Synthesis, structure and properties of one novel 2D Mn-heterocyclic carboxylic acid complex [Mn(TPA)Cl(H2O)]n

Article abstract of DOI:10.1016/j.molstruc.2011.02.054

A novel 2D layer complex [Mn(TPA)Cl(H₂O)]_n (1) has been synthesized by two methods through the reaction of MnCl₂ and TPC or TPA under hydrothermal conditions and characterized by single crystal X-ray diffraction, elemental analysis, infrared spectrometry (IR), powder X-ray diffraction (XRD) and thermogravimetric analysis (TGA), where heterocyclic carboxylic acid ligand TPA = 2-(5-(pyridin-2-yl)-2H-tetrazol-2-yl)acetic acid, TPC = 2-(5-(pyridin-2-yl)-2H-tetrazol-2-yl)acetonitrile. The distorted octahedral Mn(II) centers are bridged by carboxylic O atoms resulting in the formation of a 1D chain. Then the 1D chains are connected with each other through TPA ligands into a 2D (3,3)-connected topology framework. The H-bonding interactions extend the complex into a three-dimensional network, and such weak interactions further stabilized the complex. Furthermore, solid-state fluorescence spectrum of complex 1 exhibits intense broad emissions at 396 nm at room temperature, which is red-shifted by 21 nm relative to that of free ligand TPA.

Full text of DOI:10.1016/j.molstruc.2011.02.054

Journal of Molecular Structure 992 (2011) 106–110
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structure and properties of one novel 2D Mn-heterocyclic carboxylic
acid complex [Mn(TPA)Cl(H2O)]n
Peng Zhu a, Hui-Min Li b,
⇑
a College of Environmental Science and Engineering, Hohai University, Nanjing 210098, PR China
b Jiangxi Academy of Environmental Sciences, Nanchang 330029, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel 2D layer complex [Mn(TPA)Cl(H2O)]n (1) has been synthesized by two methods through the reac-
tion of MnCl2 and TPC or TPA under hydrothermal conditions and characterized by single crystal X-ray
diffraction, elemental analysis, infrared spectrometry (IR), powder X-ray diffraction (XRD) and thermo-
gravimetric analysis (TGA), where heterocyclic carboxylic acid ligand TPA = 2-(5-(pyridin-2-yl)-2H-tetra-
zol-2-yl)acetic acid, TPC = 2-(5-(pyridin-2-yl)-2H-tetrazol-2-yl)acetonitrile. The distorted octahedral
Mn(II) centers are bridged by carboxylic O atoms resulting in the formation of a 1D chain. Then the 1D
chains are connected with each other through TPA ligands into a 2D (3,3)-connected topology framework.
The H-bonding interactions extend the complex into a three-dimensional network, and such weak inter-
actions further stabilized the complex. Furthermore, solid-state fluorescence spectrum of complex 1
exhibits intense broad emissions at 396 nm at room temperature, which is red-shifted by 21 nm relative
to that of free ligand TPA.
Received 27 January 2011
Received in revised form 25 February 2011
Accepted 25 February 2011
Available online 4 March 2011
Keywords:
Mn(II) complex
Crystal structure
Hydrothermal condition
Fluorescence
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
As a continuation of those work, we focus our attention here
on the pyridine-tetrazole-heterocyclic nitrile (TPC) and pyridine-
Self-assembled metal–organic frameworks (MOFs) containing
central metal ions and polydentate organic ligands have been
attracting considerable attention in recent years owing to their no-
vel and diverse crystal structures, topologies [1–6] and potential
applications in the areas of luminescence, nonlinear optics, magne-
tism, catalysis, ferroelectric, electrical conductivity and gas storage
[7–11]. To get anticipant and interesting structures and desired
properties, an enormous amount of researches have being focused
on constructing novel MOFs by choosing functional metal ions and
versatile binding-ligands through hydrothermal methods. Hetero-
cyclic carboxylic acids as multifunctional building blocks have at-
tracted great attention, such as pyridine-, tetrazole-, imidazole-,
and pyrazole-carboxylic acids [12–19]. The heterocyclic N atoms
can coordinate to the metal centers, while carboxylate groups
can coordinate in monodentate, chelate or bridged modes resulting
in the formations of various MOFs with novel structures and useful
properties [20–28]. Literatures showed that pyridine acid and tet-
razole-5-carboxylic acid and their derivatives can behave as multi-
functional ligands, which improve the stability of its metal
polymers with the flexibility of the coordination modes and stereo
crystal packing forces, thus result in the tremendous network
diversity [29–34].
tetrazole-heterocyclic acid (TPA), (Scheme 1). Considering that
the heterocyclic N atoms and carboxylic acid functional group
may act as useful coordination sites, employment of the two
ligands to react with metal ions can produce intriguing struc-
tures. In this work, the novel 2D MOF [Mn(TPA)Cl(H2O)]n (1)
has been isolated under hydrothermal condition. Then, its crystal
structure, solid state luminescence and thermogravimetric analy-
sis were reported.
2. Experimental section
2.1. Material and instrument
Chemicals and solvents in this work were commercially ob-
tained and used without any further purification. Elemental analy-
sis for carbon, hydrogen and nitrogen were performed on a Vario
EL III elemental analyzer. The infrared spectra (4000–500 cmꢀ1
)
were recorded by using KBr pellet on a Shimadzu IRprestige-21
FTIR-8400S spectrometer. The X-ray powder diffraction (XRD) data
were collected with a Siemens D5005 diffractometer with Cu K
a
radiation (k = 1.5418 Å). Thermogravimetric analyses were per-
formed on a simultaneous SDT 2960 thermal analyzer under flow-
ing N2 with a heating rate of 20 °C/min from ambient temperature
to 750 °C. The fluorescent spectra were recorded on a Shimadzu
Instrument FL/FS-920 fluorescent spectrometer.
⇑
Corresponding author. Tel./fax: +86 791 8311546.
E-mail address: lhmchem@yahoo.com.cn (H.-M. Li).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.02.054

P. Zhu, H.-M. Li / Journal of Molecular Structure 992 (2011) 106–110
107
Scheme 1. The synthesis of ligands and complex 1, and the coordination modes of TPA.
2.2. Preparation of the ligands TPC and TPA
was filtered off and the colorless solution was left to stand at room
temperature. Colorless block crystals suitable for X-ray diffraction
were harvested by slow evaporation of the filtrate within one
month (Yield: 34%, based on TPA).
The ligands, TPC and TPA, were prepared according to the liter-
ature methods [35] from picolinonitrile through two steps
(Scheme 1).
Elemental analysis for 1, C8H8ClMnN5O3 (312.58): Anal. (%) calcd.
C 30.71, H 2.56, N 22.39; found C 30.59, H 2.48, N 22.23. IR spectrum
TPC: Anal. Calcd. for C8H6N6: C, 51.61; H, 3.23; N, 45.16. Found:
C, 51.49; H, 3.18; N, 45.02. 1H NMR (300 MHz, CD3OD): d 4.88 (s,
2H), 7.28 (t, 1H), 7.74 (t, 1H), 8.29 (d, 1H), 8.51 (d, 1H). ESI-MS
m/z (%): [M–H] = ꢀ185.29; [M+H] = +187.28. Main IR (cmꢀ1, KBr):
3086 (m), 2971 (m), 2280 (m), 15,718 (w), 1560 (w), 1481 (w),
1402 (s), 1323 (w), 1251 (w), 1125 (w), 1049 (w), 935 (w), 860
(m), 779 (w), 754 (s), 705 (w), 675 (w), 555 (w), 511 (w), 472
(w), 422 (w).
(KBr):
m
(cmꢀ1): 3345 (s), 3275 (w), 3041 (m), 2921 (m), 1601 (s),
1570 (w), 1547 (w), 1477 (m), 1430 (m), 1405 (s), 1304 (m), 1213
(m), 1203 (m), 845 (m), 778 (m), 731 (m), 705 (m), 668 (m).
2.4. Crystal structure determination
A single crystal of the title complex with approximate dimen-
TPA: Anal. Calcd. for C8H7N5O2: C, 46.83; H, 3.41; N, 34.15.
Found: C, 46.71; H, 3.35; N, 34.02. 1HNMR (300 MHz, CD3OD): d
4.75 (s, 2H), 7.51 (t, 1H), 7.92 (t, 1H), 8.42 (d, 1H), 8.63 (d, 1H),
sions 0.40 mm ꢁ 0.35 mm ꢁ 0.25 mm was selected for data collec-
tion at 293(2) K, using a Rigaku Saturn diffractionmeter by the
x
scan technique at room temperature with graphite monochromat-
10.53
(s,
1H).
ESI-MS
m/z
(%):
[M–H] = ꢀ204.33;
ed Mo K radiation (k = 0.071073 nm). The structure parameters
a
[M + H] = +206.32. Main IR (cmꢀ1, KBr): 3435 (s), 3138 (ms),
2988 (w), 1680 (s), 1607 (m), 1561 (w), 1480 (w), 1405 (s), 1327
(w), 1289 (m), 1247 (w), 1181 (w), 1163 (w), 1119 (w), 1051 (w),
1008 (w), 932 (w), 860 (m), 779 (w), 754 (s), 705 (w), 675 (w),
555 (w), 511 (w), 472 (w), 422 (w).
were obtained by CrystalClear [36] with the h range for data collec-
tion from 3.11 to 27.45°. Of the 12,457 reflections collected, there
were 2866 unique reflections (Rint = 0.0244). The absorption cor-
rection was carried out by multi-scan method. The structure was
solved by direct methods with SHELXS-97 and refined by full ma-
trix least squares on F2 with SHELXL-97 [37]. All non-hydrogen
atoms were refined with anisotropic thermal parameters. Hydro-
gen atoms bonded to the carbon atoms were placed in calculated
positions and refined as riding mode, with C–H = 0.93 Å (aromatic)
and 0.97 Å (methylene) with Uiso(H) = 1.2Ueq(C). The water hydro-
gen atoms were located in the difference Fourier maps and refined
with an O–H distance restraint [0.85(2) Å]. Detailed data collection
and refinement of the compound 1 are summarized in Table 1, and
the selected bond distances, angles and H-bonding are listed in Ta-
ble 2. CCDC: 807,071 1 contains the supplementary crystallo-
graphic data for this paper. Copies of this information may be
obtained from The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44 1233 336,033; e-mail: deposit@ccdc.cam.a-
c.uk or www: http://www.ccdc.cam.ac.uk).
2.3. Preparation of complex [Mn(TPA)Cl(H2O)]n(1)
The title complex has been synthesized by the following two
methods from different starting materials under hydrothermal
synthesis conditions.
2.3.1. Method A
A mixture of MnCl2 (10 mmol, 1.98 g), TPC (10 mmol, 1.80 g),
HCl (1.5 ml, 36%) and distilled water (18.0 ml) were placed in a
25 ml Teflon-Lined stainless steel vessel, which was heated to
140 °C for 7 days. Then the reaction was slowly cooled to room
temperature at a rate of 5 °C/h. Colorless block crystals suitable
for X-ray diffraction were obtained in 53% yield (based on TPC).
2.3.2. Method B
3. Results and discussion
A
mixture of MnCl2 (1.0 mmol, 0.198 g), TPA (1.0 mmol,
0.206 g), ethanol (5.0 ml) and distilled water (15.0 ml) were placed
in a 25 ml Teflon-Lined stainless steel vessel, which was heated to
140 °C for 5 days. Then the reaction was slowly cooled to room
temperature at a rate of 5 °C/h. The resultant white precipitate
3.1. IR, UV/Vis spectrua and powder XRD
The IR spectrum shows a series of peaks at 1570, 1477, 1203,
778 and 705 cmꢀ1 are the characteristic of aromatic ring. The

108
P. Zhu, H.-M. Li / Journal of Molecular Structure 992 (2011) 106–110
Table 1
both, the ligand and the complex, exhibit absorption bands at the
Crystal data and structure refinement parameters for 1.
range of 200–400 nm. After coordination, the absorption bands
underwent a slightly redshift, owing to the formation of the more
large conjugated system after coordination, which is consisted of
pyridine and tetrazole rings. The above spectral analyses are in
agreement with the determined crystal structure.
Powder XRD analysis: The agreement between the experimen-
tal and simulated XRD patterns indicated the phase purity of 1
(Fig. 2). The difference in reflection intensities between the simu-
lated and experimental patterns was due to the variation in pre-
ferred orientation for the powder sample during collection of the
experimental XRD data.
Empirical formula
Formula weight
Temperature (K)
Crystal size (mm)
Wavelength (Å)
Crystal system
Space group
a (Å)
C8H8ClMnN5O3
312.58
293 (2)
0.20 ꢁ 0.10 ꢁ 0.10
0.71073
monoclinic
C2/c
25.471 (5)
10.246 (2)
9.7147 (19)
99.33 (3)
2501.7 (9)
b (Å)
c (Å)
b (°)
V (Å)3
Z
8
1.66
1.276
1256
Dcalc. (mg mꢀ3
)
3.2. Description of the crystal structure
l
(mmꢀ1
F(0 0 0)
)
h range (°)
Index ranges
3.11–27.45
The complex 1 has been synthesized by the reaction of hetero-
cyclic ligands TPC or TPA with MnCl2 under hydrothermal condi-
ꢀ32 6 h 6 32, ꢀ13 6 k 6 13, ꢀ12 6 l 6 12
12,457/2866 [R(int) = 0.0244]
99.8%
2866/2/163
1.094
R1 = 0.0260, wR2 = 0.0641
R1 = 0.0293, wR2 = 0.0656
0.322 and ꢀ0.348 e Åꢀ3
Reflections collected/unique
Completeness to h = 27.45°
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
tions. Single-crystal X-ray analysis reveals that complex
1
crystallized in the monoclinic space group C2/c. The asymmetrical
unit consists of one Mn(II) ion, one TPA anion, one chloride anion
and one coordinated water molecule. The carboxyl group was
deprotonated to maintain the charge balance. The coordination
environment of complex 1 with the atomic labeling is shown in
Fig. 3. The Mn1 sits in an irregular six-coordinate (MnN2O3Cl) envi-
ronment composed of two chelate nitrogen donors from one TPA
ligand, two bridging-bidentate carboxyl oxygen atoms (O1A and
Largest diff. peak and hole
aR1
bwR2
=
R
¼
||Fo| ꢀ |Fc|/
R|Fo|.
n
h
i
h
io
1=2
P
P
2
2
wðF2o ꢀ F2c Þ
=
w ðF2oÞ
.
Table 2
0
Selected bond-length (AÅ), bond-angle (°) and hydrogen-bonding (Å, °) of compound 1.
Mn(1)–O(1W)
Mn(1)–O(2)
Mn(1)–N(1)
2.1352(14)
2.1542(13)
2.3548(15)
Mn(1)–O(1)
Mn(1)–N(2)
Mn(1)–Cl(2)
2.1452(12)
2.3204(14)
2.4961(7)
O(1W)–Mn(1)–O(1)
O(1)–Mn(1)–O(2)
O(1)–Mn(1)–N(2)
O(1W)–Mn(1)–N(1)
O(2)–Mn(1)–N(1)
O(1W)–Mn(1)–Cl(2)
O(2)–Mn(1)–Cl(2)
N(1)–Mn(1)–Cl(2)
97.38(6)
95.72(5)
86.91(5)
104.91(6)
88.71(5)
87.96(4)
175.10(4)
86.48(4)
O(1W)–Mn(1)–O(2)
O(1W)–Mn(1)–N(2)
O(2)–Mn(1)–N(2)
O(1)–Mn(1)–N(1)
N(2)–Mn(1)–N(1)
O(1)–Mn(1)–Cl(2)
N(2)–Mn(1)–Cl(2)
92.35(5)
175.68(6)
86.69(5)
157.09(5)
70.87(5)
89.09(4)
92.63(4)
D–Hꢂ ꢂ ꢂA
d(D–H)
d(Hꢂ ꢂ ꢂA)
d(Dꢂ ꢂ ꢂA)
\(DHA)
O1W–H1WAꢂ ꢂ ꢂCl2
O1W–H1WBꢂ ꢂ ꢂCl2
O1W–H1WBꢂ ꢂ ꢂO1
0.75
0.69
0.69
2.48
2.54
2.55
3.200(15)
3.171(16)
2.973(2)
163.7
153.7
122.8
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1/2, y ꢀ 1/2,
ꢀz + 1/2; #2 ꢀx + 1/2, ꢀy + 1/2, ꢀz; #3 ꢀx + 1/2, y + 1/2, ꢀz + 1/2.
Fig. 1. UV spectra of the ligand and compound 1 in the solid state at room
temperature.
bands at 1547, 1430 cmꢀ1 are attributed to the tetrazole group
[35]. To compare with the IR spectrum of raw material TPC, the ab-
sence of a strong peak at 2280 cmꢀ1 for 1 indicates that the cyano
group has been completely hydrolyzed. Moreover, the new double
peaks at 1601 cmꢀ1 and 1405 cmꢀ1 showed that the carboxyl was
deprotonated to generate COOꢀ anion upon reaction with the cen-
tral metal ion, which is agreement with its X-ray single structure.
The double peaks are the characteristics of
s(COOꢀ), respectively. And the difference between the asymmetric
stretching and symmetric stretching bands of the carboxyl group
s(C@O)) is 196 cmꢀ1, which indicates strong
m
as(COOꢀ) and
m
(
D
m
=
m
as(C@O) ꢀ
m
coordination of the carboxylate oxygen to the mental center
through 1,3-bidentate bridging fashion. The broad band around
3345 cmꢀ1 indicates the presence of
of coordinated water molecule.
v(O–H) stretching frequency
The UV/Vis spectrum of the ligand and complex 1 was mea-
sured in the solid state at room temperature (Fig. 1). It shows that
Fig. 2. Simulated and experimental powder X-ray diffraction patterns of 1.

P. Zhu, H.-M. Li / Journal of Molecular Structure 992 (2011) 106–110
109
Fig. 3. View of the coordination environment of Mn(II) and TPA in complex 1. Hydrogen atoms have been omitted for clarity, displacement ellipsoids are drawn at the 30%
probability level. Symmetry codes: A: ꢀx + 1/2, y ꢀ 1/2, ꢀz + 1/2; ꢀx + 1/2, ꢀy + 1/2, ꢀz; ꢀx + 1/2, y + 1/2, ꢀz + 1/2.
O2A) from two different TPA ligands and the another oxygen atom
from the coordinated water molecule (O1W), and a terminal Cl1
atom. That is to say, each Mn(II) atom adopts a slightly distorted
octahedral geometry with the small O(N)–Mn–O(N, Cl) angles
range from 70.87(5)° to 104.91 (6)° and the Mn–O(N) distances
range from 2.1352(1) Å to 2.3548(1) Å, deviating from the values
of an ideal octahedron. The Mn1–N1 = 2.3548(1) Å and Mn1–
N2 = 2.3204 (1) Å bond length are a little bit longer than the nor-
mal range. Along c-axis direction, the neighboring metal centers
Mn1 and Mn1B ions are bridged by carboxylic O1A and O2A atoms
resulting in the formation of [Mn–O–C–O–Mn]n 1D-chain with a
Mnꢂ ꢂ ꢂMn distance of 5.2705(9) Å. The 1D chains are parallel and
linked with each other through TPA ligands into a 2-D sheet paral-
lel to the (1 0 0) plane. To get better insight into the framework
structure, its topological analysis was carried out. As discussed
above, every Mn(II) center can be seen as one nod, each Mn(II)
nod coordinated with three TPA ligands, thus can be defined as
3-connector. And each ligand links three Mn(II) nod, it can be con-
sidered as a 3-connecting node. According to the simplification
principle of the TOPOS software [38], the overall network topology
was described as a (3,3)-connected framework (Fig. 4). The O1W
aqua molecule was involved in the O–Hꢂ ꢂ ꢂO and O–Hꢂ ꢂ ꢂCl H-bonds
Fig. 4. The 2D (3,3)-connected topologic structure of 1.
Fig. 5. The simplified O–Hꢂ ꢂ ꢂO and O–Hꢂ ꢂ ꢂCl H-bonds network of 1 viewed along the c-axis in which pyridine rings are omitted for clarity.

110
P. Zhu, H.-M. Li / Journal of Molecular Structure 992 (2011) 106–110
experimental conditions. The emission of complex is red-shifted
about 21 nm compared to that of free ligand TPA. Obviously, this
strong emission come from the heterocyclic carboxylic acid ligand,
and the large red-shift effect may be attributed to the coordination
or an excited state of a metal-perturbing intraligand. That is, both
the rigidity of conjugated ring and the conjugation effect of ligand
were increased after coordination. It plays the main role to lumi-
nescence intensity and red-shift effect. Complex 1 is air-stable
and insoluble in water and common organic solvents. This coordi-
nation polymer may be excellent candidate for potential photolu-
minescence material because they are highly thermally stable.
4. Conclusions
In conclusion, a novel 2D layer complex [Mn(TPA)Cl(H2O)]n (1)
was prepared by two methods through employing heterocyclic ni-
trile or heterocyclic carboxylic acid ligands under hydrothermal
conditions. We studied here the structure, TGA and fluorescence
properties of the coordination polymer. This material provides a
new impetus to construction of novel functional material with
potentially useful physical properties.
Fig. 6. The TGA curve for complex 1.
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3.3. Thermogravimetric analysis
The TGA curve shows that the complex 1 begins to decompose
at 135 °C displaying two stages of mass loss (Fig. 6). The first
weight loss of 5.89% (calc 5.76%) from 135 to 240 °C is consistent
with the release of a coordinated water molecule. The degradation
of the TPA occurs in the second step above 335 °C. Due to decom-
position of the network, the total observed weight loss at 750 °C is
76.12%, and the final presumably residual is Mn3O4. It is concluded
that the framework is very stable and worthy of further investiga-
tion as candidate of thermally stable material.
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The solid-state fluorescent property of the complex was inves-
tigated at room temperature. As illustrated in Fig. 7, upon excita-
tion of the solid sample at k = 335 nm, the intense broad
emission bands at 396 nm was observed. Moreover, for excitation
wavelength between 280 and 380 nm, the free TPA ligand presents
a weak photoluminescence emission at 375 nm under the same