Tetranuclear [2×2] square-grid lanthanide(III) complexes: Syntheses, structures, and magnetic properties

Article abstract of DOI:10.1002/ejic.201402326

The reactions of lanthanide(III) nitrate salts (Dy^III, Tb ^III, Gd^III, and Er^III) with the aroylhydrazone-based multidentate ligand 6-(hydroxymethyl)-N′-[1-(pyridin- 2-yl)ethylidene]picolinohydrazide (LH₂) in the presence of Et ₃N in a molar ratio of 1:1:4 afforded a series of homometallic tetranuclear lanthanide(III) complexes, [Ln₄(LH)₄(μ ₂-OH)₃(μ₂-OMe)]4NO ₃·xMeOH·yH₂O (1, Ln = Dy, x = 2, y = 4; 2, Ln = Tb, x = 2, y = 4; 3, Ln = Gd, x = 2, y = 5; and 4, Ln = Er, x = 3, y = 3). X-ray diffraction studies revealed that all of the complexes contain a tetracationic [2×2] square-grid-like [Ln₄(μ₂-OH) ₃(μ₂-OMe)(μ₂-O)₄] ⁴⁺ core, which is assembled by the concerted coordination action of four monoanionic [LH]^- ligands along with three μ₂-OH ligands and a μ₂-OMe ligand. All of the lanthanide centers are eight-coordinate and adopt distorted triangular-dodecahedral coordination geometries with two different types of coordination environments (6O,2N and 4O,4N). The magnetic susceptibility measurements of the complexes reveal both the presence of all-antiferromagnetic coupling interactions as well as both isotropic (3) and anisotropic (1, 2, 4) single-ion contributions, which do not result in slow relaxation characteristics typical of single-molecule magnets. The reactions of a multicompartmental ligand with rare-earth(III) nitrate salts afford a series of homometallic Ln₄ complexes [Ln = Dy, Tb, Gd, and Er] with [2×2] square-grid topology. Magnetic studies reveal the presence of all-antiferromagnetic exchange interactions and ligand-field-induced effects for the Dy, Tb, and Er complexes, whereas an isotropic model suffices for the Gd complex.

Full text of DOI:10.1002/ejic.201402326

Job/Unit: I42326
/KAP1
Date: 21-07-14 11:50:32
Pages: 10
FULL PAPER
DOI:10.1002/ejic.201402326
Tetranuclear [2؋2] Square-Grid Lanthanide(III)
Complexes: Syntheses, Structures, and Magnetic
Properties
Sourav Biswas,[a] Sourav Das,[a] Jan van Leusen,[b] Paul Kögerler,*[b]
and Vadapalli Chandrasekhar*[a,c]
Keywords: Lanthanides / Cluster compounds / Schiff bases / Magnetic properties
The reactions of lanthanide(III) nitrate salts (DyIII, TbIII, GdIII,
and ErIII) with the aroylhydrazone-based multidentate ligand
6-(hydroxymethyl)-NЈ-[1-(pyridin-2-yl)ethylidene]picolino-
hydrazide (LH2) in the presence of Et3N in a molar ratio of
1:1:4 afforded a series of homometallic tetranuclear lantha-
nation action of four monoanionic [LH]– ligands along with
three μ2-OH ligands and a μ2-OMe ligand. All of the lanthan-
ide centers are eight-coordinate and adopt distorted triangu-
lar-dodecahedral coordination geometries with two different
types of coordination environments (6O,2N and 4O,4N). The
magnetic susceptibility measurements of the complexes re-
veal both the presence of all-antiferromagnetic coupling in-
teractions as well as both isotropic (3) and anisotropic (1, 2,
4) single-ion contributions, which do not result in slow relax-
ation characteristics typical of single-molecule magnets.
nide(III)
complexes,
[Ln4(LH)4(μ2-OH)3(μ2-OMe)]4NO3·
xMeOH·yH2O (1, Ln = Dy, x = 2, y = 4; 2, Ln = Tb, x = 2, y =
4; 3, Ln = Gd, x = 2, y = 5; and 4, Ln = Er, x = 3, y = 3). X-ray
diffraction studies revealed that all of the complexes contain
a tetracationic [2ϫ2] square-grid-like [Ln4(μ2-OH)3(μ2-OMe)-
(μ2-O)4]4+ core, which is assembled by the concerted coordi-
To understand the formation of planar tetranuclear lan-
thanide arrays with grid-type geometry, we have now de-
signed a new aroylhydrazone-based Schiff base ligand,
6-(hydroxymethyl)-NЈ-[1-(pyridin-2-yl)ethylidene]picolino-
hydrazide (LH2). The reaction of LH2 with Ln(NO3)3·
xH2O (Ln = Dy, Tb, Gd, and Er; x = 5 for Dy, Tb, Er and
x = 6 for Gd) afforded the tetranuclear [2ϫ2] square-grid
Introduction
Polynuclear lanthanide(III) complexes are increasingly
studied for a variety of reasons including their applications
in catalysis,[1] luminescence,[2] molecular magnetism,[3] and
biological imaging.[4] Various types of ligands have been
employed to assemble such polynuclear compounds, the nu-
clearity of which can be varied from 1 to 60.[5] Among such
compounds, the tetranuclear complexes possess large struc-
tural diversity (Table S1, Supporting Information). Despite
the significant amount of structural diversity that the tetra-
nuclear analogues possess, only three examples are known
in which the lanthanide ions are arranged in a planar
square-type geometry.[6–8] On the other hand, we have re-
cently reported a planar rhombus-shaped tetranuclear en-
semble (Scheme 1, a).[9]
complexes
1–4,
[Ln4(LH)4(μ2-OH)3(μ2-OMe)]4NO3·
xMeOH·yH2O (Dy, x = 2, y = 4; Tb, x = 2, y = 4; Gd, x
= 2, y = 5; and Er, x = 3, y = 3). The synthesis, structure,
and magnetism of these complexes are discussed herein.
Results and Discussion
Synthesis and Structural Characterization
[a] Department of Chemistry, Indian Institute of Technology
Kanpur,
A survey of the recent literature reveals that the employ-
ment of multidentate Schiff base ligands is a very promising
method for obtaining multinuclear homometallic 4f com-
plexes. Among these, aroylhydrazone-based Schiff base li-
gands are attractive because of their keto–enol tautomeri-
zation, which provides an additional feature for the forma-
tion of polynuclear aggregates. We have previously utilized
such a ligand to afford a tetranuclear complex containing
two dinuclear subunits (Scheme 1, b).[10] In the current
study, we have employed a multisite coordinating compart-
mental Schiff base ligand, (E)-6-(hydroxymethyl)-NЈ-
Kanpur 208016, India
E-mail: vc@iitk.ac.in
http://www.iitk.ac.in
[b] Institut für Anorganische Chemie, RWTH Aachen University,
52074 Aachen, Germany
E-mail: paul.koegerler@ac.rwth-aachen.de
http://www.ac.rwth-aachen.de
[c] National Institute of Science Education and Research,
Institute of Physics Campus, Sachivalaya Marg,
PO: Sainik School, Bhubaneswar 751005, India
http://www.niser.ac.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402326.
Eur. J. Inorg. Chem. 0000, 0–0
1
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I42326
/KAP1
Date: 21-07-14 11:50:32
Pages: 10
www.eurjic.org
FULL PAPER
Scheme 1. Synthesis of (a) rhombus-shaped tetranuclear lanthanide complexes[9] and (b) Ln4 complexes containing two dinuclear sub-
units.[10]
Scheme 2. Synthesis of LH2. The coordination pockets are indicated.
[1-(pyridin-2-yl)ethylidene]picolinohydrazide (LH2). It was X-ray Crystal Structures of 1–4
prepared by two-step synthetic protocol, in which the first
step involves the preparation of 6-(hydroxymethyl)picolino-
Single-crystal X-ray analysis revealed that 1–4 crystallize
hydrazide (B1), which undergoes a Schiff base condensation in the monoclinic system in the space group P21/n with Z
reaction with 2-acetylpyridine (B2) to afford LH2 = 4. All of the complexes are tetracationic in nature and
(Scheme 2).
contain four nitrate anions to balance the charge. Owing to
The ligand LH2 has six potential coordination sites with the structural similarity of 1–4, only the structure of 2 is
two distinct compartments; one of these possesses a pen- described in detail here. The molecular structure of 2 is
dant –CH2OH arm, a pyridine nitrogen atom, and a com- shown in Figure 1a, and those of 1, 3, and 4 are given in
mon bridging enolate oxygen atom (chelating ONO donor). the Supporting Information (Figures S1–S3). Selected bond
The other compartment consists of the common bridging parameters of 2 are summarized in the Table 1. The other
enolate oxygen atom, an imino nitrogen atom, and a pyr- bond parameters including those of 1, 3, and 4 are listed in
idine nitrogen atom (tridentate ONN donor; Scheme 2). the Supporting Information (Tables S2–S4).
The sequential reaction of LH2 with lanthanide salts in the
The molecular structure of 2 reveals that the four TbIII
presence of triethylamine in a 1:1:4 stoichiometric ratio af- ions are tightly held together by four heptadentate monode-
forded the homometallic [2ϫ2] square-grid lanthanide com- protonated [LH]– Schiff base ligands. Each ligand binds to
plexes [Ln4(LH)4(μ2-OH)3(μ2-OMe)]4NO3·xMeOH·yH2O two TbIII ions through the two tridentate NNO and NOO
(1: Dy, x = 2, y = 4; 2: Tb, x = 2, y = 4; 3: Gd, x = 2, y = pockets with further assistance from the bridging enolizable
5; and 4: Er, x = 3, y = 3) in excellent yields (Ն60%, hydrazone oxygen atom. In addition, 2 contains three μ-OH
Scheme 3; see Experimental Section).
ligands and one μ-OMe ligand (Figure 1, b). Interestingly,
Eur. J. Inorg. Chem. 0000, 0–0
2
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I42326
/KAP1
Date: 21-07-14 11:50:32
Pages: 10
www.eurjic.org
FULL PAPER
Scheme 3. Synthesis of tetranuclear [2ϫ2] square-grid lantha-
nide(III) complexes 1–4.
the formation of 2 involves exclusively the enol form of the
ligand [LH]–. This may be contrasted with the situation in
the Ln4 complexes in Scheme 1 (b), in which both the keto
and the enol forms of NЈ-(2-hydroxy-3-methoxybenzyl-
idene)-6-(hydroxymethyl)picolinohydrazide are used.
Figure 1. (a) Molecular structure of 2 (hydrogen atoms, the solvent
molecules, and all nitrate anions have been omitted for clarity). (b)
The [2ϫ2] square core of 2.
The tetracationic [Tb4(μ2-OH)3(μ2-OMe)(μ2-O)4]4+ core
of the complex possesses an almost [2ϫ2] square-grid top- tion centers are very similar and are in the range ca. 2.517–
ology. As mentioned above, only three such examples were 2.568 Å. The Tb–O bond lengths vary depending upon the
known previously.[7,17,18] The overall structure of 2 contains nature of the oxygen atom: the range ca. 2.326–2.414 Å cor-
two distinct eight-coordinate TbIII ions; one of them con- responds to the Tb–Oenolate bonds, whereas the range
tains a 6O,2N coordination environment, whereas the other 2.264–2.321 Å corresponds to the Tb–OHbridging bonds. An
possesses a 4O,4N coordination environment (Figure 2). inspection of the Tb–Tb distances reveals that there is a
The Tb–N distances of the two different types of coordina- slight deviation from a perfect square geometry.
Table 1. Selected bond lengths [Å] and angles [°] for 2.
Bond
Length
Bond
Length
Bonds
Angle
Tb(1)–O(3)
Tb(1)–O(4)
Tb(1)–O(7)
Tb(1)–O(8)
Tb(1)–O(9)
Tb(1)–N(1)
Tb(1)–N(9)
Tb(2)–O(4)
Tb(2)–O(6)
Tb(2)–O(10)
Tb(2)–O(11)
Tb(2)–N(5)
Tb(2)–N(6)
Tb(2)–N(11)
Tb(2)–N(12)
2.400(5)
2.372(4)
2.410(5)
2.346(5)
2.277(5)
2.550(6)
2.529(6)
2.352(4)
2.331(5)
2.294(5)
2.298(4)
2.569(6)
2.521(6)
2.518(6)
2.541(6)
Tb(3)–O(2)
Tb(3)O(12)
Tb(3)–O(5)
Tb(3)–O(6)
Tb(3)–O(10)
Tb(3)–O(1)
Tb(3)–N(8)
Tb(3)N(16)
Tb(4)–O(8)
Tb(4)–O(9)
Tb(4)–O(12)
Tb(4)–O(1)
Tb(4)–N(3)
Tb(4)–N(4)
Tb(4)–N(13)
Tb(4)–N(14)
2.407(5)
2.276 (5)
2.413(5)
2.362(5)
2.320(5)
2.346(5)
2.517(6)
2.538(6)
2.343(4)
2.263(5)
2.265(5)
2.327(4)
2.537(6)
2.562(6)
2.567(6)
2.564(6)
Tb(2)–O(11)–Tb(1) 111.33(18)
Tb(2)–O(10)–Tb(3) 112.5(2)
Tb(4)–O(12)–Tb(3) 112.1(2)
Tb(4)–O(9)–Tb(1)
Tb(4)–O(8)–Tb(1)
Tb(4)–O(1)–Tb(3)
Tb(2)–O(6)–Tb(3)
Tb(2)–O(4)–Tb(1)
113.9(2)
108.48(18)
107.43(19)
109.69(18)
107.19(17)
Eur. J. Inorg. Chem. 0000, 0–0
3
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I42326
/KAP1
Date: 21-07-14 11:50:32
Pages: 10
www.eurjic.org
FULL PAPER
As mentioned above, three tetranuclear square-grid lan-
thanide complexes with aroylhydrazone-based ligands have
been reported previously (Figure 3). The metric parameters
in these complexes are quite similar to those in the present
instance, in spite of the differences in their structural fea-
tures (Table 2).
Table 2. Comparison of the bond lengths [Å] and angles [°] of tetra-
nuclear complexes with a [2ϫ2] square-grid structure.
Figure 2. (a) Distorted triangular-dodecahedral geometries around
(a) the Tb3+ ion with a 6O,2N coordination environment and (b)
the Tb3+ ion with a 4O,4N coordination environment.
Magnetic Properties
The computational framework CONDON[11] has been
used in the analysis of the magnetochemical data of 1–4.
The simulations account for all of the microscopic aspects
necessary to model the 4f electronic structure, in particular
the relevant single-ion effects and coupling interactions. In
addition, ligand-field effects, spin–orbit coupling, and the
external magnetic field have been considered. Standard val-
ues were employed for spectroscopic parameters such as the
Slater–Condon parameters F2, F4, and F6 and the single-
electron spin–orbit coupling energies ζ4f. Alternatively,
CONDON implements an effective isotropic spin model,
which was used for 3 (GdIII).
The magnetic properties of 1–4 are primarily charac-
terized by the single-ion effects and exchange interactions
of the lanthanide ions that form the [2ϫ2] square core (Fig-
ure 1). The single-ion effects of the lanthanides were deter-
mined by electron–electron repulsions, spin–orbit coupling,
and ligand-field effects (magnitude of interactions in
decreasing order). These remove the degeneracy of the
ground states of the free ions [1: DyIII (6H15/2), 2: TbIII
(7F6), 3: GdIII (8S7/2), and 4: ErIII (4I15/2)].
Owing to the simple nature of the magnetism of GdIII
compounds and to develop a general understanding of the
exchange interaction pathways in 1–4, compound 3 was an-
alyzed first. The magnetic susceptibility of 3 was measured
at three different applied magnetic fields (0.1, 3, and 5 T;
Figure 3). The χMT value of 30.9 cm3 Kmol–1 at 290 K is in
the range commonly expected for four noninteracting GdIII
centers (30.4–31.2 cm3 Kmol–1).[12] As the temperature de-
Figure 3. Previously reported tetranuclear [2ϫ2] square-grid com-
plexes.[6–8]
Eur. J. Inorg. Chem. 0000, 0–0
4
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I42326
/KAP1
Date: 21-07-14 11:50:32
Pages: 10
www.eurjic.org
FULL PAPER
creases, the χMT value continuously decreases, which indi-
cates that there are saturation effects in the single-ion con-
tribution and/or dominant antiferromagnetic coupling of
the GdIII centers.
The data of 3 were modeled by an effective isotropic spin
Hamiltonian that describes a system of isotropic S = 7/2
centers. Further analysis showed that three different ex-
change interaction pathways are sufficient to describe the
magnetic susceptibility data in 3. They are directly related
to the Gd···Gd distances in the slightly distorted [2ϫ2]
square core (Figure 4): |J1| (shortest)Ͼ |J2| (ϫ2, medium)Ͼ
|J3| (largest distance). Thus, the exchange interaction Ham-
iltonian is:
ˆ
ˆ ˆ ˆ ˆ ˆ ˆ
= –2J1HGd1·HGd2 – 2J2(HGd2·HGd3 + HGd3·HGd4) –
Hex
ˆ
ˆ
2J3HGd4·HGd1
Figure 5. Temperature dependence of χMT of 1, 2, and 4 at B =
0.1 T.
The simple description of the magnetism of 3 is inappli-
cable for 1, 2, and 4 as the ligand field here causes the mag-
netic susceptibility of each lanthanide center to be aniso-
tropic. The ligand field of each center may be described by
a slightly distorted D2d symmetry (Figure 2): two perpen-
dicular planes each host four ligand atoms (O or N) that
form an arc around the lanthanide ion. In a further
approximation, the numbers of the considered states of the
full basis sets for each cluster (1: 20024, 2: 30034, 4: 3644
states) have to be reduced as the amount of available com-
puter memory remains a limiting factor in such calcula-
tions. The reduction can be taken care of by implying the
combined model:[14] the full Hamiltonian including ex-
change interactions is applied to the ground state (and usu-
ally the following excited states). The exchange interactions
of a definite number of higher excited states are additionally
treated in the molecular-field approximation. Thus, aniso-
tropic exchange interactions and a reduction of the basis
Figure 4. Temperature dependence of χMT of 3 at different applied
magnetic fields. The single-ion effects of four noninteracting GdIII
centers are shown for comparison. Inset: coupling scheme.
The result of the corresponding fit is depicted in Figure 4 sets are taken into account by using this model. On the
(solid lines) for an effective g value of geff = 1.9925 (quality- basis of analyses of the splitting of the energy states in D2d-
of-fit parameter SQ = 1.5% including field dependence of symmetric ligand fields, it is sufficient to take eight micro-
the magnetization at 2 K, not shown). To distinguish ex- states (related to four Kramer’s doublets) for the full Hamil-
change interaction contributions from single-ion effects, the tonian and an additional eight states for the molecular-field
simulated curves with the exchange interactions omitted are approximation, that is, 16 (2J + 1 states of ground mul-
shown as dashed lines.
tiplet) microstates, for each DyIII ion in 1. In 2 and 4, the
The least-squares fit reveals that all of the exchange in- numbers of considered states are 7 + 6 = 13 for each TbIII
teractions are antiferromagnetic, which results in a singlet ion and 8 + 8 = 16 for each ErIII ion, respectively. In gene-
ground state for the [2ϫ2] square Gd4 core. The exchange ral, these are states of mixed quantum numbers. Owing to
interaction parameters J1 = –0.11 cm–1, J2 = –0.06 cm–1, the similar structures of 1–4, the coupling scheme found in
and J3 = –0.03 cm–1 are within the range expected for 3 has been assumed for all compounds. Although the ex-
(weakly) interacting lanthanide ions (|J| Յ 1 cm–1).[13]
change interaction Hamiltonian is formally the same in all
For 1, 2, and 4, the χMT values of 55.0 (1), 46.6 (2), and cases, be aware of the decisive difference in the treatment of
44.1 cm3 Kmol–1 (4) at 290 K (Figure 5) are in or slightly 3 versus that for 1, 2 and 4: although the spin operators
lower than the intervals expected for the four correspond- represent effective spins for 3, they represent the true spins
ing, noninteracting LnIII centers [52.0–56.2 (DyIII), 47.1– for the other compounds and, thus, allow an anisotropic
48.0 (TbIII), and 44.2–45.1 cm3 Kmol–1 (ErIII)].[12] As the description of the exchange interactions.
temperature decreases, the χMT values continuously de-
The results of the fitting procedures are summarized in
crease at 0.1 T.
Table 3 and depicted as solid lines in Figure 5. As in 3, all
Eur. J. Inorg. Chem. 0000, 0–0
5
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I42326
/KAP1
Date: 21-07-14 11:50:32
Pages: 10
www.eurjic.org
FULL PAPER
Figure 6. Splitting patterns of the ground multiplets of each lanthanide center (single-ion splitting) in 1, 2, and 4.
exchange interaction parameters Ji are negative, which re-
In addition to the direct current (dc) measurements,
veals that there are weak antiferromagnetic interactions alternating current (ac) measurements (3 Oe amplitude)
within the [2ϫ2] square cores of each compound 1–4. Fur- have been performed on 1–4 at zero dc field. No out-of-
ther, the closer the lanthanide centers are within the cores, phase signals have been observed down to 2 K; thus, 1–4
the larger the magnitudes of the interactions become. To show no single-molecule magnet (SMM) behavior down to
gain further insight into the meaning of the fitted ligand- this temperature.
k
field parameters Bq (Wybourne notation) combined with
the used spectroscopic parameters, the splittings of the
ground multiplets of each individual center of 1, 2, and 4
have been calculated and they are shown in Figure 6.
Conclusions
We report the synthesis and structural and magnetic
characterization of tetranuclear lanthanide complexes [Ln
= Dy (1), Tb (2), Gd (3), and Er (4)] that exhibit a [2ϫ2]
square-grid topology. Aroylhydrazone-based Schiff base li-
gand has been employed to assemble the tetranuclear com-
plexes, and the enol form of the ligand is exclusively uti-
lized. Whereas a simple isotropic model was sufficient to
reproduce the temperature- and field-dependent magnetic
susceptibility of the Gd analogue, a comprehensive model
that takes into account all relevant single-ion effects in ad-
dition to the intramolecular nearest-neighbor exchange in-
teractions was necessary to describe the anisotropic deriva-
tives 1, 2, and 4. All of the compounds were found to exhi-
bit weak antiferromagnetic coupling. Also, ac susceptibility
measurements down to 2 K at both zero and small dc fields
did not reveal any out-of-phase signals characteristic of the
slow magnetization relaxation of SMMs.
Table 3. Magnetochemical analysis details (all energy values in
cm–1) of 1–4.
1
2
3
4
F2[a]
*F4[a]
F6[a]
94500
66320.1
50707.0
1900
78
81
–42
–356
–342
–
–0.14
–0.03
–0.01
0.6%
97650
68530.8
52397.2
1705
42
45
567
–195
130
–
–0.30
–0.04
–0.02
0.4%
–
–
–
–
–
–
–
–
97425
68372.9
52276.5
2393
–326
42
[a]
ζ4f
2
B04
B04
B46
B06
B4
238
–845
–786
–
–0.18
–0.11
–0.04
0.8%
–
geff
J1
J2
1.9925
–0.11
–0.06
–0.03
1.5%
J3
SQ[b]
[a] Values are taken from ref.[15] and used as constants in the least-
squares fitting procedures. [b] The goodness-of-fit parameter SQ is
Experimental Section
Reagents and General Procedures: The solvents and other general
reagents used in this work were purified according to standard pro-
cedures.[17] Pyridine-2,6-dicarboxylic acid, sodium borohydride,
Dy(NO3)3·5H2O,Ho(NO3)3·5H2O,Tb(NO3)3·5H2O,andGd(NO3)3·
6H2O were obtained from Sigma–Aldrich and used as received.
Hydrazine hydrate (80%), 2-acetylpyridine, and sodium sulfate (an-
hydrous) were obtained from SD Fine Chemicals, Mumbai, India,
and used as received. Methyl-6-(hydroxymethyl)picolinate and 6-
(hydroxymethyl)picolinohydrazide[10] were prepared according to
literature procedures.
defined as
.
The calculations show a moderate energy splitting of the
Dy and Tb ground states and common levels of Er states.
Additionally, the MJ values (according to Hellwege)[16] of
each state are given in Figure 6; the (two) largest contri-
butions in the corresponding wave function are shown. The
numbers reveal the mixed nature of the states. Note that the
centers are weakly coupled and, thus, the states of the whole
compounds exhibit mostly states that are centered around
these (relative) values.
Instrumentation: The melting points were measured with a JSGW
melting point apparatus. The IR spectra were recorded with sam-
Eur. J. Inorg. Chem. 0000, 0–0
6
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I42326
/KAP1
Date: 21-07-14 11:50:32
Pages: 10
www.eurjic.org
FULL PAPER
ples as KBr pellets with a Bruker Vector 22 FTIR spectrophotome-
ter operating at 400–4000 cm–1. Elemental analyses of the com-
pounds were obtained with a Thermoquest CE instruments, EA/
110 model CHNS-O analyzer. The electrospray ionization mass
spectrometry (ESI-MS) spectra were recorded with a Micromass
Quattro II triple quadrupole mass spectrometer. The 1H NMR
spectra were recorded with samples in CD3OD solutions with a
JEOL JNM LAMBDA 400 model spectrometer operating at
400 MHz; chemical shifts are reported in parts per million (ppm)
and referenced with respect to internal tetramethylsilane.
tropic displacement parameters. The crystallographic figures were
generated by using the Diamond 3.1e software.[18f] The crystal data
and the cell parameters for 1–4 are summarized in Table 4.
CCDC-996793 (for 1), -996794 (for 2), -996795 (for 3), and -996796
(for 4) contain the crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
6-(Hydroxymethyl)-NЈ-[1-(pyridin-2-yl)ethylidene]picolinohydrazide:
An ethanolic solution of 2-acetylpyridine (1.0 mL, 8.97 mmol) was
added dropwise to a stirred solution of 6-(hydroxymethyl)picoli-
nohydrazide (1.5 g, 8.97 mmol) in ethanol, and the resulting solu-
tion was heated to reflux for 5 h. Then, the solution was allowed
to reach room temperature before it was placed in a refrigerator
overnight. The white precipitate was collected by filtration, washed
successively with cooled methanol and diethyl ether, and finally
dried, yield = 1.62 g (66.81%). C14H14N4O2 (270.29): calcd. C
62.21, H 5.22, N 20.73; found C 62.17, H 5.11, N 20.01, m.p. 190,
°C. 1H NMR (CD3OD): δ = 2.55 (s, 3 H, CH3), 4.79 (s, 2 H, CH2),
7.4 (t, 1 H, Py-H), 7.83 (t, 1 H, Py-H), 8.02 (t,1 H, Py-H), 7.70 (d,
1 H, Py-H), 8.12 (d, 1 H, Py-H), 8.35 (d, 1 H, Py-H), 8.5 (d, 1 H,
Magnetic Measurements: The magnetic susceptibility data of 1–4
were obtained with a Quantum Design MPMS-5XL superconduct-
ing quantum interference device (SQUID) magnetometer. Polycrys-
talline samples were compacted and immobilized into cylindrical
polytetrafluoroethylene (PTFE) capsules under an Ar atmosphere.
The data were acquired as a function of the field and temperature.
All data were corrected for the contribution of the sample holder
(PTFE capsule), and the diamagnetic contributions of 1–4 were
calculated from Pascal’s constants (1: –1.08ϫ10–3 cm3 mol–1,
2:
–1.09ϫ10–3 cm3 mol–1,
3:
–1.07ϫ10–3 cm3 mol–1,
4: –1.10ϫ10–3 cm3 mol–1).
Py-H) 8.9 (s, NH) ppm. FTIR (KBr): ν = 3314 ν(O–H), 1682
˜
ν(C=O), 1597 (C=N)imine, 1580 ν(C=N)Py cm–1. ESI-MS, m/z=
X-ray Crystallography: The crystal data were collected with a
Bruker SMART CCD diffractometer (Mo-Kα radiation, λ =
0.71073 Å). The SMART[18a] program was used for the collection
of frames of data, indexing of reflections, and determination of
the lattice parameters, SAINT[18a] was used for integration of the
intensity of reflections and scaling, SADABS[18b] was used for ab-
sorption correction, and SHELXTL[18c,18d] was used for space-
group and structure determination and least-squares refinements
on F2. All of the structures were solved by direct methods by using
271.11 [M + H]+.
General Procedure for the Synthesis of Homometallic Complexes 1–
4: A general procedure was employed for the preparation of homo-
metallic complexes 1–4. To a methanolic solution (40 mL) of H2L,
Ln(NO3)3·nH2O (For 1, n = 6; 2, n = 5; 3, n = 1; 4, n = 5) was
added under stirring. Approximately 15 min later, triethylamine
was added dropwise to generate a clear light yellow solution, and
the reaction mixture was stirred for 12 h. Then, the resulting solu-
the program SHELXS-97[18e] and refined by full-matrix least- tion was concentrated and filtered. Slow diffusion of diethyl ether
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 non-hydrogen atoms were refined with aniso-
into the filtrate gave colorless single crystals suitable for X-ray dif-
fraction after one week. Specific details of each reaction and the
characterization data of the products are given below.
Table 4. Crystal data and structure refinement parameters of 1–4.
1
2
3
4
Formula
M /g
C59H67Dy4N20O30
2186.33
C59H74Tb4N20O30
2179.11
C59H59Gd4N20O31
2173.27
C60H67Er4N20O30
2217.38
Crystal system
Space group
a /Å
b /Å
c /Å
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/n
11.804(5)
23.017(5)
29.117(5)
90.763(5)
7910(4)
11.830(6)
22.959(11)
29.140(14)
90.730(10)
7915.0(7)
4
1.829
3.623
4272.0
11.909(4)
22.973(8)
29.131(10)
91.050(6)
7968(5)
11.776(5)
22.881(5)
29.049(5)
90.587(5)
7827(4)
β /°
V/Å3
Z
4
4
4
ρcalcd. /gcm–3
μ /mm–1
F(000)
1.836
3.827
4260.0
1.811
3.379
4228.0
1.882
4.339
4316.0
Crystal size /mm
θ range (°)
Limiting indices
0.068ϫ0.043ϫ0.038
4.11 to 25.03
0.055ϫ0.039ϫ0.021
4.11 to 25.03
0.059ϫ0.035ϫ0.026
4.08 to 25.03
0.044ϫ0.031ϫ0.018
4.13 to 25.03
–10Յ hՅ 14, –27Յ kՅ 27, –12Յ hՅ 14, –27Յ kՅ 27, –14Յ hՅ 7, –27Յ kՅ 27, –14Յ hՅ 13, –26Յ kՅ 27,
–34Յ lՅ 29
40877
–34Յ lՅ 32
53585
–33Յ lՅ 34
40664
–34Յ lՅ 28
40609
Reflections collected
Independent reflections
Completeness to θ (%)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [IϾ 2θ(I)]
R indices (all data)
13902 [R(int) = 0.071]
99.5
13902/15/995
13916 [R(int) = 0.046]
99.5
13916/4/1010
14012 [R(int) = 0.074]
99.4
14012/8/1019
0.993
R1 = 0.0586, wR2 = 0.1378 R1 = 0.0606, wR2 = 0.1476
R1 = 0.1133, wR2 = 0.1702 R1 = 0.0940, wR2 = 0.1705
1.916 and –1.454
13724 [R(int) = 0.076]
99.4
13724/33/1014
1.014
1.020
1.030
R1 = 0.0595, wR2 = 0.1475
R1 = 0.0909, wR2 = 0.1699
R1 = 0.0404, wR2 = 0.0959
R1 = 0.0590, wR2 = 0.1038
1.784 and –1.845
Largest diff. peak and hole /eÅ–3 2.757 and –1.555
3.110 and –2.469
Eur. J. Inorg. Chem. 0000, 0–0
7
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I42326
/KAP1
Date: 21-07-14 11:50:32
Pages: 10
www.eurjic.org
FULL PAPER
2009, 3890; d) K. Binnemans, Coord. Chem. Rev. 2009, 109,
4283; e) M. D. Ward, Coord. Chem. Rev. 2007, 251, 1663; f) S.
Sivakumar, M. L. P. Reddy, J. Mater. Chem. 2012, 22, 10852.
[Dy4(LH)4(μ2-OH)3(μ2-OMe)][NO3]4·2MeOH·4H2O (1): Quanti-
ties: Dy(NO3)3·5H2O (0.0649 g, 0.15 mmol), LH2(0.04 g,
0.15 mmol), Et3N (0.078 mL, 0.6 mmol), yield 0.055 g, 68.75%
[3]
a) D. Gatteschi, A. Caneschi, L. Pardi, R. Sessoli, Science
1994, 265, 1054; b) R. Sessoli, L. H. Tsai, R. A. Schake, S.
Wang, B. J. Vincent, K. Folting, D. Gatteschi, G. Christou,
N. D. Hendrickson, J. Am. Chem. Soc. 1993, 115, 1804; c) A.
Yamashita, A. Watanabe, S. Akine, T. Nabeshima, M. Nakano,
T. Yamamura, T. Kajiwara, Angew. Chem. Int. Ed. 2011, 50,
4016; Angew. Chem. 2011, 123, 4102; d) E. Colacio, J. Ruiz,
A. J. Mota, M. A. Palacios, E. Cremades, E. Ruiz, F. J. White,
E. K. Brechin, Inorg. Chem. 2012, 51, 5857; e) F. Tuna, C. A.
Smith, M. Bodensteiner, L. Ungur, L. F. Chibotaru, E. J. L.
McInnes, R. E. P. Winpenny, D. Collison, R. A. Layfield, An-
gew. Chem. Int. Ed. 2012, 51, 6976; Angew. Chem. 2012, 124,
7082; f) V. Mereacre, Angew. Chem. Int. Ed. 2012, 51, 9922;
Angew. Chem. 2012, 124, 10060; g) J. Goura, J. P. S. Walsh, F.
Tuna, V. Chandrasekhar, Inorg. Chem. 2014, 53, 3385; h) S.
Das, A. Dey, S. Biswas, E. Colacio, V. Chandrasekhar, Inorg.
Chem. 2014, 53, 3417; i) V. E. Campbell, H. Bolvin, E. Rivière,
R. Guillot, W. Wernsdorfer, T. Mallah, Inorg. Chem. 2014, 53,
2598.
(based on Dy), m.p. Ͼ250 °C. IR (KBr): ν = 3426 (b), 3071 (b),
˜
2734 (w), 1611 (s), 1591 (s), 1569 (s), 1540 (s), 1472 (w), 1425 (w),
1369 (s), 1348 (s), 1184 (w), 1162 (w), 1128 (w), 1103 (w), 1035
(w), 1010 (w), 983 (w), 840 (w), 821 (w), 782 (w), 751 (w) cm–1.
C59H67Dy4N20O30 (2186.33): calcd. C 32.41, H 3.09, N 12.81;
found C 32.08, H 3.01, N 12.76.
[Tb4(LH)4(μ2-OH)3(μ2-OMe)][NO3]4·2MeOH·4H2O (2): Quanti-
ties: Tb(NO3)3·5H2O (0.0643 g, 0.15 mmol), LH2(0.04 g,
0.15 mmol), Et3N (0.078 mL, 0.6 mmol), yield 0.05 g, 62.1% (based
on Tb), m.p. Ͼ250 °C. IR (KBr): ν = 3420 (b), 3071 (b), 2734 (w),
˜
1611 (s), 1591 (s), 1569 (s), 1541 (s), 1475 (w), 1433 (w), 1371 (s),
1350 (s), 1180 (w), 1161 (w), 1132 (w), 1103 (w), 1033 (w), 1007 (w),
981 (w), 849 (w), 821 (w), 775 (w), 757 (w) cm–1. C59H74N20O30Tb4
(2179.11): calcd. C 32.52, H 3.42, N 12.86; found C 32.01, H 3.39,
N 12.71.
[Gd4(LH)4(μ2-OH)3(μ2-OMe)][NO3]4·2MeOH·5H2O (3): Quanti-
ties: Gd(NO3)3·6H2O (0.067 g, 0.15 mmol), LH2(0.04 g,
0.15 mmol), Et3N (0.078 mL, 0.6 mmol), yield 0.052 g, 64.47%
[4]
[5]
a) A. Picot, A. D’Aléo, P. L. Baldeck, A. Grichine, A. Duper-
ray, C. Andraud, O. Maury, J. Am. Chem. Soc. 2008, 130, 1532;
b) M. Bottrill, L. Kwok, N. Long, Chem. Soc. Rev. 2006, 35,
557.
(based on Gd), m.p. Ͼ250 °C. IR (KBr): ν = 3424 (b), 3072 (b),
˜
2734 (w), 1611 (s), 1591 (s), 1572 (s), 1543 (s), 1472 (w), 1429 (w),
1371 (s), 1350 (s), 1185 (w), 1162 (w), 1132 (w), 1103 (w), 1035
(w), 1010 (w), 987 (w), 849 (w), 821 (w), 782 (w), 757 (w) cm–1.
C59H59Gd4N20O31 (2173.27): calcd. C 32.61, H 2.74, N 12.89;
found C 32.50, H 3.27, N 12.53.
a) J. J. Baldoví, S. C.-Serra, J. M. Clemente-Juan, E. Coronado,
A. G.-Ariño, A. Palii, Inorg. Chem. 2012, 51, 12565; b) P. H.
Lin, T. J. Burchell, R. Clerac, M. Murugesu, Angew. Chem. Int.
Ed. 2008, 47, 8848; Angew. Chem. 2008, 120, 8980; c) M. T.
Gamer, Y. Lan, P. W. Roesky, A. K. Powell, R. Clerac, Inorg.
Chem. 2008, 47, 6581; d) B. Hussain, D. Savard, T. J. Burchell,
W. Wernsdorfer, M. Murugesu, Chem. Commun. 2009, 1100; e)
X.-J. Zheng, L.-P. Jin, S. Gao, Inorg. Chem. 2004, 43, 1600; f)
T. Kajiwara, H. Wu, T. Ito, N. Iki, S. Miyano, Angew. Chem.
Int. Ed. 2004, 43, 1832; Angew. Chem. 2004, 116, 1868; g) G.-
F. Xu, P. Gamez, S. J. Teat, J. Tang, Dalton Trans. 2010, 39,
4353; h) L. G. Westin, M. Kritikos, A. Caneschi, Chem. Com-
mun. 2003, 1012; i) P. C. Andrews, T. Beck, C. M. Forsyth,
B. H. Fraser, P. C. Junk, M. Massi, P. W. Roesky, Dalton Trans.
2007, 5651; j) A. S. R. Chesman, D. R. Turner, B. Moubaraki,
K. S. Murray, G. B. Deacon, S. R. Batten, Chem. Eur. J. 2009,
15, 5203; k) R. Wang, D. Song, S. Wang, Chem. Commun.
2002, 368; l) R. Wang, Z. Zheng, T. Jin, R. J. Staples, Angew.
Chem. Int. Ed. 1999, 38, 1813; Angew. Chem. 1999, 111, 1929;
m) X. Gu, D. Xue, Inorg. Chem. 2007, 46, 3212; n) X.-J. Kong,
Y. Wu, L.-S. Long, L.-S. Zheng, Z. Zheng, J. Am. Chem. Soc.
2009, 131, 6918.
[Er4(LH)4(μ2-OH)3(μ2-OMe)][NO3]4·3MeOH·3H2O (4): Quanti-
ties: Er(NO3)3·5H2O (0.066 g, 0.15 mmol), LH2(0.04 g, 0.15 mmol),
Et3N (0.078 mL, 0.6 mmol), yield 0.058 g, 70.3% (based on Er),
m.p. Ͼ250 °C. IR (KBr): ν = 3424 (b), 3072 (b), 2734 (w), 1610 (s),
˜
1589 (s), 1572 (s), 1538 (s), 1465 (w), 1426 (w), 1371 (s), 1350 (s),
1185 (w), 1160 (w), 1132 (w), 1103 (w), 1038 (w), 1015 (w), 987
(w), 845 (w), 831 (w), 789 (w), 756 (w) cm–1. C60H67Er4N20O30
(2217.38): calcd. C 32.50, H 3.05, N 12.63; found C 32.39, H 3.18,
N 12.50.
Supporting Information (see footnote on the first page of this arti-
cle): Literature-reported topologies of tetranuclear lanthanide com-
plexes, molecular structures of 1, 3, and 4, and list of bond lengths
and angles.
Acknowledgments
[6]
S. Xue, L. Zhao, Y.-N. Guo, J. Tang, Dalton Trans. 2012, 41,
351.
The authors are thankful to the Department of Science and Tech-
nology (DST), New Delhi for financial support. S. B. and S. D.
thank the Council of Scientific and Industrial Research (CSIR),
India for Senior Research Fellowships. V. C. is thankful to the De-
partment of Science and Technology for a J. C. Bose National Fel-
lowship.
[7]
N. M. Randell, M. U. Anwar, M. W. Drover, L. N. Dawe, L. K.
Thompson, Inorg. Chem. 2013, 52, 6731.
M. U. Anwar, L. K. Thompson, L. N. Dawe, F. Habibb, M.
Murugesu, Chem. Commun. 2012, 48, 4576.
V. Chandrasekhar, S. Hossain, S. Das, S. Biswas, J.-P. Sutter,
Inorg. Chem. 2013, 52, 6346.
V. Chandrasekhar, S. Das, A. Dey, S. Hossain, J.-P. Sutter, In-
org. Chem. 2013, 52, 11956.
M. Speldrich, H. Schilder, H. Lueken, P. Kögerler, Isr. J. Chem.
2011, 51, 215; see also http://www.condon.fh-aachen.de/.
H. Lueken, Magnetochemie, Teubner, Stuttgart, Germany,
1999.
B. Wang, S. Jiang, X. Wang, S. Gaom, Lanthanide Based Mag-
netic Molecular Materials, in: Rare Earth Coordination Chemis-
try: Fundamentals and Applications (Ed.: C. Huang), Wiley,
Chichester, UK, 2010, and references cited therein.
a) M. E. Lines, J. Chem. Phys. 1971, 55, 2977; b) H. Lueken,
P. Hannibal, K. Handrick, J. Schmitz, Z. Kristallogr. 1989, 186,
185.
[8]
[9]
[10]
[11]
[12]
[13]
[1] a) P. W. Roesky, G. C.-Melchor, A. Zulys, Chem. Commun.
2004, 738; b) X. Yu, S. Y. Seo, M. J. Tobin, J. Am. Chem. Soc.
2007, 129, 7244; c) T. N. Parac-Vogt, K. Deleersnyder, K.
Binnemans, Eur. J. Org. Chem. 2005, 1810; d) F. Pohlki, S.
Doye, Chem. Soc. Rev. 2003, 32, 104; e) P. W. Roesky, T. E.
Müller, Angew. Chem. Int. Ed. 2003, 42, 2708; Angew. Chem.
2003, 115, 2812.
[2] a) M. Romanelli, G. A. Kumar, T. J. Emge, R. E. Riman, J. G.
Brennan, Angew. Chem. Int. Ed. 2008, 47, 6049; Angew. Chem.
2008, 120, 6138; b) C. M. G. dos Santos, A. J. Harte, S. J.
Quinn, T. Gunnlaugsson, Coord. Chem. Rev. 2008, 252, 2512;
c) S. Faulkner, L. Natrajan, S. William, D. Sykes, Dalton Trans.
[14]
Eur. J. Inorg. Chem. 0000, 0–0
8
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I42326
/KAP1
Date: 21-07-14 11:50:32
Pages: 10
www.eurjic.org
FULL PAPER
[15] J. S. Griffith, The Theory of Transition-Metal Ions, Cambridge
University Press, Cambridge, 1961.
Correction, v. 2.05, University of Göttingen, Germany, 2002; c)
SHELXTL Reference Manual, ver. 6.1, Bruker Analytical X-
ray Systems, Madison, 2000; d) G. M. Sheldrick, SHELXTL,
v. 6.12, Bruker AXS Inc., Madison, 2001; e) G. M. Sheldrick,
SHELXL97, Program for Crystal Structure Refinement, Uni-
versity of Göttingen, Germany, 1997; f) K. Bradenburg, Dia-
mond, v. 3.1eM, Crystal Impact, Bonn, Germany, 2005.
Received: April 17, 2014
[16] K. H. Hellwege, Ann. Phys. 1948, 439, 95.
[17] B. S. Furniss, A. J. Hannaford, P. W. G. Smith, Tatchell, A. R.
Vogel’s Textbook of Practical Organic Chemistry, 5th ed.,
ELBS, Longman, London, 1989.
[18] a) SMART & SAINT Software Reference Manuals, v. 6.45,
Bruker Analytical X-ray Systems, Inc., Madison, 2003; b)
G. M. Sheldrick, SADABS, Software for Empirical Absorption
Published Online: ᭿
Eur. J. Inorg. Chem. 0000, 0–0
9
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I42326
/KAP1
Date: 21-07-14 11:50:32
Pages: 10
www.eurjic.org
FULL PAPER
Lanthanide Complexes
S. Biswas, S. Das, J. van Leusen,
P. Kögerler,* V. Chandrasekhar* ..... 1–10
The reactions of a multicompartmental lig-
and with rare-earth(III) nitrate salts af-
ford a series of homometallic Ln4 com-
plexes [Ln = Dy, Tb, Gd, and Er] with
[2ϫ2] square-grid topology. Magnetic stud-
ies reveal the presence of all-antiferromag-
netic exchange interactions and ligand-
field-induced effects for the Dy, Tb, and Er
complexes, whereas an isotropic model suf-
fices for the Gd complex.
Tetranuclear [2ϫ2] Square-Grid Lantha-
nide(III) Complexes: Syntheses, Structures,
and Magnetic Properties
Keywords: Lanthanides
/ Cluster com-
pounds / Schiff bases / Magnetic properties
Eur. J. Inorg. Chem. 0000, 0–0
10
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim