Synthesis, structure, and magnetic properties of a family of heterometallic pentanuclear [Co4Ln] (Ln = GdIII, DyIII, TbIII, and HoIII) assemblies

Article abstract of DOI:10.1002/ejic.201300413

The reaction of 6-formyl-2-(hydroxymethyl)-4-methylphenol (LH₂) with appropriate lanthanide salts followed by reaction with Co(OAc) ₂·4H₂O afforded the pentanuclear heterobimetalllic compounds [Co₄Ln(L)₄(OAc)₂(S) ₄](NO₃)(S) [Ln^III = Gd^III, S = MeOH (1); Ln^III = Dy^III, S = H₂O (2); Ln ^III = Tb^III, S = MeOH (3); Ln^III = Ho ^III, S = MeOH (4)] in good yields. All the compounds are stable in solution as confirmed by ESI-MS studies. These complexes contain a distorted Co₄ tetrahedral core, which encapsulates a central lanthanide ion. The Co^II and Ln^III ions are in an all-oxygen environments. All the Co^II ions possess a distorted octahedral geometry, and the Ln^III ions are in a distorted square-antiprismatic geometry. The magnetic properties of 1-4 have been investigated in the temperature range 2-300 K. In addition, the magnetic properties of 1 were fitted by using a Hamiltonian of the type H = H_SO + H_axial + H_exchange + H_Zeeman. A moderately strong antiferromagnetic interaction between the nearest-neighbour Co^II ions was found, whereas the magnetic interaction between the Co^II ions and the corresponding Ln ^III ions is negligible. The reaction of 6-formyl-2-(hydroxymethyl)-4- methylphenol with lanthanide salts followed by reaction with Co(OAc) ₂·4H₂O affords new pentanuclear heterobimetalllic compounds with a [Co₄Ln] core. Magnetic studies on these compounds reveal a moderately strong antiferromagnetic interaction between the Co ^II ions, whereas the interactions between the Co^II and Ln^III ions are negligible. Copyright

Full text of DOI:10.1002/ejic.201300413

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Heterometallic Complexes
V. Chandrasekhar,* S. Das, A. Dey,
S. Hossain, F. Lloret, E. Pardo ....... 1–10
The reaction of 6-formyl-2-(hydroxy-
methyl)-4-methylphenol with lanthanide
salts followed by reaction with Co(OAc)
4H O affords new pentanuclear heterobi-
metalllic compounds with a [Co Ln] core.
2
·
Synthesis, Structure, and Magnetic Proper-
ties of a Family of Heterometallic Penta-
2
4
III
III
III
nuclear [Co
and Ho ) Assemblies
4
Ln] (Ln = Gd , Dy , Tb
,
Magnetic studies on these compounds re-
veal a moderately strong antiferromagnetic
III
II
interaction between the Co ions, whereas
II
III
Keywords: Lanthanides / Bridging ligands /
Heterometallic complexes / Antiferromag-
netic interactions
the interactions between the Co and Ln
ions are negligible.
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DOI:10.1002/ejic.201300413
Synthesis, Structure, and Magnetic Properties of a Family
III
of Heterometallic Pentanuclear [Co Ln] (Ln = Gd ,
4
III
III
III
Dy , Tb , and Ho ) Assemblies
[
a,b]
[a]
[a]
Vadapalli Chandrasekhar,*
Sourav Das, Atanu Dey,
[a]
[c]
[c]
Sakiat Hossain, Francesc Lloret, and Emilio Pardo
Keywords: Lanthanides / Bridging ligands / Heterometallic complexes / Antiferromagnetic interactions
The reaction of 6-formyl-2-(hydroxymethyl)-4-methylphenol
LH ) with appropriate lanthanide salts followed by reaction
with Co(OAc) ·4H O afforded the pentanuclear heterobimet-
4 3
alllic compounds [Co ](NO )(S) [Ln = Gd ,
ions possess a distorted octahedral geometry, and the LnIII
ions are in a distorted square-antiprismatic geometry. The
magnetic properties of 1–4 have been investigated in the
temperature range 2–300 K. In addition, the magnetic prop-
erties of 1 were fitted by using a Hamiltonian of the type H
= HSO + Haxial + Hexchange + HZeeman. A moderately strong
antiferromagnetic interaction between the nearest-neigh-
(
2
2
2
III
III
4
Ln(L)
4
III
(OAc)
2
(S)
III
III
III
S = MeOH (1); Ln = Dy , S = H O (2); Ln = Tb , S =
2
III
III
MeOH (3); Ln = Ho , S = MeOH (4)] in good yields. All the
compounds are stable in solution as confirmed by ESI-MS
II
studies. These complexes contain a distorted Co
4
tetrahedral
bour Co ions was found, whereas the magnetic interaction
II
II
III
core, which encapsulates a central lanthanide ion. The Co
between the Co ions and the corresponding Ln ions is neg-
ligible.
III
II
and Ln ions are in an all-oxygen environments. All the Co
Introduction
method has been the bedrock for the preparation of a large
number of multimetallic aggregates with interesting mag-
Molecular polynuclear metal aggregates are of consider-
able contemporary interest in view of their intriguing and
[4a–4f,6]
netic properties.
However, in spite of the success of
this methodology, there have been many efforts to design
ligands that interact with transition metal/lanthanide metal
[1]
[2]
interesting structures, relevance to nanoscience, cataly-
sis[ as well as applications in the area of molecule-based
3]
[7]
ions in a partially or fully controllable way. In this regard,
[
4]
magnetic materials. One of the principal challenges for the
synthetic chemist in this field is to devise appropriate li-
gands and strategies that can allow modulation of the nu-
clearity of the polynuclear ensemble and also to ensure pre-
cise placement of metal ions within the overall structure.
This task is by no means trivial and consequently this area
we have recently investigated the metalation behaviour of
the
phosphorus-supported
tris-hydrazone
ligand
S=P[N(Me)N=CH–C H -2-OH-3-OMe] with transition
6
3
3
metal/lanthanide ions and have found that 3d homotrime-
[8]
[7g,9]
tallic and 3d/4f heterotrimetallic
compounds could be
readily prepared from these reactions. Interestingly, we have
[
5]
of research is dominated by serendipity-based synthesis,
+
observed that a family of [L Co Ln] systems in which Ln
2
2
which involves the use of polytopic ligands that interact
with transition metal ions, generally in the presence of other
ancillary ligands, to form compounds with nuclearity and
structures that could not have been predicted a priori. This
III
III
III
III
=
Gd , Tb , Dy and Ho behave as single-molecule
[7g,9c]
[10]
magnets.
Such cobalt-containing magnetic materials
and those containing Co–Ln heterobimetallic motifs
have now become quite an active field of research.
[7g,9c,11]
[10a]
In
view of this, we were interested to see if we could use other
types of ligands that would allow the assembly of polynu-
clear heterometallic compounds containing cobalt(II) and
lanthanide(III) ions. Accordingly, we have utilized 6-formyl-
[
a] Department of Chemistry, Indian Institute of Technology
Kanpur,
Kanpur 208016, India
E-mail: vc@iitk.ac.in
Homepage: http://www.iitk.ac.in
b] Tata Institute of Fundamental Research, Centre for
Interdisciplinary Sciences,
2
-(hydroxymethyl)-4-methylphenol (LH ) to synthesize the
[
[
2
first examples of heterometallic pentanuclear Co–Ln com-
2
1 Brundavan Colony, Narsingi, Hyderabad 500075, India
III
III
plexes: [Co Ln(L) (OAc) (S) ](NO )(S) [Ln = Gd , S =
4
4
2
III
4
3
Homepage: http://www.tifrh.res.in
III
III
III
c] Departament de Química Inorgànica, Instituto de Ciencia
Molecular (ICMOL), Universitat de València,
MeOH (1); Ln = Dy , S = H O (2); Ln = Tb , S =
2
III
III
MeOH (3); Ln = Ho , S = MeOH (4)]. The synthesis,
structure and magnetism of this new family of hetero-
metallic compounds are discussed in this article.
4
6980 Paterna, València, Spain
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300413
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Results and Discussion
Synthesis
Although the Schiff-base formed between LH and pro-
2
pylenediamine was previously used by Powell and co-
workers for the synthesis of 3d/4f heterometallic complex-
es,[ the ligand LH itself has not been utilized previously
6o]
2
for metalation. Accordingly, the reaction of LH with ap-
2
propriate lanthanide salts followed by reaction with Co-
(
OAc) ·4H O in a 4:1:4 stoichiometric ratio in the presence
2 2
of triethylamine afforded a series of pentanuclear heterobi-
metallic compounds [Co Ln(L) (OAc) (S) ](NO )(S) [Ln =
4
4
2
4
3
Gd, S = MeOH (1); Ln = Dy, S = H O (2); Ln = Tb, S =
2
MeOH (3); Ln = Ho, S = MeOH (4)] in good yields
(Ͼ 60%, Scheme 1, see also, Experimental Section). Inter-
estingly, although several types of heterometallic Co–Ln
II
[7g]
[9c]
systems [e.g., Co Ln (Ln = Tb, Dy, Ho, Eu, Gd and
2
[11e]
II
[11b]
Ln = La, Gd, Tb, Dy);
Co Ln (Ln = Dy,
Ln =
2
2
[
11h]
[11k]
III
Gd, Tb, Y
and Ln = Y, Gd, Tb, Dy);
Co Ln (Ln
2
2
[
11j]
[11i]
II
=
Dy);
Dy
and Ln = Dy, Tb, Gd);
Co 2Ln (Ln =
10
II
[
11d]
II
III
[11g]
Co 2Co Ln (Ln = Y, Gd, Dy);
Co Ln (Ln
4
4
4
2
[
11c]
CoII6Ln
[11a]
=
Dy, Ho);
(Ln = Eu, Sm, Tb, Ho, Er, Tm);
II
II
[11l]
Co Ln , Co Ln (Ln = Gd)]
have been reported, this
8
8
4
6
is the first instance of the synthesis of a heterometallic
Co Ln assembly.
4
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
=
1167.87 corresponding to
+
[
[
[
C H Co GdO ] for 1, m/z = 1173.87 corresponding to
4
0
38
4
16
+
C H Co DyO ] for 2, m/z = 1168.87 corresponding to
4
0
38
4
16
+
C H Co TbO ] for 3 and m/z = 1174.89 corresponding
4
0
38
4
16
+
to [C H Co HoO ] for 4. A representative ESI-MS
4
0
38
4
16
spectrum of 1 is shown in Figure 1.
The IR spectrum of the ligand LH shows a sharp peak
2
Figure 1. (a) ESI-MS spectrum of 1. (b) Simulated isotopic pattern.
–
1
at 1644 cm for the C=O group. However, upon metalation
(
1–4) this peak shifts to lower energy by ca. 8–10 cm–1 (see ca. 1554 cm–1 is seen in the IR spectra of 1–4 and is as-
Supporting Information) as the C=O unit of the ligand par- signed to the asymmetric stretching of the bridging acetate
ticipates in coordination. Another strong peak at ligand (see Supporting Information).
Scheme 1. Synthesis of 1–4.
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The UV/Vis spectra of LH and 1–4 in MeOH are shown of 1 are summarized in the caption of Figure 2. Other bond
2
in Supporting Information. We maintained the concentra- parameters including those of 2–4 are given in the Support-
–
4
tion of all compounds at 10 m. The ligand shows two ing Information.
characteristic absorption peak at 341 and 261 nm owing to The molecular structure of 1 (Figures 2 and 3) contains
II
III
the π–π* transitions of the C=O group and benzene ring, a severely distorted tetrahedral Co4 Gd core in which the
II
respectively. All of the complexes 1–4 show similar patterns corners of the tetrahedron are occupied by the Co ions
in the 200–500 nm range. Owing to metalation, both the (Figure 3, a). To the best of our knowledge, this kind of a
ligand-centred peaks shifted to longer wavelength by ca. 10 structural form in mixed 3d/4f complexes is unprecedented.
and 40 nm, respectively. These may be attributed as charge- The intermetallic distances and angles vary considerably.
transfer (CT) bands (see Supporting Information).
The two Co Gd fragments contained within the Co Gd
2
4
core are almost orthogonal [80.17(2)°] to each other (Fig-
ure 3, b). An interesting aspect of the structure is that the
X-ray Crystal Structures of 1–4
central gadolinium ion is a part of six GdCoO four-mem-
2
bered rings (Figure 3, b). The entire Co Gd core is held
together by the concerted coordination of four dianionic
4
Single-crystal X-ray diffraction studies reveal that 1–4
are isostructural and crystallize in the monoclinic space
group P2 /n. All the complexes are monocationic and con-
1
tain one nitrate counteranion. Owing to the similarity in
the structural features of 1–4, the structure of 1 will be de-
scribed as a representative example. The molecular struc-
ture of 1 is shown in Figure 2, and those of 2–4 are given
in the Supporting Information. Selected bond parameters
Figure 2. Cationic part of 1 (hydrogen atoms and solvent molecules
have been omitted for clarity). Bond lengths [Å] and angles [°]:
Gd1–O1 2.391(3), Gd1–O2 2.346(3), Gd1–O4 2.374(3), Gd1–O5
2
.345(3), Gd1–O7 2.385(3), Gd1–O8 2.338(3), Gd1–O10 2.384(3),
Gd1–O11 2.332(3), Co1–O1 2.111(3), Co1–O8 2.089(3), Co1–O9
.057(3), Co1–O10 2.141(3), Co1–O13 2.038(3), Co2–O1 2.135(3),
Co2–O5 2.076(3), Co2–O6 2.074(3), Co2–O10 2.109(3), Co2–O14
.053(3), Co3–O2 2.124(3), Co3–O3 2.053(3), Co3–O4 2.129(3),
Co3–O7 2.080(3), Co3–O15 2.038(3), Co4–O4 2.103(3), Co4–O7 Figure 3. (a) Co
.151(3), Co4–O11 2.076(3), Co4–O12 2.066(3), Co4–O16 2.016(3), angles [°]: Co1–Co2 3.154(9), Co1–Co3 5.991(1), Co1–Co4
Co1–O1–Gd1 88.62(11), Co1–O8–Gd1 90.60(12), Co1–O10–Gd1 5.822(1), Co2–Co3 5.850(9), Co2–Co4 5.965(1), Co3–Co4 3.1249,
8.12(11), Co2–O1–Gd1 88.33(11), Co2–O5–Gd1 91.02(11), Co2– Co1–Gd1 3.151(7), Co2–Gd1 3.159(7), Co3–Gd1 3.149(7), Co4–
O10–Gd1 89.11(11), Co3–O2–Gd1 89.46(12), Co3–O4–Gd1 Gd1 3.163(7), Co1–Gd1–Co2 59.67(1), Co1–Gd1–Co3 143.91(1),
8.61(11), Co3–O7– Gd1 89.47(12), Co4–O4–Gd1 89.69(11), Co4– Co1–Gd1–Co4 134.44(1), Co2–Gd1–Co3 136.04(1), Co2–Gd1–
2
2
4
Gd core of 1. Intermetallic distances [Å] and
2
8
8
O7– Gd1 88.28(11), Co4–O11–Gd1 91.53(12), Co1–O1–Co2 Co4 141.35(1), Co4–Gd1–Co3 59.33(1). (b) Four-membered
9
5.93(12), Co1–O10–Co2 95.80(12), Co3–O4–Co4 95.19(12), Co3–
[CoGdO
halves.
2
] rings of 1 showing the orthogonal disposition of the two
O7–Co4 95.19(13).
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L2– ligands. Each ligand provides one alcoholic μ -oxygen coordination sphere is also found around the central lan-
3
atom, one phenolic μ -oxygen and one aldehydic oxygen thanide ion. This is achieved by through coordination to
2
atom (Scheme 2).
four phenolate oxygen atoms and four alcoholate oxygen
atoms. The eight-coordinate lanthanide ion possesses a dis-
torted square antiprism geometry (Figure 4, b).
The Co–O bond lengths are in the range 2.013–2.151 Å
(Figure 1). The Co–O–Co and Co–O–Ln angles lie in rather
narrow ranges 95.19(12)–98.0(3) and 88.12(11)–91.43(16)°,
respectively. The bond lengths around the lanthanide ions
show almost the expected general tendency towards shorter
values over the series 1, 3, 2, 4, which is consistent with the
phenomenon of lanthanide contraction (Table 1).
Table 1. Comparison of selected Ln–O bond lengths [Å] of 1–4.
Scheme 2.
1
(
3
2
4
LnIII = GdIII) (Ln = Tb )( Ln = Dy ) (Ln = HoIII)
III
III
III
III
III
The alcoholic μ -oxygen atom (O1, O4) functions as a
bridge between two terminal Co ions and the central Gd
ions, the μ -phenolic oxygen atom (O2, O5) bridges a Co
ion with a Gd ion, and the aldehydic oxygen atoms (O3,
O6) binds in a unidentate manner with a Co ion. In ad-
dition to the binding provided by L , the Co core is fur-
ther held together as a result of two η :η :μ -binding acet-
3
Ln–Ophenolate 2.340(3)
Ln–Obenzylic 2.384(3)
2.325(4)
2.368(4)
2.313(8)
2.355(7)
2.304(4)
2.348(4)
II
III
II
2
III
II
2
–
4
1
1
Magnetic Studies
2
ate anions. Each acetate ligand is involved in a syn–syn
The direct current (dc) magnetic properties of 1–4 in the
form of the χ T vs. T plots (χ is the dc molar magnetic
susceptibility per Co 4Ln unit) have been investigated in
bridge between two adjacent terminal cobalt ions. The co-
M
M
II
ordination sphere of each of the Co ions is completed by
II
III
the coordination of either one MeOH molecule (1, 3 and 4)
the temperature range 2.0–300 K (Figure 5). The χ T val-
M
or one H O molecule (2). As a result of this cumulative
3
–1
2
ues of 19.05 (1), 25.28 (2), 23.00 (3) and 25.24 cm mol K
4) at room temperature are very close to those expected for
coordination action, an all-oxygen coordination environ-
(
II
ment is achieved around each Co ion in all of the com-
II
the sum of four non-interacting octahedral high-spin Co
II
plexes; the coordination polyhedron around each Co is
ions with an important orbital contribution (χ T ≈
M
distorted octahedral geometry (Figure 4, a). An all-oxygen
3
–1
[12]
2
.90 cm mol K)
and the corresponding lanthanide ion
1: Gd , χ T = 7.88 cm mol K with S = 7/2, L = 0,
S7/2, g = 2; 2: Dy , χ T = 14.15 cm mol K with S =
III
3
–1
(
M
8
III
3
–1
M
6
III
5/2,
L
=
5, H15/2
,
g
=
4/3; 3: Tb , χ T
=
M
3
–1
7
1
1.81 cm mol K with S = 3, L = 3, F , g = 3/2; and 4:
6
III
3
–1
5
Ho , χ T = 14.05 cm mol K with S = 2, L = 6, I , g =
M
8
5
/4). The lack of orbital contribution to the magnetic mo-
III
ment in Gd ions makes the magnetic properties of 1 the
easiest to analyse. Upon cooling, the χ T value for 1 de-
M
creases very smoothly down to ca. 150 K and then de-
creases faster, owing to the significant spin–orbit coupling
II
(
SOC) of the Co ions, to reach an incipient plateau with
3
–1
a χ T value of 7.86 cm mol K at 2 K. The magnetic prop-
erties of 2–4 are more complicated
M
[
13]
because of the in-
tervening first-order angular momentum and crystal field
III
III
III
effects for the Dy (2), Tb (3) and Ho (4) ions. Upon
cooling, χ T for all of them decreases gradually and then
M
more rapidly below ca. 125, 90 and 80 K, respectively, to
3
–1
reach values of 8.90, 10.62 and 6.47 cm mol K at 2 K,
respectively.
Scheme 3 shows the different exchange pathways present
in 1. To fit the magnetic properties of 1, we considered the
magnetic coupling between the cobalt(II) and gadolini-
um(III) ions (J ) but also two different magnetic couplings
0
between the cobalt(II) ions (J and J , see Scheme 3). The
magnetic susceptibility data of 1 were analyzed through a
b) Distorted square-antiprismatic geometry around the Gd ion. spin Hamiltonian model that takes into account the SOC
1
2
Figure 4. (a) Distorted octahedral geometry around the Co2+ ion.
(
3
+
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Scheme 3. Simplified diagram showing the considered magnetic in-
teractions as well as the angles between the magnetic centres for 1.
These parameters are similar to those obtained for other
[
14c–14i]
six-coordinate cobalt(II) compounds.
During the fit
process, we observed that J could have both positive and
0
negative values, always much smaller than J and J , and
1
2
with no influence on the final result. Therefore, it was fixed
–1
to zero (J = 0 cm ) in the fit process. The value of g
0
Gd
was also fixed in the fit (gGd = 2.0). The inset of Figure 5
a) show that the χ T curve tends to a plateau with a value
(
M
corresponding to that expected for S = 7/2. Therefore, the
magnetic behaviour at low temperature is similar to that
T for 1 (᭺). The solid expected for a single gadolinium(III) ion, which suggests
Figure 5. (a) Temperature dependence of χ
line corresponds to the best fit (see text). The inset shows the be-
haviour in the low temperature region. (b) Temperature dependence
M
that the four antiferromagnetically coupled cobalt(II) ions
cancel each other. The same result is observed from the
magnetization curve, in which the saturation value tends to
of χ
M
T for 2 (Δ), 3 (᭺) and 4 (᭛). The inset shows the temperature
T for 1–4 with the theoretical χ T values for the
Co ions subtracted.
dependence of χ
M
M
II
7 μ
are slightly different from those of 1 and, therefore, dif-
ferent values for the corresponding J and J can be ex-
(Figure 6). Although the structural parameters for 2–
B
4
effects in the cobalt(II) ions [Equation (2)], the axial orbital
splitting [Equation (3)], the magnetic exchange [see Equa-
tion (4)] and the Zeeman effect [Equation (5)].
1
2
pected, we can assume that they are very close. Moreover,
taking into account that J has no influence on the mag-
0
netic behaviour of 1–4, we have determined the theoretical
λ is the spin–orbit coupling parameter, α is an orbital
reduction factor (α = κA), and Δ is the axial orbital splitting
of the T term. We consider L = 1 by using the isomor-
1
phism between a T term and a P orbital: ||T || = –α ||P||.
1
1
To avoid overparameterization, we consider the ligand field
on each cobalt(II) ion to be the same (same α, λ and Δ
values). Owing to the enormous size of the resulting matrix
(
165888ϫ165888), we use the approach indicated in the lit-
[
14a]
erature.
The least-squares fit of the magnetic suscep-
[
14b]
tibility data of 1 through the VPMAG program
=
Δ = +330(5) cm , J = –7.0(1) cm and J = –5.2(1) cm . at 2.0 K.
gave α
–
1
–1.20(1) (e.g., A = 1.4 and κ = 0.86), λ = –160(3) cm ,
Figure 6. Field dependence of M of 1 (ᮀ), 2 (Δ), 3 (᭺) and 4 (᭛)
–
1
–1
–1
1
2
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curve of χ T for the four cobalt(II) ions interacting antifer- trometer operating at 400.0 MHz. Chemical shifts are reported in
M
parts per million (ppm) and are referenced with respect to internal
tetramethylsilane ( H).
romagnetically (J and J ) and we have subtracted this data
from the experimental curves. The resulting curves are
shown in the inset of Figure 5 (b) and clearly show the ex-
1
2
1
Magnetic Measurements: Variable-temperature (2.0–300 K) dc
pected behaviour for the corresponding isolated mononu- magnetic susceptibility measurements for 1–4 under an applied
clear lanthanide(III) complexes.[
13c]
field of 100 (T Ͻ 20 K) and 1000 G (T Ն 20 K) and variable-field
II
Finally, despite the large magnetic anisotropy of Co , (0–5.0 T) magnetization measurements at 2.0 K were performed
III
III
III
with a Quantum Design superconducting quantum interference de-
vice (SQUID) magnetometer. The magnetic susceptibility data were
corrected for the diamagnetism of the constituent atoms and the
sample holder. The dc magnetic measurements were performed
with samples that were powdered and restrained to prevent any
displacement owing to magnetic anisotropy.
Tb , Dy and Ho ions, we did not observed out-of-
phase alternating current (ac) susceptibility signals. This
demonstrates the lack of slow magnetic relaxation effects
for 1–4, which are typical of single-molecule magnets
(SMMs).
X-ray Crystallography: The crystal data for the compounds were
collected with a Bruker SMART CCD diffractometer (Mo-K
α
radi-
Conclusions
ation, λ = 0.71073 Å). The program SMART[
16a]
was used to collect
Previously, we utilized a phosphorus-supported hydraz- frames of data, index reflections and determine lattice parameters,
SAINT[
16a]
was used for integration of the intensity of reflections
one ligand, S=P[N(Me)N=CH–C H –2-OH–3-OMe]
6
3
3
[16b]
+
[7g,9c]
and scaling, SADABS
was used for absorption correction, and
(
LH ) to prepare a trinuclear [L Co Ln] 3d/4f family.
3 2 2
SHELXTL[
16c,16d]
was used for space group and structure determi-
However, the coordination features of LH do not allow the
3
2
nation and least-squares refinements on F . All the structures were
solved by direct methods by using the program SHELXS-97
and refined by full-matrix least-squares methods against F with
nuclearity of the metal ensemble to increase beyond three.
To provide greater opportunity for polynuclear formation,
we chose to utilize the ligand 6-formyl-2-(hydroxymethyl)-
[
16e]
2
[16e]
SHELXL-97.
tions and their positions were refined by a riding model. All non-
semble a new family of pentanuclear heterobimetalllic com- hydrogen atoms were refined with anisotropic displacement param-
Hydrogen atoms were fixed at calculated posi-
4
-methylphenol (LH ). Accordingly, we were able to as-
2
III
III
pounds [Co Ln(L) (OAc) (S) ](NO )(S) [Ln = Gd , S = eters. The crystallographic figures were generated by using Dia-
4
4
2
4
3
III
III
III
III
[16f]
MeOH (1); Ln = Dy , S = H O (2); Ln = Tb , S = mond 3.1e software.
The crystal data and the cell parameters
2
III
III
for 1–4 are summarized in Table 2.
MeOH (3); Ln = Ho , S = MeOH (4)] The core of these
complexes is made up of a distorted Co tetrahedron, and
the centre of the core contains the lanthanide ion; the lan-
4
CCDC-927025 (for 1), -927026 (for 2), -927027 (for 3) and -927028
(
for 4) contain the supplementary crystallographic data for this pa-
thanide ion is connected to the cobalt ions through the per. These data can be obtained free of charge from The Cambridge
–
phenolate and [–CH O] parts of the ligand. For 1–4, the Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
2
II
magnetic coupling between the Co ions through the acet- request/cif.
ate bridge is antiferromagnetic, whereas the interaction be-
tween the Co ions and the corresponding Ln ion can be
considered negligible, which indicates that the overall mag-
6
-Formyl-2-(hydroxymethyl)-4-methylphenol (LH
2
): The procedure
II
III
used for the preparation of this compound has been adapted and
modified from a previously published synthetic method.
[17]
A
netic properties of this family of compounds are dominated round-bottomed flask was charged with 2,6-bis(hydroxymethyl)-4-
by the crystal field effects of the lanthanide(III) ions 2–4 methylphenol (5 g, 30 mmol) and chloroform (500 mL). Manga-
nese dioxide (16 g, 184 mmol) was added portionwise to the stirred
solution. After 24 h, the reaction mixture was filtered, and the sol-
vent was evaporated to give a crude product. This was purified by
and the antiferromagnetic coupling of the cobalt(II) ions 1–
4.
column chromatography to afford a pale yellow solid, yield 2.88 g
58.3%), m.p. 72–74 °C, (ref. 74–76 °C).[
18]
C
H
10
O
3
(166.18):
):
(
9
Experimental Section
1
calcd. C 65.05, H 6.07; found C 65.09, H 6.16. H NMR (CDCl
3
Reagents and General Procedures: Solvents and other general rea-
gents used in this work were purified according to standard pro-
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.
[
15]
cedures.
cals, Mumbai, India. 2,6-Bis(hydroxymethyl)-4-methylphenol,
MnO , Dy(NO ·H O, Ho(NO ·5H O, Tb(NO ·5H O and
Gd(NO ·5H O were obtained from Sigma Aldrich Chemical Co.
2 2
Co(OAc) ·4H O was obtained from S.D. Fine Chemi-
General Procedure for the Synthesis of Heterometallic Complexes 1–
4: The following general procedure was utilized for the preparation
2
3
)
3
2
3
)
3
2
3
)
3
2
of 1–4. To a solution of LH
2
in methanol (30 mL), Ln(NO
3
)
3
·nH
2
O
3
)
3
2
(For 1, n = 6; 2, n = 1; 3, n = 5; 4, n = 5) was added. The mixture
and used as received.
was stirred for 10 min at room temperature, and Co(OAc)
2
·4H
2
O
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 . Elemental analyses of the compounds were ob-
tained with a Thermoquest CE instruments CHNS-O analyzer
and triethylamine were added. After this, the reaction mixture was
stirred for a further period of 12 h to afford a clear solution. This
was filtered, and the filtrate was evaporated to dryness. The residue
obtained was washed with diethyl ether, dried, redissolved in meth-
anol/chloroform (1:1) and kept for crystallization by slow evapora-
tion. After 2 weeks, a pure red-brown 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
(EA/110 model). Electrospray ionization mass spectra (ESI-MS)
were recorded with a Micromass Quattro II triple quadrupole mass
spectrometer. 1H NMR spectra were recorded with samples in
3
CDCl solutions with a JEOL JNM LAMBDA 400 model spec-
Eur. J. Inorg. Chem. 0000, 0–0
7
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I30413
/KAP1
Date: 01-07-13 10:08:57
Pages: 10
www.eurjic.org
FULL PAPER
Table 2. Crystal data and structure refinement parameters of 1–4.
1
2
3
4
Formula
M /g
Crystal system
Space group
a /Å
b /Å
c /Å
C
45
H
58Co
4
GdNO24
C
40
H
51Co
4
DyNO25
C
45
H
58Co
4
TbNO24
C
45 4
H58Co HoNO24
1389.89
monoclinic
P2 /n
12.1863(14)
21.220(2)
19.913(2)
90.824(2)
5149.0(10)
4
1.793
2.617
2796
0.091ϫ0.072ϫ0.045
4.09 to 25.03
–14 Յ h Յ 14;
1344.04
monoclinic
P2 /n
12.686(5)
20.309(5)
19.586(5)
106.070(5)
4849(3)
4
1.841
2.950
2688
0.09ϫ0.073ϫ0.044
4.09 to 25.03
–14 Յ h Յ 15;
–24 Յ k Յ 23;
–23 Յ l Յ 15
24588
1391.56
monoclinic
P2 /n
12.167(5)
21.188(5)
19.934(5)
90.801(5)
5138(3)
4
1397.57
monoclinic
P2 /n
12.1862(11)
21.1954(18)
19.9284(17)
90.535(2)
5147.1(8)
4
1.804
2.867
1
1
1
1
β /°
V /Å
3
Z
–
3
ρ
c
/gcm
1.799
2.709
2800
–
1
μ /mm
F(000)
2808
Cryst size /mm3
θ range /°
0.092ϫ0.071ϫ0.051
4.09 to 25.02
–13 Յ h Յ 14;
–25 Յ k Յ 25;
–23 Յ l Յ 20
26123
9014 [R(int) = 0.0868]
99.1
full-matrix least-squares full-matrix least-squares
0.085ϫ0.069ϫ0.044
4.09 to 25.03
–14 Յ h Յ 14
–25 Յ k Յ 24
–14 Յ l Յ 23
26603
Limiting indices
–
–
25 Յ k Յ 13;
22 Յ l Յ 23
Reflections collected
Independent reflections
Completeness to θ /%
Refinement method
26197
9055 [R(int) = 0.0385]
99.4
8503 [R(int) = 0.0668]
99.3
9037 [R(int) = 0.0744]
99.2
full-matrix least-squares full-matrix least-squares
on F2
on F
2
on F
2
on F
2
Data/restraints/parameters 9055/8/700
8503/39/650
1.037
9014/8/700
0.986
9037/8/700
0.982
Goodness-of-fit on F2
1.036
= 0.0411, wR
.0969
= 0.0525, wR
.1030
2.436 and –0.648
Final R indices [I Ͼ 2θ(I)]
R
1
2
2
=
=
R
1
= 0.0763, wR
0.1919
= 0.1125, wR
0.2244
2.634 and –1.538
2
=
=
R
1
= 0.0504, wR
0.1034
= 0.0786, wR
0.1164
1.596 and –0.758
2
=
=
R
1
= 0.0457 wR
0.0759
= 0.0766 wR
0.0873
1.076 and –0.703
2
=
=
0
R indices (all data)
R
1
R
1
2
R
1
2
R
1
2
0
Largest diff. peak and
hole /eÅ–3
[
(
(
7
3
1
1
Co
4
Gd(L)
0.11 g, 0.45 mmol), Gd(NO
0.075 g, 0.45 mmol) and Et N(0.19 mL, 1.35 mmol), yield 0.11 g,
0.3% (based on Gd), m.p. 160 °C (dec.). IR (KBr): ν˜ = 3411 (br), 61.7% (based on Ho), m.p. 160 °C (dec.). IR (KBr): ν˜ = 3388 (br),
004 (m), 2921 (w), 2851 (w), 1640 (s), 1551 (s), 1441 (s), 1422 (s), 2925 (m), 2921 (w), 2857 (w), 2678 (w),1633 (s), 1554 (s), 1441 (s),
4
(OAc)
2
(MeOH)
4
](NO
3
)(MeOH) (1): Co(OAc)
2
·4H
2
O
[Co
(0.11 g, 0.45 mmol), Ho(NO
(0.075 g, 0.45 mmol) and Et N(0.19 mL, 1.35 mmol), yield 0.097 g,
4
Ho(L)
4
(OAc)
2
(MeOH)
4
](NO
3
)(MeOH) (4): Co(OAc)
2 2
·4H O
3
)
3
·6H
2
O (0.050 g, 0.11 mmol), LH
2
3
)
3
·5H
2
O (0.05 g, 0.11 mmol), LH
2
3
3
384 (s), 1347 (s), 1312 (s), 1253 (m), 1219 (s), 2677 (w) 1172 (s), 1422 (s), 1383 (s), 1309 (s), 1254 (m), 1221 (s), 1175 (s), 1050 (s),
030 (s), 976 (s), 863 (m), 776 (s), 713 (s), 667 (m), 540 (s), 485 (s) 1008 (m), 980 (s), 880 (m), 774 (s), 714 (s), 670 (m), 540 (s), 485 (s)
–
1
+
–1
+
cm .
ESI-MS:
GdNO24 (1389.99): calcd. C 38.89, H 4.21, N 1.01;
found C 38.21, H 3.98, N 1.12.
m/z
=
1167.87
[C40
H38Co
4
GdO16] .
4
cm . ESI-MS: m/z = 1174.89, [C40H38Co HoO16] . C45H58Co4-
C
45
H
58Co
4
HoNO24 (1396.99): calcd. C 38.67, H 4.18, N 1.00; found C 38.19,
H 4.01, N 1.09.
[
(
(
6
2
1
9
Co Dy(L) (OAc) (H O) ](NO )(H
0.11 g, 0.45 mmol), Dy(NO ·H
0.075 g, 0.45 mmol) and Et
4
4
2
2
4
3
2
O)
2
(2):
Co(OAc)
2
·4H
2
O
Supporting Information (see footnote on the first page of this arti-
cle): ESI-MS, IR and UV/Vis spectra, molecular structures of 2–4,
and list of bond lengths and angles.
3
)
3
2
O (0.039 g, 0.11 mmol), LH
2
3
N(0.19 mL, 1.35 mmol), yield 0.093 g,
1.4% (based on Dy), m.p. 160 °C (dec.). IR (KBr): ν˜ = 3389 (br),
932 (m), 2853 (w), 2678 (w), 1634 (s), 1554 (s), 1440 (s), 1422 (s),
383 (s), 1309 (s), 1253 (m), 1221 (s), 1175 (s), 1049 (s), 1008(m),
80 (s), 880 (m), 774 (s), 714 (s), 660 (m), 540 (s), 486 (s) cm .
Acknowledgments
–
1
+
The authors are thankful to the Department of Science and Tech-
nology (DST), New Delhi for financial support and a J. C. Bose
National Fellowship (to V. C.). S. D., A. D. and S. H. thank Coun-
cil of Scientific and Industrial Research (CSIR), New Delhi for
Senior Research Fellowships.
ESI-MS: m/z = 1173.87 [C40
1344.94): calcd. C 35.74, H 3.84, N 1.04; found C 35.08, H 3.43,
N 1.14.
4 4
H38Co DyO16] . C40H51Co DyNO25
(
[
(
(
6
2
1
1
Co Tb(L)
0.11 g, 0.45 mmol), Tb(NO
0.075 g, 0.45 mmol) and Et N(0.19 mL, 1.35 mmol), yield 0.095 g,
0.6% (based on Tb), m.p. 160 °C (dec.). IR (KBr): ν˜ = 3388 (br),
4
4
(OAc)
2
(MeOH)
4
](NO
3
)(MeOH) (3): Co(OAc)
2 2
·4H O
3
)
3
·5H
2
O (0.049 g, 0.11 mmol), LH
2
3
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.08, N 1.12.
4 4
H38Co TbO16] . C45H58Co N-
O
4
Eur. J. Inorg. Chem. 0000, 0–0
8
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I30413
/KAP1
Date: 01-07-13 10:08:57
Pages: 10
www.eurjic.org
FULL PAPER
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I30413
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Date: 01-07-13 10:08:57
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Received: March 29, 2013
Published Online: ᭿
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