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A new type of multifunctional single ionic dysprosium complex based on chiral salen-type Schiff base ligand
Inorganica Chimica Acta 423 (2014) 540–544
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
A new type of multifunctional single ionic dysprosium complex based on chiral salen-type Schiff base ligand Yan Sui ⇑, Xiao-Niu Fang, Rong-Hua Hu, Jia Li, Dong-Sheng Liu ⇑ School of Chemistry and Chemical Engineering, The Key Laboratory of Coordination Chemistry of Jiangxi Province, Institute of Applied Chemistry of Jinggangshan University, Jinggangshan University, Jiangxi 343009, PR China
a r t i c l e
i n f o
Article history: Received 4 August 2014 Received in revised form 11 September 2014 Accepted 15 September 2014 Available online 22 September 2014 Keywords: (1R,2R)-1,2-cyclohexylenediamine Schiff base Dysprosium complex Ferroelectric Luminescence
a b s t r a c t A new type of multifunctional single ionic chiral dysprosium complex (DyL) was obtained by the reaction of Dy(NO3)3 and salen-type Schiff base ligand N,N0 -bis(3,5-dichlorosalicylidene)-(1R,2R)-1,2-cyclohexylenediamine. In the synthesis reaction, Dy(III) was found not only to be the central metal to coordinate with two Schiff base ligands, but also the Lewis acid catalyst to promote the partial decomposition of salen-type Schiff base ligand. Complex DyL crystallizes in a chiral and polar space group P21. The central metal Dy(III) adopts eight-coordinated square antiprism geometry with D absolute configuration. Complex DyL exhibits good SHG and ferroelectric properties. The single-crystal sample of DyL displays an obvious ferroelectric behavior with a remnant polarization (Pr) of ca. 4.51 lC cm2 and Ec of ca. 28.11 kV cm1. The solid luminescent spectrum of DyL presents characteristic emission 4F9/2 ? 6H15/2 and 4F9/2 ? 6H13/2 transitions of Dy(III). Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction For the past few decades, significant attention has been paid to the design and synthesis of various noncentrosymmetric ferroelectric compounds [1–5], for their potential applications in ferroelectric random-access memories (FeRAM), switchable nonlinear optical devices, electro-optical devices, and light modulators [6–9]. Recently, the design and construction of molecule-based metal–organic coordination compounds with hybridized physical properties, such as magnetic, second-order nonlinear optical (NLO), ferroelectric, photoluminescent, catalytic properties and gas adsorption is a challenging topic for synthetic chemists [10–14]. To date, studies on the multifunctional material with ferroelectric and luminescent properties have mainly focused on inorganic compounds, and there are few reports on the molecular compounds [15–19]. In recent years, a great number of multifunctional lanthanide complexes have been prepared utilizing various multidentate ligands [20–23]. ‘H2salen’ (N,N0 -ethylenebis(salicylideneimine) and its variations have been widely used as multidentate ligands to incorporate both f- and d-block transition metals, some of which exhibit interesting magnetic and luminescent properties [24–29]. But in the absence of d-block transition metals, only a few lanthanide complexes with salen-type Schiff base ligands have been docu⇑ Corresponding authors. E-mail addresses: [email protected] (Y. Sui), [email protected] (D.-S. Liu). http://dx.doi.org/10.1016/j.ica.2014.09.015 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.
mented, having polynuclear cluster or coordination polymer structures [30–33], and single ionic rare earth complex are very rare. Comparing with neutral metal–organic framework, the ionic metal– organic coordination compounds will be more effective in enlarging the polarity and ferroelectricity due to the existence of the separated positive and negative charge [34–37]. In addition, the imine N atoms have seldom been used to connect lanthanide ions owing to their poor affinity for hard Lewis acid metal ions [38]. If a strong electron-withdrawing group is introduced, it will facilitate the coordination of lanthanide ions to N-donor ligands [39–41]. In previous paper, we have reported one couple of ion ferroelectric based on chiral Schiff base nickel complexes with a polarization value higher than KDP [42]. As our continuous interest in molecular ferroelectric materials, a new type of single ionic rare earth complex was designed and synthesized utilizing the charge difference between ligand and central metal. Meanwhile the electron-withdrawing group (ACl) was introduced to fulfill the coordination of the imine N atoms with lanthanide ions. To the best of our knowledge, it is the first time that single ionic rare earth complex coordinating with all N and O atoms of salen-type Schiff-base ligands is obtained. Lanthanide ion is firstly found to catalyze the partial decomposition of salen-type Schiff base. Complex DyL was obtained by the reaction of dysprosium nitrate and salen-type Schiff base ligand N,N0 -bis(3,5-dichlorosalicylidene)-(1R,2R)-1,2-cyclohexylenediamine (Scheme 1). The structure, ferroelectric and luminescent properties were reported in this paper.
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Scheme 1. Synthesis routine of complex DyL.
2. Experimental 2.1. General materials and methods (1R,2R)-()-1,2-cyclohexanediamine and 3,5-diclorosalicylaldehyde were obtained from Aldrich company. All other reagents and solvents were purchased from commercial sources and used as received. The IR spectrum was performed on a Bruker Vector 22 FT-IR spectrometer with KBr discs in the 4000–400 cm1 range. The electric hysteresis loops were recorded on a Ferroelectric Tester Multiferroic made by Radiant Technologies, Inc. Complex dielectric permittivity was performed using automatic impedance TongHui 2828 Analyzer. The measuring AC voltage was 1 V. Fluorescence measurement was conducted on Perkin Elmer LS-55 spectrofluorometer with both excitation and emission slits set at 5 nm. 2.2. Synthesis of Schiff base ligand A mixture of (1R,2R)-()-1,2-cyclohexanediamine (0.1140 g, 1 mmol) and 3,5-diclorosalicylaldehyde (0.3820 g, 2 mmol) in 50 mL ethanol was heated at 60 °C for 1.5 h, and then cooled to room temperature. The precipitate was collected, re-crystallized in ethanol solution and dried under vacuum. FT-IR (KBr, cm1): 3015(s), 2928(m), 1642(s), 1606(m), 1574(m), 1482(s).
Mo Ka radiation (k = 0.71073 Å). Absorption correction was applied using SADABS [43]. The structure was solved by direct methods and refined with the full-matrix least-squares technique using SHELXS-97 and SHELXTL-97 programs, respectively [44]. Anisotropic thermal parameters were applied to all non-hydrogen atoms. The H atoms were positioned geometrically and treated as riding on their parent atoms, with CAH distances of 0.97 Å (methylene) and 0.96 Å (methyl). Crystal data as well as details of data collection and refinement for the compounds are summarized in Table 1. 3. Results and discussion 3.1. Crystal structural descriptions Complex DyL crystallizes in a chiral and polar space group P21. Its crystal structure is shown in Fig. 1. Selected bond lengths and Table 1 Crystal data and structure refinements for DyL.
2.3. Synthesis of complex DyL The obtained Schiff base ligand (0.1840 g, 0.4 mmol) was dissolved in 30 mL of ethanol, and then Dy(NO3)36H2O (0.1864 g, 0.4 mmol) was added and refluxed for about 4 h. The mixed solution was cooled to r.t. and left to stand undisturbed. Upon slow evaporation at r.t. for several days, single crystals suitable for X-ray analysis were collected. FT-IR (KBr, cm1): 3329(s), 3010(s), 2942(m), 1658(s), 1640(s), 1600(m), 1571(m), 1457(s). 2.4. X-ray crystallography Diffraction intensities for DyL were collected at 293(2) K on a Bruker Apex II CCD diffractometer with graphite-monochromated
a
Compound
DyL
Empirical formula Formula weight Crystal system Space group a (Å) b (Å) c (Å) b (°) V (Å3) Z Dcalc (Mg m3) h range (°) Collected reflections Unique reflections Parameters T (K) R1 [I > 2r(I)], wR2 (all data)a Goodness-of-fit (GOF) Flack parameter Dqmax (e Å1) Dqmin (e Å1)
C57H61Cl10DyN6O7 1459.12 monoclinic P21 11.4982 (10) 21.5339 (19) 12.9149 (11) 98.335 (1) 3164.0 (5) 2 1.532 2.4–27.8 18 879 9884 734 293 (2) 0.022, 0.057 0.92 0.001 (5) 0.51 0.36
R1 = R||Fo| |Fc||/R|Fo|, wR2 = [Rw(|F2o| |F2c |)2/Rw(|F2o|)2]1/2.
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Y. Sui et al. / Inorganica Chimica Acta 423 (2014) 540–544 Table 3 The list of hydrogen bonds parameters (Å, °). DAH A
DAH
H A
D A
O6AH6D O7 N6AH6C O6 N6AH6B O3 N6AH6A O1 O5AH5 N5 O7AH7A O4i
0.82 0.89 0.89 0.89 0.82 0.84
1.95 1.89 2.00 1.87 1.92 2.02
2.746 2.778 2.735 2.739 2.632 2.836
DAH A (6) (6) (4) (4) (5) (4)
165 178 139 166 145 165
Symmetry code: (i) x 1, y, z.
Fig. 1. The molecular structure of complex DyL, showing 30% probability displacement ellipsoids.
Table 2 Selected bond length (Å) and bond angle (°) of the complex DyL. Dy1AO1 Dy1AO2 Dy1AO3 Dy1AO4 O1ADy1AO3 O1ADy1AN1 O1ADy1AN2 O1ADy1AN3 O1ADy1AN4 O2ADy1AO1 O2ADy1AO3 O2ADy1AO4 O2ADy1AN1 O2ADy1AN2 O2ADy1AN3 O2ADy1AN4 O3ADy1AN1 O3ADy1AN2
2.334 (2) 2.232 (2) 2.335 (2) 2.267 (2) 88.73 (8) 69.87 (11) 136.71 (10) 78.11 (11) 74.06 (9) 148.79 (10) 98.28 (9) 91.96 (9) 141.34 (10) 74.22 (9) 75.56 (10) 80.48 (10) 76.95 (9) 75.28 (9)
Dy1AN1 Dy1AN2 Dy1AN3 Dy1AN4 O3ADy1AN3 O3ADy1AN4 O4ADy1AO1 O4ADy1AO3 O4ADy1AN1 O4ADy1AN2 O4ADy1AN3 O4ADy1AN4 N1ADy1AN2 N1ADy1AN4 N2ADy1AN4 N3ADy1AN1 N3ADy1AN2 N3ADy1AN4
2.518 (3) 2.519 (3) 2.505 (3) 2.540 (3) 71.20 (9) 137.37 (9) 97.67 (9) 148.69 (8) 76.63 (9) 79.26 (9) 140.11 (9) 73.43 (9) 67.42 (10) 128.74 (10) 141.80 (10) 134.83 (12) 130.34 (10) 67.24 (10)
angles are given in Table 2. The anisotropic displacement parameters and other structure information have been deposited at the Cambridge Crystallographic Data Centre under the registration number CCDC 1012592.
Complex DyL consists of one Dy(III) complex anion, one organic cation and two ethanol molecules. The central metal Dy(III) adopts eight-coordinated square antiprism geometry with D absolute configuration [45], coordinating with four phenolate O atoms and four imine N atoms from two Schiff base ligands (Fig. 2a and b). The organic cation is a single Schiff base of 1,2-cyclohexanediamine, obtained from the in situ partial decomposition of salen-type Schiff base ligand L, and the yielded amino group is pronated to balance the charge of complex anion. Dy(III) acts as not only the central metal to coordinate to two salen-type Schiff base ligand L, but also the Lewis acid catalyst in partial decomposition of ligand L. It is a rare example that rare earth single ionic complex coordinating with all N and O atoms of salen-type Schiff base ligand. Besides the intramolecular hydrogen bonds, there exist intermolecular typical H-bonds to join adjacent molecules into three-dimensional frameworks (Table 3). The distances between the mass centers of phenyl rings (C1C6) and (C35C40), (C15C20) and (C21C26) are 3.556 Å and 3.611 Å, respectively. Meanwhile, the distance between the mass centers of phenyl rings (C15C20) and (C41C46) is 3.687 Å (Fig. 2c). These short distances indicate strong p–p interactions. 3.2. Ferroelectric, second-order nonlinear optical and dielectric properties The second-order nonlinear optical effect of DyL was determined on a LAB130 Pulsed Nd: YAG laser according to the principle proposed by Kurtz and Perry [46], and preliminary studies of powder samples of DyL showed second harmonic generation (SHG) efficiency with approximately 0.8 times that of urea. The ferroelectric behaviors of DyL were also examined given that P21 space group point belongs to the C2 polar point groups required for ferroelectric materials [47,48]. The ferroelectric property was investigated at room temperature with single crystal
Fig. 2. (a) The coordinating mode of central metal in complex DyL; (b) the eight-coordinated square antiprism geometry with D absolute configuration of central metal Dy(III); (c) the p–p interactions of complex DyL.
Y. Sui et al. / Inorganica Chimica Acta 423 (2014) 540–544
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Fig. 3. (a, left) Electric hysteresis loop of DyL at r.t. for single crystal sample; (b, right) Temperature dependence of the dielectric constant of DyL at various frequencies. Inset: dielectric constant at high frequencies.
samples and shown in Fig. 3. The single-crystal sample of DyL indeed displayed an obvious ferroelectric behavior with a remnant polarization (Pr) of ca. 4.51 lC cm2 and Ec of ca. 28.11 kV cm1. The almost perfect loop shape indicated the reality of ferroelectricity [49]. The value of Pr is very close to that of Ps, which are much larger than that of the classical organic–inorganic ferroelectrics triglycine sulfate (TGS; Ps = 3.0 lC cm2) and NaKC4H4O64H2O (Rosal salt; Ps = 0.25 lC cm2). We think that the noncentrosymmetric structure containing multi-electron-withdrawing groups (ACl) and separated positive and negative charge are helpful to bring about the large spontaneous electric dipole moments. In addition, possible configuration transformation of cyclohexyl groups and temperature-dependent imine–enamine tautomerism of Schiff base (named thermochromism) usually induce the switching of molecular polarity (ferroelectricity) [50,51]. The ferroelectric properties of powdered samples of DyL in pellets were also investigated at r.t. (Fig. S1). Due to the irregular arrangement of polar direction in powdered samples, the observed hysteresis loops are not very ideal. Because the leakage current is extremely low (less than 108 A cm2) under the employed conditions (Fig. S2), the observed hysteresis loop is clearly due to ferroelectricity. The temperature dependent dielectric constant was measured at different frequencies and showed in Fig. 3b. A dielectric peak appeared at about 82 °C, indicating the presence of a phase transition at this temperature. But the relatively broad peaks indicated the complexity of the ferroelectric–paraelectric phase transition
mechanism. More than one kind of domains may be existed in the crystal. The phase transition should be arisen from the interaction of different kinds of electric domains. 3.3. Luminescent property The solid luminescent spectrum of DyL was measured at room temperature and shown in Fig. 4, which presents two apparent emission bands under the excitation of 375 nm with the maximum emission wavelengths are 484 and 571 nm, corresponding to the characteristic emission 4F9/2 ? 6H15/2 and 4F9/2 ? 6H13/2 transitions of Dy(III), respectively [52,53]. It is obvious that the intensity of the blue emission corresponding to 4F9/2 ? 6H15/2 transition is much stronger than that of the yellow one, which indicates that the Schiff base ligand is becoming to the sensitization of blue luminescence of Dy(III) [54,55]. 4. Conclusions In summary, we have demonstrated a new type of multifunctional single ionic Dy(III) complex (DyL) based on chiral salen-type Schiff base ligand with luminescent and ferroelectric behavior. Dy(III) acts as not only the central metal to coordinate with two Schiff base ligands, but also the Lewis acid catalyst to promote the partial decomposition of salen-type Schiff base ligand. The potential applications of multifunctional single ionic Dy(III) complex (DyL) based on chiral salen-type Schiff base ligand will be further studied. Acknowledgments This work was supported by National Natural Science Foundation of China (21361012 and 21461012), Department of Science and Technology of Jiangxi Province (20114BAB203027, 20121BB G70014 and 20133ACG70007), Education Department of Jiangxi Province (KJLD12034, GJJ14556 and JXJG-11-15-6). Appendix A. Supplementary material
Fig. 4. Emission spectrum of DyL (kex = 375 nm).
CCDC 1012592 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam. ac.uk/data_request/cif. Supplementary data associated with this
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Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
A new type of multifunctional single ionic dysprosium complex based on chiral salen-type Schiff base ligand Yan Sui ⇑, Xiao-Niu Fang, Rong-Hua Hu, Jia Li, Dong-Sheng Liu ⇑ School of Chemistry and Chemical Engineering, The Key Laboratory of Coordination Chemistry of Jiangxi Province, Institute of Applied Chemistry of Jinggangshan University, Jinggangshan University, Jiangxi 343009, PR China
a r t i c l e
i n f o
Article history: Received 4 August 2014 Received in revised form 11 September 2014 Accepted 15 September 2014 Available online 22 September 2014 Keywords: (1R,2R)-1,2-cyclohexylenediamine Schiff base Dysprosium complex Ferroelectric Luminescence
a b s t r a c t A new type of multifunctional single ionic chiral dysprosium complex (DyL) was obtained by the reaction of Dy(NO3)3 and salen-type Schiff base ligand N,N0 -bis(3,5-dichlorosalicylidene)-(1R,2R)-1,2-cyclohexylenediamine. In the synthesis reaction, Dy(III) was found not only to be the central metal to coordinate with two Schiff base ligands, but also the Lewis acid catalyst to promote the partial decomposition of salen-type Schiff base ligand. Complex DyL crystallizes in a chiral and polar space group P21. The central metal Dy(III) adopts eight-coordinated square antiprism geometry with D absolute configuration. Complex DyL exhibits good SHG and ferroelectric properties. The single-crystal sample of DyL displays an obvious ferroelectric behavior with a remnant polarization (Pr) of ca. 4.51 lC cm2 and Ec of ca. 28.11 kV cm1. The solid luminescent spectrum of DyL presents characteristic emission 4F9/2 ? 6H15/2 and 4F9/2 ? 6H13/2 transitions of Dy(III). Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction For the past few decades, significant attention has been paid to the design and synthesis of various noncentrosymmetric ferroelectric compounds [1–5], for their potential applications in ferroelectric random-access memories (FeRAM), switchable nonlinear optical devices, electro-optical devices, and light modulators [6–9]. Recently, the design and construction of molecule-based metal–organic coordination compounds with hybridized physical properties, such as magnetic, second-order nonlinear optical (NLO), ferroelectric, photoluminescent, catalytic properties and gas adsorption is a challenging topic for synthetic chemists [10–14]. To date, studies on the multifunctional material with ferroelectric and luminescent properties have mainly focused on inorganic compounds, and there are few reports on the molecular compounds [15–19]. In recent years, a great number of multifunctional lanthanide complexes have been prepared utilizing various multidentate ligands [20–23]. ‘H2salen’ (N,N0 -ethylenebis(salicylideneimine) and its variations have been widely used as multidentate ligands to incorporate both f- and d-block transition metals, some of which exhibit interesting magnetic and luminescent properties [24–29]. But in the absence of d-block transition metals, only a few lanthanide complexes with salen-type Schiff base ligands have been docu⇑ Corresponding authors. E-mail addresses: [email protected] (Y. Sui), [email protected] (D.-S. Liu). http://dx.doi.org/10.1016/j.ica.2014.09.015 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.
mented, having polynuclear cluster or coordination polymer structures [30–33], and single ionic rare earth complex are very rare. Comparing with neutral metal–organic framework, the ionic metal– organic coordination compounds will be more effective in enlarging the polarity and ferroelectricity due to the existence of the separated positive and negative charge [34–37]. In addition, the imine N atoms have seldom been used to connect lanthanide ions owing to their poor affinity for hard Lewis acid metal ions [38]. If a strong electron-withdrawing group is introduced, it will facilitate the coordination of lanthanide ions to N-donor ligands [39–41]. In previous paper, we have reported one couple of ion ferroelectric based on chiral Schiff base nickel complexes with a polarization value higher than KDP [42]. As our continuous interest in molecular ferroelectric materials, a new type of single ionic rare earth complex was designed and synthesized utilizing the charge difference between ligand and central metal. Meanwhile the electron-withdrawing group (ACl) was introduced to fulfill the coordination of the imine N atoms with lanthanide ions. To the best of our knowledge, it is the first time that single ionic rare earth complex coordinating with all N and O atoms of salen-type Schiff-base ligands is obtained. Lanthanide ion is firstly found to catalyze the partial decomposition of salen-type Schiff base. Complex DyL was obtained by the reaction of dysprosium nitrate and salen-type Schiff base ligand N,N0 -bis(3,5-dichlorosalicylidene)-(1R,2R)-1,2-cyclohexylenediamine (Scheme 1). The structure, ferroelectric and luminescent properties were reported in this paper.
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Scheme 1. Synthesis routine of complex DyL.
2. Experimental 2.1. General materials and methods (1R,2R)-()-1,2-cyclohexanediamine and 3,5-diclorosalicylaldehyde were obtained from Aldrich company. All other reagents and solvents were purchased from commercial sources and used as received. The IR spectrum was performed on a Bruker Vector 22 FT-IR spectrometer with KBr discs in the 4000–400 cm1 range. The electric hysteresis loops were recorded on a Ferroelectric Tester Multiferroic made by Radiant Technologies, Inc. Complex dielectric permittivity was performed using automatic impedance TongHui 2828 Analyzer. The measuring AC voltage was 1 V. Fluorescence measurement was conducted on Perkin Elmer LS-55 spectrofluorometer with both excitation and emission slits set at 5 nm. 2.2. Synthesis of Schiff base ligand A mixture of (1R,2R)-()-1,2-cyclohexanediamine (0.1140 g, 1 mmol) and 3,5-diclorosalicylaldehyde (0.3820 g, 2 mmol) in 50 mL ethanol was heated at 60 °C for 1.5 h, and then cooled to room temperature. The precipitate was collected, re-crystallized in ethanol solution and dried under vacuum. FT-IR (KBr, cm1): 3015(s), 2928(m), 1642(s), 1606(m), 1574(m), 1482(s).
Mo Ka radiation (k = 0.71073 Å). Absorption correction was applied using SADABS [43]. The structure was solved by direct methods and refined with the full-matrix least-squares technique using SHELXS-97 and SHELXTL-97 programs, respectively [44]. Anisotropic thermal parameters were applied to all non-hydrogen atoms. The H atoms were positioned geometrically and treated as riding on their parent atoms, with CAH distances of 0.97 Å (methylene) and 0.96 Å (methyl). Crystal data as well as details of data collection and refinement for the compounds are summarized in Table 1. 3. Results and discussion 3.1. Crystal structural descriptions Complex DyL crystallizes in a chiral and polar space group P21. Its crystal structure is shown in Fig. 1. Selected bond lengths and Table 1 Crystal data and structure refinements for DyL.
2.3. Synthesis of complex DyL The obtained Schiff base ligand (0.1840 g, 0.4 mmol) was dissolved in 30 mL of ethanol, and then Dy(NO3)36H2O (0.1864 g, 0.4 mmol) was added and refluxed for about 4 h. The mixed solution was cooled to r.t. and left to stand undisturbed. Upon slow evaporation at r.t. for several days, single crystals suitable for X-ray analysis were collected. FT-IR (KBr, cm1): 3329(s), 3010(s), 2942(m), 1658(s), 1640(s), 1600(m), 1571(m), 1457(s). 2.4. X-ray crystallography Diffraction intensities for DyL were collected at 293(2) K on a Bruker Apex II CCD diffractometer with graphite-monochromated
a
Compound
DyL
Empirical formula Formula weight Crystal system Space group a (Å) b (Å) c (Å) b (°) V (Å3) Z Dcalc (Mg m3) h range (°) Collected reflections Unique reflections Parameters T (K) R1 [I > 2r(I)], wR2 (all data)a Goodness-of-fit (GOF) Flack parameter Dqmax (e Å1) Dqmin (e Å1)
C57H61Cl10DyN6O7 1459.12 monoclinic P21 11.4982 (10) 21.5339 (19) 12.9149 (11) 98.335 (1) 3164.0 (5) 2 1.532 2.4–27.8 18 879 9884 734 293 (2) 0.022, 0.057 0.92 0.001 (5) 0.51 0.36
R1 = R||Fo| |Fc||/R|Fo|, wR2 = [Rw(|F2o| |F2c |)2/Rw(|F2o|)2]1/2.
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Y. Sui et al. / Inorganica Chimica Acta 423 (2014) 540–544 Table 3 The list of hydrogen bonds parameters (Å, °). DAH A
DAH
H A
D A
O6AH6D O7 N6AH6C O6 N6AH6B O3 N6AH6A O1 O5AH5 N5 O7AH7A O4i
0.82 0.89 0.89 0.89 0.82 0.84
1.95 1.89 2.00 1.87 1.92 2.02
2.746 2.778 2.735 2.739 2.632 2.836
DAH A (6) (6) (4) (4) (5) (4)
165 178 139 166 145 165
Symmetry code: (i) x 1, y, z.
Fig. 1. The molecular structure of complex DyL, showing 30% probability displacement ellipsoids.
Table 2 Selected bond length (Å) and bond angle (°) of the complex DyL. Dy1AO1 Dy1AO2 Dy1AO3 Dy1AO4 O1ADy1AO3 O1ADy1AN1 O1ADy1AN2 O1ADy1AN3 O1ADy1AN4 O2ADy1AO1 O2ADy1AO3 O2ADy1AO4 O2ADy1AN1 O2ADy1AN2 O2ADy1AN3 O2ADy1AN4 O3ADy1AN1 O3ADy1AN2
2.334 (2) 2.232 (2) 2.335 (2) 2.267 (2) 88.73 (8) 69.87 (11) 136.71 (10) 78.11 (11) 74.06 (9) 148.79 (10) 98.28 (9) 91.96 (9) 141.34 (10) 74.22 (9) 75.56 (10) 80.48 (10) 76.95 (9) 75.28 (9)
Dy1AN1 Dy1AN2 Dy1AN3 Dy1AN4 O3ADy1AN3 O3ADy1AN4 O4ADy1AO1 O4ADy1AO3 O4ADy1AN1 O4ADy1AN2 O4ADy1AN3 O4ADy1AN4 N1ADy1AN2 N1ADy1AN4 N2ADy1AN4 N3ADy1AN1 N3ADy1AN2 N3ADy1AN4
2.518 (3) 2.519 (3) 2.505 (3) 2.540 (3) 71.20 (9) 137.37 (9) 97.67 (9) 148.69 (8) 76.63 (9) 79.26 (9) 140.11 (9) 73.43 (9) 67.42 (10) 128.74 (10) 141.80 (10) 134.83 (12) 130.34 (10) 67.24 (10)
angles are given in Table 2. The anisotropic displacement parameters and other structure information have been deposited at the Cambridge Crystallographic Data Centre under the registration number CCDC 1012592.
Complex DyL consists of one Dy(III) complex anion, one organic cation and two ethanol molecules. The central metal Dy(III) adopts eight-coordinated square antiprism geometry with D absolute configuration [45], coordinating with four phenolate O atoms and four imine N atoms from two Schiff base ligands (Fig. 2a and b). The organic cation is a single Schiff base of 1,2-cyclohexanediamine, obtained from the in situ partial decomposition of salen-type Schiff base ligand L, and the yielded amino group is pronated to balance the charge of complex anion. Dy(III) acts as not only the central metal to coordinate to two salen-type Schiff base ligand L, but also the Lewis acid catalyst in partial decomposition of ligand L. It is a rare example that rare earth single ionic complex coordinating with all N and O atoms of salen-type Schiff base ligand. Besides the intramolecular hydrogen bonds, there exist intermolecular typical H-bonds to join adjacent molecules into three-dimensional frameworks (Table 3). The distances between the mass centers of phenyl rings (C1C6) and (C35C40), (C15C20) and (C21C26) are 3.556 Å and 3.611 Å, respectively. Meanwhile, the distance between the mass centers of phenyl rings (C15C20) and (C41C46) is 3.687 Å (Fig. 2c). These short distances indicate strong p–p interactions. 3.2. Ferroelectric, second-order nonlinear optical and dielectric properties The second-order nonlinear optical effect of DyL was determined on a LAB130 Pulsed Nd: YAG laser according to the principle proposed by Kurtz and Perry [46], and preliminary studies of powder samples of DyL showed second harmonic generation (SHG) efficiency with approximately 0.8 times that of urea. The ferroelectric behaviors of DyL were also examined given that P21 space group point belongs to the C2 polar point groups required for ferroelectric materials [47,48]. The ferroelectric property was investigated at room temperature with single crystal
Fig. 2. (a) The coordinating mode of central metal in complex DyL; (b) the eight-coordinated square antiprism geometry with D absolute configuration of central metal Dy(III); (c) the p–p interactions of complex DyL.
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Fig. 3. (a, left) Electric hysteresis loop of DyL at r.t. for single crystal sample; (b, right) Temperature dependence of the dielectric constant of DyL at various frequencies. Inset: dielectric constant at high frequencies.
samples and shown in Fig. 3. The single-crystal sample of DyL indeed displayed an obvious ferroelectric behavior with a remnant polarization (Pr) of ca. 4.51 lC cm2 and Ec of ca. 28.11 kV cm1. The almost perfect loop shape indicated the reality of ferroelectricity [49]. The value of Pr is very close to that of Ps, which are much larger than that of the classical organic–inorganic ferroelectrics triglycine sulfate (TGS; Ps = 3.0 lC cm2) and NaKC4H4O64H2O (Rosal salt; Ps = 0.25 lC cm2). We think that the noncentrosymmetric structure containing multi-electron-withdrawing groups (ACl) and separated positive and negative charge are helpful to bring about the large spontaneous electric dipole moments. In addition, possible configuration transformation of cyclohexyl groups and temperature-dependent imine–enamine tautomerism of Schiff base (named thermochromism) usually induce the switching of molecular polarity (ferroelectricity) [50,51]. The ferroelectric properties of powdered samples of DyL in pellets were also investigated at r.t. (Fig. S1). Due to the irregular arrangement of polar direction in powdered samples, the observed hysteresis loops are not very ideal. Because the leakage current is extremely low (less than 108 A cm2) under the employed conditions (Fig. S2), the observed hysteresis loop is clearly due to ferroelectricity. The temperature dependent dielectric constant was measured at different frequencies and showed in Fig. 3b. A dielectric peak appeared at about 82 °C, indicating the presence of a phase transition at this temperature. But the relatively broad peaks indicated the complexity of the ferroelectric–paraelectric phase transition
mechanism. More than one kind of domains may be existed in the crystal. The phase transition should be arisen from the interaction of different kinds of electric domains. 3.3. Luminescent property The solid luminescent spectrum of DyL was measured at room temperature and shown in Fig. 4, which presents two apparent emission bands under the excitation of 375 nm with the maximum emission wavelengths are 484 and 571 nm, corresponding to the characteristic emission 4F9/2 ? 6H15/2 and 4F9/2 ? 6H13/2 transitions of Dy(III), respectively [52,53]. It is obvious that the intensity of the blue emission corresponding to 4F9/2 ? 6H15/2 transition is much stronger than that of the yellow one, which indicates that the Schiff base ligand is becoming to the sensitization of blue luminescence of Dy(III) [54,55]. 4. Conclusions In summary, we have demonstrated a new type of multifunctional single ionic Dy(III) complex (DyL) based on chiral salen-type Schiff base ligand with luminescent and ferroelectric behavior. Dy(III) acts as not only the central metal to coordinate with two Schiff base ligands, but also the Lewis acid catalyst to promote the partial decomposition of salen-type Schiff base ligand. The potential applications of multifunctional single ionic Dy(III) complex (DyL) based on chiral salen-type Schiff base ligand will be further studied. Acknowledgments This work was supported by National Natural Science Foundation of China (21361012 and 21461012), Department of Science and Technology of Jiangxi Province (20114BAB203027, 20121BB G70014 and 20133ACG70007), Education Department of Jiangxi Province (KJLD12034, GJJ14556 and JXJG-11-15-6). Appendix A. Supplementary material
Fig. 4. Emission spectrum of DyL (kex = 375 nm).
CCDC 1012592 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam. ac.uk/data_request/cif. Supplementary data associated with this
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