Decanuclear Ln10 Wheels and Vertex-Shared Spirocyclic Ln5 Cores: Synthesis, Structure, SMM Behavior, and MCE Properties

Article abstract of DOI:10.1002/chem.201501992

The reaction of a Schiff base ligand (LH₃) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln₁₀ (Ln=Dy(1), Tb(2), and Gd (3)) and pentanuclear Ln₅ complexes (Ln=Gd (4), Tb (5), and Dy (6)), respectively. The formation of Ln₁₀ and Ln₅ complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes (1-6) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (U_eff)=16.12(8) K and relaxation time (τ_o)=3.3×10^-5 s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out-of-phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: -ΔS_m=26.6 J kg^-1 K^-1 at T=2.2 K for 3 and -ΔS_m=27.1 J kg^-1 K^-1 at T=2.4 K for 4, both for an applied field change of 7 T. Homometallic complexes: The reaction of a multidentate flexible Schiff base ligand (LH₃; see figure) with [LnCl₃]6 H₂O affords homometallic decanuclear complexes, [Ln₁₀(LH)₁₀(κ²-Piv)₁₀] (Ln=Dy, Tb, and Gd), and homometallic pentanuclear complexes, [Ln₅(LH)₄(μ₂-η¹η¹Piv)₄(η¹Piv)(S)] (Ln=Dy, Tb, and Gd). The Dy³⁺ analogues exhibit single-molecule magnet (SMM) behavior, whereas the Gd³⁺ complexes show a significant magnetocaloric effect (MCE).

Full text of DOI:10.1002/chem.201501992

DOI: 10.1002/chem.201501992
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&
Lanthanide Complexes
Decanuclear Ln10 Wheels and Vertex-Shared Spirocyclic Ln5 Cores:
Synthesis, Structure, SMM Behavior, and MCE Properties**
Sourav Das,[a, b] Atanu Dey,[a] Subrata Kundu,[a] Sourav Biswas,[a]
Ramakirushnan Suriya Narayanan,[c] Silvia Titos-Padilla,[d] Giulia Lorusso,[e]
Marco Evangelisti,[e] Enrique Colacio,*[d] and Vadapalli Chandrasekhar*[a, c]
Abstract: The reaction of a Schiff base ligand (LH3) with lan-
thanide salts, pivalic acid and triethylamine in 1:1:1:3 and
4:5:8:20 stoichiometric ratios results in the formation of dec-
anuclear Ln10 (Ln=Dy(1), Tb(2), and Gd (3)) and pentanu-
clear Ln5 complexes (Ln=Gd (4), Tb (5), and Dy (6)), respec-
tively. The formation of Ln10 and Ln5 complexes are fully gov-
erned by the stoichiometry of the reagents used. Detailed
magnetic studies on these complexes (1–6) have been car-
ried out. Complex 1 shows a SMM behavior with an effective
energy barrier for the reversal of the magnetization (Ueff)=
16.12(8) K and relaxation time (to)=3.3”10À5 s under
4000 Oe direct current (dc) field. Complex 6 shows the fre-
quency dependent maxima in the out-of-phase signal under
zero dc field, without achieving maxima above 2 K. Com-
plexes 3 and 4 show a large magnetocaloric effect with the
following characteristic values: ÀDSm =26.6 JkgÀ1 KÀ1 at T=
2.2 K for 3 and ÀDSm =27.1 JkgÀ1 KÀ1 at T=2.4 K for 4, both
for an applied field change of 7 T.
Introduction
modulation of the nuclearity and topology of such complexes
is an endeavor that is being pursued vigorously by chemists,
whereas the magnetic properties of such complexes (single-
molecule magnetism[2] and magnetocaloric effect[3]) are of in-
terest to chemists and physicists alike. In this context, polynuc-
lear lanthanide complexes where the nuclearity is 5 or 10 are
quite sparse. Our interest in such systems has emanated from
our recent forays in this field in which we have been able, by
utilizing hydrazone Schiff base ligands, to assemble tetra-,[4a,b]
hexa-[4c] and octanuclear[4d] complexes. The latter possessed
a new cyclooctadiene-type of conformation.[4d] We were inter-
ested to extend the nuclearity of the macrocycle through a ju-
dicious choice of a suitable multidentate ligand. Caneschi,
et al. has previously reported a Dy10 macrocycle using methoxy
ethanol as the ligand but only measured its static magnetis-
m.[5a] Since then, other examples, though sparse, are becoming
known. Similar to decanuclear complexes,[5] pentanuclear[6] an-
alogues are equally rare; in fact, only four previous families are
known. It is worth noting that some cyclic Dy3,[7] Dy4,[8] and
Polynuclear lanthanide complexes have caught the imagina-
tion of chemists and physicists in recent years for a variety of
reasons.[1] Discovering new synthetic methods that allow the
[a] Dr. S. Das, Dr. A. Dey, Dr. S. Kundu, S. Biswas, Prof. V. Chandrasekhar
Department of Chemistry
Indian Institute of Technology Kanpur
Kanpur-208016 (India)
E-mail: vc@iitk.ac.in
Homepage: http://www.iitk.ac.in
[b] Dr. S. Das
Department of Emerging Materials Science
DGIST, Daegu 711-873 (Korea)
Homepage: http://www.dgist.ac.kr
[c] Dr. R. S. Narayanan, Prof. V. Chandrasekhar
National Institute of Science Education and Research
Institute of Physics Campus, Sachivalaya Marg
PO: Sainik School, Bhubaneswar - 751 005 (India)
Homepage: http://www.niser.ac.in
[9]
Dy6 complexes have been shown to exhibit a toroidal mag-
[d] Dr. S. Titos-Padilla, Prof. E. Colacio
Departamento de Química Inorgµnica, Facultad de Ciencias
Universidad de Granada, Avenida de Fuentenueva s/n
18071 Granada (Spain)
netic moment in the ground state, which is due to the non-
collinear arrangement of the local magnetic moments of the
individual DyIII centers. Moreover, most of these systems pres-
ent SMM behavior, which is associated with the thermally ex-
cited spin states of the Dyn molecule. These systems, also
called single-molecule toroics (SMTs), are promising candidates
for future applications in quantum computing and information
storage. It should be mentioned that the linkage of two and
even more cyclic Dy3 SMTs give rise to coupled systems in
which the toroidal ground sate is robust because the easy
axial anisotropy axes are very difficult to modify by the interac-
tion between the coupled units.[9,10]
Homepage: http://www.ugr.es
[e] Dr. G. Lorusso, Dr. M. Evangelisti
Instituto de Ciencia de Materiales de Aragón and
Departamento de Física de la Materia Condensada
CSIC-Universidad de Zaragoza, 50009 Zaragoza (Spain)
Homepage: http://molchip.unizar.es/
[**] MCE=Magnetocaloric effect; SMM=Single-molecule magnet.
Supporting information for this article (including molecular structures of 2–
5, details of the structural parameters for compounds 2–5 and magnetic
data) is available on the WWW under http://dx.doi.org/10.1002/
chem.201501992.
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Herein, we report a new chelating, flexible, and sterically un-
encumbered multisite coordinating ligand (E)-2-((2-hydroxy-
ethylimino)methyl)-6-(hydroxymethyl)-4-methylphenol
(LH3),
which allows the assembly of both deca- and pentanuclear lan-
thanide complexes. Most interestingly, both these new families
of polynuclear lanthanide complexes do not contain oxide/hy-
droxide ligands, which are commonly found in many such
complexes. Accordingly, herein, we report the synthesis, struc-
tural characterization, and magnetic studies of [Ln10(LH)10(k2-
Piv)10]·XCHCl3·YCH3CN·PH2O·QMeOH (1, Ln=DyIII, X=9, Y=4;
2, Ln=TbIII, X=8, Y=4; 3, Ln=GdIII, X=8, Y=3, P=5;) and
[Ln5(LH)4(m2-h1h1Piv)4(h1Piv)(S)]·XH2O·YCH3OH (4, Ln=GdIII, S=
MeOH, X=3, Y=1; 5, Ln=TbIII, S=H2O, X=3, Y=2; 6, Ln=
DyIII, S=MeOH, X=2, Y=1). Whereas 1–3 are metallamacrocy-
cles, compounds 4–6 possess a pentanuclear core constructed
by two Ln3 triangles sharing a common lanthanide ion.
Results and Discussion
Synthesis
Recently, we have been experimenting with various types of li-
gands for the purpose of knowing their discriminatory capabili-
ty in terms of directing homonuclear lanthanide assemblies
versus heteronuclear 3d/4f complexes.[11] Thus, the ligands, 2-
(hydroxymethyl)-6-carbaldehyde-4-methylphenol (C2) and the
Schiff base derivative (2-(2-hydroxy-3-(hydroxymethyl)-5-meth-
ylbenzylideneamino)-2-methylpropane1,3-diol) afforded penta-
nuclear M4Ln[11a,b] and M2Ln[11c,d,e] derivatives respectively
(Scheme 1).
Neither of these ligands, however, was able to assemble ho-
monuclear lanthanide complexes. We reasoned that whereas
C2 does not possess enough flexible coordinating pockets, its
Schiff base derivative 2-(2-hydroxy-3-(hydroxymethyl)-5-methyl-
benzylideneamino)-2-methylpropane1,3-diol (Scheme 1b) has
two ÀCH2OH arms fused to the same carbon center making it
a rigid system. Such rigid ligands are generally not suitable for
polynuclear lanthanide complex assembly. To overcome these
drawbacks we have designed a new chelating, flexible, and
sterically unencumbered multisite coordinating compartmental
Schiff base ligand (E)-2-((2-hydroxyethylimino)methyl)-6-(hy-
droxymethyl)-4-methylphenol (LH3). The ligand LH3 was pre-
pared by a two-step synthetic protocol involving the conver-
sion of the precursor C1 to C2 and its subsequent condensa-
tion with 2-amino ethanol (Scheme 2).
Scheme 1. a) Pentanuclear M4Ln[11a,b] and b) trinuclear M2Ln[11c,d,e] derived
from C2 and its Schiff base derivative, respectively.
LH3 contains two coordination compartments; one of these
possesses a phenolic oxygen and a benzyl oxygen atom (che-
lating OO donor). The other compartment consists of a phenol-
ic oxygen and a flexible ethanolamine group (tridentate ONO
donor) (Scheme 3).
Scheme 2. Synthesis of LH3.
Thus, potentially LH3 contains four divergent coordinating
centers all of which are anticipated to participate in coordina-
tion to construct a homometallic ensemble. Also, we are aware
that the ÀCH2OH unit can bind both in its native and depro-
tonated forms. In the latter it can act as a bridging ligand and
enable formation of larger polynuclear complexes. In this syn-
thesis we also utilized pivalic acid as a co-ligand because of
the propensity of the pivalate ion to bridge adjacent metal
centers.[12,4b,d] Treatment of LH3 with LnIII salts along with pival-
ic acid in the presence of triethylamine under two different
conditions afforded deca- (1–3) and pentanuclear complexes
(4–6) (Scheme 4).
A subtle variation in stoichiometry, including that of the
base triethylamine, causes an interesting deprotonation behav-
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ior. Thus, in the decanuclear com-
plexes, 1–3, the =NÀCH2CH2OH is
deprotonated whereas the
À
CH2OH arm is not. In the case of
the pentanuclear complexes the
situation is reversed. The molecular
structures of 1–6 were delineated
by their single-crystal diffraction
studies as outlined below.
Scheme 3. The two distinct
coordination compartments
of LH3. Site 1 contains a chelat-
ing OO coordination manifold
whereas Site 2 provides ONO
cavity.
X-ray crystal structures of 1–3
Figure 1. a) Molecular structure of 1 (hydrogen atoms and the solvent mole-
cules have been omitted for clarity). b) The Dy10 metallacycle possessing
a chair–chair–chair conformation.
Single-crystal X-ray analysis reveals
that 1–3 crystallize in the triclinic
¯
system in the centrosymmetric P1
space group with Z=2. The asym-
metric unit of 1–3 consists of two half molecules, that is,
[Ln5(LH)5(Piv)5] in which Ln=Dy (1), Tb (2), and Gd (3). Because
of the structural similarity of 1–3, only the structure of 1 is de-
scribed, here, in detail. The others are given in the Supporting
Information.
The crystal structure of 1 (Fig-
ure 1a) reveals it to be a macrocy-
cle that is assembled as a result of
the cumulative coordination action
of ten [LH]2À ligands, each of
The molecular structure of 1 is given in Figure 1; those of 2
and 3 are given in the Supporting Information (Figures S1 and
S2). Selected bond parameters of 1 are summarized in the
Table 1. Other bond parameters including those of 2 and 3 are
given in the Supporting Information (the Supporting Informa-
tion, Tables S1 and S2).
which binds in a
m3-h2:h1:h2:h1
fashion (Scheme 5). In addition to
[LH]2À, ten pivalate ions participate
in coordination, each of which
being involved in binding to only
one DyIII ion. Most interestingly,
Scheme 5. Binding mode of
the ligand [LH]2À with DyIII
ions.
compound 1 does not contain
any other common ligands such
as oxide or hydroxide, which are
generally found in polynuclear
lanthanide complexes.
An analysis of the molecular
structure of 1 reveals that the
macrocycle contains intercon-
nected Dy2O2 four-membered
rings possessing spirocyclic DyIII
nodes. The macrocycle itself is
20-membered, considering the
shortest DyÀOÀDy pathway. The
DyIII ions organize themselves in
the complex in a chair–chair–
chair conformation (Figure 1b).
The assembly of the macrocy-
cle 1 is accomplished in the fol-
lowing manner. The four-mem-
bered non-planar Dy2O2 ring is
built by the coordination action
of bridging phenolate and
=NCH2CH2OÀ that emanate from
two different ligands. The inter-
DyIII distances and the DyÀOÀDy
angles in the four-membered
rings are in the range 3.797–
3.831 Š
and
105.60
(2)–
Scheme 4. Synthesis of the homometallic Ln10 macrocyclic complexes 1–3 in which the deprotonated oxygen
atom of ethanolamine acts as a bridging group in LH3 (left side); synthesis of the homometallic Ln5 complexes
where the deprotonated benzylic oxygen atom acts as capping m3-O unit (right side).
114.85(1)8 respectively. All the
DyIII centers are eight-coordinate
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other example of decanuclear
complexes {Ln10} (Ln=Dy or Gd)
reveals that nine DyIII metal ions
are present in a ring whereas
a tenth DyIII metal ion is located
at the center of the structure.[5b]
Finally, another Dy10 ensemble is
known containing vertex-fused
Dy3 triangles[5c] (Figure 3).
Table 1. Selected bond length [Š] and bond angle [8] parameters for 1.[a]
Dy(1P)-O(13P)[a]
Dy(1P)-O(1P)
Dy(1P)-O(2P)
Dy(1P)-O(6P)
Dy(1P)-O(5P)
Dy(1P)-O(17P)
Dy(1P)-O(16P)
Dy(1P)-N(1P)
Dy(1P)-Dy(5P)[a]
Dy(2P)-O(1P)
Dy(2P)-O(4P)
Dy(2P)-O(5P)
Dy(2P)-O(9P)
Dy(2P)-O(8P)
Dy(2P)-O(19P)
Dy(2P)-N(2P)
2.237(4)
2.294(4)
2.386(4)
2.402(4)
2.438(4)
2.454(4)
2.459(4)
2.466(5)
3.8107(4)
2.247(4)
2.303(4)
2.356(4)
2.397(4)
2.424(4)
2.438(5)
2.468(5)
Dy(2P)-O(18P)
Dy(3P)-O(4P)
Dy(3P)-O(7P)
Dy(3P)-O(8P)
Dy(3P)-O(12P)
Dy(3P)-O(11P)
Dy(3P)-N(3P)
Dy(3P)-O(21P)
Dy(3P)-O(20P)
Dy(4P)-O(7P)
Dy(4P)-O(10P)
Dy(4P)-O(11P)
Dy(4P)-O(15P)
Dy(4P)-O(14P)
Dy(4P)-O(23P)
Dy(4P)-N(4P)
Dy(4P)-O(22P)
2.474(4)
2.237(4)
2.300(4)
2.363(4)
2.395(4)
2.431(4)
2.447(5)
2.462(4)
2.498(4)
2.232(4)
2.303(4)
2.371(4)
2.380(4)
2.418(4)
2.447(4)
2.464(5)
2.508(4)
Dy(5P)-O(14P)
Dy(5P)-O(14P)
Dy(5P)-O(3P)
Dy(5P)-O(2P)*
Dy(5P)-N(5P)
Dy(5P)-O(24P)
Dy(5P)-O(25P)
Dy(4P)-C(71P)
2.376(4)
2.376(4)
2.414(4)
2.420(4)
2.455(5)
2.462(4)
2.467(4)
2.849(6)
Dy(5P)-O(10P)
Dy(5P)-O(13P)
2.242(4)
2.304(4)
Dy(2P)-O(1P)-Dy(1P)
Dy(1P)-O(2P)-Dy(5P)*
Dy(3P)-O(4P)-Dy(2P)
Dy(2P)-O(5P)-Dy(1P)
Dy(4P)-O(7P)-Dy(3P)
Dy(3P)-O(8P)-Dy(2P)
Dy(5P)-O(10P)-Dy(4P)
Dy(4P)-O(11P)-Dy(3P)
Dy(1P)*-O(13P)-Dy(5P)
Dy(5P)-O(14P)-Dy(4P)
114.61(17)
104.91(15)
113.53(16)
105.70(15)
114.85(19)
104.97(14)
114.63(16)
105.33(15)
114.10(16)
105.85(14)
X-ray crystal structures of 4–6
X-ray crystallographic analysis of
4–6 reveals that all these com-
plexes crystallize in the mono-
clinic system in the P21 chiral
space group with Z=2. Com-
pounds 4–6 are neutral and pos-
sess a nearly similar structural ar-
rangement with only minor
[a] Symmetry transformations used to generate equivalent atoms: 1Àx+1, Ày+1, Àz+1.
Figure 2. a) Twenty-membered macrocyclic core. b) A distorted-triangular
dodecahedral geometry around the DyIII ion.
(7O, 1N) and possess a distorted-triangular dodecahedral ge-
ometry (Figure 2b).
A few further comments on the molecular structure of 1.
With respect to the mean plane (considering all the Dy atoms)
of the macrocycle, alternate Dy atoms lie above and below
(average 0.578 (7) Š) the plane (Figure 2a). Interestingly, each
LH2À alternately is placed above and below the plane of the
Dy10 wheel. Complex 1 displays strong intramolecular OÀH···O
(2.187 (6) Š) hydrogen-bonding interactions between the pival-
ic carboxylate oxygen atoms and the Dy-coordinated benzyl al-
cohol (ÀCH2OH) arms (Figure 1a). The supramolecular structure
of 1 reveals a 2D architecture, in which a chloroform channel is
found where the trapped chloroform molecules are stabilized
by hydrogen-bonding interactions (Supporting Information,
Figures S3 and S4). An idea about the macrocyclic ring size of
1 can be obtained from the distances between the symmetry
equivalent Dy atoms, which are in the range 11.696 (6) to
11.976 (7) Š.
Figure 3. Examples of reported discrete decanuclear lanthanide complexes.
structural variations (Scheme 4 and Supporting Information).
The asymmetric unit of 4–6 consists of a full molecule
[Ln5(LH)4(m2-h1h1Piv)4(h1Piv)(MeOH/H2O)]. The refined Flack pa-
rameters of 4–6 are 0.010(13), À0.003(10), and 0.013(11), re-
spectively, indicating the crystallization of enantiopure forms.
In view of their structural similarity, we describe, herein, the
molecular structure of 6 as a representative example; the
structural details of 4 and 5 are given in the Supporting Infor-
mation (Figures S5 and S6). A perspective view of the molecu-
lar structure of 6 is depicted in Figure 4. The caption of Fig-
In spite of the large interest in 4f complexes, surprisingly,
only a few Ln10 complexes are known in literature. As men-
tioned earlier, in 2003 Caneschi and co-workers first reported
a Dy10 wheel containing methoxyethanol as a bridging ligan-
d.[5a] The molecular topology of 1 is similar to this literature
precedent although the ligands used are entirely different. An-
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Figure 4. Molecular structure of 6 (hydrogen atoms and the solvent mole-
cules have been omitted for clarity). Selected bond lengths [Š] and bond
angle [o] parameters are as follows: Dy(1)-O(2)=2.343(7); Dy(1)-
O(6)=2.382(7); Dy(1)-O(9)=2.396(7); Dy(1)-N(1)=2.452(10); Dy(1)-
O(1)=2.516(8); Dy(2)-O(5)=2.317(6); Dy(2)-O(12)=2.404(6); Dy(2)-
N(2)=2.433(8); Dy(2)-O(3)=2.460(7); Dy(2)-O(4)=2.513(8); Dy(3)-
O(8)=2.367(6); Dy(3)-O(3)=2.425(6); Dy(3)-N(3)=2.437(8); Dy(3)-
O(12)=2.456(6); Dy(3)-O(7)=2.535(7); Dy(4)-O(11)=2.327(7); Dy(4)-
O(6)=2.445(7); Dy(4)-N(4)=2.451(9); Dy(4)-O(9)=2.460(7); Dy(4)-
O(10)=2.474(8); Dy(5)-O(3)=2.300(6); Dy(5)-O(9)=2.302(7); Dy(5)-
O(12)=2.313(6); Dy(5)-O(6)=2.330(6); Dy(5)-O(5)=2.366(6); Dy(5)-
O(11)=2.368(6); Dy(5)-O(8)=2.377(6); Dy(5)-O(2)=2.399(7); Dy(5)-O(3)-
Dy(3)=97.06(2); Dy(3)-O(3)-Dy(2)=97.07(2); Dy(5)-O(3)-Dy(2)=96.16(2);
Dy(2)-O(5)-Dy(5)=98.33(2); Dy(5)-O(6)-Dy(1)=97.41(2); Dy(5)-O(6)-
Dy(4)=95.79(2); Dy(1)-O(6)-Dy(4)=98.17(3); Dy(3)-O(8)-Dy(5)=96.53(2);
Dy(5)-O(9)-Dy(1)=97.74(3); Dy(5)-O(9)-Dy(4)=96.10(3); Dy(1)-O(9)-
Dy(4)=97.32(2); Dy(4)-O(11)-Dy(5)=98.02(2); Dy(5)-O(12)-Dy(2)=97.28(2);
Dy(5)-O(12)-Dy(3)=95.74(2); Dy(2)-O(12)-Dy(3)=97.66(2).
Figure 5. a) Vertex-fused triangular unit capped by two m3-O alkoxy group
from above or below face of the triangle. Intermetallic distances [Š] and
angles [8]: Dy2-Dy3=3.658(12); Dy2-Dy5=3.541(9); Dy3-Dy5=3.540(12);
Dy5-Dy4=3.542(9); Dy1-Dy4=3.648(8); Dy5-Dy1=3.539(13); Dy2-Dy3-
Dy5=58.91(1); Dy5-Dy2-Dy3=62.21(2); Dy3-Dy2-Dy5=58.87(1); Dy5-Dy4-
Dy1=58.94(1); Dy4-Dy5-Dy1=60.02(2); Dy5-Dy1-Dy4=59.09(2); b) Non-
planar disposition of the vertex fused triangular unit.
separate ligands. The m2-O phenolate oxygen atoms bridge the
edges of the triangles. In addition to the binding provided by
LH2À, the peripheral DyIII ions are further held together as
a result of two m2-h1:h1 binding action of the pivalate anions.
Finally, to satisfy the charge and coordination requirements,
other pivalate anions coordinate the terminal DyIII ions in
a monodentate fashion.
As mentioned above, the pentanuclear Dy5 core consists of
two interconnected Dy3 motifs. The dihedral angle between
these two is 60.78(2)8. In addition, the central dysprosium ion
(Dy5) is part of six Dy2O2 four-membered rings (Figure 5b).
Finally, the central DyIII in 6 is eight-coordinated in an all-
oxygen coordination environment and in a distorted-triangular
dodecahedral geometry (Figure 6a). In contrast, the peripheral
DyIII ions, although also eight-coordinate, possess a different
coordination environment (7O,1N) and geometry (distorted
square antiprism geometry) (Figure 6b).
ures 4 and 5a summarizes the selected bond parameters of 6.
The molecular structures and selected bond parameters of the
other two compounds (4 and 5) are given in the Supporting
Information (Figure S5 and S6, Tables S3–S4).
The molecular structure of 6 reveals that the five DyIII ions
are held together by four doubly deprotonated [LH]2À hepta-
dentate Schiff base ligands. Each such ligand holds four differ-
ent DyIII ions in a m4-h3:h2:h1:h1 fashion (Scheme 6).
Each ligand provides one benzyl alcoholic m3-oxygen atom,
one phenolic m2-oxygen, and one unidentate flexible chelating
ethanolamine group (bidentate NO donor) (Scheme 6). Further
analysis of the structure of 6 re-
Interestingly, again, it is surprising to note that only a handful
of Ln5 complexes[6] whose magnetic behavior has been well-
studied are known in the literature. Some of these are sum-
marized in Figure 7, revealing that three structural types are
thus far known, that is, square-pyramidal,[6a–c] trigonal bipyra-
midal[6d] and butterfly-shaped.[6e] The current family, thus repre-
sents a new structural type among pentanuclear Ln5 com-
plexes. Again, similar to the decanuclear complexes, the penta-
nuclear complexes reported herein do not contain O2À/OHÀ li-
gands.
veals some interesting features.
Compound 6 contains a pentanu-
clear [Dy5(m3-O)4(m2-O)4]+7 core con-
sisting of triangular motifs [Dy3(m3-
O)2(m2-O)2]+5 that are fused with
each other through a common
vertex (Dy5) (Figure 5). Each trian-
gular unit is capped by two m3-O
Scheme 6. Binding mode of
the ligand [LH]2À with DyIII
ions.
deprotonated
benzyl
alcohol
oxygen atoms derived from two
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Figure 6. Different geometries around octa-coordinated DyIII ions: a) Distort-
ed-triangular dodecahedral and b) distorted square-antiprism geometry.
Figure 8. Temperature dependence of the cMT product for complexes 1–6.
The black solid lines show the best fits for complexes 3 and 4.
300–2 K were measured in an applied magnetic field of 0.1 T
(Figure 8).
The room temperature cMT values for complexes 1–6 are
close to those calculated for isolated LnIII ions in the free-ion
approximation (Table 2).
We start with the simpler cases concerning the Gd com-
plexes 3 and 4. On cooling, the cMT product for 3 and 4 re-
mains almost constant until ꢀ75 and 100 K, respectively, and
then it decreases sharply down to 2 K. Because Gd3+ ions pres-
ent no first order spin–orbit coupling, the decrease of the cMT
product at low temperature is mainly due to the presence of
a very weak antiferromagnetic interaction between the Gd3+
ions and/or zero-field splitting (ZFS) effects of the ground
state. This is supported by the field dependence of the mag-
netization at 2 K for 3 and 4, which are well below the Brillouin
function for ten and five non-interacting Gd3+ ions, respective-
ly (Figure 9). At high field the saturation of the magnetization
Figure 9. Field dependence of the magnetization for complexes 1–6 at 2 K.
The black solid lines represent the Brillouin function for non-interacting
Gd3+ ions.
is almost complete at 5 T, reaching values that agree well with
the theoretical saturation values for ten and five Gd3+ ions, re-
spectively.
The magnitude of the antiferromagnetic exchange interac-
tion in 3 could not be determined by diagonalization matrix
methods because of the extremely high dimension of the ma-
trices to be diagonalized for a Gd10 system. Nevertheless, to es-
timate the value of the magnetic exchange coupling mediated
by the m-alkoxido/m-phenoxido pathway in 3 we have used
a very crude model, in which each wheel has been considered
to be formed by ten mononuclear Gd units and the intermo-
nonuclear interactions calculated by using the molecular field
Figure 7. Examples of reported discrete pentanuclear lanthanide com-
plexes[6] having a) square pyramidal, b) trigonal bipyramidal, and c) butterfly
core.
Magnetothermal properties
The temperature dependence of cMT for complexes 1–6 (cM is
the molar magnetic susceptibility per Lnn unit) in the range
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dialkoxo and diphenoxo-bridged
Gd3+ complexes, with or without
carboxylate bridges connecting
the Gd3+ ions.[13] The structural
differences between the Gd2O2
bridging fragments involving
short and long Gd···Gd distances
could be responsible for the dif-
ferent magnetic coupling of the
two magnetic pathways. In this
regard, theoretical and experi-
mental studies carried out on
oxygen-bridged Gd2 complexes
Table 2. Direct current magnetic data for 1–6.
Compound
Spin-orbit ground
state of the Ln3+ ion
cMT theoretical[a]/at 300 K/
at 2 K [cm3 KmolÀ1
Calculated saturation value[b]
/
M at 2 K and 5 T [NmB]
]
1
6
3
4
2
5
6H15/2, gJ =4/3
6H15/2, gJ =4/3
8S7/2, gJ =2
141.7/141.30/99.19
70.85/74.17/34.99
78.75/82.12/41.56
39.375/40.77/22.67
118.2/123.80/64.64
59.10/64.65/17.09
100/55.54
50/30.59
35/34.40
70.0/70.64
90/50.12
45/27.43
8S7/2, gJ =2
7F6, gJ =3/2
7F6, gJ =3/2
n
Nb2
3k
3
ST ðST þ1ÞÀLðLþ1Þ
.
2JðJþ1Þ
[a] Calculated with cMT ¼
g2j JðJ þ 1Þg; [b] Calculated with M ¼ NgJJmB; J ¼ L þ S; gJ ¼ 2 þ
theory. Taking into account the above considerations, the ex-
perimental data were analyzed with the following Hamiltonian:
X
0
^
^
^
i Si
H ¼ zJ < Sz > Sz þ gibH
The best fitting parameters were zJ’=À0.0127(1) cmÀ1 and
g=2.054(1). Although the obtained values are similar to the re-
ported coupling constants for dialkoxo- and diphenoxo-
bridged Gd3+ complexes, with or without carboxylate bridges
connecting the Gd3+ ions,[13] they should be taken with cau-
tion because of 1) the crudeness of the model and 2) the pos-
sible existence of ZFS splitting of the Gd3+ ions.
Figure 10. Coupling scheme for complex 4.
As indicated above, compound 4 exhibits a structure that
consists of two vertex fused triangles with two different types
of bridging units between the Gd3+ ions: i) Di-m3-dialkoxido/m-
phenoxido, linking the central Gd3+ ion to the outer counter-
parts with GdÀGd distances of approximately 3.540 Š, and
ii) di-m3-dialkoxido/di-m-syn-syn pivalato connecting each
couple of outer Gd3+ ions with GdÀGd distances of approxi-
mately 3.650 Š. Although the GdÀGd distances slightly differ
between the two fused triangles, to analyze the magnetic
properties the four GdÀGd distances corresponding to the
type (i) bridging fragments were considered to be all equal.
Likewise, the two outer type (ii) distances were considered to
be equal. Taking into account the above considerations, the
magnetic properties of 4 were modeled using the following
two-J isotropic Hamiltonian:
(alkoxido, phenoxido, and carboxylate) complexes have sug-
gested that J becomes more negative as the GdÀOÀGd, and
consequently the Gd···Gd, decrease.[13a,f] The extracted J values
for 3 and 4 agree well with this hypothesis as the former,
which has larger GdÀOÀGd angles and GdÀGd distances, ex-
hibits the weaker GdÀGd magnetic exchange interactions. In 4,
the shorter di-m3-dialkoxido/m-phenoxido magnetic exchange
pathway, linking the central and outer Gd3+ ions exhibits the
stronger magnetic exchange coupling, whereas the long di-m3-
dialkoxido/di-m-syn-syn pivalato pathway shows
a much
weaker magnetic coupling, as expected. Nevertheless, more
examples of well magneto-structural characterized oxygen-
bridged Gdn complexes are needed to confirm the above as-
sumption.
We have studied the magnetothermal properties of 3 and 4
because 1) the magnetic interactions between the Gd3+ ions
are relatively weak for both compounds; 2) the Gd3+ ion
shows negligible anisotropy due to the absence of orbital con-
^
^
^
^
^
^
^
^
^
H ¼ ÀJ1ðSGd1SGd5 þ SGd2SGd5 þ SGd3SGd5 þ SGd4SGd5ÞÀ
^
^
^
^
J2ðSGd1SGd4 þ SGd2SGd3
Þ
tribution; 3) the Gd3+ exhibits the largest single-ion spin (SGd
=
in which J1 and J2 describe the magnetic exchange pathways
involving short and long Gd···Gd distances, respectively (Fig-
ures 5 and 10).
7/2) arising from the 4f7 electron configuration. These charac-
teristics are known to favor a large MCE,[3a] that is, the change
of the magnetic entropy (DSm) following a change of the ap-
plied field. The entropy changes that characterize 3 and 4 can
be calculated straightforwardly from the experimental heat ca-
pacity, C, (the Supporting Information, Figure S7) after obtain-
ing the entropy according to the following expression:
The DGd is assumed negligible, because this ion is rather iso-
tropic. The simultaneous fit of the experimental magnetization
and susceptibility data with the above Hamiltonian using the
PHI program[14] afforded the following set of parameters: J1 =
À0.15 cmÀ1, J2 =À0.072 cmÀ1 and g=2.04 with R=5”10À5
(R=S(cobsT ccalcT)2/S(cobsT)2), in which ccalc and cobs denote cal-
culated and observed molar magnetic susceptibilities, respec-
tively. As in the case of compound 3, the obtained values are
in good agreement with the reported coupling constants for
T
Z
CðT; BÞ
SðT; BÞ ¼
dT
T
0
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Likewise, DSm can also be calculated from the magnetization
data (the Supporting Information, Figure S9) by making use of
the Maxwell relation:
As for the Dy3+ (1 and 6) and Tb3+ (2 and 5) complexes, the
cMT product steadily decreases down to 2 K, which is due to
the depopulation of the excited mj sublevels of the Dy3+ and
6
Tb3+ ions. This behavior arises from the splitting of the H15/2
7
and F6 ground terms, respectively, by the ligand field, and/or
Bf
ꢀ
ꢁ
Z
possible very weak intermolecular interactions between the
Ln3+ ions.
@MðT; BÞ
DSm ¼ ðT; DBÞ ¼
dB
dT
B
The field dependence of the magnetization for the Dy3+ and
Tb3+ complexes is given in Figure 10. The M versus H plot at
2 K for these complexes shows a relatively rapid increase in
the magnetization at low field to reach almost the saturation
for magnetic fields of 5 T. The observed values at 5 T are rather
lower than expected, which is due to crystal-field effects lead-
ing to significant magnetic anisotropy.[16]
Bi
in which Bi and Bf are the initial and final applied magnetic
fields. Figure 11 shows the dependence of ÀDSm on tempera-
Dy3+ complexes are good candidates to exhibit SMM behav-
ior because: 1) Dy3+ is a Kramers ion and therefore the ground
6
state bistability is guaranteed; 2) it has a large moment H15/2
spin orbit ground component, and 3) the f electronic cloud is
largely anisotropic with an oblate shape, which can be stabi-
lized by an axial crystal field that minimizes the repulsive inter-
actions between the ligands and f-electron charge cloud.[17] Be-
cause the axial ligand field can be easily attained by serendipi-
ty in low symmetry Dy3+ complexes, easy-axis anisotropy of
the ground state and consequently SMM behavior is often ob-
served for these complexes. In view of the above considera-
tions, the low symmetry DyO7N and DyO8 coordination envi-
ronments observed for 1 and 6 could lead to SMM behavior.
To know if compounds containing Dy3+ (1 and 6) and Tb3+ (2
and 5) exhibit slow relaxation of the magnetization and SMM
behavior, alternating current (ac) magnetic susceptibility meas-
urements as a function of the temperature and frequency
were performed under zero and with small applied magnetic
dc fields. The results of these measurements demonstrate that
only compound 6 exhibits frequency dependence of the out-
of-phase (c“M) signals under zero dc field and therefore slow
relaxation and probably SMM behavior (Figure 12).
However, no maxima are observed in the temperature de-
pendence of c’’M above 2 K at frequencies reaching 1500 Hz,
which does not allow us to extract the value of the thermal ac-
Figure 11. The dependence of the magnetic entropy change on temperature
and selected applied field changes, for 3 (a) and 4 (b), as obtained from
heat capacity and magnetization data.
ture and applied field changes for both compounds. Note the
nice agreement between the results obtained through both
methods, thus validating the approaches employed. For the
largest applied field change DB=7 T, the maximum value of
ÀDSm is 26.6 JkgÀ1 KÀ1 at T=2.2 K for 3 and 27.1 JkgÀ1 KÀ1 at
T=2.4 K for 4. Under our experimental conditions, the weak
though not negligible antiferromagnetic interactions between
the Gd3+ ions inhibit ÀDSm(T,DB) to attain the maximum en-
tropy value per mole involved, that is, nRln(2SGd +1)=20.8 R=
29.7 JkgÀ1 KÀ1 for 3 and 10.4 R=35.4 JkgÀ1 KÀ1 for 4. Finally,
the so-obtained ÀDSm values for DB=7 T are similar to those
found for other Gd5 and Gd10 complexes, but lower than those
found for other magnetically denser Gdn polynuclear com-
plexes.[15] The results for 3 and 4 suggest that these systems
can be used as molecular magnetic refrigerants.
Figure 12. In-phase (c’M) and out-of-phase (c’’M) signals under zero dc field
for 6.
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tivated energy barrier for the relaxation of the magnetization.
When the ac measurements were performed in the presence
of a small external dc field in the range 1000–4000 Oe, to fully
or partly suppress the possible fast quantum tunneling relaxa-
tion, the temperature dependence of c’’M for 6 did not signifi-
cantly change with field. However, compound 1 shows a clear
frequency dependence the out-of-phase (c“M) signals below
ꢀ10 K under a Hdc =2000 Oe, typical of thermally activated re-
laxation process (the Supporting Information, Figure S9). The
c”M signals are broad with maxima in the 6.75 (1488 Hz)–5.22 K
(280 Hz) range and a tail below ꢀ4 K (c“M does not go to zero
below the maxima but increases up to 2 K). This can be attrib-
uted to overlapping of different relaxation processes, including
a faster quantum tunneling relaxation, which is responsible of
the low temperature tail. The presence of five crystallographi-
cally independent Dy3+ ions in the structure with very close
DyO8 coordination environments could be responsible for the
existence of different overlapping thermally activated relaxa-
tion processes. It is worth noting that even two single-ion re-
laxation processes have been observed for complexes contain-
ing crystallographically equivalent Dy3+ sites.[16] At Hdc =0.4 T
the quantum tunneling of magnetization (QTM) is almost sup-
pressed (the tail at low temperature almost disappears) and
the high temperature peaks remain roughly at the same tem-
peratures as those observed under 0.2 T dc applied field but
exhibit lower intensity (Figure 13). The fact that magnetic fields
existence of a broad distribution of relaxation times. The fit of
the frequency dependence of c“M at each temperature to the
generalized Debye model allowed us to extract the relaxation
time t at different temperatures. The results were then used to
construct the Arrhenius plot shown in Figure 13. The linear fit
of the data (t vs. 1/T) afforded an effective energy barrier for
the reversal of the magnetization of 16.12(8) K with to =3.3”
10À5 s. The to value is still larger than that usually observed for
pure thermally activated processes (typical values are found in
the 10À7–10À10 s range), thus supporting that the QTM has not
been fully suppressed after the application of a dc field of
0.4 T, which could be due to hyperfine and intermolecular in-
teractions. It is worth mentioning that the extracted to value
for 1 is similar to the values previously reported for a large
number of Dy clusters in the same temperature range.[12c,18]
The fast relaxation of the magnetization observed for com-
pounds 1 and 6, even in the presence of applied magnetic
field, could be due to quantum tunneling leading to apparent-
ly lower Ueff values. It has been recently proposed from theo-
retical and experimental studies on a dinuclear Dy2 complex[19]
that Dy···Dy intramolecular magnetic exchange interactions in
polymetallic Dy3+ complexes have the effect of quenching the
SMM behavior when the anisotropic axis of the Dy3+ ions are
not parallel. In complex 1 with a Dy10 wheel structure, as well
as in compound 6, whose structure is made of two vertex-shar-
ing Dy3 triangles turned away from each other, in principle, the
principal anisotropic axes could not be parallel and therefore
the Ln···Ln interactions could reduce the barrier to magnetiza-
tion reversal.
Although the DyIII ions in 1 are not strictly in the same plane
(they are located alternatively 0.57 Š above and below the
plane), the structure is centrosymmetric and, therefore, the ani-
sotropic axes on opposite Dy centers, if they exist, would be
parallel but having opposite senses. This result, together with
the antiferromagnetic interaction between the DyIII ions, might
generate a net quasi-toroidal moment for the projections of
the local magnetic moments on to the plane of the wheel. Ab
initio calculations are planned for the near future to determine
if compound 1 is a SMT.
Conclusion
The present work describes the synthesis, structures, and mag-
netic properties of decanuclear Ln10 as well as pentanuclear
Ln5 complexes by using a multisite coordination ligand (LH3).
The formation of Ln10 and Ln5 complexes are fully governed by
the stoichiometry of the regents used. The dynamic magnetic
studies for complex 1 show the SMM behavior with the follow-
ing characteristics: Ueff =16.12(8) K and to =3.3”10À5 s under
0.4 T dc field. However, complex 6 shows the frequency de-
pendent maxima in the out-of-phase signal under zero dc
field, without achieving maxima above 2 K. Complexes 3 and 4
show a significant magnetocaloric effect with the following
characteristic values: ÀDSm =26.6 JkgÀ1 KÀ1 at T=2.2 K for 3
and ÀDSm =27.1 JkgÀ1 KÀ1 at T=2.4 K for 4, both for an ap-
plied field change of 7 T.
Figure 13. In-phase (c’M) and out-of-phase (c“M) signals under 0.4 T dc field
and Arrhenius plot for 1.
as high as 0.4 T are not able to fully eliminate the QTM relaxa-
tion process suggests that the remaining QTM process has its
origin in hyperfine and intramolecular/intermolecular magnetic
interactions.
The Cole–Cole diagram in the temperature range 4.8 K (the
Supporting Information, Figure S10) exhibits semicircular
shapes that can be fitted using the generalized Debye model.
This affords a values in the range 0.55–0.64, which support the
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Experimental Section
Table 3. Crystal data and structure refinement parameters of 1–3.
Reagents and general procedures
1
2
3
Solvents and other general reagents used in this work
were purified according to standard procedures.[20] 2,6-
Bis(hydroxymethyl)-4-methylphenol, activated manga-
nese (IV) dioxide (MnO2), [DyCl3]·6H2O, [TbCl3]·6H2O,
[HoCl3]·6H2O, and [GdCl3]·6H2O were obtained from
Sigma Aldrich Chemical Co. and were used as received.
2-Amino ethanol and sodium sulfate (anhydrous) were
obtained from S.D. Fine Chemicals, Mumbai, India, and
were used as received. 2-(Hydroxymethyl)-6-carbalde-
hyde-4-methylphenol was prepared according to a litera-
ture procedure.[11a]
formula
MgÀ1
crystal system
space group
a [Š]
b [Š]
c [Š]
a [8]
b [8]
C177H241Cl27Dy10N14O50 C176H240Cl24N14O50Tb1 C176H240Cl24Gd10N14O53
5946.99
triclinic
5791.82
triclinic
5823.11
triclinic
¯
P1
¯
P1
¯
P1
22.0177(11)
23.0226(11)
24.8075(12)
63.2250(10)
83.5980(10)
82.6300(10)
11113.5(9)
2
22.0256(15)
23.0524(15)
24.7831(17)
63.3580(10)
83.503(2)
82.659(2)
11133.1(13)
2
22.112(2)
23.103(2)
24.886(2)
63.227(2)
83.387(2)
82.508(2)
11 230.6(19)
2
g [8]
V [Š3]
Z
1c [gcmÀ3
]
1.777
1.728
1.722
m [mmÀ1
F(000)
]
3.714
3.491
3.267
Instrumentation
5840
5704
5732
cryst size [mm3]
q range [deg]
limiting indices
0.067”0.043”0.033 0.035”0.021”0.016 0.035”0.026”0.016
Melting points were measured using a JSGW melting
point apparatus and are uncorrected. IR spectra were re-
corded as KBr pellets on a Bruker Vector 22 FT IR spec-
trophotometer operating at 400–4000 cmÀ1. Elemental
analyses of the compounds were obtained from Thermo-
quest CE instruments CHNS-O, EA/110 model.
2.00 to 25.50
À26< =h< =24
À27< =k< =27
À30< =l< =29
80704
4.08 to 25.03
À26< =h< =25
À25< =k< =27
À29< =l< =29
74945
4.09 to 19.55
À20< =h< =20
À21< =k< =18
À23< =l< =22
40633
reflns collected
independent reflns 41251[R(int)=0.0326] 38974
[R(int)=0.0572]
99.1
19255 [Rint =0.0581,
R
sigma =0.0799]
completeness to q 99.7
98.8
Magnetic measurements
[%]
refinement
method
data/restraints/pa- 41251/44/2575
rameters
goodness-of-fit on 1.016
F2
final R indices
[I>2q(I)]
R indices (all data) R1 =0.0572,
wR2 =0.0914
largest diff. peak
and hole [eŠ
full-matrix-block
least-squares on F2
full-matrix-block
full-matrix-block
Field dependence of the magnetization at different tem-
peratures 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. Alter-
nating 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 torque-
ing of the microcrystals.
least-squares on F2 least-squares on F2
38974/46/2526
1.025
19255/606/2556
1.044
R1 =0.0368,
wR2 =0.0832
R1 =0.0576,
wR2 =0.1360
R1 =0.0904,
wR2 =0.153
4.830 and À1.694
R1 =0.0590,
wR2 =0.1591
R1 =0.0742,
wR2 =0.1719
4.22 and À1.32
3.602 and À1.606
À3
]
and their positions were refined by a riding model. All non-hydro-
gen atoms were refined with anisotropic displacement parameters.
Non-positive definite atoms present in compound 3 were treated
with ISOR restraints and refined using the Olex-2 software.[21f] The
crystallographic figures have been generated using Diamond 3.1e
software.[21g] The crystal data and the cell parameters for com-
pounds 1–6 are summarized in Tables 3 and 4. CCDC 1401022 (1),
1401023 (2), 1401024 (3), 1401025 (4), 1401026 (5), and
1401027 (6) contain the supplementary crystallographic data for
this paper. These data are provided free of charge by The Cam-
bridge Crystallographic Data Centre.
Heat capacity measurements
The heat capacity measurements for 3 and 4 were carried out for
temperatures down to 0.3 K by using a Quantum Design 9T-PPMS,
3
equipped with a He cryostat. The experiments were performed on
thin pressed pellets (ca. 1 mg) of a polycrystalline sample, thermal-
ized by about 0.2 mg of Apiezon N grease, whose contribution
was subtracted by using a phenomenonological expression.
X-ray crystallography
Single crystals of 1–6 were coated with light hydrocarbon oil and
mounted in the 100 K dinitrogen stream of a Bruker SMART APEX
CCD diffractometer equipped with a CRYO Industries low-tempera-
ture apparatus and intensity data were collected using graphite-
monochromated MoKa radiation (l=0.71073 Š). The program
SMART[21a] was used for collecting frames of data, indexing reflec-
tions, and determining lattice parameters, SAINT[21a] for integration
of the intensity of reflections and scaling, SADABS[21b] for absorp-
tion correction, and SHELXTL[21c,d] for space group and structure de-
termination and least-squares refinements on F2. All the structures
were solved by direct methods using the program SHELXS-97[21e]
and refined by full-matrix least-squares methods against F2 with
SHELXL-97.[21e] Hydrogen atoms were fixed at calculated positions
Syntheses
(E)-2-((2-Hydroxyethylimino)methyl)-6-(hydroxymethyl)-4-meth-
ylphenol (LH3): 2-Amino ethanol (0.37 g, 6.07 mmol) dissolved in
dry methanol (10 mL) was added dropwise over a period of 10 min
to a stirred solution of C2 (1.01 g, 6.07 mmol) in dry methanol
(20 mL). The resulting reaction mixture was heated under reflux for
4 h. Then, the reaction mixture was cooled to room temperature.
Thereafter the solvent was concentrated in vacuum to 10 mL and
kept in a refrigerator at 08C for 2 h to obtain a bright-yellow crys-
talline solid, which was further suction-filtered, washed with
a small amount of cold methanol, and air-dried. Yield: 1.06 g,
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1265 (s), 1237 (w), 1174 (w), 1067 (s), 974 (w), 918 (w),
806 cmÀ1 (s); elemental analysis calcd (%) for
C177H241Cl27Dy10N14O50 (5947.07): C 35.75, H 4.08, N 3.30;
found: C 36.01, H 4.21, N 3.35.
[Tb10(LH)10(k2-Piv)10]·8CHCl3·4CH3CN (2): Quantities: LH3
(0.06 g, 0.28 mmol), [TbCl3]·6H2O (0.10 g, 0.28 mmol),
Et3N (0.08 g, 0.84 mmol), PivH (0.03 g, 0.28 mmol). Yield:
0.082 g, 51% (based on Tb). Mp: 1498C (d); IR (KBr): n˜ =
3125 (b), 2958 (w), 2917 (w), 2826 (w), 1643 (s), 1556 (s),
1541 (s), 1481 (s), 1449 (s), 1363 (s), 1260 (s), 1224 (w),
1174 (w), 1067 (s), 972 (w), 898 (w), 805 cmÀ1 (s); elemen-
tal analysis calcd (%) for C176H240Cl24N14O50Tb10 (5791.96):
C 36.50, H 4.18, N 3.39; found: C 36.72, H 4.25, N 3.40.
[Gd10(LH)10(k2-Piv)10]·8CHCl3·4CH3CN·3H2O (3): Quanti-
ties: LH3 (0.06 g, 0.28 mmol), [GdCl3]·6H2O (0.10 g,
0.28 mmol), Et3N (0.08 g, 0.84 mmol), PivH (0.03 g,
0.28 mmol). Yield: 0.043 g, 26% (based on Gd); M.p.
1518C (d); IR (KBr): n˜ =3122 (b), 2960 (w), 2921 (w), 2828
(w), 1643 (s), 1547 (s), 1531 (s), 1485 (s), 1428 (s), 1358
(s), 1263 (s), 1220 (w), 1174 (w), 1087 (s), 972 (w), 897
(w), 803 cmÀ1 (s); elemental analysis calcd (%) for
C176H240Cl24Gd10N14O53 (5823.11): C 36.3, H 4.15, N 3.36;
found: C 36.01, H 4.18, N 3.24.
Table 4. Crystal data and structure refinement parameters of 4–6.
4
5
6
formula
MgÀ1
crystal system
space group
a [Š]
C81H129Gd5N4 O31
2441.13
monoclinic
P21
14.419(5)
23.412(5)
16.087(5)
115.287(5)
4910(3)
2
C79H123N4O30Tb5
2403.41
monoclinic
P21
14.282(5)
22.202(5)
15.875(5)
110.874(5)
4703(2)
2
C81H127Dy5N4O30
2449.37
monoclinic
P21
14.445(5)
23.212(5)
15.963(5)
114.046(5)
4888(3)
2
b [Š]
c [Š1]
b [8]
V [Š3]
Z
1c [gcmÀ3
]
1.651
3.405
2422
1.697
3.786
2380
1.664
3.849
2422
m [mmÀ1
F(000)
]
crystal size [mm3]
q range [deg]
0.044”0.021”0.015 0.062”0.037”0.024 0.058”0.038”0.021
4.12 to 25.03
À17< =h< =17
À27< =k< =27
À19< =l< =16
33772
4.11 to 25.03
À17< =h< =14
À26< =k< =26
À14< =l< =18
31225
4.10 to 25.03
À17< =h< =11
À27< =k< =27
À17< =l< =19
32535
16934
[R(int)=0.0449]
99.4
full-matrix least-
squares on F2
16934/12/1113
1.019
R1 =0.0435,
wR2 =0.1053
R1 =0.0524,
wR2 =0.1096
1.724 and À1.070
limiting indices
reflns collected
independent reflns
17214
15993
[R(int)=0.0478]
[R(int)=0.0368]
99.5
full-matrix least-
squares on F2
15993/15/1044
1.029
completeness to q [%] 99.5
refinement method full-matrix least-
squares on F2
data/restraints/params 17214/30/1094
goodness-of-fit on F2 1.034
General synthetic procedure for the preparation of
the complexes 4–6: All the metal complexes (4–6) were
synthesized according to the following procedure. LH3
(0.06 g, 0.28 mmol) was dissolved in methanol (10 mL).
[LnCl3]·6H2O (0.35 mmol) was added to this solution and
the reaction mixture was stirred at room temperature for
10 min. At this stage excess triethylamine (0.14 g,
1.40 mmol) was added dropwise to this solution. Within
few minutes, the solution was getting turbid. Then, piv-
alic acid (PivH) (0.057 g, 0.56 mmol) was added to the
mixture and was stirred for a further period of 8 h at
room temperature to afford a clear yellow solution,
final R indices
[I>2q(I)]
R indices (all data)
R1 =0.0508,
wR2 =0.1098
R1 =0.0672,
wR2 =0.1160
R1 =0.0394,
wR2 =0.0834
R1 =0.0502,
wR2 =0.0873
2.250 and À1.451
largest diff. peak and 1.536 and À1.302
À3
hole [eŠ
]
flack parameter
0.010(13)
-0.003(10)
0.013(11)
83.5%. M.p. 958C; H NMR (CDCl3): d=8.51 (s, 1H, imino), 7.59 (s,
1H, Ar-H), 7.24 (s, 1H, Ar-H), 4.71 (s, 2H, CH2OH), 3.90 (t, 2H, CH2),
2.85 (t, 2H, CH2), 1.29 ppm (s, 3H, CH3); FTIR (KBr): n˜ =3309 (b),
2975 (m), 2865 (m), 1635 (s), 1460 (s), 1360 (w), 1264 (s), 1090 (w),
1074 (s), 971 (w), 864 (s) cmÀ11; elemental analysis calcd (%) for
C11H15NO3 (209.2417): C 63.14, H 7.23, N 6.69; found: C 63.21, H
7.28, N 6.72.
which was filtered and kept for crystallization in slow evaporation.
After about one week, block-shaped, colorless crystals, suitable for
X-ray crystallography were obtained. Specific details of each reac-
tion and the characterization data of the products obtained are
given below.
[Gd5(LH)4(m2-h1h1Piv)4(h1Piv)3(CH3OH)]·CH3OH·3H2O (4): Quanti-
ties: LH3 (0.06 g, 0.28 mmol), [GdCl3]·6H2O (0.13 g, 0.35 mmol), Et3N
(0.14 g, 1.40 mmol), PivH (0.057 g, 0.56 mmol). Yield: 0.095 g,
55.59% (based on Gd). M.p. 2308C (d); IR (KBr): n˜ =3397 (b), 2955
(s), 2677 (w), 1648 (s), 1581(s), 1538 (s), 1453 (s), 1374 (s), 1308 (s),
1226 (s), 1178 (w), 1044 (s), 1018 (s), 976 (w), 898 (s), 863 cmÀ1 (w);
elemental analysis calcd (%) for C81H129 Gd5N4O31 (2441.14): C 39.85,
H 5.33, N 2.30; found: C 40.03, H 5.38, N 2.43.
[Tb5(LH)4(m2-h1h1Piv)4(h1Piv)3(H2O)]·3H2O (5): Quantities: LH3
(0.06 g, 0.28 mmol), [TbCl3]·6H2O (0.13 g, 0.35 mmol), Et3N (0.14 g,
1.40 mmol), PivH (0.057 g, 0.56 mmol). Yield: 0.102 g, 60.62%
(based on Tb). M.p. 2308C (d); IR (KBr): n˜ =3390 (b), 2955 (s), 2676
(w), 1649 (s), 1584 (s), 1539 (s), 1454 (s), 1374 (s), 1303 (s), 1227 (s),
1177 (w), 1046 (s), 1018 (s), 977 (w), 897 (s), 863 cmÀ1 (w); elemen-
tal analysis calcd (%) for C79H123N4O30Tb5 (2403.47): C 39.48, H 5.16,
N 2.33; found: C 39.67, H 5.25, N 5.41.
[Dy5(LH)4(m2-h1h1Piv)4(h1Piv)3(H2O)]·CH3OH·2H2O (6): Quantities:
LH3 (0.06 g, 0.28 mmol), [DyCl3]·6H2O (0.13 g, 0.35 mmol), Et3N
(0.14 g, 1.40 mmol), PivH (0.057 g, 0.56 mmol). Yield: 0.099 g,
57.74% (based on Dy). M.p. 2308C (d); IR (KBr): n˜ =3388 (b), 2956
(s), 2666 (w), 1649 (s), 1586 (s), 1541 (s), 1454 (s), 1360 (s), 1304 (s),
1226 (s), 1178 (w), 1048 (s), 1018 (s), 977 (w), 899 (s), 860 cmÀ1 (w);
General synthetic procedure for the preparation of complexes
1–3: A general procedure was used for the preparation of these
complexes (1–3). [LnCl3]·6H2O (0.28 mmol) was added to a solution
of LH3 (0.06 g, 0.28 mmol) in methanol (5 mL), and the reaction
mixture was stirred at room temperature for 5 min. Then, subse-
quently triethylamine (0.08 g, 0.84 mmol) and pivalic acid (PivH)
(0.03 g, 0.28 mmol) were added dropwise to this stirring solution.
Then, the solution was stirred for a further period of 2 h at room
temperature to afford a light-yellow precipitate that was filtered
and washed with cold methanol (2 mL). Then this precipitate redis-
solved in 10 mL of acetonirile/chloroform (1:1) solvent mixture and
kept for crystallization in slow evaporation. After about one week,
block-shaped, colorless crystals, suitable for X-ray crystallography
were obtained. Specific details of each reaction and the characteri-
zation data of the products obtained are given below.
[Dy10(LH)10(k2-Piv)10]·9CHCl3·4CH3CN (1): Quantities: LH3 (0.06 g,
0.28 mmol), [DyCl3]·6H2O (0.10 g, 0.28 mmol), Et3N (0.08 g,
0.84 mmol), PivH (0.03 g, 0.28 mmol). Yield: 0.078 g, 47% (based
on Dy). M.p. 1468C (d); IR (KBr): n˜ =3120 (b), 2955 (w), 2916 (w),
2828 (w), 1646 (s), 1561 (s), 1541 (s), 1482 (s), 1422 (s), 1361 (s),
Chem. Eur. J. 2015, 21, 16955 – 16967
www.chemeurj.org
16965
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Full Paper
Zhao, J. Tang, X.-Y. Zhang, H.-J. Zhang, Chem. Eur. J. 2009, 15, 10335–
10338.
elemental analysis calcd (%) for C81H127 Dy5N4O30 (2449.38): C 39.72,
H 5.23, N 2.29; found: C 39.79, H 5.31, N 2.35.
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Acknowledgements
We are thankful to the Department of Science and Technology,
New Delhi, for financial support. S.D., A.D., S.K., and S.B. thank
CSIR, India for Senior Research Fellowship. V.C. is thankful to
the Department of Science and Technology for a J. C. Bose Na-
tional Fellowship. EC is thankful for financial support to Minis-
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CTQ-2011-24478, CTQ2014-56312-P, the Junta de Andalucía
(FQM-195 and the Project of excellence P11-FQM-7756), the
University of Granada financial support. M.E. acknowledges fi-
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C03-01. ST thanks the Junta de Andalucía for a postdoctoral
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magnetic properties · X-ray diffraction
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Received: May 21, 2015
Published online on September 30, 2015
Chem. Eur. J. 2015, 21, 16955 – 16967
www.chemeurj.org
16967
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim