive (σ+) and negative
(σ−), and the applied field (M+ and M−) to avoid experimental
errors, provide an XMCD signal (see Figure 6). Magnetization
Figure 5. Magnetization vs field hysteresis loops for 1 at 2 K (dashed
line) and 4 K (solid line).
metal-cluster SMMs show steps in the hysteresis due to faster
relaxation via resonant tunneling of the magnetization (QTM),
Figure 6. XAS polarization dependent spectra measured at Dy M3,4-edges. The XMCD signal is obtained from the subtraction of the positive (σ+)
and negative (σ−) polarized XAS, as continuous (black) and dashed (red) lines, respectively.
E
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(d) Robin, A. Y.; Fromm, K. M. Coord. Chem. Rev. 2006, 250, 2127−
2157. (e) Robson, R. Dalton Trans. 2008, 5113−5131.
curves have been measured at the maximum of the dichroic
spectra. At 7 K, the extracted hysteresis shows paramagnetic
behavior.
Photoluminescence Properties. The solid-state photo-
luminescent spectrum for 1 shows the characteristic emission
(2) (a) Batten, S. R.; Neville, S. M.; Turner, D. R. Coordination
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4
line sample at 360 nm, which can be ascribed to the F9/2
→
6H15/2 and 4F9/2 → 6H13/2 transitions of DyIII (see Figure S9a in
Supporting Information). For 5, the three characteristic
emissions upon excitation at 370 nm (see Figure S9b in the
Supporting Information) should be properly attributed to D4
→ FJ (J = 3, 4, 5, and 6), D4 → F6 (490 nm), D4 → F5
5
7
5
7
5
7
5
7
5
7
(546 nm), D4 → F4 (586 nm), and D4 → F3 (622 nm)
transitions of TbIII.
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CONCLUSIONS
■
In conclusion, a family of lanthanide−organic coordination
frameworks have been prepared based on 5-hydroxyisophthalic
acid. Notably, the DyIII complex 1 is an organized array of
SMMs, with frequency-dependent out-of-phase ac susceptibility
signals and magnetization hysteresis at 4 K. Our present
findings will further enrich the crystal engineering strategy and
provide the possibility of controlling the formation of desired
lanthanide−organic crystalline materials. Following this lead,
more efforts on H3L-based coordination frameworks with other
light rare-earth ions from LaIII to SmIII across the lanthanide
period are underway, for developing new functional coordina-
tion polymers with higher-connected topology and interesting
properties.
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ASSOCIATED CONTENT
* Supporting Information
■
Gaita-Arino, A.; Camon
́
, A.; Evangelisti, M.; Luis, F.; Martínez-Per
́
ez,
̃
S
M. J.; Sese,
́
J. J. Am. Chem. Soc. 2012, 134, 14982−14990. (d) Zhu, Y.-
Selected bond parameters (Tables S1−S5), PXRD patterns
(Figure S1), TGA curves (Figure S2), further structural figures
(Figures S3−S5), Curie−Weiss plots (Figure S6), Cole−Cole
plot for 1 (Figure S7), Curie−Weiss fitting parameters (Table
S6), continuous shape measures for the Ln(III) centers (Figure
S8 and Table S7), and solid-state fluorescent spectra for 1 and
5 (Figure S9). This material is available free of charge via the
Internet at http://pubs.acs.org.
Y.; Cui, C.; Zhang, Y.-Q.; Jia, J.-H.; Guo, X.; Gao, C.; Qian, K.; Jiang,
S.-D.; Wang, B.-W.; Wang, Z.-M.; Gao, S. Chem. Sci. 2013, 4, 1802−
1806.
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Luzon, J.; Etienne, M.; Sessoli, R.; Powell, A. K. Angew. Chem., Int. Ed.
2010, 49, 6352−6356. (b) Rinehart, J. D.; Fang, M.; Evans, W. J.;
Long, J. R. Nat. Chem. 2011, 3, 538−542. (c) Gatteschi, D.; Sessoli, R.
Angew. Chem., Int. Ed. 2003, 42, 268−297. (d) Liu, J.-L.; Chen, Y.-C.;
́
Li, Q.-W.; Gomez-Coca, S.; Aravena, D.; Ruiz, E.; Lin, W.-Q.; Leng, J.-
D.; Tong, M.-L. Chem. Commun. 2013, 49, 6549−6551.
(8) Christou, G.; Gatteschi, D.; Hendrickson, D. N.; Sessoli, R. MRS
Bull. 2000, 25, 66−77.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: chunsenliu@zzuli.edu.cn (C.-S.L.).
*E-mail: dumiao@public.tpt.tj.cn (M.D.).
■
(9) (a) Liu, C.-M.; Zhang, D.-Q.; Hao, X.; Zhu, D.-B. Chem. - Eur. J.
2011, 17, 12285−12288. (b) Han, S.-D.; Song, W.-C.; Zhao, J.-P.;
Yang, Q.; Liu, S.-J.; Lia, Y.; Bu, X.-H. Chem. Commun. 2013, 49, 871−
873.
Notes
The authors declare no competing financial interest.
(10) (a) Sessoli, R.; Tsai, H.-L.; Schake, A. R.; Wang, S.; Vincent, J.
B.; Folting, K.; Gatteschi, D.; Christou, G.; Hendrickson, D. N. J. Am.
Chem. Soc. 1993, 115, 1804−1816. (b) Lampropoulos, C.; Murugesu,
M.; Harter, A. G.; Wernsdofer, W.; Hill, S.; Dalal, N. S.; Reyes, A. P.;
Kuhns, P. L.; Abboud, K. A.; Christou, G. Inorg. Chem. 2013, 52, 258−
272. (c) Wang, H.; Hamanaka, S.; Yokoyama, T.; Yoshikawa, H.;
Awaga, K. Chem. - Asian J. 2011, 6, 1074−1079.
(11) (a) Stamatatos, T. C.; Abboud, K. A.; Wernsdorfer, W.;
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M.; Habrych, M.; Wernsdorfer, W.; Abboud, K. A.; Christou, G. J. Am.
Chem. Soc. 2004, 126, 4766−4767. (c) Murugesu, M.; Takahashi, S.;
Wilson, A.; Abboud, K. A.; Wernsdorfer, W.; Hill, S.; Christou, G.
Inorg. Chem. 2008, 47, 9459−9470.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (21031002, 91122005, and 21171151),
Plan for Scientific Innovation Talent of Henan Province, and
the Program for New Century Excellent Talents in University
(NCET-10-0143). E.C.S. acknowledges the financial support
from the Spanish Government (Grant CTQ2012-32247 and
́
Ramon y Cajal contract).
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