ОПТИКА И СПЕКТРОСКОПИЯ, 2015, том 118, № 1, с. 64-69
СПЕКТРОСКОПИЯ ^^^^^^^^^^
КОНДЕНСИРОВАННОГО СОСТОЯНИЯ
УДК 543.42
CRYSTAL STRUCTURE, INFRARED SPECTRA AND LUMINESCENCE OF A 1D Cd COORDINATION POLYMER WITH 4-NITROPHTHALIC ACID AND 1,10-PHENANTHROLINE MONOHYDRATE LIGANDS © 2015 г. Li-Juan Han, Ya-Jie Kong, Ning Sheng
Key Laboratory of Inorganic Chemistry in Universities of Shandong, Department of Chemistry and Chemical Engineering,
Jining University, Qufu, Shandong, 273155, China E-mail: yajiekong80@gmail.com Received April 18, 2014
A new one-dimensional (1D) coordination polymer, [Cd(NPTA)(1,10-phen)(H2O)]n (1) (H2NPTA = 4-ni-trophthalic acid; 1,10-phen = 1,10-phenanthroline monohydrate), has been synthesized under hydrothermal conditions and characterized by elemental analysis, single-crystal X-ray diffraction, solid state emission spectra, FT-IR spectra, and thermogravimetric analyses. The compound belongs to triclinic system with
space group P 1, and exhibits a one-dimensional linear chain. Each Cd with a strongly distorted octahedral coordination geometry is six-coordinated by two N atoms from one 1,10-phenanthroline ligand, three O atoms from two carboxylate groups of two different NPTA2- ligands and one O atom from lattice water. Layer supramolecular architecture is formed by medium п—п stacking interactions between two neighboring phenanthroline rings from two independent linear chains. Studies on luminescent property of 1 exhibit the solid state emission originating from an intra ligand п ^ п* transition of NPTA2- ligand. DOI: 10.7868/S0030403415010183
INTRODUCTION
Nowadays, the research interest on transition metal coordination polymers is increasing rapidly because of their potential applications in the areas of materials chemistry such as catalysis, nonlinear optics, electronics, photoluminescence, and adsorption [1—9]. It is well known that the construction of coordination polymers is mainly dependent on several factors such as the organic ligand, the geometric requirements of the metal atom, the temperature, the solvent system and the anion template effect etc. [10—15]. Among these factors, the organic ligand plays an important role because changing it can control and adjust the coordination frameworks and topologies [16—19]. Since a carboxylate group can bridge metal ions and lock their position into M—O—C clusters, which can act as rigid entities and improve the stabilization of the compounds, di- and polycarboxylic acids are widely used as bridging ligands to construct coordination frameworks with versatile structures [20—25]. As a member of dicarboxylate ligands, 4-nitrophthalic acid (H2NPTA) contains four potential metal binding sites, which can yield the formation of a coordination polymer through multiple bonding interactions, adopt different conformations and coordination modes, and provide abundant structural motifs. However, coordination polymers assembled from 4-nitrophthalic acid ligand have rarely been reported [26].
In order to synthesize novel monometallic NPTA2-coordination polymers, the reaction of d10 metal salts of cadmium acetate with H2NPTA and 1,10-phenan-throline monohydrate ligand (flexible N-donor ligand, is excellent bridging ligand for the construction of coordination polymer) was carried out in hydrothermal conditions. Luckily, we obtained one novel monometallic coordination polymer, [Cd(NPTA)(1,10-phen)(H20)]„ (1) (H2NPTA = = 4-nitrophthalic acid, 1,10-phen = 1, 10-phenan-throline monohydrate). In this paper, we report the synthesis, structural characterization, FT-IR spectrum, thermal stability and luminescent property of the compound 1.
EXPERIMENTAL
Materials and Instrumentation
All starting materials and reagents were of analytical grade and obtained from commercial sources without further purification. Elemental analyses for C, H and N were performed on a Vario EL III elemental analyzer. FT-IR spectrum was recorded from KBr pellets in the range from 4000 to 400 cm-1 on a Bruker VECTOR 22 spectrometer. Luminescence excitation and emission spectra were performed on Edinburgh FLS-920 fluorescence spectrometer using a 450-w xenon lamp as excitation source at room temperature, the excitation and emission slits are 3 and 5 nm, re-
N
>N Cd _q-H H
œ M
N
o' SG
Fig. 1. Schematic molecular structure of the title compound.
C20 ,-C19 C11
C15 C16
N1
O6
spectively. All the spectra are corrected and the intensities are determined with integrated area. Luminescence life time and absolute quantum yield (QY) were measured on Absolute PL quantum yield spectrometer C11347 (HAMAMATSU), using a LED and a 450-w xenon lamp as excitation source, respectively. Ther-mogravimetric analysis (TGA) was performed on a SDT 2960 thermal analyzer from room temperature to 800° C at a heating rate of 1°C/min under nitrogen flow.
Synthesis of the Compound
A mixture containing Cd(CH3COO)2 • 2H2O (133 mg, 0.50 mmol), H2NPTA (106 mg, 0.50 mmol), 1,10-phenanthroline (100 mg, 0.50 mmol) and NaOH (40 mg, 1.0 mmol) in 8 ml of water was sealed in a teflon lined autoclave and heated under autogenic pressure to 125°C for three days and then allowed to cool to room temperature at a rate of 1°C/hour. Colorless sheet-shaped crystals were obtained that was collected by filtration, washed several times with distilled water, and dried in air. Yield: 106.5 mg, 41% yield based on Cd2+ (Fig. 1). Elemental analysis: calculated for C20H13N3O7Cd (Mr = 519.75): C, 46.22%; H, 2.52%; N, 8.08%; found: C, 46.99%; H, 2.47%; N, 8.20%. IR (cm-1): 3450 (w, br), 3100 (w), 1620 (s), 1585 (m), 1540 (m), 1426 (m), 1392 (s), 1346 (vs), 854 (s), 729 (s).
X-ray Single Crystal Structure Determination
A colorless crystal of the compound with dimensions of 0.15 x 0.10 x 0.08 mm was mounted on goniometer of a Bruker Smart APEX II CCD diffractome-ter. Measurements were performed at 173 K using graphite-monochromated Mo^a radiation (X = = 0.71073 A). The data integration and reduction were carried out with SAINT-plus software [27]. For each data set, empirical absorption correction was applied to the collected reflections with SADABS [28], and the space group was determined using XPREP [29]. The structure was solved by the direct methods using SHELXTL-97 [30] and refined on F2 by full matrix least squares using the SHELXL-97 [31] program
Fig. 2. Molecular structure of the title compound drawn with displacement ellipsoids at 30% probability level. All hydrogen atoms have been omitted for clarity.
package. All non-hydrogen atoms were refined aniso-tropically. The H atoms have been refined as follows: the hydrogen atoms attached to carbon atoms were positioned geometrically and treated as riding atoms using SHELXL default parameters. The H atoms of water molecule were located from difference Fourier maps. The molecular graphics were done using XP in SHELXTL [32] and DIAMOND [33]. Crystal data and structural refinement parameters are summarized in Table 1 and selected bond distances and bond angles are listed in Table 2. CCDC reference number of 988820 contains the supplementary crystallographic data for compound 1, which can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
RESULTS AND DISCUSSION
Description of the Crystal Structure X-ray crystallographic analysis revealed that the title compound crystallizes in triclinic space group P 1 with the molecule residing on a general position, as illustrated in Fig. 2. The asymmetric unit is composed of one crystallographically independent Cd centers, one NPTA2- anion, one 1,10-phenanthroline ligand and one lattice water molecule. As shown in Fig. 3, the coordination mode of n 1: n2 for NPTA2- ligand is found in the crystal structure. The NPTA2- ligand acts as a ^3-bridge to link two cadmium ions: the carboxy-lates at C8 is monondentate bridging to cadmium ions, the carboxylate at C7 is bidentate chelating to another cadmium ions. Each Cd with a strongly distorted octahedral coordination geometry is six-coordinated by two N atoms from one 1,10-phen ligand, three O atoms from two carboxylate groups of two different NPTA2- ligands and one O atom from lattice water. The bond lengths of Cd-O are in the range of 2.216(6)-2.530(7) A. The two carboxylic groups of NPTA2- ligands coordinate with two Cd atoms to form a Cd-NPTA chain. Consequently, a one-dimensional linear chain is exhibited in Fig. 3.
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Table 1. Crystal data and structure refinement for the title compound
Empirical formula C20H13CdN3O7
Formula weight 519.73
Crystal color Colorless
Crystal size (mm) 0.15 x 0.10 x 0.08
Crystal system Triclinic
space group P 1
a, A 7.292(2)
b, A 10.508(4)
c, A 12.250(4)
a, deg 84.955(7)
P, deg 80.460(10)
Y, deg 81.754(10)
Volume, A3 914.1(5)
Z 2
dcalcd, g/cm3 1.888
p., mm-1 1.248
F(000) 516
X, A 0.71073
Temperature 173(2)K
9 range, deg 2.12 to 25.66
Max. and min. transmission 0.904 and 0.829
Refinement method full-matrix
least-squares on F2
Data/restraints/parameters 3013/2/288
Goodness of fit on F2 1.047
Final R indices [I > 2a(I)]a) Rx = 0.0655
wR2 = 0.1617
R indices (all data) R1 = 0.0780
wR2 = 0.1720
a) R1 = S|[F0| - |Fc||/S|F01; WR2 = [2w(if — if )2/SwF^ ]1/2.
Interestingly, it is worth noting that new layer su-pramolecular structure was formed by medium n—n stacking interactions [34—37] between two neighboring phenanthroline rings from two independent linear
Table 2. Selected bond lengths (A ) and angles (deg) for the title compound
Bond lengths, A
O(1)—Cd(1)#1 2.317(6)
O(4)—Cd(1) 2.216(6)
O(1W)—Cd(1) 2.354(7)
O(2)—Cd(1)#1 2.530(7)
N(2)—Cd(1) 2.317(7)
N(3)—Cd(1) 2.353(7)
Bond angles, deg
O(4)—Cd(1)—N(2) 127.4(2)
O(4)—Cd(1)—N(3) 108.0(3)
N(2)—Cd(1)—N(3) 71.9(3)
O(4)—Cd(1)—O(1W) 80.9(2)
O(4)—Cd(1)—O(2)#2 83.5(2)
O(1)#2—Cd(1)—O(2)#2 53.5(2)
N(2)—Cd(1)—O(2)#2 85.1(2)
N(3)—Cd(1)—O(2)#2 156.8(3)
Symmetry transformations used to generate equiva
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