YANG Ying-Qun LI Yu-Lin

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Synthesis, Fluorescence and Magnetic Properties of a New Europium(Ⅲ) Complex Eu(C14H9O3)2(C12H8N2)2(NO3)①

YANG Ying-Qun②LI Yu-Lin②

(421008)

A new europium(III) complex Eu(C14H9O3)2(C12H8N2)2(NO3)has been synthesized with 2-benzoylbenzoic acid and 1,10-phenanthroline as ligands. Crystal data for the complex are as follows: monoclinic, space group21/,= 9.6733(6),= 22.9521(14),= 19.7701(12) ?,= 94.9800(10)o,= 4372.8(5) ?3,D= 1.557 g/cm3,= 4,(Mo) = 1.501 mm-1,(000) = 2064, the final= 0.0214 and= 0.0510. The Eu(III) ion is coordinated by ten atoms to give a bicapped square antiprism coordination geometry. The complex shows two intense fluorescence emission bands arising from the transitions of Eu3+:50→71(594 nm) and50→72(618 nm). In addition, itsdecreases from 1.29767cm3×mol-1×K at300 K to 0.01531cm3×mol-1×K at 2 K.

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

1 INTRODUCTION

In recent years, lanthanide organic framework complexes have captured the extensive interest of researchers not only because of their intriguing topological structures but also of their potential applications in a wide variety of fields, such as luminescence, magnetism and catalysis[1-6]. It is well-known that lanthanide ions have higher coordination numbers, more flexible coordination geometries, large radius and high affinity for oxygen atom. A lot of lanthanide complexes have been constructed with aromatic carboxyl acids which have variable coordination modes and strong coordination ability[7-10]. Nowadays, in this field, much attention has been focused on Eu(III) com- plexes possessing novel structures and proper- ties[11-15].2-Benzoylbenzoate acid is an important aromatic carboxylic acid, and lanthanide complexes with 2-benzoylbenzoate acid and its derivativesas ligands have been reported in the literature[16-18].

We once synthesized and reported one Eu(III) complex Eu(L)3(Phen)2[19]with 2-benzoylbenzoate acid. Subsequently, we accidentally obtained in an experiment one new complex Eu(C14H9O3)2(C12H8N2)2(NO3), the structure of which is similar to that of Eu(L)3(Phen)2. With great interest, we determined its structure by X-ray diffraction and further measured its fluorescent and magnetic properties, and the results are reported herein.

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.Magnetic measurements in the range of2～300 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). A fluorescencespectrum was obtained at room temperature on a WGY-10 fluorescence spectrophotometer.

2.2 Synthesis of the complex

A mixture of 2-benzoylbenzoic acid (0.47 mmol), 1,10-phenanthroline (0.43 mmol) and europium(III) nitrate hexahydrate (0.21 mmol) was dissolved in 7 mL mixed solvent of N,N-dimethylformamide and water (volume ratio 5:2). The pH value of the solution was adjusted to about 6.5 by adding 0.05 mL sodium hydroxide solution (1 mol×L-1). The mixture was heated under a water-bath at 323 K for 8 h. Afterwards, the mixture was filtered, and the filtrate was put at room temperature for slow volatilization. Colorless single crystals suitable for X-ray diffraction analysis were obtained after five weeks. Yield: 40.2%. Anal. Calcd. (%) for Eu(C14H9O3)2(C12H8N2)2(NO3): C, 60.95; H, 3.34; N, 6.83. Found (%): C, 60.89; H, 3.33; N, 6.82.

2.3 Structure determination and refinement

The X-ray diffraction measurement for the com- plex was carried out on a Bruker SMART APEX CCD area detector at 296(2) K by using graphite- monochromatized Mo(= 0.71073 ?) radiation. The structure was solved by direct methods and refined by a full-matrix least-squares technique using the SHELXS-97 and SHELXL-97 programs[20]. 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= 0.0214 and= 0.0510 (= 1/[2(F2) + (0.0265)2+ 1.3703], where= (F2+ 2F2)/3), (?/)max= 0.003 and= 1.012.

3 RESULTS AND DISCUSSION

3.1 Structural description

Fig. 1 shows the molecular structure of the complex. Fig. 2 displays the coordination polyhe- dron for the 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 at 30% displacement ellipsoids with atomic numbering (All hydrogen atoms are omitted for clarity)

Fig. 2. Bicapped square antiprism coordination geometry of the central Eu(III) ion of the title complex

As shown in Fig. 1, the complexconsists of one central Eu(III) ion, two 2-benzoylbenzoic acid anions, two 1,10-phenanthroline molecules and one nitrate anion. Eu(III) ion is coordinated by six oxygen atoms from two 2-benzoylbenzoic acid anions and one nitrate anion, respectively, and four nitrogen atoms from two 1,10-phenanthroline molecules. In contrast to the Eu(III) of complexEu(L)3(Phen)2which has a single-capped square antiprism coordination geometry, the Eu(III) ion of the title complex adopts a distorted bicapped square antiprism coordination geometry (Fig. 2) because a 2-benzoylbenzoic acidanion is replaced by a nitrate anion.In the coordination geometry of the title complex, the two cap positions are occupied by N(1) and N(3) atoms. Atoms O(2), O(8), N(2) and O(4)give the upper plane of the square antiprism, and atoms O(1), O(7), O(5) and N(4) determine the plane below.Their dihedral angle of the two planes is 1.6o. The bond lengthsof Eu(1)–N(1), Eu(1)–N(3), Eu(1)–N(2) and Eu(1)–N(4) are2.6515(18), 2.689(2), 2.643(2) and 2.591(2)?, respectively. The bond angles N(1)–Eu(1)–N(3), O(7)–Eu(1)–O(1), O(5)–Eu(1)–O(1),O(1)–Eu(1)–N(4), O(5)–Eu(1)– O(7), O(7)–Eu(1)–N(4)and O(5)–Eu(1)–N(4)are171.24(6)o, 74.07(8)o, 133.78(6)o, 73.60(7)o, 96.11(6)o, 130.16(7)o and 80.38(7)o, respectively.Owing to the occupancy of N(1) and N(3) in capping positions,Eu(1)–N(1) and Eu(1)–N(3)are longer than the other Eu–N bonds, and the bond angle of N(1)–Eu(1)–N(3) is larger than the other angles. The above bond features are characteristic of this typeof polyhedron. The bond lengths Eu(1)–O(1),Eu(1)–O(2), Eu(1)–O(4),Eu(1)–O(5),Eu(1)–O(7) and Eu(1)–O(8) are 2.4864(18), 2.4530(16),2.5296(17), 2.4284(17), 2.4857(19) and 2.5473(18)?, respectively with their average to be 2.4884?, which falls in the normal range.

3.2 Fluorescent property

The fluorescent properties of the complex in the solid state were measured at room temperature in the range of 550～670 nm. The emission spectrum is shown in Fig. 3. As shown in Fig. 3, when the excitation wavelength is 315 nm, the complexexhibits one emission band at 594 nm and one stronger band at 618 nm, which corresponds to the transitions of Eu3+:50→71and50→72, respectively. They are the characteristic fluorescence peaks ofEu(III) ion. Besides, the fluorescence intensity of the title complex is weaker than that of the complex Eu(L)3(Phen)2. We attribute this difference in fluorescence intensity to their different structures, because the ligands 1,10-phenanthroline molecule and 2-benzoylbenzoic acid anion can transmit energy more effectively than the nitrate anion.

Fig. 3. Fluorescence emission spectrum of the title complex at room temperature

3.3 Magnetic properties

The magnetic susceptibility of the complexwas investigatedfrom 2 to 300 K with an applied magnetic field of 2 kOe. The temperature depen- dence of the molar magnetic susceptibility of the title complex is revealed in Fig.4in the forms ofXT and 1/X..As shown in Fig. 4, thevalue ofdecreases from 1.29767cm3×mol-1×K at 300 K to 0.01531cm3×mol-1×K at 2 K. In addition, thedata in the temperature range of 160～300 K are in linear relationship in the form of 1/. The linear regression equation is 1= 0.3913+ 114.09, and the correlation coefficient is 0.9978. Such magnetic behavior is the ressult of electrons leaving the excited state.

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

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13 June 2018;

5 September 2018 (CCDC 994408)

① This project was supported by the Construct Program of the Key Discipline in Hunan Province

E-mails: yingqunyq@163.com and liyuling18@126.com

10.14102/j.cnki.0254-5861.2011-2110