1D slide-fastener-like coordination polymers of Mn(II) derived from pyrazine-2,3,5,6-tetracarboxylic acid

Article abstract of DOI:10.1016/j.molstruc.2008.07.027

Two new 1D slide-fastener-like coordination polymers {[Mn₂(pztc)(phen)₂(H₂O)₂]·4H₂O}_n (1) and {[Mn₂(pztc)(bpy)₂(H₂O)₂]·2H₂O}_n (2) have been synthesized by the reactions of pyrazine-2,3,5,6-tetracarboxylic acid (pztcH₄) and Mn(OAc)₂·4H₂O in the presence of 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy) under hydrothermal conditions and characterized by elemental analyses, FT-IR, TGA and X-ray diffraction. In complex 1 and 2, metal ions are bridged by pyrazine-2,3,5,6-tetracarboxylate, coordinating in a hexadentate manner, so forming 1D polymeric chains. The remaining coordination sites of the metal ions are occupied by one O atom of water molecule and two N atoms of the terminal ligand (phen or bpy). IR spectra and thermal analysis data are in agreement with the crystal structure.

Full text of DOI:10.1016/j.molstruc.2008.07.027

Journal of Molecular Structure 918 (2009) 97–100
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
1D slide-fastener-like coordination polymers of Mn(II) derived from
pyrazine-2,3,5,6-tetracarboxylic acid
*
Hong-Ling Gao, Yan-Ping Zhang, Ai-Hong Yang, Su-Rong Fang, Jian-Zhong Cui
Department of Chemistry, Tianjin University, Tianjin 300072, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new 1D slide-fastener-like coordination polymers {[Mn2(pztc)(phen)2(H2O)2]ꢀ4H2O}n (1) and
{[Mn2(pztc)(bpy)2(H2O)2]ꢀ2H2O}n (2) have been synthesized by the reactions of pyrazine-2,3,5,6-tetra-
carboxylic acid (pztcH4) and Mn(OAc)2ꢀ4H2O in the presence of 1,10-phenanthroline (phen) or 2,20-bipyr-
idine (bpy) under hydrothermal conditions and characterized by elemental analyses, FT-IR, TGA and X-
ray diffraction. In complex 1 and 2, metal ions are bridged by pyrazine-2,3,5,6-tetracarboxylate, coordi-
nating in a hexadentate manner, so forming 1D polymeric chains. The remaining coordination sites of the
metal ions are occupied by one O atom of water molecule and two N atoms of the terminal ligand (phen
or bpy). IR spectra and thermal analysis data are in agreement with the crystal structure.
Ó 2008 Elsevier B.V. All rights reserved.
Received 22 May 2008
Accepted 16 July 2008
Available online 6 August 2008
Keywords:
Mn(II) complex
Pyrazine-2,3,5,6-tetracarboxylic acid
Crystal structures
1D coordination polymers
1. Introduction
plexes, namely {[Mn2(pztc)(phen)2(H2O)2]ꢀ4H2O}n (1) and
{[Mn2(pztc)(bpy)2(H2O)2]ꢀ2H2O}n (2).
Metal–organic frameworks (MOFs) have attracted great interest
in recent years because of their potential applications in magne-
tism, electrical conductivity, catalysis, separation, gas storage, ion
exchange, and nonlinear optical materials [1–3]. The connection
of metal–organic coordination polymers based on transition met-
als and multifunctional bridging ligands has proven to be a prom-
ising field. Polycarboxylic acid and their transition metal
complexes have been extensively investigated on coordination
and/or covalent crystal engineering [4,5]. The structures and the
optical or magnetic properties of metal–organic compounds with
pyrazinyl-carboxylic acids have proven to be of great interest in
many fields, such as solid chemistry and material chemistry. Pyra-
zine-2,3,5,6-tetracarboxylic acid (pztcH4), a preferred multifunc-
tional nitrogen and oxygen-donor connector with diverse
chelating and bridging mode for constructing coordination com-
plex, has been utilized to generate MOFs. There are a few re-
searches of complexes with pyrazine-2,3,5,6-tetracarboxylic acid
have achieved in the last years [6–8]. However, its coordination
chemistry remains largely unexplored compared with those of
benzene polycarboxylate ligands. To the best of our knowledge,
there is no report about 1D coordination polymers containing pyr-
azine-2,3,5,6-tetracaboxylic acid and 1,10-phenanthroline or 2,20-
bipyridine as ligands. In this contribution, pyrazine-2,3,5,6-tetra-
carboxylic acid (pztcH4) and 1,10-phenanthroline (phen) or 2,20-
bipyridine (bpy) were employed to synthesize two novel 1D com-
2. Experimental
2.1. General
All reagents were purchased commercially and used without
further purification. Deionized water was used for the conven-
tional synthesis. Elemental analyses of carbon, hydrogen and nitro-
gen were carried out with a Perkin-Elmer 240 analyzer. The
infrared spectra of the complexes in KBr pellets were obtained
on a BIO-RAD FTS 3000 instrument in the range of 4000–
400 cmꢁ1. Thermal analysis curves (TG) were obtained from a NET-
ZSCH TG 209 thermal analyzer in a static air atmosphere using a
sample size of 5–10 mg with a heating rate of 10 °C minꢁ1
.
2.2. Syntheses of pyrazine-2,3,5,6-tetracarboxylic acid (pztcH4) and
the complexes
Pyrazine-2,3,5,6-tetracarboxylic acid was synthesized in 59%
yield by oxidation of 2,3,5,6-tetramethylpyrazine by aqueous
KMnO4.
The mixtures of pztcH4 (0.1 mmol, 0.0260 g), Mn(OAc)2ꢀ4H2O
(0.2 mmol, 0.0492 g), 1,10-phenanthroline (phen) (0.2 mmol,
0.0360 g) and 15.0 mL water were sealed in a 25 mL stainless steel
reactor with teflon liner and heated to 150 °C and kept at this tem-
perature for 72 h, and then slowly cooled to 30 °C at a rate of
1.4 °C/h. The yellow crystals of 1 suitable for X-ray analysis were
obtained in 43% yield (based on pztcH4).
* Corresponding author. Fax: +86 22 27403475.
E-mail address: cuijianzhong@tju.edu.cn (J.-Z. Cui).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.07.027

98
H.-L. Gao et al. / Journal of Molecular Structure 918 (2009) 97–100
Table 1
Table 2
Crystal data and structure refinement for compounds 1 – 2
Selected bond lengths [Å] and angles [°] for 1–2
Compound
C32H28Mn2N6O14
1
C28H24Mn2N6O12
2
1
2
Formula weight (g molꢁ1
Crystal system
Space group
a (Å)
b (Å)
c (Å)
)
830.48
746.41
Monoclinic
P2(1)/c
9.2560(15)
20.212(3)
7.8527(13)
90
100.834(3)
90
1442.9(4)
2
Mn(1)–O(1)
Mn(1)–O(5)
Mn(1)–O(3)#1
Mn(1)–N(2)
Mn(1)–N(3)
Mn(1)–N(1)#1
N(1)–Mn(1)#1
O(3)–Mn(1)#1
O(1)–Mn(1)–O(5)
O(1)–Mn(1)–O(3)#1
O(5)–Mn(1)–O(3)#1
O(1)–Mn(1)–N(2)
O(5)–Mn(1)–N(2)
O(3)#1–Mn(1)–N(2)
O(1)–Mn(1)–N(3)
O(5)–Mn(1)–N(3)
O(3)#1–Mn(1)–N(3)
N(2)–Mn(1)–N(3)
O(1)–Mn(1)–N(1)#1
O(5)–Mn(1)–N(1)#1
O(3)#1–Mn(1)–N(1)#1
N(2)–Mn(1)–N(1)#1
N(3)–Mn(1)–N(1)#1
2.1129(13)
2.1313(15)
2.1539(13)
2.2423(15)
2.2668(15)
2.3709(14)
2.3709(14)
2.1539(13)
86.11(6)
164.36(4)
82.28(6)
102.86(5)
98.31(7)
Mn(1)–O(3)#1
Mn(1)–O(1)
Mn(1)–O(5)
Mn(1)–N(2)
Mn(1)–N(3)
Mn(1)–N(1)
O(3)–Mn(1)#1
2.1261(10)
2.1697(11)
2.1996(13)
2.2262(14)
2.2811(14)
2.3316(13)
2.1261(10)
Triclinic
ꢁ
P1
7.763(3)
8.931(3)
12.717(4)
67.952(7)
82.638(14)
84.101(13)
809.1(5)
1
a
(°)
b (°)
c
(°)
O(3)#1–Mn(1)–O(1)
O(3)#1–Mn(1)–O(5)
O(1)–Mn(1)–O(5)
O(3)#1–Mn(1)–N(2)
O(1)–Mn(1)–N(2)
O(5)–Mn(1)–N(2)
O(3)#1–Mn(1)–N(3)
O(1)–Mn(1)–N(3)
O(5)–Mn(1)–N(3)
N(2)–Mn(1)–N(3)
O(3)#1–Mn(1)–N(1)
O(1)–Mn(1)–N(1)
O(5)–Mn(1)–N(1)
N(2)–Mn(1)–N(1)
N(3)–Mn(1)–N(1)
169.89(4)
86.93(4)
83.04(4)
95.95(5)
87.85(5)
104.87(5)
98.76(4)
91.31(4)
174.00(4)
72.79(5)
105.10(4)
73.37(4)
87.81(5)
156.04(5)
92.50(5)
V (Å3)
Z
Calculated density (g cmꢁ3
)
1.704
0.865
424
1.718
0.954
760
Absorption coefficient (mmꢁ1
F(000)
)
89.20(5)
Crystal size (mm3)
h range for data collection (°)
Index ranges
0.12 ꢂ 0.10 ꢂ 0.06
0.22 ꢂ 0.20 ꢂ 0.12
100.83(5)
170.38(6)
92.01(5)
73.77(6)
98.12(5)
97.03(7)
73.09(5)
154.72(5)
88.64(5)
1.74–27.85
2.02–26.42
ꢁ9 6 h 6 10
ꢁ11 6 k 6 11
ꢁ16 6 l 6 16
Full-matrix
ꢁ11 6 h 6 11
ꢁ25 6 k 6 11
ꢁ9 6 l 6 9
Refinement method
Independent reflections
Goodness-of-fit on F2
Full-matrix
least-squares on F2
3752
least-squares on F2
2959 [R(int) = 0 .0341]
[R(int) = 0.0258]
1.091
0.0301, 0.0714
0.0400, 0.0754
0.364 and ꢁ0.262
1.061
Symmetry transformations used to generate equivalent atoms for compound 1: #
1x, y, z + 1; for 2: #1 ꢁx, ꢁy + 1, ꢁz.
Final R1 and wR2 [I > 2
R1 and wR2 [all data]
r
(I)]
0.0333, 0.0811
0.0489, 0.0875
0.370 and ꢁ0.361
0
Largest diff. Peak and hole (e ÅAꢁ3
)
Anal. Found: C, 46.22; H, 3.43; N, 10.17% for 1 and C, 45.11; H,
3.27; N, 11.23% for 2. Calc. for C32H28Mn2N6O14 (1): C, 46.28; H,
3.40; N, 10.12%; C28H24Zn2N6O12 (2): C, 45.06; H, 3.24; N,
11.26%.
Compound 2 was prepared by similar methods to 1 only using
the 2,20-bipyridine (bpy) instead of 1,10-phenanthroline (phen)
at 160ꢀC. The well blocked-shaped yellow crystals of 2 suitable
for X-ray analysis were obtained in 45% yield (based on pztcH4).
Fig. 1. The 1D slide-fastener-like chain of complex 1(a) and 2(b), H atoms and uncoordinated water molecules are omitted.

H.-L. Gao et al. / Journal of Molecular Structure 918 (2009) 97–100
99
Fig. 2. 2D structure of the complex 1(a) and 2(b) connected by hydrogen bonds.
2.3. X-ray crystallography
Structure measurements of complexes were performed on a
computer controlled Bruker SMART 1000 CCD diffractometer
equipped with graphite-monochromated Mo-K
a
radiation with
100
80
60
40
20
radiation wavelength 0.71073 Å by using the
x
-scan technique.
The structures were solved by direct methods and refined with
the full-matrix least-squares technique using the SHELX-97 and
SHELXL-97 programs [9,10]. Anisotropic thermal parameters were
assigned to all non-hydrogen atoms. The organic hydrogen atoms
were generated geometrically; the hydrogen atoms of the water
molecules were located from difference maps and refined with iso-
tropic temperature factors. Analytical expressions of neutral-atom
scattering factors were employed, and anomalous dispersion cor-
rections were incorporated [11]. The crystallographic data and se-
lected bond lengths and angles are listed in Table 1 and Table 2,
respectively. CCDC-648149 1 and CCDC-648148 2 contain the sup-
plementary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.can.ac.uk/conts/retriev-
ing.html (or from the Cambridge Crystallographic Centre, 12 Union
Road, Cambridge CB21EZ, UK; fax: +44 1223 336033; or
deposit@ccdc.cam.ac.uk).
0
100
200
300
400
500
600
700
800
º
Temperature / C
Fig. 3. TGA curves of 1.

100
H.-L. Gao et al. / Journal of Molecular Structure 918 (2009) 97–100
of water molecules. The absence of the characteristic bands at
3. Results and discussion
3.1. Structure description
around 1700 cmꢁ1 in 1 indicates the complete deprotonation of
the ligand upon reaction with the central metal ions [15]. The IR
spectra of compounds 1 and 2 are consistent with the crystal struc-
ture of them, respectively.
All the compounds once isolated, are air-stable and can retain
their structural integrity at room temperature for a considerable
length of time. Complex 1 crystallizes in the triclinic space group
3.3. Thermal analysis
ꢁ
P1. The molecular structure and coordination environments of me-
The molecular structures of 1 and 2 are very similar, therefore
only the TGA of 1 is operated. The thermal behaviors of complex
1 were examined by TGA under the atmosphere of air. Thermal
curves of 1 are illustrated in Fig. 3. The TGA curve in Fig. 3 shows
that 1 begins to decompose at 100 °C displaying three stages of
mass loss. The first mass loss of 8.62% from 100 to 120 °C is due
to the loss of the four lattice water molecules (calculated value
8.69%). The second weight loss of 4.42% between 145 and 189 °C
is consistent with the mass loss of the two coordinated water mol-
ecules. The degradation of the phen and pztc occurs in the third
step in the temperature range of 294–354 °C. The remaining mass
of 20.10% is presumably MnO2 that is in agreement with the calcu-
lated value of 20.92%.
tal centers in 1 are shown in Fig. 1.The single-crystal X-ray diffrac-
tion analysis reveals that the symmetric unit of 1 consists of two
Mn(II) ions, one pztc4ꢁ, two phen molecules, two coordinated
water molecules and four uncoordinated water molecules. The
Mn(II) ion is hexacoordinated and exhibits a distorted octahedron
geometrical coordination environment. The equatorial coordina-
tion to Mn(II) ion is provided by one N atom of pztc4ꢁ, two N atoms
of phen and a water molecule. The two axial sites of the metal cen-
ter are occupied by one carboxylate O atom of the coordinated of
pztc4ꢁ and a carboxylate O atom from the neighboring pztc4ꢁli-
gand (Fig. 1(a)).
Complex 2 crystallize in the monoclinic space group P21/c. The
structures of the two complexes are very similar, except that 1,10-
phenanthroline in 1 were replaced by 2,20-bipyridine in 2. The
coordination environment of metal centers in 2 is shown in
Fig. 1(b).
4. Conclusions
The coordination numbers of metal ion in 2 were also six.
Among them two oxygen atoms (O1, O3) were from two carboxyl
groups of different pztc4ꢁ molecules and one oxygen atom (O5)
was from a terminal water. The other three nitrogen atoms (N1,
N2, and N3) were from the pyrazinyl and pyridyl rings. The average
bond lengths of Mn–O and Mn–N were 2.1657 and 2.2796 Å for
complex 2 and the two corresponding values of compound 1 are
2.1327 and 2.2933 Å, respectively. The selected bond lengths and
angles are listed in Table 2.
The ligand pyrazine-2,3,5,6-teracarboxylic acid was an extre-
mely flexible ligand in coordination chemistry with 3d metals.
We have synthesized two new 1D slide-fastener-like complexes
by reaction of Mn(II) with pyrazine-2,3,5,6-tetracarboxylic acid
and 1,10-phenanthroline(phen) or 2,20-bipyridine(bpy) under
hydrothermal conditions at 150 °C and 160 °C, respectively. The
packing structures of 1 and 2 form two-dimensional supramolecu-
lar structures with the aid of intermolecular p–p interactions and
hydrogen bonds. They are the first two 1D coordination polymers
using both pyrazine-2,3,5,6-tetracaboxylic acid and 1,10-phenan-
throline or 2,20-bipyridine as organic linkers. Efforts to further
investigate other luminescent chelating compounds and decarbox-
ylation mechanism of pyrazine-2,3,5,6-tetracaboxylic acid in coor-
dination polymers are underway in our laboratory.
For compounds 1 and 2, the pyrazinyl rings of pztc4ꢁ are com-
pletely parallel to each other. The planes of phen or bpy are com-
pletely parallel to each other, too. Each pztc4ꢁ ligand can be
described as hexadenate ligands linking four metal centers through
its four carboxylate groups and two N atoms, to afford 1D slide-fas-
tener-like chain (Fig. 1). The distances between Mn1E and Mn1F in
complex 1 and 2 are 5.694 and 5.601 Å, while the Mn1E–Mn1D dis-
tance are 7.492 and 7.407 Å, respectively. The coordination mode
of the all four carboxylate groups is monodentate (Fig. 1). The dis-
tances of adjacent phen or bpy rings between the two neighboring
chains are both 3.427 Å in 1 and 2.That means there are intermo-
Acknowledgments
The present work was supported by the Natural Science Foun-
dation of Tianjin (No. 08JCZDJC22400) and the Scientific Research
Foundation for the Returned Overseas Chinese Scholars, Education
Ministry of China.
lecular
p–p stacking interactions between the phen or bpy planes.
These 1D slide-fastener-like chains are further assembled via
p–p
interactions and hydrogen bonds (between H atoms of phen or
bpy and O atoms of pztc4ꢁ or water molecule) to give rise to 2D
layer supramolecular structure (Fig. 2).
The crystal structure of complex 1 and 2 are quite different from
the reported compounds [12] and the decarboxylation of pyrazine-
2,3,5,6-tetracarboxylic acid do not occur[13], either. It may be due
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