Hydroxide-free cubane-shaped tetranuclear [Ln4] complexes

Article abstract of DOI:10.1021/ic402827b

The reaction of the lanthanide(III) chloride salts [Gd(III), Tb(III), and Dy(III)] with a new chelating, flexible, and sterically unencumbered multisite coordinating compartmental Schiff-base ligand (E)-2-((6-(hydroxymethyl)pyridin- 2-yl)methyleneamino)phenol (LH₂) and pivalic acid (PivH) in the presence of triethylamine (Et₃N) affords a series of tetranuclear Ln(III) coordination compounds, [Ln₄(L)₄(μ₂- η¹η¹Piv)₄]·xH ₂O·yCH₃OH (1, Ln = Gd(III), x = 3, y = 6; 2, Ln = Tb(III), x = 6, y = 2; 3, Ln = Dy(III), x = 4, y = 6). X-ray diffraction studies reveal that the molecular structure contains a distorted cubane-like [Ln ₄(μ₃-OR)₄]⁺⁸ core, which is formed by the concerted coordination action of four dianionic L^2- Schiff-base ligands. Each lanthanide ion is eight-coordinated (2N, 6O) to form a distorted-triangular dodecahedral geometry. Alternating current susceptibility measurements of complex 3 reveal frequency- and temperature-dependent two-step out-of-phase signals under zero direct current (dc) field, which is characteristic of single-molecule magnet behavior. Analysis of the dynamic magnetic data under an applied dc field of 1000 Oe to fully or partly suppress the quantum tunneling of magnetization relaxation process affords the anisotropic barriers and pre-exponential factors: δ/k_B = 73(2) K, ₀ = 4.4 × 10^-8 s; δ/k_B = 47.2(9) K, ₀ = 5.0 × 10^-7 s for the slow and fast relaxations, respectively.

Full text of DOI:10.1021/ic402827b

Article
pubs.acs.org/IC
Hydroxide-Free Cubane-Shaped Tetranuclear [Ln4] Complexes
Sourav Das,† Atanu Dey,† Sourav Biswas,† Enrique Colacio,*,‡ and Vadapalli Chandrasekhar*,†,§
†Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India
‡Departamento de Química Inorgan
Spain
́
ica, Facultad de Ciencias, Universidad de Granada, Avenida de Fuentenueva s/n, 18071 Granada,
§National Institute of Science Education and Research, Institute of Physics Campus, Sachivalaya Marg, PO: Sainik School,
Bhubaneswar - 751 005, India
S
* Supporting Information
ABSTRACT: The reaction of the lanthanide(III) chloride salts [Gd(III), Tb(III), and
Dy(III)] with a new chelating, flexible, and sterically unencumbered multisite
coordinating compartmental Schiff-base ligand (E)-2-((6-(hydroxymethyl)pyridin-2-
yl)methyleneamino)phenol (LH2) and pivalic acid (PivH) in the presence of
triethylamine (Et3N) affords a series of tetranuclear Ln(III) coordination compounds,
[Ln4(L)4(μ2-η1η1Piv)4]·xH2O·yCH3OH (1, Ln = Gd(III), x = 3, y = 6; 2, Ln = Tb(III),
x = 6, y = 2; 3, Ln = Dy(III), x = 4, y = 6). X-ray diffraction studies reveal that the
molecular structure contains a distorted cubane-like [Ln4(μ3-OR)4]+8 core, which is
formed by the concerted coordination action of four dianionic L2− Schiff-base ligands.
Each lanthanide ion is eight-coordinated (2N, 6O) to form a distorted-triangular
dodecahedral geometry. Alternating current susceptibility measurements of complex 3
reveal frequency- and temperature-dependent two-step out-of-phase signals under zero
direct current (dc) field, which is characteristic of single-molecule magnet behavior.
Analysis of the dynamic magnetic data under an applied dc field of 1000 Oe to fully or partly suppress the quantum tunneling of
magnetization relaxation process affords the anisotropic barriers and pre-exponential factors: Δ/kB = 73(2) K, τ0 = 4.4 × 10−8 s;
Δ/kB = 47.2(9) K, τ0 = 5.0 × 10−7 s for the slow and fast relaxations, respectively.
the mere fact that the latter possesses a high ground-state spin
does not lend it the SMM behavior. On substitution of a central
INTRODUCTION
■
Single-molecule magnets (SMMs) have been attracting interest
from several points of view. Their potential applications in
high-density information storage and processing, quantum
computation, molecular spintronics,1 and molecular refriger-
ation2 are important factors that have motivated study of these
systems. More importantly, however, the fundamental physics
that is at the bottom of this behavior has intrigued and spurred
intense interdisciplinary research in this area.3 From a chemist’s
point of view, the interest in this field has been to utilize the
understanding of the factors responsible for SMM behavior and
create molecular ensembles that would behave as molecular
magnets. The two important factors that seem to be directly
responsible for SMM properties are the spin ground state (S)
and uniaxial Ising-like anisotropy (D), which lead to an energy
barrier of U [where U = |D|S2 for an integer spin and U = |D|(S2
− 1/4) for a noninteger spin].4 Chemically these two
ingredients (S and D) can be achieved by different strategies.
Polynuclear transition-metal complexes, under favorable geo-
metric situations, can possess large ground-state spin values.
Thus, the first SMM, [MnIII8MnIV4O12(O2CMe)16(H2O)4]5,
containing an inner core of 4 Mn4+ and an outer ring of 8 Mn3+,
has a ground-state spin of S = 10. The highest ground-state spin
Mn(II) by a Dy(III) ion in the compound [MnIII12MnII -
6
DyIII(μ4-O)8(μ3-Cl)6.5(μ3-N3)1.5(HL)12(MeOH)6]Cl3·
25MeOH7 (H3L = 2,6-bis(hydroxymethyl)-4-methylphenol),
the latter complex displays SMM behavior. Such experiments,
focusing on the magnetic anisotropy of lanthanide ions, have
created a lot of interest in lanthanide complexes of varying
nuclearity.8 On the basis of such studies, it is now known that
lanthanide complexes can also function as mononuclear SMMs9
as first shown by Ishikawa’s double-decker complex,
[Pc2Tb]−.9a The importance of homonuclear lanthanide
complexes in molecular magnetism has increased since the
discovery that {Dy5}10 and {Dy4K2}11 complexes show the
highest barriers of energy for reversal of magnetization in any
system so far. We have been interested in homo-12 and
heterometallic13 systems in general and in their utility in
molecule-based magnets in particular. Among the structural
topologies that have been investigated for polynuclear metal
complexes, cubane cores are well-known among transition-
metal complexes14 but are much less investigated with the
lanthanide ions,15 particularly because these syntheses are
challenging. Not surprisingly, thus far, there have been only a
achieved thus far is by the complex [MnIII12MnII (μ4-O)8(μ3,η1-
7
N3)8(HL)12(MeCN)6]Cl2·10MeOH·MeCN6 (H3L = 2,6-bis-
(hydroxymethyl)-4-methylphenol), where S = 83/2. However,
Received: November 12, 2013
Published: March 27, 2014
© 2014 American Chemical Society
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Table 1. Crystal Data and Structure Refinement Parameters of Complexes 1−3
1
2
3
formula
C78H104N8O25 Gd4
2182.69
C74H84N8O24Tb4
2105.17
C78H100Dy4N8O26
2215.66
M/g
crystal system
space group
a/Å
monoclinic
P21/c
monoclinic
P21/c
monoclinic
P21/c
18.788(5)
17.781(3)
18.644(5)
16.890(5)
28.125(5)
103.149(5)
8624(4)
b/Å
16.882(5)
17.155(3)
c/Å
27.893(5)
26.846(4)
β (deg)
V/Å3
102.470(5)
8638(4)
100.194(3)
8060(2)
Z
4
4
4
ρc/g cm−3
μ/mm−1
F(000)
1.678
1.735
1.706
3.109
3.546
3.505
4336
4144
4384
cryst size (mm3)
θ range (deg)
limiting indices
0.056 × 0.038 × 0.021
4.09 to 25.03
−22 ≤ h ≤ 22
−20 ≤ k ≤ 10
−33 ≤ l ≤ 33
44 268
0.056 × 0.042 × 0.037
4.13 to 25.03
−21 ≤ h ≤ 11
−20 ≤ k ≤ 20
−31 ≤ l ≤ 31
45 166
0.052 × 0.036 × 0.019
2.04 to 25.50
−22 ≤ h ≤ 22
−20 ≤ k ≤ 19
−27 ≤ l ≤ 34
60 389
reflns collected
ind reflns
15 167 [R(int) = 0.0784]
14 155 [R(int) = 0.0578]
16 064 [R(int) = 0.0835]
completeness to θ (%)
refinement method
data/restraints/params
goodness-of-fit on F2
final R indices
99.5
99.5
99.9
full-matrix least-squares on F2
15 167/2/1060
1.042
full-matrix least-squares on F2
14 155/0/1007
1.011
full-matrix least-squares on F2
16 064/62/1051
1.029
R1 = 0.0718
wR2 = 0.1655
R1 = 0.1073
wR2 = 0.1860
1.920 and −1.145
R1 = 0.0398
wR2 = 0.0911
R1 = 0.0629
wR2 = 0.1010
2.357 and −1.428
R1 = 0.0571
[I > 2θ(I)]
wR2 = 0.1423
R indices (all data)
R1 = 0.0942
wR2 = 0.1632
largest diff. peak and hole (e·Å−3
)
2.636 and −1.725
operating at 400−4000 cm−1. Elemental analyses of the compounds
were obtained from Thermoquest CE instruments CHNS-O, EA/110
model. 1H NMR spectra were recorded in CDCl3 solutions on a JEOL
JNM LAMBDA 400 model spectrometer operating at 400 MHz;
chemical shifts are reported in parts per million (ppm) and are
referenced with respect to internal tetramethylsilane (1H).
Magnetic Measurements. Field dependence of the magnet-
ization at different temperatures and variable temperature (2−300 K)
magnetic susceptibility measurements on polycrystalline samples were
carried out with a Quantum Design SQUID MPMS XL-5 device
operating at different magnetic fields. Alternating current (ac)
susceptibility measurements were performed using an oscillating ac
field of 3.5 Oe and ac frequencies ranging from 1 to 1500 Hz. The
experimental susceptibilities were corrected for the sample holder and
diamagnetism of the constituent atoms by using Pascal’s tables. A
pellet of the sample cut into very small pieces was placed in the sample
holder to prevent any torquing of the microcrystals.
few such examples whose magnetism has been properly
investigated, such as [Dy4(μ3-OH)4(isonicotinate)6(py)-
(CH3 OH)7 ](ClO4 )2 ·py·4CH3 OH,1 5 a [Dy4 (HL)4 -
(C6H4NH2COO)2(μ3-OH)4(μ-OH)2(H2O)4]·4CH3CN·
12H2O15b (where LH2 = 2-{[(2-hydroxy-3-methoxyphenyl)-
methylidene]amino}benzoic acid), and [Ln4(OH)4(TBSOC)2-
(H2O)4(CH3OH)4]·4H2O15c (H4TBSOC = p-tert-
butylsulfonylcalix[4]arene; Ln = Dy, Ho). We report, herein,
a new chelating, flexible, and sterically unencumbered multisite
coordinating compartmental Schiff-base ligand, (E)-2-((6-
(hydroxymethyl)pyridin-2-yl)methyleneamino)phenol (LH2).
Using this ligand, we were able to assemble a series of neutral
tetranuclear cubane-shaped {Ln(III)}4 complexes (Ln = Gd,
Tb, and Dy). Magnetic studies on these complexes revealed
that the Dy(III) analogue is an SMM. Unlike the previous
examples reported, the current family of cubane-shaped
tetranuclear Ln4 ensembles do not possess bridging hydroxide
ligands.
X-ray Crystallography. The crystal data for the compounds were
collected on a Bruker SMART CCD diffractometer (Mo Kα radiation,
λ = 0.710 73 Å). The program SMART18 was used for collecting
a
frames of data, indexing reflections, and determining lattice
parameters; the SAINT18a program was used for integration of the
intensity of reflections and scaling; the SADABS18b program was used
for absorption correction; and the SHELXTL18c,d program was used
for space group, structure determination, and least-squares refinements
on F2. All the structures were solved by direct methods using the
program SHELXS-9718e and refined by full-matrix least-squares
methods against F2 with SHELXL-97.18e Hydrogen atoms were fixed
at calculated positions, and their positions were refined by a riding
model. All the non-hydrogen atoms were refined with anisotropic
displacement parameters. The crystallographic figures were generated
using Diamond 3.1e software.18f The crystal data and the cell
parameters for compounds 1−3 are summarized in Table 1.
EXPERIMENTAL SECTION
■
Solvents and other general reagents used in this work were purified
according to standard procedures.16 2,6-Bis(hydroxymethyl)pyridine
(C1), activated manganese(IV) dioxide (MnO2), DyCl3·6H2O, TbCl3·
6H2O, and GdCl3·6H2O were obtained from Sigma Aldrich Chemical
Co. and were used as received. 2-Aminophenol and sodium sulfate
(anhydrous) were obtained from SD Fine Chemicals, Mumbai, India
and were used as such. 6-Hydroxymethyl-2-pyridinecarboxaldehyde
(C2) was prepared according to a literature procedure.17
Instrumentation. Melting points were measured using a JSGW
melting point apparatus and are uncorrected. IR spectra were recorded
as KBr pellets on a Bruker Vector 22 FT-IR spectrophotometer
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Synthesis. (E)-2-((6-(Hydroxymethyl)pyridin-2-yl)-
methyleneamino)phenol (LH2). To a stirred solution of C2 (1.50 g,
10.93 mmol) in dry methanol (20 mL), 2-aminophenol (1.19 g, 10.93
mmol), also dissolved in dry methanol (20 mL), was added dropwise
over a period of 15 min, and the resulting reaction mixture was stirred
for 24 h under N2 atmosphere at room temperature. Then, the solvent
was concentrated in vacuo to 10 mL and kept in a refrigerator at 0 °C
for 5 h to get a reddish brown solid. Yield: 2.10 g, 84.16%. Mp: 116
°C. Fourier transform infrared (FT-IR) (KBr) cm−1: 3061 (b), 2914
(m), 2841 (m), 1627 (m), 1585 (s), 1486 (s), 1445 (s) 1372 (s), 1336
(s), 1299 (s), 1226 (s), 1200 (s), 1137(s), 1089(m), 1031(m),
954(m). 1H NMR (CDCl3, δ, ppm): 8.77 (s, 1H, imino), 8.03 (d, 1H,
Ar−H), 7.82 (t, 1H, Py−H), 7.37 (d, 2H, Py−H), 7.25 (t, 1H, Ar−H),
7.03 (s, 1H, Ar−H), 6.93 (t, 1H, Ar−H), 4.83 (s, 2H, CH2OH). Anal.
Calcd for C13H12N2O2: C, 68.41; H, 5.30; N, 12.27 Found: C, 68.30;
H, 5.28; N, 12.19%.
Scheme 1. Synthesis of LH2
General Synthetic Procedure for the Preparation of Complexes
1−3. All the metal complexes (1−3) were synthesized according to
the following procedure. Ligand LH2 (0.06 g, 0.26 mmol) was
dissolved in methanol (10 mL). To this solution, LnCl3·6H2O (0.26
mmol) was added, and the reaction mixture was stirred at room
temperature for 10 min. At this stage triethylamine (0.09 g, 0.9 mmol)
was added dropwise to this solution. Then, pivalic acid (PivH) (0.026
g, 0.26 mmol) was added to the mixture, which was stirred for a
further period of 6 h at room temperature to afford a reddish
precipitate, which was washed with diethyl ether, dried, and
redissolved in chloroform/methanol (1:1) and kept for crystallization.
After about 10 d, block-shaped red crystals suitable for X-ray
crystallography were obtained by slow evaporation of the solvent
mixture. Specific details of each reaction and the characterization data
of the products obtained are given below.
adjacent metal centers.12b,19 Accordingly, the reaction of LH2,
LnCl3·nH2O, and pivalic acid (in a 1:1:1 stoichiometric ratio, in
the presence of 4 equiv of triethylamine as the base) in
methanol/chloroform (1:1) allowed the formation of neutral
tetranuclear Ln(III) complexes 1−3, [Ln4(L)4(μ2-η1η1Piv)4]·
xH2O·yCH3OH (1, Ln = Gd(III), x = 3, y = 6; 2, Ln = Tb(III),
x = 6, y = 2; 3, Ln = Dy(III), x = 4, y = 6), which were shown to
be present in a distorted cubane-type topology (see Scheme 2).
X-ray Crystal Structures of Compounds 1−3. Single-
crystal X-ray diffraction studies reveal that compounds 1−3 are
isostructural and crystallize in the monoclinic space group P21/
c with Z = 4. All the compounds are neutral and have the same
structural topology, namely, a distorted cubane-type tetrame-
tallic core. In view of their structural similarity, only the
[Gd4(L)4(μ2-η1η1Piv)4]·6CH3OH·3H2O (1). Quantities: LH2 (0.06 g,
0.26 mmol), GdCl3·6H2O (0.097 g, 0.26 mmol), Et3N (0.12 mL, 0.9
mmol), PivH (0.026 g, 0.26 mmol). Yield: 0.072 g, 51.07% (based on
Gd). Mp: 183 °C (dec). IR (KBr) cm−1: 3389(b), 3060(w), 2959(s),
1586(s), 1574(s), 1477(s), 1421(s), 1374(s), 1361(s), 1288(s),
1225(w), 1180(w), 1151(s), 1016(w), 930(w), 874(w), 829(s).
Anal. Calcd for C78H106 N8O25Gd4 (2186.42): C, 42.88; H, 4.89; N,
5.13. Found: C, 42.79; H, 4.91; N, 5.23%.
Scheme 2. Synthesis of Compounds 1−3
[Tb4(L)4(μ2-η1η1Piv)4]·2CH3OH·6H2O (2). Quantities: LH3 (0.06 g,
0.26 mmol), TbCl3·5H2O (0.097 g, 0.26 mmol), Et3N (0.12 mL, 0.9
mmol), PivH (0.026 g, 0.26 mmol). Yield: 0.075 g, 54.8% (based on
Tb). Mp: 185 °C (dec). IR (KBr) (cm−1): 3395(b), 3060(w), 2959(s),
1587(s), 1574(s), 1556(s), 1478(s), 1421(s), 1375(s), 1361(s),
1289(s), 1226(w), 1181(w), 1152(s), 1017(w), 934(w), 860(w).
Anal. Calcd for C74H96N8O24Tb4 (2116.36): C, 41.98; H, 4.57; N,
5.29. Found: C, 42.10; H, 4.36; N, 5.38%.
[Dy4(L)4(μ2-η1η1Piv)4]·6CH3OH·4H2O (3). Quantities: LH3 (0.06 g,
0.26 mmol), DyCl3·5H2O (0.097 g, 0.26 mmol), Et3N (0.12 mL, 0.9
mmol), PivH (0.026 g, 0.26 mmol). Yield: 0.071 g, 49.30% (based on
Dy). Mp: 185 °C (dec). IR (KBr) (cm−1): 3392(b), 3062(w),
2959(s), 1587(s), 1575(s), 1559(s), 1477(s), 1421(s), 1374(s),
1361(s), 1290(s), 1225(w), 1180(w), 1112(w), 1016(s), 928(w),
854(w). Anal. Calcd for C78H108N8O26Dy4 (2228.45): C, 42.13; H,
4.90; N, 5.04. Found: C, 42.01; H, 4.79; N, 5.13%.
RESULTS AND DISCUSSION
■
Synthesis. The multisite coordinating Schiff-base ligand
LH2 was prepared by a two-step synthetic protocol involving
the conversion of the precursor C1 to C2, which was
subsequently condensed with 2-amino phenol (Scheme 1).
Ligand LH2 contains four divergent coordinating centers: a
phenolic unit, an imino, a pyridine nitrogen, and a pendant
CH2OH arm. We expected this semiflexible unsymmetrical
Schiff-base ligand to accommodate one lanthanide metal ion.
However, the presence of the −CH2OH arm was expected to
allow the assembly to proliferate. We used pivalic acid as a
coligand because of the propensity of the pivalate ion to bridge
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Table 2. Selected Bond Distance (Å) and Bond Angle (deg) Parameters of Compound 3
Dy(1)−O(2)
Dy(1)−O(9)
Dy(1)−O(16)
Dy(1)−O(1)
Dy(1)−O(7)
Dy(1)−O(3)
Dy(1)−N(1)
Dy(1)−N(2)
Dy(1)−Dy(4)
Dy(1)−Dy(2)
Dy(2)−O(4)
Dy(2)−O(10)
Dy(2)−O(11)
Dy(2)−O(3)
Dy(2)−O(5)
Dy(2)−O(1)
Dy(2)−N(3)
Dy(2)−N(4)
2.273(7)
2.305(7)
2.325(7)
2.370(7)
2.472(6)
2.491(7)
2.501(8)
2.548(9)
3.708(11)
3.721(10)
2.263(7)
2.353(7)
2.359(7)
2.367(7)
2.470(6)
2.475(7)
2.476(9)
2.524(8)
Dy(2)−Dy(3)
Dy(3)−O(6)
Dy(3)−O(12)
Dy(3)−O(13)
Dy(3)−O(5)
Dy(3)−O(3)
Dy(3)−O(7)
Dy(3)−N(5)
Dy(3)−N(6)
Dy(3)−Dy(4)
Dy(4)−O(8)
Dy(4)−O(14)
Dy(4)−O(15)
Dy(4)−O(7)
Dy(4)−O(5)
Dy(4)−N(7)
Dy(4)−O(1)
3.707 (9)
2.272(7)
2.315(7)
2.325(7)
2.361(7)
2.466(6)
2.481(7)
2.496(8)
2.530(8)
3.684(8)
2.254(7)
2.323(7)
2.331(7)
2.357(7)
2.474(7)
2.493(8)
2.495(7)
Dy(1)−O(1)−Dy(2)
Dy(1)−O(1)−Dy(4)
Dy(2)−O(1)−Dy(4)
Dy(2)−O(3)−Dy(3)
Dy(2)−O(3)−Dy(1)
Dy(3)−O(3)−Dy(1)
Dy(3)−O(5)−Dy(2)
Dy(3)−O(5)−Dy(4)
Dy(2)−O(5)−Dy(4)
Dy(4)−O(7)−Dy(1)
Dy(4)−O(7)−Dy(3)
Dy(1)−O(7)−Dy(3)
100.4(2)
99.3(2)
114.1(3)
100.2(2)
100.0(2)
113.9(2)
100.2(2)
99.3(2)
115.1(2)
100.3(2)
99.2(2)
114.1(2)
molecular structure of 3 will be described; the structural details
of 1−2 are given in the Supporting Information (Figures S1
and S2). Selected bond parameters of 3 are summarized in
Table 2. The molecular structures and selected bond
parameters of the other two compounds are given in the
Supporting Information (Figures S1 and S2, Tables S1 and S2).
A perspective view of the molecular structure of 3 is depicted in
Figure 1.
deprotonated alkoxy oxygen atoms. The latter are involved in
bridging three neighboring Dy(III) ions [Dy−Oalkoxy = 2.36−
2.49 Å] to construct a distorted cubane-like [Dy4(μ3-OR)4]+8
core (Figures 1 and 2a). Within the core, the intramolecular
Dy···Dy distances are in the range of 3.68−4.15 Å. In addition
to the binding provided by L2−, all the Dy(III) ions in the Dy4
cubane core are further held together as a result of four μ2-η1:η1
binding of pivalate anion, which satisfies the charge as well as
the coordination environment. Each pivalate ligand is involved
in a syn, syn bridge among all adjacent Dy(III) ions with an
average distance of 2.31−2.35 Å. Each dysprosium ion is eight-
coordinated (2N, 6O) and forms distorted triangular
dodecahedral geometry (Figure 2b and SHAPE20 calculations
in the Supporting Information).
The Dy−Ophenoxy bond lengths are in the range of ∼2.25−
2.27 Å, which are slightly shorter than Dy−Oalkoxy bond lengths
(∼2.36−2.49 Å). Two different types of nitrogens are
coordinated to each Dy(III) ions. Bond lengths of coordinated
imino nitrogens are in the range of ∼2.52−2.54 Å, which are
slightly longer than those of pyridine ring nitrogen [Dy−
NPyridine = 2.47−2.49 Å]. The Dy−O−Dy angles lie in rather
wide ranges: 99.20(2)−115.10(2)°. The bond lengths around
the lanthanide ions show almost the expected general tendency
toward shorter values over the series 1, 2, and 3, which is
consistent with the phenomenon of lanthanide contraction
(Table 3).
As pointed out above, there are only three discrete Dy4
complexes possessing distorted cubane geometries whose
magnetic properties have been well explored and are known
in the literature. These are illustrated in Figure 3. In these cases,
the corners of the cubane are occupied by Dy and μ3-OH− ions.
In the current instance, in contrast, the oxygen atom
(−CH2O)− present in the vertex of the cube is derived from
the ligand [L]2−. The metric parameters involved in the current
instance are similar to those found in the literature and are
summarized in Table 4.
Magnetic Studies. The temperature dependence of χMT
for complexes 1−3 (χM is the molar magnetic susceptibility per
Ln4III unit) in the temperature range of 300−2 K was measured
with an applied magnetic field of 1000 Oe, and the results are
displayed in Figure 4.
Figure 1. Molecular structure of 3 (hydrogen atoms and the solvent
molecules have been omitted for clarity).
The molecular structure of 3 (Figures 1 and 2a) contains a
distorted cubane-like [Dy4(μ3-OR)4]+8 core, which is formed by
the concerted coordination action of four dianionic L2− Schiff-
base ligands in a μ3-η3:η1:η1:η1 fashion. Here, each ligand
provides one phenolate oxygen, one imino nitrogen, one
pyridine nitrogen, and one μ3-alkoxy oxygen group (Scheme 3).
Potentially, each ligand can accommodate one Dy(III) in its
chelating (O, N, N, O) cavity. Thus, in compound 3, four
Dy(L)+ building units are self-assembled through fully
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Figure 2. (a) Distorted cubane core of complex 3. (b) Distorted triangular dodecahedral geometry around Dy3+ ion.
Scheme 3. Binding Mode of the Ligand [L]2− with
Dysprosium(III) Ions
isotropic. The fit of the experimental susceptibility data with the
above Hamiltonian, using the MAGMUN program,21 afforded
the following set of parameters: J1 = −0.03 cm−1, J2 = −0.13
cm−1, g = 2.03, and R = 3 × 10−7 (R = Σ(χobsT χcalcT)2/
Σ(χobsT)2, where χcalc and χobs denote calculated and observed
molar magnetic susceptibilities, respectively). The obtained
values are in good agreement with the reported coupling
constants for other dialkoxo and diphenoxo-bridged Gd3+
complexes.22,12b The structural differences between the
Gd2O2 bridging fragments involving short and long Gd···Gd
distances could be responsible for the differing magnetic
coupling of the two magnetic pathways. Thus, while the
magnetic exchange pathways involving short Gd···Gd distances
are folded (due to coordination of the nonplanar syn-syn
pivalate bridging ligand), with Gd−O−Gd bridging angles of
∼98°, those involving long Gd···Gd distances are planar, with
Gd−O−Gd bridging angles of ∼114°. Nevertheless, more
examples of dialkoxo-bridged complexes are needed to evaluate
the influence of the structural factors of the Gd2O2 bridging
fragment on the magnetic coupling.
III
Let us start with the simple case of the Gd4 complex 1. At
room temperature, the χMT value for 1 of 32.42 cm3 mol−1 K is
close to that expected for four noninteracting GdIII ions (31.5
cm3 mol−1 K, with S = 7/2 and g = 2). On lowering the
temperature, the χMT for 1 remains constant until ∼25 K and
then shows an abrupt decrease to reach a value of 15.91 cm3
mol−1 K at 2 K. This behavior is most likely due to
intramolecular antiferromagnetic interactions between the
GdIII ions.
As expected for four noninteracting Gd3+ ions, the
experimental magnetization values (Figure 5) are well below
the Brillouin function, which is mainly due to the
antiferromagnetic interaction between the metal ions as well
as to the local magnetic anisotropy of the Gd3+ ions. The
saturation of the magnetization is almost complete at 5 T,
reaching a value of 28.34 NμB, which agrees well with the
theoretical saturation value for four Gd3+ ions with g = 2.03 of
28.42 NμB.
The room-temperature χMT values of complexes 2 and 3 are
48.31 and 56.51 cm3 mol−1 K, respectively, which are in rather
good agreement with the expected theoretical values using the
free ion approximation (47.28 and 56.72 cm3 mol−1 K for 2 and
The Gd4O4 cubane unit in 1 is of the 4 + 2 type with two
long (∼4.15 Å) and four short (∼3.7 Å) Gd···Gd distances. In
keeping with this, the magnetic properties of 1 were analyzed
using following simplest two-J isotropic Hamiltonian:
H = −J (SGd1 Gd4
S
+ SGd1 Gd2
S
+ SGd2SGd3 + SGd3SGd4)
1
− J2(SGd1 Gd3
S
+ SGd2SGd4)
where J1 and J2 describe the magnetic exchange pathways
involving short and long Gd···Gd distances, respectively (Figure
4). The DGd is assumed to be negligible as this ion is rather
Table 3. Comparison of Selected Average Ln−O and Ln−N Bond Lengths (Å) of Compounds 1−3
1 (Ln(III) = Gd(III))
2 (Ln(III) = Tb(III))
3 (Ln(III) = Dy(III))
Ln−Ophenolate
Ln−Oalkoxy
Ln−Opivalate
Ln−Nimine
Ln−NPy
2.292(8)
2.463(7)
2.365(8)
2.559(10)
2.515(10)
2.285(4)
2.446(4)
2.342(4)
2.544(5)
2.506(5)
2.265(7)
2.439(7)
2.329(7)
2.533(8)
2.491(8)
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3, respectively) for four noninteracting lanthanide ions: Tb3+
(7F6, S = 3, L = 3, g = 3/2, C = 11.82 cm3 mol−1 K) and Dy3+
(6H15/2, S = 5/2, L = 5, g = 4/3, C = 14 cm3 mol−1 K). The
product χT decreases with decreasing temperature, first slowly
to ∼50 K for compound 2 and to ∼100 K for compound 3 and
then rapidly to 33.25 and 39.98 cm3 mol−1 K at 2.0 K,
respectively. This behavior is due to the effects of the thermal
depopulation of the mJ sublevels of the 2S+1ΓJ ground state of
the Ln3+ ion, which are originated by the crystal field, together
with weak Ln3+···Ln3+ antiferromagnetic interactions. The
existence of very weak antiferromagnetic interactions in theses
complexes is not unexpected in view of the fact that
isostructural Gd3+, Tb3+, and Dy3+ complexes generally display
magnetic exchange interactions of the same nature.23,13b
The field dependence of the magnetization at 2 K shows a
rapid increase of the magnetization at low field and a linear
increase at high field to reach values of 23.5 and 24.47 NμB for
compounds 2 and 3 (Figure 5), respectively, which are
considerably smaller than the expected saturation magnet-
ization values, Ms/NμB = 4gJJ, for four Ln3+ ions. This behavior
suggests the presence of a significant magnetic anisotropy
arising from the ligand-field effects, which eliminates the 16-
fold degeneracy of the 6H15/2 ground state. In fact, the observed
values at 5 T per Ln3+ ion are similar to those estimated for
mononuclear Ln3+ complexes where considerable ligand-field
effects have been taken into account.24
Dynamic ac magnetic susceptibility measurements as a
function of the temperature at different frequencies were
performed on microcrystalline powder samples of complexes 2
and 3. Complex 2 did not show any out-of-phase (χ″M) signal,
either under zero external field or under an applied field of
1000 Oe. This behavior indicates that either the energy barrier
for the flipping of the magnetization is not high enough to trap
the magnetization in one of the equivalent configurations above
2 K or there exists quantum tunnelling of the magnetization
(QTM), leading to a flipping rate that is too fast to observe the
maximum in the χ″M above 2 K. Complex 3, however, shows
typical SMM behavior (Figure 6 and Supporting Information,
Figure S3) below 13 K under zero dc applied field with two
out-of-phase peaks in the 5.75 K (300)−6.25 K (1400 Hz)
range (fast relaxation, FR) and 8.5 K (300 Hz)−10.5 K (1400
Hz) range (slow relaxation, SR). Note that the χ″M component
increases below the maxima of the FR process, which can be
taken as a clear indication of QTM.
The Cole−Cole diagram (Figure 6, inset) exhibits a
semicircular shape in the 3.75−9 K range, which is due to
the coalescence of the FR and SR peaks. The data can be fitted
to the Debye model, affording α values (this parameter
determines the width of the distribution of relaxation times, so
that α = 1 corresponds to an infinitely wide distribution of
relaxation times, whereas α = 0 represents a process with only a
single relaxation time) between 0.34 (3.75 K) and 0.52 (9 K),
which are compatible with the existence of more than one
relaxation process in the whole temperature range. In the range
of 3.75−6.25 K, the fit of the frequency dependence of the χ″M
signal, at each temperature, to the generalized Debye model
(Figure 7) permits the relaxation times to be extracted, which
are plotted as a function of 1/T (Figure 7, inset). The fit of the
high-temperature data (5.25 to 6.25 K) to the Arrhenius law (τ
= τ0 exp(Ueff/kBT)) afforded an effective thermal energy barrier
Ueff = 23.8(1) K and with a pre-exponential factor τ0 = 1.35 ×
10−5 s. This τ0 value is much larger than expected for a SMM.
This together with the fact that relaxation times deviate from
Figure 3. Examples of reported discrete tetranuclear lanthanide
complexes having the cubane core.
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Table 4. Comparison of Bond Lengths (Å) and Bond Angles (deg) in the Dy4(μ3-O)4 Cubane Core Present in Ln4 Complexes
Dy−Ohydroxy
Dy−Oalkoxy
2.36−2.49
Dy−Dy
Dy−O−Dy
reference
this work
[Dy4(L)4(μ2-η1η1Piv)2]·4H2O·6CH3OH
[Dy4(μ3-OH)4(isonicotinate)6(py)(CH3OH)7](ClO4)2·py·4CH3OH
[Dy4(HL)4(C6H4NH2COO)2(μ3-OH)4(μ-OH)2(H2O)4] ·4CH3CN·12H2O
3.68−4.15
3.72−3.85
3.58−3.81
2.57−2.73
99.20−115.10
103.63−110.1
99.00−109.50
105.7−107.9
2.33−2.40
2.34−2.37
15a, Figure 3a
15b, Figure 3b
15c, Figure 3c
a
b
[Dy4(OH)4(TBSOC)2(H2O)4(CH3OH)4]·4H2O
2.33−2.36
a
b
LH2 = 2-{[(2-hydroxy-3-methoxyphenyl)methylidene]amino}benzoic acid. (H4TBSOC = p-tert-butylsulfonylcalix[4]arene).
Figure 4. (left) Temperature dependence of the χMT for compounds 1−3. Solid line represents the best fit of the experimental data. (right) 2J
coupling scheme for compound 1.
Figure 5. Field dependence of the magnetization for compounds 1−3.
Solid lines are just a guide to the eye. The dashed line represents the
Brillouin function for four noninteracting Gd3+ ions.
Figure 7. Frequency dependence of χ″M for compound 3 under a zero
dc field. (inset) Temperature dependence of the relaxation times for 3
under a zero dc field. (black line) The best fitting of the experimental
data to the Arrhenius equation. (red line) The best fit to an Orbach
and QTM process.
linearity in the low-temperature region (Figure 7) agrees with
the simultaneous occurrence of both QTM and Orbach
thermally activated processes. In view of this, we have fitted
the temperature dependence of the relaxation time to the
following equation that considers the simultaneous occurrence
of both the thermal and QTM processes:
τ−1 = τQT−1 + τ0−1exp(−U /kT)
(1)
eff
Figure 6. Temperature dependence of the out-of-phase ac signals
(χ″M) under zero applied dc field for 3. Solid lines are a guide to the
eye. (inset) Cole−Cole plot for 3. Solid lines represent the best fitting
to the Debye model.
An excellent fit over the full temperature range was obtained
with the following parameters: Ueff = 43.4(9) K with τ0 = 8 ×
10−7 s and τQT = 0.001 97(2) s. As expected, when the effects of
the QTM process are taken into consideration, the Ueff and τ0
values increase and decrease, respectively. The absence of well-
separated peaks in the χ″M versus T and χ″M versus ν plots
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prevents extraction of reliable Ueff and τ0 values for the SR
process.
The ac measurements, in the presence of a small external dc
field of 1000 Oe (Figure 8 and Supporting Information, Figure
due to the SR process can be observed. The fit of the data using
the generalized Debye model afforded α values in the ranges of
0.34 (5.75 K)−0.26 (5 K) and 0.08 (10 K)−0.16 (8 K) for the
FR and SR regions, respectively, which supports the existence
of multiple relaxation processes for the former (in good accord
with the ineffective suppression of the QTM) and a relatively
narrow distribution of the relaxation times for the latter.
The χ″M versus frequency curves were fitted by using the
sum of two modified Debye functions25 (Figure 9), and from
Figure 8. Temperature dependence of the out-of-phase ac signals
(χ″M) under an applied dc field of 1000 Oe for compound 3. Solid
lines are a guide to the eye. (inset) Cole−Cole plot for 3 under an
applied dc field of 1000 Oe. Solid lines represent the best fitting to the
Debye model.
Figure 9. Frequency dependence of χ″M for 3 under a 1000 Oe dc
field. (inset) Temperature dependence of the relaxation times for 3
under an applied dc field of 1000 Oe. (black line) The best fit of the
experimental data to the Arrhenius equation. (red line) The best fit to
an Orbach and QTM process.
S4) to fully or partly suppress the QTM, show that (i) the two
peaks are rather well-resolved, so that maxima are clearly
observed for both processes, (ii) the χ″M signal peaks appear
virtually at the same temperatures as those observed under zero
dc applied field and exhibit similar intensity, and (iii) χ″M
components do not go to zero below the maxima of the FR
process, which can be taken as a clear indication that the QTM
process has not been efficiently suppressed. Note that position
of the peaks does not significantly shift when the dc applied
magnetic field is increased to 3000 Oe (Supporting
Information, Figure S5). However, the peaks for the FR
process increase in intensity with regard to those for the SR
process. Moreover, magnetic fields as high as 3000 Oe are not
able to fully eliminate the QTM relaxation process, which
suggests that the remaining QTM process is promoted by
intermolecular magnetic dipolar interactions. An appropriate
manner to try to eliminate the intermolecular interactions and
therefore the QTM process is that of diluting the sample with
an isostructural diamagnetic complex, such as YIII4. These
experiments are planned for the near future in case we are able
to cocrystallize the DyIII complex with the isotructural YIII
diamagnetic complex. In spite of this, changes occurring in the
temperature and frequency dependence of the χ″M component
of the ac susceptibility make it easier to analyze the data and to
extract reliable parameters for the FR and SR relaxation
processes.
The Cole−Cole plot, between 5 and 5.75 K, shows an almost
single semicircle corresponding to the FR. However, as the
temperature is increased, the FR and SR processes are both
observed in the range of 6−8 K; from this latter temperature,
the faster process gradually moves beyond the high-frequency
range of the magnetometer (<1500 Hz), and only a semicircle
the extracted relaxation times the corresponding Arrhenius
plots were constructed (Figure 9 inset), which led to τ0 = 2.7 ×
10−6 s and Ueff = 37(1) K for the FR process and τ0 = 4. 4 ×
10−8 s and Ueff = 73(2) K for the SR process. As observed for
the relaxation times extracted at zero field for the FR process,
the data at 1000 Oe also deviate from linearity in the low-
temperature region, and τ0 is much larger than expected for an
SMM. Both facts point out that both QTM and Orbach
thermally activated processes occur simultaneously. In fact, a
good fit of the data in the 3.5−5.75 K range is obtained with 1
and the following parameters: Ueff = 47.2(9) K with τ0 = 5 ×
10−7 s and τQT = 0.0157(9) s. It seems that in the presence of
an external field of 1000 Oe, the QTM is partly suppressed, but
the relaxation of the magnetization does not significantly slow
with regard to the same process under zero dc applied field.
The Arrhenius plots, constructed from the temperatures and
frequencies of the maxima observed for the χ″M signals in
Figure 8, lead virtually to the same results, as expected (see
Figure S6). It is worth mentioning that the values of the
effective energy barrier for the FR and SR processes in 3 are at
the high end of the range found for the limited number of Dy4
SMMs so far reported, and they are the largest values ever
found for Dy4O4 cubane complexes. In addition, the pre-
exponential factor τ0 is typical of SMMs.8
4
4
It is worth mentioning that DyIII-containing polynuclear
complexes usually exhibit very weak Dy···Dy exchange
interactions because of the limited radial extension of their
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inner f orbitals. Consequently, in these systems the SR of the
magnetization is mainly due to the large moment and strong
magnetic anisotropy of the individual DyIII centers rather than
to the fully exchange-coupled molecule. Therefore, polynuclear
complexes can exhibit several relaxation processes correspond-
ing to multiple slow relaxing DyIII centers. In the absence of
significant magnetic exchange coupling between the DyIII ions,
the relaxation of the individual ions allows for the occurrence of
QTM at zero applied field. It has been shown that significant
exchange coupling between the DyIII ions mitigates the QTM
process.26 In view of the above results for the GdIII complex 1,
the Dy···Dy exchange interactions in 3 are expected to be very
weak, and therefore the relaxation process should have a single-
ion origin with QTM at zero field. The existence of a tail at low
temperature and zero applied field in the χ″M versus T plot of 3
could support this assumption. Assuming the single-ion origin
of the magnetic relaxation in 3, the existence of two thermally
activated relaxation processes could be due to (i) the
noncrystallographic equivalence of the four DyIII ions with
small differences between distances and angles in their
corresponding DyO8 coordination polyhedra and (ii) the
existence of two competing relaxation pathways via excited
states, which depends on the transverse field each DyIII ion
experiences from its neighboring DyIII ions.11
ACKNOWLEDGMENTS
■
We are thankful to the Department of Science and Technology,
New Delhi, for financial support. S.D., A.D., and S.B. thank
CSIR, India for Senior Research Fellowship. V.C. is thankful to
the Department of Science and Technology (DST) for a J. C.
Bose National Fellowship. E.C. is thankful for financial support
from the Spanish Ministerio de Ciencia e Innovacion
́
(MICINN) (Project CTQ-2011-24478), the Junta de Andalu-
́
cia (FQM-195, the Project of Excellence P11-FQM-7756), and
the University of Granada. We are grateful to Nuria Clos,
Unitat de Mesures Magnet
logics, Universitat de Barcelona, Spain, for his help with the
̀
iques, Centers Cinetifics i Tecno-
̀
magnetic measurements.
REFERENCES
■
(1) (a) Christou, G.; Gatteschi, D.; Hendrickson, D. N.; Sessoli, R.
Mater. Res. Bull. 2000, 25, 66−71. (b) Sessoli, R.; Gatteschi, D.;
Caneschi, A.; Novak, M. A. Nature 1993, 365, 141−143. (c) Affronte,
M. J. Mater. Chem. 2009, 19, 1731−1737. (d) Stamp, P. C. E.; Gaita-
Arino, A. J. Mater. Chem. 2009, 19, 1718−1730. (e) Aromı, G.; Aguila,
D.; Gamez, P.; Luis, F.; Roubeau, O. Chem. Soc. Rev. 2012, 41, 537−
546. (f) Ardavan, A.; Rival, O.; Morton, J. J. L.; Blundell, S. J.;
Tyryshkin, A. M.; Timco, G. A.; Winpenny, R. E. P. Phys. Rev. Lett.
2007, 98, 057201−057204. (g) Bogani, L.; Wernsdorfer, W. Nat.
Mater. 2008, 7, 179−186. (h) Leuenberger, M. N.; Loss, D. Nature
2001, 410, 789−793.
(2) (a) Peng, J. B.; Zhang, Q. C.; Kong, X. J.; Ren, Y. P.; Long, L. S.;
Huang, R. B.; Zheng, L. S.; Zheng, Z. P. Angew. Chem., Int. Ed. 2011,
50, 10649−10652. (b) Zheng, Y. Z.; Evangelisti, M.; Winpenny, R. E.
P. Angew. Chem., Int. Ed. 2011, 50, 3692−3695. (c) Liu, S.-J.; Zhao, J.-
P.; Tao, J.; Jia, J.-M.; Han, S.-D.; Li, Y.; Chen, Y.-C.; Bu, X.-H. Inorg.
Chem. 2013, 52, 9163−9698. (d) Biswas, S.; Adhikary, A.; Goswami,
S.; Konar, S. Dalton Trans. 2013, 42, 13331−13334.
(3) (a) Mannini, M.; Pineider, F.; Danieli, C.; Totti, F.; Sorace, L.;
Sainctavit, P.; Arrio, M. A.; Otero, E.; Joly, L.; Cezar, J. C.; Cornia, A.;
Sessoli, R. Nature 2010, 468, 417−421. (b) Bokacheva, L.; Kent, A. D.;
Walters, M. A. Phys. Rev. Lett. 2000, 85, 4803−4806. (c) Hill, S.;
Edwards, R. S.; Aliaga-Alcalde, N.; Christou, G. Science 2003, 302,
1015−1018. (d) Friedman, J. R.; Patel, V.; Chen, W.; Tolpygo, S. K.;
Lukens, J. E. Nature 2000, 406, 43−46.
(4) (a) Aromi, O. G.; Brechin, E. K. Struct. Bonding (Berlin, Ger.)
2006, 122, 1−67. (b) Sessoli, R.; Powell, A. K. Coord. Chem. Rev. 2009,
253, 2328−2341.
CONCLUSIONS
■
To summarize, we report the synthesis and the structural and
magnetic characterization of tetranuclear lanthanide complexes
having a distorted cubane-type tetrametallic core. The assembly
of these complexes has been accomplished by the use of a
semiflexible unsymmetrical Schiff-base ligand containing a
distinct binding pocket for lanthanide metal ions. However,
the deprotonated (−CH2O)− arm of the ligand along with the
ancillary pivalate ions allows the assembly to proliferate. The
magnetic studies involving the ac susceptibility measurements
reveal that among compounds 1, 2, and 3, only compound 3
exhibits an SR of magnetization below 10 K. This compound
shows two relaxation processes that lead to two energy barriers
(73 and 47 K) and time constants (τ0 = 4.4 × 10−8 s, τ0 = 5.0 ×
10−7 s).
(5) (a) Gatteschi, D.; Sessoli, R.; Villain, J. Molecular Nanomagnets;
Oxford University Press: Oxford, 2006. (b) Sessoli, R.; Hui, L.; Schake,
A. R.; Wang, S.; Vincent, J. B.; Folting, K.; Gatteschi, D.; Christou, G.
J. Am. Chem. Soc. 1993, 115, 1804−1816.
ASSOCIATED CONTENT
■
S
* Supporting Information
Molecular structures of 1 and 2, details of structural parameters
for compounds 1 and 2, and magnetic data for 3. This material
is available free of charge via the Internet at http://pubs.acs.org.
Crystallographic data (excluding structure factors) for the
structures in this Paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication Nos. CCDC 963386−963388. Copies of the data
can be obtained, free of charge, on application to CCDC, 12
Union Road, Cambridge CB2 1EZ, U.K.: http://www.ccdc.
cam.ac.uk/cgi-bin/catreq.cgi, e-mail: data_request@ccdc.cam.
ac.uk, or fax: +44 1223 336033.
́
(6) Ako, A. M.; Hewitt, I. J.; Mereacre, V.; Clerac, R.; Wernsdorfer,
W.; Anson, C. E.; Powell, A. K. Angew. Chem., Int. Ed. 2006, 45, 4926−
4929.
́
(7) Ako, A. M.; Mereacre, V.; Clerac, R.; Wernsdorfer, W.; Hewitt, I.
J.; Anson, C. E.; Powell, A. K. Chem. Commun. 2009, 544−546.
(8) Woodruff, D. N.; Winpenny, R. E. P.; Layfield, R. A. Chem. Rev.
2013, 113, 5110−5148 and references therein.
(9) (a) Ishikawa, N.; Sugita, M.; Ishikawa, T.; Koshihara, S.-y.; Kaizu,
Y. J. Am. Chem. Soc. 2003, 125, 8694−8695. (b) Ishikawa, N.; Sugita,
M.; Wernsdorfer, W. J. Am. Chem. Soc. 2005, 127, 3650−3651.
̀ ́
(c) Fatila, E. M.; Rouzieres, M.; M. Jennings, C. A.; Lough, J.; Clerac,
R.; Preuss, K. E. J. Am. Chem. Soc. 2013, 135, 9596−9599. (d) Liu, C.-
M.; Zhang, D.-Q.; Zhu, D.-B. Inorg. Chem. 2013, 52, 8933−8940.
(e) Campbell, V. E.; Guillot, R.; Riviere, E.; Brun, P.-T.; Wernsdorfer,
W.; Mallah, T. Inorg. Chem. 2013, 52, 5194−5200.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: vc@iitk.ac.in. (V.C.)
*E-mail: ecolacio@ugr.es. (E.C.)
(10) Blagg, R. J.; Muryn, C. A.; McInnes, E. J. L.; Tuna, F.;
Winpenny, R. E. P. Angew. Chem., Int. Ed. 2011, 50, 6530−6533.
(11) Blagg, R. J.; Ungur, L.; Tuna, F.; Speak, J.; Comar, P.; Collison,
D.; Wernsdorfer, W.; McInnes, E. J. L.; Chibotaru, L. F.; Winpenny, R.
E. P. Nat. Chem. 2013, 5, 673−678.
Notes
The authors declare no competing financial interest.
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(12) (a) Chandrasekhar, V.; Hossain, S.; Das, S.; Biswas, S.; Sutter, J.
P. Inorg. Chem. 2013, 52, 6346−6353. (b) Chandrasekhar, V.; Bag, P.;
Colacio, E. Inorg. Chem. 2013, 52, 4562−4570. (c) Chandrasekhar, V.;
Dey, A.; Mota, A. J.; Colacio, E. Inorg. Chem. 2013, 52, 4554−4561.
(d) Chandrasekhar, V.; Das, S.; Dey, A.; Hossain, S.; Sutter, J.-P. Inorg.
Chem. 2013, 52, 11956−11965.
C.; Giovenzana, G. B.; Palmisano, G.; Sisti, M. Org. Biomol. Chem.
2007, 5, 2441−2447. (c) Hutchinson, D. J.; Hanton, L. R.; Moratti, S.
C. Inorg. Chem. 2010, 49, 5923−5934.
(18) (a) SMART & SAINT Software Reference manuals, Version 6.45;
Bruker Analytical X-ray Systems, Inc.: Madison, WI, 2003.
(b) Sheldrick, G. M. SADABS, a software for empirical absorption
correction, Ver. 2.05; University of Gottingen: Gottingen, Germany,
̈
̈
(13) (a) Chandrasekhar, V.; Pandian, B. M.; Azhakar, R.; Vittal, J. J.;
2002. (c) SHELXTL Reference Manual, Ver. 6.1; Bruker Analytical X-
ray Systems, Inc.: Madison, WI, 2000. (d) Sheldrick, G. M. SHELXTL,
Ver. 6.12; Bruker AXS, Inc.: Madison, WI, 2001. (e) Sheldrick, G. M.
SHELXL97, Program for Crystal Structure Refinement; University of
Cler
Pandian, B. M.; Vittal, J. J.; Cler
1157. (c) Chandrasekhar, V.; Dey, A.; Das, S.; Rouzier
́
ac, R. Inorg. Chem. 2007, 46, 5140−5142. (b) Chandrasekhar, V.;
ac, R. Inorg. Chem. 2009, 48, 1148−
es, M.; Clerac,
́
́
́
R. Inorg. Chem. 2013, 52, 2588−2598. (d) Chandrasekhar, V.; Bag, P.;
Gottingen: Gottingen, Germany, 1997. (f) Bradenburg, K. Diamond,
̈
̈
Speldrich, M.; Leusen, J.; Kogerler, P. Inorg. Chem. 2013, 52, 5035−
̈
Ver. 3.1eM; Crystal Impact GbR: Bonn, Germany, 2005.
5044. (e) Chandrasekhar, V.; Das, S.; Dey, A.; Hossain, S.; Lloret, F.;
Pardo, E. Eur. J. Inorg. Chem. 2013, 4506−4514.
(19) (a) Abbas, G.; Lan, Y.; Kostakis, G. E.; Wernsdorfer, W.; Anson,
C. E.; Powell, A. K. Inorg. Chem. 2010, 49, 8067−8072. (b) Abbas, G.;
Lan, Y.; Kostakis, G.; Anson, C. E.; Powell, A. K. Inorg. Chim. Acta
2008, 361, 3494−3499. (c) Liu, S.-J.; Zhao, J.-P.; Song, W.-C.; Han, S.-
D.; Liu, Z.-Y.; Bu, X.-H. Inorg. Chem. 2013, 52, 2103−2109.
(d) Langley, S. K.; Chilton, N. F.; Gass, I. A.; Moubaraki, B.;
Murray, K. S. Dalton Trans. 2011, 40, 12656−12659. (e) Mereacre, V.;
Prodius, D.; Lan, Y. H.; Turta, C.; Anson, C. E.; Powell, A. K. Chem.
Eur. J. 2011, 17, 123−128. (f) Rinck, J.; Novitchi, G.; Heuvel, W. V.
D.; Ungur, L.; Lan, Y. H.; Wernsdorfer, W.; Anson, C. E.; Chibotaru,
L. F.; Powell, A. K. Angew. Chem., Int. Ed. 2010, 49, 7583−7587.
(g) Zheng, Y. Z.; Evangelisti, M.; Winpenny, R. E. P. Angew. Chem.,
Int. Ed. 2011, 50, 3692−3695.
(20) (a) Alvarez, S.; Alemany, P.; Casanova, D.; Cirera, J.; Llunell,
M.; Avnir, D. Coord. Chem. Rev. 2005, 249, 1693−1780. (b) Casanova,
D.; Llunell, M.; Alemany, P.; Alvarez, S. Chem.Eur. J. 2005, 11,
1479−1494.
(21) MAGMUN 4.0/OW0L is available as a combined package free
of charge from the authors at http://www.ucs.mun.ca/lthomp/.
MAGMUN has been developed by Dr. Xu, Z. and Thompson, L. K.
(Memorial University), and OW01.exe was developed by Dr.
Waldmann, O. (University of Bern). The software calculates the
total spin state values (S) and their associated energies (E), using the
Kambe approach, and then substitutes the S and E values into the van
Vleck equation to generate the variable-temperature susceptibility
profile (degenerate states are accounted for).
(14) (a) Petit, S.; Neugebauer, P.; Pilet, G.; Chastanet, G.; Barra, A.-
L.; Antunes, A. B.; Wernsdorfer, W.; Luneau, D. Inorg. Chem. 2012, 51,
6645−6654. (b) Papadakis, R.; Rivier
̀
e, E.; Giorgi, M.; Jamet, H.;
Rousselot-Pailley, P.; Reglier, M.; Simaan, A. J.; Tron, T. Inorg. Chem.
́
2013, 52, 5824−5830. (c) Guedes, G. P.; Soriano, S.; Comerlato, N.
M.; Speziali, N. L.; Lahti, P. M.; Novak, M. A.; Vaz, M. G. F. Eur. J.
Inorg. Chem. 2012, 5642−5648. (d) Oshio, H.; Hoshino, N.; Ito, T.;
Nakano, M. J. Am. Chem. Soc. 2004, 126, 8805−8812. (e) Piga, F.;
Moro, F.; Krivokapic, I.; Blake, A. J.; Edge, R.; McInnes, E. J. L.; Evans,
D. J.; McMastera, J.; Slageren, J. v. Chem. Commun. 2012, 48, 2430−
2432. (f) Moragues-Canovas, M.; Helliwell, M.; Ricard, L.; Riviere, E.;
Wernsdorfer, W.; Brechin, E.; Mallah, T. Eur. J. Inorg. Chem. 2004,
2219−2222. (g) Yang, E. C.; Wernsdorfer, W.; Zakharov, L. N.;
Karaki, Y.; Yamaguchi, A.; Isidro, R. M.; Lu, G. D.; Wilson, S. A.;
Rheingold, A. L.; Ishimoto, H.; Hendrickson, D. N. Inorg. Chem. 2006,
45, 529−546. (h) Galloway, K. W.; Whyte, A. M.; Wernsdorfer, W.;
Sanchez-Benitez, J.; Kamenev, K. V.; Parkin, A.; Peacock, R. D.;
Murrie, M. Inorg. Chem. 2008, 47, 7438−7442. (i) Isele, K.; Gigon, F.;
Williams, A. F.; Bernardinelli, G.; Franz, P.; Decurtins, S. Dalton Trans.
2007, 332−341. (j) Venegas-Yazigi, D.; Cano, J.; Ruiz, E.; Alvarez, S.
Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 384, 123−125.
(k) Gao, Y.; Zhao, L.; Xu, X.; Xu, G.-F.; Guo, Y.-N.; Tang, J.; Liu, Z.
Inorg. Chem. 2011, 50, 1304−1308. (l) Aronica, C.; Chastanet, G.;
Pilet, G.; Le Guennic, B.; Robert, V.; Wernsdorfer, W.; Luneau, D.
Inorg. Chem. 2007, 46, 6108−6119. (m) Zhao, X. Q.; Lan, Y. H.; Zhao,
B.; Cheng, P.; Anson, C. E.; Powell, A. K. Dalton Trans. 2010, 39,
4911−4917. (n) Nohra, B.; Mialane, P.; Dolbecq, A.; Riviere, E.;
Marrot, J.; Secheresse, F. Chem. Commun. 2009, 2703−2711. (o) Das,
A.; Klinke, F. J.; Demeshko, S.; Meyer, S.; Dechert, S.; Meyer, F. Inorg.
Chem. 2012, 51, 8141−8149. (p) Yang, E.-C.; Wernsdorfer, W.; Hill,
S.; Edwards, R. S.; Nakano, M.; Maccagnano, S.; Zakharov, L. N.;
Rheingold, A. L.; Christou, G.; Hendrickson, D. N. Polyhedron 2003,
22, 1727−1733.
(22) (a) Costes, J. P.; Dupuis, A.; Laurent, J. P. Inorg. Chim. Acta
1998, 268, 125−130. (b) John, D.; Urland, W. Eur. J. Inorg. Chem.
2006, 3503−3509 and references therein. (c) Avecilla, F.; Platas-
Iglesias, C.; Rodríguez-Cortinas, R.; Guillemot, G.; Bunzli, J. C. G.;
̃
̈
Brondino, C. D.; Geraldes, C. F. G. C.; de Blas, A.; Rodríguez-Blas, T.
J. Chem. Soc., Dalton Trans. 2002, 4658−4665. (d) Long, J.; Habib, F.;
Lin, P.-H.; Korobkov, I.; Enright, G.; Ungur, L.; Wernsdorfer, W.;
Chibotaru, L. F.; Murugesu, M. J. Am. Chem. Soc. 2011, 133, 5319−
5328.
(15) (a) Gao, Y. J.; Xu, G. F.; Zhao, L.; Tang, J.; Liu, Z. L. Inorg.
Chem. 2009, 48, 11495−11497. (b) Ke, H. S.; Gamez, P.; Zhao, L.; Xu,
G. F.; Xue, S. F.; Tang, J. Inorg. Chem. 2010, 49, 7549−7557. (c) Liu,
C.-M.; Zhang, D.-Q.; Hao, X.; Zhu, D.-B. Cryst. Growth Des. 2012, 12,
2948−2954. (d) Chesman, A. S. R.; Turner, D. R.; Moubaraki, B.;
Murray, K. S.; Deacon, G. B.; Batten, S. R. Dalton Trans. 2012, 41,
3751−3757. (e) Savard, D.; Lin, P.-H.; Burchell, T. J.; Korobkov, I.;
(23) Colacio, E.; Ruiz, J.; Mota, A. J.; Palacios, M. A.; Cremades, E.;
Ruiz, E.; White, F. J.; Brechin, E. K. Inorg. Chem. 2012, 51, 5857−
5858.
́
(24) Ruiz, J.; Mota, A. J.; Rodríguez-Dieguez, A.; Titos, S.; Herrera, J.
M.; Ruiz, E.; Cremades, E.; Costes, J. P.; Colacio, E. Chem Commun.
2012, 48, 7916−7918 and references therein.
́
(25) Domingo, N.; Luis, F.; Nakano, M.; Munto, M.; Gomez, J.;
́
Wernsdorfer, W.; Clerac, R.; Murugesu, M. Inorg. Chem. 2009, 48,
Chaboy, J.; Ventosa, N.; Campo, J.; Veciana, J.; Ruiz-Molina, D. Phys.
Rev. B 2009, 79, 214404−214409.
11748−11754. (f) Kong, X.-J.; Long, L.-S.; Zheng, L.-S.; Wang, R.;
Zheng, Z. Inorg. Chem. 2009, 48, 3268−3273. (g) Gerasko, O. A.;
Mainicheva, E. A.; Naumova, M. I.; Yurjeva, O. P.; Alberola, A.; Vicent,
C.; Llusar, R.; Fedin, V. P. Eur. J. Inorg. Chem. 2008, 416−424. (h) Ma,
B.-Q.; Zhang, D.-S.; Gao, S.; Jin, T.-Z.; Yan, C.-H.; Xu, G.-X. Angew.
Chem., Int. Ed. 2000, 39, 3644−3646. (i) Baskar, V.; Roesky, P. W.
Dalton Trans. 2006, 676−679. (j) Zheng, Z. P. Chem. Commun. 2001,
2521−2529. (k) Kong, X. J.; Wu, Y. L.; Long, L. S.; Zheng, L. S.;
Zheng, Z. P. J. Am. Chem. Soc. 2009, 131, 6918−6919.
(26) (a) Long, J.; Habib, F.; Lin, P.-H.; Korobkov, I.; Enright, G.;
Ungur, L.; Wernsdorfer, W.; Chibotaru, L. F.; Murugesu, M. J. Am.
Chem. Soc. 2011, 133, 5319−5328. (b) Rinehart, J. D.; Fang, M.;
Evans, W. J.; Long, J. R. Nat. Chem. 2011, 3, 538−542. (c) Demir, S.;
Zadrozny, J. M.; Nippe, M.; Long, J. R. J. Am. Chem. Soc. 2012, 134,
18546−18549.
(16) Furniss, B. S.; Hannaford, A. J.; Smith, P. W. G.; Tatchell, A. R.
Vogel’s Textbook of Practical Organic Chemistry, 5th ed.; ELBS,
Longman: London, 1989.
(17) (a) Ziessel, R.; Nguyen, P.; Douce, L.; Cesario, M.; Estournes,
C. Org. Lett. 2004, 6, 2865−2868. (b) Artali, R.; Botta, M.; Cavallotti,
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