Polynuclear complexes incorporating Cu(II) and Mn(II) centers bridged by acetylenedicarboxylate: Structure, thermal stability and magnetism

Article abstract of DOI:10.1016/j.molstruc.2006.06.021

Two acetylenedicarboxylate complexes, [Mn₂(C₄O₄)(phen)₄(H₂O)₂](ClO₄)₂·H₂O (1) and [Cu(C₄O₄)(2,2′-bpy)]_n (2), have been synthesized and characterized by elemental analyses and IR spectra. Mn^II ions have distorted octahedral coordination geometry and bridged by C₄O₄^2- to form a binuclear structure. Thermal analysis shows C₄O₄^2- released in the range of 180-280 °C. Cu^II is five-coordinated by 2,2′-bipyridine and three oxygen atoms from three different C₄O₄^2- ligands, leading to a square-pyramidal coordination geometry. Each C₄O₄^2- links three Cu^II centers through bifunctional carboxylate to form a polymeric structure of (4, 4) layers with nodes being dimer of Cu₂O₂ and bridges of C₄O₄^2-. Its variable-temperature magnetism was also investigated.

Full text of DOI:10.1016/j.molstruc.2006.06.021

Journal of Molecular Structure 829 (2007) 155–160
www.elsevier.com/locate/molstruc
Polynuclear complexes incorporating Cu(II) and Mn(II) centers
bridged by acetylenedicarboxylate: Structure, thermal stability
and magnetism
*
Min Shao, Ming-Xing Li , Hui Dai, Wen-Cong Lu, Bao-Li An
Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, China
Received 11 April 2006; received in revised form 12 June 2006; accepted 16 June 2006
Available online 27 July 2006
Abstract
Two acetylenedicarboxylate complexes, [Mn2(C4O4)(phen)4(H2O)2](ClO4)2ÆH2O (1) and [Cu(C4O4)(2,20-bpy)]n (2), have been synthe-
sized and characterized by elemental analyses and IR spectra. MnII ions have distorted octahedral coordination geometry and bridged by
C4O4 to form a binuclear structure. Thermal analysis shows C4O4 released in the range of 180–280 ꢀC. CuII is five-coordinated by
2,20-bipyridine and three oxygen atoms from three different C4O42ꢀ ligands, leading to a square-pyramidal coordination geometry. Each
C4O42ꢀ links three CuII centers through bifunctional carboxylate to form a polymeric structure of (4,4) layers with nodes being dimer of
Cu2O2 and bridges of C4O42ꢀ. Its variable-temperature magnetism was also investigated.
2ꢀ
2ꢀ
ꢁ 2006 Elsevier B.V. All rights reserved.
Keywords: Copper; Manganese; Acetylenedicarboxylate; Crystal structure; Thermal analysis; Magnetism
1. Introduction
and [Cd(C4O4) (H2O)3]n [12–14], metal-organic framework
[Zn(C4O4)2 (HTEA)2]n [15], rare-earth complexes
[Eu2(C4O4) (CO3)2(H2O)2] and [Ln2(C4O4)3(H2O)6] [16,17].
We present here two new acetylenedicarboxylate complexes
[Mn2(C4O4)(phen)4(H2O)2] (ClO4)2ÆH2O (1) and [Cu(C4O4)
(2,20-bpy)]n (2). Complex 1 is dimer in which two Mn(II)
ions are bridged by C4O42ꢀ, while complex 2 is a polymeric
complex of (4,4) layers with nodes being dimer of Cu2O2
and bridges of C4O42ꢀ. Their IR spectra, thermal stability
and magnetism are also reported.
Coordination polymers are of great interest due to their
intriguing structural motifs and potential applications in
optical, electronic, magnetic, and porous materials [1–3].
Many of them are based on metal carboxylates [4], such
as dicarboxylate succinate, maleate and terephthalate
[5–9], polycarboxylate 1,3,5-benzenetricarboxylate and
1,2,4,5-benzenetetracarboxylate complexes [10,11]. Analo-
gous to rigid aromatic dicarboxylate terephthalate,
acetylenedicarboxylate (C4O42ꢀ) is a linear dicarboxylate
dianion with shorter bridge and acetylene replacing
aromatic group, which is a potential worthy bridging
ligand in constructing coordination polymer. Up to now,
2. Experimental
2.1. Materials and physical measurement
only
a
few acetylenedicarboxylate complexes were
reported, such as linear complexes [Co(C4O4)(H2O)4]n
All chemicals were purchased from commercial sources
and were used as received without further purification. Ele-
mental analyses were performed on a Perkin-Elmer 240C
analyzer. Infrared spectra were recorded on a Nicolet
A370 FT-IR spectrometer in the 4000–400 cmꢀ1 region
*
Corresponding author. Tel.: +86 21 66132401; fax: +86 21 66132797.
E-mail address: mx_li@mail.shu.edu.cn (M.-X. Li).
0022-2860/$ - see front matter ꢁ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.06.021

156
M. Shao et al. / Journal of Molecular Structure 829 (2007) 155–160
Table 1
Crystal data and structure refinement for complex 1 and 2
1
2
Empirical formula
Formula weight
Crystal system
Space group
C52H38Mn2Cl2N8O15
1195.68
Triclinic
P1
11.880(4)
13.975(4)
17.188(5)
C14H8CuN2O4
331.76
Monoclinic
P2(1)/c
9.842(2)
14.782(3)
8.549(2)
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
104.342(4)
106.854(3)
96.405(4)
2593.6(14)
2
1.531
0.668
0.10 · 0.10 · 0.02
293(2)
1220
90
102.34(3)
90
1215.0(4)
3
˚
V (A )
Z
4
Dc (gÆcmꢀ3
)
1.814
1.816
0.20 · 0.18 · 0.16
291(2)
l (mmꢀ1
)
Crystal size (mm3)
T (K)
F000
668
Reflections collected
Unique reflections
Data/restraints/parameters
R [I > 2r(I)]
10845
4195
8982 [Rint = 0.0174]
8982/10/756
R1 = 0.0605, wR2 = 0.1445
R1 = 0.0986, wR2 = 0.1730
1.032
2468 [Rint = 0.0587]
2468/0/191
R1 = 0.0502, wR2 = 0.1199
R1 = 0.0734, wR2 = 0.1294
1.123
R (all data)
Goodness-of fit on F2
Largest diff. peak and hole
ꢀ3
ꢀ3
˚
˚
0.855 and ꢀ0.417 eÆA
0.654 and ꢀ0.775 eÆA
using KBr disks. TG-DSC analysis was carried out on a
Netzsch STA 449C thermal instrument at a heating rate
of 10 ꢀCminꢀ1 in the atmosphere. Magnetic susceptibilities
(2–300 K) were measured using a Quantum Design PPMS-
9 magnetometer and diamagnetic correction was made
with Pascal’s constants.
methanol solution. The resulting solution was left undis-
turbed at room temperature for 3 weeks. Blue crystals 2
were harvested, washed with cool water and dried in air.
The yield is 73% based on Cu. IR (cmꢀ1, KBr): 3060(w),
1641(s), 1620(s), 1600(m), 1474(w), 1444(m), 1333(s),
1295(s), 1153(w), 1004(w), 764(m), 728(w), 687(m). Anal.
calcd. for C14H8CuN2O4: C, 50.68; H, 2.43; N, 8.44.
Found: C, 51.12; H, 2.41; N, 8.39.
2.2. Synthesis
[Mn2(C4O4)(phen)4(H2O)2](ClO4)2ÆH2O (1). Five millili-
ters of aqueous solution containing acetylenedicarboxylic
acid (0.029 g, 0.25 mmol), piperidine (0.043 g, 0.50 mmol)
was added to 5 mL aqueous solution of Mn(ClO4)2Æ6H2O
(0.181 g, 0.50 mmol) under stirring. To this mixture was
added 5 mL methanol solution of 1,10-phenanthroline
(0.180 g, 1.0 mmol). The resulting solution was left undis-
turbed at room temperature for 2 weeks. Light yellow crys-
tals 1 were harvested, washed with cool water and dried in
air. The yield is 45% based on Mn. IR (cmꢀ1, KBr):
3431(w), 3215(w), 3059(w), 1623(s), 1590(s), 1517(m),
1425(m), 1323(s), 1103(vs), 846(m), 728(m), 623(w). Anal.
calcd. for C52H38Mn2Cl2N8O15: C, 52.24; H, 3.20; N,
9.37. Found: C, 51.92; H, 3.22; N, 9.31. CAUTION! Per-
chlorate complexes of metal ions in the presence of organic
ligands are potentially explosive. Only a small amount of
material should be handled with care.
2.3. X-ray crystallography
Data collection for 1 was performed on a Bruker
Smart Apex CCD diffractometer and for 2 on a Rigaku
RAXIS-IV IP diffractometer, using graphite-monochro-
˚
matic Mo Ka radiation (k = 0.71073 A). Determinations
of the crystal system, orientation matrix and cell dimen-
sions were performed according to the established proce-
dures. Lorentz polarization and absorption correction
were applied. The structures were solved by direct
method and refined by full-matrix least-squares on F2
using SHELX-97 program package [18]. All non-
hydrogen atoms were refined anisotropically, and hydro-
gen atoms were added geometrically. The crystal
data and structure refinement results are summarized in
Table 1.
[Cu(C4O4)(2,20-bpy)]n (2). Five milliliters of aqueous
solution containing acetylenedicarboxylic acid (0.057 g,
0.50 mmol) and piperidine (0.085 g, 1.0 mmol) was added
to 5 mL aqueous solution of Cu(NO3)2Æ3H2O (0.121 g,
0.50 mmol) under stirring. To this mixture was added
0.078 g (0.50 mmol) 2,20-bipyridine dissolved in 5 mL
3. Results and discussion
3.1. Synthesis and IR spectra
Acetylenedicarboxylic acid mixed with piperidine
2ꢀ
to yield C4O4
dianion, here piperidine acted as an

M. Shao et al. / Journal of Molecular Structure 829 (2007) 155–160
157
2ꢀ
Table 2
organic base. Piperidine salt of C4O4
reacted with
Mn(ClO4)2Æ6H2O and phen to produce a binuclear
manganese complex 1. IR spectrum indicated 1 possess-
es C4O42ꢀ, phen and water as ligands. Absorption
peaks at 1623 and 1323 cmꢀ1 are assigned to
mas(COOꢀ) and ms(COOꢀ) stretching vibrations of coor-
˚
Selected bond lengths (A) and angles (ꢀ) for complex 1
Mn(1)–O(1)
Mn(1)–O(5)
Mn(1)–N(1)
Mn(1)–N(2)
Mn(1)–N(3)
Mn(1)–N(4)
2.160(3)
2.192(4)
2.247(4)
2.254(4)
2.275(4)
2.268(4)
Mn(2)–O(3)
Mn(2)–O(6)
Mn(2)–N(5)
Mn(2)–N(6)
Mn(2)–N(7)
Mn(2)–N(8)
2.112(9)
2.146(4)
2.259(4)
2.313(3)
2.277(4)
2.273(4)
dinated carboxylic groups, respectively.
A
300 cmꢀ1
separation between mas(COOꢀ) and ms(COOꢀ) is signifi-
O(1)–Mn(1)–O(5)
O(1)–Mn(1)–N(1)
O(1)–Mn(1)–N(2)
O(1)–Mn(1)–N(3)
O(1)–Mn(1)–N(4)
O(5)–Mn(1)–N(2)
N(1)–Mn(1)–N(3)
N(1)–Mn(1)–N(2)
N(3)–Mn(1)–N(4)
87.89(13)
99.82(13)
88.09(13)
90.68(15)
163.26(15)
168.69(16)
163.15(15)
73.95(16)
73.35(17)
O(3)–Mn(2)–O(6)
O(3)–Mn(2)–N(7)
O(3)–Mn(2)–N(8)
O(3)–Mn(2)–N(5)
O(3)–Mn(2)–N(6)
O(6)–Mn(2)–N(7)
N(5)–Mn(2)–N(8)
N(5)–Mn(2)–N(6)
N(7)–Mn(2)–N(8)
84.7(3)
100.9(3)
102.7(3)
95.6(3)
167.5(3)
165.98(15)
158.96(13)
72.77(13)
73.33(13)
cantly larger than the 200 cmꢀ1 value of free carboxyl-
2ꢀ
ate, indicating that the carboxylic groups of C4O4
coordinate to Mn(II) in a monodentate mode [19].
The characteristic strong absorption of ClO4 appears
ꢀ
at 1103 cmꢀ1
.
Broad bands at ca. 3431 and
3215 cmꢀ1 are attributed to the vibration absorptions
of lattice water and coordinated water, respectively.
Elemental analysis confirmed the formula [Mn2(C4O4)(-
phen)4 (H2O)2](ClO4)2ÆH2O.
2ꢀ
two ms(COOꢀ) absorptions at 1333, 1295 cmꢀ1, which indi-
cated that the carboxylic groups of C4O4 coordinate to
Cu(II) in different modes. Crystal structure analysis further
revealed that the carboxylic groups coordinate to Cu(II) in
two modes.
When piperidine salt of C4O4
reacts with
2ꢀ
Cu(NO3)2Æ3H2O and 2,20-bipy, a polymeric complex 2
was prepared. IR spectrum and elemental analysis suggest-
ed 2 has formula [Cu(C4O4)(2,20- bpy)]n. Complex 2 shows
two mas(COOꢀ) absorption peaks at 1641, 1620 cmꢀ1 and
Fig. 1. Molecular structure and packing diagram of complex 1 (perchlorate anions were omitted for clarity).

158
M. Shao et al. / Journal of Molecular Structure 829 (2007) 155–160
Table 3
Selected bond lengths (A) and angles (ꢀ) for complex 2
3.2. Structures description
˚
Cu(1)–O(1)
Cu(1)–O(4B)
Cu(1)–O(4A)
Cu(1)–N(1)
Cu(1)–N(2)
1.931(3)
1.978(3)
2.350(3)
2.013(3)
2.008(3)
C(11)–O(1)
C(11)–O(2)
C(14)–O(3)
C(14)–O(4)
C(12)–C(13)
1.285(5)
1.227(5)
1.224(5)
1.277(5)
1.197(6)
[Mn2(C4O4)(phen)4(H2O)2](ClO4)2ÆH2O 1 is a binuclear
complex. Its molecular structure is shown in Fig. 1, while
selected bond lengths and angles are listed in Table 2.
Acetylenedicarboxylate acts as bridging ligand, which is
bound on each side to two Mn(II) ions through the mono-
dentate carboxylate coordination mode. Mn(II) is six-coor-
dinated and possesses a N4O2 coordination environment by
one carboxylate O atom, four phen N atoms and one water
O(1)–Cu(1)–O(4B)
N(2)–Cu(1)–O(4B)
N(1)–Cu(1)–O(4B)
N(2)–Cu(1)–O(4A)
N(1)–Cu(1)–O(4A)
Cu(1)–O(4A)–Cu(1C)
90.42(12)
172.52(13)
91.07(13)
100.15(11)
92.33(12)
101.80(12)
O(1)–Cu(1)–N(2)
O(1)–Cu(1)–N(1)
O(1)–Cu(1)–O(4A)
O(4A)–Cu(1)–O(4B)
C(11)–C(12)–C(13)
C(12)–C(13)–C(14)
97.00(13)
172.87(13)
94.80(12)
78.20(12)
175.5(4)
˚
molecule. Mn(1)–O(1) bond length is 2.160(3) A, and
171.7(4)
˚
Mn(1)–O(5) is 2.192(4) A. Mn(1)–N average length is
˚
2.261 A. The bond lengths are in agreement with those in
the structure of [Mn2(terephthalate)(phen)4(H2O)2]n
(ClO4)2n [20]. Larger deviations of bond angles from 90ꢀ
of the idealized octahedral geometry, N(1)–Mn(1)–
N(2) = 73.95(16)ꢀ and N(3)–Mn(1)–N(4) = 73.35(17)ꢀ,
indicate Mn(1) has a distorted octahedral coordination
sphere. The basal plane is formed by atoms N(1), N(2),
N(3), O(5), and the axial sites are occupied by atoms
O(1), N(4). Two phen are in cis position around Mn(1),
and their planes are nearly perpendicular to each other.
oxylate dianions with Cu(1)–O(1) bond length of
˚
˚
1.931(3) A, Cu(1)–O(4A) 2.350(3) A, and Cu(1)–O(4B)
˚
1.978(3) A. Cu(1)–O(4A) bond length is obviously longer
than others. The coordination structure can be best
described as a square-pyramidal geometry. The basal plane
is formed by atoms O(1), N(1), N(2), O(4B), and the axial
site is occupied by O(4A). Acetylenedicarboxylate is almost
linear, while two carboxylic groups are non-coplanar with
a torsion angle of 70.25ꢀ. Cu(1)ꢁ ꢁ ꢁCu(1A) separation is
2ꢀ
C4O4 links [Mn(phen)2(H2O)]+ units to form a dimer.
˚
˚
˚
Mn(1)ꢁ ꢁ ꢁMn(2) separation is 9.874(2) A. In addition, there
7.58 A, and Cu(1)ꢁ ꢁ ꢁCu(1C) separation is 3.37 A. The coor-
dination basal plane of Cu(1) is parallel to the plane of
Cu(1C).
exist remarkable p–p stacking interactions between adja-
cent phen ligands, while perchlorate anions act as counter
ions appear in the crystal lattice.
2ꢀ
It is interesting to note that each C4O4 ligand links
[Cu(C4O4)(bipy)]n 2 is a polymeric complex. Its molecu-
lar structure and packing diagram are illustrated in Fig. 2,
while selected bond lengths and angles are listed in Table 3.
Cu(1) is five-coordinated by two 2,20-bipy N atoms and
three O atoms belonging to three different acetylenedicarb-
three copper centers through two terminal carboxylate
groups. One carboxylate acts as monodentate mode, while
the other carboxylate exhibits an unusual bidentate bridg-
ing mode, linking two CuII centers using O atom to form a
dimer of Cu2O2 (Cu–O–Cu angle 101.80ꢀ), which is rarely
Fig. 2. Molecular structure of complex 2.

M. Shao et al. / Journal of Molecular Structure 829 (2007) 155–160
159
a total weight-loss of 42.49% (calcd. 42.77%). The final,
thermal stable brown residue is MnO2 (found 12.27%,
calcd. 14.54%).
Variable-temperature magnetic susceptibilities of 2 have
been measured in the range of 2–300 K (Fig. 4). The data
can be best fitted with Curie-Weiss law, vꢀm1 ¼ T=ðC ꢀ hÞ
with a Weiss constant h = ꢀ1.5 K. The effective magnetic
moment (leff) per Cu(II) unit at 300 K is 1.70 B.M., which
is close to the spin-only value of free Cu2+ ion (S = 1/2,
1.73 B.M.). When temperature is lowered, leff keeps no
change between 11 and 300 K, and then decreases slowly
to 1.56 B.M. at 2.02 K. These results indicate a very weak
antiferromagnetic interaction in complex 2, especially in
the dimer of Cu2O2.
Fig. 3. TG-DSC thermal analysis curves of complex 1.
Magneto-structural correlation of carboxylate polynu-
clear complexes has been widely studied [23]. Although
acetylenedicarboxylate is a worthy bridging ligand in con-
structing coordination polymer, we consider this bridge is
still too long and the conjugation effect between carboxylic
groups and ethynyl group is too weak to propagate mag-
netic interaction [20]. Usually, Cu2O2 dimer shows obvious
magnetic couple. Most of oxygen- or carboxylate-bridging
CuII dimers exhibit stronger antiferromagnetic couple [24].
However, the copper complex 2 has poor magnetic interac-
tion. Further analysis shows that the CuII magnetic orbital
ðdx2ꢀy2 Þ defines the unpaired electron lying on basal plane
of square-pyramidal coordination geometry. Poor overlap
between the two parallel magnetic orbital in the Cu2O2
dimer leads to the lack of magnetic interaction.
observed in previous reports [21]. The structure of 2 is prac-
tically a complicated two-dimensional (4,4) network with
2ꢀ
nodes of Cu2O2 and bridges of C4O4
.
3.3. Thermal stability and magnetism
TG-DSC analysis showed the thermal decomposition
procedure of 1 as Fig. 3. The first endothermic process
occurred in the temperature range of 80–130 ꢀC, which cor-
responds to the release of lattice water and coordinated
water (found 4.57%, calcd. 4.52%). The second weight-loss
step appeared in the range of 180–280 ꢀC with an exother-
mic peak at 209 ꢀC, which corresponds to the decomposi-
2ꢀ
tion of C4O4 (found 7.28%, calcd. 8.03%). This rather
low decomposed temperature indicated that the acetylen-
edicarboxylate complex is thermal unstable [17].
McCormick has reported that linear chain complex
[Cu(C4O4)(H2O)3] was unstable at room temperature and
decomposed explosively when heated [22]. The following
weight-loss step indicated that one phen per
[Mn(phen)2(H2O)] unit released in the range of
300–420 ꢀC (found 31.96%, calcd. 30.14%). Another phen
may be lost later, following by a strong exothermic process
4. Conclusion
Two novel polynuclear complexes were prepared using
acetylenedicarboxylate as bridging ligand. The binuclear
manganese complex is stable up to 180 ꢀC. The copper
complex has polymeric structure, where each acetylenedi-
carboxylate bridges three copper centers to form two-di-
mensional (4,4) network with nodes being dimer of
Cu2O2 and bridges of C4O42ꢀ. Poor overlap between the
two parallel magnetic orbital in the Cu2O2 dimer leads to
the lack of magnetic interaction.
ꢀ
of ClO4 decomposition. These processes occurred in the
range of 430–680 ꢀC, and overlapped in the TG curve with
0.20
3.0
0.18
1000
950
900
850
800
750
700
650
2.5
2.0
0.16
1.5
0.14
µ
1.0
0.5
0.12
600
-1
550
0.0
m
0
50 100 150 200 250 300
T/K
0.10
0.08
0.06
0.04
0.02
0.00
500
450
400
350
300
250
200
150
100
50
m
0
0
50
100
150
200
250
300
T/K
Fig. 4. Temperature-dependent magnetic susceptibilities of complex 2.

160
M. Shao et al. / Journal of Molecular Structure 829 (2007) 155–160
[5] G.H. Cui, J.R. Li, R.H. Zhang, X.H. Bu, J. Mol. Struct. 740 (2005)
Acknowledgements
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This work was supported by the Development Founda-
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the Research Foundation for Returned Chinese Scholars
Overseas of the Ministry of Education of China.
Appendix A. Supplementary data
[11] N. Hao, Y.G. Li, E.B. Wang, E.H. Shen, C.W. Hu, L. Xu, J. Mol.
Struct. 697 (2004) 1.
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Center, CCDC-281904 for Complex 1 and CCDC-251792
for complex 2. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Center, 12, Union
Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033).
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.
2006.06.021.
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