配合物[Eu(4-MOBA)3(terpy)(H2O)]2的合成、表征、熱分解機理及性質

霍建霞　宋素偉　靳成偉　任　寧　耿麗娜　張建軍,*(河北師范大學分析測試中心，石家莊0500；河北師范大學化學與材料科學學院，石家莊0500；邯鄲學院化學化工與材料學院，河北邯鄲056005；中石油京唐液化天然氣有限公司，河北唐山060)

配合物[Eu(4-MOBA)3(terpy)(H2O)]2的合成、表征、熱分解機理及性質

霍建霞1,2宋素偉4靳成偉1,2任寧3,*耿麗娜2張建軍1,2,*
(1河北師范大學分析測試中心，石家莊050024；2河北師范大學化學與材料科學學院，石家莊050024；3邯鄲學院化學化工與材料學院，河北邯鄲056005；4中石油京唐液化天然氣有限公司，河北唐山063210)

合成了一個新的配合物[Eu(4-MOBA)3(terpy)(H2O)]2(4-MOBA：4-甲氧基苯甲酸根，terpy：2,2′:6′,2′-三聯吡啶)。采用傅里葉變換紅外(FTIR)光譜、元素分析和X射線粉末衍射(XRD)技術對標題配合物進行了表征，用X射線單晶衍射儀測定了配合物的晶體結構，在配合物中每個Eu3+離子與一個三聯吡啶分子、一個水分子和三個羧酸分子結合，配位數為9，羧酸基團的配位模式包含三種：雙齒螯合，橋連雙齒，單齒。根據熱重-差示掃描量熱/傅里葉變換紅外(TG-DSC/FTIR)聯用技術，研究了配合物的熱分解機理。配合物的發射光譜顯示出Eu3+離子的特征熒光發射，表明三聯吡啶和4-甲氧基苯甲酸在該體系中可作為敏化集團。另外，文中還討論了配合物對白色念珠菌和大腸桿菌的抑菌活性。

鑭系配合物；晶體結構；熱分解機理；熒光；2,2′:6′,2′-三聯吡啶；抑菌活性

[Article]

www.whxb.pku.edu.cn

1　Introduction

Amassive interest in Ln3+complexes is registered in more recent times,which stems from their possible use in biomedical and telecommunication fields and for various photonic applications1－9. The absorption coefficients of the optical transitions for lanthanide ions are,however,very low which limits their practical application considerably.This drawback can be overcome through the use of organic ligand,which acts as an antenna or sensitizer,absorbing excitation light and transferring energy to the lanthanide ions,thus greatly improves the characteristic emission of rare earth ions10－14. In order to obtain strong luminescent intensities,Eu3+ions need a cleverly designed environment consisting of organic ligands with chromophoric groups to absorb efficiently light and subsequently populate the excited states of Eu3+ions via energy transfer.

On the other hand,the lanthanide complexes with biological activities can be used at various fields,just as many studies of researchers15－20.The results show that,under certain conditions, Ln3+ions can not inhibit the Candida albicans and Escherichia coli,while the complexes synthesized by organic ligands and Ln3+can inhibit the Candida albicans and Escherichia coli well21.

In this report,a new Eu complex with 4-methoxybenzoic acid and 2,2′:6′,2″-terpyridine was synthesized.The complex was measured by series of elementary methods.Moreover,the luminescent properties and bacteriostatic activities of the complex were discussed,and thermal decomposition mechanism of the complex was also presented.

2　Materials and methods

2.1Materials and physical measurements

All chemicals were commercially purchased and used without further purification.EuCl3?6H2O was prepared by reaction of Eu2O3and hydrochloric acid in aqueous solution.

The Eu3+is determined by ethylenediamine tetraacetic acid (EDTA)titration using xylenol oranges as an indicator.C,N,and H analyses were performed using a Vario-EL III elemental analyzer(Elementar,Germany).Infrared spectrum(4000－400 cm－1) was obtained with KBr discs on a TENSOR27 spectrometer (Bruker,Germany).X-ray powder diffraction identification was carried out for the crystalline analyses by a D8ADVANCE X-ray diffractometer in a scanning range of 5°－40°(2θ)with Cu Kαradiation(λ=0.15418 nm，Bruker,Germany).The data of single crystal X-ray diffraction were collected on a Smart-1000 diffractometer(Bruker,Germany).The crystal data and refinement details for the complex are presented in Table 1.The fluorescent spectrum of complex(solid)was recorded on an F-4500 Hitachi spectrophotometer at room temperature.Thermogravimetry-differential scanning calorimetry/Fourier transform infrared(TGDSC/FTIR)was described by using the STA 449 F3(Netzsch, Germany)coupled with TENSOR27 Fourier Transform Infrared Spectrometer(Bruker,Germany).Using the filter paper disc (diameter 6 mm)diffusion method,antibacterial activity of the EuCl3?6H2O,ligands and complex were tested.

Table 1　Crystallographic data for the complex

2.2Preparation

Europium salt(0.2 mmol)was dissolved in mensurable distilled water,and 4-methoxybenzoic acid(0.6 mmol)and terpyridine(0.2 mmol)were dissolved in mensurable ethanol solvent(95%).The pH value of mixed ligands was adjusted around 5－7 with NaOH (mol?L－1)solution.Then the mixture of the two ligands solution was added dropwise into the EuCl3?6H2O solution,stirred for about 7 h at room temperature,and then deposited for 12 h.Finally,the precipitates were obtained by filtration.Single crystal of complex was collected from the mother liquor after two weeks at room temperature.Elemental analyses for complex,calcd.(%): C 54.68,H 4.00,N 4.91,Eu 17.74;found(%):C 53.88,H 3.94, N 4.75,Eu 18.14.

3　Results and discussion

3.1Infrared spectra

The absorption bands of 4-methoxybenzoic acid,2,2′:6′,2″-terpyridine and complex[Eu(4-MOBA)3(terpy)(H2O)]2are listed in Table 2.For the complex,the νas(COO―)vibration is identified as the strong band at 1535 cm－1.The band assigned to the vibration of νs(COO―)is observed at 1414 cm－1.The characteristic absorption peak at 1687 cm－1of νC＝Ofor 4-MOHBA disappeared in the complex,and the band assigned to the vibration of ν(Eu―O)is ob-served at 408 cm－1in the complex.These facts may indicate that the carboxylate groups are bonded to Eu3+ions.The band in the free terpy at 1581 and 833－764 cm－1assigned to νC＝Nand δC―H, respectively.The band νC＝Nand δC―Hin the IR spectra of complex is slightly shifted to higher frequency.The result suggests that the nitrogen atoms of terpy ligand also coordinate to the Eu3+ion.

Table 2　IR bands for free ligands and complex

3.2X-ray powder diffraction

The X-ray power diffraction of free ligands and complex are shown in Fig.1.Compared with two ligands,the relative intensity and diffraction angles of the main diffraction peaks for the complex are significantly different.There are some new diffraction peaks in the complex,while the diffraction peaks of the two ligands were disappeared in the complex.Therefore,the complex is a kind of new substance,instead of the mixture of two ligands and europium salt22.

Fig.1　X-ray power diffraction patterns of complex and free ligands (a)complex,(b)terpy,(c)4-MOHBA

3.3Structural description of[Eu(4-MOBA)3(terpy)?(H2O)]2

The structure and coordination geometry of the complex are shown in Fig.2.Selected bond lengths for the complex are listed in Table 3.The complex crystallizes in monoclinic crystal system and P2(1)/c space group.The crystal structure data of the complex reveal that the dinuclear unit consists of two Eu3+ions,six 4-methoxybenzoic acid ligands,two terpy ligands and two coordinated water molecules.The asymmetry unit contains only half of the dinuclear unit,that is,the two Eu3+ions are equivalent.Each Eu3+ion is coordinated to a tridentate terpy,a bound water and three 4-methoxybenzoic acid ligands,which adopt different coordination modes:bidentate,monodentate,and bridging bidentate. As a result,the nine-coordinated Eu3+ion center adopts a distorted monocapped square antiprismatic molecular geometry.Eu1―O bond distances for the bidentate 4-methoxybenzoic acid(O7 and O8)are 0.2515(7)and 0.2469(7)nm,respectively.The two Eu3+ions are connected to form a binuclear molecular dimer via a bridging bidentate 4-methoxybenzoic acid(O4 and O5)with Eu1―O bond distances of 0.2308(8)nm to O4 and 0.2342(8)nm to O5.A monodentate 4-methoxybenzoic acid(O1)is also coordinated to the Eu3+ion center and the Eu1―O1 bond distanceis 0.2393(8)nm,whereas the coordinated water molecule has a Eu1―O10 bond distance of 0.2517(7)nm.Completing the coordination sphere of the Eu3+ion is a tridentate terpy molecule, which is bound through its three nitrogen atoms(N1,N2,N3)with an average Eu1―N bond distance of 0.2614 nm.The average distance of Eu1―O(O1,O4,O5,O6,O7)bond is 0.2405 nm, which is shorter than the distance of Eu1―N bond.It indicates that the terpy ligands loss much easier than 4-methoxybenzoic acid ligands.

Table 3　Selected bond lengths for the complex

Fig.2　Crystal structure of complex(a),coordination geometry of Eu3+ion(b)

What′s more,the dinuclear units of the complex are assembled into 1D chain by two offset face-to-face π…π weak stacking interactions between terpyridine rings containing N2 and N1 on neighboring as shown in Fig.3.The distance of the terpyridine rings is 0.4194 nm.

Fig.3　Dinuclear units of complex formed 1D chain by offset face-to-face π…π weak stacking interactions

Fig.4　TG-DTG and DSC curves of complex

Table 4　Thermal decomposition data for the complex

3.4Thermal decomposition processes of the complexes

The TG/DTG-DSC methods were used to describe thermal decomposition of synthesized complex in air as shown in the Fig.4.The thermal decomposition results are presented in Table 4.The gaseous products from TG experiments were also detected online and identified by using three-dimensional infrared spectra as shown in Fig.5.According to the TG-DTG curves of the complex,we can know that the complex has five decomposition steps.For the complex,the first decomposition step occurs in the temperature range of 353.15－387.15 K with a weight loss of 2.53%against calculated weight loss of 2.10%for two water molecules,which can be ascribed to the loss of two coordinated water molecules.On the DSC curve,endothermic peak is observed at about 372.45 K,which can prove the decomposition of two water molecules.The second and third decomposition steps occur in the temperature range of 387.15－491.15 K and 491.15－645.15 K with a weight loss of 9.21%and 27.06%,respectively,against calculated weight loss of 27.47%for all terpy,corresponding to the loss of terpy and part of 4-methoxybenzoic acid ligands.The fourth and fifth decomposition steps take place in the temperature range of 645.15－715.15 K and 715.15－853.15 K with a weight loss of 20.71%and 20.90%,respectively.There is a weak exothermic peak(689.25 K)and a strong exothermic peak(733.05 K) on the DSC curve,corresponding to the degradation and oxidation of the remains of 4-methoxybenzoic acid ligands.As a result,the total weight loss is 80.41%against calculated weight value of 79.46%,indicating that the residue is Eu2O3.From the three-dimensional infrared spectra of the complex as shown in Fig.5,there are two characteristics absorption process.The first step for the weak absorption peak(3852－3570,1843－1795 cm－1)mainlyattributed to the coordination water decomposition as shown in Fig.6 at 385.15 K.From the FTIR spectra at 726.15 K,the strong absorption bands of CO2(2360－2344,667 cm－1)are observed.In addition,there are some small molecular absorption,such as H2O (3899－3575,1850－1710 cm－1),vC=O(1846－1650 cm－1)alkanes (1508－1343 cm－1)and alkenes(1690－1640 cm－1),indicating that the aromatic rings of the 4-methoxybenzoic acid ligands may be broken,which is consistent with the analysis of TG.

Fig.5　Stacked plot of the FTIR spectra of the evolved gases for the complex as observed in the online(TG/FTIR)system at the heating rate of 10 K?min－1

Fig.6　FTIR spectra of the evolved gases for the complex at 385.15 and 726.15 K

Fig.7　Emission spectra of the complex

3.5Photoluminescence investigation

The luminescent properties of complex[Eu(4-MOBA)3(terpy)? (H2O)]2have been investigated at room temperature.The emission spectra of the complex is shown in Fig.7,and the excitation wavelength is 394 nm.The emission spectrum shows peaks at 580, 595,618,651,and 695 nm,which originated from5D0→7FJ(J= 0,1,2,3,4)transitions of Eu3+,respectively.The5D0→7F2transition of Eu3+corresponding to hypersensitive transition has a high intensity,indicates that the Eu3+is located at a low-symmetry local site without an inversion center23,24.The complex exhibits strong emission bands of Eu3+ion.It indicates that the energytransfer from the ligands to the Eu3+by intersystem crossing is efficient,which is probably attributed to the matching of energy levels between excited states of ligands and excited states of Eu3+25.Moreover,it proves that 4-MOBA and terpy are good chromophore to absorb energy and transfer to Eu3+ions,emitting the characteristic fluorescence of Eu3+ion.

Table 5　Bacteriostatic activities of ligands and complex with three different concentrations at 303.15 K

3.6Bacteriostatic activities

The bacteriostatic activities of complex and ligands to Candida albicans(fungus)and Escherichia coli(bacteria)were determined with three different concentrations at 303.15 K.The bacteriostatic activities data were presented by the diameter of bacteriostatic ring as shown in Table 5.The results show that the complex has good bacteriostatic action to Candida albicans and Escherichia coli. What′s more,the bacteriostatic activities of the complex enhanced with the increase of the concentration in the range of tested concentrations.The bacteriostatic mechanism is presumably that the complex has a good lipophilic nature arising from chelation26.

4　Conclusions

In summary,we synthesized a new europium complex with ligands 4-methoxybenzoic acid and 2,2′:6′,2″-terpyridine,which was confirmed by elemental analysis,FTIR and XRD.The complex crystallizes in monoclinic crystal system and P2(1)/c space group.Each Eu3+ion is coordinated to a tridentate terpy,a bound water molecule and three 4-methoxybenzoic acid ligands adopting three coordination modes:bidentate,monodentate,and bridging bidentate.As a result,the nine-coordinated Eu3+ion center adopts a distorted monocapped square antiprismatic molecular geometry.Thermal decomposition process of the complex was discussed by TG-DSC/FTIR technology and IR spectra of the evolved gases show complex broken down into H2O,CO2and other gaseous molecules as well as the gaseous organic fragments. What′s more,the europium complex had good fluorescence properties due to the antenna effect of ligands and had good bacteriostatic action to Candida albicans and Escherichia coli. Therefore,the complex[Eu(4-MOBA)3(terpy)(H2O)]2can be used at optical material and biological fields.

Supplementary data:Crystallographic data for the structure reported in this paper are deposited in the Cambridge Crystallographic Data Center with CCDD reference number 1409015 for the complex.

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Synthesis,Characterization,Thermal Decomposition Mechanism and Properties of the[Eu(4-MOBA)3(terpy)(H2O)]2Complex

HUO Jian-Xia1,2SONG Su-Wei4JIN Cheng-Wei1,2REN Ning3,*GENG Li-Na2ZHANG Jian-Jun1,2,*
(1TestingandAnalysisCenter,HebeiNormalUniversity,Shijiazhuang050024,P.R.China;2CollegeofChemistry&MaterialScience, HebeiNormalUniversity,Shijiazhuang050024,P.R.China;3CollegeofChemicalEngineering&Material,HandanUniversity, Handan056005,HebeiProvince,P.R.China;4PetroChinaJingtangLNGCo.,Ltd.,Tangshan063210,HebeiProvince,P.R.China)

A new complex[Eu(4-MOBA)3(terpy)(H2O)]2(4-MOBA:4-methoxybenzoate,terpy:2,2′:6′,2′-terpyridine)was synthesized.The complex was characterized using Fourier transform infrared(FTIR) spectroscopy,elemental analysis,and powder X-ray diffraction(XRD).The structure of the complex was determined using single-crystal XRD.In the complex,each Eu3+ion is nine coordinated to one terpy molecule, one water molecule and three carboxylate groups.The carboxylate groups are bonded to the Eu3+ion in three modes:bidentate,bridging bidentate,and monodentate.Based on thermogravimetry-differential scanning calorimetry/Fourier transform infrared(TG-DSC/FTIR)measurements,we determined the thermal decomposition mechanism.The emission spectra of the complex exhibited characteristic luminescence,suggesting that terpy and 4-methoxybenzoic acid can act as sensitizing chromophores in this system.Also,bacteriostatic activities for the complex to Candida albicans and Escherichia coli are discussed.

Lanthanide complex;Crystal structure;Thermal decomposition mechanism;Luminescence; 2,2′:6′,2′-Terpyridine;Antimicrobial activity

December 29,2015;Revised:February 15,2016;Published on Web:February 17,2016.*Corresponding authors.ZHANG Jian-Jun,Email:jjzhang6@126.com.REN Ning,Email:ningren9@163.com;Tel:+86-31180786457. The project was supported by the National Natural Science Foundation of China(31201305，21473049)and Natural Science Foundation of Hebei Province,China(B2016205207).

O642

10.3866/PKU.WHXB201602173

國家自然科學基金(31201305,21473049)和河北省自然科學基金(B2016205207)資助項目