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Synthesis, Crystal Structure and Characterizations of -
Zn (II) Complex with pmtpo and NCS (Pmtpo = 2-(2pyridylmethylthio)-5-(4-pyridyl)-1,3,4-oxadiazole) a
a
a
E. Ye , Ben-Lai Wu , Yun-Yin Niu & Hong-Yun Zhang a
a
Department of Chemistry, Zhengzhou University, Zhengzhou, P.R. China
Available online: 05 Nov 2008
To cite this article: E. Ye, Ben-Lai Wu, Yun-Yin Niu & Hong-Yun Zhang (2008): Synthesis, Crystal Structure and -
Characterizations of Zn (II) Complex with pmtpo and NCS (Pmtpo = 2-(2-pyridylmethylthio)-5-(4-pyridyl)-1,3,4oxadiazole), Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 38:9, 716-720 To link to this article: http://dx.doi.org/10.1080/15533170802440888
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 38:716–720, 2008 Copyright © Taylor & Francis Group, LLC ISSN: 1553-3174 print / 1553-3182 online DOI: 10.1080/15533170802440888
Synthesis, Crystal Structure and Characterizations of Zn (II) Complex with pmtpo and NCS− (Pmtpo = 2-(2-pyridylmethylthio)-5-(4-pyridyl)-1,3,4-oxadiazole) E. Ye, Ben-Lai Wu, Yun-Yin Niu, and Hong-Yun Zhang
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Department of Chemistry, Zhengzhou University, Zhengzhou, P.R. China
The reaction of zinc(II) sulfate with ligand pmtpo and KSCN gave rise to a supramolecular complex, [Zn(pmtpo)2 (NCS)2 ], (Pmtpo = 2-(2-pyridylmethylthio)-5-(4-pyridyl)-1,3,4-oxadiazole), which was characterized by X-ray diffraction analysis, UV and IR spectra. This complex is crystallized in a monoclinic space group C2/c and in the complex crystal structure, the center Zn(II) ion has a tetrahedron coordination environment. The structure is extended by weak (4-pyridyl)C–H· · · SCN− hydrogen bonding and two-sorted weak π − π packing interactions. The fluorescent property and thermal stability of the complex are researched. Keywords
1,3,4-oxadiazole, fluorescent property, supramolecular compound, thermal ability, zinc(II) complex.
INTRODUCTION Material science is a rapidly growing area of interest. The study of structural design or modification of the coordination framework is especially rapidly expanding, due to the fact that the self assembly of the functional metal-organic coordination compounds can be achieved by careful choice of organic ligands, inorganic metal species, metal coordination geometry preference, inorganic counterion, solvent system and metal salt-toligand ratio.[1−11] Among these factors, organic ligands play a very important role in dictating polymer framework topology. More recently, the design and construction of supramolecular architecture by self-assembly of small building blocks has increasingly become a major research area[12−14] due to their potential applications in many fields such as selective clathration,[15,16] molecular recognition,[17,18] catalysis[19,20] and storage material. In order to design and synthesize new supramolecular complexes we selected two types of ligands, pmtpo (pmtpo = 2-(2-pyridyl-
Received 24 June 2008; accepted 30 August 2008. We gratefully acknowledge financial support from the National Natural Science Foundation of China (20771094, 20671083) and the Science and Technology Key Task of Henan Province (0524270061). Address correspondence to Hong-Yun Zhang, Dept. of Chemistry, Zhengzhou 450052, P.R. China. E-mail:
[email protected],
[email protected]
methylthio)-5-(4-pyridyl)-1,3,4-oxadiazole) and SCN− ion as well as ZnSO4 ·7H2 O as candidates, and successfully assemble a new supramolecular complex, [Zn(pmtpo)2 (NCS)2 ]. To the best of our knowledge, 1,3,4-oxadiazole exhibiting the corresponding biological properties such as antiphlogosis and antisepsis have not only given rise to an extensive variety of applications in both medicine and agriculture, but have also been derived for many multidentate ligands. Up to now, a great many of the compositions with symmetrical organic ligands containing oxadiazole ring have been prepared as far as we know.[21] However, coordination compounds with asymmetrical ligands containing 1,3,4-oxadiazole group are discussed uncommonly.[22] The pseudohalide thiocyanate (SCN− ) is well known to coordinate to metal centers as a monodentate ligand utilizing its sulfur or nitrogen atom, or as an end-to-end bridging ligand between two metal centers through both sulfur and nitrogen atoms or as a single atom bridging ligand.[23] Herein we report the synthesis, crystal structure, fluorescence and thermal property of Zn(II) complex with an asymmetrical oxadiazole derivative ligand (pmtpo) and SCN− . EXPERIMENTAL Materials and Physical Measurement Reagents and solvents for the synthesized ligand and complex all were analytical pure grade. 2-Picolyl chloride hydrochloride was purchased from Alfa Aesar, iso-nicotinyl hydrazide from Shang Hai State-operated Chemical Company, and others from TianJin Reagent Factory, and used without further purification. 2-(2-Pyridylmethylthio)-5-(pyridine-4-yl)1,3,4-oxadiazole (pmtpo) was synthesized following a procedure reported previously[24] with a yield of 65%. Melting point was taken on a XT-5 microscope melting point apparatus. IR spectra were recorded on a Nicolet IR-470 spectrometer from KBr pellets in a range 4000–400 cm−1 . UV spectra were scanned on UnicoTMUV-2102 PC spectrophotometer using a solution in DMF (1 × 10−5 mol/L). Crystallographic data was measured on a Bruker APEX-II area˚ detector diffractometer with Mo-Ka radiation (λ = 0.71073 A). Thermal analysis curve were scanned in a range of 35–700◦ C
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SYNTHESIS OF ZN(II) COMPLEX
with argon atmosphere on STA 409 PC thermal analyzer. The fluorescent spectra were determined in DMF (1 × 10−4 M) at room temperature on HITRCHI F-4500 fluorophotometer.
TABLE 2 ˚ and bond angles (◦ ) of the complex Selected bond lengths(A)
Synthesis of [Zn(pmtpo)2 (NCS)2 ] To a solution of ZnSO4 ·7H2 O (0.0286 g, 0.1 mmol) in 10 mL methanol was slowly added dropwise a solution of pmtpo (0.0540 g, 0.2 mmol) in 5 mL methanol with vigorous stirring, and then potassium thiocyanate (0.0194 g, 0.2 mmol) in 10 mL aqueous solution was slowly added dropwise to the above mixed solution with continuously stirring for 30 min. The reaction mixture was filtered, allowing the filtrate for slow evaporation at ambient temperature. About two weeks later, the colorless block crystals suitable for X-ray single crystal diffraction analysis were collected by filtered, washed with methanol and acetone, and dried in air. Yield 0.055 g (38%). IR (KBr, υ cm−1 ): 3046 m, 2094 s, 2078 s,1442 w, 1389 w, 1191 m, 1134 s, 844 m, 817 m, 723 w, 711 m.
Zn1–N5 Zn1–N1
1.9356(18) 2.0283(16)
Zn1–N5A Zn1–N1A
1.9357(19) 2.0284(16)
N5–Zn1–N5A N5A–Zn1–N1 N5A–Zn1–N1A
107.09(11) 104.38(7) 117.01(7)
N5–Zn1–N1 N5–Zn1–N1A N1–Zn1–N1A
117.01(7) 104.39(7) 107.51(9)
X-ray Structural Determination Crystallographic data for the title compound were collected at 291(2) K on a Bruker APEX-II area-detector diffractometer ˚ Absorption corrections with Mo-Ka radiation (λ = 0.71073A). were applied by using SADABS. The structure was solved with direct methods and refined with full-matrix least-squares techniques on F 2 using the SHELXTL program package. All of the TABLE 1 Crystallographic data and structural refinement for the complex Parameter name Empirical formula Formula weight Crystal system Space group Crystal size (mm) Temperature(K) a/A˚ b/A˚ c/A˚ α/◦ β/◦ γ /◦ ˚ V / A3 Z Dc /g.cm−3 Reflens collected Data/restraints wR1 [I>2σ (I)] wR2 (all data) Good of fit on F2 ˚ Largest peak, hole (e·A−3)
Data C28 H2 0N10 O2 S4 Zn 722.15 Monoclinic C2/c 0.40 × 0.25 × 0.21 291.2 16.635(6) 6.5834(19) 29.692(9) 90 105.829(12) 90 3128.3(17) 4 1.533 11088/2896 [R(int) = 0.0201] 2896/0/204 0.0276, 0.0680 0.0334, 0.0715 1.033 0.271, −0.296
II1
A: −x+1, y, −z+1/2.
non-hydrogen atoms were refined anisotropically. The hydrogen atoms were assigned with common isotropic displacement factors and included in the final refinement by using geometrical restrains. Crystal data are summarized in detail in Table 1. Selected bond lengths and bond angles are listed in Table 2. RESULTS AND DISCUSSION Description of the Crystal Structure of the Complex Single-crystal X-ray diffraction analysis reveals that the complex crystallizes in a monoclinic space group C2/c. Crystal structural unit is show in Figure 1, and the crystal structural parameters, the selected bond distances and angles are given in Tables 1 and 2, respectively. The crystal structural unit consists of one Zn(II) center, two pmtpo molecules and two SCN− ions. Two nitrogen atoms from two 4-pyridyl groups of two pmtpo molecules and two nitrogen atoms from two SCN− ions are located in the four apexs of a tetrahedron, and thus form a tetrahedron coordination environment for the Zn(II) center. The ˚ is longer than Zn–N− bond distance Zn–Npy (2.0283(16) A) SCN ˚ It is also longer than mean value(2.007 A) ˚ of (1.9356(18) A). Zn–N in the literature,[25] and shorter than Zn–N value (2.038 ˚ in other literature.[26] The bond angles N5–Zn–N1 and N5A– A) Zn–N1A = 117.01◦ , N5A–Zn–N1 and N5–Zn–N1A = 104.38◦ , are all close to normal angle for a tetrahedron (109◦ 28 ), so the coordination sphere around Zn(II) is a slight distorted tetrahedron geometry. As for ligand pmtpo, the dihedral angles of 4-pyridyl plane with 1,3,4-oxadiazole plane, 2-pyridyl plane with 1,3,4-oxadiazole plane and 4-pyridyl plane with 2-pyridyl plane are 14.8◦ , 4.1◦ and 17.2◦ , respectively. In the crystal structure of the complex there is weak (4pyridyl)C–H· · ·SCN− hydrogen bonding between adjacent structural units. As a result, the structural units are connected into an infinite 1D chain along c axis through the weak intermolecular interactions (Figure 2). Moreover, there are twosorted weak π -π packing interactions shown in Figure 3: One occurs between the 4-pyridyl ring and the 2-pyridyl ring in adjacent structural units with the ring center distance 3.900 ˚ and the other is between the 2-pyridyl ring and the 1,3,4A, oxadiazole ring in adjacent structural units with the ring center ˚ The complex is constructed into complicated distance 3.801 A. supramolecular configuration through the weak intermolecular
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FIG. 1.
The coordination geometry around Zn(II) centers in the complex.
interactions inversely, which can simultaneously stabilize the supramolecular structure. IR Spectrum of the Complex In IR spectrum of the complex, the characteristic vibration absorption peaks of the framework C=N and C=C of pyridyl ring of pmtpo ligand appeared in a range of 1650–1470 cm−1 , and the flexural vibration absorption peaks of C–H of aromatic ring appeared in a range of 776–766 cm−1 . The strong and sharp-pointed absorption peak appearing at 2090 cm−1 can be attributed to expansion vibration of SCN.−[26] The results of IR spectrum of the complex are consistent with the conclusion of X-ray diffraction analysis. FIG. 2. 1-D chain (viewed down thecaxis) constructed via weak (4-pyridyl) C–H· · ·SCN− hydrogen bonding.
FIG. 3.
Two-sorted intermolecular π -π interactions in the complex.
UV Spectra of the Complex and Ligand pmtpo UV spectra of the complex and pmtpo ligand in DMF (1 × 10−5 mol/L) (shown in Figure 5) are determined at room temperature. The UV spectrum of pmtpo displays a strong absorption peak at 281.5 nm, which perhaps attributes to π -π * transition in the ligand. Meanwhile, the UV spectrum
FIG. 4. Stacking drawing of crystal structure in the complex.
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FIG. 7. TG-DTG curves of the complex.
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FIG. 5. The UV spectra of the complex and the ligand.
of the complex is very similar to that of pmtpo only with the absorption strength being reduced. It is deduced that the UV spectrum of the complex is also π -π * transition of intraligand. Fluorescent Spectra of the Complex and pmtpo The fluorezcent spectra of pmtpo and the complex in DMF (1 × 10−4 mol/L) are shown in Figure 6. Under excited at 310 nm, the largest emission wave-length of pmtpo appears near 373 nm, while the largest emission wave-length of the complex appears at 382 nm. Comparing with that of pmtpo, the peak shape of fluorescent spectrum of the complex does not change, only with the peak position red shifting for 9 nm and the strength heightening, which may result from increasing conjugated system of the complex and reducing emission energy owing to
pmtpo coordination to Zn(II). It is seen from these results that the fluorescent emission spectrum of the complex neither MLCT (metal-to-ligand charge transfer) nor LMCT (ligand-to-metal charge transfer), which may be fluorescent emission of intraligand under Zn(II) perturbation.
TG-DSC Curve of the Complex The complex TG-DSC curve is shown in Figure 7. At 198◦ C; the complex began decomposition with corresponding small endothermic peak, and up to 340◦ C a weight loss is 36.82%, corresponding to C–S bond cleavage in the ligand backbone (calc.32.68%). At 340◦ C; a strong decomposition reaction occurred with a corresponding exothermal peak, and up to 547◦ C the resulting weight loss is 54.19% corresponding to the ligand being further decomposed. The remains of 45.81% probably are metal zinc and deposition carbon from organic ligand decomposed.
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FIG. 6. The emission spectra of the complex and the ligand.
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