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Syntheses, Crystal Structures and Magnetic Properties of Mixed-valenceLinear Trinuclear Cobalt and 2D Nickel Complexes
Tian-Fu Liu, Zai-Xin Wang
PII: S1387-7003(13)00004-XDOI: doi: 10.1016/j.inoche.2012.12.020Reference: INOCHE 4922
To appear in: Inorganic Chemistry Communications
Received date: 31 July 2012Accepted date: 21 December 2012
Please cite this article as: Tian-Fu Liu, Zai-Xin Wang, Syntheses, Crystal Structuresand Magnetic Properties of Mixed-valence Linear Trinuclear Cobalt and 2D Nickel Com-plexes, Inorganic Chemistry Communications (2013), doi: 10.1016/j.inoche.2012.12.020
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Syntheses, Crystal Structures and Magnetic Properties of
Mixed-valence Linear Trinuclear Cobalt and 2D Nickel Complexes
Tian-Fu Liu* and Zai-Xin Wang
School of Chemistry, Beijing Institute of Technology, Beijing, 100081, P. R. China
Corresponding author: tel.: +86 10 68912667; fax: +86 10 68914780.
E-mail: [email protected]
ABSTRACT: Two new complexes, [CoL2]2[Co(CH3OH)4] (1), and [Ni2L2(CH3OH)2]n
(2) (H2L = 2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid), have been
synthesized and structurally characterized. Single-crystal X-ray analysis reveals that
complex 1 is linear trinuclear mixed valence cobalt complex, while complex 2 is a 2D
complex by double naphtholate bridged and syn-anti carboxylate bridged. Magnetic
susceptibility measurements indicate that 1 shows mononuclear CoII behavior whereas
2 exhibits an antiferromagnetism behavior.
Keywords: cobalt complex; nickel complex; crystal structure; magnetic property
Over the past two decades, the rational design and synthesis of molecule-based
magnetic materials have attracted considerable interest [1-5]. In order to design
coordination complexes with interesting structure and performance, the match of
metal centers with suitable ligands is one of the most important factors [6]. The
tetradentate Schiff base ligands, derived from the condensation of an amino acid and
salicylaldehyde derivative, have been used extensively to construct various
polynuclear and coordination polymers of CoII and Ni
II that show interesting structural
and magnetic properties [7-11]. The carboxylate anion has shown versatile
coordinating ability to variety of transition metal ions through different coordination
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(syn-anti, syn-syn and anti-anti) modes and efficiently mediates ferromagnetic (FM)
and antiferromagnetic (AFM) coupling between metal centers [12-15]; and the
phenolate anion has also shown efficiently magnetic transmission capacity [16, 17].
We report in this article the synthesis, crystal structures and the magnetic properties of
two complexes [CoL2]2[Co(CH3OH)4] (1) and [Ni2L2(CH3OH)2]n (2) using
2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid [18] (H2L , Scheme 1) as
building block ligands.
Scheme 1
The reaction of Co(ClO4)26H2O, H2L and NaOH in a 1:1:2 molar ratios in MeOH
gave a red-brown solution from which (1) was subsequently isolated in 40% yields. In
a similar reaction, but employing Ni(ClO4)26H2O with H2L and NaOH in 1:1:2 ratio
in MeOH gave a green solution from which 2 was isolated in 45% yield [19]. The IR
spectra of complexes 1 and 2 are quite similar: the discussion is confined to the most
important vibrations of the 4000-400 cm-1
region in terms of the structure. A broad
peak centered at 3424 cm-1
is most likely due to the νOH group. The νC=N and νC-O
vibration is assigned to the strong-intensity band at 1630, 1600 and 1544 cm-1
.
Fig. 1
The structure of the linear trinuclear cobalt compound 1 [CoL2]2[Co(CH3OH)4] is
provided in Fig. S1 [20]. The deprotonated ligand L acts as a dianionic tetradentate
ligand: one naphtholate oxygen, one carboxyl and one Schiff base nitrogen in one
ligand are bound to the terminal cobalt ions and the other carboxyl is chelated to the
central cobalt ion. All cobalt are octahedral, they are connected by two bridging
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carboxyl, forming a linear trinuclear cobalt structure unit (Fig. 1) with a
Co–O-C–O–Co–O-C–O–Co core and the neighboring Co---Co distance is 5.225(1) Å.
The trinuclear cobalt complex molecule is strictly linear by symmetry, and the central
cobalt atom (Co2) is on a crystallographic symmetry center. The equatorial plane of
the octahedron is perfectly planar and the cobalt ion (Co2) lies in this plane. The plane
coordination sites are occupied by methanol molecules. The terminal cobalt ions have
an octahedral surrounding with another ligand. Co1 is in the +3 oxidation state, and
Co2 is in the +2 oxidation state, as confirmed by combination of bond-length
considerations, BVS calculations, and charge-balance [21]. The terminal Co–O and
Co–N bond lengths for Co–O(naphtholate), Co–O(carbonyl) and Ni–N(-C=N) are
1.887(2), 1.934(1) and 1.881(2) Å, respectively. They are slightly shorter than the
central Co-O bond lengths for Co–O(carbonyl) which are 2.062(2) and 2.072(1) Å
respectively. Adjacent molecules are linked by intermolecular H bonds to form a 2D
infinite layer structure (Fig. S2), and there is no obvious π-π stacking interaction
between naphtholates.
Fig. 2
Crystal structure of 2 [Ni2L2(CH3OH)2]n exhibits a 2D character. The
crystallographically independent Ni(II) atoms, Ni1, is hexa-coordinated in the form of
deformed octahedral cis NiO3O2N; three atoms are from the Schiff base H2L, one
oxygen atom from methanol, with Ni-N distance of 1.979(3) Å, and Ni-O distances in
the range of 2.013(2) to 2.146(3) Å (Fig. S3). The Ni(II) ions are related by inversion
centers and bridged by naphtholate oxygen atoms forming a binuclear unit with the
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Ni-Ni distances being 3.108(1) Å (Fig. 2). Furthermore, each unit is connected by
carboxylate bridging using syn-anti mode, resulting in a 2D layer with Ni---Ni
distance between the dimer units of 5.460(2) Å (Fig. S4). There are intramolecular
hydrogen bonding in the layers and no obvious π-π stacking interaction between
naphtholates.
Fig. 3
The temperature dependence of the χMT vs. T in a field of 1 kOe for 1 is shown in Fig.
3, where χM is the magnetic susceptibility per Co3 unit. The χMT value at 300 K is ca.
3.31 cm3
mol-1
K, which is greater than the spin-only value expected for a high-spin
CoII and corresponds to the presence of the Co
III(l.s., S = 0)–Co
II(h.s., S = 3/2)–Co
III(l.s., S = 0)
trinuclear systems. The decrease of the magnetic moment at low-temperature is most
likely due to zero-filed splitting of CoII. Therefore, in order to estimate the magnitude
of zero-filed splitting, the magnetic susceptibility data were fitted to Co(II) ions (S =
3/2) with the Hamiltonian in the form ZFSH S D S ,
taking into account the TIP of
octahedral Co(III) ions possessing a 1A1g ground state [22]. The best least squares
fitting was obtained with g = 2.43, D = -4.79 cm-1
and TIP = 0.00168 cm3 mol
-1 with R
= 7.7110-5
(R value is defined as 22])[(/)()( obsMcalcMobsM ).
Fig. 4
In the case of 2, the χMT value is 2.61 cm3
mol-1
K at room temperature, greater than
those expected for two spin only NiII with S = 1. Upon cooling, the χMT values
decrease more and more rapidly, indicating an antiferromagnetic behavior (Fig. 4).
The maxima of χM is observed at 20 K, suggesting antiferromagnetic ordering. The
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Neel temperature, TN, determined by the peaks of d(χMT)/dT, is 9.0 K. The
field-dependent magnetizations (insert Fig. 8), even at 1.8 K and 70 kOe, being 0.27
B, far from the saturated values, confirm the significant antiferromagnetic
interactions in material.
Regarding the structure feature, 2 consists of two types of bridges connecting the
Ni(II) sites. While layer consists of double symmetric 2 naphtholate-O bridges that
lead to the formation of the dimer locally. These dimers which are subsequently
interconnected through syn-anti carboxylate bridges give rise to the infinite 2D layer.
It should be noted that complex 2 exhibits four types of magnetic exchange
interactions between two Ni(II) ions: (1) a doubly naphtholate-bridged Ni(II) dimer,
(2) A carboxylate bridged Ni(II) dimer, (3) Ni(II) dimer intralayer, and (4) interlayer
(Fig. 7). Actually, because of the long distance of COO-, the overlap of magnetic
orbitals through the O atoms of COO- is weak. Hence, the double naphtholate-bridged
Ni(II) dimer cage plays an important role in the magnetic properties.
Therefore, the magnetic susceptibility data of 2 were fitted to the modified
Bleaney-Bowers equation for two interacting Ni(II) ions (S = 1) with the Hamiltonian
in the form 1 2H JS S taking into account the interaction between the dimers [23].
The susceptibility equation for such a dimeric system, with an interdimer parameter
zJ’, can be written as follows:
2 2' 2 exp( / ) 5exp(3 / )
1 3exp( / ) 5exp(3 / )M
N g J kT J kT
kT J kT J kT
'
2 21 (2 ' )
MM
MZJ Ng
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where N, g, and k parameters in the equation bear their usual meanings. The best
least squares fitting was obtained with g = 2.23, J = -8.12 cm-1
and J’ = 0.71 cm-1
with
R = 5.8710-6
(R value is defined as 22])[(/)()( obsMcalcMobsM ).
In summary, the tetradentate Schiff base ligand
2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid produces two new
complexes, linear trinuclear mixed valence cobalt complex [CoL2]2[Co(CH3OH)4]
and 2D nickel complex [Ni2L2(CH3OH)2]n, respectively. Compound 1 shows a
mononuclear CoII whereas 2 exhibits an antiferromagnetism behavior. Magnetic
investigation reveals 2 naphtholate bridge transmitting antiferromagnetic interaction
and syn-anti carboxylate bridge transmitting ferromagnetic coupling in complex 2.
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Supplementary materials
Crystallographic data for the structural analysis have been deposited with the
Cambridge Crystallographic Data Center, CCDC 887618 & 887619, for complexes 1
& 2. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html.
Acknowledgement
We are very grateful to the Natural Science Foundation Council of China (NSFC)
(grant No. 21171021), Beijing National Laboratory for Molecular Sciences (BNLMS)
and Scientific Research Foundation for the Returned Overseas Chinese Scholars,
State Education Ministry for financial support.
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[19] Caution! Perchlorate compounds are potentially explosive, especially in the presence of organic
ligands. Only a small amount of these materials should be prepared and handled with
care.Preparation of complex (1): A solution of Co(ClO4)26H2O (365 mg, 1 mmol) was added to a
solution of 2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid (229 mg, 1 mmol) and NaOH
(2 mmol) in MeOH (25 ml). The solution was stirred for 5 min and filtered, and the red-brown filtrate
left undisturbed to concentrate slowly by evaporation. Red-brown crystals appeared within a few days
in 40% yield. Elemental analysis for 1: Calculated (%) for C56H52Co3N4O16: C, 55.4; H, 4.3; N, 4.6; Found:
C, 55.3; H, 4.3; N, 4.5. Preparation of complex (2): Ni(ClO4)26H2O (364 mg, 1 mmol),
2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid (229 mg, 1 mmol) and NaOH (2 mmol) in
MeOH (25 ml) were allowed to stir for 1 h at room temperature. The solution was left undisturbed to
slowly evaporate at room temperature. X-ray quality dark green crystals of 1 were obtained in 45%
yield. Elemental analysis for 2: Calculated (%) for C14H13NNiO4: C, 52.9; H, 4.1; N, 4.4; Found: C, 52.9; H,
4.3; N, 4.2.
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c=11.8496(15) Å, β= 111.176(2)°, V= 2585.9(6) Ǻ3, Z = 2, Dc =1.559 g/cm
3, μ = 1.029 mm
−1, F(000)
=1250, R1 = 0.0323 and wR =0.0965 for 15339 independent reflections (Rint =0.0288) and 5868
observed reflections (I > 2σ(I)); for 2, monoclinic system, space group P21/c, a= 13.0970(7), b=
7.0797(2), c=14.1771(5) Å, β= 101.260(4)°, V= 1289.24(9) Ǻ3, Z = 4, Dc =1.638 g/cm
3, μ = 1.517 mm
−1,
F(000) =656, R1 = 0.0390 and wR = 0.0835 for 4951 independent reflections (Rint =0.0546) and 2274
observed reflections (I > 2σ(I)).
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Figure Captions
Scheme 1 The structures of H2L ligand (a) and coordination models (b).
Fig. 1 Perspective view of the trinuclear complex 1 (30% thermal probability
ellipsoids, for clarity hydrogen atoms are omitted).
Fig. 2 Partial view of the crystal structure of 2 displaying the bis(chelate)type bridging
ability of the L2-
ligand. (symmetry codes: A -x+1, -y+1, -z+1; B -x+1, y-1/2, -z+1/2;
C -x+1, y+1/2, -z+1/2)
Fig 3 Plot of χMT vs T for 1. The solid line represent the best fit of the experimental
data.
Fig 4 Plot of χMT vs T for 2. The solid line represent the best fit of the experimental
data. Inset: field-dependent magnetization of 2 at 1.8 K.
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(a) (b)
(E)-2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid
Scheme 1
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Fig. 1
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Fig. 2
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0 50 100 150 200 250 300
1.5
2.0
2.5
3.0
3.5
M
T (
cm
3 K
mo
l-1
)
T (K)
Fig 3
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0 50 100 150 200 250 300
0.01
0.02
0.03
0.04
0.05
0.06
0 10 20 30 40 50 60 700.00
0.05
0.10
0.15
0.20
0.25
0.30
M (
N
H (KOe)
T (K)
M
(c
m3
mo
l-1
)
0.0
0.4
0.8
1.2
1.6
2.0
2.4 M
T (c
m3
K m
ol -1
)
Fig 4
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Graphical abstract
Two new complexes, [CoL2]2[Co(CH3OH)4] (1), and [Ni2L2(CH3OH)2]n (2) (H2L =
2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid), were successfully
synthesized and magnetic properties studied.
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Highlights
► A linear trunuclear cobalt 1 and a 2D nickel complex 2 have been characterized.
► Magnetic measurements reveal 1 shows mononuclear CoII behavior whereas 2
exhibits an antiferromagnetism behavior.