Synthesis and Fluorescent and Magnetic Properties of a New Europium Complex Eu(C20H14O3N)3(2,2?-bipy)(H2O)·H2O①

YANG Ying-Qun KUANG Yun-Fei ZHU Xiao-Ming

Synthesis and Fluorescent and Magnetic Properties of a New Europium Complex Eu(C20H14O3N)3(2,2?-bipy)(H2O)·H2O①

YANG Ying-Quna,b②KUANG Yun-Feia, b②ZHU Xiao-Minga, b②

a(o421008)b(421008)

europium(Ⅲ) complex, crystal structure, fluorescent and magnetic properties;

1 INTRODUCTION

Although the high and variable coordination numbers and flexible coordination environments of lanthanide ions make it difficult to controlthe reactions and the final structures of lanthanide complexes, the lanthanide organic frameworks have goodoptical, electrical and magnetic properties such as high color purity, long fluorescence lifetime, high efficiency of light conversion and wide emission spectrum wavelength distribution, and the design of novel lanthanide organic frameworks has attracted much attention inthe field of crystal engineering[1-9].It is wellknown that the aromatic carboxylic acid ligandsplay an important role in constructing novel andstable lanthanide organic frameworks mainlybecause of the versatile ligating abilities of -COOmoieties including bidentate-chelating, bidentate-bridging orchelating-bridging modes, and also due to theenhanced affinity of lanthanide ions towards such Odonors, which allows the formation of clusters,cage structures or open frameworks[10-15].Among diverse aromatic carboxylic acid ligands, 2-diphenylanine carbonyl benzoic acid and its derivatives can bewidely used as multidentate ligands to synthesize various complexes,such as Tb(HDPAB)3IP[16]and C32H25NO3Sn·C7H8[17].With the aim of proceeding previous jobs[18], we report herein a new lanthanide complex Eu(C20H14O3N)3(2,2?-bipy)(H2O)·H2O based on2-diphenylanine carbonyl benzoic acid.The complex shows two intense fluorescence emission bands arising from the transitions of Eu3+:50→71(592 nm) and50→72(616 nm), respectively.In the temperature range of 300～2 K, the complex exhibitsantiferromagnetism.

2 EXPERIMENTAL

2.1 Reagents and instruments

The reagents were obtained from commercial sources and used without further purification.C, H and N analyses were conducted with a PE-2400(II) apparatus.A fluorescencespectrum was obtained at room temperature on a HORIBA QuantaMaster 8000 fluorescence spectrophotometer.Magne-tic measurements in the range of 300～2 K were performed on a MPMS-SQUID magnetometer at a field of2 kOe on a crystalline sample in the temperature settle mode (1 kOe = 7.96 × 104A×m-1).

2.2 Synthesis of the complex

A mixture of 2,2?-bipyridine (0.25 mmol) and europium(Ⅲ) nitrate hexahydrate (0.10 mmol) was dissolved in 9 mL mixed solvent of ethanol and water (volume ratio 2:7), and heated under a water-bath at 323 K for 0.5 h.The solution was poured into a glass test-tube.Then 5 mL ethanol solution with pH 5～6 containing sodium hydroxideand 2-diphenylanine carbonyl benzoic acid (0.15 mmol) was added to this test-tube whichwas covered with plastic film.The mixture was put at room temperature for slow diffusion.Colorless single crystals suitable for X-ray diffraction analysis were obtained after three weeks.Yield: 30.2%.Anal.Calcd.(%) for C70H54EuN5O11: C, 65.01; H, 4.21; N, 5.41.Found (%): C, 64.94; H, 4.20; N, 5.40.IR(/cm–1): 1649(vs), 1589(vs), 1551(s), 1489(s), 769(m), 700(m), 619 (w), 542 (w), 442 (w), 420 (w).

2.3 Structure determination and refinement

The X-ray diffraction measurement for the complex was carried out on a Bruker SMART APEX CCD area detector at 100.00(10) K by using graphite-monochromatized Mo(= 0.71073 ?) radiation.The structure was solved by direct methods and refined by full-matrix least-squares with the SHELXL-2015 program package[19].Corrections forfactors and empirical adsorption adjustment were applied and all non-hydrogen atoms were refined with anisotropic thermal parameters.The final refinement including hydrogen atoms converged to= 0.0447 and= 0.0578(= 1/[2(F2) + (0.0078)2], where= (F2+ 2F2)/3), (?/)max= 0.002 and= 0.959.

3 RESULTS AND DISCUSSION

3.1 Structural description

Fig.1 shows the molecular structure of the complex and the coordination polyhedron for the central Eu(III) ion.Selected bond lengths and bond angles are listed in Table 1.

Table 1.Selected Bond Lengths (?) and Bond Angles (°) of the Complex

Fig.1.Molecular structure of the title complex and the coordination polyhedron for the Eu(III) ion at 30% displacement ellipsoids

As shown in Fig.1, the complex consists of one central Eu(III) ion, three 2-diphenylanine carbonyl benzoic acid anions, one 2,2?-bipyridine molecule and two water molecules.Eu(III) ion is coordinated by seven oxygen atoms from three 2-diphenylanine carbonyl benzoic acid anions and one water molecule, respectively, and two nitrogen atoms from one 2,2?-bipyridine molecule.The central Eu(III) ion adopts a distorted monocapped square antiprism coordination geometry.In the coordination polyhedron (EuN2O7), the cap position is occupied by O(1) atom.Atoms N(1), N(2), O(10) and O(2) give the upper plane of the square antiprism, and atoms O(8), O(5), O(4) and O(7) determine the plane below.Their plane equations are 2.800+ 15.838+ 6.925= 14.5218 and 3.235+ 15.747+ 5.430= 16.0981, respectively.The dihedral angle of the two planes is 6.0o.The O–Eu–O angles are between 53.36(8) and 152.70(9)o, and the N–Eu–Oanglesrange from 70.96(10)to153.73(9)o.The Eu–O bond lengths change from2.379(3) to 2.525(3) ?, and their average is 2.459?, which falls in the normal range[20].

Compared with Tb(HDPAB)3IP[16]synthesized by the same ligand 2-diphenyl carbonyl benzoic acid, the title complex with water molecules contains extensive hydrogen bonds, which is conducive to the stability of the complex.The bond lengths of O(10)–H(10A)···O(1), O(10)–H(10A)···O(3), O(10)–H(10B)···O(11), O(11)–H(11A)···O(9) and O(11)–H(11B)···O(9) are2.665(5), 3.315(4), 2.695(4), 2.898(4) and 2.784(4) ?, respectively.Their bond anglesare102, 145, 142, 174 and 147o, respectively.In addition,stacking interaction can be observed between adjacent 2,2?-bipy molecules in the title complex, and the shortest centroid-to-centroiddistance is 3.495 ? (Fig.2).

Fig.2.-stacking of the neighboring molecules

3.2 Fluorescent property

The complex and 2-diphenylanine carbonyl benzoic acidligand were dissolved in a mixture of ethanol and water (volume ratio of 5:1), respectively.The fluorescent properties of these two solutions were measured at room temperature in the range of 357～675 nm.The emission spectra of the complex and 2-diphenylamine carbonylbenzoic acid ligand are shown in Fig.3.As shown in Fig.3, under 349 nm excitation, 2-diphenylamine carbonylbenzoic acid ligand shows one wide fluorescence emission bandin the range of 360 to 395 nm.When the excitation wavelength is 396 nm, the complex shows two intense fluorescence emission bands at 592 and 616 nm, corresponding to the transitions of Eu3+:50→71and50→72, respectively.They are the characteristic fluorescence peaks of Eu(Ⅲ) ion, and the fluorescence is stronger at 616 nm.

3.3 Magnetic properties

The magnetic susceptibility of the complex was investigatedin the temperature range of 300～2 K with an applied magnetic field of 2 kOe.The temperature dependence of the molar magnetic susceptibility of the complex is revealed in Fig.4in the forms ofXT and 1/X..The product ofXT is 1.13666cm3×K×mol-1at 300 K.Upon cooling, theXT gradually decreases to the corresponding product of 0.01733cm3×K×mol-1at 2 K.In addition, as shown in Fig.4, in the temperature range of 300～150K,thedata are in linear relationship in the form of 1/.The linear regression equation is 1/=0.419+134.18, and the correlation coefficient is 0.9907.According tothe Curie-Weiss law,X=/(?), the Weiss constant () can be obtainedasnegative value.Suchmagnetic behavior indicates that the title complex isan antiferromagnetism system at low temperature[21].

Fig.3.Both excitation and emission spectra of the complex at room temperature

Fig.4.Temperature dependence of the magnetic susceptibility of the complex in the form ofXT and 1/X.

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24 August 2020;

10 October 2020 (CCDC1848487)

① This project was supported by the Foundation of Key Laboratory of Functional Metal-organic Compounds of Hunan Province (MO20K05), and the Foundation of Key Laboratory of Functional Organometallic Materials,University of Hunan Province

E-mail: yingqunyq@163.com or zxmhnhy@163.com.

Yang Ying-Qun and Kuang Yun-Fei made equal contributions to this work

10.14102/j.cnki.0254–5861.2011–2969