научная статья по теме SYNTHESIS, CRYSTAL STRUCTURE, AND LUMINESCENCE PROPERTIES OF A ONE-DIMENSIONAL EUROPIUM(III) POLYMER Химия

Текст научной статьи на тему «SYNTHESIS, CRYSTAL STRUCTURE, AND LUMINESCENCE PROPERTIES OF A ONE-DIMENSIONAL EUROPIUM(III) POLYMER»

КООРДИНАЦИОННАЯ ХИМИЯ, 2009, том 35, № 1, с. 32-36

УДК 541.49

SYNTHESIS, CRYSTAL STRUCTURE, AND LUMINESCENCE PROPERTIES OF A ONE-DIMENSIONAL EUROPIUM(III) POLYMER

© 2009 H. Zhong1, 2*, H. L. Xie2, and S. H. Duan2

Provincial Key Laboratory of Coordination Chemistry, Jinggangshan University, Jian, 343009, PR. China 2College of Chemistry and Chemical Engineering, Jinggangshan University, Jian, 343009, PR. China

*E-mail: hua_zh@163.com Received January 30, 2008

In the title complex [Eu2(C8H7O3)6(C12H8N2)2]n, which has an inversion center midway between two Eu(III) atoms of the structural unit, forms a one-dimensional polymer bridged by two mondentate, two bidentate, and two tridentate carboxylate groups with an Eu-Eu separation of 4.1853 (7) A. Each Eu atom is nine-coordinated by two N atoms of a 1,10-phenanthroline (Phen) ligand and seven O atoms from six phenoxyacetate ligands, to form a distorted tricapped trigonal prismatic. The luminescence spectrum of the polymer indicates that the intensity of the emission wavelength at 619 nm is the strongest among all emission wavelengths and the second Phen ligand shows an enhancement effect on the luminescence of the complex.

INTRODUCTION

As well as known, owing to the lanthanides exhibiting large radii, high coordination numbers and special luminescence properties, a growing attention has been paid to the investigation of lanthanide coordination polymers [1-5]. Ligands coordinating with lanthanides play an important role during emission process, so, in recent years, many ligands containing bi- or multidentate oxygen, nitrogen, or sulfur donors have been used to build lanthanide coordination polymers [6-8]. Among the ligand systems, one ligand containing carboxylate groups is popularly used in synthetic systems for the construction of polymeric structures because of their various coordination modes to metal cations, such as monodentate, chelating bidentate, bridging bidentate, and bridging tridentate [9]. This proved lanthanide(III) aromatic carboxylates display good luminescence properties due to the high efficiency of light conversion of aromatic carboxylic groups [10], and another bidentate chelating ligand like 1,10-phenanthroline or dipy-ridine with symmetric and conjugated structure can not only result in the effective intramolecular energy transfers from the excited state of the ligands to the emitting level of the lanthanide ions, but also prevent the coordination of water molecules with O-H vibration to quench the luminescence of lanthanide ions [11-12]. However, most of reported lanthanide coordination polymers are hydrated and/or contain inner coordinated water molecules [13-15]. Considered Eu(III) has more excellent luminescence properties in their ternary complexes with aromatic acids and ligands containing nitrogen than their carboxylate hydrates. The aim of this work is to prepare and study the luminescence properties of the anhydrous mixed lanthanides complexes with phenoxyacetate and 1,10-phenanthroline. Herein, we report the solvothermal synthesis, structural

features, and luminescence properties of a novel lanthanide coordination polymer [E^^H^^C^^^]« (I).

EXPERIMENTAL

Apparatus and reagents. All the reagents and solvents from commercial sources were of AR grade purity. Element analysis of carbon, hydrogen, and nitrogen was performed with a Flash-EA1112 elemental analyzer. The emission and excitation spectra of the samples were obtained using a Perkin-Elmer LS 55 luminescence spectrometer with a Xe flash lamp at room temperature. The excitation and emission slits were set at 2.5 nm. The excitation spectra were automatically corrected for the variation in the lamp intensity by a second photomultiplier and a beam-splitter. The emission spectra were corrected by dividing the measured emission intensity by the ratio of the observed spectrum of a calibrated W-lamp and its known spectrum from 300 to 900 nm. All of the spectra were measured with a scan speed of 1000 nm/min.

X-Ray diffraction analysis. A yellow single crystal with dimensions of 0.32 x 0.13 x 0.08 mm was selected for diffraction analysis. Data collection was performed on a Bruker APEX-II CCD area-detector diffractometer equipped with a graphite-monochromatized Mo^a radiation (k = 0.71073 A) at 273(2) K. A total of 26 800 reflections were collected by using an rn-20 scan mode, of which 7358 were unique with Rint = 0.0426 and used in the succeeding structure calculations. Data intensity was corrected by the Lorentz polarization factors and empirical absorption. The non-hydrogen atoms were solved by direct methods and subsequent difference Fourier synthesis. The hydrogen atoms were calculated in ideal positions and refined with a riding model. The final cycle of full-matrix least-squares refinement was based on 4933 observed re-

Table 1. Selected bond lengths (A) and bond angles (deg) in I*

Bond d, À Bond d, À Bond d, À

Eu(1)—O(1) 2.497(3) Eu(1)—O(2)1 2.554(3) Eu(1)—O(4) 2.408(3)

Eu(1)—O(5)11 2.537(4) Eu(1)—O(7) 2.533(3) Eu(1)—O(8) 2.802(4)

Eu(1)—O(8y 2.389(4) Eu(1)—N(1) 2.701(5) Eu(1)—N(2) 2.701(5)

Angle œ, deg Angle œ, deg Angle œ, deg

O(1)Eu(1)O(4) 146.00(12) O(1)Eu(1)O(7) 73.40(12) O(1)Eu(1)O(8) 65.74(11)

O(4)Eu(1)O(7) 138.94(12) O(4)Eu(1)O(8) 139.13(11) O(7)Eu(1)O(8) 47.78(10)

O(1)Eu(1)N(1) 127.86(12) O(4)Eu(1)N(1) 76.50(13) O(7)Eu(1)N(1) 64.21(12)

O(8)Eu(1)N(1) 102.26(13) O(1)Eu(1)N(2) 79.81(13) O(4)Eu(1)N(2) 97.28(12)

O(7)Eu(1)N(2) 74.65(12) O(8)Eu(1)N(2) 118.24(11) N(1)Eu(1)N(2) 61.26(15)

O(1)Eu(1)O(2)1 129.29(12) O(1)Eu(1)O(5)11 68.68(12) O(2)Eu(1)O(8)1 65.54(11)

O(4)Eu(1)O(2)1 74.83(11) O(4)Eu(1)O(5)11 78.17(12) O(5)11Eu(1)O(2)1 142.28(12)

O(5)11Eu(1)O(8) 129.73(12) O(7)Eu(1)O(2)1 84.25(12) O(7)Eu(1)O(5)11 132.73(11)

O(8)1Eu(1)O(1) 78.64(12) O(8)1Eu(1)O(2)1 74.56(12) O(8)1Eu(1)O(4) 87.84(13)

O(8)1Eu(1)O(5)11 78.61(13) O(8)1Eu(1)O(7) 120.35(13) O(8)1Eu(1)O(8) 72.81(14)

O(2)1Eu(1)N(1) 76.04(13) O(5)11Eu(1)N(1) 122.26(14) O(8)1Eu(1)N(1) 149.41(13)

O(2)1Eu(1)N(2) 137.14(14) O(5)11Eu(1)N(2) 71.82(14) O(8)1Eu(1)N(2) 148.15(14)

* Symmetry codes: 1 - x + 2, —y, —z + 2; 11 - x + 2, —y + 1, —z + 2; 111 —x + 3/2, y + 1/2, —z + 3/2; lv x, y - 1, z (see in Table 2 too).

flections (I > 2a(I)) and 403 variable parameters and converged with weighed agreement factors. The final refinement including hydrogen atoms converged to 0.0478 and

wR = 0.1371 (w = 1/[a2 (f2) + (0.0939P)2 + 0.7782P], where P = (f2 + 2 F2C) /3), S = 0.999, (A/a)max = 0.002, (Ap)max = 1.132 and (Ap)min = -0.867 e A-3. All calculations were performed with SHELXTL-97 program package [16].

Synthesis of the complex. Crystals of the title complex were synthesized using the solvothermal method in a 23-ml teflon-lined Parr bomb, which was then sealed. Anhydrous europium(III) chloride (258.5 mg, 1 mmol), Phen (198.2 mg, 1 mmol), phenoxyacetate (302.2 mg, 2 mmol), and tetrahydrofuran (10 ml) were placed into the bomb and sealed. The bomb was then heated under autogenous pressure up to 413 K over the course of 7 days and allowed to cool at room temperature for 24 h. Upon opening the bomb, a clear colorless solution was decanted from small yellow crystals. These crystals were washed with ethanol and allowed to air-drying at room temperature. The yield, as calculated with respect to the europium chloride, was 45.3%.

For C72H58Eu2N4O18

anal. calcd, %: C, 54.99; H, 3.69; N, 3.56.

Found, %: C, 55.06; H, 3.72; N, 3.59.

RESULTS AND DISCUSSION

Complex I crystallizes in monoclinic crystal system, space group P2x/n with a = 19.8127(11), b = 8.4405(16), c = 21.0036(14) A, p = 108.017(3)°, V = 3340.2(7) A3, C^E^^O^, Mr = 1571.14, Z=2, pCaM = 1.562 g/cm3, p = 1.936 mm-1, F(000) = 1576. The molecule of I features a dinuclear structure and the Eu atoms are bridged by two tridentate, two bidentate, and four monodentate carbox-ylate groups with an inversion center between the two Eu3 ions. Eu(1) is coordinated by one Phen ligand via N(1) and N(2) atoms, two bridging bidentate phenoxyacetate ligands via O(1) and O(2)i, two bridging tridentate phe-noxyacetate ligands via O(7), O(8), and O(8)i, and two chelating mondentate phenoxyacetate ligands via O(4) and O(5)ii with a distorted tricapped trigonal prism geometry (Fig. 1). The quadrangular faces are defined by two nitrogen atoms from the chelating Phen ligand, one carboxylate oxygen atom from the bidentate phenoxyacetate ligand, and the other carboxylate oxygen atom from the tridentate phenoxyacetate ligand (O(2)i, O(8)i, N(1), and N(2)) with a mean deviation of 0.2752 A from the least-squares plane. The two N atoms and two C atoms of Phen and one Eu atom make up a five-membered ring with Eu-N bond distances of 2.694(4) and 2.701(5) A and an NEuN angle of 61.26(15)° (Table 1), which is one of the most stable structures and helps to stabilize the whole structure of the complex. The average Eu-N bonds of complex I (2.697 A) is slightly longer than those of [Eu(p-MOBA)3(Phen)] (2.624 A) and [Eu(DBM)3(Phen)] (2.656 A) [17, 18]. The Eu-O distances are in the range of 2.389(4)-2.802(4) A, which could be that the carboxylate groups are bound

C(17) C(16)

C(26)

C(21) O(4) O(6)

C(28) C(10)

C(22) C(23C)C(7(8)) 27) C(24) C(5) V

Fig. 1. Molecular structure of the complex I with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level (symmetry codes: (i) -x + 2, -y, -z + 2; (ii) -x + 2, -y + 1, -z + 2; (iii) x, y - 1, z). All H atoms are omitted for clarity.

to the Eu3+ ions in three different coordination fashions. This shows that there is a different degree of electron delocalization in the area of O-C-O atoms. The average of the bridging bidentate Eu-O bonds (2.525(8) A) is slightly shorter than that of the bridging tridentate Eu-O bonds (2.575(3) A), which in turn is longer than the average of the chelating mondentate Eu-O bonds (2.472(8) A). The Eu-O bonds in I are longer than the equivalent bonds in the reported coordination com-

pound [

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