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Structural diversity and luminescent properties of europium(III) complexes with acrylic acid ligands
Journal of Molecular Structure 891 (2008) 298–304
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Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Structural diversity and luminescent properties of europium(III) complexes with acrylic acid ligands Jun Yan, Yongmiao Guo, Hui Li *, Xiaoping Sun, Zhen Wang Department of Chemistry, College of Science, Beijing Institute of Technology, No. 5 South Street, Zhongguancun, Beijing 100081, PR China
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Article history: Received 1 February 2008 Received in revised form 29 March 2008 Accepted 31 March 2008 Available online 7 April 2008 Keywords: Europium complex Hydrogen bond Supramolecular architecture Acrylic acid
a b s t r a c t Three Europium complexes: [Eu(L1)3(H2O)2]2 (L1 = (E)-3-(2– hydroxyl-phenyl)-acrylic acid) (1), [[Eu(L2)3(H2O)]H2O (L2 = (E)-3-(3-hydroxyl-phenyl)-acrylic acid) (2), and [[Eu(L3)3(H2O)2] (L3 = (E)-3(4-hydroxyl-phenyl)-acrylic acid) (3) were synthesized and structurally analyzed by IR, elemental analysis, and the single-crystal X-ray diffraction method. Complex 1 adopts a dinuclear structure, while complexes 2 and 3 are a one-dimensional coordination polymer. The complex 2 possesses a helical H-bonding between the adjacent two chains with homochirality in crystalline solid state. All the complexes form a 3D supramolecular framework by O–HO hydrogen bonding and p–p interaction in the crystal lattices. The solid photoluminescence of the three complexes has also been investigated at room temperature. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction The carboxylate-type ligand is a kind of ubiquitous ligand in coordination chemistry. Lanthanide carboxylate complexes exhibit unusual structure and properties [1–6]. They have wide potential applications in material science [7–9]. Among these studies, the synthesis and characterization of europium(III) carboxylate complex is an area of current interest. Europium(III) complexes display rich luminescent properties coupled with long excited state lifetimes and narrow emission lines making them ideal components for fluorescent probes [10], electroluminescent devices [11], as well as photocatalysts [12]. Our work in this area is focused on looking at lanthanide complexes coordinated with a variety of ‘‘antenna” ligands. Acrylic acid ligands are new kinds of carboxylate ligand and the common feature in the structure of the ligands is the carboxylato group conjugated with benzene ring through C@C double bond, which makes the electronic density delocalized in the ligand. We have studied the structures of La(III) and Ho(III) complexes with the acrylic ligands [13,14]. The results have shown versatile coordination modes and interesting supramolecular chemistry. They coordinate La(III) ions to form 1D coordination polymers, while getting a dimeric complex with Ho(III) ions. To extend these studies, the Eu(III) complexes with the three ligands: [Eu1(L1)3(H2O)2]2 (L1 = (E)-3-(2– hydroxyl-phenyl)-acrylic * Corresponding author. Tel.: +86 10 82575113. E-mail address: [email protected] (H. Li). 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.03.050
acid) (1), [[Eu(L2)3(H2O)]H2O (L2 = (E)-3-(3-hydroxyl-phenyl)-acrylic acid) (2), and [[Eu(L3)3(H2O)2] (L3 = (E)-3-(4-hydroxylphenyl)-acrylic acid) (3) were prepared. Herein, we report their structures and solid-state luminescent properties. 2. Experimental 2.1. General All reagents were obtained from commercial sources and used without further purification. Infrared spectra were recorded as KBr pellets on a Nicolet 170SXFT/IR spectrometer. Excitation and emission spectra were obtained on a RF-5301PC spectrofluorometer equipped with a 450 W xenon lamp as the excitation source. Elemental analyses were carried out using Flash EA1112 microanalyzer. All measurements were performed at room temperature. 2.2. Synthesis 2.2.1. [Eu(L1)3(H2O)2]2 (1) A solution of EuCl36H2O (37.00 mg, 0.1 mmol) in 5 mL water was added to a solution of (E)-3-(2-hydroxyl-phenyl)-acrylic acid (49.00 mg, 0.3 mmol) and triethylamine (30.00 mg, 0.3 mmol) in 10 mL CH3OH. After stirring for half an hour, the reaction solution was filtered. Yellow needle single crystals suitable for single-crystal X-ray diffraction were obtained after 4 days by slow evaporation. Yield: 46.3 mg, 68.3% (based on Eu). Anal. Calc. for
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C27H25EuO11: C, 47.85; H, 3.69; N, 0.00. Found: C, 47.61; H, 3.75; N, 0.00. Selected IR (KBr cm 1): 3225, 1630, 1584, 1513, 1428, 1459, 748. 2.2.2. [Eu (L2)3(H2O)]H2O (2) A solution of EuCl36H2O (13.00 mg, 0.05 mmol) in 5 mL water was add with a solution of (E)-3-(3-hydroxyl-phenyl)-acrylic acid (25.00 mg, 0.15 mmol) and NaOH (6.00 mg, 0.15 mmol) in 5 mL CH3OH. After stirring for half an hour, the reaction solution was filtered. Colorless plate single crystals suitable for single-crystal Xray diffraction were obtained after 4 days by slow evaporation. Yield: 23.1 mg, 68.1% (based on Eu). Anal. Calc. for C27H27EuO12: C, 47.85; H, 3.69; N, 0.00. Found: C, 46.91; H, 3.78; N, 0.00. Selected IR (KBr cm 1): 3413, 1639, 1581, 1517, 1425, 1478, 729.
Table 2 Selected bond lengths and bond angles for 1 Eu1–O1i Eu1–O2 Eu1–O11 Eu1–O5 Eu1–O7
2.209(5) 2.361(6) 2.420(7) 2.436(6) 2.460(6)
Eu1–O8 Eu1–O10 Eu1–O1 Eu1–O4 Eu1–Eu1
2.506(7) 2.572(7) 2.575(6) 2.647(7) 3.9741(9)
O2–Eu1–O11 O2–Eu1–O7 O11–Eu1–O7 O5–Eu1–O7 O2–Eu1–O8 O5–Eu1–O8 O5–Eu1–O10 Eu1–O1–Eu1i
79.74(21) 151.58(21) 88.14(23) 74.32(23) 137.33(20) 122.91(21) 150.54(21) 112.1(2)
O7–Eu1–O10 O11–Eu1–O1 O5–Eu1–O1 O7–Eu1–O1 O8–Eu1–O1 O8–Eu1–O4 O10–Eu1–O4 O1–Eu1–O4
124.92(23) 124.82(21) 100.12(19) 146.67(20) 136.69(21) 131.63(22) 147.25(22) 73.30(22)
Symmetry codes: (i) 2 x,
2.2.3. [Eu(L3)3(H2O)2] (3) A solution of EuCl36H2O (37.00 mg, 0.1 mmol) in 5 mL CH3OH was add with a solution of hydrochloric acid (0.1 mL pH 1), and then mix with the solution of (E)-3-(4-hydroxyl-phenyl)-acrylic acid (49.00 mg, 0.3 mmol) and NaOH (12.00 mg, 0.3 mmol) in 10 mL CH3OH. And then stir for half an hour, meanwhile instill about 0.2 mL DMF. After stirring for another ten min, the reaction solution was filtered. Yellow block single crystals suitable for single-crystal X-ray diffraction were obtained after 4 days by slow evaporation. The Yield: 44.2 mg, 63.6% (based on Eu). Anal. Calc. for C27H25EuO11: C, 47.85; H, 3.69; N, 0.00. Found: C, 47.42; H, 3.65; N, 0.00. Selected IR (KBr cm 1): 3207, 1631, 1587, 1514, 1409, 1441, 732. 2.3. X-ray crystallography Single-crystal X-ray diffraction data were collected on Bruker SMART1000 CCD area detector with graphite monochromated molybdenum Mo-Ka radiation (k = 0.71073 Å) at a temperature of 293 ± 2 K. Unit-cell parameters were determined from automatic centering of 25 reflections and refined by the least-squares method. Crystallographic data are given in Table 1. Selected bond distances and angles are given in Tables 2–4. The diffraction data were corrected for Lorentz and polarization effects, and absorption (empirically from w scan data). No extinction correction was necessary for all complexes. All structures were solved by direct methods and refined using full-matrix least-squares techniques on F2 [15]. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms are located geometrically and refined by mixed methods.
y, 1 z.
Table 3 Selected bond lengths and bond angles for 2 Eu1–O5 Eu1–O2 Eu1–O7 Eu1–O16 Eu1–O10 Eu1–O3 Eu1–O8 Eu1–O4 Eu1–O11 O1–Eu2
2.340(39) 2.357(36) 2.385(47) 2.384(44) 2.461(32) 2.466(33) 2.487(49) 2.525(51) 2.592(46) 2.474(50)
012–Eu2ii 010–Eu2 Eu2–011 Eu2–04i Eu2–02i Eu2–012i Eu2–015 Eu2–09 Eu2–05 04–Eu2ii
2.475(30) 2.441(33) 2.335(40) 2.373(38) 2.466(50) 2.475(30) 2.475(46) 2.475(46) 2.551(46) 2.373(38)
O5–Eu1–O2 O5–Eu1–O7 O2–Eu1–O7 O5–Eu1–O16 O2–Eu1–O16 O7–Eu1–O16 O5–Eu1–O10 O2–Eu1–O10 O7–Eu1–O10
156.12(92) 118.43(91) 78.74(86) 79.27(62) 88.24(64) 80.36(81) 83.39(85) 87.94(86) 149.96(98)
O1–Eu2–O9 O12i–Eu2–O9 O15–Eu2–O9 O11–Eu2–O5 O4i–Eu2–O5 O10–Eu2–O5 O2i–Eu2–O5 O1–Eu2–O5 O12i–Eu2–O5
143.71(85) 86.97(85) 78.84(73) 68.59(83) 127.58(85) 140.73(90) 106.84(81) 138.67(82) 74.18(74)
Symmetry codes: (i)
1+x, y, z, (ii) 1+x, y, z.
3. Results and discussion 3.1. Description of crystal structures 3.1.1. [Eu(L1)3(H2O)2]2 (1) Each Eu(III) ion in complex 1 is coordinated with nine oxygen atoms in which seven oxygen atoms come from the L1 ligands and the other two from the coordinated water molecules (Fig. 1).
Table 1 Crystal data and structure for 1–3 Complex
1
2
3
Formula M Crystal system Space group a(Å) b(Å) c(Å) a/deg b/deg c/deg V/Å3 Z q (calculated) (g cm 3) l mm 1 h Range/deg Reflection Goodness-of-fit on F2 Final R indices (I > 2r(I)) R indices (all data)
C54H50Eu2O22 1354.86 Orthorhombic Pbcn 13.722(2) 21.885(2) 23.928(3) 90.00 90.00 90.00 7185.7(15) 4 0.626 0.895 1.75–25.01 6247/3857[R(int) = 0.0795] 1.096 R1 = 0.0606, wR2 = 0.1336 R1 = 0.1120, wR2 = 0.1691
C27H25EuO11 677.43 Triclinic P1 7.8480(16) 13.019(3) 13.636(3) 97.41(3) 97.25(3) 103.77(3) 1324.0(5) 4 6.797 9.718 1.53–28.34 7055/6444[R(int) = 0.0176] 1.092 R1 = 0.0249, wR2 = 0.0660 R1 = 0.0294, wR2 = 0.0697
C27H25EuO11 677.43 Monoclinic C2/m 14.839(12) 24.00(2) 11.538(9) 90.00 92.422(10) 90.00 4105(6) 4 2.202 3.135 1.77–28.60 12,677/4870[R(int) = 0.0986] 1.025 R1 = 0.0662, wR2 = 0.1561 R1 = 0.1560, wR2 = 0.2138
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Table 4 Selected bond lengths and bond angles for 3 Eu1–O7 Eu1–O10 Eu1–O1 Eu1–O11i Eu1–O14 Eu1–O5 Eu1–O13 Eu1–O4 Eu1–O11 Eu1–Eu2 Eu1–Eu1i Eu1–Eu2ii
2.330(8) 2.356(8) 2.389(9) 2.392(8) 2.431(9) 2.443(8) 2.545(14) 2.616(7) 2.836(8) 4.156(2) 4.358(4) 4.442(3)
Eu2–C1ii Eu2–Eu1ii O11–Eu1i O8–Eu2ii Eu2–Eu2ii Eu2–O2ii Eu2–O4 Eu2–O8 Eu2–O4ii Eu2–O2 Eu2–O15
3.238(13) 4.442(3) 2.392(8) 2.874(11) 0.915(1) 2.123(8) 2.251(7) 2.271(12) 2.445(7) 2.481(8) 2.591(18)
O7–Eu1–O14 O1–Eu1–O14 O10–Eu1–O5 O1–Eu1–O5 C1–O1–Eu1 C1–O2–Eu2ii C1–O2–Eu2 C10–O4–Eu2 C10–O4–Eu2ii C10–O4–Eu1 C19–O8–Eu2
139.24(28) 140.26(28) 147.94(25) 128.26(26) 135.55(81) 148.32(83) 137.45(81) 131.37(64) 143.40(66) 90.02(58) 103.09(92)
O8–Eu2–O7 O4ii–Eu2–O7 O2–Eu2–O7 O15–Eu2–O7 Eu2–O4–Eu1 C10–O5–Eu1 C19–O7–Eu1 C19–O7–Eu2 Eu1–O7–Eu2 C28–O10–Eu1 C28–O11–Eu1i
49.74(32) 125.79(24) 68.06(24) 68.26(43) 117.05(28) 100.40(63) 157.13(84) 74.18(73) 104.81(29) 107.38(75) 164.69(75)
Symmetry codes: (i) 1 x, 1 y, 2 z, (ii)
x, 1 y, 2 z.
The coordination geometry of Eu(III) is a distorted tricapped trigonal prism. One of the ligands is in disorder. All the L1 ligands coordinate Eu(III) ions in bidentate mode. There are two g3-O bridges linking Eu(III) to form the dimeric neutral complex. The distance between Eu(III) is 3.974 Å. The distance is shorter than that between Ho(III) ions in the corresponding complexes [14]. The band lengths of Eu(III)–O are ranged in 2.209–2.647 Å. The shortest bond lengths are bound in g3–O carboxylato bridge, and the longest bond appears in the bidentate chelate mode. The bond angle of Eu–O1–Eui is 112.1°. These dimeric molecules of 1 are assembled into a 3D supramolecular network via hydrogen bonds among the hydroxylato group and carboxylato oxygen atoms in the ligand. Fig. 2 shows a 2D square network by the H-bond between
the adjacent molecules. The details of H-bond are O9O7A, 2.779 Å, and O6O8B, 2.962 Å. Further, the 2D layer is extended to 3D network by strong hydrogen bonding (O3O5, 2.465 Å) (Fig. 3). Obviously, the 1D channel with a dimension around 13.22 Å can be found along a axis, and there is no solvent molecule located in the channel. The coordinated water molecules do not form H-bonding because of steric hindrance of the ligand in the complex. 3.1.2. [Eu (L2)3(H2O)]H2O (2) Different from the complex 1, the Eu(III) ions in the complex 2 are linked by the ligand L2 to form 1D coordination polymer (Fig. 4). Each Eu(III) ion is still nine coordinated by oxygen atoms with only one coordination water molecule and the remain from the L2. The coordination geometry of Eu(III) is a distorted tricapped trigonal prism. The bond length of Eu-O in the complex is 2.340– 2.592 Å. All the bridge ligands between Eu(III) ions are in g3-O type of carboxylato ligand. However, the hydrogen bonds formed by the coordination water molecule and the carboxylato oxygen atoms in the ligands are different with 2.777 Å (O16BO12A) and 2.786 Å (O15O3B), respectively, which are arranged along the chain alternatively. As a result, the 2 is an alternative chain with distances of Eu–EuA (4.067 Å) and Eu–EuB (4.037 Å). It is the second example of the alternative chain constructed by H-bonding as the cooresponding complex with La(III) [13]. The dihedral angle between the two adjacent planes including the two Eu(III) atoms and two bridging O atoms: 90.5°. In the crystalline lattice, the 1D coordination polymer of 2 is linked by intermolecular hydrogen bonding between the hydroxylato group and carboxylato oxygen atoms in L2 along 2D and 3D directions (O31O10, 2.665Å; O19O2O, 2.647 Å; O21O8, 2.638 Å; O18O1, 2.741 Å). From the 3D packing picture of 2 (Fig. 5), the benzene rings of L2 are packed and occupied in the channel along a axis. The distance between the centers of the adjacent benzene ring is 4.03 Å and the distance of two planes is 3.60 Å. The p–p interaction stabilizes the structure further.
Fig. 1. ORTEP diagram (50% probability) of 1 (hydrogen atoms have been omitted for clarity.) (white and black).
J. Yan et al. / Journal of Molecular Structure 891 (2008) 298–304
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Fig. 2. The 2D H-bonding framework of 1 (white and black).
Fig. 3. The 3D H-bonding framework of 1. The picture (right) is space-filling figure showing the vacant 1D channel (white and black).
The significant point of the structure is its chiral space group, P1. The reason is that interchain hydrogen-bonding along 2D and 3D directions is homo-helical (Fig. 5). Based on the topological position of the hydroxylato group in L2, the angle between it and carboxylato group is 120°. It is favored to form the helical structure. 3.1.3. [Eu(L3)3(H2O)2] (3) In complex 3, there are two kinds of coordination environments of Eu(III). Eu1 and Eu2 are eight coordinated and Eu1A and Eu1B are nine coordinated with oxygen atoms. The Eu2 is in a little disorder. Three L3 bridge ligands linked Eu1 and Eu2 ions. Two of them are g2–O type and another one is g3-O carboxylato bridge. The bridge mode between the Eu2 and Eu1B is similar. However, the Eu1 and Eu1A are linked by two g3-O carboxylato bridge ligands. Comparing with 2, the bridging modes between the Eu(III) ions in 3 are different along the chain (Fig. 6). So, it is definitely an alter-
native chain in which the distance of Eu1–Eu2 and Eu2–Eu1B is 4.156 Å and Eu1–Eu1A is 4.358 Å. To the best of our knowledge, the novel infinite alternative chain in [Eu1B–Eu2–Eu1–Eu1A]n mode has not been reported previously. The two g2–O bridges in the chain are in different configuration: the O1–C1–O2 bridge is in syn–syn configuration, and the O7–C19–O8 bridge is in syn–anti configuration. The bond lengths of Eu–O are between 2.330 and 2.836 Å, which fall in the normal scale [16–21]. Also, there are three kinds of intrachain hydrogenbonding alternatively (O15O2(2.521 Å); O14O1(2.703 Å); O7O13 (2.799 Å)). 3.2. Photoluminescent properties of three complexes The luminescences of these three complexes were investigated. All the excitation spectrums show that this kind of complex have a strong absorb near 280 nm, which due to the p–p* transition of
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Fig. 4. The 1D chain structure of 2 (Eu1A–Eu2: 4.037 Å; Eu1B–Eu2: 4.067 Å). Hydrogen atoms have been omitted for clarity (white and black).
Fig. 5. The 3D packing picture of 2. The homo-helical hydrogen bonding in 2 (right-down).
conjugated bond among carboxylato group, benzene ring and the C@C double bond in the ligand. Complex 1 and 2 emitted strongest red luminescence upon excitation at about 380 nm, and their photoluminescence spectra are similar except that the bands of 1 are weaker than those of 2 (Fig. 7). The characteristic transition of 5D0 7FJ (J = 0–4) of Eu(III) ions implies that the ligand-to-europium energy transfer is moderately efficient under the experimental coordinations [22]. The appearance of the symmetry-forbidden emission 5D0–7F0 at 580 nm indicates that Eu(III) ions occupy sites with low symmetry and without an inversion center [23]. This is in agreement with our single-crystal X-ray analysis. The 5D0–7F1 transition is a magnetic dipole transition, and its intensity varies with the crystal field strength acting on Eu(III) ions. On the other hand, the 5D0–7F2 transition is an electric dipole transition and is extremely sensitive to
the crystal field in the vicinity of Eu(III) ion. The intensity of the 5 D0–7F2 transition increases as the site symmetry of Eu(III) ions decreases. The intensity ratio I(5D0–7F2)/I(5D0–7F1) is about 4.2, which also suggests the noncentrosymmetric coordination environment of the Eu(III) ions in 1 [24]. On the other hand, the photoluminescence spectra of 3 show dual characteristic. The broad bands below 470 nm correspond to emission from the ligand itself, which is mainly due to a strong intraligand charge transfer (ILCT) from the donor hydroxylato group to the acceptor carboxylate group of the ligand [25]. The emission bond in 590 nm is due to 5D0–7F1 transition, while the bond in 617 nm for 5D0–7F2 transition of Eu(III) ion. As the luminescence of the ligand has not been fully quenched, the ligandto-metal energy transfer is inefficient for the triplet state energy that does not match the first excited energy level of the Eu(III) ions.
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Fig. 6. The 1D chain structure of 3 (white and black).
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The three-dimensional supramolecular frameworks built by Hbonding have been revealed. The homohelic H-bonding constructed by L2 ligand has been found in the crystalline solids of their complexes. The emission spectra demonstrate that the complexes, especially 2, might be good candidates for efficient luminescent materials.
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X-ray crystallographic data for complexes 1-3 in CIF format can be obtained free of charge from the director, CCDC, 12 United Road, Cambridge, CB2, 1EZ, UK (Fax: +44 1223 336033; E-mail: [email protected]). The CCDC numbers for complexes 1, 2, and 3 are 657913, 657914, and 657915, respectively.
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Acknowledgments
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The Excitation spectrum of (3) This work was supported by the Natural Science Fund Council of China (NSFC No 20571011; No. 20771014), the Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry of China (LXKYJJ200408) and The University Basic Research Foundation of Beijing Institute of Technology (BIT-UBF, No 200507B4202).
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4. Conclusions In summary, the syntheses and crystal structures of a series of Europium complexes containing the acrylic acid ligand have been reported, and their solid-state luminescent properties have been discussed. The difference in the position of hydroxylato group in the L1 to 3 L brings the diversities both in the coordination complexes and in the supramolecular interactions in the crystal lattices. The dinuclear complex and alternative chains have been obtained. The [Eu1B–Eu2–Eu1–Eu1A]n mode in the alternative chain has been found for the first time.
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Structural diversity and luminescent properties of europium(III) complexes with acrylic acid ligands Jun Yan, Yongmiao Guo, Hui Li *, Xiaoping Sun, Zhen Wang Department of Chemistry, College of Science, Beijing Institute of Technology, No. 5 South Street, Zhongguancun, Beijing 100081, PR China
a r t i c l e
i n f o
Article history: Received 1 February 2008 Received in revised form 29 March 2008 Accepted 31 March 2008 Available online 7 April 2008 Keywords: Europium complex Hydrogen bond Supramolecular architecture Acrylic acid
a b s t r a c t Three Europium complexes: [Eu(L1)3(H2O)2]2 (L1 = (E)-3-(2– hydroxyl-phenyl)-acrylic acid) (1), [[Eu(L2)3(H2O)]H2O (L2 = (E)-3-(3-hydroxyl-phenyl)-acrylic acid) (2), and [[Eu(L3)3(H2O)2] (L3 = (E)-3(4-hydroxyl-phenyl)-acrylic acid) (3) were synthesized and structurally analyzed by IR, elemental analysis, and the single-crystal X-ray diffraction method. Complex 1 adopts a dinuclear structure, while complexes 2 and 3 are a one-dimensional coordination polymer. The complex 2 possesses a helical H-bonding between the adjacent two chains with homochirality in crystalline solid state. All the complexes form a 3D supramolecular framework by O–HO hydrogen bonding and p–p interaction in the crystal lattices. The solid photoluminescence of the three complexes has also been investigated at room temperature. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction The carboxylate-type ligand is a kind of ubiquitous ligand in coordination chemistry. Lanthanide carboxylate complexes exhibit unusual structure and properties [1–6]. They have wide potential applications in material science [7–9]. Among these studies, the synthesis and characterization of europium(III) carboxylate complex is an area of current interest. Europium(III) complexes display rich luminescent properties coupled with long excited state lifetimes and narrow emission lines making them ideal components for fluorescent probes [10], electroluminescent devices [11], as well as photocatalysts [12]. Our work in this area is focused on looking at lanthanide complexes coordinated with a variety of ‘‘antenna” ligands. Acrylic acid ligands are new kinds of carboxylate ligand and the common feature in the structure of the ligands is the carboxylato group conjugated with benzene ring through C@C double bond, which makes the electronic density delocalized in the ligand. We have studied the structures of La(III) and Ho(III) complexes with the acrylic ligands [13,14]. The results have shown versatile coordination modes and interesting supramolecular chemistry. They coordinate La(III) ions to form 1D coordination polymers, while getting a dimeric complex with Ho(III) ions. To extend these studies, the Eu(III) complexes with the three ligands: [Eu1(L1)3(H2O)2]2 (L1 = (E)-3-(2– hydroxyl-phenyl)-acrylic * Corresponding author. Tel.: +86 10 82575113. E-mail address: [email protected] (H. Li). 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.03.050
acid) (1), [[Eu(L2)3(H2O)]H2O (L2 = (E)-3-(3-hydroxyl-phenyl)-acrylic acid) (2), and [[Eu(L3)3(H2O)2] (L3 = (E)-3-(4-hydroxylphenyl)-acrylic acid) (3) were prepared. Herein, we report their structures and solid-state luminescent properties. 2. Experimental 2.1. General All reagents were obtained from commercial sources and used without further purification. Infrared spectra were recorded as KBr pellets on a Nicolet 170SXFT/IR spectrometer. Excitation and emission spectra were obtained on a RF-5301PC spectrofluorometer equipped with a 450 W xenon lamp as the excitation source. Elemental analyses were carried out using Flash EA1112 microanalyzer. All measurements were performed at room temperature. 2.2. Synthesis 2.2.1. [Eu(L1)3(H2O)2]2 (1) A solution of EuCl36H2O (37.00 mg, 0.1 mmol) in 5 mL water was added to a solution of (E)-3-(2-hydroxyl-phenyl)-acrylic acid (49.00 mg, 0.3 mmol) and triethylamine (30.00 mg, 0.3 mmol) in 10 mL CH3OH. After stirring for half an hour, the reaction solution was filtered. Yellow needle single crystals suitable for single-crystal X-ray diffraction were obtained after 4 days by slow evaporation. Yield: 46.3 mg, 68.3% (based on Eu). Anal. Calc. for
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C27H25EuO11: C, 47.85; H, 3.69; N, 0.00. Found: C, 47.61; H, 3.75; N, 0.00. Selected IR (KBr cm 1): 3225, 1630, 1584, 1513, 1428, 1459, 748. 2.2.2. [Eu (L2)3(H2O)]H2O (2) A solution of EuCl36H2O (13.00 mg, 0.05 mmol) in 5 mL water was add with a solution of (E)-3-(3-hydroxyl-phenyl)-acrylic acid (25.00 mg, 0.15 mmol) and NaOH (6.00 mg, 0.15 mmol) in 5 mL CH3OH. After stirring for half an hour, the reaction solution was filtered. Colorless plate single crystals suitable for single-crystal Xray diffraction were obtained after 4 days by slow evaporation. Yield: 23.1 mg, 68.1% (based on Eu). Anal. Calc. for C27H27EuO12: C, 47.85; H, 3.69; N, 0.00. Found: C, 46.91; H, 3.78; N, 0.00. Selected IR (KBr cm 1): 3413, 1639, 1581, 1517, 1425, 1478, 729.
Table 2 Selected bond lengths and bond angles for 1 Eu1–O1i Eu1–O2 Eu1–O11 Eu1–O5 Eu1–O7
2.209(5) 2.361(6) 2.420(7) 2.436(6) 2.460(6)
Eu1–O8 Eu1–O10 Eu1–O1 Eu1–O4 Eu1–Eu1
2.506(7) 2.572(7) 2.575(6) 2.647(7) 3.9741(9)
O2–Eu1–O11 O2–Eu1–O7 O11–Eu1–O7 O5–Eu1–O7 O2–Eu1–O8 O5–Eu1–O8 O5–Eu1–O10 Eu1–O1–Eu1i
79.74(21) 151.58(21) 88.14(23) 74.32(23) 137.33(20) 122.91(21) 150.54(21) 112.1(2)
O7–Eu1–O10 O11–Eu1–O1 O5–Eu1–O1 O7–Eu1–O1 O8–Eu1–O1 O8–Eu1–O4 O10–Eu1–O4 O1–Eu1–O4
124.92(23) 124.82(21) 100.12(19) 146.67(20) 136.69(21) 131.63(22) 147.25(22) 73.30(22)
Symmetry codes: (i) 2 x,
2.2.3. [Eu(L3)3(H2O)2] (3) A solution of EuCl36H2O (37.00 mg, 0.1 mmol) in 5 mL CH3OH was add with a solution of hydrochloric acid (0.1 mL pH 1), and then mix with the solution of (E)-3-(4-hydroxyl-phenyl)-acrylic acid (49.00 mg, 0.3 mmol) and NaOH (12.00 mg, 0.3 mmol) in 10 mL CH3OH. And then stir for half an hour, meanwhile instill about 0.2 mL DMF. After stirring for another ten min, the reaction solution was filtered. Yellow block single crystals suitable for single-crystal X-ray diffraction were obtained after 4 days by slow evaporation. The Yield: 44.2 mg, 63.6% (based on Eu). Anal. Calc. for C27H25EuO11: C, 47.85; H, 3.69; N, 0.00. Found: C, 47.42; H, 3.65; N, 0.00. Selected IR (KBr cm 1): 3207, 1631, 1587, 1514, 1409, 1441, 732. 2.3. X-ray crystallography Single-crystal X-ray diffraction data were collected on Bruker SMART1000 CCD area detector with graphite monochromated molybdenum Mo-Ka radiation (k = 0.71073 Å) at a temperature of 293 ± 2 K. Unit-cell parameters were determined from automatic centering of 25 reflections and refined by the least-squares method. Crystallographic data are given in Table 1. Selected bond distances and angles are given in Tables 2–4. The diffraction data were corrected for Lorentz and polarization effects, and absorption (empirically from w scan data). No extinction correction was necessary for all complexes. All structures were solved by direct methods and refined using full-matrix least-squares techniques on F2 [15]. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms are located geometrically and refined by mixed methods.
y, 1 z.
Table 3 Selected bond lengths and bond angles for 2 Eu1–O5 Eu1–O2 Eu1–O7 Eu1–O16 Eu1–O10 Eu1–O3 Eu1–O8 Eu1–O4 Eu1–O11 O1–Eu2
2.340(39) 2.357(36) 2.385(47) 2.384(44) 2.461(32) 2.466(33) 2.487(49) 2.525(51) 2.592(46) 2.474(50)
012–Eu2ii 010–Eu2 Eu2–011 Eu2–04i Eu2–02i Eu2–012i Eu2–015 Eu2–09 Eu2–05 04–Eu2ii
2.475(30) 2.441(33) 2.335(40) 2.373(38) 2.466(50) 2.475(30) 2.475(46) 2.475(46) 2.551(46) 2.373(38)
O5–Eu1–O2 O5–Eu1–O7 O2–Eu1–O7 O5–Eu1–O16 O2–Eu1–O16 O7–Eu1–O16 O5–Eu1–O10 O2–Eu1–O10 O7–Eu1–O10
156.12(92) 118.43(91) 78.74(86) 79.27(62) 88.24(64) 80.36(81) 83.39(85) 87.94(86) 149.96(98)
O1–Eu2–O9 O12i–Eu2–O9 O15–Eu2–O9 O11–Eu2–O5 O4i–Eu2–O5 O10–Eu2–O5 O2i–Eu2–O5 O1–Eu2–O5 O12i–Eu2–O5
143.71(85) 86.97(85) 78.84(73) 68.59(83) 127.58(85) 140.73(90) 106.84(81) 138.67(82) 74.18(74)
Symmetry codes: (i)
1+x, y, z, (ii) 1+x, y, z.
3. Results and discussion 3.1. Description of crystal structures 3.1.1. [Eu(L1)3(H2O)2]2 (1) Each Eu(III) ion in complex 1 is coordinated with nine oxygen atoms in which seven oxygen atoms come from the L1 ligands and the other two from the coordinated water molecules (Fig. 1).
Table 1 Crystal data and structure for 1–3 Complex
1
2
3
Formula M Crystal system Space group a(Å) b(Å) c(Å) a/deg b/deg c/deg V/Å3 Z q (calculated) (g cm 3) l mm 1 h Range/deg Reflection Goodness-of-fit on F2 Final R indices (I > 2r(I)) R indices (all data)
C54H50Eu2O22 1354.86 Orthorhombic Pbcn 13.722(2) 21.885(2) 23.928(3) 90.00 90.00 90.00 7185.7(15) 4 0.626 0.895 1.75–25.01 6247/3857[R(int) = 0.0795] 1.096 R1 = 0.0606, wR2 = 0.1336 R1 = 0.1120, wR2 = 0.1691
C27H25EuO11 677.43 Triclinic P1 7.8480(16) 13.019(3) 13.636(3) 97.41(3) 97.25(3) 103.77(3) 1324.0(5) 4 6.797 9.718 1.53–28.34 7055/6444[R(int) = 0.0176] 1.092 R1 = 0.0249, wR2 = 0.0660 R1 = 0.0294, wR2 = 0.0697
C27H25EuO11 677.43 Monoclinic C2/m 14.839(12) 24.00(2) 11.538(9) 90.00 92.422(10) 90.00 4105(6) 4 2.202 3.135 1.77–28.60 12,677/4870[R(int) = 0.0986] 1.025 R1 = 0.0662, wR2 = 0.1561 R1 = 0.1560, wR2 = 0.2138
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Table 4 Selected bond lengths and bond angles for 3 Eu1–O7 Eu1–O10 Eu1–O1 Eu1–O11i Eu1–O14 Eu1–O5 Eu1–O13 Eu1–O4 Eu1–O11 Eu1–Eu2 Eu1–Eu1i Eu1–Eu2ii
2.330(8) 2.356(8) 2.389(9) 2.392(8) 2.431(9) 2.443(8) 2.545(14) 2.616(7) 2.836(8) 4.156(2) 4.358(4) 4.442(3)
Eu2–C1ii Eu2–Eu1ii O11–Eu1i O8–Eu2ii Eu2–Eu2ii Eu2–O2ii Eu2–O4 Eu2–O8 Eu2–O4ii Eu2–O2 Eu2–O15
3.238(13) 4.442(3) 2.392(8) 2.874(11) 0.915(1) 2.123(8) 2.251(7) 2.271(12) 2.445(7) 2.481(8) 2.591(18)
O7–Eu1–O14 O1–Eu1–O14 O10–Eu1–O5 O1–Eu1–O5 C1–O1–Eu1 C1–O2–Eu2ii C1–O2–Eu2 C10–O4–Eu2 C10–O4–Eu2ii C10–O4–Eu1 C19–O8–Eu2
139.24(28) 140.26(28) 147.94(25) 128.26(26) 135.55(81) 148.32(83) 137.45(81) 131.37(64) 143.40(66) 90.02(58) 103.09(92)
O8–Eu2–O7 O4ii–Eu2–O7 O2–Eu2–O7 O15–Eu2–O7 Eu2–O4–Eu1 C10–O5–Eu1 C19–O7–Eu1 C19–O7–Eu2 Eu1–O7–Eu2 C28–O10–Eu1 C28–O11–Eu1i
49.74(32) 125.79(24) 68.06(24) 68.26(43) 117.05(28) 100.40(63) 157.13(84) 74.18(73) 104.81(29) 107.38(75) 164.69(75)
Symmetry codes: (i) 1 x, 1 y, 2 z, (ii)
x, 1 y, 2 z.
The coordination geometry of Eu(III) is a distorted tricapped trigonal prism. One of the ligands is in disorder. All the L1 ligands coordinate Eu(III) ions in bidentate mode. There are two g3-O bridges linking Eu(III) to form the dimeric neutral complex. The distance between Eu(III) is 3.974 Å. The distance is shorter than that between Ho(III) ions in the corresponding complexes [14]. The band lengths of Eu(III)–O are ranged in 2.209–2.647 Å. The shortest bond lengths are bound in g3–O carboxylato bridge, and the longest bond appears in the bidentate chelate mode. The bond angle of Eu–O1–Eui is 112.1°. These dimeric molecules of 1 are assembled into a 3D supramolecular network via hydrogen bonds among the hydroxylato group and carboxylato oxygen atoms in the ligand. Fig. 2 shows a 2D square network by the H-bond between
the adjacent molecules. The details of H-bond are O9O7A, 2.779 Å, and O6O8B, 2.962 Å. Further, the 2D layer is extended to 3D network by strong hydrogen bonding (O3O5, 2.465 Å) (Fig. 3). Obviously, the 1D channel with a dimension around 13.22 Å can be found along a axis, and there is no solvent molecule located in the channel. The coordinated water molecules do not form H-bonding because of steric hindrance of the ligand in the complex. 3.1.2. [Eu (L2)3(H2O)]H2O (2) Different from the complex 1, the Eu(III) ions in the complex 2 are linked by the ligand L2 to form 1D coordination polymer (Fig. 4). Each Eu(III) ion is still nine coordinated by oxygen atoms with only one coordination water molecule and the remain from the L2. The coordination geometry of Eu(III) is a distorted tricapped trigonal prism. The bond length of Eu-O in the complex is 2.340– 2.592 Å. All the bridge ligands between Eu(III) ions are in g3-O type of carboxylato ligand. However, the hydrogen bonds formed by the coordination water molecule and the carboxylato oxygen atoms in the ligands are different with 2.777 Å (O16BO12A) and 2.786 Å (O15O3B), respectively, which are arranged along the chain alternatively. As a result, the 2 is an alternative chain with distances of Eu–EuA (4.067 Å) and Eu–EuB (4.037 Å). It is the second example of the alternative chain constructed by H-bonding as the cooresponding complex with La(III) [13]. The dihedral angle between the two adjacent planes including the two Eu(III) atoms and two bridging O atoms: 90.5°. In the crystalline lattice, the 1D coordination polymer of 2 is linked by intermolecular hydrogen bonding between the hydroxylato group and carboxylato oxygen atoms in L2 along 2D and 3D directions (O31O10, 2.665Å; O19O2O, 2.647 Å; O21O8, 2.638 Å; O18O1, 2.741 Å). From the 3D packing picture of 2 (Fig. 5), the benzene rings of L2 are packed and occupied in the channel along a axis. The distance between the centers of the adjacent benzene ring is 4.03 Å and the distance of two planes is 3.60 Å. The p–p interaction stabilizes the structure further.
Fig. 1. ORTEP diagram (50% probability) of 1 (hydrogen atoms have been omitted for clarity.) (white and black).
J. Yan et al. / Journal of Molecular Structure 891 (2008) 298–304
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Fig. 2. The 2D H-bonding framework of 1 (white and black).
Fig. 3. The 3D H-bonding framework of 1. The picture (right) is space-filling figure showing the vacant 1D channel (white and black).
The significant point of the structure is its chiral space group, P1. The reason is that interchain hydrogen-bonding along 2D and 3D directions is homo-helical (Fig. 5). Based on the topological position of the hydroxylato group in L2, the angle between it and carboxylato group is 120°. It is favored to form the helical structure. 3.1.3. [Eu(L3)3(H2O)2] (3) In complex 3, there are two kinds of coordination environments of Eu(III). Eu1 and Eu2 are eight coordinated and Eu1A and Eu1B are nine coordinated with oxygen atoms. The Eu2 is in a little disorder. Three L3 bridge ligands linked Eu1 and Eu2 ions. Two of them are g2–O type and another one is g3-O carboxylato bridge. The bridge mode between the Eu2 and Eu1B is similar. However, the Eu1 and Eu1A are linked by two g3-O carboxylato bridge ligands. Comparing with 2, the bridging modes between the Eu(III) ions in 3 are different along the chain (Fig. 6). So, it is definitely an alter-
native chain in which the distance of Eu1–Eu2 and Eu2–Eu1B is 4.156 Å and Eu1–Eu1A is 4.358 Å. To the best of our knowledge, the novel infinite alternative chain in [Eu1B–Eu2–Eu1–Eu1A]n mode has not been reported previously. The two g2–O bridges in the chain are in different configuration: the O1–C1–O2 bridge is in syn–syn configuration, and the O7–C19–O8 bridge is in syn–anti configuration. The bond lengths of Eu–O are between 2.330 and 2.836 Å, which fall in the normal scale [16–21]. Also, there are three kinds of intrachain hydrogenbonding alternatively (O15O2(2.521 Å); O14O1(2.703 Å); O7O13 (2.799 Å)). 3.2. Photoluminescent properties of three complexes The luminescences of these three complexes were investigated. All the excitation spectrums show that this kind of complex have a strong absorb near 280 nm, which due to the p–p* transition of
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Fig. 4. The 1D chain structure of 2 (Eu1A–Eu2: 4.037 Å; Eu1B–Eu2: 4.067 Å). Hydrogen atoms have been omitted for clarity (white and black).
Fig. 5. The 3D packing picture of 2. The homo-helical hydrogen bonding in 2 (right-down).
conjugated bond among carboxylato group, benzene ring and the C@C double bond in the ligand. Complex 1 and 2 emitted strongest red luminescence upon excitation at about 380 nm, and their photoluminescence spectra are similar except that the bands of 1 are weaker than those of 2 (Fig. 7). The characteristic transition of 5D0 7FJ (J = 0–4) of Eu(III) ions implies that the ligand-to-europium energy transfer is moderately efficient under the experimental coordinations [22]. The appearance of the symmetry-forbidden emission 5D0–7F0 at 580 nm indicates that Eu(III) ions occupy sites with low symmetry and without an inversion center [23]. This is in agreement with our single-crystal X-ray analysis. The 5D0–7F1 transition is a magnetic dipole transition, and its intensity varies with the crystal field strength acting on Eu(III) ions. On the other hand, the 5D0–7F2 transition is an electric dipole transition and is extremely sensitive to
the crystal field in the vicinity of Eu(III) ion. The intensity of the 5 D0–7F2 transition increases as the site symmetry of Eu(III) ions decreases. The intensity ratio I(5D0–7F2)/I(5D0–7F1) is about 4.2, which also suggests the noncentrosymmetric coordination environment of the Eu(III) ions in 1 [24]. On the other hand, the photoluminescence spectra of 3 show dual characteristic. The broad bands below 470 nm correspond to emission from the ligand itself, which is mainly due to a strong intraligand charge transfer (ILCT) from the donor hydroxylato group to the acceptor carboxylate group of the ligand [25]. The emission bond in 590 nm is due to 5D0–7F1 transition, while the bond in 617 nm for 5D0–7F2 transition of Eu(III) ion. As the luminescence of the ligand has not been fully quenched, the ligandto-metal energy transfer is inefficient for the triplet state energy that does not match the first excited energy level of the Eu(III) ions.
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Fig. 6. The 1D chain structure of 3 (white and black).
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Fig. 7. Solid-state excitation and emission spectra at room temperature.
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The three-dimensional supramolecular frameworks built by Hbonding have been revealed. The homohelic H-bonding constructed by L2 ligand has been found in the crystalline solids of their complexes. The emission spectra demonstrate that the complexes, especially 2, might be good candidates for efficient luminescent materials.
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X-ray crystallographic data for complexes 1-3 in CIF format can be obtained free of charge from the director, CCDC, 12 United Road, Cambridge, CB2, 1EZ, UK (Fax: +44 1223 336033; E-mail: [email protected]). The CCDC numbers for complexes 1, 2, and 3 are 657913, 657914, and 657915, respectively.
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Acknowledgments
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The Excitation spectrum of (3) This work was supported by the Natural Science Fund Council of China (NSFC No 20571011; No. 20771014), the Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry of China (LXKYJJ200408) and The University Basic Research Foundation of Beijing Institute of Technology (BIT-UBF, No 200507B4202).
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References
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4. Conclusions In summary, the syntheses and crystal structures of a series of Europium complexes containing the acrylic acid ligand have been reported, and their solid-state luminescent properties have been discussed. The difference in the position of hydroxylato group in the L1 to 3 L brings the diversities both in the coordination complexes and in the supramolecular interactions in the crystal lattices. The dinuclear complex and alternative chains have been obtained. The [Eu1B–Eu2–Eu1–Eu1A]n mode in the alternative chain has been found for the first time.
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