Linear, edge-sharing heterometallic trinuclear [CoII-LnIII-CoII] (LnIII = GdIII, DyIII, TbIII, and HoIII) complexes: Slow relaxation of magnetization in the DyIII derivative

Article abstract of DOI:10.1002/ejic.201301171

The sequential reaction of a multisite coordination ligand (LH₄) with lanthanide (III) nitrates followed by the addition of Co(NO₃)₂·6H₂O in a 4:1:2 ratio in the presence of triethylamine afforded a series of heterometallic, linear trinuclear complexes [Co₂Ln(LH₃)₄]·3NO₃ [Ln = Dy^III (1), Gd^III (2), Tb^III (3), and Ho^III (4)]. These tricationic complexes contain nitrate counteranions. The cationic portion of these complexes consists of three metal ions that are arranged in a linear fashion; a central Ln^III is present between the two terminal Co^II ions and is attached to the latter through two phenoxide bridging groups. This arrangement generates two contiguous four-membered CoLnO₂ rings. The Co^II ions are six-coordinate (2N, 4O) in a distorted octahedral geometry, whereas the central lanthanide ion is eight-coordinate (8O) in a distorted square-antiprismatic geometry. Magnetic studies of these complexes have been performed and indicate a slow relaxation of the magnetization for the Dy^III derivative 1. Linear, edge-sharing heterometallic trinuclear [Co^II-Ln^III-Co^II] [Ln^III = Dy (1), Gd (2), Tb (3), and Ho (4)] compounds have been assembled. A slow relaxation of magnetization is observed for the Dy^III derivative 1.

Full text of DOI:10.1002/ejic.201301171

FULL PAPER
DOI:10.1002/ejic.201301171
Linear, Edge-Sharing Heterometallic Trinuclear
[CoII–LnIII–CoII] (LnIII = GdIII, DyIII, TbIII, and HoIII)
Complexes: Slow Relaxation of Magnetization in the DyIII
Derivative
Vadapalli Chandrasekhar,*[a,b] Sourav Das,[a] Atanu Dey,[a]
Sakiat Hossain,[a] Subrata Kundu,[a] and Enrique Colacio*[c]
Keywords: Heterometallic complexes / Cobalt / Lanthanides / Magnetic properties / Ferromagnetic interactions / Schiff
bases
The sequential reaction of a multisite coordination ligand
(LH4) with lanthanide (III) nitrates followed by the addition
of Co(NO3)2·6H2O in a 4:1:2 ratio in the presence of triethyl-
amine afforded a series of heterometallic, linear trinuclear
complexes [Co2Ln(LH3)4]·3NO3 [Ln = DyIII (1), GdIII (2), TbIII
(3), and HoIII (4)]. These tricationic complexes contain nitrate
counteranions. The cationic portion of these complexes con-
sists of three metal ions that are arranged in a linear fashion;
a central LnIII is present between the two terminal CoII ions
and is attached to the latter through two phenoxide bridging
groups. This arrangement generates two contiguous four-
membered CoLnO2 rings. The CoII ions are six-coordinate
(2N, 4O) in a distorted octahedral geometry, whereas the
central lanthanide ion is eight-coordinate (8O) in a distorted
square-antiprismatic geometry. Magnetic studies of these
complexes have been performed and indicate a slow relax-
ation of the magnetization for the DyIII derivative 1.
Introduction
system depends on a high ground-state spin, S, and a large
magnetic anisotropy, D, several synthetic strategies were
formulated to achieve these parameters.[4] Briefly, the strate-
gies have been to synthesize polynuclear paramagnetic tran-
sition metal ion complexes [e.g., Mn(II/III),[5] Fe(II/III),[6]
CoII,[7] or NiII[8]], lanthanide ion complexes of varying nu-
clearity (e.g., Ln2,[9] Ln3,[10] Ln4,[11] Ln5,[12] Ln6),[13] and
The discovery that [Mn12O12(OAc)16(H2O)4][1] is a single-
molecule magnet (SMM), the magnetic behavior of which,
below a critical temperature, resembles that of bulk mag-
nets, has spurred extremely intense interdisciplinary re-
search activity with participation from chemists, physicists,
and materials scientists. The other types of molecular mate-
rials that have been discovered since include single-chain
magnets[2] and single-ion magnets.[3] From the point of view
of chemists, the excitement in this field has been the chal-
lenge to understand the structure–property relationships in
these systems and to design and assemble various types of
molecular systems that exhibit interesting magnetic behav-
ior. On the basis of a qualitative understanding that the
optimum requirements to extract SMM behavior from a
heterometallic 3d/4f complexes (e.g., CuII/LnIII [14]
,
NiII/
LnIII [15] MnIII/LnIII[16]). The latter, in particular, have at-
,
tracted interest because appropriate 3d and 4f metal ions
can interact favorably under suitable linkage conditions to
generate interesting magnetic properties. Among the vari-
ous systems that have been investigated, those containing
CoII/LnIII[17] have not received as much attention, although,
recent research on these compounds shows considerable
promise. We have recently reported a dinuclear mixed-val-
ent CoII/CoIII[18] complex that exhibited slow relaxation of
magnetization. Earlier, using a phosphorus-supported li-
gand, SP[N(Me)N=CH–C6H3-2-OH-3-OMe]3 (LH3), we
have prepared several homo-[19] and heterometallic trinu-
clear complexes,[20] including [L2Co2Ln]+ (Ln = Gd, Dy,
Tb, Ho, and Eu),[17f,17g] many of which showed SMM be-
havior. Spurred by this, we were interested in preparing
analogous compounds with a vastly different ligand system.
Accordingly, herein, we report the synthesis, structural
characterization, and magnetic behavior of [Co2Dy(LH3)4]·
[a] Department of Chemistry, Indian Institute of Technology
Kanpur,
Kanpur 208016, India
E-mail: vc@iitk.ac.in
http://www.iitk.ac.in
[b] Tata Institute of Fundamental Research, Centre for
Interdisciplinary Sciences,
21 Brundavan Colony, Narsingi, Hyderabad 500075, India
http://www.tifrh.res.in
[c] Departamento de QuímicaInorgánica, Facultad de Ciencias,
Universidad de Granada,
Avenida de Fuentenueva s/n, 18071 Granada, Spain
E-mail: ecolacio@ugr.es
http://www.ugr.es
3NO3·2MeOH·1.5H2O
(1),
[Co2Gd(LH3)4]·3NO3·
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301171.
2MeOH·0.5H2O (2), [Co2Tb(LH3)4]·3NO3·2MeOH·0.5H2O
Eur. J. Inorg. Chem. 2014, 397–406
397
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
(3), and [Co2Ho(LH3)4]·3NO3·2MeOH·0.5H2O (4) pre-
pared from 2-[2-hydroxy-3-(hydroxymethyl)-5-methyl-
benzylideneamino]-2-methylpropane1,3-diol (LH4). The de-
tailed magnetic studies for 1–4 indicate the presence of fer-
romagnetic behavior for the DyIII (1) and GdIII (2) ana-
logues and a slow relaxation of magnetization for 1.
Results and Discussion
Synthesis
The multisite coordination ligand LH4 contains five
binding sites: one phenolic oxygen atom, one benzyl alcohol
oxygen atom, one imino nitrogen atom, and two hydroxy
oxygen atoms. The sequential reaction of LH4 with appro-
priate lanthanide salts followed by reaction with Co(NO3)2·
6H2O in a 4:1:2 stoichiometric ratio in the presence of tri-
ethylamine afforded the trinuclear heterobimetallic com-
pounds [Co2Ln(LH3)4]·3NO3·xMeOH·yH2O [Ln = DyIII, x
= 2, y = 1.5 (1); Ln = GdIII, x = 2, y = 0.5 (2); Ln = TbIII
,
x = 2, y = 0.5 (3); Ln = HoIII, x = 2, y = 0.5 (4)], in good
yields (Ͼ60%, see Exp. Section and Scheme 1). The ESI-
MS spectra of 1–4 reveal that they retain their molecular
integrity in solution as indicated by the presence of peaks
at m/z = 430.08 corresponding to [C52H72N4O16Co2Dy]3+
for 1, 428.09 corresponding to [C52H72N4O16Co2Gd]3+ for
2, 428.41 corresponding to [C52H72N4O16Co2Tb]3+ for 3,
and 430.42 corresponding to [C52H72N4O16Co2Ho]3+ for 4.
The ESI-MS spectrum of 1, as a representative example, is
shown in Figure 1, and those of the others are in the Sup-
porting Information (Figures S1–S3).
Scheme 1. Synthesis of the trinuclear heterometallic complexes
1–4.
Figure 1. (a) Full range ESI-MS spectrum of 1. (b) Experimental mass spectral pattern of the parent ion peak. (c) The simulated isotopic
pattern for the parent ion peak shows a close resemblance with the experimental spectrum.
Eur. J. Inorg. Chem. 2014, 397–406
398
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
X-ray Crystallography
CH2OH units (O7 and O9) in a CoN2O4 coordination envi-
ronment. The coordination geometry around the CoII ion
can be described as distorted octahedral (Figure 3, a). The
central DyIII ion has an overall 8O coordination environ-
ment in a square-antiprismatic geometry (Figure 3, b). All
four [LH3]– ligands in the complex are involved in binding.
In addition to the four oxygen atoms from the benzyl
alcohol groups (O4, O5, O12, and O13), four phenolate
oxygen atoms (O3, O6, O11, and O14) are involved in coor-
dination. Each of the terminal CoII ions and the central
DyIII centers are bridged by two phenolate oxygen atoms
to generate two four-membered CoDyO2 rings, which are
at an angle of 64.8(1)° with respect to each other (Figure 2,
b). The bridging action of the phenolate oxygen atoms gen-
erates three contiguous polyhedra with common edges de-
fined by O6/O11 and O3/O14 (Figure 4). Also, as result of
the bridging phenolate coordination, the three metal ions
are placed in a linear arrangement with a Co1–Dy1–Co2
bond angle of 177.9(1)°. The average CoII–DyIII distance is
3.495(1) Å, and the CoII–CoII distance is 6.990(2) Å. The
linear arrangement of the metal ions can also be gauged
when viewed along the Co–Dy–Co axis (Figure 5). As can
be seen in Figure 5a, the four ligands involved in the as-
sembly of 1 are organized symmetrically on the top and
bottom of the trinuclear core. This arrangement can be con-
trasted with the paddle-wheel arrangement of the ligands in
the previously described [L2CoLn]+ complexes (Figure 5,
b). Complex 1 displays four strong intramolecular O–H···O
hydrogen-bonding interactions between the benzyl alcohol
oxygen atoms and the free –CH2OH arms (Figure 2).
Single-crystal X-ray diffraction studies revealed that 1–4
are isostructural and crystallize in the monoclinic space
group P21/n. All of the complexes are tricationic and con-
tain three nitrate anions to neutralize the charge. In the fol-
lowing, the molecular structure of 1 will be described as a
representative example to illustrate the common structural
features of the four complexes. The molecular structure of
1 is shown in Figure 2; those of 2–4 are in the Supporting
Information (Figure S4). Selected bond parameters of 1 are
listed in the caption of Figure 2.
Figure 2. (a) The tricationic complex 1 (hydrogen atoms, methyl
groups, and the solvent molecules have been omitted for clarity).
Selected bond lengths [Å] and angles (°): Dy(1)–O(3) 2.344(7),
Dy(1)–O(4) 2.390(7), Dy(1)–O(5) 2.410(6), Dy(1)–O(6) 2.349(5),
Dy(1)–O(11) 2.334(5), Dy(1)–O(12) 2.382(6), Dy(1)–O(13)
2.399(7), Dy(1)–O(14) 2.321(6), Co(1)–N(1) 2.050(9), Co(1)–N(4)
2.079(9), Co(1)–O(1) 2.188(10), Co(1)–O(3) 2.072(7), Co(1)–O(14)
2.026(7), Co(1)–O(15) 2.127(13), Co(2)–N(2) 2.083(8), Co(2)–N(3)
2.061(8), Co(2)–O(6) 2.052(6), Co(2)–O(7) 2.130(7), Co(2)–O(9)
2.150(7), Co(2)–O(11) 2.035(6), Co(1)–O(3)–Dy(1) 104.6(3), Co(2)–
O(6)–Dy(1) 104.9(2), Co(2)–O(11)–Dy(1) 106.0(2), Co(1)–O(14)–
Dy(1) 106.9(3). (b) The trinuclear core of 1 showing the near or-
thogonal disposition of the two four-membered CoDyO2 rings.
The heterometallic complex possesses
a trinuclear
[Co2Dy(μ2-O)4]3+ core (Figure 2), which is assembled as a
result of the cumulative coordination action of four singly
deprotonated [LH3]– ligands. Interestingly, only the phen-
olic proton is deprotonated, whereas the three –CH2OH
groups that are present remain intact. Each [LH3]– ligand
uses a phenolate oxygen atom, an imino nitrogen atom, and
the oxygen atoms of the benzyl alcohol and the
–NCH(CH3)(CH2OH)2 groups. One of the –CH2OH arms
of the latter remains noncoordinating (Scheme 2). Each of
the two terminal CoII centers is surrounded by two [LH3]–
ligands and is bound by two phenolate oxygen atoms (O6
and O11), two imino nitrogen atoms (N2 and N3), and two
Figure 3. (a) Distorted octahedral geometry around the Co2+ ion.
(b) Distorted square-antiprismatic geometry around the Dy3+ ion.
Figure 4. A view showing the edge-sharing of the three contiguous
polyhedra.
Scheme 2. Binding mode of LH4.
Eur. J. Inorg. Chem. 2014, 397–406
399
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Neighboring [Co–Dy–Co]3+ cations are connected by hy- phenolate and methoxy oxygen atoms (Figure 6). Secondly,
drogen bonds involving coordinated hydroxymethyl groups as shown in Figure 5b, the literature examples display a
and nitrate anions to give a 2D network in the ac plane. paddle-wheel arrangement of ligands about the Co–Ln–Co
(Figure S5)
axis. In the present instance, the four ligands are arranged
symmetrically in the top and bottom halves of the complex.
Thirdly, the dihedral angles between the two CoDyO2 rings
in 1 is 64.8(3)°, whereas in the literature examples these
angles are 59.7(14) and 61.4(2)°. The metric parameters in-
volved in the current instance and in the literature examples
are quite similar and are summarized in Table 1.
Magnetic Properties
The temperature dependence of χMT for 1–4 (χM is the
molar magnetic susceptibility per Co2Ln unit) in the tem-
perature range 300–2 K range was measured with an ap-
plied magnetic field of 1000 Oe, and the results are dis-
played in Figure 7.
Figure 5. (a) The linear arrangement of the metal ions in 1. (b)
The literature example with a paddle-wheel arrangement of ligands
about the Co–Ln–Co axis.[17f]
Let us to start with the Co–Gd complex 2, the magnetic
It is interesting to make a structural comparison of 1 properties of which are easier to analyze. At room tempera-
with two other linear Co2Ln complexes known in literature ture, the χMT value for 2 of 14.47 cm3 mol–1 K is larger than
(Figures 5 and 6). Firstly, in the current instance, the tri- that expected for two CoII (S = 3/2) and one GdIII (S =
cationic complex assembly is accomplished through the use 7/2) ions that are not interacting (11.625 cm3 mol–1 K with
of four unsymmetrical Schiff base ligands featuring polyhy- g = 2), maybe because of both the orbital contribution of
4
droxy and imino nitrogen atoms. The literature examples the CoII ion (with an octahedral geometry and a T1g
deal with monocationic complexes built from two symmet- ground term) and the ferromagnetic interaction between the
rical tripodal ligands containing imino nitrogen atoms and CoII and GdIII ions (see below). As the temperature de-
Figure 6. Two families of [Co2Ln]+ complexes known in literature.[17f,17g,17h]
Table 1. Comparison of bond lengths [Å] and angles [°] of the trinuclear [CoII–LnIII–CoII] complexes reported here and those reported
previously (see Figure 6).
[(LH3)4Co2Ln][NO3]3
[L2Co2Ln][NO3][17h]
[L2Co2Ln][NO3][17f,17g]
Co–Nimine
2.035(11)–2.087(8)
2.026(6)–2.091(7)
2.126(8)–2.233(8)
2.321(6)–2.378(7)
2.382(6)–2.443(6)
3.488(1)–3.508(2)
6.977(2)–7.023(2)
177.67(2)–177.99(3)
104.25(2)–106.51(2)
2.087(6)–2.125(7)
2.057(6)–2.115(4)
–
2.360(3)–2.456(5)
2.868(4)–2.983(5)
3.302(5)–3.321(1)
6.603(2)–6.634(4)
176.93(2)–178.41(5)
93.98(14)–95.40(2)
2.096(6)–2.132(6)
2.076(4)–2.107(4)
–
2.363(5)–2.396(3)
2.865(3)–2.932(2)
3.269(9)–3.310(9)
6.538(1)–6.621(1)
180.00(2)
Co–Ophenolic
Co–Oterminal hydroxo
Ln–Ophenolic
Ln–Omethoxy/benzyl hydroxide
Co–Ln
Co–Co
Co–Ln–Co
Co–O–Ln
94.31(2)–94.43(2)
Eur. J. Inorg. Chem. 2014, 397–406
400
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
was obtained for the following parameters: J = +0.97(7), g
= 2.35(1) and zJЈ = 0.0047(1). Nevertheless, the extracted J
value must be taken with caution and should be considered
only as an approximate value because of the crudeness of
the model, which does not take into account the following
factors: (1) the contribution of upper levels, (2) the distor-
tion from the octahedral symmetry of the CoII coordination
sphere, which leads to a highly anisotropic Kramer doublet
ground state (gʈ ϶ gЌ), and (3) spin states with different g
values. Nevertheless, it is worth noting that this approach
allows the extraction of a J value for the Co–Gd–Co com-
plex that is in agreement with values found by more com-
plex ab initio calculations.[26] Moreover, the extracted J
value is similar to those found for planar diphenoxo-
bridged CoII–GdIII complexes containing a compartmental
ligand (J ≈ +1 cm–1)[22–25] but is larger than that observed
for a trinuclear Co–Gd–Co complex bearing a tripodal li-
gand with three phenoxo bridges connecting GdIII and CoII
ions and a folded Gd(O)2Co bridging fragment (J =
+0.52).[17h] Experimental results on dinuclear CoII–GdIII
complexes[22–24] and DFT calculations by us and others on
di-μ-phenoxo dinuclear Gd–(O)2–Cu[27] and Gd–(O)2–Ni
complexes[28] indicate that the ferromagnetic interaction be-
tween the MII (Co, Cu, Ni) and GdIII ions increases with
the planarity of the M–O2–Gd fragment and with the in-
crease of the M–O–Gd angle. Therefore, the observed value
for 2 is not unexpected as it exhibits a Gd(O)2Co planar
fragment and large Gd–O–Co bridging angles. The magne-
tization isotherm of 2 at 2 K (Figure 8) shows a rapid in-
crease at low field, in agreement with a high-spin state for
this complex, and a rapid saturation of the magnetization
that is almost complete at the maximum applied field of 5 T
and reaches a value of 11.57 μB, close to that expected for
Figure 7. Temperature dependence of χMT for 1–4. The solid line
represents the best fit of the experimental data of 2 to the theoreti-
cal equation.
creases, the χMT value for 2 first slowly decreases from
room temperature to reach a minimum value of 13.13 K
cm3 mol–1 K at 30 K and then shows an abrupt increase to
reach a value of 24.27 cm3 mol–1 K at 2 K. The observed
high-temperature decrease is caused by the thermal depop-
ulation of the spin–orbit coupling levels arising from the
4T1g ground term, whereas the increase at low temperature
suggests a ferromagnetic interaction between the CoII and
GdIII ions. The data for 2 were analyzed by considering that
below 30 K only the lowest Kramer doublet of the CoII
ion with an effective spin Seff = 1/2 is thermally populated.
Although small differences between the bond angles and
distances affect the two bridging fragments, for simplicity,
we are going to consider the same exchange coupling for
the CoII–GdIII interactions. This effective spin is related to
the real spin by a factor of 5/3 and, therefore, the Hamilto-
nian that describes the magnetic exchange interaction be-
tween the GdIII and CoII ions is:[21]
the corresponding saturation value of 11.40 μB for gCo
=
4.4, SeffCo = 1/2, gGd = 2.0, and SGd = 7/2. In keeping with
the ferromagnetic interaction observed for 2, the experi-
mental data are well above the Brillouin curve for two CoII
(Seff = 1/2; g = 4.4) and one GdIII (g = 2.0) ion that are not
interacting.
From this Hamiltonian, the molar magnetic suscep-
tibility is calculated to be:
In this equation, A = 5J/6kT, and the same g value was
assumed for all of the spin states. All attempts to fit the
data to this equation were unsuccessful unless a term to
account for the intermolecular interactions was included in
the Hamiltonian. We used the molecular field approxi-
mation (zJЈϽSzϾSz) to take into account such interactions.
As J1 only affects the energy of the S = 7/2 state with inter-
mediate spin S* = SCo1 + SCo2 = 0, this parameter cannot
be accurately determined. In view of this and to avoid over-
Figure 8. Field dependence of the magnetization at 2 K for 1–4.
We now discuss the magnetic properties of 1, 3, and 4.
parameterization, J1 was fixed to zero. The best fit of the At room temperature, the χMT values for these complexes
magnetic susceptibility data for TϽ 30 K to the theoretical (20.37, 18.09, and 18.51 cm3 K mol–1, respectively) are
equation
higher than those calculated (17.91, 15.56, and 17.81 cm3 K
Eur. J. Inorg. Chem. 2014, 397–406
401
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
mol–1, respectively) for two CoII (S = 3/2 with gCo = 2.0) linear high-field variation of the magnetization suggests the
and one LnIII ion (DyIII 4f9, J = 15/2, S = 5/2, L = 5, presence of a significant magnetic anisotropy (arising from
6
6H15/2, gJ = 4/3; TbIII 4f8, J = 6, S = 3, L = 3, F7, gJ = the crystal-field effects on the free-ion ground state in the
5
3/2; HoIII, L = 6, S = 2, J = 8, gJ = 5/4, I8) that are not case of the LnIII ion and from spin–orbit coupling in the
interacting in the free-ion approximation.
case of the CoII ions) and/or low-lying excited states that
are partially [thermally and field-induced] populated. The
presence of low-lying excited states close in energy to the
ground state suggests that the magnetic exchange interac-
These differences are mainly caused by the orbital contri- tions for these compounds are weaker than that for 1. The
bution of the CoII ions with an octahedral geometry and a magnetization values for 3 and 4 at 5 T of 9.88 and
4T1g ground term and the possible ferromagnetic interac- 10.66 NμB, respectively, are far from those expected for
tions between CoII and LnIII ions.
TbIII and HoIII ions (13.2 and 14.2 NμB, respectively) with
As the temperature decreases from room temperature, strong easy-axis anisotropy and Jz = Ϯ6 (TbIII) and Ϯ8
the χMT values for 1 steadily decreases to reach a minimum (HoIII) ground doublets ferromagnetically coupled with two
of 10.31 cm3 mol–1 K at10 K. Below this temperature, χMT SeffCo = 1/2 ions. In these cases, the sublevels with the high-
undergoes
a sharp increase to reach a value of est ϮJz values should not be the lowest in energy and,
18.02 cm3 mol–1 K at 2 K. The decrease at high temperature therefore, the anisotropy is weaker.
is mainly caused by the depopulation of the Stark sublevels
Dynamic alternating current (ac) magnetic susceptibility
of the DyIII ions, which arise from the splitting of the measurements as a function of the temperature at different
6H15/2 ground term by the ligand field as well as to the frequencies and under zero external field show that only 1
thermal depopulation of the levels that arises from spin– exhibits a slight frequency dependence of the out-of-phase
orbit coupling in the CoII ions. The increase in χMT at low (χЈЈM) signals below ca. 10 K, typical of a thermally acti-
temperature indicates a ferromagnetic interaction between vated relaxation process (Figure S6), but does not reach a
the CoII and DyIII ions, which is not unexpected in view of neat maximum, probably because there is an overlap with a
the planarity of the CoII(diphenoxo)DyIII bridging frag- faster quantum tunneling relaxation process, even at fre-
ments. For 3 and 4, as the temperature decreases, the χMT quencies as high as 1400 Hz. This behavior seems to indi-
product decreases, first slightly to ca. 60–70 K and then cate that 1 exhibits slow relaxation of the magnetization
sharply to reach values of 9.60 and 9.11 cm3 K mol–1 at 2 K and possibly SMM behavior. However, the χЈЈM signal is
for 3 and 4, respectively. This behavior is mainly caused by quite weak with a χЈЈM/χЈM ratio of ca. 0.01. When the ac
the thermal depopulation of the Stark sublevels of the TbIII measurements were performed in the presence of a small
and HoIII ions and the spin–orbit coupling levels in the CoII external direct current (dc) field of 1000 G to fully or partly
ion. Therefore, it is not possible to know the sign of the suppress the quantum tunneling relaxation of the magne-
magnetic exchange interaction in these compounds from tization (QTM), the intensity of the signals drastically in-
the χMT versus T plot. It has been found experimentally creased but without resolution of any maximum in the χЈЈM
that, for isostructural M–Ln complexes, the sign for the versus T plot, and the signals almost do not shift with re-
MII–TbIII and MII–HoIII (MII = Co and Ni) magnetic ex- spect to those observed at the same frequencies at zero field
change interactions is the same as that of the MII–GdIII (Figure 9). The out-of-phase signals do not significantly
interaction.[15e,17f–17h,24,25,27] In view of this, ferromagnetic shift with an applied field up to 2000 G (Figure S7).
interactions are expected for 3 and 4.
Moreover, the signals undergo a sharp increase below ca.
The M versus H plot for 1 at 2 K (Figure 8) shows a 5 K. All these facts seem to indicate that the quenching of
relatively rapid increase in the magnetization at low field, the quantum tunneling of the magnetization by the field is
in accord with a high-spin state for this complex, and a almost negligible. The overlap between the thermally acti-
rapid saturation of the magnetization that is almost com- vated and QTM processes below 10 K precludes a detailed
plete above 3 T and reaches a value of 11.75 NμB. This be- analysis of the former. QTM can be caused by the existence
havior suggests the existence of a ground state well sepa- of intermolecular dipole–dipole interactions, which are
rated from the low-lying excited states that is stabilized by known to mediate quantum tunneling relaxation processes.
sufficiently large CoII–DyIII magnetic interactions. Never- In some instances, this relaxation process cannot be shut
theless, the magnetization saturation value is far from the down by the application of a static magnetic field, as in the
expected value (ca. 14.2 NμB) for a DyIII ion with strong case of 1. An appropriate manner to try to eliminate the
easy-axis anisotropy (Ising spin at low temperature with Jz intermolecular interactions and, therefore, the QTM pro-
= Ϯ15/2), ferromagnetically coupled with two SCoeff = 1/2 cess would be to dilute the sample with an isostructural
ions with gCo = 4.3. This may be because the most stable diamagnetic complex such as ZnII–YIII–ZnII. These experi-
sublevels Jz of the DyIII ions are not those with the highest ments are planned for the near future if we are able to
value of Jz = Ϯ15/2, which leads to a weaker anisotropy.
cocrystallize the CoII–DyII–CoII complex with the iso-
The field dependence of the magnetization at 2 K for 3 structural diamagnetic ZnII–YIII–ZnII complex.
and 4 (Figure 8) reveals a relatively slow increase of the
Finally, it should be noted that there are other series of
magnetization at low field compared to that of 1 and then CoII–LnIII–CoII complexes (LnIII = Gd, Td, Dy, Ho), which
a linear increase without clear saturation above 3 T. The were obtained with two different tripodal nonadadentate
Eur. J. Inorg. Chem. 2014, 397–406
402
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
benzylideneamino]-2-methylpropane1,3-diol (LH4). For 1–
4, dc measurements show ferromagnetic interactions at low
temperatures. Dynamic magnetic (ac) measurements show
that none of these compounds except 1 exhibits slow relax-
ation of the magnetization at zero applied field. For 1, the
application of external dc field, even up to 2000 G, does not
suppress the fast zero-field QTM, and the intensity of the
signals drastically increases without the observance of a
maximum.
Experimental Section
Reagents and General Procedures: Solvents and other general rea-
gents used in this work were purified according to standard pro-
cedures.[29] Co(NO3)2·6H2O and 2-amino-2-methylpropane-1,3-diol
were obtained from S. D. Fine Chemicals, Mumbai, India. 2,6-Bis-
(hydroxymethyl)-4-methylphenol, Dy(NO3)3·H2O, Ho(NO3)3·
5H2O, Tb(NO3)3·5H2O Gd(NO3)3·6H2O, and MnO2 were obtained
from Sigma Aldrich Chemical Co. and were used as received.
Instrumentation: Melting points were measured with a JSGW melt-
ing point apparatus. IR spectra were recorded with samples as KBr
pellets with a Bruker Vector 22 FTIR spectrophotometer operating
at 400–4000 cm–1. Elemental analyses of the compounds were ob-
tained with a Thermoquest CE instruments CHNS-O, EA/110
model analyzer. Electrospray ionization mass spectrometry (ESI-
MS) spectra were recorded with a Micromass Quattro II triple qua-
drupole mass spectrometer. 1H NMR spectra were recorded with
samples in CDCl3 solutions with a JEOL JNM LAMBDA 400
model spectrometer operating at 400.0 MHz; chemical shifts are
reported in parts per million (ppm) and referenced with respect to
internal tetramethylsilane (1H).
Figure 9. Temperature dependence of the in-phase χЈM (top) and
out-of-phase χЈЈM (bottom) components of the ac susceptibility for
1 measured under 1000 Oe applied dc field.
ligands.[17f,17g,17h] In both series, the CoII and LnIII ions are
connected by three phenoxo bridging groups with rather
folded Co(O)3Ln bridging fragments. These compounds ex-
hibit SMM behavior; in one of these series,[17h] this has been
proved by hysteresis measurements below 1 K. However,
with the exception of 1, in our series no SMM behavior is
observed. This may be caused by: (1) a comparatively
weaker anisotropy of the LnIII ions induced by ligand-field
effects. The other two Co–Ln–Co series contain tripodal
bridging ligands and exhibit LnO12 coordination spheres
with six short Ln–Ophenoxo distances and six long
Ln–Omethoxy distances, whereas the series described here has
a square-prismatic LnO8 coordination sphere formed by the
coordination of four phenoxo and four hydroxy oxygen
atoms. (2) The unfavorable orientation of the main local
anisotropy axes of the CoII and LnIII ions leads to a rela-
tively weak anisotropy for the whole molecule. Whereas 1–
4 are not centrosymmetric and the diphenoxo-bridging
fragments are turned from each other by 64.75°, (nonparal-
lel main anisotropy axes of the CoII ions) the complexes
of the other two series are centrosymmetric (parallel main
anisotropic axes of the CoII ions). (3) The existence of a
very efficient zero-field QTM. The extended 2D network of
hydrogen bonds in 1–4 can facilitate the fast QTM relax-
ation process.
Magnetic Measurements: The variable-temperature (2–300 K) mag-
netic susceptibility measurements on polycrystalline samples of 1–4
under an applied field of 1000 Oe were performed with a Quantum
Design superconducting quantum interference device (SQUID)
MPMS XL-5 device. The ac susceptibility measurements under dif-
ferent applied static fields were performed by using an oscillating
ac field of 3.5 Oe and ac frequencies ranging from 1 to 1500 Hz. A
pellet of the sample cut into very small pieces was placed in the
sample holder to prevent any torquing of the microcrystals.
X-ray Crystallography: The crystal data for the compounds were
collected with a Bruker SMART CCD diffractometer (Mo-Kα radi-
ation, λ = 0.71073 Å). The program SMART[30a] was used for the
collection of frames of data, indexing of reflections, and determi-
nation of the lattice parameters, SAINT[30a] was used for integra-
tion of the intensity of reflections and scaling, SADABS[30b] was
used for absorption correction, and SHELXTL[30c,30d] was used for
space-group and structure determination and least-squares refine-
ments on F2. All of the structures were solved by direct methods
by using the program SHELXS-97[30e] and refined by full-matrix
least-squares methods against F2 with SHELXL-97.[30e] 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 fig-
ures were generated by using Diamond 3.1e software.[30f] The crys-
tal data and the cell parameters for 1–4 are summarized in Table 2.
Conclusions
We have synthesized a series of linear trinuclear heterobi-
metallic compounds [Co2Ln(LH3)4]·3NO3·xMeOH·yH2O
[Ln = DyIII, x = 2, y = 1.5 (1); Ln = GdIII, x = 2, y = 0.5
(2); Ln = TbIII, x = 2, y = 0.5 (3); Ln = HoIII, x = 2, y =
CCDC-945938 (for 1), -945939 (for 2), -945940 (for 3), and -945941
(for 4) contain the crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge Crystallo-
0.5 (4)] by using 2-[2-hydroxy-3-(hydroxymethyl)-5-methyl- graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Eur. J. Inorg. Chem. 2014, 397–406
403
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Table 2. Crystal data and structure refinement parameters of 1–4.
1
2
3
4
Formula
M [g]
C
108H16o4Dy2N14O57
C108H160Co4Gd2N14O55
3084.72
C108H160Co4N14 O55Tb2
3088.06
C108H160Co4Ho2N14O55
3100.08
3127.22
Crystal system
Space group
a [Å]
b [Å]
c [Å]
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/n
15.059(5)
22.522(5)
20.168(5)
monoclinic
P21/n
15.007(5)
22.565(5)
20.108(5)
15.013(5)
22.564(5)
20.165(5)
93.007(5)
6822(3)
15.014(5)
22.567(5)
20.182(5)
93.093(5)
6828(3)
β (°)
92.938(5)
6831(3)
93.046(5)
6800(3)
V [Å3]
Z
2
2
2
2
ρcalcd. [gcm–3]
μ [mm–1]
F(000)
1.522
1.651
3204
1.500
1.524
3164
1.501
1.588
3168
1.514
1.719
3176
Crystal size [mm]
θ range [°]
Limiting indices
0.068ϫ0.049ϫ0.035
4.14 –25.03
–14Յ hՅ 17
–26Յ kՅ 26
–24Յ lՅ 19
35199
0.065ϫ0.045ϫ0.032
4.14–25.03
–17Յ hՅ 12
–26Յ kՅ 26
–20Յ lՅ 24
35398
0.069ϫ0.048ϫ0.032
4.14–25.02
–17Յ hՅ 17
–26Յ kՅ 26
–14Յ lՅ 24
35152
0.069ϫ0.046ϫ0.034
4.14–25.02
–17Յ hՅ 17
–25Յ kՅ 26
–23Յ lՅ 13
35066
Reflections collected
Independent reflections [R(int)]
Completeness to θ [%]
Refinement method
11971 (0.0620)
99.4
11981 (0.0945)
99.4
11970 (0.0745)
99.3
11935 (0.0506)
99.4
Full-matrix least-squares Full-matrix least-squares
Full-matrix least-squares
Full-matrix least-squares
on F2
on F2
on F2
on F2
Data/restraints/ parameters
Goodness-of-fit on F2
11971/55/876
1.032
11981/90/867
1.030
11970/79/837
1.027
11935/55/867
1.036
Final R indices [IϾ 2θ(I)]
R1 = 0.0792,
wR2 = 0.2159
R1 = 0.1142,
wR2 = 0.2458
R1 = 0.0900,
wR2 = 0.2471
R1 = 0.1580,
wR2 = 0.2944
1.572 and –0.970
R1 = 0.1060,
wR2 = 0.2752
R1 = 0.1586,
wR2 = 0.3136
2.064 and –0.683
R1 = 0.0785,
wR2 = 0.2152
R1 = 0.1018,
wR2 = 0.2325
2.177 and –1.139
R indices (all data)
Largest diff. peak and hole [eÅ–3] 1.836 and –0.828
6-Formyl-2-(hydroxymethyl)-4-methylphenol: The following pro-
cedure has been used for the synthesis of the title compound and
has been adapted from a previously published synthetic method.[31]
A round-bottomed flask was charged with 2,6-bis(hydroxymethyl)-
4-methylphenol (5 g, 30 mmol) and chloroform (500 mL). Manga-
nese dioxide (16 g, 184 mmol) was added portionwise to the stirring
solution. After 24 h, the reaction mixture was filtered, and the sol-
vent was evaporated to give a crude product. This was purified by
column chromatography with a silica gel column and EtOAc/n-
hexane (1:9 v/v) as the eluant to yield a pale yellow solid, yield
2.88 g (58.3%), m.p. 72–74 °C, (ref. 74–76 °C).[32] C9H10O3
General Procedure for the Synthesis of Metal Complexes 1–4: A
general procedure was applied for the preparation of 1–4. To a
stirred solution of LH4 in methanol (30 mL), Ln(NO3)3·nH2O (For
1, n = 1; 2, n = 6; 3, n = 5; 4, n = 5) was added. Then, triethylamine
was added to the above solution, and the reaction mixture was
stirred for 15 minutes. After this, a methanolic solution of Co(NO3)2·
6H2O was added dropwise. The resulting red-brown solution was
stirred for a further 12 h to afford a clear solution. This solution
was filtered, and the filtrate was evaporated to dryness. The residue
obtained was washed with diethyl ether, dried, dissolved in meth-
anol/chloroform (1:1), and kept for crystallization. After 4–7 d, a
pure crystalline product suitable for X-ray diffraction was isolated.
Specific details of each reaction and the characterization data of
the products obtained are given below.
1
(166.18): calcd. C 65.05, H 6.07; found C 65.09, H 6.16. H NMR
(CDCl3): δ = 2.33 (s, 3 H), 4.72 (s, 2 H), 7.28 (s, 1 H), 7.39 (s, 1
H), 9.85 (s, 1 H), 11.16 (s, 1 H) ppm.
2-[2-Hydroxy-3-(hydroxymethyl)-5-methylbenzylideneamino]-2-meth-
[Co2Dy(LH3)4]·3NO3·2MeOH·1.5H2O (1): Quantities: Co(NO3)2·
6H2O (0.04 g, 0.14mmol), Dy(NO3)3·H2O (0.03g, 0.07 mmol), LH4
(0.08 g, 0.29 mmol), and Et3N (0.06 mL, 0.59 mmol), yield 0.069 g,
ylpropane1,3-diol (LH4):
A
methanolic solution of 2-(hy-
droxymethyl)-6-carbaldehyde-4-methylphenol (1.01 g, 6.07 mmol)
was added dropwise to a stirred solution of 2-amino-2-methylpro-
pane-1,3-diol (0.63 g, 6.00 mmol) in methanol (30 mL) at room
temperature. After the addition was over, the reaction mixture was
heated under reflux for 6 h. Then, the reaction mixture was cooled
to room temperature, and most of the solvent was removed with a
rotary evaporator with gentle heating. The concentrate thus ob-
tained (10 mL) was kept in a refrigerator at 5 °C. The bright yellow
crystalline material obtained was collected by suction filtration,
washed with a small amount of cold methanol, and air-dried, yield
1.32 g (85.89%), m.p. 100 °C. C13H19NO4 (253.30): calcd. C 61.64,
H 7.56, N 5.53; found C 61.76, H 7.52, N 5.66. 1H NMR (CDCl3):
δ = 1.14 (s, 3 H), 2.21 (s, 3 H), 3.42 (s, 6 H), 4.46 (s, 2 H), 7.07 (s,
63% (based on Dy), m.p. Ͼ260 °C. IR (KBr): ν = 3196 (b), 2928
˜
(w), 2881 (w), 1632 (s), 1568 (s), 1454 (s), 1384 (s), 1294 (s), 1267
(s), 1171 (w), 1152 (s), 1047 (s), 999 (w), 975 (w), 818 (w), 794 (w),
692 (w), 579 (w) cm–1. ESI-MS: m/z = 430.08 [C52H72N4O16Co2-
Dy]3+. C54H83Co2DyN7O28.5 (1566.63): calcd. C 41.40, H 5.34, N
6.26; found C 41.52, H 5.23, N 6.32.
[Co2Gd(LH3)4]·3NO3·2MeOH·0.5H2O (2): Quantities: Co(NO3)2·
6H2O (0.04 g, 0.14 mmol), Gd(NO3)3·6H2O (0.03 g, 0.07 mmol),
LH4 (0.08 g, 0.29 mmol), and Et3N (0.06 mL, 0.59 mmol), yield
0.062 g, 66% (based on Gd), m.p. Ͼ260 °C. IR (KBr): ν = 3211
˜
(b), 2928 (w), 2881 (w), 1632 (s), 1567 (s), 1453 (s), 1384 (s), 1293
1 H), 7.17 (s, 1 H), 8.41 (s, 1 H) ppm. ESI-MS: m/z = 254.14 [M (s), 1243 (s), 1172 (w), 1047 (s), 997 (w), 974 (w), 818 (w), 794 (w),
+ H]+.
693 (w), 579 (w) cm–1. ESI-MS: m/z = 428.09 [C52H72N4O16Co2-
Eur. J. Inorg. Chem. 2014, 397–406
404
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Gd]3+. C54H81Co2GdN7O27.5 (1543.37): calcd. C 42.02, H 5.29, N
6.35; found C 42.31, H 5.18, N 6.43.
Jurca, A. Farghal, P.-H. Lin, I. Korobkov, M. Murugesu, D. S.
Richardson, J. Am. Chem. Soc. 2011, 133, 15814; g) N. Ishi-
kawa, M. Sugita, T. Ishikawa, S. Koshihara, S. Kaizu, J. Phys.
Chem. B 2004, 108, 11265; h) M. A. Aldamen, J. M. Clemente-
Juan, E. Coronado, C. Martí-Gastaldo, A. Gita-Arinˇo, J. Am.
Chem. Soc. 2008, 130, 8874; i) J. Ruiz, A. J. Mota, A. Rodríg-
uez-Diéguez, S. Titos, J. M. Herrera, E. Ruiz, E. Cremades, J. P.
Costes, E. Colacio, Chem. Commun. 2012, 48, 7916.
a) S. Hill, R. S. Edwards, N. Aliaga-Alcalde, G. Christou, Sci-
ence 2003, 302, 1015; b) A. L. Barra, D. Gatteschi, R. Sessoli,
Phys. Rev. B 1997, 56, 8192; c) R. Sessoli, A. K. Powell, Coord.
Chem. Rev. 2009, 253, 2328; d) W. Wernsdorfer, Adv. Chem.
Phys. 2001, 118, 99; e) D. Gatteschi, A. Caneschi, L. Pardi, R.
Sessoli, Science 1994, 265, 1054.
a) G. Christou, Polyhedron 2005, 24, 2065; b) C. J. Milios, R.
Inglis, A. Vinslava, R. Bagai, W. Wernsdorfer, S. Parsons, S. P.
Perlepes, G. Christouand, E. K. Brechin, J. Am. Chem. Soc.
2007, 129, 12505; c) A. M. Ako, I. J. Hewitt, V. Mereacre, R.
Clerac, W. Wernsdorfer, C. E. Anson, A. K. Powell, Angew.
Chem. 2006, 118, 5048; Angew. Chem. Int. Ed. 2006, 45, 4926;
d) T. Taguchi, W. Wernsdorfer, A. Abboud, G. K. Christou,
Inorg. Chem. 2010, 49, 199; e) Y.-G. Li, W. Wernsdorfer, R.
Clérac, I. J. Hewitt, C. E. Anson, A. K. Powell, Inorg. Chem.
2006, 45, 2376.
a) T. K. Prasad, G. Poneti, L. Sorace, M. J. Rodriguez-Douton,
A. L. Barra, P. Neugebauer, L. Costantino, R. Sessoli, A.
Cornia, Dalton Trans. 2012, 41, 8368; b) C. Schlegel, E. Bur-
zurí, F. Luis, F. Moro, M. Manoli, E. K. Brechin, M. Murrie,
J. V. Slageren, Chem. Eur. J. 2010, 16, 10178; c) R. Bagai, W.
Wernsdorfer, K. A. Abboud, G. Christou, J. Am. Chem. Soc.
2007, 129, 12918; d) Y. Y. Zhu, X. Guo, C. Cui, B. W. Wang,
Z. M. Wang, S. Gao, Chem. Commun. 2011, 47, 8049; e) A. M.
Ako, V. Mereacre, Y. H. Lan, W. Wernsdorfer, R. Clérac, C. E.
Anson, A. K. Powell, Inorg. Chem. 2010, 49, 1.
a) M. Murrie, Chem. Soc. Rev. 2010, 39, 1986 and references
cited therein; b) A. Ferguson, A. Parkin, J. Sanchez-Benitez,
K. Kamenev, W. Wernsdorfer, M. Murrie, Chem. Commun.
2007, 3473; c) B. Moubaraki, K. S. Murray, T. A. Hudson, R.
Robson, Eur. J. Inorg. Chem. 2008, 4525; d) K. W. Galloway,
A. M. Whyte, W. Wernsdorfer, J. Sanchez-Benitez, K. V. Ka-
menev, A. Parkin, R. D. Peacock, M. Murrie, Inorg. Chem.
2008, 47, 7438; e) M. H. Zeng, M. X. Yao, H. Liang, W. X.
Zhang, X. M. Chen, Angew. Chem. 2007, 119, 1864; Angew.
Chem. Int. Ed. 2007, 46, 1832.
a) A. K. Bouldalis, M. Pissas, C. P. Raptopoulou, V. Psycharis,
B. Abarca, R. Ballesteros, Inorg. Chem. 2008, 47, 10674; b) S.
Petit, P. Neugebauer, G. Pilet, G. Chastanet, A. L. Barra, A. B.
Antunes, W. Wernsdorfer, D. Luneau, Inorg. Chem. 2012, 51,
6645; c) A. Ferguson, J. Lawrence, A. Parkin, J. Sanchez-Beni-
tez, K. V. Kamenev, E. K. Brechin, W. Wernsdorfer, S. Hill, M.
Murrie, Dalton Trans. 2008, 6409; d) A. Bell, G. Aromi, S. J.
Teat, W. Wernsdorfer, R. E. P. Winpenny, Chem. Commun.
2005, 2808.
a) P. H. Lin, T. J. Burchell, R. Clérac, M. Murugesu, Angew.
Chem. 2008, 120, 8980; Angew. Chem. Int. Ed. 2008, 47, 8848;
b) G. F. Xu, Q. L. Wang, P. Gamez, Y. Ma, R. Clérac, J. K.
Tang, S. P. Yan, P. Cheng, D. Z. Liao, Chem. Commun. 2010,
46, 1506; c) R. A. Layfield, J. J. W. McDouall, S. A. Sulway, F.
Tuna, D. Collison, R. E. P. Winpenny, Chem. Eur. J. 2010, 16,
4442.
a) I. J. Hewitt, Y. Lan, C. E. Anson, J. Luzon, R. Sessoli, A. K.
Powell, Chem. Commun. 2009, 6765; b) J. Luzon, K. Bernot,
I. J. Hewitt, C. E. Anson, A. K. Powell, R. Sessoli, Phys. Rev.
Lett. 2008, 100, 247205; c) M. U. Anwar, S. S. Tandon, L. N.
Dawe, F. Habib, M. Murugesu, L. K. Thompson, Inorg. Chem.
2012, 51, 1028; d) F. S. Guo, J. L. Liu, J. D. Leng, Z. S. Meng,
Z. J. Lin, M. L. Tong, S. Gao, L. Ungur, L. F. Chibotaru,
Chem. Eur. J. 2011, 17, 2458.
[Co2Tb(LH3)4]·3NO3·2MeOH·0.5H2O (3): Quantities: Co(NO3)2·
6H2O (0.04 g, 0.14 mmol), Tb(NO3)3·5H2O (0.03 g, 0.07 mmol),
LH4 (0.08 g, 0.29 mmol), and Et3N (0.06 mL, 0.59 mmol), yield
0.071 g, 64% (based on Tb), m.p. Ͼ260 °C. IR (KBr): ν = 3198
˜
(b), 2929 (w), 2888 (w), 1632 (s), 1567 (s), 1453 (s), 1386 (s), 1294
(s), 1242 (s), 1150 (w), 1046 (s), 999 (w), 975 (w), 820 (w), 794 (w),
693 (w), 580 (w) cm–1. ESI-MS: m/z = 428.41 [C52H72N4O16Co2-
Tb]3+. C54H81Co2N7O27.5Tb (1544.31): calcd. C 41.98, H 5.28, N
6.35; found C 42.21, H 5.15, N 6.41.
[4]
[5]
[Co2Ho(LH3)4]·3NO3·2MeOH·0.5H2O (4): Quantities: Co(NO3)2·
6H2O (0.04 g, 0.14 mmol), Ho(NO3)3·5H2O (0.03 g, 0.07 mmol),
LH4 (0.08 g, 0.29 mmol), and Et3N (0.06 mL, 0.59 mmol), yield
0.068 g, 61% (based on Ho), m.p. Ͼ260 °C. IR (KBr): ν = 3220
˜
(b), 2924 (w), 2882 (w), 1632 (s), 1567 (s), 1454 (s), 1384 (s), 1294
(s), 1224 (s), 1171 (w), 1048 (s), 998 (w), 974 (w), 819 (w), 794 (w),
693 (w), 578 (w) cm–1. ESI-MS: m/z = 430.42 [C52H72N4O16Co2-
Ho]3+. C54H81Co2HoN7O27.5 (1550.31): calcd. C 41.82, H 5.26, N
6.32; found C 42.13, H 5.12, N 6.45.
Supporting Information (see footnote on the first page of this arti-
cle): ESI-MS, tricationic portion of 2–4, hydrogen-bond 2D net-
work for 1, H-bonding for 1, list of bond lengths and angles, tem-
perature dependece of the AC susceptibility for complex 1 at zero
field, and field dependence of the out-of-phase component at
1200 Hz.
[6]
[7]
[8]
Acknowledgments
The authors are thankful to the Department of Science and Tech-
nology (DST), New Delhi, for financial support. S. D., A. D., S. H.
and S. K. thank the Council of Scientific and Industrial Research
(CSIR), New Delhi for Senior Research Fellowships. V. C. is thank-
ful to the Department of Science and Technology for a J. C. Bose
National Fellowship. E. C. thanks the Spanish Ministerio de Cien-
cia e Innovación (MICINN) (project number CTQ-2011-24478),
the Junta de Andalucia (FQM-195 and Project of excellence, P11-
FQM-7756), and the University of Granada for financial support.
[1] a) D. Gatteschi, R. Sessoli, J. Villain, Molecular Nanomagnets,
Oxford University Press, Oxford, UK, 2006; b) R. Sessoli, L.
Hui, A. R. Schake, S. Wang, J. B. Vincent, K. Folting, D. Gat-
teschi, G. Christou, J. Am. Chem. Soc. 1993, 115, 1804.
[2] a) H. Miyasaka, T. Madanbashi, A. Saitoh, N. Motokawa, R.
Ishikawa, M. Yamashita, S. Bahr, W. Wernsdorfer, R. Clerac,
Chem. Eur. J. 2012, 18, 3942; b) J. Boeckmann, C. Nather,
Chem. Commun. 2011, 47, 7104; c) T. S. Venkatakrishnan, S.
Sahoo, N. Brefuel, C. Duhayon, C. Paulsen, A.-L. Barra, S.
Ramasesha, J.-P. Sutter, J. Am. Chem. Soc. 2010, 132, 6047; d)
T. D. Harris, M. V. Bennett, R. Clerac, J. R. Long, J. Am.
Chem. Soc. 2010, 132, 3980; e) X. Feng, T. D. Harris, J. R.
Long, Chem. Sci. 2011, 2, 1688; f) E. Pardo, C. Train, R. Les-
couezec, Y. Journaux, J. Pasan, C. Ruiz-Perez, F. S. Delgado,
R. Ruiz-Garcia, F. Lloret, P. Carley, Chem. Commun. 2010, 46,
2322.
[3] a) D. E. Freedman, W. H. Harman, T. D. Harris, G. J. Long,
C. J. Chang, J. R. Long, J. Am. Chem. Soc. 2010, 132, 1224; b)
S.-D. Jiang, B.-W. Wang, H.-L. Sun, Z.-M. Wang, S. Gao, J.
Am. Chem. Soc. 2011, 133, 4730; c) J. Vallejo, I. Castro, R.
Ruiz-Garcia, J. Cano, M. Julve, F. Lloret, G. De Munno, W.
Wernsdorfer, E. Pardo, J. Am. Chem. Soc. 2012, 134, 15704; d)
J. M. Zadrozny, J. R. Long, J. Am. Chem. Soc. 2011, 133,
20732; e) D. Weismann, Y. Sun, Y. Lan, G. Wolmershäuser,
A. K. Powell, H. Sitzmann, Chem. Eur. J. 2011, 17, 4700; f) T.
[9]
[10]
[11]
a) Y. Bi, X.-T. Wang, W. Liao, X. Wang, R. Deng, H. Zhang,
S. Gao, Inorg. Chem. 2009, 48, 11743; b) H.-S. Ke, G.-F. Xu, Y.-
Eur. J. Inorg. Chem. 2014, 397–406
405
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
N. Guo, P. Gamez, C. M. Beavers, S. J. Teat, J. K. Tang, Chem.
Commun. 2010, 46, 6057; c) Y. N. Guo, G. F. Xu, P. Gamez, L.
Zhao, S. Y. Lin, R. P. Deng, J. K. Tang, H. J. Zhang, J. Am.
Chem. Soc. 2010, 132, 8538; d) S. Y. Lin, L. Zhao, H. Ke, Y. N.
Guo, J. K. Tang, Y. Guoa, J. Dou, Dalton Trans. 2012, 41,
3248; e) G. Abbas, Y. Lan, G. E. Kostakis, W. Wernsdorfer,
C. E. Anson, A. K. Powell, Inorg. Chem. 2010, 49, 8067; f) V.
Chandrasekhar, S. Hossain, S. Das, S. Biswas, J. P. Sutter, Inorg.
Chem. 2013, 52, 6346.
Chem. Commun. 2011, 47, 8659; e) Y.-Z. Zheng, M. Evange-
listi, R. E. P. Winpenny, Chem. Sci. 2011, 2, 99; f) V. Chandra-
sekhar, B. M. Pandian, J. J. Vittal, R. Clérac, Inorg. Chem.
2009, 48, 1148; g) V. Chandrasekhar, B. M. Pandian, R.
Azhakar, J. J. Vittal, R. Clérac, Inorg. Chem. 2007, 46, 5140; h)
T. Yamaguchi, J. P. Costes, Y. Kishima, M. Kojima, Y. Sunat-
suki, N. Brefuel, J. P. Tuchagues, L. Vendier, W. Wernsdorfer,
Inorg. Chem. 2010, 49, 9125.
[18] V. Chandrasekhar, A. Dey, A. J. Mota, E. Colacio, Inorg.
Chem. 2013, 52, 4554.
[12] a) M. T. Gamer, Y. Lan, P. W. Roesky, A. K. Powell, R. Clérac,
Inorg. Chem. 2008, 47, 6581; b) J. B. Peng, X. J. Kong, Y. P.
Ren, L. S. Long, R. B. Huang, L. S. Zheng, Inorg. Chem. 2012,
51, 2186; c) R. J. Blagg, C. A. Muryn, E. J. L. McInnes, F.
Tuna, R. E. P. Winpenny, Angew. Chem. 2011, 123, 6660; An-
gew. Chem. Int. Ed. 2011, 50, 6530.
[13] a) B. Hussain, D. Savard, T. J. Burchell, W. Wernsdorfer, M.
Murugesu, Chem. Commun. 2009, 1100; b) I. J. Hewitt, J. K.
Tang, N. T. Madhu, C. E. Anson, Y. Lan, J. Luzon, M. Eti-
enne, R. Sessoli, A. K. Powell, Angew. Chem. 2010, 122, 6496;
Angew. Chem. Int. Ed. 2010, 49, 6352; c) S. Xue, L. Zhao, Y. N.
Guo, P. Zhang, J. K. Tang, Chem. Commun. 2012, 48, 8946; d)
Y. N. Guo, X. H. Chen, S. Xue, J. K. Tang, Inorg. Chem. 2012,
51, 4035; e) H. Tian, M. Wang, L. Zhao, Y. N. Guo, Y. Guo,
J. K. Tang, Z. Liu, Chem. Eur. J. 2012, 18, 442.
[14] a) G. Novitchi, G. Pilet, L. Ungur, V. V. Moshchalkov, W.
Wernsdorfer, L. F. Chibotaru, D. Luneau, A. K. Powell, Chem.
Sci. 2012, 3, 1169; b) S. K. Langley, L. Ungur, N. F. Chilton,
B. Moubaraki, L. F. Chibotaru, K. S. Murray, Chem. Eur. J.
2011, 17, 9209; c) G. Novitchi, W. Wernsdorfer, L. F. Chibot-
aru, J.-P. Costes, C. E. Anson, A. K. Powell, Angew. Chem.
2009, 121, 1642; Angew. Chem. Int. Ed. 2009, 48, 1614; d) F.
Mori, T. Nyui, T. Ishida, T. Nogami, K.-Y. Choi, H. Nojiri, J.
Am. Chem. Soc. 2006, 128, 1440; e) V. Chandrasekhar, A. Dey,
S. Das, M. Rouziéres, R. Clérac, Inorg. Chem. 2013, 52, 2588.
[15] a) C. G. Efthymiou, T. C. Stamatatos, C. Papatriantafyllopou-
lou, A. J. Tasiopoulos, W. Wernsdorfer, S. P. Perlepes, G.
Christou, Inorg. Chem. 2010, 49, 9737; b) T. D. Pasatoiu, J.-P.
Sutter, A. M. Madalan, F. Z. C. Fellah, C. Duhayon, M. And-
[19] a) V. Chandrasekhar, R. Azhakar, B. Murugesapandian, T.
Senapati, P. Bag, M. D. Pandey, S. K. Maurya, D. Goswami,
Inorg. Chem. 2010, 49, 4008; b) V. Chandrasekhar, R. Azhakar,
J. Bickley, A. Steiner, Chem. Commun. 2005, 459; c) V. Chand-
rasekhar, R. Azhakar, G. T. S. Andavan, V. Krishnan, S. Zacch-
ini, J. Bickley, A. Steiner, R. J. Butcher, P. Kögerler, Inorg.
Chem. 2003, 42, 5989; d) V. Chandrasekhar, R. Azhakar, S.
Zacchini, J. Bickley, A. Steiner, Inorg. Chem. 2005, 44, 4608; e)
V. Chandrasekhar, R. Azhakar, B. M. Pandian, J. Bickley, A.
Steiner, Eur. J. Inorg. Chem. 2008, 7, 1116; f) V. Chandrasekhar,
B. M. Pandian, Acc. Chem. Res. 2009, 42, 1047.
[20] a) V. Chandrasekhar, B. M. Pandian, R. Boomishankar, A.
Steiner, J. J. Vittal, A. Houri, R. Clérac, Inorg. Chem. 2008, 47,
4918; b) V. Chandrasekhar, B. M. Pandian, R. Boomishankar,
A. Steiner, R. Clérac, Dalton Trans. 2008, 38, 5143.
[21] M. E. J. Lines, J. Chem. Phys. 1971, 55, 2977.
[22] J. P. Costes, F. Dahan, A. Dupuis, J. P. Laurent, C. R. Acad.
Sci., Ser. IIc 1998, 1, 417.
[23] J. P. Costes, F. Dahan, J. Garcia Tojal, Chem. Eur. J. 2002, 8,
5430.
[24] E. Colacio, J. Ruiz, A. J. Mota, M. A. Palacios, E. Ruiz, E.
Cremades, M. M. Hänninen, R. Sillanpää, E. K. Brechin, C.
R. Chim. 2012, 15, 878.
[25] M. Towatari, K. Nishi, T. Fujinami, N. Matsumoto, Y. Sunat-
suki, M. Kojima, N. Mochida, T. Ishida, N. Re, J. Mrozinski,
Inorg. Chem. 2013, 52, 6160.
[26] L. Ungur, M. Thewissen, J.-P. Costes, W. Wernsdorfer, L. F.
Chibotaru, Inorg. Chem. 2013, 52, 6328.
ruh, Inorg. Chem. 2011, 50, 5890; c) K. Xiong, X. Wang, F. [27] a) J. Cirera, E. Ruiz, C. R. Chim. 2008, 11, 1227; b) G. Rajara-
Jiang, Y. Gai, W. Xu, K. Su, X. Li, D. Yuan, M. Hong, Chem.
Commun. 2012, 48, 7456; d) F. Pointillart, K. Bernot, R. Ses-
soli, D. Gatteschi, Chem. Eur. J. 2007, 13, 1602; e) 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.
man, F. Totti, A. Bencini, A. Caneschi, R. Sessoli, D. Gattes-
chi, Dalton Trans. 2009, 3153.
[28] a) S. K. Singh, N. K. Tibrewal, G. Rajaraman, Dalton Trans.
2011, 40, 10897.
[29] B. S. Furniss, A. J. Hannaford, P. W. G. Smith, A. R. Tatchell,
Vogel’s Textbook of Practical Organic Chemistry, 5th ed.,
ELBS, Longman, London, 1989.
[30] a) SMART & SAINT Software Reference manuals, v.6.45,
Bruker AXS, Madison, WI, 2003; b) G. M. Sheldrick, SAD-
ABS, a software for empirical absorption correction, v.2.05, Uni-
versity of Göttingen, Germany, 2002; c) SHELXTL Reference
Manual, v.6.1, Bruker AXS, Madison, WI, 2000; d) G. M. Shel-
drick, SHELXTL, v.6.12, Bruker AXS, Madison, WI, 2001; e)
G. M. Sheldrick, SHELXL97, Program for Crystal Structure
Refinement, University of Göttingen, Germany, 1997; f) K.
Bradenburg, Diamond, v.3.1eM, Crystal Impact GbR, Bonn,
2005.
[31] a) R.-G. Xie, Z.-J. Zhang, J.-M. Yan, D.-Q. Yuan, Synth. Com-
mun. 1994, 24, 53; b) E. Lambert, B. Chabut, S. Chardon-Nob-
lat, A. Deronzier, G. Chottard, A. Bousseksou, J.-P. Tuchagues,
J. Laugier, M. Bardet, J.-M. Latour, J. Am. Chem. Soc. 1997,
119, 9424.
[16] a) T. C. Stamatatos, S. J. Teat, W. Wernsdorfer, G. Christou,
Angew. Chem. 2009, 121, 529; Angew. Chem. Int. Ed. 2009, 48,
521; b) V. Mereacre, A. M. Ako, R. Clérac, W. Wernsdorfer,
I. J. Hewitt, C. E. Anson, A. K. Powell, Chem. Eur. J. 2008, 14,
3577; c) M. Li, Y. Lan, A. M. Ako, W. Wernsdorfer, C. E. An-
son, G. Buth, A. K. Powell, Z. Wang, S. Gao, Inorg. Chem.
2010, 49, 11587; d) C. Papatriantafyllopoulou, K. A. Abboud,
G. Christou, Inorg. Chem. 2011, 50, 8959; e) J.-L. Liu, F.-S.
Guo, Z.-S. Meng, Y.-Z. Zheng, J.-D. Leng, M.-L. Tong, L. Un-
gur, L. F. Chibotaru, K. J. Heroux, D. N. Hendrickson, Chem.
Sci. 2011, 2, 1268; f) H. Ke, L. Zhao, Y. Guoa, J. K. Tang,
Dalton Trans. 2012, 41, 2314; g) V. Chandrasekhar, P. Bag, M.
Speldrich, J. Leusen, P. Kögerler, Inorg. Chem. 2013, 52, 5035.
[17] a) G. J. Sopasis, M. Orfanoudaki, P. Zarmpas, A. Philippidis,
M. Siczek, T. Lis, J. R. O’Brien, C. J. Milios, Inorg. Chem. 2012,
51, 1170; b) K. C. Mondal, A. Sundt, Y. Lan, G. E. Kostakis,
O. Waldmann, L. Ungur, L. F. Chibotaru, C. E. Anson, A. K.
Powell, Angew. Chem. 2012, 124, 7668; Angew. Chem. Int. Ed. [32] W. Huang, S. Gou, D. Hu, Q. Meng, Synth. Commun. 2000,
2012, 51, 7550; c) Y. Liu, Z. Chen, J. Ren, X. Q. Zhao, P.
Cheng, B. Zhao, Inorg. Chem. 2012, 51, 7433; d) L.-F. Zou, L.
Zhao, Y.-N. Guo, G.-M. Yu, Y. Guo, J. K. Tang, Y.-H. Li,
30, 1555.
Received: September 10, 2013
Published Online: November 26, 2013
Eur. J. Inorg. Chem. 2014, 397–406
406
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim