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Synthesis, crystal structure and nonlinear optical property of a Zinc(II) complex base on the reduced Schiff-base ligand
Inorganic Chemistry Communications 22 (2012) 82–84
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis, crystal structure and nonlinear optical property of a Zinc(II) complex base on the reduced Schiff-base ligand Shao-Ming Ying ⁎ MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, PR China Department of chemistry, Ningde Normal University, Ningde, 352100, PR China
a r t i c l e
i n f o
Article history: Received 2 March 2012 Accepted 15 May 2012 Available online 24 May 2012 Keywords: Hydrothermal synthesis Reduced Schiff base Second harmonic generation Crystal structure
a b s t r a c t By hydrothermal reactions of Zn(II) nitrate with N-(4-carboxyl)benzyl-L-alanine acid (H2L), a novel Zn(II) complex, namely, [Zn(HL)2(H2O)2] (1), have been obtained. Single crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the C2 space group and displays a 0D dimensional structure. The Zn(II) ions are four-coordinated and each Zn(II) ion coordinated with two HL anions forming a [Zn(HL)2(H2O)2] unit. The stacking of such units by hydrogen bonds results in its supramolecular structure. Complex 1 shows a second harmonic generation response that is ~ 1.5 times that of KDP (KH2PO4). © 2012 Elsevier B.V. All rights reserved.
Noncentrosymmetric (NCS) compounds are of great interest because of their potential applications in many areas such as pyroelectricity, ferroelectricity, and especially second-order nonlinear optical (NLO) materials [1–4]. In the past a few decades, second-order nonlinear optical materials have gained much attention because of their application in the domains of photoelectronics and photonics [5–8]. A number of materials exhibiting a second-order NLO effect have also been reported [9–18]. We can divide the NLO materials into three types: inorganic, organic and organic–inorganic hybrid according to the composition of the material. The essential requirement for such NLO materials is that the second-order NLO chromophores designed at the molecular level must be assembled into a noncentrosymmetric (NCS) structure. In the inorganic–organic hybrid systems, the dipolar alignment of the noncentrosymmetric components in a bulk structure is a challenge because they normally tend to be arranged in opposite directions, forming a centrosymmetric structure. Several approaches have been developed to resolve this problem: introducing Jahn–Teller-distorted cations (such as Ti4+, Nb5+, and W6+) or lone-pair cations (such as Pb 2+), using the chiral ligands or the asymmetric ligands and introducing the polar guest molecules into the molecule systems [19]. To induce NCS structures, the use of introduction of the chiral ligands or the asymmetric ligands is a convenient and efficient method [20]. For this purpose, we introduce the reduced Schiff-base ligand to obtain the NLO material. We mainly studied the reduced Schiff-base
⁎ MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, PR China. Tel.: + 86 13859660287; fax: + 86 20 84112245. E-mail address: [email protected]. 1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2012.05.026
ligands which have a chiral carbon atom. We can obtain the reduced Schiff-base ligands of this type by react the amino acids which have the chiral carbon atom with the aldehyde group to get the Schiffbases and then reduce the C_N bond. Up to now, to the best of our knowledge, second-harmonic-generation (SHG)-active metal complexes base on the reduced Schiff-base ligands of this type is still few [21]. As an initial research work, we selected N-(4-carboxyl)benzylL-alanine acid (as shown in Fig. S1) as a reduced Schiff-base ligand, due to its following characteristics: (a) it contains a phenyl ring which may be a source of the second-order NLO effect; (b) it is a flexible ligand which contains two carboxylate moieties and a secondary amine group, can show various coordination modes, maybe can lead to the formation of an asymmetric structure. Herein, we report a novel SHG-active Zn(II) complex assembled from the above reduced Schiff-base ligand, namely, [Zn(HL)2(H2O)2]. H2L was synthesized according to the procedures previously described [22–24]. The single crystal of H2L also was obtained [25,26]. Complex 1 was hydrothermally synthesized by Zn(NO3)2·6H2O and H2L ligand in a mixed solution of water, ethanol and N,N-dimethylformamide (DMF) at 80 °C for 4 days [27]. Single crystal X-ray diffraction analysis [28] reveals that complex 1 crystallizes in the C2 space group and displays a 0D dimensional structure. In complex 1, the Zn(II) ions are fourcoordinated by two oxygen atoms from two HL anions and two water molecules (Fig. 1). The Zn\O distances ranges from 1.951(3) to 1.996(3)Å, which are comparable to those reported for other Zn(II) carboxylates [29]. The HL anions is unidentate. Only a oxygen atom of the carboxylate group on the phenyl coordinated to a Zn(II) ion. Each Zn(II) ion coordinated with two HL anions forming a [Zn(HL)2(H2O)2] unit. The stacking of such units by hydrogen bonds [O(3)…O(1)W, symmetry code: 0.5+x, 1.5+y, z, bond distance is 2.659(4)Å; N(1)…O(4),
S-M. Ying / Inorganic Chemistry Communications 22 (2012) 82–84
83
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TG/%
80
60
40
20
Fig. 1. Asymmetric unit of complex 1 drawn at 30% probability thermal ellipsoids. Hydrogen atoms were omitted for clarity. Symmetry codes for the generated atoms: A, 1 − x, y, 2 − z.
symmetry code: 1.5−x, −0.5+y, 1−z, bond distance is 2.808(5)Å] results in its crystallization in the chiral C2 space group [Fig. 2]. The simulated and experimental powder X-ray diffraction (PXRD) patterns of complex 1 are in good agreement with each other (as shown in Fig. S2), indicating the phase purity of the products. The thermal behavior of complex 1 was studied to reveal its thermal stability (Fig. 3). Complex 1 can stable till 185 °C. It exhibits two stages weight loss. The first dues to the release of the coordinated water molecules and the decompose of the organic ligands [from 185 °C to 475 °C, the observed weight loss of this step is 34.0%, close to the calculated value 34.7%, if the residues is Zn(NO3)2.]. The second step started at 475 °C, and didn't stop till 900 °C, the terminal of our test. The solid-state photoluminescent spectra of complex 1 at room temperature are depicted in Fig. 4. The steady-state photoluminescent spectrum of the free H2L ligand is depicted in Fig. S3. The H2L ligand displays emission peaks at 414 nm upon excitation at 314 nm. The complex 1 displays emission peaks at 422 nm upon excitation at 317 nm. Compared with the emission spectrums of the ligand, red shift of emission bands of this complex has been observed. The emission band of complex 1 is probably originated from the intraligand luminescent emission [30]. This result indicates that complex 1 would be candidates for potential photoactive materials. With the fact that complex 1 crystallizes in a noncentrosymmetric (NCS) space group (C2), we studied the SHG measurement on sieved powdered samples of 1. The relative SHG signal intensity vs. particle size for ground crystals of 1 was shown in Fig. 5, which indicates that the complex was phase-matchable, according to the rule proposed by Kurtz and Perry [31]. Complex 1 exhibits a SHG efficiency about 1.5 times that of KDP (KH2PO4) by comparing the second-harmonic signal
0
100
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300
400
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600
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800
900
T/centigrade Fig. 3. The TGA curve of complex 1.
produced by samples of 1 and KDP (KH2PO4) in the same particle range of 150–210 μm.
Conclusion In summary, we have successfully synthesized a novel Zn(II) complex base on the flexible N-(4-carboxyl)benzyl-L-alanine acid ligand. Complex 1 displays a 0D dimensional structure and crystallizes in the C2 space group which maybe induce by the use of the chiral ligan. It shows a second harmonic generation response that is ~1.5 times that of KDP. It also would be candidates for potential photoactive materials. The present work serves as an elegant example in which the use of introduction of the chiral ligands or the asymmetric ligands is a convenient and efficient method to induce NCS structures. We are currently extending such a synthetic technique to explore other SHG-active materials base on ligands of this type.
Acknowledgments This work was supported by the National Natural Science Foundation of China (90922031 and 21001120) and the Research Program of Ningde Normal University (2011H103, 2011Y001 and 2011J001). We thank Prof. Jiang-Gao Mao and Dr. Jian-Han Zhang for their kind help with the SHG measurements.
a
Intensity (a. u.)
b
0
c
emission excitation
Zn N O C
300 320 340 360 380 400 420 440 460 480 500 520
Wavelength (nm) Fig. 2. View of the structure of complex 1 down the b-axis. Hydrogen atoms were omitted for clarity. Hydrogen bonds are represented by dashed lines.
Fig. 4. The solid-state photoluminescent spectra of complex 1.
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S-M. Ying / Inorganic Chemistry Communications 22 (2012) 82–84
SHG Intensity (arb.)
100 80 60 40 20 0 40
80
120
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Particle Size (µm) Fig. 5. The phase matching curve for 1. The curve is to guide the eye and is not a fit to the data.
Appendix A. Supplementary material CCDC 862839 to 862840 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internat.)C44 1223 336 033; E-mail: [email protected]]. More details about this paper can be found at http://dx.doi.org/10. 1016/j.inoche.2012.05.026.
References [1] S.B. Lang, D.K. Das-Gupta, in: H.S. Nalwa (Ed.), Handbook of Advanced Electronic and Photonic Materials and Devices, vol. 4, Academic Press, San Francisco, 2001, pp. 1–55. [2] C. Chen, G. Liu, Recent advances in nonlinear optical and electro-optical materials, Annu. Rev. Mater. Sci. 16 (1986) 203–243. [3] K.M. Ok, E.O. Chi, P.S. Halasyamani, Bulk characterization methods for noncentrosymmetric materials: second-harmonic generation, piezoelectricity, pyroelectricity, and ferroelectricity, Chem. Soc. Rev. 35 (2006) 710–717. [4] M.E. Lines, A.M. Glass, Principles and Applications of Ferroelectrics and Related Materials, Oxford University Press, Oxford, U.K, 1991. [5] O.R. Evans, W. Lin, Crystal engineering of NLO materials based on metal-organic coordination networks, Acc. Chem. Res. 35 (2002) 511–522. [6] S. Jayanty, P. Gangopadhyay, T.P. Radhakrishnan, Steering molecular dipoles from centrosymmetric to a noncentrosymmetric and SHG active assembly using remote functionality and complexation, J. Mater. Chem. 12 (2002) 2792–2797. [7] M.J. Prakash, T.P. Radhakrishnan, SHG active crystals of a remote functionalized achiral NLO-phore assembled through Zinc(II) complexation, Inorg. Chem. 45 (2006) 9758–9764. [8] Z. Guo, R. Cao, X. Wang, H. Li, W. Yuan, G. Wang, H. Wu, J. Li, A multifunctional 3D ferroelectric and NLO-active porous metal-organic framework, J. Am. Chem. Soc. 131 (2009) 6894–6895. [9] P. Gangopadhyay, N.K.M.N. Srinivas, D.N. Rao, T.P. Radhakrishnan, Control of supramolecular organization by molecular structure and symmetry leading to the induction and enhancement of solid state SHG, Opt. Mater. 21 (2003) 55–59. [10] M. Ravi, T.P. Radhakrishnan, Analysis of the large hyperpolarizabilities of push– pull quinonoid molecules, J. Phys. Chem. 99 (1995) 17624–17627. [11] Q.-Y. Chen, Y. Li, F.-K. Zheng, W.-Q. Zou, M.-F. Wu, G.-C. Guo, A.-Q. Wu, J.-S. Huang, A 3D-diamond-like tetrazole-based Zn(II) coordination polymer: crystal structure, nonlinear optical effect and luminescent property, Inorg. Chem. Commun. 11 (2008) 969–971. [12] J.-H. Zhang, C.-L. Hu, X. Xu, F. Kong, J.-G. Mao, New second-order NLO materials based on polymeric borate clusters and GeO4 tetrahedra: a combined experimental and theoretical study, Inorg. Chem. 50 (2011) 1973–1982.
[13] C.-F. Sun, C.-L. Hu, X. Xu, B.-P. Yang, J.-G. Mao, Explorations of new second-order nonlinear optical materials in the potassium vanadyl iodate system, J. Am. Chem. Soc. 133 (2011) 5561–5572. [14] Y.-T. Wang, H.-H. Fan, H.-Z. Wang, X.-M. Chen, A solvothermally in situ generated mixed-ligand approach for NLO-active metal-organic framework materials, Inorg. Chem. 44 (2005) 4148–4150. [15] P. Becker, Borate materials in nonlinear optics, Adv. Mater. 10 (1998) 979–992. [16] C.-T. Chen, Y.-B. Wang, B.-C. Wu, K.-C. Wu, W.-L. Zeng, L.-H. Yu, Design and synthesis of an ultraviolet-transparent nonlinear optical crystal Sr2Be2B2O7, Nature 373 (1995) 322–325. [17] M.E. Hagerman, K.R. Poeppelmeier, Review of the structure and processingdefect-property relationships of potassium titanyl phosphate: a strategy for novel thin-film photonic devices, Chem. Mater. 7 (1995) 602–621. [18] G.-J. Cao, W.-H. Fang, S.-T. Zheng, G.-Y. Yang, (CH3NH3)2[Ge(B4O9)]: an organically-templated chiral borogermanate with second-order nonlinear and ferroelectric properties, Inorg. Chem. Commun. 13 (2010) 1047–1049. [19] J.-T. Li, D.-K. Cao, T. Akutagawa, L.-M. Zheng, Zn3(4-OOCC6H4PO3)2: a polar metal phosphonate with pillared layered structure showing SHG-activity and large dielectric anisotropy, Dalton Trans. 39 (2010) 8606–8608. [20] Z.-Y. Du, Y.-H. Sun, X. Xu, G.-H. Xu, Y.-R. Xie, Orientation of second-harmonicgeneration-active phenylsulfonyl chromophores attached on layered lead(II) phosphonates, Eur. J. Inorg. Chem. (2010) 4865–4869. [21] X.-L. Yang, M.-H. Xie, C. Zou, C.-D. Wu, Syntheses, crystal structures and optical properties of six homochiral coordination networks based on phenyl acidamino acids, CrystEngComm 13 (2011) 6422–6430. [22] M.C. Das, P.K. Bharadwaj, A porous coordination polymer exhibiting reversible single-crystal to single-crystal substitution reactions at Mn(II) centers by nitrile guest molecules, J. Am. Chem. Soc. 131 (2009) 10942–10949. [23] M.C. Das, P.K. Bharadwaj, Effect of bulkiness on reversible substitution reaction at mnii center with concomitant movement of the lattice DMF: observation through single-crystal to single-crystal fashion, Chem. Eur. J. 16 (2010) 5070–5077. [24] Synthesis of H2L: a mixture of KOH (50 mmol, 2.79 g) and Alanine (50 mmol, 4.45 g) in 20 mL CH3OH was stirred for 30 minutes at room temperature. A mixture of 4-Carboxybenzaldehyde (50 mmol, 7.50 g) and KOH (50 mmol, 2.80 g) in 40 mL CH3OH also was stirred for 30 minutes at room temperature. Then the latter was added slowly to the former. The resulting solution was refluxed for 6 h. Then excess NaBH4 was added after the solution was cooled in an ice bath. After 30 minutes, the solution was acidified with concentrated HCl to a pH of 3.5–5.0. The resulting solid was filtered off, washed with water and ethanol, and recrystallized from water/ethanol (1:1) (yield 45%). ESI-MS (methanol) m/z: 224.2, [M+H]+. [25] The single crystal of H2L also was obtained as follow: A mixture of H2L (0.2 mmol, 45 mg) in 10 mL H2O was stirred for 10 minutes at room temperature. Then 0.1 M NaOH was added drop by drop to adjust the pH value at about 5.0. Then the solution was filtered. Put the filtrate at room temperature. Two weeks later, white block crystals of H2L were obtained. [26] Crystal data for H2L: C11H13NO4, Mr = 223.22, Monoclinic, space group P21, a = 7.178(2), b = 5.8900(19), c = 12.785(4) Å, β = 99.136(6)° V = 533.7(3) Å3, Z = 2, R1(wR2) [I>2σ(I)] = 0.0400(0.0807). More details see crystal structure determination section and Table S1 and Table S2 in supporting information. [27] Synthesis of complex 1: A mixture of Zn(NO3)2•6H2O (0.089 g, 0.3 mmol), H2L (0.067 g, 0.3 mmol), 1 mL DMF, 6 mL EtOH and 6 mL deionized water was sealed into a steel bomb equipped with a Teflon liner (15 mL), and then heated at 80 °C for 4 days. White needle crystals of complex 1 were recovered in ca. 40% yield based on Zn. Elemental analyses for 1, C22H28N2O10Zn (Mr = 545.83): C, 48.19; H, 5.04; N, 5.12%; Calcd.: C, 48.37; H, 5.13; N, 5.13%. IR data (KBr, cm- 1): 3055(s), 1632(s), 1600(s), 1553(s), 1487(s), 1462(s), 1402(s), 1366(s), 1335(s), 1292(s), 1223(m), 1184(m), 1142(m), 1094(m), 1063(m), 1003(m), 862(s), 820(m), 777(s), 712(m), 663(m), 542(m). [28] Crystal data for complex 1: C22H28N2O10Zn, Mr= 545.83, Monoclinic, space group C2, a = 19.5298(11), b = 5.7560(3), c =11.1250(10) Å, β = 99.743(3), V= 1232.56(15) Å3, Z = 2, R1(wR2) [I>2σ(I)]= 0.0316(0.0713), Flack Parameter is 0.003(18). More details see crystal structure determination section and Table S1 and Table S2 in supporting information. [29] S.-M. Ying, J.-G. Mao, Synthesis, crystal structures and characterizations of three new layered Zn(II) and Cd(II) aminodiphosphonates, J. Mol. Struct. 783 (2006) 13–20. [30] V.W.-W. Yam, K.K.-W. Lo, Luminescent polynuclear d10 metal complexes, Chem. Soc. Rev. 28 (1999) 323–334. [31] S.K. Kurtz, T.T. Perry, A powder technique for the evaluation of nonlinear optical materials, J. Appl. Phys. 39 (1968) 3798–3823.
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis, crystal structure and nonlinear optical property of a Zinc(II) complex base on the reduced Schiff-base ligand Shao-Ming Ying ⁎ MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, PR China Department of chemistry, Ningde Normal University, Ningde, 352100, PR China
a r t i c l e
i n f o
Article history: Received 2 March 2012 Accepted 15 May 2012 Available online 24 May 2012 Keywords: Hydrothermal synthesis Reduced Schiff base Second harmonic generation Crystal structure
a b s t r a c t By hydrothermal reactions of Zn(II) nitrate with N-(4-carboxyl)benzyl-L-alanine acid (H2L), a novel Zn(II) complex, namely, [Zn(HL)2(H2O)2] (1), have been obtained. Single crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the C2 space group and displays a 0D dimensional structure. The Zn(II) ions are four-coordinated and each Zn(II) ion coordinated with two HL anions forming a [Zn(HL)2(H2O)2] unit. The stacking of such units by hydrogen bonds results in its supramolecular structure. Complex 1 shows a second harmonic generation response that is ~ 1.5 times that of KDP (KH2PO4). © 2012 Elsevier B.V. All rights reserved.
Noncentrosymmetric (NCS) compounds are of great interest because of their potential applications in many areas such as pyroelectricity, ferroelectricity, and especially second-order nonlinear optical (NLO) materials [1–4]. In the past a few decades, second-order nonlinear optical materials have gained much attention because of their application in the domains of photoelectronics and photonics [5–8]. A number of materials exhibiting a second-order NLO effect have also been reported [9–18]. We can divide the NLO materials into three types: inorganic, organic and organic–inorganic hybrid according to the composition of the material. The essential requirement for such NLO materials is that the second-order NLO chromophores designed at the molecular level must be assembled into a noncentrosymmetric (NCS) structure. In the inorganic–organic hybrid systems, the dipolar alignment of the noncentrosymmetric components in a bulk structure is a challenge because they normally tend to be arranged in opposite directions, forming a centrosymmetric structure. Several approaches have been developed to resolve this problem: introducing Jahn–Teller-distorted cations (such as Ti4+, Nb5+, and W6+) or lone-pair cations (such as Pb 2+), using the chiral ligands or the asymmetric ligands and introducing the polar guest molecules into the molecule systems [19]. To induce NCS structures, the use of introduction of the chiral ligands or the asymmetric ligands is a convenient and efficient method [20]. For this purpose, we introduce the reduced Schiff-base ligand to obtain the NLO material. We mainly studied the reduced Schiff-base
⁎ MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, PR China. Tel.: + 86 13859660287; fax: + 86 20 84112245. E-mail address: [email protected]. 1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2012.05.026
ligands which have a chiral carbon atom. We can obtain the reduced Schiff-base ligands of this type by react the amino acids which have the chiral carbon atom with the aldehyde group to get the Schiffbases and then reduce the C_N bond. Up to now, to the best of our knowledge, second-harmonic-generation (SHG)-active metal complexes base on the reduced Schiff-base ligands of this type is still few [21]. As an initial research work, we selected N-(4-carboxyl)benzylL-alanine acid (as shown in Fig. S1) as a reduced Schiff-base ligand, due to its following characteristics: (a) it contains a phenyl ring which may be a source of the second-order NLO effect; (b) it is a flexible ligand which contains two carboxylate moieties and a secondary amine group, can show various coordination modes, maybe can lead to the formation of an asymmetric structure. Herein, we report a novel SHG-active Zn(II) complex assembled from the above reduced Schiff-base ligand, namely, [Zn(HL)2(H2O)2]. H2L was synthesized according to the procedures previously described [22–24]. The single crystal of H2L also was obtained [25,26]. Complex 1 was hydrothermally synthesized by Zn(NO3)2·6H2O and H2L ligand in a mixed solution of water, ethanol and N,N-dimethylformamide (DMF) at 80 °C for 4 days [27]. Single crystal X-ray diffraction analysis [28] reveals that complex 1 crystallizes in the C2 space group and displays a 0D dimensional structure. In complex 1, the Zn(II) ions are fourcoordinated by two oxygen atoms from two HL anions and two water molecules (Fig. 1). The Zn\O distances ranges from 1.951(3) to 1.996(3)Å, which are comparable to those reported for other Zn(II) carboxylates [29]. The HL anions is unidentate. Only a oxygen atom of the carboxylate group on the phenyl coordinated to a Zn(II) ion. Each Zn(II) ion coordinated with two HL anions forming a [Zn(HL)2(H2O)2] unit. The stacking of such units by hydrogen bonds [O(3)…O(1)W, symmetry code: 0.5+x, 1.5+y, z, bond distance is 2.659(4)Å; N(1)…O(4),
S-M. Ying / Inorganic Chemistry Communications 22 (2012) 82–84
83
100
TG/%
80
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40
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Fig. 1. Asymmetric unit of complex 1 drawn at 30% probability thermal ellipsoids. Hydrogen atoms were omitted for clarity. Symmetry codes for the generated atoms: A, 1 − x, y, 2 − z.
symmetry code: 1.5−x, −0.5+y, 1−z, bond distance is 2.808(5)Å] results in its crystallization in the chiral C2 space group [Fig. 2]. The simulated and experimental powder X-ray diffraction (PXRD) patterns of complex 1 are in good agreement with each other (as shown in Fig. S2), indicating the phase purity of the products. The thermal behavior of complex 1 was studied to reveal its thermal stability (Fig. 3). Complex 1 can stable till 185 °C. It exhibits two stages weight loss. The first dues to the release of the coordinated water molecules and the decompose of the organic ligands [from 185 °C to 475 °C, the observed weight loss of this step is 34.0%, close to the calculated value 34.7%, if the residues is Zn(NO3)2.]. The second step started at 475 °C, and didn't stop till 900 °C, the terminal of our test. The solid-state photoluminescent spectra of complex 1 at room temperature are depicted in Fig. 4. The steady-state photoluminescent spectrum of the free H2L ligand is depicted in Fig. S3. The H2L ligand displays emission peaks at 414 nm upon excitation at 314 nm. The complex 1 displays emission peaks at 422 nm upon excitation at 317 nm. Compared with the emission spectrums of the ligand, red shift of emission bands of this complex has been observed. The emission band of complex 1 is probably originated from the intraligand luminescent emission [30]. This result indicates that complex 1 would be candidates for potential photoactive materials. With the fact that complex 1 crystallizes in a noncentrosymmetric (NCS) space group (C2), we studied the SHG measurement on sieved powdered samples of 1. The relative SHG signal intensity vs. particle size for ground crystals of 1 was shown in Fig. 5, which indicates that the complex was phase-matchable, according to the rule proposed by Kurtz and Perry [31]. Complex 1 exhibits a SHG efficiency about 1.5 times that of KDP (KH2PO4) by comparing the second-harmonic signal
0
100
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300
400
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900
T/centigrade Fig. 3. The TGA curve of complex 1.
produced by samples of 1 and KDP (KH2PO4) in the same particle range of 150–210 μm.
Conclusion In summary, we have successfully synthesized a novel Zn(II) complex base on the flexible N-(4-carboxyl)benzyl-L-alanine acid ligand. Complex 1 displays a 0D dimensional structure and crystallizes in the C2 space group which maybe induce by the use of the chiral ligan. It shows a second harmonic generation response that is ~1.5 times that of KDP. It also would be candidates for potential photoactive materials. The present work serves as an elegant example in which the use of introduction of the chiral ligands or the asymmetric ligands is a convenient and efficient method to induce NCS structures. We are currently extending such a synthetic technique to explore other SHG-active materials base on ligands of this type.
Acknowledgments This work was supported by the National Natural Science Foundation of China (90922031 and 21001120) and the Research Program of Ningde Normal University (2011H103, 2011Y001 and 2011J001). We thank Prof. Jiang-Gao Mao and Dr. Jian-Han Zhang for their kind help with the SHG measurements.
a
Intensity (a. u.)
b
0
c
emission excitation
Zn N O C
300 320 340 360 380 400 420 440 460 480 500 520
Wavelength (nm) Fig. 2. View of the structure of complex 1 down the b-axis. Hydrogen atoms were omitted for clarity. Hydrogen bonds are represented by dashed lines.
Fig. 4. The solid-state photoluminescent spectra of complex 1.
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S-M. Ying / Inorganic Chemistry Communications 22 (2012) 82–84
SHG Intensity (arb.)
100 80 60 40 20 0 40
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Particle Size (µm) Fig. 5. The phase matching curve for 1. The curve is to guide the eye and is not a fit to the data.
Appendix A. Supplementary material CCDC 862839 to 862840 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internat.)C44 1223 336 033; E-mail: [email protected]]. More details about this paper can be found at http://dx.doi.org/10. 1016/j.inoche.2012.05.026.
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[25] The single crystal of H2L also was obtained as follow: A mixture of H2L (0.2 mmol, 45 mg) in 10 mL H2O was stirred for 10 minutes at room temperature. Then 0.1 M NaOH was added drop by drop to adjust the pH value at about 5.0. Then the solution was filtered. Put the filtrate at room temperature. Two weeks later, white block crystals of H2L were obtained. [26] Crystal data for H2L: C11H13NO4, Mr = 223.22, Monoclinic, space group P21, a = 7.178(2), b = 5.8900(19), c = 12.785(4) Å, β = 99.136(6)° V = 533.7(3) Å3, Z = 2, R1(wR2) [I>2σ(I)] = 0.0400(0.0807). More details see crystal structure determination section and Table S1 and Table S2 in supporting information. [27] Synthesis of complex 1: A mixture of Zn(NO3)2•6H2O (0.089 g, 0.3 mmol), H2L (0.067 g, 0.3 mmol), 1 mL DMF, 6 mL EtOH and 6 mL deionized water was sealed into a steel bomb equipped with a Teflon liner (15 mL), and then heated at 80 °C for 4 days. White needle crystals of complex 1 were recovered in ca. 40% yield based on Zn. Elemental analyses for 1, C22H28N2O10Zn (Mr = 545.83): C, 48.19; H, 5.04; N, 5.12%; Calcd.: C, 48.37; H, 5.13; N, 5.13%. IR data (KBr, cm- 1): 3055(s), 1632(s), 1600(s), 1553(s), 1487(s), 1462(s), 1402(s), 1366(s), 1335(s), 1292(s), 1223(m), 1184(m), 1142(m), 1094(m), 1063(m), 1003(m), 862(s), 820(m), 777(s), 712(m), 663(m), 542(m). [28] Crystal data for complex 1: C22H28N2O10Zn, Mr= 545.83, Monoclinic, space group C2, a = 19.5298(11), b = 5.7560(3), c =11.1250(10) Å, β = 99.743(3), V= 1232.56(15) Å3, Z = 2, R1(wR2) [I>2σ(I)]= 0.0316(0.0713), Flack Parameter is 0.003(18). More details see crystal structure determination section and Table S1 and Table S2 in supporting information. [29] S.-M. Ying, J.-G. Mao, Synthesis, crystal structures and characterizations of three new layered Zn(II) and Cd(II) aminodiphosphonates, J. Mol. Struct. 783 (2006) 13–20. [30] V.W.-W. Yam, K.K.-W. 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