Four tetra-nuclear lanthanide complexes based on 8-hydroxyquinolin derivatives: magnetic refrigeration and single-molecule magnet behaviour

Article abstract of DOI:10.1039/C8NJ02161A

Four tetra-nuclear lanthanide complexes: {[Ln₄(L)₆(tmhd)₄(μ₃-OH)₂]·mH₂O} (Ln = Gd (1, m = 0), Tb (2, m = 3), Dy (3, m = 0), Ho (4, m = 0); L = 5-((pyridin-4-ylmethylene)amino)quinolin-8-ol, tmhd = 2,2,6,6-tetramethylheptane-3,5-dione) were fabricated and structurally characterized. Compounds 1-4 are isostructural and belong to the monoclinic system with space group P2₁/n. The cores of the complexes contain a tetranuclear arrangement of Ln^III ions, which is bridged by the two pyramidal μ₃-OH^- ions, and the four Ln^III ions are precisely coplanar. The magnetic study reveals that 1 exhibits cryogenic magnetic refrigeration property (-ΔS_m = 20.85 J K^-1 kg^-1), whereas compound 3 exhibits slow relaxation of the magnetization.

Full text of DOI:10.1039/C8NJ02161A

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The role of atropisomers on the photo-reactivity and fatigue of
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Four Tetra-nuclear Lanthanide Complexes based on
8-hydroxyquinolin derivatives: Magnetic refrigeration and
Single-Molecule Magnet behaviour†
Ming Fang,a,* Li-Jun Shao,a Tian-Xing Shi,a Ying-Ying Chen,a Hong
Yu,a Peng-Fei Li,a Wen-Min Wangb, ∗Bin Zhaoc,*
Abstract：
Four tetraꢀnuclear lanthanide complexes: {[Ln4(L)6(tmhd)4(µ3ꢀOH)2]·mH2O} (Ln =
Gd (1, m = 0), Tb (2, m = 3), Dy (3, m = 0), Ho (4, m = 0); L =
5ꢀ((pyridinꢀ4ꢀylmethylene)amino)quinolinꢀ8ꢀol,
tmhd
=
2,2,6,6ꢀtetramethylheptaneꢀ3,5ꢀdione) were fabricated and structurally characterized.
Compounds 1ꢀ4 are isostructural belonging to the monoclinic system with space
group P21/n. The core of the complexes contain a tetranuclear arrangement of LnIII
ions which is bridged by two pyramidal ꢀ3ꢀOHꢀ ions, and the four LnIII ions are
precisely coplanar. Magnetic study reveals that 1 exhibits cryogenic magnetic
refrigeration property (−ꢁSm = 20.85 J K−1 kg−1), whereas compound 3 exhibits slow
relaxation of the magnetization.
Keyword: Lanthanide, Tetraꢀnuclear compounds, Magnetocaloric effect,
Singleꢀmolecule magnet behaviour, 8ꢀhydroxyquinolin derivatives
Introduction
There is no doubt that the investigation of lanthanide (III) complexes is a highly
a Department of Chemistry, Hebei Normal University of Science & Technology, Qinhuangdao
066004, Hebei province, P. R.China. Eꢂmail:fangmingchem@163.com
b Department of Chemistry, Taiyuan Normal University, Jinzhong 030619, PR China. Eꢂmail:
wangwenmin0506@126.com
c Department of Chemistry, Key Laboratory of Advanced Energy Material Chemistry , MOE, and
TKL of Metal and Molecule Based Material Chemistry, Nankai University, Tianjin 300071, China..
Eꢂmail: zhaobin@nankai.edu.cn
† Electronic supplementary information (ESI) available: Selected bond lengths and angles. CCDC
1830533ꢀ1830536. For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c000000x/

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active research topic due to their employment in luminescence,[1] magnetism, [2] gas
adsorption and separation,[3] catalysis,[4] and so on. Among above potential
applications, the study of single molecule magnets (SMMs) and molecular magnetic
refrigeration attract innumerable attentions.[5,6] Since Mn12O12(O2CCH3)16(H2O)4
[7]
which behaves as a magnet at the molecular level, was reported, the study of bistable
molecular magnetic materials is a highly active research topic in the chemistry and
physics communities due to their potential applications in high density magnetic data
storage and spintronic devices[8] and quantum computing.[9] Subsequently, numerous
new Ln(III)ꢀbased molecules behaving as SMMs were discovered over the last
decades, and display excellent and interesting magnetic behaviors. Lately, the record
of effective energy barrier (Ueff) has been broken continually, and not long ago a
mononuclear Dy (III) compound with the Ueff as large as 1025 K was reported by
Tong and coꢀworker;[10] shortly afterwards, the group of Zheng reports a nearly
perfect pentagonal bipyramidal Dy compound with the largest effective energy barrier
U
eff = 1815 K;[11a] recently, Layfield group reported a dysprosium metallocene with a
largest energy barrier Ueff = 1837 K, setting a new record in this field.[11b] These
important reports attract more and more researcher to focus on the study of SMMs.
Molecular magnetic coolers, which are based on the magnetocaloric effect (MCE),
are another research focus. Due to the environmental safety and energy efficiency,
magnetocaloric materials have been proposed to replace the expensive and
increasingly rare Heꢀ3 in ultralow temperature refrigeration.[12] In general, an
outstanding molecular magnetic cooler should bear the features of a large spin ground
state S, negligible magnetic anisotropy, dominant ferromagnetic interaction and high
magnetic density.[13] Thus, Gd3+ is a common constituent element for molecular
8
refrigerant materials, because it is favored by it having a S7/2 groundꢀstate term
(S=7/2, L=0), with high spin and zero orbital momentum, and therefore no spinꢀorbit
coupling is possible. To date, a large number of impressive compounds associated
with molecular magnetic cooling have been reported, and the largest record of ꢀꢁSm
has been broken frequently.[14]
Therefore, there is a continuing need to search for new molecular systems that

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have improved magnetic properties for better understanding and practical applications.
In this contribution, four tetrenuclear lanthanide complexes with a general formula
{[Ln4(L)6(tmhd)4(µ3ꢀOH)2]·mH2O} (Ln = Gd (1, m = 0), Tb (2, m = 3), Dy (3, m = 0),
Ho (4, m = 0); L = 5ꢀ((pyridinꢀ4ꢀylmethylene)amino)quinolinꢀ8ꢀol, tmhd =
2,2,6,6ꢀtetramethylheptaneꢀ3,5ꢀdione) were fabricated and structurally characterized.
Magnetic study reveals that 1 exhibits cryogenic magnetic refrigeration property,
whereas compound 3 exhibits slow relaxation of the magnetization.
Experimental section
Materials and Physical Measurements.
All chemicals purchased were of reagent grade and used without further
purification. Water used in the reactions is distilled water. Analyses for C, H and N
were carried out on a PerkinꢀElmer analyzer. Powder Xꢀray diffraction measurements
were recorded on a Rigaku Ultima IV instrument using Cu Kα radiation (λ = 1.54056
Å), with a scan speed of 5° min−1 in the range of 2θ = 5–50°. Magnetic susceptibilities
were performed on a Quantum Design PPMSꢀ9 ACMS magnetometer. Diamagnetic
corrections were made with Pascal’s constants for all the constituent atoms.
Crystallographic studies.
Singleꢀcrystal Xꢀray diffraction measurements of 1 - 4 were carried out at room
temperature on a Rigaku Saturn724 CCD Xꢀray diffractometer equipped with
graphitemonochromated MoKα radiation (λ = 0.71073 Å). Lorentz polarization and
absorption corrections were applied. The structures were solved by direct methods
and refined by fullꢀmatrix leastꢀsquares techniques using the SHELXSꢀ97 and
SHELXLꢀ97 programs.[15] All the nonhydrogen atoms were refined with anisotropic
parameters while H atoms were placed in calculated positions and refined using a
riding model. Crystallographic data for 1 – 4 were summarized in Table 1. Selected
bond lengths and angles were summarized in Table S1ꢀS4.
Synthesis of 5-aminoquinolin-8-ol.
A mixture of 5ꢀnitroquinolinꢀ8ꢀol (50 mmol) and 5 % Pd/C (0.75 g), which was
used as catalyst, in a 1.3 % ratio in absolute isopropanol was heated to 65 °C, and

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then 12 mL of 85 % hydrazine hydrate was dropped into the mixture over 1 h. It was
heated to 90 °C and refluxed for 6 h. Finally, the solvent was removed, and
dichloromethane was used to wash the grass green solid product (yield: 50.8%).
Elemental analysis (%): Calcd for C9H8ON2 (Fw = 160.42): C 67.32, H 5.00, N 17.50.
Found: C 67.28, H 4.97, N 17.82.
Table 1. Crystallographic Data and Structure Refinements for 1-4
1
2
3
4
formula
C134H138N18O16Gd4
C134H144N18O19Tb4
C134H138N18O16Dy4
C134H138N18O16Ho4
Mr (g mol−1)
T (K)
2885.62
293(2)
2946.35
133(2)
2906.62
293(2)
2916.34
149.99
cryst syst
Space group
a (Å)
monoclinic
P21/n
monoclinic
P2(1)/n
monoclinic
P21/n
monoclinic
P 21/n
19.1634(7)
17.2152(6)
22.4329(8)
90
18.975(3)
17.373(2)
22.320(3)
90
18.9972(7)
17.3458(6)
22.3245(8)
90
19.1765(13)
17.1770(11)
22.4477(14)
90
b (Å)
c (Å)
α
β
(
°
)
114.6210(10)
114.548(4)
114.8280(10)
114.520(2)
(°
)
90
6727.8(4)
2
90
6692.8(17)
2
90
6676.5(4)
2
90
6727.3(8)
2
γ
(°)
V (Å3)
Z
cryst size (mm3)
Dc (g cm−3)
ꢀ (mm−1)
Rint
0.35 x 0.24 x 0.11
1.424
0.20×0.18×0.14
1.462
0.25 x 0.14 x 0.11
1.446
0.32 x 0.23 x 0.13
1.440
2.013
2.158
2.280
2.393
0.0540
0.0466
0.0426
0.0742
limiting indices
ꢀ22<=h<=22,
ꢀ20<=k<=20,
ꢀ26<=l<=26
76780
ꢀ22<=h<=22,
ꢀ17<=k<=20,
ꢀ26<=l<=26
57351
ꢀ22<=h<=22,
ꢀ20<=k<=20,
ꢀ26<=l<=26
125364
ꢀ22<=h<=22,
ꢀ20<=k<=20,
ꢀ26<=l<=26
82176
reflns collected
params
828
946
813
768
GOF on F2
1.079
1.051
1.062
1.083
R1, wR2 [I >2σ(I)]
R1, wR2 (all date)
0.0310, 0.0693
0.0483, 0.0789
0.0324, 0.0981
0.0362,0.1003
0.0311, 0.0721
0.0417, 0.0788
0.0543,0.1188
0.0738, 0.1310
Synthesis of 5-((pyridin-4-ylmethylene)amino)quinolin-8-ol (HL)
The Schiff base ligand 5ꢀ((pyridinꢀ4ꢀylmethylene)amino)quinolinꢀ8ꢀol (HL) was
synthesized in a simple aldimine condensation reaction of 5ꢀaminoquinolinꢀ8ꢀol (10
mmol) with isonicotinaldehyde (10 mmol) in 50 mL ethanol with the catalyze of 5
drops formic acid (Scheme 1). The reaction mixture was stirred for 5 h at 85 . The

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product was isolated from the mixture and it was purified by recrystallization from a
mixed solvent of ethanol and acetone (3/1, v/v). The purified product was obtained as
a green solid (yield 2.1 g, 80.2%).
Scheme 1. The synthesis of HL
.
Synthesis of Complexes 1−5
The compounds 1-4 were obtained by the reaction of Ln(tmhd)3·2H2O (0.025 mmol;
Ln(III) = Gd (1), Tb (2), Dy (3), Ho (4)) and HL (0.025 mmol) in mixture solution
containing 20 mL acetonitrile and 3 mL CH2Cl2. The ensuing yellow solution was
stirred at room temperature for about 4 h. After filtration, the resultant solution was
left unperturbed to evaporate slowly. Yellow block shaped crystals suitable for
singleꢀcrystal Xꢀray data collection was isolated after about 5 days. Yield: 52%, 45%,
56% and 48% based on HL for 1ꢀ4, respectively. Elemental analysis calcd (%) for
C
C
134H138N18O16Gd4 (1): C 55.77, H 4.82, N 8.74; found: C 55.62, H 4.87 N 8.68; for
134H144N18O19Tb4 (2): C 54.62, H 4.93, N 8.56; found: C 54.74, H 4.89, N8.62; for
C134H138N18O16Dy4 (3): C 55.37, H 4.79, N 8.67; found: C 55.35, H 4.64, N 8.71; for
C134H138N18O16Ho4 (4): C 55.19, H 4.77, N 8.65; found: C 55.27, H 4.89, N 8.57. The
IR spectra of 1ꢀ4 are given in electronic supplementary information (Figure S1ꢀS4).
Results and Discussion
Single crystal Xꢀray diffraction reveals that the four compounds are isostructural,
crystallizing in the monoclinic space group P21/n (Table 1) , with Z = 2. The structure
of 3 (Ln = Dy) will be described here as a representative example of the series. The
core of the complex (Figure 1a) contains a tetranuclear arrangement of DyIII ions with
crystallographic inversion symmetry. The four DyIII ions are precisely coplanar

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(Figure 1b), bridged by the two Oꢀatoms derived from pyramidal ꢀ3ꢀOHꢀ ions (O2) ,
with the DyꢀO2 distances 2.338(3), 2.408(3) and 2.328(3) Å, and the DyꢀO2ꢀDy
angles 112.35(12), 99.05(11) and 107.54(11)o, and a Dy—Dy distance of 3.6033(3),
3.8764(3) and 3.8285(4) Å. The two oxygen atoms (O2) of the ꢀ3ꢀOHꢀ ligands are
located on opposite sides of the Dy4 plane and are displaced out of that plane by
0.904 Å. Dy1 is chelated by two oxygen atoms of tmhd− ligand and two independent
L− ligands via the pyridyl nitrogen and the phenoxy oxygen atoms, which connect to
Dy2. Dy1 also coordinate with another phenoxy oxygen atoms which bridge with Dy2,
and one ꢀ3 oxygen atoms. Dy2 is coordinated with two bridging phenoxy oxygen
atoms, two ꢀ3 oxygen atoms, and chelated by one tmhd− and one independent L−
ligand. Both Dy1 and Dy2 are eightꢀcoordinated, and the coordination geometry for
the eightꢀcoordinated Dy1 and Dy2 can be described as a distorted bicapped trigonal
prism (Figure S5). The coordination and bridging modes of the ligands are shown in
Scheme 2. The DyꢀO bond lengths are in the range of 2.285(3)ꢀ 2.408(3) Å. The DyꢀN
bond lengths are 2.533(3), 2.587(4) and 2.536(4) Å.
a

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b
Figure 1. Perspective view (a) and side view (core only) (b) of 3 (all hydrogen atoms are omitted
for clarity).
Scheme 2. Coordination Modes of L− ligand.
The average LnꢀO bond lengths (Å) for 1–4 were listed in Table 2. These values are
comparable to those of the already reported lanthanide complexes.[16] The average
LnꢀO distances display a decrease trend with the increase of atomic number from Gd
to Ho, demonstrating the existence of lanthanide contraction effect. [17]
Table 2. The statistical data of bond lengths (
Å) and angles (°) for 1–4.
Complexes The range of Ln–O bond lengths / Å Average Ln–O bond lengths / Å
2.317(3)–2.451(3)
2.300(2)–2.427(2)
2.284(3)ꢀ 2.411(3)
2.315(5)–2.444(4)
2.387(3)
2.371(5)
2.361(3)
2.385(4)
1Gd
2Tb
3Dy
4Ho
Powder X-ray diffraction (PXRD)
The purity of crystalline powders of 1ꢀ4 were confirmed by powder Xꢀray
diffraction (PXRD) (Figure S6), the experimental PXRD patterns are consistent with
the corresponding simulated from the single crystal data, suggesting the phase purity
of the samples.

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Luminescence properties of 2
The solidꢀstate luminescence property of 2 was investigated at the exciting
wavelength of 305 nm at room temperature. As shown in Figure S7, the emission
spectrum of 2 exhibits the characteristic emissions of TbIII ion. The emission spectrum
presents four peaks at 491, 546, 587 and 621 nm which are assigned to the transition
of 5D4 to 7FJ (J = 6, 5, 4, 3). Among them, the emission peak at 546 nm (5D4→7F5) is
clearly stronger than the other three ones.
Magnetic Properties of 1-4
The magnetic susceptibilities of 1ꢀ4 were measured on the microcrystalline samples
in the temperature range from 2 to 300 K and under 1000 Oe field, as shown in Figure
2. At room temperature, the χMT value for 1ꢀ4 is 31.73, 47.46, 56.52 and 56.27 cm3 K
molꢀ1, respectively, which is close to the corresponding theoretical value of 31.52,
47.28, 56.68 and 56.28 cm3 K molꢀ1 expected for four magnetically Ln3+ ions: Gd3+ in
the 8S7/2 ground state (g = 2) for 1, Tb3+ in the 7F6 ground state (g = 3/2) for 2, Dy3+ in
6
the H15/2 ground state (g = 4/3) for 3 and Ho3+ in the 5I8 ground state (g = 5/4) for 4.
For 1, the χMT value stays almost constant in the temperature range 300−25 K and
then decreases rapidly to a minimum value of 18.98 cm3 K mol−1 at 2 K, which
indicates the presence of a weak antiferromagnetic interaction between the adjacent
Gd3+ ions. Based on the Hamiltonian Ĥ = ꢀJŜAŜB with ŜA = ŜB = 7/2, a corresponding
equation as following was deduced, and the magnetic properties of 1 can be
appropriately described by it.[18]
2Ng 2 β 2 eJ / kT + 5e3J / kT +14e6J / kT + 30e10J / kT + 55e15J / kT + 91e21J / kT +140e28J / kT
χM = 2*
×
kT
1+ 3eJ / kT + 5e3J / kT + 7e6J / kT + 9e10J / kT +11e15J / kT +13e21J / kT +15e28J / kT
Leastꢀsquares fitting of the experimental data leads to J = ꢀ0.14 cmꢀ1, g = 1.98, and
the agreement factor R, defined as R = ∑(χobsd–χcalcd)2/∑(χobsd)2, is 4.8×10−1. The
negative and small J value indicates very weak antiferromagnetic coupling interaction
between adjacent Gd3+. For lanthanide ions, the 4f electrons are well shielded by
outerꢀshell electrons, compared with 3d electrons, the interaction of 4f electrons from
adjacent lanthanide ions is rather weak.

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Figure 2 The plots of χMT versus T for 1(◇), 2(●), 3(▲) and 4(▼) under 1000 Oe field.
For 2ꢀ4, as the temperature is lowered, χMT values decreases slightly to 25 K,
then decrease quickly to 28.84, 31.40 and 27.39 cm3 K molꢀ1, respectively. The
decrease observed in the χMT values is most likely due to a combination of some very
weak antiferromagnetic interactions between adjacent lanthanide ions and/or the
thermal depopulation of Stark sublevels.[19]
The magnetization data of 1 is performed at a field of 0−8 T between 2 and 10 K.
As shown in Figure 4, the M versus H curves display a gradual increase with the
increasing field and saturation values of 28.19 Nβ for 1 at 80 kOe and 2 K, which is
extremely close to the theoretical value of 28 Nβ for four individual Gd(III) (S = 7/2,
g = 2) ions. Magnetic entropy changes ꢁSm of 1 can be calculated from the M versus
H data to evaluate the MCE. ꢁSm are calculated by using the Maxwell equation:
ꢁSm(T) = ∫ [∂M(T, H)/∂T]H dH
(1)
According to eq 1, [20] the −ꢁSm values of 1 can be obtained; the plots of −ꢁSm versus
T are shown in Figure 3 (Right). For 1, the maximum value of −ꢁSm is 20.85 J K−1
kg−1 (calculated as 4Rln(2S+1), expected maximum −ꢁSm is 23.97 J K−1 kg−1 for a

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field change ꢁH = 7 T at 2.0 K. The difference of −ꢁSm between the experimental and
theoretical values for 1 might be due to the antiferromagnetic interaction in 1. [21] The
maximum −ꢁSm of 1 is smaller than the antiferromagnetic {Gd4} complexes which
have been reported:[22] [Gd4(µ3ꢀOH)2(L)2L1L2(HOCH3)2]·11H2O {H2L
2,3ꢀbis((E)ꢀ(2ꢀhydroxyꢀ3ꢀmethoxy benzylidene) amino) maleonitrile, HL1
(2ꢀaminoꢀ3ꢀ((E)ꢀ(2ꢀhydroxyꢀ3ꢀmethoxy benzylidene)amino)maleonitrile), H3L2
=
=
=
((1E,3Z,8Z,10E)ꢀ1,6,11ꢀtris(2ꢀhydroxyꢀ3ꢀmethoxyphenyl)ꢀ2,5,7,10ꢀtetraazaundecaꢀ1,
3,8,10ꢀtetraeneꢀ3,4,8,9ꢀtetracarbonitrile), −ꢁSm =27.2 J kgꢀ1 Kꢀ1 for ꢁH = 7 T at 3 K};
[Ln4L4(OH)2](OAc)2·4H2O
{H2L=butanedihydrazidebridged
bis(3ꢀethoxysalicylaldehyde) ligand, −ꢁSm =24.4 J kgꢀ1 Kꢀ1 for ꢁH = 7 T at 3 K }. For
1, the smaller ꢀꢁSm is mainly due to the relatively larger magnetic density (MW/NGd
ratio, MW/NGd = 721.4).
Figure 3. (Left) M versus H plots for 1 at T = 2.0−10.0 K and H = 0−80 kOe. (Right) Temperature
dependence of magnetic entropy change (−ꢁSm) as calculated from the magnetization data of 1 at
T = 2−10.0 K and 0−7 T.
In order to investigate the dynamics of magnetization, the temperature dependences
alternating current (AC) magnetic measurements on 3 have been performed with a 3
Oe ac magnetic field and under 0 dc field. The measurement was made in the
111−2311 Hz frequency range and at temperatures between 2 and 20 K (Figure 4), and
compound 3 displays clear both in phase (χ′) and outꢀofꢀphase (χ″) ac susceptibility
signals at low tempertaure, which is the typical of slow relaxation of the
magnetization.

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Figure 4 Temperature dependence of the inꢀphase (χ′) and outꢀofꢀphase (χ″) ac susceptibilities for
3 in Hdc= 0 Oe with an oscillation of 3.0 Oe.
In addition, to further probe the dynamics of magnetization of 3, frequency
sweeping ac susceptibilities (Figure 5) were measured at 2ꢀ10 K under the zero dc
fields, and the shape and frequency dependence further confirm the presence of
singleꢀmolecule magnet behavior in 3. The Cole–Cole plots of 3 are shown in Figure
7. A generalized Debye model was used in an attempt to fit the ColeꢀCole diagram of
3 (Figure 6), and in the temperature range 3ꢀ10 K, α parameters are in the range of
0.32−0.68. The relatively large distribution coefficients α of the Dy4 complexes
indicate that there is a wide distribution of relaxation time in 3.[23] In fact, the plots at
low temperature, especially at 2 K, cannot be well fitted by the generalized Debye
functions. The clear distortion of the semicircle below 5 K indicates that another low
temperature relaxation process might start to occur in this system below 5 K.
Figure 5. Frequency dependence of the inꢀphase (χ′) and outꢀofꢀphase (χ’’) ac susceptibilities for 3

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at 2.0−10.0 K in Hdc= 0 Oe.
Figure 6. The coleꢀcole plot at different temperature in Hdc= 0 Oe.
The Arrhenius plot exhibit an obvious curvature (Figure 7), indicating that a
combination of the relaxation pathways has to be taken into account so as to
understand the relaxation behavior. Data in the entire 3–10 K temperature range were
analyzed by using the following equation:[24]
ꢀ1
lnτ = ꢀln[ATm + B + CTn + τ0 exp(ꢀUeff / kBT)]
ꢀ1
where ATm + B, CTn, and τ0 exp(Ueff / kBT) represent direct, Raman, and Orbach
relaxation processes, respectively. Leastꢀsquares fitting of lnτ versus Tꢀ1 leads to A
= 0.3759, n = 5.02, C = 0.0171, Ueff = 45.7K, τ0 = 1.23×10ꢀ7 s and the agreement
factor R, defined as R = ∑(χobsd–χcalcd)2/∑(χobsd)2, is 9.39×10−3. The obtained
anisotropic energy barrier (Ueff) and preꢀexponential factor (τ0) is comparable to those
previously reported for Dyꢀbased compounds.[22,23c]

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Figure 7. lnτ versus T−1 plots for 3. The red solid lines represent the leastꢀsquares fits of the
experimental data to the Arrhenius law.
Conclusions
In summary, four lanthanide coordination complexes based on 8ꢀhydroxyquinolin
derivatives have been constructed and structurally characterized. Systematic magnetic
studies for them have been performed, 1 exhibits cryogenic magnetic refrigeration
property with −ꢁSm = 20.85 J K−1 kg−1 for a field change ꢁH = 7 T at 2.0 K.
Compound 3 exhibits slow relaxation of the magnetization with Ueff = 45.7K and the
preexponential factor τ0 = 1.23×10ꢀ7 s.
Acknowledgments
We gratefully acknowledge the National Natural Science Foundation of China
(21501043).
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Table of contents
Four Tetra-nuclear lanthanide complexes were fabricated and structurally
characterized. 1-Gd exhibits cryogenic magnetic refrigeration property and 3-Dy
displays slow relaxation of the magnetization.