ARTICLE pubs.acs.org/crystal
Novel Luminescent Three-Dimensional Heterometallic Complexes with 2-Fold Interpenetrating (3,6)-Connected Nets Rui Feng,†,‡ Lian Chen,† Qi-Hui Chen,† Xiao-Chen Shan,†,‡ Yan-Li Gai,†,‡ Fei-Long Jiang,*,† and Mao-Chun Hong*,† †
State Key Laboratory of Structure Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian, 350002, China ‡ Graduate School of the Chinese Academy of Sciences, Beijing, 100049, China
bS Supporting Information ABSTRACT: A series of novel three-dimensional (3D) 3d-4f heterometallic coordination complexes, [{LnZn(bpdc)2(OAc)(H2O)2} 3 H2O]n (Ln = Nd (1), Sm (2), Eu (3), Tb (4), Dy (5), Er (6); H2bpdc = 2,20 -bipyridyl-4,40 -dicarboxylic acid; HOAc = acetic acid), have been successfully synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. All complexes are isostructural and display new 2-fold interpenetrating (3,6)-connected network topology. The luminescent properties of 15 in the solid state at room temperature have been studied in detail. It is the first series of luminescent 3d4f heterometallic complexes with bpdc2 ligands, and it has been found that the energy transitions from the ligands to Eu3þ and Tb3þ are more effective than those to Sm3þ and Nd3þ, and the energy transition from the ligand to Dy3þ is in between. Furthermore, thermogravimetric analysis and powder X-ray diffraction are also investigated.
’ INTRODUCTION In recent years, the design and syntheses of 3d-4f heterometallic frameworks have attracted much attention due to their intriguing structural topology1 and their potential applications as magnetism,2 adsorption,3 catalysis,4 ion-exchange,5 luminescence materials,6 and so on. Many 3d-4f heterometallic complexes have been reported and most of the research attention is placed on the magnetic complexes,7 while the luminescent 3d-4f heterometallic complexes have received much less attention.8 Considering the development of the luminescent monometallic complexes containing lanthanide ions or d10 transition metal ions,9 we should be able to anticipate the importance of the heterometallic complexes with both lanthanide and d10 metal ions on the luminescence materials. On the other hand, considerable research effort has been devoted to the design and syntheses of novel 3d-4f heterometallic complexes;10 however, the syntheses is still a challenging task for the coordination characteristics of the metal ions to the organic ligands. The high coordination numbers and flexible coordination geometries of lanthanide ions11 make it difficult to control the preparation of the complexes. So the selection of suitable organic ligands is crucial. And according to the hardsoft acidbase principle,12 the lanthanide ions are hard acids and prefer oxygen to nitrogen donors, while the d-block transition metal ions are borderline acids and have a strong tendency to coordinate to N-donors as well as to O-donors. As a result, multidentate ligands containing N- and O-donor atoms are good r 2011 American Chemical Society
candidate in the construction of novel 3d-4f heterometallic complexes. For example, nicotinic acid,13 isonicotinic acid,14 and pyridine dicarboxylic acid15 have been employed extensively. However, as a ligand, the 2,20 -bipyridyl-4,40 -dicarboxylic acid (H2bpdc) is mainly applied in the construction of monometallic complexes,16 and only one sample of magnetic 3D heterometallic frameworks17 has been reported up to now. Herein we report the syntheses, structures, and luminescent properties of a series of novel Ln-Zn complexes based on H2bpdc ligands: [{LnZn(bpdc)2(OAc)(H2O)2} 3 H2O]n (Ln = Nd (1), Sm (2), Eu (3), Tb (4), Dy (5), Er (6); H2bpdc = 2,20 -bipyridyl-4,40 dicarboxylic acid; HOAc = acetic acid).
’ EXPERIMENTAL SECTION All chemicals are purchased commercially and used without further purification. Infrared spectra were recorded with KBr pellets on a PerkinElmer Spectrum One FT-IR spectrometer. Elemental analyses for C, H, N were carried out on a Vario EL III elemental analyzer. Thermal gravimetric analyses were performed with a heating rate of 10 °C 3 min1 using a NETZSCH STA 449C simultaneous thermogravimetric-differential scanning calorimetry (TG-DSC) instrument. Powder X-ray diffraction patterns were collected using a diffractometer (RIGAKU DMAX2500 or MiniFlex II) with Cu KR radiation (λ = 1.5406 Å). Received: December 10, 2010 Revised: April 1, 2011 Published: April 06, 2011 1705
dx.doi.org/10.1021/cg101642j | Cryst. Growth Des. 2011, 11, 1705–1712
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Table 1. Crystal and Structure Refinement Details for Complexes 16 complex
1
2
3
4
5
6 C26H21N4O13ErZn
formula
C26H21N4O13NdZn
C26H21N4O13SmZn
C26H21N4O13EuZn
C26H21N4O13TbZn
C26H21N4O13DyZn
fw
807.08
813.19
814.80
821.76
825.34
830.10
temperature (K)
293(2)
293(2)
293(2)
293(2)
293(2)
293(2)
crystal system
monoclinic
monoclinic
monoclinic
monoclinic
monoclinic
monoclinic
space group
P21/c
P21/c
P21/c
P21/c
P21/c
P21/c
a (Å)
7.819(2)
7.794(3)
7.7939(19)
7.777(2)
7.766(3)
7.7470(17)
b (Å)
12.561(3)
12.535(5)
12.520(3)
12.488(3)
12.471(5)
12.440(3)
c (Å) β (°)
29.962(7) 92.663(5)
30.012(12) 92.953(5)
29.982(7) 92.952(4)
29.956(8) 93.123(4)
29.941(13) 93.191(8)
29.949(7) 93.328(4)
volume (Å3)
2939.8(12)
2928(2)
2921.8(12)
2905.1(13)
2895(2)
2881.3(11)
Z
4
4
4
4
4
4
Dc (g/cm3)
1.824
1.845
1.852
1.879
1.893
1.914
F000
1596
1604
1608
1616
1620
1628
μ (mm1)
2.636
2.879
3.022
3.315
3.464
3.800
crystal size (mm)
0.10 0.04 0.04
0.15 0.15 0.10
0.06 0.05 0.04
0.10 0.10 0.08
0.10 0.10 0.07
0.12 0.10 0.10
Rint final GOF
0.0357 1.085
0.0462 1.109
0.0440 1.092
0.0505 1.084
0.1136 1.146
0.0340 1.064
R1 [I > 2σ(I)]
0.0396
0.0504
0.0473
0.0459
0.0848
0.0389
wR2 [I > 2σ(I)]
0.0826
0.1099
0.1023
0.0987
0.1601
0.0898
Emission spectra, excitation spectra, and transient decays were recorded on an Edinburgh FLS920 (or Horiba Jobin Yvon Fluorolog-3) spectrophotometer analyzer. The key to construct the desirable frameworks of 3d-4f heterometallic complexes is the selection of suitable organic building blocks and metal ions. The H2bpdc as a multidentate N- and O-donor ligand possesses the capacity to coordinate transition metal ions (d10-metal, Zn2þ) by its chelating bidentate pyridine groups, and to bridge Ln3þ metal centers by its dicarboxylate groups with various coordination modes. Although most of the reported 3d-4f heterometallic complexes comprise magnetic transition metal ions, we are interested in the 3d10-4f heterometallic complexes with useful luminescent properties. Considering the coordination numbers of Zn2þ and Ln3þ ions (six and eight mostly, respectively) and coordination modes of H2bpdc, a reasonable ratio of three reactants would be given. Moreover, the acetate anion employed here can link the metal centers as a bridge to construct the framework,18 while it also neutralizes the positive charge of the products. Synthesis of [{NdZn(bpdc)2(OAc)(H2O)2} 3 H2O]n (1). A mixture of Nd(OAc)3 3 6H2O (85.9 mg, 0.2 mmol), Zn(OAc)2 (43.9 mg, 0.2 mmol), H2bpdc (97.6 mg, 0.4 mmol), and H2O (10 mL) was placed in a Teflon-lined stainless steel bomb at 160 °C for 3 days and then cooled to room temperature at a rate of ∼10 °C/h. Violet square-crystals were obtained (yield: 84% based on Nd). Anal. for C26H21N4O13NdZn (%): Calcd.: C, 38.69; H, 2.62; N, 6.94. Found: C, 38.79; H, 2.79; N, 7.12. IR (KBr pellet, cm1): 3401 (m), 1599 (s), 1548 (vs), 1404 (vs), 1292 (w), 1234 (m), 1019 (m), 779 (s), 705 (s). Synthesis of [{SmZn(bpdc)2(OAc)(H2O)2} 3 H2O]n (2). A procedure similar to that of 1 was applied to prepare 2 except that Nd(OAc)3 3 6H2O was replaced by Sm(OAc)3 3 6H2O (87.1 mg, 0.2 mmol). Light pink square-crystals were obtained (yield: 79% based on Sm). Anal. for C26H21N4O13SmZn (%): Calcd.: C, 38.40; H, 2.60; N, 6.89. Found: C, 38.13; H, 2.91; N, 7.05. IR (KBr pellet, cm1): 3114 (s), 1603 (s), 1550 (m), 1367 (vs), 1293 (m), 1243 (m), 1014 (s), 767 (s), 683 (vs). Synthesis of [{EuZn(bpdc)2(OAc)(H2O)2} 3 H2O]n (3). A procedure similar to that of 1 was applied to prepare 3 except that Nd(OAc)3 3 6H2O was replaced by Eu(OAc)3 3 6H2O (87.4 mg, 0.2 mmol). White square-crystals were obtained (yield: 63% based
on Eu). Anal. for C26H21N4O13EuZn (%): Calcd.: C, 38.32; H, 2.60; N, 6.88. Found: C, 38.64; H, 2.69; N, 7.00. IR (KBr pellet, cm1): 3116 (s), 1603 (m), 1548 (w), 1404 (vs), 1292 (w), 1233 (m), 1019 (s), 778 (m), 695 (s). When the above Eu(OAc)3 3 6H2O was replaced by both Eu(NO3)3 3 6H2O (or EuCl3 3 6H2O) (x mmol) and NaOAc 3 3H2O (3x mmol) (x > 0.2), complex 3 was also obtained. Synthesis of [{TbZn(bpdc)2(OAc)(H2O)2} 3 H2O]n (4). A procedure similar to that of 1 was applied to prepare 4 except that Nd(OAc)3 3 6H2O was replaced by Tb(OAc)3 3 6H2O (88.8 mg, 0.2 mmol). Light pink square-crystals were obtained (yield: 71% based on Tb). Anal. for C26H21N4O13TbZn (%): Calcd.: C, 38.00; H, 2.58; N, 6.82. Found: C, 38.28; H, 3.08; N, 6.73. IR (KBr pellet, cm1): 3113 (s), 1603 (m), 1550 (s), 1367 (vs), 1295 (m), 1242 (w), 1014 (s), 766 (m), 683 (s). Synthesis of [{DyZn(bpdc)2(OAc)(H2O)2} 3 H2O]n (5). A procedure similar to that of 1 was applied to prepare 5 except that Nd(OAc)3 3 6H2O was replaced by Dy(OAc)3 3 10H2O (102.6 mg, 0.2 mmol). Light pink square-crystals were obtained (yield: 88% based on Dy). Anal. for C26H21N4O13DyZn (%): Calcd.: C, 37.84; H, 2.56; N, 6.79. Found: C, 38.12; H, 3.11; N, 7.07. IR (KBr pellet, cm1): 3393 (vs), 1604 (s), 1550 (vs), 1375 (vs), 1293 (w), 1242 (m), 1014 (s), 779 (s), 696 (vs). Synthesis of [{ErZn(bpdc)2(OAc)(H2O)2} 3 H2O]n (6). A procedure similar to that of 1 was applied to prepare 6 except that Nd(OAc)3 3 6H2O was replaced by Er(OAc)3 3 6H2O (90.5 mg, 0.2 mmol). Pink square-crystals were obtained (yield: 80% based on Er). Anal. for C26H21N4O13ErZn (%): Calcd.: C, 37.62; H, 2.55; N, 6.75. Found: C, 37.96; H, 2.91; N, 6.94. IR (KBr pellet, cm1): 3215 (vs), 1607 (m), 1550 (vs), 1404 (s), 1290 (w), 1238 (m), 1017 (s), 784 (s), 697 (vs). IR Spectroscopy. The IR spectra of complexes 16 are similar. The strong and broad bands at ∼3300 cm1 can be attributed to the stretching vibration of OH in H2O and CH in aromatic rings. The strong bands in the range of 16101370 cm1 are assigned as the asymmetric and symmetric stretching vibrations of the carboxylate groups. The bands at ∼770 cm1 and ∼690 cm1 are the characteristic peaks of CH in aromatic rings. X-ray Crystallographic Determination. The crystal structures data of complexes 16 were performed at 293(2) K on a RIGAKU 1706
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Table 2. Selected Bond Lengths (Å) and Angles (°) for Complex 3a Bond Eu1—O1i
2.364(4)
Eu1—O5
2.472(4)
Zn1—O8iii
2.096(4)
Eu1—O9ii
2.413(4)
Eu1—O3
2.504(4)
Zn1—N1iv
2.118(4)
Eu1—O10
2.441(5)
Eu1—O6
2.522(4)
Zn1—N4
2.140(4)
Eu1—O12
2.460(4)
Eu1—O9
2.577(4)
Zn1—N2iv
2.181(4)
Eu1—O4
2.462(4)
Zn1—O11
2.088(4)
Zn1—N3
2.182(4)
Angle O1i—Eu1—O9ii
82.59(14)
O10—Eu1—O3
83.60(16)
O1i—Eu1—O10 O9ii—Eu1—O10
150.27(16) 115.15(13)
O12—Eu1—O3 O4—Eu1—O3
145.64(13) 52.51(12)
O6—Eu1—O9 O11—Zn1—O8iii
O3—Eu1—O9
119.01(14) 94.86(15)
74.44(12)
95.77(16)
O1i—Eu1—O12
74.90(13)
O5—Eu1—O3
76.82(13)
O11—Zn1—N1iv
O9ii—Eu1—O12
77.76(14)
O1i—Eu1—O6
81.25(15)
O8iii—Zn1—N1iv
93.66(16)
O10—Eu1—O12
85.42(16)
O9ii—Eu1—O6
155.16(13)
O11—Zn1—N4
91.16(16)
O1i—Eu1—O4
73.84(13)
O10—Eu1—O6
73.41(16)
O8iii—Zn1—N4
93.69(16)
O9ii—Eu1—O4
80.70(14)
O12—Eu1—O6
79.90(14)
N1iv—Zn1—N4
169.44(17)
O10—Eu1—O4
130.24(16)
O4—Eu1—O6
112.41(15)
O11—Zn1—N2iv
91.95(16)
O12—Eu1—O4 O1i—Eu1—O5
143.88(13) 100.13(16)
O5—Eu1—O6 O3—Eu1—O6
51.93(13) 127.08(13)
O8iii—Zn1—N2iv N1iv—Zn1—N2iv
168.14(16) 75.98(16)
O9ii—Eu1—O5
150.56(13)
O1i—Eu1—O9
137.81(13)
N4—Zn1—N2iv
95.87(16)
O10—Eu1—O5
76.34(16)
O9ii—Eu1—O9
64.11(14)
O11—Zn1—N3
167.07(15)
O12—Eu1—O5
131.45(14)
O10—Eu1—O9
51.06(12)
O8iii—Zn1—N3
87.21(15)
O4—Eu1—O5
72.14(15)
O12—Eu1—O9
73.35(12)
N1iv—Zn1—N3
96.83(16)
O1i—Eu1—O3
124.87(13)
O4—Eu1—O9
121.51(13)
N4—Zn1—N3
75.96(16)
O9ii—Eu1—O3
77.73(13)
O5—Eu1—O9
121.70(15)
N2iv—Zn1—N3
88.31(16)
a Symmetry codes: (i) x, 1 þ y, z; (ii) 2 x, 1 y, 1 z; (iii) x, 1/2 þ y, 1/2 z; (iv) 2 x, 1/2 þ y, 1/2 z; (v) x, 1 þ y, z; (vi) 2 x, 1/2 þ y, 1/ 2 z; (vii) x, 1/2 þ y, 1/2 z.
free water molecules could not be found because of disorder. Crystallographic data of complexes 16 are listed in Table 1. Selected bond lengths and angles of complexes 16 listed in Table 2 and Tables S15 (Supporting Information).
’ RESULTS AND DISCUSSION
Figure 1. View of the asymmetry unit of complex 3. All H atoms are omitted for clarity. SATURN70 (for 1, 3) or a RIGAKU MERCURY (for 2, 4, 5, 6) CCD diffractometer with graphite-monochromated Mo KR radiation (λ = 0.71073 Å). All structures were solved by direct methods and refined using full-matrix least-squares techniques on F2 using the SHELXTL software suite.19 No extinction correction was necessary for all complexes. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms for CH were placed in geometrically idealized positions and refined using a riding model. The hydrogen atoms belonging to the coordinated water molecules were found in the electron density map and also refined by riding, while the hydrogen atoms of the
Crystal Structure Description of Complexes 16. The single-crystal X-ray analysis of the complexes reveals that they are isomorphous and crystallize in the same monoclinic space group P21/c. Thus, we select complex 3 as the representative example to describe here in detail. As shown in Figure 1 and Figure S1 (Supporting Information), the asymmetry unit consists of one crystallographically unique Eu3þ ion, one Zn2þ ion, two bpdc2 ligands, one OAc ligand, two coordinated water molecules, and one free water molecule. Each Eu3þ ion coordinates to nine oxygen atoms: five carboxylic oxygen atoms from three bpdc2 ligands, three carboxylic oxygen atoms from two OAc ligands, and one oxygen atom from one coordinated water molecule. So the Eu1 centers are nine-coordinated. The EuO bond lengths vary from 2.364(4) to 2.577(4) Å and the OEuO bond angles are in the range of 51.06(12)155.16(13)°. The Zn centers are all six-coordinated by four nitrogen atoms from two bpdc2 ligands, one oxygen atom from one bpdc2 ligand, and one oxygen atom from one water molecule. The ZnO and ZnN bond lengths range from 2.088(4) to 2.096(4) Å and from 2.118(4) to 2.182(4) Å, respectively, which are similar to those found in the related Zn(II) complexes.20 For 16, all the lanthanide ions are nine-coordinated, and the average LnO distances are 2.505(5), 2.480(1), 2.468(7), 1707
dx.doi.org/10.1021/cg101642j |Cryst. Growth Des. 2011, 11, 1705–1712
Crystal Growth & Design 2.445(2), 2.429(4), and 2.411(1) Å, respectively. The average LnO distances decrease with an increase in atomic number due to the lanthanide contraction effect.21 As shown in Scheme 1a,b, the bpdc2 ligands exhibit two kinds of coordination modes: (a) for coordination mode I, one oxygen atom of a carboxyl coordinates to a zinc center with the monodentate mode, and two oxygen atoms of another carboxyl coordinate to the europium center with the chelating bidentate mode, while two nitrogen atoms coordinate to another zinc center with the chelating bidentate mode; (b) for coordination mode II, one oxygen atom of a carboxyl coordinates to an europium center with the monodentate mode, and two oxygen atoms of another carboxyl coordinate to another europium center with the chelating bidentate mode, while two nitrogen atoms coordinate to a zinc center with the chelating bidentate mode. And the OAc ligands display one kind of coordination mode: two carboxylic oxygen atoms coordinate to two europium centers with the tridentate bridging mode (Scheme 1c). All carboxyl groups of these ligands are deprotonated, in agreement with the IR data (Supporting Information, Figure S2) in which no strong absorption peaks around 1700 cm1 (COOH) are observed.22 In structure of 3, two europium centers, Eu1 and Eu1A (A = symmetry code: 2 x, 1 y, 1 z), are linked by two bridging tridentate OAc ligands to give a dinuclear unit. The distance of Eu1 and Eu1A is 4.230 Å, and the Eu1O9Eu1A bond angle is 115.89°. As shown in Figure 2a, these dinuclear units build up a ladder chain along the b axis through the bpdc2 ligands with the coordination mode II, and the ladder chains are connected to the zinc centers by the bpdc2 ligands with the coordination modes I and II to construct a 3D framework with two kinds of
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one-dimensional (1D) channels along the b axis: channel-A and channel-B (Figure 2c). In channel-A, the distances between the nearest opposite zinc centers and the nearest opposite centers of the dinuclear europium are 11.014 and 19.993 Å, respectively. And in channel-B, the corresponding distances are 13.445 and 16.245 Å. The lattice water molecules are located in the channelA. As we all know, the structure with large porosity is unstable,23 and as a result, two independent 3D structures interpenetrate each other (Figure 2d). Interestingly, even with the interpenetration the molecules still have the solvent-accessible volume of the channels about 2921.8 Å3 in the unit cell, which accounts for 10.2% of the total cell volume as calculated by a PLATON program after taking off the lattice and coordinated water molecules. To better understand the structure of 3, the topological analysis approach is employed. As shown in Figure 3, this net contains three kinds of nodes: the dinuclear europium ions can be considered as a six-connected node, while the zinc ion can be considered as a three-connected node, and the bpdc2 ligand also as a three-connected node. But bpdc2 three-connected nodes display two types: one of them connects with two Eu3þ ions and one Zn2þ ion, the other one connects with one Eu3þ ion and two Zn2þ ions. Thus, this network can be described as an Archimedean-type net with three nonequivalent points, and its
Scheme 1. Coordination Modes of bpdc2 and OAc in 3
Figure 3. (a) A single network in complex 3 viewed from the b axis (the dinuclear europium, zinc and bpdc2 nodes are shown as green, blue, and red, respectively). (b) The 2-fold interpenetrating nets of 3 (the two different colors represent two different sets).
Figure 2. (a) The ladder chain viewed along the a axis. (b) The ladder chain viewed along the b axis. (c) The single molecule viewed along the b axis. (d) The 2-fold interpenetrating 3D structure viewed along the b axis. (The H atoms and water molecules are omitted for clarity.) 1708
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Figure 4. Emission spectra of complexes 1 (a and b), 2 (c), 3 (d), 4 (e), and 5 (f) excited at 330 nm in solid state at room temperature.
Sch€afli symbol is (4281010212)(83)(482), which, to our knowledge, has not been reported so far. X-ray Powder Diffraction (XRD). The powder XRD patterns of complexes 16 in the region of 2θ = 545° are shown in the Figure S3 (Supporting Information). For these complexes, the experimental XRD peaks are consistent with the XRD peaks that are simulated from the structure data. As a result, we can draw a conclusion that the samples are single phase. Thermal Gravimetric Analyses (TGA). To investigate their thermal stabilities, the thermogravimetric analyses were performed on complexes 16 with a heating rate of 10 °C 3 min1 using a NETZSCH STA 449C under N2 atmosphere at the temperature from 30 to 900 °C (Supporting Information, Figure S4). Since complexes 16 are isostructural, complex 3 was selected to describe in detail here. As the TG curve illustrated in Figure S4a, the weight loss of 2.27% between 30 and 150 °C is attributed to the loss of one free water molecule (calcd 2.21%), the weight loss of 4.40% between 150 and 330 °C is attributed to the loss of two coordinated water molecules (calcd 4.42%), and
above 330 °C the framework of complex 3 continued to decompose. Photoluminescent Properties. The solid-state photoluminescent properties of complexes 15 were investigated at room temperature and the emission spectra excited at 330 nm are illustrated in Figure 4. Complex 1 displays emission bands at visible and near-IR regions. One peak at 382 nm with a shoulder peak at 453 nm is detected at the visible region (Figure 4a). The peak at 382 nm is due to an intraligand transition by comparing to the luminescence of free H2bpdc ligand (Supporting Information, Figure S5), while the shoulder peak at 453 nm may be due to ligandmetal charge transfer (LMCT) from the conjugated system on the bpdc2 ligands to Zn2þ by comparing to the luminescence of the complex with Zn2þ and bpdc2, [{Zn(bpdc)(H2O)3} 3 3H2O]n (Supporting Information, Figure S6). Additionally, complex 1 exhibits the characteristic transitions of Nd3þ ion at the near-IR region (Figure 4b): three weak peaks centered at 898, 1061, and 1331 nm are attributed to the 4 F3/2 f 4I9/2, 4F3/2 f 4I11/2, and 4F3/2 f 4I13/2 transitions, 1709
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Figure 5. (a) The luminescence decay curves for complex 3 by monitoring the 5D0 f 7F2 transition of Eu3þ and excited at 330 nm in the solid state. (b) The luminescence decay curves for complex 4 by monitoring the 5D4 f 7F5 transition of Tb3þ and excited at 330 nm in the solid state. (The scattering points are experimental data, and the solid lines are the fitting results according to the monoexponential function.)
respectively. This is in agreement with the emission spectra of the previously reported Nd3þ complexes.24 For complex 2, four weak peaks at 562 nm, 599 nm, 645 and 708 nm are attributed to the 4G5/2 f 6H5/2, 4G5/2 f 6H7/2, 4 G5/2 f 6H9/2 and 4G5/2 f 6H11/2 transitions of Sm3þ ion, respectively (Figure 4c). And similar to 1, the ligand-related emission band, one intense peak at 380 nm with a shoulder peak at 455 nm is also detected. The above emission spectrum of 2 indicates that the energy transition from ligand to Sm3þ ion is ineffective. And the lifetime was measured by monitoring the emission lines (4G5/2 f 6H9/2) of Sm3þ ions, when excited at 330 nm (Figure S7a, Supporting Information), exhibiting biexponential behavior (τ1 = 3.942 106 s (47.77%), τ2 = 1.346 105 s (52.23%)) due to the weak luminescence of 2. As we know, the luminescent intensity is also affected by some outside factors such as signal-to-noise and so on during the luminescence measurement. The weaker luminescence can be affected to a greater extent. Complex 3 displays intense red luminescence and exhibits the characteristic transitions of the Eu3þ ion with a decay lifetime of 491.8 μs (Figure 5a). As shown in Figure 4d, the peaks at 580, 593, 616, and 694 nm are attributed to the 5D0 f 7F0, 5D0 f 7F1, 5 D0 f 7F2, and 5D0 f 7F4 transitions, respectively. The most intense transition is 5D0 f 7F2, which dominates the red emission light. The intensity of the 5D0 f 7F2 transition (electric dipole) is much stronger than that of the 5D0 f 7F1 transition (magnetic dipole). Moreover, it is well-known that the 5 D0 f 7F0 transition is strictly forbidden in a field of symmetry and is only allowed for Cs, Cn, and Cnv site symmetries according to the ED selection rule.25 Thus, the experimental results reveal that Eu3þ ions in 3 locate at the low-symmetry sites without inversion centers,26 which is in good agreement with our singlecrystal X-ray analysis. Complex 4 displays intense green luminescence and exhibits the characteristic transitions of the Tb3þ ion (Figure 4e) with a decay lifetime of 649.8 μs (Figure 5b). There are four characteristic peaks centered at 490, 545, 586, and 621 nm, which are attributed to the 5D4 f 7F6, 5D4 f 7F5, 5D4 f 7F5, and 5D4 f 7 F3 transitions, respectively. Complex 5 displays five sets of bands in the solid state (Figure 4f): one weak ligand-related peak is located at 384 nm, and the other four peaks centered at 481, 574, 662, and 752 nm are attributed to the 4F9/2 f 6H15/2, 4F9/2 f 6 H13/2, 4F9/2 f 6H11/2 and 4F9/2 f 6H9/2 þ 6F11/2 transitions of
Dy3þ ions, respectively. The 4F9/2 f 6H13/2 transition is most intense and determines the yellow emission light. And the lifetime was measured by monitoring the most intense emission lines (4F9/2 f 6H13/2) of Dy3þ ions, when excited at 330 nm (Figure S7b, Supporting Information), exhibiting biexponential behavior (τ1 = 3.256 106 s (25.08%), τ2 = 8.165 106 s (74.92%)). Compared with the emission spectra of the above five complexes, both the ligand-related emission peaks and the characteristic transitions of lanthanide ions are observed in complexes 1, 2 and 5. But for complexes 3 and 4, we only detect the characteristic transitions of the lanthanide ions. And the intensity of the ligand-related emission peaks is strong in complexes 1 and 2 while weak in 5. So the intensities of energy transitions from the ligands to lanthanide ions change in the order of Eu3þ, Tb3þ > Dy3þ > Sm3þ, Nd3þ, which may be because of the different band gaps of various Ln3þ ions. If the band gaps are wide, it would be hard to be quenched, and conversely when the band gaps are narrow it would be easy to be quenched. To study the effect of the water molecules on the emission spectra of these complexes, we measured the XRD and emission spectra of these samples which have been heated at different temperatures under N2 atmosphere. Complex 3 was selected as a representative example to describe here in detail since complexes 16 are isomorphous. As shown in Figure S8a (Supporting Information), complex 3 still held its framework at 200 °C and then began to decompose gradually until 250 °C. And from the TG curve of complex 3 (Figure S4a), we know that all the free water molecules have been lost between 30 and 150 °C, one coordinated water molecule was lost at 200 °C and a majority of another coordinated water molecule was lost until 250 °C. Thus, we draw the conclusion that the complexes can keep their frameworks even when one coordinated water molecule is lost at 200 °C, and along with the loss of another coordinated water molecule the frameworks decompose gradually. The emission spectra of complex 3 at different temperatures are illustrated in Figure S8b (Supporting Information), the emission spectra of complex 3 at 200 °C and at room temperature are both almost alike. As the temperature increases, the intensities of the emission spectra become weak. From above, we presume that the coordinated water molecules maybe removed from the metal centers gradually. The loss of free water molecules and then the initial removal of water ligand from the zinc center both do 1710
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Crystal Growth & Design not have the observable effect on the intensity of the emission spectra, while the continuing removal of water ligand coordinated with lanthanide center has a great effect on the emission spectra of complex 3.
’ CONCLUSIONS In summary, six novel 3D Ln-Zn coordination complexes have been successfully constructed through the self-assembly of H2bpdc and mixed metal salts under hydrothermal conditions. They are isostructural and exhibit a new 2-fold interpenetrating (3,6)-connected network topology, (4281010212)(83)(482). The detailed luminescent properties of complexes 15 in the solid state at room temperature have been investigated. It is found that the energy transitions from the ligands to Eu3þ and Tb3þ are more effective than those to Sm3þ and Nd3þ, and the energy transition from the ligand to Dy3þ is in between. To the best of our knowledge, these are the first series of luminescent heterometallic complexes based on the bpdc2 ligands, and they may have potential application in luminescent materials. ’ ASSOCIATED CONTENT
bS
Supporting Information. Additional structural and photoluminescent figures, X-ray powder diffraction, TGA curves, and crystallographic file for complexes 16 in CIF format. This material is available free of charge via the Internet at http://pubs. acs.org. CCDC-784535 (1), 784534 (2), 784533 (3), 784538 (4), 784536 (5), and 784537 (6) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected] (M.-C.H.),
[email protected] (F.-L. J.); fax: þ86-591-83794946; tel: þ86-591-83792460.
’ ACKNOWLEDGMENT We are thankful for financial support from 973 Program (2011CB932504), Key Project from CAS (KJCX2.YW.319), National Nature Science Foundation of China (20971121), and the Nature Science Foundation of Fujian Province. ’ REFERENCES (1) (a) Novitchi, G.; Wernsdorfer, W.; Chibotaru, L. F.; Costes, J. P.; Anson, C. E.; Powell, A. K. Angew. Chem., Int. Ed. 2009, 48, 1614–1619. (b) Cheng, J. W.; Zhang, J.; Zheng, S. T.; Yang, G. Y. Chem.—Eur. J. 2008, 14, 88–97. (c) Kong, X. J.; Long, L. S.; Huang, R. B.; Zheng, L. S.; Harris, T. D.; Zheng, Z. P. Chem. Commun. 2009, 4354–4356. (d) Yang, Y. T.; Luo, F.; Che, Y. X.; Zheng, J. M. Cryst. Growth Des. 2008, 8, 3508–3510. (e) Cai, Y. P.; Zhou, X. X.; Zhou, Z. Y.; Zhu, S. Z.; Thallapally, P. K.; Liu, J. Inorg. Chem. 2009, 48, 6341–6343. (f) Chen, L. F.; Zhang, J.; Ren, G. Q.; Li, Z. J.; Qin, Y. Y.; Yin, P. X.; Cheng, J. K.; Yao, Y. G. CrystEngcomm 2008, 10, 1088–1092. (g) Ma, J. X.; Huang, X. F.; Song, Y.; Song, X. Q.; Liu, W. S. Inorg. Chem. 2009, 48, 6326–6328. (h) Gao, H. L.; Zhao, B.; Zhao, X. O.; Song, Y.; Cheng, P.; Liao, D. Z.; Yan, S. P. Inorg. Chem. 2008, 47, 11057–11061. (i) Guillou, O.; Daiguebonne, C.; Camara, M.; Kerbellec, N. Inorg. Chem. 2006, 45, 8468–8470. (2) (a) Liang, Y. C.; Cao, R.; Su, W. P.; Hong, M. C.; Zhang, W. J. Angew. Chem., Int. Ed. 2000, 39, 3304–3307. (b) Huang, Y. G.; Wang,
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