From a dissymmetrical oxamidate ligand to a 2D coordination polymer: Synthesis, crystal structure and magnetic properties

Article abstract of DOI:10.1515/znb-2010-1010

A new dissymmetrical oxamidate ligand has been used to construct a metal-organic network. Using this ligand, a novel coordination polymer, namely {[Cu(obea)]₂Cu.CH₃OH.H₂O}_n (1) [H₃obea = N1-(2-carboxyphenyl)-N2-(2-hydroxyethyl)oxalamide] has been synthesized and characterized by single-crystal X-ray analysis. The structure of complex 1 consists of neutral trinuclear complex units. Through syn-anti carboxylate bridges, the complex features a 2D structure with a helical substructure. Its magnetic properties have been investigated.

Full text of DOI:10.1515/znb-2010-1010

From a Dissymmetrical Oxamidate Ligand to a 2D Coordination Polymer:
Synthesis, Crystal Structure and Magnetic Properties
Bao Lin Liua, Juan Danga, Shuang Quan Zangb, Qing Lun Wangc, and Ruo Jie Taoa
a Institute of Molecular and Crystal Engineering, College of Chemistry and Chemical Engineering,
Henan University, Kaifeng 475001, P. R. China
b Department of Chemistry, Zhengzhou University, Henan 450052, P. R. China
c Department of Chemistry, Nankai University, Tianjin 300071, P. R. China
Reprint requests to Prof. Ruo Jie Tao. Fax: +86-378-3881960. E-mail: rjtao@henu.edu.cn
Z. Naturforsch. 2010, 65b, 1240 – 1244; received May 23, 2010
A new dissymmetrical oxamidate ligand has been used to construct a metal-organic network. Using
this ligand, a novel coordination polymer, namely {[Cu(obea)]2Cu·CH3OH·H2O}n (1) [H3obea =
N1-(2-carboxyphenyl)-N2-(2-hydroxyethyl)oxalamide] has been synthesized and characterized by
single-crystal X-ray analysis. The structure of complex 1 consists of neutral trinuclear complex units.
Through syn-anti carboxylate bridges, the complex features a 2D structure with a helical substructure.
Its magnetic properties have been investigated.
Key words: Oxamidate Ligand, Crystal Structure, Magnetic Properties
Introduction
The crystal engineering of solid-state metal coor-
dination supramolecules is one of the most active re-
search topics of current chemistry and molecular sci-
ence due to the theoretical aspects related to the topolo-
gies of novel networks with inner cavities and channels
[1], as well as their potential applications in catalysis
[2], host-guest chemistry [3], and molecular electron-
ics [4]. Self-assembly of suitably designed ligands with
transition metal ions allows the creation of inorganic
architectures with defined geometry and special prop-
erties [5 – 7].
Scheme 1. Synthetic route to ligand H3obea.
It is well known that a carboxylate group can bridge
two metal ions to give rise to a wide variety of polynu-
clear complexes ranging from discrete entities to three-
dimensional systems [8 – 10]. In these complexes, a
carboxylate group can assume many types of bridg-
ing conformations, the most important being triatomic
syn-syn, anti-anti, syn-anti, and monoatomic [11]. As
expected, the magnetic properties are closely related
to the bridging conformation adopted by the carboxy-
late group in these polynuclear systems. It should be
noted that, as far as we know, only a few fully struc-
turally and magnetically characterized singly syn-anti
carboxylate-bridged complexes have been reported so
far [12– 15].
of these ligands is the easy transformation of cis-trans
conformations, which makes it practical to design tun-
able molecular materials with extended structures and
desired properties. The flexibility can give rise to a rich
variety of complexes and extended structures, but it al-
lows much less control over the final type of complex
obtained [16].
With these facts in mind, the new dissymmet-
rical ligand N1-(2-carboxyphenyl)-N2-(2-hydroxy-
ethyl)oxalamide, abbreviated as H3obea, has been pre-
pared in this work (Scheme 1). Based on this lig-
and, we describe the synthesis, crystal structure and
magnetic properties of a novel coordination polymer,
Oxamidate derivatives are known to be versatile or- namely {[Cu(obea)]2Cu·CH3OH·H2O}n (1), which
ganic ligands. One of the most outstanding characters is a 2D framework containing both dissymmetri-
c
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B. L. Liu et al. · From a Dissymmetrical Oxamidate Ligand to a 2D Coordination Polymer
1241
Table 1. Crystallographic data and refinement parameters for
cal trans-oxamidate bridges and syn-anti carboxylate
bridges.
complex 1.
Empirical formula
Formula weight
Crystal system
Space group
C23H22N4O12Cu3
737.07
monoclinic
P21/c
10.5442(10)
7.1479(7)
17.5062(17)
105.465(2)
1271.7(2)
2
1.93
2.6
293(2)
0.71073
−11 ≤ h ≤ 12, −8 ≤ k ≤ 7,
−20 ≤ l ≤ 20
6119 / 2238 / 0.0581
228
0.0492 / 0.1248
0.0690 / 0.1317
1.064
Experimental Section
Materials
˚
a, A
˚
b, A
Cu(ClO4)2·6H2O was prepared as an in-house reagent.
Other chemicals were commercial reagent grade and used
without further purification.
Caution! Perchlorates are potentially explosive, thus only
a small amount of material should be prepared and handled
with care.
˚
c, A
β, deg
3
˚
V, A
Z
Dcalc, g cm−3
µ(MoKα ), mm−1
T, K
˚
λ, A
Synthesis of the ligand H obea
3
Index ranges
A 50 mmol (6.83 g) portion of ethyl oxalyl chloride in
10 mL of THF (THF = tetrahydrofuran) was added dropwise
into 40 mL of a THF solution of 50 mmol (6.86 g) of an-
thranilic acid. After 1 h, the mixture was added dropwise
to a solution which contained 20 mL of absolute ethanol
and 30 mL of ethanolamine at 0 ◦C. The resulting solu-
tion was stirred for 24 h, and H3obea was precipitated as a
colorless powder, washed with diethyl ether and dried un-
der vacuum. Yield: 10.8 g (86 %). – Anal. for C11H12N2O5:
calcd. C 52.38, H 4.79, N 11.11; found C 52.36, H 4.80,
N 11.14 %. – IR (KBr): νC=O(oxamidate group) = 1636;
Refl. total / independ. / Rint
Ref. parameters
R1 / wR2a [I ≥ 2 σ(I)]
R1 / wR2a (all data)
Goodness-of-fitb
−3
˚
∆ρfin (max / min), e A
0.875 / −0.495
a
2
R1 = ΣꢀFo| − |Fcꢀ/Σ|Fo|, wR2 = [Σw(Fo − Fc2)2/Σw(Fo2)2]1/2
,
=
−
w
=
[σ2(Fo2) + (0.0720 P)2 + 0.1919 P]−1
,
where
P
b
2
(Max(Fo2,0) + 2Fc2)/3;
param)]1/2
GoF
=
[Σw(Fo − Fc2)2/(nobs
n
.
˚
Table 2. Selected bond lengths (A) and angles (deg) for com-
νas(COO) (νCOOH un-ionized) = 1672 cm−1
.
plex 1.
Cu(1)-N(2)#1
Cu(1)-O(3)#1
Cu(2)-O(1)
Cu(2)-N(1)
Cu(2)-O(1W)
1.932(4) Cu(1)-N(2)
1.964(3) Cu(1)-O(3)
1.894(4) Cu(2)-O(4)
1.959(4) Cu(2)-O(2)#2
2.533(9) Cu(2)-O(6)
1.932(4)
1.964(3)
1.934(3)
1.958(3)
2.549(10)
Synthesis of the complex {[Cu(obea)] Cu·CH OH·H O}n
2
3
2
(1)
H3obea (0.1 mmol, 0.0252 g), NaOH (0.3 mmol, 0.012 g)
N(2)-Cu(1)-N(2)#1
N(2)-Cu(1)-O(3)#1
N(2)-Cu(1)-O(3)
O(1)-Cu(2)-O(2)#2
O(1)-Cu(2)-O(4)
O(4)-Cu(2)-N(1)
O(1)-Cu(2)-O(1W)
180
96.10(15) N(2)#1-Cu(1)-O(3)
83.90(15) O(3)#1-Cu(1)-O(3) 180
N(2)#1-Cu(1)-O(3)#1 83.90(15)
96.10(15)
and CuCl2·2H2O (0.1 mmol, 0.017 g) were dissolved in wa-
ter (5 mL) in a test tube. A solution of Cu(ClO4)2·6H2O
(0.1 mmol, 0.0371 g) in methanol (5 mL) was then care-
fully added to the top of this solution without disturbing it.
Blue block-shaped single crystals suitable for X-ray analy-
sis were obtained after four weeks. Yield: 46%. – Anal. for
C23H21N4O12Cu3: calcd. C 37.53, H 2.88, N 7.61; found:
86.20(15) O(4)-Cu(2)-O(2)#2
172.93(18) O(1)-Cu(2)-N(1)
93.94(15)
93.43(15)
86.55(15) O(2)#2-Cu(2)-N(1) 178.98(15)
88.0(3) O(4)-Cu(2)-O(1W)
98.9(3)
78.9(2)
87.6(3)
102.4(2)
O(2)#2-Cu(2)-O(1W) 100.2(2) N(1)-Cu(2)-O(1W)
C 37.43, H 2.83, N 7.67 %. – IR (KBr): νC=O = 1628 cm−1
.
O(1)-Cu(2)-O(6)
85.5(3) O(4)-Cu(2)-O(6)
78.6(2) N(1)-Cu(2)-O(6)
O(2)#2-Cu(2)-O(6)
O(1W)-Cu(2)-O(6) 173.5(3)
Physical measurements
Symmetry codes: #1 −x+1, −y+1, −z+2; #2 −x, y+1/2, −z+3/2;
#3
−x, y−1/2, −z+3/2.
Elemental analyses for carbon, hydrogen and nitrogen
were performed on a Perkin-Elmer 2400II elemental an-
alyzer. The infrared spectra were recorded on an Avatar-
360 spectrometer using KBr pellets in the range of 400 –
X-Ray analysis
A single crystal with dimensions 0.14 × 0.13 ×
4000 cm−1. Variable temperature magnetic susceptibility 0.06 mm3 was used for the structure determination using a
data were obtained on microcrystalline samples from 5 to Bruker SMART APEX CCD diffractometer with graphite-
˚
300 K in a magnetic field of 10 KG, using a Quantum De- monochromatized MoKα radiation (λ = 0.71073 A) at r. t.
sign MPMS-7 SQUID magnetometer. Diamagnetic correc- (ω scan technique). Lorentz, polarization and absorption
tions were made with Pascal parameters for all constituent corrections were applied. The crystal structure was solved
atoms.
by Direct Methods with the SHELXTL program and refined
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1242
B. L. Liu et al. · From a Dissymmetrical Oxamidate Ligand to a 2D Coordination Polymer
by full-matrix least-squares procedures with anisotropic dis-
placement parameters for all non-hydrogen atoms [17]. All
H atoms could be detected in the difference electron density
maps. Nevertheless, they were positioned at idealized posi-
tions and refined using a riding model. Analytical expres-
sions of neutral-atom scattering factors were employed, and
anomalous dispersion corrections were incorporated. Crys-
tallographic data are summarized in Table 1. Selected bond
lengths and bond angles are shown in Table 2.
CCDC-706284 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data request/cif.
Fig. 1. Trinuclear unit of complex 1 (symmetry codes:
#1 −x + 3, −y + 3, −z; #2 −x + 2, −y + 1/2, −z − 1/2;
#3 −x+2, y−1/2, −z−1/2; hydrogen atoms, methanol and
water molecule are omitted for clarity).
Results and Discussion
IR spectra
The ligand H3obea exhibits one νC=O vibration
band of the oxamidate group at ca. 1636 cm−1 [18],
one νas(COO) vibration band at ca. 1672 cm−1 (νCOOH
un-ionized) [19], and νN−H bands of the oxamidate
group at ca. 3082 and 3102 cm−1. These bands are all
missing in the spectrum of the complex because of the
loss of the protons of both the COOH and N-H (oxami-
date group) groups. It must be noted that one new sharp
strong band observed in the complex 1 (1628 cm−1) is
the result of an overlap between νas(COO) of the ionized
carboxylate group and the vibration of the oxamidate
group (νC=O) acting in a bidendate mode. No peak can
be assigned unambiguously to metal-ligand vibrations
in the range below 600 cm−1, since the ligand itself has
several absorptions in this region.
Description of the crystal structure
Fig. 2. The 2D structure of complex 1 as seen along the
crystallographic a axis (hydrogen atoms, methanol and water
molecules are omitted for clarity).
X-Ray single crystal structure analysis has revealed
that complex 1 crystallizes in the space group P21/c.
As shown in Fig. 1, complex 1 consists of a trinu- gen atom (O2#2) from another trans-oxamidate bridge.
clear neutral molecule, one water molecule, and one The axial positions are filled with one oxygen atom
methanol molecule. The trinuclear neutral molecule (O1W) from water, and one oxygen atom (O6) from
has a centrosymmetric structure with a Cu1 ion in its methanol. Fig. 1 indicates that O5 is disordered over
center. Two oxamidate anions act as bridges between two sites.
the central and the outer metal ions. The Cu–Cu dis-
These trinuclear units are linked by coordinative
˚
tance through the oxamido bridge is 5.189(5) A. The bonds between carboxylic oxygen atoms and Cu ions
coordination geometry around the Cu1 ion is approxi- to form a novel double helical 2D coordination poly-
mately square-planar, composed of two oxygen atoms mer, as illustrated in Fig. 2.
and two nitrogen atoms from two trans-oxamidate
As noted earlier, each carboxylate group in the dis-
bridges. The Cu2 ion has a distorted octahedral coordi- symmetrical ligand is in the syn-anti conformation and
nation, the equational positions being composed of two bridges two copper atoms via its two oxygen atoms.
oxygen atoms (O1, O4), and one nitrogen atom (N1) The bridging Cu-O-C-O-Cu pathway observed here
of the trans-oxamidate bridge, and one carboxylic oxy- gives rise to an interesting helical structure. Besides the
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B. L. Liu et al. · From a Dissymmetrical Oxamidate Ligand to a 2D Coordination Polymer
1243
χM and µeff versus Tare shown in Fig. 3. At r. t., the
µeff value of complex 1 is 3.20 µB, which is slightly
larger than that expected for uncoupled trinuclear ions
(3.00 µB). Upon cooling, the µeff value of the complex
decreases regularly, approaching a minimum around
30 K with µeff = 2.15 µB. Finally, the µeff value of com-
plex 1 increases as the temperature is further lowered
to 5 K, which is possibly due to a ferromagnetic inter-
action between the trinuclear units through the syn-anti
carboxylate bridges.
Conclusion
Fig. 3. χM versus T and µeff versus Tplots for complex 1.
In summary, a novel helical 2D coordination poly-
mer has been synthesized and characterized struc-
turally and magnetically. In this complex, trinuclear
units are linked by coordination bonds between car-
boxylic oxygen atoms and Cu ions to form a novel 2D
coordination polymer. To our knowledge, complex 1 is
the only helical coordination polymer containing both
dissymmetrical trans-oxamidate bridges and syn-anti
carboxylate bridges. The magnetic properties were dis-
cussed with respect to the crystal structure.
syn-anti mode of the carboxylate, the cis arrangement
of the two carboxylate ligands around the metal ion is
important for the occurrence of the helical structure.
Because left-handed and right-handed helical chains
coexist in the crystal structure, the whole crystal does
not exhibit chirality. The occurrence of a helical struc-
ture in compound 1 is attributable to the fact that the
steric orientation of the carboxyl groups is remarkably
flexible.
Acknowledgement
Magnetic properties
We acknowledge the generous financial support of
the Natural Science Foundation of Henan Province (No.
092300410031).
The magnetic susceptibility of the complex has been
measured in the range of 5 – 300 K. The curves of
[1] a) B. F. Hoskins, R. Robson, J. Am. Chem. Soc. 1990,
112, 1546 – 1554; b) R. Robson, B. F. Abrahams, S. R.
Batten, R. W. Gable, B. F. Hoskins, J. Liu, Supramolec-
ular Architecture, American Chemical Society, Wash-
ington, DC, 1992, chapter 19; c) O. M. Yaghi, G. Li,
Angew. Chem. 1995, 107, 232 – 234; Angew. Chem.,
Int. Ed. Engl. 1995, 34, 207 – 209; d) J. R. Black, N. R.
Champness, W. Levason, G. Reid, Inorg. Chem. 1996,
35, 4432 – 4438; e) L. Carlucci, G. Ciani, D. M. Pros-
erpio, A. Sironi, Inorg. Chem. 1995, 34, 5698 – 5700.
[2] M. Fujita, Y. J. Kwon, S. Washizu, K. Ogura, J. Am.
Chem. Soc. 1994, 116, 1151 – 1552.
[3] a) O. M. Yaghi, C. E. Davis, G. Li, H. Li, J. Am.
Chem. Soc. 1997, 119, 2861 – 2868; b) S. Kawata,
S. Kitagawa, H. Kumagai, C. Kudo, H. Kamesaki,
T. Ishiyama, R. Suzuki, M. Kondo, M. Katada, Inorg.
Chem. 1996, 35, 4449 – 4461; c) H. Zhang, X. Wang,
B. K. Teo, J. Am. Chem. Soc. 1996, 118, 11813 –
11821.
1949; b) H. Miyasaka, N. Matsumoto, H. Okawa,
N. Re, E. Gallo, C. Floriani, J. Am. Chem. Soc. 1996,
118, 981 – 994.
[5] a) J. M. Lehn, Supramolecular Chemistry: Concepts
and Perspectives, VCH, Weinheim, 1995; b) O. M.
Yaghi in Access in Nanoporous Materials, (Eds.: T. L.
Pinnavania, M. F. Thorpe), Plenum, New York 1995,
pp. 111.
[6] a) O. Sato, T. Iyoda, A. Fujishima, K. Hashimoto, Sci-
ence 1996, 271, 49 – 51; b) H. J. Choi, M. P. Suh, J. Am.
Chem. Soc. 1998, 120, 10622 – 10628.
[7] a) S. R. Batten, R. Robson, Angew. Chem. 1998, 110,
1558 – 1595; Angew. Chem. Int. Ed. 1998, 37, 1460 –
1494; b) P. J. Hagraman, D. Hagraman, J. Zubieta,
Angew. Chem. 1999, 111, 2798 – 2848; Angew. Chem.
Int. Ed. 1999, 38, 2638 – 2684; c) A. J. Blake, N. R.
Champness, P. Hubberstey, W. S. Li, M. A. Withersby,
M. Schro¨der, Coord. Chem. Rev. 1999, 183, 117 – 138.
[8] R. J. Doedens, Prog. Inorg. Chem. 1976, 21, 209 – 231.
[9] S. J. Rettig, R. C. Thompson, J. Trotter, S. Xia, Inorg.
Chem. 1999, 38, 1360 – 1363.
[4] a) M. S. E. Fallah, E. Rentschler, A. Caneschi, R. Ses-
soli, D. Gatteschi, Angew. Chem. 1996, 108, 2081 –
2083; Angew. Chem., Int. Ed. Engl. 1996, 35, 1947 –
[10] V. Tangoulis, G. Psomas, C. Dendrinou-Samara, C. P.
Unauthenticated
Download Date | 4/16/18 9:07 AM

1244
B. L. Liu et al. · From a Dissymmetrical Oxamidate Ligand to a 2D Coordination Polymer
Raptopoulou, A. Terzis, D. P. Kessissoglou, Inorg.
Chem. 1996, 35, 7655 – 7660.
[11] E. Colacio, J. M. Dom´ınguez-Vera, M. Ghazi, R. Kive-
ka¨s, M. Klinga, J. M. Moreno, Eur. J. Inorg. Chem.
1999, 441 – 445.
[12] E. Colacio, J. M. Dominguez-Vera, R. Kiveka¨s, J. M.
Moreno, A. Romerosa, J. Ruiz, Inorg. Chim. Acta
1993, 212, 115 – 121.
[13] K. K. Nanda, A. W. Addison, E. Sinn, L. K. Thompson,
Inorg. Chem. 1996, 35, 5966 – 5967.
[14] D. Schulz, T. Weyhermu¨ller, K. Wieghardt, C. Butzlaff,
A. X. Trautwein, Inorg. Chim. Acta 1996, 247, 387 –
394.
[15] S. Sen, M. K. Saha, T. Gupta, A. K. Karmakar, P. Kun-
du, S. Mitra, M. B. Hursthouse, K. M. A. Malik, J.
Chem. Crystallogr. 1998, 28, 771 – 777.
[16] a) H. Ojima, K. Nonoyama, Coord. Chem. Rev. 1988,
92, 85; b) R. Ruiz, J. Faus, F. Lloret, M. Julve, Y. Jour-
naux, Coord. Chem. Rev. 1999, 193, 1069 – 1117.
[17] a) R. H. Blessing, Acta Crystallogr. 1995, A51, 33 –
38; b) G. M. Sheldrick, SHELXTL (version 5.1), Bruker
Analytical X-ray Systems Inc., Madison, Wisconsin
(USA) 1997. See also: G. M. Sheldrick, Acta Crystal-
logr. 1990, A46, 467 – 473; ibid. 2008, A64, 112 – 122.
[18] K. Nakamoto, Infrared and Raman Spectra of Inor-
ganic and Coordination Compounds, 5th ed., Part B,
John Wiley, New York, 1997.
[19] Y. Akhiff, J. Server-Carrio´, J. Garc´ı-Lozano, E. Es-
criva´, J. V. Folgado, L. Soto, Inorg. Chem. 1999, 38,
1174 – 1185.
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