A 2D coordination polymer with canted ferromagnetism constructed from ferromagnetic [NiIICoII] nodes

Article abstract of DOI:10.1021/ic800946v

A bimetallic coordination polymer, _∞²[{LNi ^IICo^II}(dca)₂], has been constructed from heterobinuclear [Ni^IICo^II] nodes and dicyanamido spacers [L^2- is the dianion of the Schiff base resulting from the 2:1 condensation of 3-methoxysalicyladehyde with 1,3-propanediamine; L^2- = N,N′-propylenebis(3-methoxysalycilideneiminato)]. The intranode Co ^II-Ni^II interaction was found to be ferromagnetic because of the orthogonality of the magnetic orbitale. Below 12 K, the onset of the canted ferromagnetic ordering is observed.

Full text of DOI:10.1021/ic800946v

Inorg. Chem. 2008, 47, 6590-6592
A 2D Coordination Polymer with Canted Ferromagnetism Constructed
from Ferromagnetic [NiIICoII] Nodes
Diana G. Branzea,† Lorenzo Sorace,‡ Catalin Maxim,† Marius Andruh,*,† and Andrea Caneschi*,‡
Inorganic Chemistry Laboratory, Faculty of Chemistry, UniVersity of Bucharest, Street DumbraVa
Rosie no. 23, 020464 Bucharest, Romania, and Laboratory of Molecular Magnetism, Dipartimento
di Chimica e UdR INSTM di Firenze, UniVersita` degli Studi di Firenze, Polo Scientifico, Via della
Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy
Received May 25, 2008
A bimetallic coordination polymer, ∞2[{LNiIICoII}(dca)2], has been
constructed from heterobinuclear [NiIICoII] nodes and dicyanamido
spacers [L2- is the dianion of the Schiff base resulting from the
2:1 condensation of 3-methoxysalicyladehyde with 1,3-propanedi-
amine; L2- ) N,N′-propylenebis(3-methoxysalycilideneiminato)].
The intranode CoII-NiII interaction was found to be ferromagnetic
because of the orthogonality of the magnetic orbitals. Below 12
K, the onset of the canted ferromagnetic ordering is observed.
tion polymers with various dimensionalities and network
topologies.6 We have found that these ligands can also
accommodate two different 3d metal ions (CuII and CoII):
the first metal ion is hosted into the N2O2 compartment, while
the second one occupies the O2O2′ compartment.7 The
disposition of the oxygen atoms defining the second com-
partment is favorable for coordination to 4f ions, allowing
them to achieve high coordination numbers. On the other
hand, when 3d metal ions are hosted into this compartment,
their stereochemistry is strongly distorted, with four short
and two long coordination bonds that involve the methoxy
groups.7 For example, the reaction between [LCu] and cobalt
perchlorate followed by the addition of sodium dicyanamide
led to a 1D coordination polymer, [{LCuCo}(dca)2] (1), with
dicyanamido bridges connecting a copper ion from one node
with the cobalt ion from another one (Chart 1a).7b
The node-and-spacer paradigm is largely employed for the
construction of coordination polymers.1 It relies upon the
strong directionality of the coordination bonds established
between the metal ions (nodes and connectors) and the
exodentate ligands (spacers and linkers). Coordination
polymers can be constructed from oligonuclear nodes as
well.2 The metal ions interact with the divergent ligand
through their easily accessible coordination sites. The pres-
ence of two or more metal ions confers to the node a higher
geometrical flexibility. Moreover, the metal-metal intra- and
internode interactions can lead to new redox, electric, or
magnetic properties.2,3
We have developed an alternative way to obtain hetero-
metallic systems, by connecting preformed heterometallic
nodes with various spacers.4 The nuclearity of the nodes can
be controlled by choosing appropriate compartmental ligands.
For example, the dissymmetric side-off Schiff bases derived
from o-vanillin were specially designed to generate 3d-4f
complexes.5 The second compartment, O2O2′, is sufficiently
large to accommodate 4f metal ions. Such complexes were
successfully used as nodes in constructing 3d-4f coordina-
A terminal dicyanamido ligand is coordinated to the cobalt
ion. The copper ion, occupying the N2O2 compartment, is
pentacoordinated, with the bridging dca- group coordinated
into the apical position. The analysis of this structure raised
(2) For example, see: (a) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem.
Res. 2001, 34, 759. (b) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.;
Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001,
34, 319. (c) Aquino, M. A. S. Coord. Chem. ReV. 2004, 248, 1025.
(d) Huang, W.; Gou, S.; Hu, D.; Chantrapromma, S.; Fun, H.-K.;
Meng, Q. Inorg. Chem. 2001, 40, 1712. (e) Asokan, A.; Varaghese,
B.; Caneschi, A.; Manoharan, P. T. Inorg. Chem. 1998, 37, 228. (f)
Papaefstathiou, G. S.; Georgiev, I. G.; MacGillivray, L. R. Chem.
Commun. 2005, 673.
(3) For example, see: (a) Liao, Y.; Shum, W. W.; Miller, J. S. J. Am.
Chem. Soc. 2002, 124, 9337;(b) Vos, T. E.; Liao, Y.; Shum, W. W.;
Her, J.-H.; Stephens, P. W.; Reiff, W. M.; Miller, J. S. J. Am. Chem.
Soc. 2004, 126, 11630. (c) Pascu, M.; Lloret, F.; Avarvari, N.; Julve,
M.; Andruh, M. Inorg. Chem. 2004, 43, 5189. (d) Shiga, T.; Okawa,
H.; Kitagawa, S.; Ohba, M. J. Am. Chem. Soc. 2006, 128, 16426.
(4) (a) Andruh, M. Pure Appl. Chem. 2005, 77, 1685. (b) Andruh, M.
Chem. Commun. 2007, 2565.
* To whom correspondence should be addressed. E-mail: martius.andruh@
dnt.ro (M.A.), (A.C.).
(5) Costes, J.-P.; Dahan, F.; Dupuis, A.; Laurent, J.-P. Inorg. Chem. 1996,
35, 2400.
†
University of Bucharest.
Universita` degli Studi di Firenze.
(6) (a) Gheorghe, R.; Cucos, P.; Andruh, M.; Costes, J.-P.; Donnadieu,
B.; Shova, S. Chem.sEur. J. 2006, 12, 187. (b) Gheorghe, R.; Andruh,
M.; Costes, J.-P.; Donnadieu, B. Chem. Commun. 2003, 2778.
(7) (a) Costes, J.-P.; Gheorghe, R.; Andruh, M.; Shova, S.; Clemente Juan,
J.-M. New J. Chem. 2006, 30, 572. (b) Branzea, D. G.; Guerri, A.;
Fabelo, O.; Ruiz-Pe´rez, C.; Chamoreau, L.-M.; Sangregorio, C.;
Caneschi, A.; Andruh, M. Cryst. Growth Des. 2008, 8, 941.
‡
(1) (a) Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1990, 112, 1546.
(b) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460.
(c) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004,
43, 2334. (d) Janiak, C. Dalton Trans. 2003, 2781. (e) Champness,
N. R. Dalton Trans. 2006, 877.
6590 Inorganic Chemistry, Vol. 47, No. 15, 2008
10.1021/ic800946v CCC: $40.75  2008 American Chemical Society
Published on Web 06/27/2008

COMMUNICATION
Chart 1
Figure 1. Perspective view of the 2D network of 2.
the following question: is it possible to increase the
dimensionality of the coordination polymer by replacing the
CuII ion with a metal ion preferring a higher coordination
number, let us say six (Chart 1b)? In order to answer this
question, we synthesized the [NiL] precursor [L2- is the
dianion of the Schiff base resulting from the 2:1 condensation
of 3-methoxysalicyladehyde with 1,3-propanediamine; L2-
) N,N′-propylenebis(3-methoxysalycilideneiminato)]. Indeed
the reaction of [NiL] with cobalt(II) perchlorate and sodium
dicyanamide leads to ∞2[{LNiIICoII}(dca)2] (2),8 whose crystal
structure has been solved.9 As expected, a 2D coordination
polymer is assembled (Figure 1). The NiII ions exhibit a
slightly elongated octahedral geometry [the basal plane is
described by two nitrogen and two oxygen atoms from the
compartmental ligand, with metal-ligand distances varying
between 2.022(4) and 2.038(4) Å; the apical positions are
occupied by the nitrogen atoms arising from the dicyanamido
ligands: Ni1-N3 ) 2.099(4), Ni1-N4 ) 2.129(4) Å]. As
far as the coordination geometry of the cobalt ion concerned,
this is more delicate to state precisely. At first sight, a
tetrahedral environment comprising two phenoxo oxygen
atoms of the bridge [Co1-O1 ) 1.992(3); Co1-O2 )
1.991(3) Å] and two nitrogen atoms from the two coordinated
dicyanamido ions [Co1-N4A ) 1.980(4); Co1-N5A )
2.004(4) Å] can be noticed. The values of the Co-O
Figure 2. ꢀT vs T plot for 2 measured at 1 kOe and M vs H at 1.9 K
(inset).
(methoxy oxygen atoms) distances [2.570(3) and 2.584(4)
Å], longer than those in [{LCuCo}(dca)2], indicate that they
can be considered as weakly coordinated. The intranode
Ni · · · Co distance is 3.085 Å.
A useful tool to diagnose the stereochemistry of the CoII
ion is the UV-vis spectroscopy. The diffuse-reflectance
spectrum of 2 is a superposition of the absorption bands of
the two chromophores (Figure S1 in the Supporting Informa-
tion). The intense band located at ∼600 nm is similar to the
one exhibited by cobalt(II) complexes with a tetrahedral
4
4
geometry and can be assigned to the A2 f T1(P) transi-
tion.10 Another characteristic band for tetrahedral cobalt(II)
complexes is located in the NIR region. This band is assigned
4
4
to the A2 f T1(F) transition. When the symmetry of the
4
CoII ion decreases from Td to C2V, the T1(F) level is split
4
4
4
into A2 + B1 + B2 levels and three bands are expected.
Indeed, in the NIR region, compound 2 shows a large band
with a maximum at 1350 nm and two shoulders at about
1100 and 1500 nm (Figure S1 in the Supporting Information).
This is in agreement with the results of the ꢀT vs T
measurements (actually MT/H vs T; Figure 2), which show
a room temperature value for 2 of 3.18 cm3 K mol-1. This
value is in agreement with that expected from the sum of
the independent contributions of a tetrahedral CoII (2.0 <
ꢀT < 2.6 cm3 K mol-1) and an octahedral NiII (ꢀT ∼ 1.1
cm3 K mol-1), whereas it is too low to be compatible with
a distorted octahedral CoII center (2.5 < ꢀT < 3.1 cm3 K
(8) A total of 2 mmol of o-vanillin in THF was deprotonated with 2 mmol
of LiOH and then reacted with an aqueuos solution of
Ni(CH3COO)2 ·4H2O. To the resulting green suspension were added
dropwise 2 mmol of 1,3-propanediamine, and the resulting mixture
was stirred for 1 h, which led to the formation of [NiL] as a green
precipitate, which was filtered off, washed with water and THF, and
dried in air. Yield: 91%. To an acetonitrile/ethanol (20 mL, 1:1)
solution of [NiL] (0.04 mmol) was added solid Co(ClO4)2 ·6H2O (0.04
mmol), and the resulting mixture was stirred for 30 min. To the mixture
was added an aqueous solution of NaN(CN)2 (0.08 mmol), and the
resulting mixture was stirred for other 10 min. Dark-mauve crystals
were obtained upon slow evaporation.
(9) Crystallographic analysis of 2: C23H20CoNiN8O4, M ) 590.11 g mol-1
,
monoclinic, space group P21n, a ) 9.400 Å, b ) 15.340 Å, c ) 17.637
Å, ꢁ ) 100.00°, V ) 2504.7 Å3, Z ) 4, T ) 293 K, Dc ) 1.565 g
cm-3, µ ) 1.460 mm-1, R1 ) 0.0507, wR2 ) 0.0646, GOF ) 0.786.
CCDC reference number for 2: 68815.
(10) Lever, A. B. P. Inorganic Elecronic Spectroscopy, 2nd ed.; Elsevier:
New York, 1984; pp 496-497.
Inorganic Chemistry, Vol. 47, No. 15, 2008 6591

COMMUNICATION
NiII ions only interacting through µ1,5-dca groups.13 In 2, both
the high-field magnetization value at low temperatures and
the value of a ꢀT maximum in high field are consistent with
each NiCo node being ferromagnetically coupled (a full
5
population of the S ) /2 state would give ꢀT ) 5.3 cm3 K
mol-1 and M ) 30 720 cm3 Oe mol-1 for gave ) 2.2). This
is reasonable if one considers the electronic configurations
of the two ions (t2 6eg for NiII and e4t2 for CoII), giving
2
3
g
rise to orthogonal arrangements of the magnetic orbitals. On
the other hand, there is no easy way to evaluate the
interaction between adjacent Ni-Co nodes, which should,
however, be quite weak, considering that observed in
ꢁ-Co(dca)2 and [Ni(dca)3]- derivatives. However, the ob-
servation of the weak ferromagnetic transition suggests that
this interaction should be weakly ferromagnetic, with the
order occurring between ferromagnetic sheets, interacting
antiferromagnetically through dipolar interactions. It has to
be noted that, because the shortest interlayer interactions
involve either the two different metal centers or noncen-
trosymmetric CoII and NiII pairs, the proposed mechanism
fulfills the symmetry requirements for the observation of a
canted magnetic structure.14
Figure 3. ZFC (empty triangles) and FC (full squares) magnetization curves
for 2 in a field of 50 Oe. In the inset, dM/dH vs H curves at 5 K (empty
diamonds) and 1.9 K (full squares) are reported, evidencing the occurrence
of the metamagnetic transition.
Finally it has to be noted that the ꢀ′ vs T plot evidences
another feature around 8 K, namely, a weakly frequency-
dependent peak in ꢀ′. The variation of the temperature at which
the peak occurs as a function of the frequency strongly suggests
that this second peak should be related to the introduction of
glassiness in the system. Indeed, φ, defined as
Figure 4. Plot of ꢀ′ (upper) and ꢀ′′ (lower) vs T for 2 at variable frequencies.
The dotted arrow highlights the occurrence of a second, frequency-dependent
feature around 8 K.
mol-1).11,12 Upon a decrease in the temperature, the ꢀT
product slowly decreases down to 40 K (3.06 cm3 K mol-1)
and then rapidly increases up to a maximum of 4.5 cm3 K
mol-1 (in a field of 1 kOe) at 12 K, after which its value
drops to 2.5 cm3 K mol-1 at 2 K. The zero-field-cooled
(ZFC)/field-cooled (FC) curve (Figure 3) clearly evidences
that this behavior should be attributed to the onset of a
magnetic ordering process below 12 K, where the two curves
show a bifurcation. This is confirmed by the presence of a
frequency-independent signal for the in-phase alternating
current susceptibility (Figure 4). The existence of a small
but detectable signal in ꢀ′′ further indicates that the magnetic
ordering results in a magnetized state. The low-field M vs
H curves (Figure S2 in the Supporting Information) at
different temperatures indicate that the resulting state should
be a weak ferromagnetic one, undergoing a metamagnetic
transition at 1600 and 250 Oe at 2 and 5 K, respectively
(inset of Figure 3). Below 8 K, the M vs H cycle shows an
appreciable hysteresis (Figure S3 in the Supporting Informa-
tion; Hc ) 100 Oe and Mr ) 90 cm3 Oe mol-1 at 5 K; Hc )
250 Oe and Mr ) 250 cm3 Oe mol-1 at 1.9 K).
Tpeak(νmin) - Tpeak(νmax
Tpeak(νmin)log(νmax ⁄ νmin
)
ꢂ )
(1)
)
takes a value of 0.03, which is in the expected range for
spin-glass behavior.15 This suggests a re-entrant spin-glass
transition, with the coexistence of both glassy and ordered
16
behavior below 8 K. In conclusion, we have illustrated
that the dimensionality of the coordination polymers, when
constructed from heterobinuclear tectons, can be controlled
by choosing the appropriate pair of metal ions. Moreover,
such compounds exhibit interesting magnetic properties.
Further work on other systems constructed from heterome-
tallic nodes is in progress.
Acknowledgment. Financial support from the CEEX
Program (Project D11-17), CNCSIS (TD47/2007), and EC
”MAGMANet” NMP3-CT-2005-515767 is gratefully ac-
knowledged.
Supporting Information Available: Solid-state UV-vis-NIR
spectrum, M vs H, and magnetic hysteresis cycles at 1.9 and 5 K
for 2. This material is available free of charge via the Internet at
http://pubs.acs.org.
The detection of a weak ferromagnetic transition in 2 at
12 K should be compared with 9 K of the weak ferromag-
netic transition observed with ꢁ-Co(dca)2, containing tetra-
hedral CoII centers connected through µ1,5-dca bridges, and
with the absence of magnetic order in [Ni(dca)3]- containing
IC800946V
(13) van der Werff, P. M.; Batten, S. R.; Jensen, P.; Moubaraki, B.; Murray,
K. S.; Cashion, J. D. Cryst. Growth Des. 2004, 4, 503, and references
cited therein.
(14) Moriya, T. In Magnetism; Rado, G. T., Suhl, H., Eds.; Academic Press:
New York, 1963; Vol. I, p 85.
(11) Banci, L.; Bencini, A.; Benelli, C.; Gatteschi, D.; Zanchini, C. Struct.
Bonding (Berlin) 1982, 52, 37.
(15) Mydosh, J. A. Spin glasses: an Experimental Introduction; Taylor &
Francis: London, 1993.
(12) Boudreaux, E. A.; Mulay, L. N. Theory and Applications of Molecular
Paramagnetism; Wiley: New York, 1986.
(16) Fischer, K. H.; Hertz, J. A. Spin Glasses; Cambridge University Press:
Cambridge, U.K., 1991.
6592 Inorganic Chemistry, Vol. 47, No. 15, 2008