One-dimensional metal-organic frameworks based on N-heterocyclic ligand and 5-amino-isophthalic acid: Synthesis, structure, and photoluminescent properties

Article abstract of DOI:10.1080/15533174.2016.1228672

One complex [Mn(dnpt)(aic)]_n [dnpt D 2-(4-nitrophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, aic D 5- Amino-isophthalic acid] was obtained from hydrothermal reaction and was characterized by elemental analysis, IR, and single-crystal X-ray dif

Full text of DOI:10.1080/15533174.2016.1228672

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One 1D metal-organic frameworks based on N-heterocyclic ligand and 5-
Amino-isophthalic acid: synthesis, structure, and photoluminescent
properties
Li Yan, Jia Li
Key Laboratory of Preparation and Applications of Environmental Friendly Materials, Ministry
of Education, Jilin Normal University, Siping, Jilin 136000, China
* Corresponding author: Li Yan
E-mail: jlnulijia@163.com
Abstract: One complex [Mn(dnpt)(aic)]n [dnpt = 2-(4-nitrophenyl)-1H-imidazo[4,5-
f][1,10]phenanthroline, aic = 5-Amino-isophthalic acid] was obtained from hydrothermal
reaction and characterized by elemental analysis, IR, and single-crystal X-ray diffraction. The
crystal structure shows that the manganese ion is coordinated with two nitrogen atoms of one
dnpt molecule and four oxygen atoms from three aic molecules, forming a distorted octahedral
coordination geometry. Each Mn(II) atom is linked by aic ligands with neighbor Mn(II) atoms,
forming an infinite one-dimensional (1D) double-chain structure. The luminescent properties for
the ligand and complex 1 are also discussed in detail. CCDC 1030059
Key words: hydrothermal synthesis; Mn(II) complex, crystal structure, fluorescence, 5-Amino-
isophthalic acid
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1 Introduction
The designed synthesis and characterization of metal-organic frameworks (MOFs) have
achieved considerable progress in recent years. The increasing interest in this field is justified not
only for their fascinating molecular structures, but also for their potential applications in
catalysts, luminescent materials, gas storage, magnetic materials[1-3] and so on. Consequently,
numerous new complexes have been produced mostly by using appropriate organic ligands,
especially bridging ligands containing multi-dentate oxygen, nitrogen, or sulfur donors to
coordinate with the transition metal centers[4-6]. Among poly-carboxylates, the best studied are
dicarboxylates, tricarboxylates, and biphenyldicarboxylates. 2-(Pyridin-2-yl)pyridine, 4-(pyridin-
4-yl)pyridine, and 1,10-phenanthroline can act as terminal ligands and provide supramolecular
interaction sites for molecular recognition. Take 5-Amino-isophthalic acid (aic) ligand for
example, this ligand can function in chelating bis-bidentate, bis-monodentate, mono-
bidentate(syn–syn), bridging bis-bidentate, monodentate–bidentate or chelating/bridging bis-
bidentate modes. Among the organic ligands, the chelate 1,10-phenanthroline (phen) and its
derivatives have been extensively used in the preparation of many MOFs with versatile
topologies. It is because their excellent coordinating capacities, hydrogen bond donors and
acceptors, and potential supramolecular recognition sites for π-π stacking interactions. The
polycyclic aromatic bidentate ligands, such as 2,2-bipyridine, 4,4-bipyridine and 1,10-
phenanthroline, are frequently used corporately with polycarboxylates, leading to many novel
architectures[7-9]. In order to obtain novel functional carboxyl complexs and investigate their
structure-function relationship, we synthesized a new ligand 2-(3-chlorophenyl)-1H-imidazo[4,5-
f][1,10]phenanthroline (dnpt) (scheme 1), and then a novel 1D complex [Mn(dnpt)(aic)]n (1) was
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synthesized. In this paper, we research the synthesis, crystallography, and luminescent properties
of complex (1).
2 Experimental
2.1 Reagents and instruments
With the exception of the ligand dnpt, all the other chemicals from commercial sources were
of AR grade and used without further purification. Thermogravimetric analysis was performed
using a Perkin-Elmer TG-7 analyzer at the rate of 10 ℃/min rise of temperature in nitrogen
atmosphere. The FT-IR spectrum was recorded with KBr pellets on a Perkin-Elmer 240C
spectrometer. Crystal structure determination was carried out on a Bruker SMART APEX II
CCD X-ray diffractometer. Elemental analyses of C, H and N were performed on a PE-2400
elemental analyzer. Fluorescence spectra were recorded on a FLSP 920 Edinburgh fluorescence
spectrometer.
2.2 Synthesis of the ligand (dnpt)
A mixture of 4- nitrobenzaldehyde (0.38 g, 2.5 mmol), 1,10-phenanthroline-5,6-dione (0.525
g, 2.5 mmol), ammonium acetate (3.88 g, 50 mmol) and glacial acetic acid were refluxed for 12
h, cooled the mixture to room temperature and added concentrated aqueous ammonia to
neutralize, we collected a yellow precipitate and washed with water. The crude product dissolved
in ethanol was purified by filtration on silica gel (60–100 mesh; ethanol), then the principal
yellow band was collected. Yellow products were obtained by evaporation of the solution[10]
2.3 Syntheses and crystal growth
.
A mixture of A mixture of dnpt (0.10 g, 0.3 mmol), MnSO4.H2O (0.051 g, 0.3 mmol), aic
(1.000 g, 0.6 mmol) in H2O (18ml) was stirred for 30 min in air, then transferred to a 25 mL
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Telfon-lined stainless steel autoclave and heated to 160 ℃for 3 d. After cooling to room
temperature at a rate of 5 ℃·h-1, yellow block crystals of 1 were obtained. The crystals were
filtered, washed with distilled water and dried at ambient temperature to give a yield of about
81% yield based on Mn. C26H17MnN6O6: calcd. C 54.36, H 4.74, N 14.63%; found: C 54.38, H
4.71, N 14.59%. IR (KBr, cm–1): 3435(s), 1611(s), 1546(vs), 1339(vs), 1225(s), 1078(s), 751(s),
706(s).
2.4 X-ray structure determination
The diffraction data was collected on a Bruker SMART APEX II CCD diffractometer
equipped with a graphite-monochromated MoKa radiation (λ=0.71073 Å) at 293(2) K in the
range of 1.56≤θ≤25.18°. All the structures were solved by direct methods using the program
SHELXS-97[11] and refined by full-matrix least-squares techniques against F2 using the
SHELXTL-97 crystallographic software package[12]. All non-hydrogen atoms were easily found
from the difference Fourier map and refined anisotropically, whereas the hydrogen atoms of the
organic molecules were placed by geometrical considerations and were added to the structure
factor calculation. The detailed crystallographic data and structure refinement parameters for the
title complex are summarized in Table 1.
3 Results and discussion
3.1 Description of the structure
Single-crystal X-ray diffraction analysis reveals that complex 1 possesses a discrete one-
dimensional structure that crystallizes in space group C2/c. The molecular structure of complex 1
is shown in Fig. 1, and the 1 D chain of the complex is displayed in Fig. 2. The 2D structure of
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complex 1 linked by N–H···O hydrogen bonds is suggested in Fig. 3. Selected bond distances
and angles are presented in Table 2.
The asymmetric unit of 1 (show in Fig.1) consists of one Mn2+ ion, two dnpt free ligands, and
two aic ligands. The central Mn2+ ion adopts slightly distorted octahedral geometry coordinated
by two nitrogen atoms (N1, N2) from one dnpt ligand, and four O atoms (O1, O2, O3, O4 ) from
three different aic2- ligands. The bond distances of Mn–O in 1 are from 2.13 to 2.28 Å, and those
of Mn–N bond distances fall in the 2.23 to 2.27 Å range. The O(N)-Mn-N(O) angles range are
from 89.70 to 144.70°. The distances of Mn–O/N bond lengths are all consistent with
corresponding bond lengths found in the literature[13-15]
.
The aic ligands adopt two different coordination modes: (1) one aic ligand coordinates to three
Mn ions through four carboxylic oxygen atoms in mono-bridging and bidentate chelating
fashion; (2) another aic ligand coordinates to three Mn ions through three carboxylic oxygen
atoms in mono-bridging chelating fashion, which give rise to a 1D double-chain structure (Fig.
2). It should be mentioned that in the unit of 1, two types of rings formed: 8-membered ring with
the distance of Mn···Mn is 3.104 Å; The 16-membered ring with the distance of Mn···Mn is
7.650 Å.
The bond distances of C-C and C-N within the aromatic rings are normal. Moreover, there
are two kinds of hydrogen bonds in the title complex: N-H···O, and C-H···O hydrogen bonds.
Hydrogen bonding interactions are usually important in the synthesis of supramolecular
architectures.
3.2 Photoluminescent properties
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The PL spectrum of title complex was investigated in the solid state at room temperature. As
indicated in Fig. 3, the emission peaks are 556 upon excitation at 325nm. In order to understand
the nature of these emission bands, the PL properties of free ligand dnpt were analyzed, showing
it exhibits the strongest emission peaks at about 447 nm (excitation at 325 nm) from 300 to 800
nm. Compared with the PL spectrum of free ligand, the red shifts for 1 may be due to the
chelating and bridging effects of the relevant ligands to the metal atoms. The emission bands for
the free ligands are probably attributable to the π*-n transitions. However, the effect of the
microenvironment between ligands and complex on the luminescence properties still needs
further investigations.
3.3 UV–Vis Absorption Spectra
The UV–Vis absorption spectra of dnpt ligand and complex 1 are determined in the solid state
at room temperature. The result suggests that complex 1 exhibits absorption bands at 412 nm
(Fig. 4). The ligand dnpt shows two absorption bands at 232 and 274 nm. The absorption band of
complex 1 is red-shifted by 138–180 nm relative to that of free ligand dnpt. After coordination,
the formation of more large conjugated system may be the reason for the strong red-shift. The
above analyses for UV–Vis spectral are in agreement with the determined crystal structure of
complex 1.
Acknowledgement
We thank the National Natural Science Foundation of China (No. 21406085), and the Science
Development Project of Jilin Province of China (20130522071JH) for financial support.
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[11] Sheldrick G M. SHELXS-97, Program for the Solution of Crystal Structure, University of
Göttingen, 1997.
[12] Sheldrick G M. SHELXS-97, Program for the Refinement of Crystal Structure, University of
Göttingen, 1997.
[13] A.R. Biju, M.V. Rajasekharan. J. Mol. Struct. 875, 457 (2008)
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Table 1 Crystal data and structure refinement parameters for the title complex
Empirical formula
C26H17MnN6O6
564.40
Formula weight
Size/mm
0.285x0.178x0.146
1.56 -25.18
monoclinic
P-1
θrange for date collection/(°)
Crystal system
space group
a/Å
13.783(3)
26.154(6)
14.301(3)
111.249(4)
4804.7(1)
1.552
b/Å
c/Å
β/(°)
V/Å 3
D/(g.cm-3)
Z
8
F(000)
2224
μ/mm
0.609
Reflections collected
Independent reflections
Final GOF
13936
4306
0.878
R1 ,wR2 [I > 2σ(I)]
Largest diff. peak and hole/(e.Å-3)
0.1415, 0.2821
3.487, -2.553
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Table 2 Selected bond lengths [Å] and bond angles [°] for the title complex
bond
Dist.
bond
Dist.
Mn(1)-O(3)
Mn(1)-O(1)
Mn(1)-N(1)
Angle
2.138(10)
2.281(9)
2.236(9)
(°)
Mn(1)-O(2)
2.221(9)
2.225(10)
2.274(10)
(°)
Mn(1)-O(4)
Mn(1)-N(2)
Angle
O(3)-Mn(1)-O(2)
91.9(3)
107.1(4)
58.2(3)
120.1(4)
90.4(3)
94.2(4)
163.2(4)
74.8(3)
O(3)-Mn(1)-O(4)
O(3)-Mn(1)-O(1)
O(4)-Mn(1)-O(1)
O(2)-Mn(1)-N(1)
N(1)-Mn(1)-O(1)
O(2)-Mn(1)-N(2)
O(1)-Mn(1)-N(2)
86.4(4)
148.4(3)
92.8(4)
144.7(4)
91.4(3)
89.7(4)
95.3(4)
O(2)-Mn(1)-O(4)
O(2)-Mn(1)-O(1)
O(3)-Mn(1)-N(1)
N(1)-Mn(1)-O(4)
O(3)-Mn(1)-N(2)
O(4)-Mn(1)-N(2)
N(1)-Mn(1)-N(2)
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Fig.1 the molecular complex 1 (hydrogen atoms were omitted)
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Fig.2 simplified 1D chain structure of complex 1 (hydrogen atoms and dnpt ligands were
omitted)
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Fig.3 Luminescent spectrum of complex 1 and ligands in solid state at room temperature
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Fig.4 UV–Vis spectrum of complex 1 in solid state at room temperature
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Scheme 1 the synthesis of dnpt
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