Exploiting single-molecule magnets of β-diketone dysprosium complexes with C3v symmetry: Suppression of quantum tunneling of magnetization

Article abstract of DOI:10.1039/c5tc00321k

A series of four β-diketone mononuclear dysprosium complexes, namely, Dy(EIFD)₃(H₂O)·CH₂Cl₂ (1), Dy(EIFD)₃(DMF)·CH₂Cl₂ (2), Dy(EIFD)₃(DMSO) (3), and Dy(EIFD)₃

Full text of DOI:10.1039/c5tc00321k

Journal of
Materials Chemistry C
View Article Online
View Journal | View Issue
PAPER
Exploiting single-molecule magnets of b-diketone
dysprosium complexes with C3v symmetry:
suppression of quantum tunneling of
magnetization†
Cite this: J. Mater. Chem. C, 2015,
3, 4407
Yanping Dong,ab Pengfei Yan,a Xiaoyan Zou,a Tianqi Liua and Guangming Li*a
A series of four b-diketone mononuclear dysprosium complexes, namely, Dy(EIFD)3(H2O)ꢀCH2Cl2 (1),
Dy(EIFD)3(DMF)ꢀCH2Cl2 (2), Dy(EIFD)3(DMSO) (3), and Dy(EIFD)3(TPPO) (4) (EIFD: 1-(1-ethyl-1H-indol-3-yl)-
4,4,4-trifluorobutane-1,3-dione, TPPO: triphenylphosphine oxide), have been isolated by the reactions of a
newly designed b-diketone EIFD, DyCl3ꢀ6H2O and DMF, DMSO, TPPO, respectively. X-ray crystallographic
analysis reveals that complexes 1–4 are isomorphic mononuclear structures in which the Dy(III) ion is
rarely seven-coordinated with C3v geometry. Magnetic studies indicate that all complexes 1–4 are single-
molecule magnets. The correlations between magnetism and the distortion of the coordination symmetry
around the Dy(III) ions have been investigated. Notably, the quantum tunneling of magnetization (QTM),
which universally exists in the lanthanide complexes, has been effectively suppressed in this system more
related to the less deviation from the ideal C3v symmetry.
Received 1st February 2015,
Accepted 23rd March 2015
DOI: 10.1039/c5tc00321k
www.rsc.org/MaterialsC
number of Dy-based SMMs or SIMs of mononuclear, multi-
nuclear and chain forms have been reported.2c,8 In particular,
Introduction
The spins of single metal centers potentially acting as magnets the mononuclear Dy(III) ion complexes have been at the forefront
are coupled with large intrinsic magnetic anisotropy.1 Molecules of major advances in the field of SMMs yielding higher effective
exhibiting such behavior are called Single-Molecule Magnets energy barriers for spin reversal and higher blocking tempera-
(SMMs) or Single-Ion Magnets (SIMs).2 Since the discovery that tures.9 While the energy barriers change through alternation of
Mn12OAc3 exhibits SMM features, it has received considerable coordination geometry around the center Dy(III) ion.10 Obviously,
attention in the past two decades owing to its quantum tunneling the geometry of the ligand field (LF) is the most important factor
and slow relaxation of molecular origin.4 This has led to the to construct the magnetic anisotropy of SMMs or SIMs since
opportunity of potential applications in memory storage, quantum the dynamic magnetism is governed by the ground-multiplet
computing, molecular spintronics and other devices.5 An area of substructure.2d,11 Theoretical and experimental studies have
particular concern is improving the knowledge of the magneto- demonstrated that LF can split the (2J + 1)-fold ground state of
chemical properties of SMMs, leading to the persistent investiga- the Ln(III) ion, which can stabilize sublevels with a large |MJ|
tion of 4f lanthanide elements as magnetic centers,6 which may value.12 It is interesting that the spin dynamics can be modified
bring significant anisotropy to the system. Then, the Ln(III) ion of by the careful adjustment of the ligand around the Ln(III) ion
particular interest is usually the Dy(III) ion due to its large magnetic center, achieving an easy axis of magnetization.13 Thus it is
moment and odd-electron configuration.7 As a result, a large significant to study how to obtain the magnetism of Dy(III) ion
based SMMS or SIMs via a suitable ligand field. However, despite
many mononuclear Dy(III) ion complexes having been studied,
there is a lack of a complete and comparative theory on under-
standing the relationship between the structure and magnetism.
a Key Laboratory of Functional Inorganic Material Chemistry (MOE),
School of Chemistry and Materials Science, Heilongjiang University,
No. 74, Xuefu Road, Nangang District, Harbin, Heilongjiang 150080, P. R. China.
Notably, b-diketone ligands, which are important in sensitizing
the luminescence of lanthanide complexes,14 have generated
increasing interest in the field of SMMs15 because of a high-order
single axis defining the local symmetry and providing a suitable
ligand field.7,13,16 So far, eight-coordinated b-diketone dysprosium
complexes2d,10,17 with D4d or D2d symmetry and nine-coordinated7
E-mail: gmli_2000@163.com; Fax: +86-451-86608458, +86-451-86673647;
Tel: +86-451-86608458
b Department of Food and Pharmaceutical Engineering, Suihua University, Suihua,
Heilongjiang 152061, P. R. China
† Electronic supplementary information (ESI) available: FT-IR spectra, UV spectra,
additional magnetic measurements, powder X-ray diffraction, selected bond
lengths and angles for complexes 1–4. CCDC 1039484–1039487. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/c5tc00321k b-diketone dysprosium complexes are familiar to chemistry
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C, 2015, 3, 4407--4415 | 4407

View Article Online
Paper
Journal of Materials Chemistry C
researchers, and all show the fast zero-field quantum tunneling of 4.26 (dd, J = 14.0, 6.9 Hz, 2H), 1.57 (t, J = 7.0 Hz, 3H). m/z =
magnetization (QTM). Nevertheless, low-coordinated b-diketone 187.1 (M+).
dysprosium complexes, e.g. seven-coordinated complexes, have
never been reported. Furthermore, lowering the coordination
number can efficiently suppress the zero-field QTM, which
Synthesis of 1-(1-ethyl-1H-indol-3-yl)-4,4,4-trifluorobutane-1,3-dione
(EIFD)
drives Dy(III) ion complexes to behave as strong SMMs.1a Keeping A typical procedure of Claisen Condensation was used, as shown in
it in mind, a series of mononuclear seven-coordinated b-diketone Scheme S2, ESI.† EIE (1.4979 g, 8.0 mmol) and ethyl trifluoroacetate
dysprosium complexes with a local symmetry close to a C3v-capped (1.2785 g, 9.0 mmol) were added into toluene (30 mL), and the mixed
octahedron have been originally synthesized by using a newly solution was allowed to stir for 10 min. To this solution,
designed b-diketone, namely, 1-(1-ethyl-1H-indol-3-yl)-4,4,4-trifluoro- t-BuOK (1.0099 g, 9.0 mmol) was added into the mixture till the
butane-1,3-dione. Magnetic analysis reveals that all complexes 1–4 reaction was over. The resulting solution was quenched with water
are single-molecule magnets. Herein, the correlation between the and acidified to pH 2–3 using hydrochloric acid (2 M solution). Then,
coordination geometry of the Dy(III) ion and the magnetism of the the suspension was extracted twice with CH2Cl2 (50 mL). The organic
complexes has been discussed, quantified by some parameters of layer was dried over Na2SO4, and the solvent was evaporated leading
judging the symmetry of the ligand field.
to a buff solid. The buff solid product was isolated by recrystalliza-
tion from ethanol (1.6995 g, yield of 75% based on EIE). Elemental
analysis (%) calcd for C14H12F3NO2 (283.25): C, 59.36; H, 4.24. Found:
C, 59.37; H, 4.27. IR (KBr, n/cmꢁ1): 3433 (s), 1530 (s), 1277 (s), 1212
(s), 1144 (s), 750 (m). 1H NMR (400 MHz, CDCl3): d 15.86 (s, 1H), 8.24
(d, J = 4.4 Hz, 1H), 7.91 (s, 1H), 7.15–7.55 (m, 3H), 6.37 (s, 1H), 4.26
(dd, J = 14.0, 6.9 Hz, 2H), 1.57 (t, J = 7.0 Hz, 3H). m/z = 283.08 (M+).
Experimental section
Materials and instruments
Dysprosium oxide (Dy2O3, 99.99%) was purchased from Gan
Zhou rare earth Chemical Plant (Jiang Xi, China). Triphenyl-
phosphine oxide (98%, A. R.) was purchased from Beijing Fine
Chemical Co. (Beijing, China), and 1-(1H-indol-3-yl) ethanone
and ethyl trifluoroacetate were purchased from Shanghai
D&R Finechem Co. (Shanghai, China). All chemicals except
DyCl3ꢀ6H2O and EIFD were obtained from commercial sources
and used without further purification. DyCl3ꢀ6H2O was prepared
by the reactions of Dy2O3 and HCl in aqueous solution. Elemental
(C, H and N) analyses were performed on a Perkin-Elmer 2400
analyzer. FT-IR spectra were collected on a Perkin-Elmer 100
spectrophotometer by using KBr pellets in the range of 4000–
450 cmꢁ1. UV spectra were recorded on a Perkin-Elmer Lambda
35 spectrometer. Powder X-ray diffraction (PXRD) data were
recorded on a Rigaku D/Max-3B X-ray diffractometer with CuKa
as the radiation source (l = 0.15406 nm) in the angular range of
y = 5–501 at room temperature. The magnetic susceptibilities
of complexes 1–4 were measured using a Quantum Design
VSM superconducting quantum interference device (SQUID)
magnetometer. The magnetic corrections were obtained by using
Pascal’s constants.
Synthesis of Dy(EIFD)3(H2O)ꢀCH2Cl2 (1)
Complex 1 was prepared by mixing EIFD (0.4249 g, 1.5 mmol),
NaOH (0.0600 g, 1.5 mmol) and DyCl3ꢀ6H2O (0.1885 g, 0.5 mmol)
in CH3OH for 24 h at room temperature. Single crystals suitable
for XRD were obtained from dichloromethane/hexane in 5 or
7 days. Yield: 1.4154 g (85.0%). Elemental analysis (%) calcd for
C43H35DyF9N3O7 (1110.14): C, 46.52; H, 3.15; N, 3.79. Found: C,
46.50; H, 3.18; N, 3.83. IR (KBr, n/cmꢁ1): 3378 (s), 1589 (s), 1539
(s), 1383 (s), 1281 (s), 1214 (s), 1127 (s), 799 (w), 669 (m). UV-Vis
(CH3OH, lmax/nm): 218, 265 and 386.
Synthesis of Dy(EIFD)3(DMF)ꢀCH2Cl2 (2)
Complex 2 was prepared by mixing complex 1 (0.0555 g,
0.05 mmol) and an appropriate amount of DMF. Single crystals
suitable for XRD were obtained from dichloromethane/hexane
in 2 or 3 days. Yield: 0.0988 g (88.0%). Elemental analysis (%)
calcd for C91H78Cl2Dy2F18N8O14 (2245.52): C, 48.67; H, 3.47; N,
4.99. Found: C, 48.60; H, 3.51; N, 4.95. IR (KBr, n cmꢁ1): 2990 (w),
1600 (s), 1543 (s), 1375 (s), 1281(s), 1215 (s), 1129 (s), 791 (s), 744
(m), 668 (m). UV-Vis (CH3OH, lmax/nm): 213, 267 and 354.
Synthesis of 1-(1-ethyl-1H-indol-3-yl)ethanone (EIE)
Synthesis of Dy(EIFD)3(DMSO) (3)
1-(1H-Indol-3-yl)ethanone (1.5920 g, 10.0 mmol), NaOH (0.4000 g,
10.0 mmol) and C2H5Br (1.3248 g, 12.2 mmol) were added into Complex 3 was prepared by mixing complex 1 (0.0555 g,
acetone (150 mL), and the mixed solution was heated to reflux 0.05 mmol) and an appropriate amount of DMSO. Single crystals
until the reaction was over. The product was isolated by solvent suitable for XRD were obtained from dichloromethane/hexane in
evaporation and acidified to pH 2–3 using hydrochloric acid 2 or 3 days. Yield: 0.0473 g (87.0%). Elemental analysis (%) calcd
(2 M solution). Then, the suspension was extracted twice with for C44H39DyF9N3 O7S (1087.35): C, 48.60; H, 3.59; N, 3.87.
CH2Cl2 (30 mL). The organic layer was dried over Na2SO4, and Found: C, 48.66; H, 3.62; N, 3.84. IR (KBr, n/cmꢁ1): 2990 (w),
the solvent was evaporated leading to a buff solid. The proce- 1599 (s), 1543 (s), 1375 (s), 1279 (s), 1214 (s), 1129 (s), 801 (s), 744
dure can be seen as shown in Scheme S1 (ESI†). (1.5895 g, yield (m), 669 (m). UV-Vis (CH3OH, lmax/nm): 214, 267 and 354.
of 85% based on 1-(1H-indol-3-yl)ethanone). Elemental analysis
Synthesis of Dy(EIFD)3(TPPO) (4)
(%) calcd for C12H13NO (187.24): C, 76.97; H, 6.94. Found: C,
1
76.95; H, 6.97. H NMR (400 MHz, CDCl3) d 15.86 (s, 1H), 8.24 Complex 4 was prepared by mixing equimolar quantities of
(d, J = 4.4 Hz, 1H), 7.91 (s, 1H), 7.15-7.55 (m, 3H), 6.37 (s, 1H), complex 1 (1.1110 g, 1.0 mmol) and triphenylphosphine oxide
4408 | J. Mater. Chem. C, 2015, 3, 4407--4415
This journal is ©The Royal Society of Chemistry 2015

View Article Online
Journal of Materials Chemistry C
Paper
Table 1 Crystal data and structure refinement for complexes 1–4
Complexes
1
2
3
4
Empirical formula
Formula weight
Color
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a (deg)
b (deg)
C43H35Cl2DyF9N3O7
1110.14
Buff
Triclinic
%
P1
12.8051(4)
13.0203(4)
15.2674(6)
101.396(3)
102.641(3)
109.004(3)
2246.47(13)
2
1.641
1.872
1102.0
0.0391
C91H78Cl2Dy2F18N8O14
2245.52
Buff
Triclinic
%
P1
12.928(5)
13.333(5)
15.388(5)
94.383(5)
100.445(5)
109.447(5)
2432.7(15)
1
1.533
1.677
1120.0
0.0563
C44H39DyF9N3O7S
1087.35
Buff
Triclinic
%
P1
12.2553(6)
13.2445(6)
15.0997(7)
94.560(4)
93.878(4)
109.954(4)
2284.71(19)
2
1.581
1.769
1086.0
0.0352
C60H48DyF9N3O7P
1287.49
Buff
Triclinic
%
P1
12.960(5)
13.524(5)
18.921(5)
70.340(5)
81.202(5)
62.275(5)
2764.4(17)
2
1.547
1.467
1294.0
0.0373
g (deg)
V (Å3)
Z
r (g cm3)
m (mmꢁ1
F(000)
)
R1,a [I 4 2s(I)]
wR2,b [I 4 2s(I)]
R1,a (all data)
wR2,b (all date)
GOF on F2
0.0837
0.0526
0.0874
0.980
0.1552
0.0666
0.1646
1.040
0.0907
0.0414
0.0958
1.018
0.0932
0.0436
0.0987
1.039
P
P
P
a
b
2
R1
=
77Fo7 – 7Fc77/7F07. wR2 = [ w(Fo – Fc2)2/ w(Fo2)2]1/2
.
(0.2783 g, 1.0 mmol) in CH3OH for 24 h at room temperature. (Fig. S2, ESI†), which result from the singlet–singlet p–p* enol
Single crystals suitable for XRD were obtained from dichloro- absorption of the b-diketonate. In comparison with the absorp-
methane/hexane in 5 or 7 days. Yield: 1.0944 g (85.0%). tion band of EIFD, the absorption maxima are blue-shifted
Elemental analysis (%) calcd for C60H48DyF9N3O7P (1287.49): 27 nm for complexes 1–4, which result from the perturbation of
C, 55.97; H, 3.73; N, 3.26. Found: C, 55.94; H, 3.77; N, 3.29. IR the coordination of the Dy(III) ion.
(KBr, n cmꢁ1): 2982 (w), 1599 (s), 1537 (s), 1379 (s), 1279 (s),
PXRD analysis of complexes 1–4
1179 (s), 1129 (s), 794 (m), 748 (m), 668 (m), 541 (s). UV-Vis
(CH3OH, lmax/nm): 213, 266 and 357.
Powder X-ray diffraction (PXRD) patterns of complexes 1–4 are
in agreement with the simulated patterns (Fig. S12–15, ESI†).
PXRD analysis further demonstrates that the crystal structures
of complexes 1–4 are truly representative of the bulk materials.
The differences in intensity are due to the preferred orientation
of the powder samples.
X-ray crystallography
Single-crystal X-ray data of complexes 1–4 were collected on an
Oxford Xcalibur Gemini Ultra diffractometer with graphite-
monochromated Mo Ka (l = 0.71073 Å) at room temperature.
Empirical absorption corrections based on equivalent reflec-
tions were applied. The structures of complexes 1–4 were solved
by direct methods and refined by full-matrix least-squares
methods on F2 using a SHELXS-97 crystallographic software
package.18 All non-hydrogen atoms are anisotropically refined.
All crystal data and structure refinement details for complexes
1–4 are summarized in Table 1. The selected bond lengths and
angles for complexes 1–4 are given in Table S1 (ESI†).
Structural descriptions of 1–4
X-ray crystallographic analysis reveals that complexes 1–4 are
all mononuclear structures and they crystallize in the triclinic
%
space groups P1. The central Dy(III) ions in complexes are all
seven-coordinated to six oxygen atoms from three EIFD ligands
and one oxygen atom from H2O, DMF, DMSO and TPPO
molecules (Fig. 1a–d). The average bond length of the Dy–O
(EIFD oxygen atoms) is 2.302 Å for 1, which is slightly shorter
than that of Dy–O (water oxygen atom, 2.379 Å). This is
attributed to the stronger ionic bond of Dy–O (EIFD oxygen
atoms) compared to the covalent bond of Dy–O (water oxygen
Results and discussion
Synthesis and spectral analysis of complexes 1–4
Ligands and complexes 1–4 were synthesized as shown in atoms). In the structures of complexes 2–4 (Fig. 1b–d), one H2O
Schemes S1–S3, ESI.† The IR spectrum of complex 1 exhibits molecule is substituted by another oxygen atom from DMF,
the typical broad absorption in the region 3000–3500 cmꢁ1
,
DMSO, and TPPO, respectively. The average bond length of the
which proposes the presence of water molecules in the complex 1 Dy–O is 2.309 Å, 2.309 Å, and 2.311 Å for complexes 2–4. It is
(Fig. S1, ESI†). In contrast, the absence of a broad band in the notable that the intermolecular forces in complexes 2 and 3 are
region 3000–3500 cmꢁ1 for complexes 2, 3 and 4 suggests that the similar but different from complex 4.
water molecules have been substituted by the neutral donors.19
Obviously, the coordination geometries of the Dy(III) ion in
The UV-Vis spectra show that there are obvious absorption bands complexes 1–4 are all distorted C3v-capped octahedrons (Fig. 1e–h)
at around 384 nm for EIFD and 357 nm for complexes 1–4 according to the semiquantitative method of polytopal analysis.20
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C, 2015, 3, 4407--4415 | 4409

View Article Online
Paper
Journal of Materials Chemistry C
Fig. 2 C3v-capped octahedron shape characteristics. The d angles listed
are associated with edges identified by double lines.
Fig. 3 Coordination geometry of Dy(III) core with d1 and d2 representing
the distance of Dy(III) ion to the centers of the top plane and bottom plane
and the bending angle a, defined as the angle of center-Dy(III)-center.
complexes 2 and 3 are similar, having a lower coordination
symmetry than that for complex 1. However, complex 4 is midway
between the C3v-capped octahedron and C2v monocapped trigonal
prism, indicating the most distorted and lowest symmetry among
the four complexes.
Moreover, another kind of representation of coordination
geometries is also discussed, including l, d and a (Fig. 3).
Detailed structural parameters of the Dy(III) ion such as plane
center distances (d1 and d2), the plane center distance (l), and
bending angles of center-Dy(III)-center (a) for complexes 1–4 are
summarized in Table 3. It is noted that the distances from the
centre of the Dy(III) ion to the two planes are different from
complexes 1–4. The distances in complex 1 are the shortest,
those in complex 4 are the longest and those in complexes 2–3
are in the middle.
Fig. 1 The crystal structures of complexes 1 (a), 2 (b), 3 (c) and 4 (d)
showing general ligand configurations. Local coordination geometry of
the Dy(III) ion for complexes 1 (e), 2 (f), 3 (g) and 4 (h) (hydrogen atoms are
omitted for clarity).
Relevant dihedral d angles for complexes 1–4 are summarized in
Table 2. The d angles are descripted in Fig. 2. The angle data for
the ideal and observed ML7 structures are all 24.21 for the three
d values. We notice first of all that, for the complex 1, d1, d2 and d3
are 11.8, 23.2 and 13.11, which are close to an ideal C3v-capped
octahedron. d1 and d3 values are almost equal indicating a higher
symmetry coordination sphere. For complexes 2–4, the d values
deviate more from an ideal C3v-capped octahedron in which
Magnetic properties
Static magnetic properties
In order to probe the magnetic behavior of complexes 1–4,
direct current (dc) magnetic susceptibility studies of 1–4 have
Table 2 d (deg) values for complexes 1–4
1
2
3
4
Faces
C3v
d1
d2
d3
O2[O1O5]O3
O3[O4O5]O6
O3[O1O4]O7
11.8
23.2
13.1
O6[O5O3]O4
O7[O1O5]O6
O2[O1O3]O6
23.8
3.6
22.7
O3[O1O4]O2
O5[O4O6]O2
O7[O1O6]O2
28.5
25.2
13.9
O13[O11O14]O10
O10[O9O14]O12
O11[O8O10]O9
32.7
42.2
32.5
24.2
24.2
24.2
4410 | J. Mater. Chem. C, 2015, 3, 4407--4415
This journal is ©The Royal Society of Chemistry 2015

View Article Online
Journal of Materials Chemistry C
Paper
Table 3 Summary of Dy to plane center distances, plane center distances and bending angles for complexes 1–421
1
2
3
4
Dy to top plane center distance (d1, Å)
Dy to bottom plane center distance (d2, Å)
Center distance between top and bottom planes (l, Å)
Bending angle (a, deg)
1.5647
1.0768
2.6368
173.072
1.5891
1.1015
2.6904
178.579
1.5926
1.0856
2.6561
175.278
1.6053
1.1095
2.7134
176.313
been carried out in an applied magnetic field of 100 Oe over the With increasing frequency, the maxima of the magnetic suscepti-
temperature range 300–1.8 K.22 As shown in Fig. 4, the observed wmT bility shift to high temperature, which is the feature of a super-
products at 300 K are 14.11, 14.02, 14.10, and 14.09 cm3 K molꢁ1 for paramagnet.1b,17a,24 Only in the very low temperature region, below
1, 2, 3 and 4, respectively, in agreement with the g = 4/3 of the 6H15/2 2.5 K, there is a slight quantum tunneling effect, which can almost
ground state of the Dy(III) ion (C = 14.18 cm3 K molꢁ1). Upon cooling, be ignored. Then a preliminary investigation into complexes 2–4
the wmT value for the four complexes decreases gradually over the under the zero dc field was also conducted. However, the peaks can
temperature range of 300–100 K and more rapidly below 100 K, only be found at frequencies higher than 100 Hz for complexes 2 and
which is mostly due to crystal-field effects (i.e. thermal depopulation 3, and complex 4 shows only a poorly defined peak (Fig. S3–S5 in the
of the Ln(III) ion Stark sublevels) and possible antiferromagnetic ESI†). Upon cooling, w00 increases again below 3.0 K for complexes
dipole–dipole interactions between the molecules.23 Notably, the 2 and 3, and this indicates the onset of pure quantum, as often seen
magnetic moment is still far from the theoretical value (gJ ꢂ J = 4/3 ꢂ in other lanthanide SMMs.10a The applied dc field is required to
15/2 = 10 mB), which can reach 5.3 mB (1), 6.8 mB (2), 5.4 mB (3) and suppress the QTM and is able to slow the temperature dependent
5.1 mB (4) at 1.8 K. It is highly attributed to crystal field effects on the maxima to the slowest relaxation frequency. Then, subsequent
6
Dy(III) ion that eliminates the degeneracy of the H15/2 ground studies with an applied dc field of 2000 Oe revealed temperature
state.16a The nonsuperimposition of the M versus H/T curves on a dependent in-of-phase (w0) and out-of-phase (w00) behavior. The
single curve reveals the existence of low-lying excited states and/or complete ac experiment was conducted in a dc field of 2000 Oe,
significant magnetic anisotropy in complexes 1–4 (Fig. 4, inset).14d
whereby the QTM has been effectively suppressed for complexes 1–4
In addition, the field cooled (FC) and zero-field cooled (ZFC) (Fig. 6, and Fig. S6, and S7 in the ESI†).
magnetization measurements of complexes 1–4 were further
A further investigation was conducted on complex 1 by a
performed (Fig. S16–S19 in the ESI†). These results unani- thorough in-of-phase (w0) and out-of-phase (w00) vs. frequency (n)
mously suggest that the magnetization signals of complexes measurement at temperatures between 2 and 12 K under the
1–4 are similar. The FC–ZFC curves show no divergence, zero dc field (Fig. 7). A fit to the Arrhenius law t = t0 exp (Ea/kBT)
certifying that there were no magnetic ordering and magnetic of the peak maxima gave an energy barrier of Ea = 56.7 K and a
phase transition in accordance with wmT vs. T plots.
pre-exponential time constant of t0 = 3.7 ꢂ 10ꢁ7. Although this
phenomenon was not observed under the zero dc field for
complexes 2–3 (Fig. S8, S9 in the ESI†), it was found under a
2000 Oe field, with frequency dependence of in-phase (w0) and
out-of-phase (w00) ac susceptibility of Ea = 28.7 K, t0 = 2.5 ꢂ 10ꢁ7
for complex 2 and Ea = 27.8 K, t0 = 1.0 ꢂ 10ꢁ6 for complex 3,
respectively (Fig. 8). Unfortunately, this frequency dependence
phenomenon was not observed for complex 4 under any dc field.
Obviously, the barrier height (Ueff/kB) from complexes 1 to 3
takes on a depressive tendency, which is correlated to the
Dynamic magnetic properties
AC susceptibility curves of the complex 1 revealed the temperature
dependent peaks in the in-of-phase (w0) and out-of-phase (w00) vs.
measurement (T) under the zero dc field, signaling ‘‘freezing’’ of
the spins by the anisotropy barriers and indicating the presence
of slow relaxation of the magnetization (Fig. 5).10a In addition,
the low-frequency peaks occur in the lower temperature region.
Fig. 4 Temperature dependence of wmT at 100 Oe for complexes 1–4
in the range 1.8–300 K. Inset: Field dependence of magnetization for
complexes 1–4 at 1.8 K.
Fig. 5 Temperature dependence of the in-phase (w0) and out-of-phase
(w00) ac susceptibility of complex 1 under 0 Oe in the frequency range
10–1000 Hz.
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C, 2015, 3, 4407--4415 | 4411

View Article Online
Paper
Journal of Materials Chemistry C
Fig. 6 Temperature dependence of the in-phase (w0) and out-of-phase (w00) ac susceptibility of complexes 2 (left) and 3 (right) under 2000 Oe in the
frequency range 10–1000 Hz.
aspects, the slight differences may affect the nature of single-ion
anisotropy of the Dy(III) ion through the single-axial degree of
distortion of coordination geometry, and therefore generates the
different dynamic magnetic behavior for complexes 1–4. In
contrast with our previous report17c and another groups’
report,11b,16a,b,26 the energy barrier for complex 1 is higher than
those of mononuclear lanthanide complexes based on common
b-diketone ligands, suggesting the larger local symmetry and the
ligand field effect in our present system. However, the energy
barrier for complex 1 is still lower than that observed for a series
of classical eight-coordinated mononuclear [Dy(acac)-auxiliary]
Fig. 7 Frequency dependence of the in-phase (w0) and out-of-phase (w00)
ac susceptibility under 0 Oe in the temperature range 2.0–12 K for
complexes.10b,17a,b The main reason is attributed to the
decreased coordination numbers and molecular symmetry, as
complex 1.
well as the weakened strength of the ligand field.21a According to
the ac susceptibility of frequency and the temperature dependence
between 2.0 and 12.0 K, the magnetization relaxation time t of
complex 1 is 0.0997 s (Fig. 9). Notably, the relaxation time of
complex 1 is the longest among those previously reported for the
pure b-diketone dysprosium analogue with D4d and D2d symme-
try,10a,b,17 further proving that, above 2.5 K, the relaxation becomes
thermally activated (Arrhenius-like behavior), unlike the traditional
eight-coordinated geometry b-diketone dysprosium complexes with
coexisting thermally activated and quantum tunneling regimes.
This system has almost no obvious quantum regime in the whole
temperature range.
distortion of the coordination geometry around the center
Dy(III) ion due to different auxiliary ligands. As we can see from
the structural descriptions, complex 1, first of all, is the most
close to an ideal C3v-capped octahedron with the high symmetry
while complexes 2–4 are deviated more from the ideal C3v-capped
octahedron, which is in good agreement with the magnetic
properties. On the other hand, due to the Kramer ion of the
Dy(III) ion, the shortest distances of l and d in complex 1 enable
the Dy(III) ion to be a more oblate electron, generating strong
single-ion anisotropy for SMM.25 Herein the distances of l and d
in complexes 2–4 are all longer than complex 1, leading to
weaker single-ion anisotropy. On the basis of the above two
Cole–Cole plots of the ac data of complex 1 can be fitted to
the generalized Debye model (Fig. 10), where wT is the isothermal
Fig. 8 Frequency dependence of the in-phase (w0) and out-of-phase (w00) ac susceptibility under 2000 Oe in the temperature range 2.0–10 K for
complexes 2 (left) and 3 (right).
4412 | J. Mater. Chem. C, 2015, 3, 4407--4415
This journal is ©The Royal Society of Chemistry 2015

View Article Online
Journal of Materials Chemistry C
Paper
Table 4 Fitted parameters of the Cole–Cole plots for complex 1 at Hdc
=
0 Oe
T/K wS
wT
a
T/K wS
wT
a
2.0 0.43244 5.52038 0.25926 6.0
2.5 0.35860 4.82926 0.26597 6.5
3.0 0.28189 4.75016 0.30403 7.0
3.5 0.25763 3.93669 0.26994 7.5
4.0 0.25813 3.32001 0.23068 8.0
4.5 0.25387 2.90182 0.20615 9.0
0.28812 2.15754 0.15739
0.31634 1.98911 0.13895
0.34146 1.84919 0.12536
0.39825 1.72553 0.09065
0.40657 1.62146 0.09204
0.43839 1.44561 0.09024
5.0 0.24698 2.60083 0.19324 10.0 0.53813 1.30842 0.09236
5.5 0.26152 2.35780 0.17661
Fig. 9 Arrhenius plot showing the relaxation time of the magnetization
for complex 1 under 0 Oe, complexes 2 and 3 under 2000 Oe. Red line is a
fit to the Arrhenius equation.
susceptibility, wS is the adiabatic susceptibility, n is the frequency
of the ac field, and t is the relaxation time of the system.20,21,27
wT ꢁ wS
w
¼ wS þ
ðvÞ
1ꢁa
1 þ ðivtÞ
However, on the basis of the Cole–Cole analysis, t0 is still larger
than expected for a thermally activated relaxation mechanism for
complex 1 under 0 Oe. This may be partially explained by large a
values for the modified Debye fit of complex 1, where between 10
and 2 K a values are 0.09–0.30 and they increase significantly at
lower temperatures (Table 4). The result indicates that a single
relaxation time is mainly involved in the present relaxation process.
The Cole–Cole plots for complexes 2 and 3 give the same semicircle
plots under 2000 Oe (Fig. S10 in the ESI†), where between 5 and 2 K
a values are 0.09–0.21 for complex 2 and 0.09–0.28 for complex 3
(Table S2, ESI†). It is worth noting that Cole–Cole plots of complex
1 are familiar with the 1: 20 dilution sample of the Gao and Tang
group,10a proving the weak dipole–dipole interactions between the
dysprosium centers. Weakened dipole–dipole interactions further
illustrate complex 1 as being the most close to the ideal C3v-capped
octahedron with almost no QTM. However, complexes 2–4 deviated
more from an ideal C3v-capped octahedron indicating a more QTM
effect.
Fig. 11 Hysteresis loop for complex 1 at 1.8 K.
conducted at 1.8 K with a sweep rate of 50 Oe sꢁ1, the hysteresis
loops of complex 1 are wider than those for complexes 2 and 3
within ꢃ4 kOe (Fig. 11, Fig. S11 in the ESI†). The M–H data do
not exhibit a hysteresis phenomenon at 1.8 K for complex 4.
This further suggests that complexes 1–3 are typical SMMs.
Conclusion
Isolation of a series of four EIFD dysprosium lanthanide complexes
1–4 verifies that the newly designed b-diketone EIFD is able to
stabilize the Dy(III) ion forming unique seven-coordinated mono-
nuclear Dy(III) complexes with C3v symmetry which afford the SMMs
of complexes 1–4. The introduction of the auxiliary ligands of DMF,
DMSO and TPPO slightly tunes the distortion of the coordination
symmetry and the ligand field around the Dy(III) ion. It results in the
difference of the energy barriers between complexes 1–4. Namely, the
higher symmetry of the coordination geometry results in the higher
energy barriers. Notably, QTM is more effectively suppressed in this
system, which is more related to the less deviation from the ideal C3v
symmetry. Therefore, this approach may provide an effective path to
suppress the QTM, which universally exists in the lanthanide
complexes.
Magnetic hysteresis is another important characteristic of
the magnetic bistability of SMMs. When the dc magnetism is
Notes
The authors declare no competing financial interest.
Acknowledgements
This work is financially supported by the National Natural Science
Foundation of China (No. 21471051, 51272069 and 51402092).
Fig. 10 Cole–Cole plots measured at 2.0–10.0 K under 0 Oe for complex 1.
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C, 2015, 3, 4407--4415 | 4413

View Article Online
Paper
Journal of Materials Chemistry C
11 (a) S. Takamatsu, T. Ishikawa, S.-y. Koshihara and N. Ishikawa,
Inorg. Chem., 2007, 46, 7250–7252; (b) Y. Wang, X. L. Li,
T. W. Wang, Y. Song and X. Z. You, Inorg. Chem., 2010, 49,
969–976.
12 (a) N. Ishikawa, J. Phys. Chem. A, 2003, 107, 5831–5835;
(b) N. Ishikawa, M. Sugita, T. Ishikawa, S.-y. Koshihara and
Y. Kaizu, J. Phys. Chem. B, 2004, 108, 11265–11271; (c) N. I
shikawa, M. Sugita and W. Wernsdorfer, Angew. Chem., Int.
Ed., 2005, 44, 2931–2935; (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,
18115–18126.
13 D. P. Li, X. P. Zhang, T. W. Wang, B. B. Ma, C. H. Li, Y. Z. Li
and X. Z. You, Chem. Commun., 2011, 47, 6867–6869.
14 (a) P. P. Lima, M. M. Nolasco, F. A. A. Paz, R. A. S. Ferreira,
R. L. Longo, O. L. Malta and L. D. Carlos, Chem. Mater.,
2013, 25, 586–598; (b) J. Shi, Y. Hou, W. Chu, X. Shi, H. Gu,
B. Wang and Z. Sun, Inorg. Chem., 2013, 52, 5013–5022;
(c) J. Li, H. Li, P. Yan, P. Chen, G. Hou and G. Li, Inorg.
Chem., 2012, 51, 5050–5057; (d) G. Abbas, Y. Lan, G. E.
Kostakis, W. Wernsdorfer, C. E. Anson and A. K. Powell,
Inorg. Chem., 2010, 49, 8067–8072; (e) S. Biju, Y. K. Eom, J.-C.
G. Bu¨nzli and H. K. Kim, J. Mater. Chem. C, 2013, 1,
6935–6944; ( f ) M. Pietraszkiewicz, M. Maciejczyk,
I. D. W. Samuel and S. Zhang, J. Mater. Chem. C, 2013, 1,
8028–8032; (g) V. Divya and M. L. P. Reddy, J. Mater. Chem. C,
2013, 1, 160–170.
15 K. Bernot, J. Luzon, L. Bogani, M. Etienne, C. Sangregorio,
M. Shanmugam, A. Caneschi, R. Sessoli and D. Gatteschi,
J. Am. Chem. Soc., 2009, 131, 5573–5579.
16 (a) Y. L. Wang, Y. Ma, X. Yang, J. Tang, P. Cheng,
Q. L. Wang, L. C. Li and D. Z. Liao, Inorg. Chem., 2013, 52,
7380–7386; (b) C. M. Liu, D. Q. Zhang and D. B. Zhu, Inorg.
Chem., 2013, 52, 8933–8940; (c) W. B. Sun, B. L. Han,
P. H. Lin, H. F. Li, P. Chen, Y. M. Tian, M. Murugesu and
P. F. Yan, Dalton Trans., 2013, 42, 13397–13403.
17 (a) S. D. Jiang, B. W. Wang, G. Su, Z. M. Wang and S. Gao,
Angew. Chem., Int. Ed., 2010, 49, 7448–7451; (b) G. J. Chen,
C. Y. Gao, J. L. Tian, J. K. Tang, W. Gu, X. Liu, S. P. Yan,
D. Z. Liao and P. Cheng, Dalton Trans., 2011, 40, 5579–5583;
(c) J. Zhu, C. Z. Wang, F. Luan, T. Q. Liu, P. F. Yan and
G. M. Li, Inorg. Chem., 2014, 53, 8895–8901.
18 G. M. Sheldrick, ActaFound. Crystallogr., 2008, 64, 112–122.
19 A. Bellusci, G. Barberio, A. Crispini, M. Ghedini, M. La Deda
and D. Pucci, Inorg. Chem., 2005, 44, 1818–1825.
References
1 (a) P. Zhang, L. Zhang, C. Wang, S. Xue, S. Y. Lin and
J. Tang, J. Am. Chem. Soc., 2014, 136, 4484–4487; (b) J. J. Le
Roy, M. Jeletic, S. I. Gorelsky, I. Korobkov, L. Ungur,
L. F. Chibotaru and M. Murugesu, J. Am. Chem. Soc., 2013,
135, 3502–3510.
2 (a) N. Ishikawa, M. Sugita, T. Ishikawa, S.-y. Koshihara and
Y. Kaizu, J. Am. Chem. Soc., 2003, 125, 8694–8695; (b) N. Magnani,
C. Apostolidis, A. Morgenstern, E. Colineau, J. C. Griveau,
H. Bolvin, O. Walter and R. Caciuffo, Angew. Chem., Int. Ed.,
2011, 50, 1696–1698; (c) S. D. Jiang, B. W. Wang, H. L. Sun,
Z. M. Wang and S. Gao, J. Am. Chem. Soc., 2011, 133, 4730–4733;
(d) D. P. Li, T. W. Wang, C. H. Li, D. S. Liu, Y. Z. Li and X. Z. You,
Chem. Commun., 2010, 46, 2929–2931; (e) M. A. AlDamen,
´
J. M. Clemente-Juan, E. Coronado, C. Martı-Gastaldo and
˜
A. Gaita-Arino, J. Am. Chem. Soc., 2008, 130, 8874–8875.
3 R. Sessoli, H. L. Tsai, A. R. Schake, S. Wang, J. B. Vincent,
K. Folting, D. Gatteschi, G. Christou and D. N. Hendrickson,
J. Am. Chem. Soc., 1993, 115, 1804–1816.
4 A. Caneschi, D. Gatteschi, R. Sessoli, A. L. Barra, L. C. Brunel
and M. Guillot, J. Am. Chem. Soc., 1991, 113, 5873–5874.
5 D. N. Woodruff, R. E. Winpenny and R. A. Layfield, Chem.
Rev., 2013, 113, 5110–5148.
6 (a) R. Sessoli and A. K. Powell, Coord. Chem. Rev., 2009, 253,
2328–2341; (b) F. Habib and M. Murugesu, Chem. Soc. Rev.,
2013, 42, 3278–3288; (c) L. Sorace, C. Benelli and
D. Gatteschi, Chem. Soc. Rev., 2011, 40, 3092–3104.
7 N. F. Chilton, S. K. Langley, B. Moubaraki, A. Soncini,
S. R. Batten and K. S. Murray, Chem. Sci., 2013, 4, 1719–1730.
8 (a) L. Zhao, J. Wu, H. Ke and J. Tang, CrystEngComm, 2013, 15,
5301–5306; (b) S. Y. Lin, L. Zhao, Y. N. Guo, P. Zhang, Y. Guo
and J. Tang, Inorg. Chem., 2012, 51, 10522–10528; (c) A. K. Jami,
V. Baskar and E. C. Sanudo, Inorg. Chem., 2013, 52, 2432–2438;
(d) B. Hussain, D. Savard, T. J. Burchell, W. Wernsdorfer and
M. Murugesu, Chem. Commun., 2009, 1100–1102; (e) D. T.
Thielemann, M. Klinger, T. J. Wolf, Y. Lan, W. Wernsdorfer,
M. Busse, P. W. Roesky, A. N. Unterreiner, A. K. Powell,
P. C. Junk and G. B. Deacon, Inorg. Chem., 2011, 50,
11990–12000; ( f ) P. Hu, X. Wang, Y. Ma, Q. Wang, L. Li and
D. Liao, Dalton Trans., 2014, 43, 2234–2243; (g) F. Habib, P.-H.
Lin, J. Long, I. Korobkov, W. Wernsdorfer and M. Murugesu,
J. Am. Chem. Soc., 2011, 133, 8830–8833; (h) J. Tang, I. Hewitt,
N. T. Madhu, G. Chastanet, W. Wernsdorfer, C. E. Anson,
C. Benelli, R. Sessoli and A. K. Powell, Angew. Chem., Int. Ed.,
2006, 45, 1729–1733; (i) I. J. Hewitt, Y. Lan, C. E. Anson,
J. Luzon, R. Sessoli and A. K. Powell, Chem. Commun., 2009,
6765–6767.
20 E. L. Muetterties and L. J. Guggenberger, J. Am. Chem. Soc.,
1974, 96, 1748–1756.
9 F. Habib, G. Brunet, V. Vieru, I. Korobkov, L. F. Chibotaru
and M. Murugesu, J. Am. Chem. Soc., 2013, 135,
13242–13245.
10 (a) Y. Bi, Y. N. Guo, L. Zhao, Y. Guo, S. Y. Lin, S. D. Jiang,
J. Tang, B. W. Wang and S. Gao, Chem. – Eur. J., 2011, 17,
12476–12481; (b) G. J. Chen, Y. N. Guo, J. L. Tian, J. Tang,
W. Gu, X. Liu, S. P. Yan, P. Cheng and D. Z. Liao,
Chem. – Eur. J., 2012, 18, 2484–2487.
21 (a) F. Gao, L. Cui, W. Liu, L. Hu, Y. W. Zhong, Y. Z. Li and
J. L. Zuo, Inorg. Chem., 2013, 52, 11164–11172; (b) M. X. Yao,
Q. Zheng, F. Gao, Y. Z. Li, Y. Song and J. L. Zuo, Dalton
Trans., 2012, 41, 13682–13690.
22 (a) M. L. Kahn, R. Ballou, P. Porcher, O. Kahn and J.-P.
Sutter, Chem. – Eur. J., 2002, 8, 525–531; (b) M. L. Kahn, J.-P.
Sutter, S. Golhen, P. Guionneau, L. Ouahab, O. Kahn and
D. Chasseau, J. Am. Chem. Soc., 2000, 122, 3413–3421.
4414 | J. Mater. Chem. C, 2015, 3, 4407--4415
This journal is ©The Royal Society of Chemistry 2015

View Article Online
Journal of Materials Chemistry C
Paper
23 G. Abbas, Y. Lan, G. E. Kostakis, W. Wernsdorfer, C. E. Anson
and A. K. Powell, Inorg. Chem., 2010, 49, 8067–8072.
24 Y. Ma, G. F. Xu, X. Yang, L. C. Li, J. Tang, S. P. Yan, P. Cheng
and D. Z. Liao, Chem. Commun., 2010, 46, 8264–8266.
25 J. D. Rinehart and J. R. Long, Chem. Sci., 2011, 2, 2078–2085.
26 (a) P. Hu, M. Zhu, X. Mei, H. Tian, Y. Ma, L. Li and
D. Liao, Dalton Trans., 2012, 41, 14651–14656; (b) G. J.
2014, 16, 2283–2289; (d) M. Menelaou, F. Ouharrou,
L. Rodriguez, O. Roubeau, S. J. Teat and N. Aliaga-Alcalde,
Chem. – Eur. J., 2012, 18, 11545–11549; (e) D. Zeng,
M. Ren, S. S. Bao and L. M. Zheng, Inorg. Chem., 2014, 53,
795–801; ( f ) L. Norel, M. Feng, K. Bernot, T. Roisnel,
T. Guizouarn, K. Costuas and S. Rigaut, Inorg. Chem.,
2014, 53, 2361–2363.
Chen, Y. Zhou, G. X. Jin and Y. B. Dong, Dalton Trans., 27 S. M. J. Aubin, Z. Sun, L. Pardi, J. Krzystek, K. Folting, L.-C.
2014, 43, 16659–16665; (c) Y.-L. Wang, B. Gu, Y. Ma, C. Xing,
Q.-L. Wang, L.-C. Li, P. Cheng and D.-Z. Liao, CrystEngComm,
Brunel, A. L. Rheingold, G. Christou and D. N. Hendrickson,
Inorg. Chem., 1999, 38, 5329–5340.
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C, 2015, 3, 4407--4415 | 4415