Synthesis, structure, and magnetic properties of a tetranuclear copper(fII) complex with a triazenido ligand

Article abstract of DOI:10.1007/s11243-010-9401-y

The reaction of methyl anthranilate, sodium nitrite, and 2-aminopyridine produces a triazenide, namely, 1-[(2-carboxymethyl)benzene]-3-[2-pyridine] triazene (HL). In the presence of Et₃N, the reaction of HL and CuCl₂?2H₂O

Full text of DOI:10.1007/s11243-010-9401-y

Transition Met Chem (2010) 35:835–839
DOI 10.1007/s11243-010-9401-y
Synthesis, structure, and magnetic properties of a tetranuclear
copper(fII) complex with a triazenido ligand
•
Wei Li Xing-Wu Tan Wen-Jun Lei
•
•
•
Shu-Zhong Zhan De-Rong Cao
Received: 27 April 2010 / Accepted: 12 July 2010 / Published online: 28 July 2010
Ó Springer Science+Business Media B.V. 2010
Abstract The reaction of methyl anthranilate, sodium
nitrite, and 2-aminopyridine produces a triazenide, namely,
1-[(2-carboxymethyl)benzene]-3-[2-pyridine]triazene (HL).
In the presence of Et3N, the reaction of HL and CuCl2ꢀ2H2O
gives a l4-oxo-bridged tetranuclear copper(II) complex
[Cu4OL3Cl3]ꢀ1.5THF (1ꢀ1.5THF), which has been charac-
terized by X-ray crystallography and magnetic susceptibility
measurements.
development of new magnetic materials and catalysts
[11–13].
Although tetranuclear {Cu4(l4–O)} cores have been
known for some time and studied extensively [14–18], rel-
atively few copper complexes with other polydentate
ligands, such as triazenide ligands, have been developed. We
have synthesized a new triazenide ligand, 1-[(2-carboxy-
methyl)benzene]-3-[2-pyridine]triazene (HL) by modifica-
tion of a literature procedure [19]. The reaction of HL and
CuCl2ꢀ2H2O gives a tetranuclear copper(II) complex 1. In
this paper, we describe the synthesis and characterization
of HL, and its complex 1, as well as the magnetic properties
of 1.
Introduction
Polynuclear copper complexes have received increasing
attention in recent years, owing to their applications in
metallobiochemistry [1–3], materials science [4–7], and
theoretical chemistry [8]. Particular interest has been
directed toward the exchange phenomena in di- and poly-
nuclear complexes of copper(II), which have led to
valuable insights into their magnetostructural correlations
[9, 10].
Experimental
1H NMR spectra were measured on a Bruker AM 500
spectrometer in CDCl3 solution. Magnetic susceptibility
data for powder samples were collected in the temperature
range 2–300 K with a Quantum Design SQUID Magne-
The use of different bridging and polydentate ligands
has afforded an impressive array of coordination com-
plexes with new architectures. Among them, the triazene
ligands have attracted our attention, as these compounds
have remarkable bridging ability to afford multinuclear
complexes possessing potentially useful properties for the
tometer MPMS XL-7. Effective magnetic moment was
calculated by the equation leff = g[ ZS(S ? 1)]1/2
where vM is the molar magnetic susceptibility.
P
,
Synthesis of HL
A solution of methyl anthranilate (10 mmol) in water
(5 mL) was mixed with 1 molꢀL-1 HCl (30 mL, 30 mmol)
at 0 °C. An aqueous solution (15%) of sodium nitrite
(15 mmol) was added dropwise with stirring. Once the
amine was dissolved, a 15% solution of 2-aminopyridine
(10 mmol) in ethanol was added at 0 °C and the mixture
was stirred for 6 h. The reaction mixture was neutralized
with 15% aqueous NaCH3CO2 to give a yellow precipitate.
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-010-9401-y) contains supplementary
material, which is available to authorized users.
W. Li ꢀ X.-W. Tan ꢀ W.-J. Lei ꢀ S.-Z. Zhan (&) ꢀ D.-R. Cao
College of Chemistry and Chemical Engineering, South China
University of Technology, Guangzhou 510640, China
e-mail: shzhzhan@scut.edu.cn
123

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Transition Met Chem (2010) 35:835–839
The reaction mixture was filtered, and the solid was
purified by crystallization at -4 °C from 9:1 ethyl acetate/
hexanes to obtain yellow crystals, which were collected
and dried in vacuo (1.8 g, 70%). Anal. Found (calcd) for
C13H12N4O2: C 60.7 (60.9), H 4.8 (4.7), N 21.7 (21.9).
1H NMR (CDCl3): d 8.58 (d, J = 1 Hz, 1H, py),
8.05 (d, J = 2.6 Hz, 1H, Py), 7.96 (d, J = 2.8 Hz, 1H, Py),
7.82 (t, J = 2.7 Hz, 1H, Py), 7.60 (t, J = 2.7 Hz, 2H, Ar),
7.25 (t, J = 1.7 Hz, 1H, Py), 7.16 (t, J = 2.7 Hz, 1 Hz,
Py), 3.97 (s, 3H, –OCH3).
Table 1 Crystallographic data for HL and 1ꢀ1.5THF
Parameter
HL
1ꢀ1.5THF
Empirical formula
Formula weight
C13H12N4O2 C44.5H43Cl3Cu4N12O8.5
256.27
0.71073
Monoclinic
P2(1)/c
15.064(3)
6.197(1)
27.545(6)
90
1,242.42
0.71073
Monoclinic
P21/n
˚
k (A)
Crystal system
Space group
˚
a/A
11.2188(5)
22.3976(9)
20.4830(4)
90
˚
b/A
˚
c/A
Synthesis of complex 1
a/°
b/°
c/°
99.30(3)
90
98.8850(10)
90
To a solution of the ligand (0.26 g, 1 mmol) and triethyl-
amine (0.10 g, 1 mmol) in THF/methanol (15 mL, 1:1),
CuCl2ꢀ2H2O (0.17 g, 1 mmol) was added and the mixture
was stirred for 15 min. The solution was allowed to slowly
evaporate to afford dark green crystals, which were col-
lected and dried in vacuo (0.21 g, 56%). Anal. Found
(calcd) for C39H33Cl3Cu4N12O7: C 39.9 (41.0), H 2.9 (2.9),
N 14.3 (14.7).
3
˚
V/A
2,537.3(9)
4
5,085.1(4)
4
Z
Dc/Mgm-3
1.342
1.623
F(000)
1,072
2,516
h range for data collection 3.09–27.48°
Reflections collected/unique 21,893/5,713 30,079/8,700
3.08–27.48°
Data/restraints/parameters
Goodness of fit on F2
5,713/0/344
1.154
8,700/675/649
0.984
X-ray crystallography
Final R indices
[I [ 2sigma(I)]
R1 = 0.1123 R1 = 0.0419
Data were collected with a Bruker SMART CCD area
detector using graphite monochromated Mo-K radiation
˚
(0.71073 A) at room temperature for HL, and at 150 K for
wR2 = 0.3209 wR2 = 0.1075
R1 = 0.1454 R1 = 0.0555
wR2 = 0.3504 wR2 = 0.1172
R indices (all data)
complex 1. Empirical absorption corrections were applied
using the SADABS program [20]. Structures were solved
using direct methods and the non-hydrogen atoms were
refined anisotropically. All the hydrogen atoms of the
ligands were placed in calculated positions with fixed
isotropic thermal parameters and included in the structure
factor calculations in the final stage of full-matrix least-
squares refinement. All calculations were performed using
the SHELXTL computer program [21]. Table 1 gives
details of the crystal parameters, data collection and
refinement for HL and 1ꢀ1.5THF. The selected bond dis-
tances and angles for compounds HL, and 1ꢀ1.5THF are
listed in Tables 2 and 3.
˚
Table 2 Selected bond lengths (A) and angles (°) for HL
Bond distances
N(1)–N(2)
1.333(4)
1.376(5)
N(2)–N(3)
1.268(4)
N(1)–C(1)
Bond angles
C(1)–N(1)–N(2)
N(2)–N(3)–C(6)
119.7(3)
113.0(3)
N(1)–N(2)–N(3)
N(4)–C(1)–N(1)
111.8(3)
114.5(3)
view of HL is displayed in Fig. 1. HL contains a rigid
N(2)=N(3) double bond and a potential NNNNO donor set.
The N(1)–N(2) and N(2)–N(3) bond distances are 1.333(4)
˚
and 1.268(4) A, respectively.
X-ray quality crystals of 1 were obtained by slow
evaporation of a THF solution of 1. The ORTEP view of 1,
excluding solvent molecules, is illustrated in Fig. 2. The
structure of 1 is completed by four nitrogen atoms of the
deprotonated ligand (L-), a l4-bridging oxygen atom, and
three l-chloride atoms. The tetrahedron around the central
oxygen O(1), with Cu–O(1) distances of 1.939(3),
Results and discussion
1-[(2-carboxymethyl)benzene]-3-[2-pyridine]triazene (HL)
was synthesized by the reaction of methyl anthranilate,
sodium nitrite, and 2-aminopyridine (Scheme 1 and Fig. s1
1
for H NMR spectrum of HL). In the presence of Et3N,
complex 1 was obtained as deep green crystals in good
yield by the reaction of HL and CuCl2ꢀ2H2O in THF/
methanol.
˚
1.941(2), 1.919(3) and 1.932(2) A for Cu(1)–Cu(4)
(Table 3) shows unusually high distortion. The observed
bond angles vary from 103.89(11) and 112.01(13)° for
Cu(1)–O(1)–Cu(3) and Cu(3)–O(1)–Cu(4) to 115.16(12)
X-ray quality crystals of HL were obtained by hexane
diffusion into an ethyl acetate solution of HL. An ORTEP
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Transition Met Chem (2010) 35:835–839
837
˚
in the range 1.967(4)–2.014(3) A for Cu(1)–N, and
˚
1.964(3)–2.022(3) A for Cu(2)–N. The Cu–Cl bond lengths
˚
are within the range of 2.3319(11)–2.4228(11) A for Cu(1),
˚
Table 3 Selected bond distances (A) and angles (°) for complex
1ꢀ1.5THF
Bond distances
˚
and 2.2957(10)–2.5920(12) A for Cu(2), respectively.
Cu(1)–O(1)
Cu(1)–N(11)
Cu(1)–Cl(2)
Cu(2)–N(1)
Cu(2)–Cl(3)
Cu(3)–O(1)
Cu(3)–N(7)
Cu(3)–Cl(2)
Cu(4)–O(4)
Cu(4)–N(12)
Bond angles
1.939(3)
2.014(3)
Cu(1)–N(9)
Cu(1)–Cl(1)
1.967(4)
2.3319(11)
1.941(2)
2.022(3)
2.5920(12)
1.963(3)
2.101(3)
1.932(2)
1.984(3)
2.6575(11)
Cu(1) and Cu(2) are connected by one l4–O bridge and one
chloride bridge, with the bond angle Cu(1)-Cl(3)-Cu(2) of
76.20(3)°.
Cu(3) and Cu(4) are both coordinated by three nitrogen
atoms from two L- ligands, one l4–O atom, and one
chloride atom. The Cu–N bond lengths are 1.963(3)–
2.4228(11) Cu(2)–O(1)
1.964(3) Cu(2)–N(3)
2.2957(10) Cu(2)–Cl(1)
1.919(3)
2.039(3)
Cu(3)-N(5)
Cu(3)–N(4)
˚
2.101(3) A and the Cu–Cl distances are 2.3855(11) and
˚
2.6575(11) A, respectively. Pairs Cu(1), Cu(3) and Cu(2),
2.3855(11) Cu(4)–O(1)
1.970(3)
1.997(3)
Cu(4)–N(8)
Cu(4)–Cl(3)
Cu(4) are connected by one l4–O bridge and one chloride
bridge with bond angles Cu(1)–Cl(2)–Cu(3) of 78.36(3)°
and Cu(4)–Cl(3)–Cu(2) of 77.13(3)°.
Cu(3)–O(1)–Cu(4) 12.01(13)
Cu(3)–O(1)–Cu(1) 103.89(11)
Cu(4)–O(1)–Cu(1) 115.99(12) Cu(3)–O(1)–Cu(2) 115.16(12)
Cu(4)–O(1)–Cu(2) 106.36(11) Cu(1)–O(1)–Cu(2) 103.41(12)
Magnetic properties of 1
Cu(1)–Cl(1)–Cu(2) 76.20(3)
Cu(2)–Cl(3)-Cu(4) 77.13(3)
Cu(1)–Cl(2)–Cu(3) 78.36(3)
Magnetic susceptibility data for a solid sample of 1 was
collected in the temperature range 2–300 K (Fig. 3).
Complex 1 has a low room-temperature magnetic moment
(leff = 1.09 lB (300 K)), indicating significant antiferro-
magnetic coupling between the copper(II) centers. Three
different exchange pathways can occur in complex 1,
involving Cu–N–Cu, Cu–O–Cu, and Cu–Cl–Cu. Consid-
ering the relatively large average Cu–Cl distances in 1 and
the well-known magneto-structural correlations for equiv-
alent Cu–Cl–Cu systems [22], a significant contribution of
the Cu–Cl–Cu pathway in 1 can be excluded. It was found
that for (l-carboxylato)copper(II) systems, only those
compounds which exhibit an approximately square planar
copper coordination show a strong contribution of the
carboxylato ligand to the overall exchange [23–25]. The
effect of other bridging ligands such as Cl should only
slightly modulate the extent of coupling.
CO2Me
CO2Me
NaNO2
N
NH2
H2N
+
N
N
H
N
N
Scheme 1 Schematic representation of the synthesis of HL
To explain the magnetic behavior of complex 1, its
structure can consequently be reduced to a central Cu4N6O
core which can be described as O(1)-connected Cu2N2
rings, as shown in Fig. 4. The Cu–Cl–Cu and Cu–N–N–Cu
pathways in 1 are assumed to have only a second-order
effect upon the magnetic exchange between the copper
centers. The tetranuclear copper(II) complex can be for-
mally divided into two dinuclear Cu2N2O subunits. The
intradimer coupling via the oxygen atom is assumed to be
larger than the interdimer exchange interactions. Hence
initially a molecular field model [26] was used to approx-
imate the case where interdimer magnetic coupling (i.e.,
the exchange between the di-l-oxo-bridged copper centers)
is expected to dominate the relatively weaker interdimer
coupling.
Fig. 1 ORTEP view of ligand (HL)
and 115.99(12)° for Cu(2)–O(1)–Cu(3) and Cu(1)–O(1)–
Cu(4). This distortion is attributed to the steric bulk of the
chelating ligands, which contract each of the two copper
centers within the tetranuclear unit (Cu(l), Cu(2) and
Cu(3), Cu(4)), associated with a reduction of the corre-
sponding Cu–O–Cu bond angles.
In complex 1, Cu(1) and Cu(2) are both coordinated by
two nitrogen atoms from L-, one l4–O atom, and two
chloride atoms, respectively. The Cu–N bond lengths fall
The experimental data can be fitted by the following
model. The spin Hamiltonian for complex 1, assuming
interaction in each pair can be properly described in terms
123

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Transition Met Chem (2010) 35:835–839
Fig. 2 ORTEP view of 1. THF
molecules are omitted for clarity
.0020
.0015
.0010
.0005
0.0000
-.0005
-.0010
-.0015
0
100
200
300
T/K
Fig. 3 Plot of the temperature dependence of the vM for complex 1 at
5000 Oe
Fig. 4 Connection of the [Cu4N6(l4–O)] core
of the Heisenberg Hamiltonian of the form H = - JijSiꢀSj,
is given in Eq. 1.
with SA = S1 ? S2, SB = S3 ? S4, ST = SA ? SB, and S =
l/2, specifying ST, SA, SB, and S uniquely defines an eigenstate
of the Hamiltonian which will be represented by the notation
|T, SA, SB[and which has the energy given by Eq. 3.
H ¼ ꢁ 2½J12S1 ꢀ S2 þ J13S1 ꢀ S3 þ J14S1 ꢀ S4
þ J23S2 ꢀ S3 þ J24S2 ꢀ S4 þ J34S3 ꢀ S4ꢂ
ð1Þ
For an arrangement of copper(II) ions as shown in
Fig. 4, Eq. 1 simplifies directly to Eq. 2.
EðST;SA;SBÞ ¼ ꢁJ12½SAðSA þ1ÞþSBðSB þ1Þꢁ4SðSþ1Þꢂ
ꢁJ13½ST ðST þ1ÞꢁSAðSA þ1ÞꢁSBðSB þ1Þꢂ
H ¼ ꢁ 2½J12ðS1 ꢀ S2 þ S3 ꢀ S4Þ
þ J13ðS1 ꢀ S3 þ S1 ꢀ S4 þ S2 ꢀ S3 þ S2 ꢀ S4Þꢂ
ð2Þ
ð3Þ
123

Transition Met Chem (2010) 35:835–839
839
The susceptibility can then be expressed theoretically by
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