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[Zn(BDC)(H2O)2]n: a novel blue luminescent coordination polymer constructed from BDC-bridged 1-D chains via interchain hydrogen bonds (BDC = 1,4-benzenedicarboxylate)
Inorganic Chemistry Communications 5 (2002) 1017–1021 www.elsevier.com/locate/inoche
½ZnðBDCÞðH2OÞ2n: a novel blue luminescent coordination polymer constructed from BDC-bridged 1-D chains via interchain hydrogen bonds (BDC ¼ 1,4-benzenedicarboxylate) Li-Na Zhu a, Lei Z. Zhang a, Wen-Zhen Wang a, Dai-Zheng Liao Peng Cheng a, Zong-Hui Jiang a,b, Shi-Ping Yan a b
a,*
,
a Department of Chemistry, Nankai University, Tianjin 300071, PR China State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing University, Nanjing 210093, PR China
Received 28 May 2002; Accepted 16 September 2002
Abstract A novel coordination polymer ½ZnðBDCÞðH2 OÞ2 n 1 (where BDC ¼ 1,4-benzenedicarboxylate), has been synthesized and , b ¼ 5:058ð7Þ A , c ¼ 12:196ð16Þ characterized by X-ray diffraction. 1 crystallizes in the monoclinic space group C2/c, a ¼ 15:09ð2Þ A 3 A, b ¼ 103:62ð2Þ°, V ¼ 904ð2Þ A , Z ¼ 4. The most striking feature of 1 is that it consists of a high-dimensional network structure constructed from BDC-bridged 1-D chains via interchain hydrogen bonds. The coordination sphere of the zinc(II) ion is a distorted tetrahedron completed by four oxygen atoms from two water molecules and two BDC ligands. BDC adopts the bis-monodentated (syn–anti) coordination mode linking two adjacent zinc(II) ions. 1 shows strong blue photoluminescence as the result of the fluorescence from the intraligand emission excited state. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Zinc; Coordination polymer; Crystal structure; Luminescence
1. Introduction In recent years, much attention has been paid to the design and synthesis of high-dimensional coordination polymers with specific properties [1,2]. Molecular materials constructed by robust covalent bonds and/or weak intermolecular interaction have become an important kind of advanced materials, which motivated the studies of magnetic materials, electronic devices, catalysis and separation science to the molecular level [3–5]. 1,4-Benzenedicarboxylate (BDC) is a versatile bridging ligand, able to be manifested by the formation of binuclear metal complexes [6–9], 1-D [10–13], 2-D [14,15], and 3-D [16,17] coordination polymers. One remarkable example of BDC-bridged metal complex is Zn4 OðBDCÞ6 ðDMFÞ8 ðC6 H5 ClÞ, a three-dimensional coordinatively saturated framework resulting in a *
Corresponding author. Fax: +86-22-23502779. E-mail address: [email protected] (D.-Z. Liao).
structure with higher apparent surface area and pore volume than most porous crystalline zeolites [18]. Coordinatively unsaturated metal centers in the extended porous framework of Zn3 ðBDCÞ3 6CH3 OH and Zn(BDC)(DMF)ðH2 OÞ have also been addressed and show a clear preference for the inclusion of alcohol and gas sorption properties [19,20]. Apart from the aesthetically attractive structural aspect of these novel compounds, high-dimensional coordination polymer offers the opportunity for potential applications in many areas of optoelectronics [21,22]. On the other hand, blue luminescent metal complexes and coordination polymers have been of our particular interest because they are one of the key color components required for fullcolor electroluminescent displays [23,24]. In our previous works, we have performed spectroscopic studies of a zinc(II) complex within the 1-D nanoporous channels host [25] and a 2-D sheet-like zinc(II) coordination polymer [26], both of which show strong blue luminescence. In this present contribution, we have obtained
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L.-N. Zhu et al. / Inorganic Chemistry Communications 5 (2002) 1017–1021
[Zn(BDC)ðH2 OÞ2 n 1, a high-dimensional coordination polymer constructed from BDC-bridged 1-D zigzag chains via interchain hydrogen bonds. Moreover, 1 displays a very strong blue emission in the aqueous solution. Herein we report the synthesis and the structure of 1, together with its photoluminescence behavior, which forms the subject of this communication.
ference map, the positions of all H atoms were geometrically idealized and allowed to ride on their parent atoms. The largest peak and hole on the final difference3 , reFourier map had values of 0.204 and )0.360 e A spectively. Other relevant parameters of the crystal structures are listed in Table 1. Selected bond lengths and angles are given in Table 2.
2. Experimental
Table 1 Crystallographic data and structure refinement for ½ZnðBDCÞðH2 OÞ2 n
All the solvents and chemicals were reagent grade and used without further purification. Elemental analyses of carbon and hydrogen were carried out with a Perkin– Elmer analyzer model 240. The infrared spectra were recorded as KBr discs on a Shimadzu IR-408 infrared spectrophotometer in the 4000–600 cm1 region. Both the excitation and emission spectra were measured on Acton Research SpectroPro-300i spectrophotometer with a xenon arc lamp as the excitation light source. 2.1. Preparation of 1 A methanol solution (10 ml) of 1,4-benzenedicarboxylate piperidine salt (0.1 mmol) was added to an aqueous solution (10 ml) of Zn ðClO4 Þ2 6H2 O (0.1 mmol). White precipitates were obtained rapidly. After stirring for half an hour, the white precipitates were filtered in 80% overall yield. Colorless single crystals suitable for X-ray diffraction were obtained by slow evaporation from the filtrate, which was the same as the white power. Anal. Calc. for C8 H8 O6 Zn: C, 36.25; H, 3.04; found: C, 36.20; H, 3.10. IR spectrum (cm1 ): 1570 (CO 2 ; ma ), 1405 (CO2 ; ms ), 1360 (CO2 ; ms ). 2.2. X-ray structure determination for 1 A colorless cuboid crystal with dimensions of 0:30 0:25 0:20 mm3 was mounted on a computercontrolled Bruker SMART 1000 CCD diffractometer equipped with graphite-monochromatized Mo Ka ra at 293(2) diation with radiation wavelength 0.71073 A K. Cell parameters were determined by a least-squares calculations with h angle ranging from 2.78° to 25.02°. The intensities were collected using multi-scans mode. Empirical absorption corrections, following the procedure SADABS were applied [27]. 1496 reflections measured in the hkl range )17 to 15, )6 to 5, and )14 to 10. A total of 768 independent reflections were collected giving 418 observed reflections with I > 2rðIÞ. The structures were solved by direct-methods using SHELXS-97 [28] and refined using SHELXL-97 [29]. 768 reflections and 77 parameters using 2 restraints were refined by a full-matrix least-squares method on F 2 ðw ¼ 1=½r2 ðFo2 Þ þ ð0:0369P Þ2 þ 0:0000P ] where P ¼ ðFo2 þ 2Fc2 Þ=3Þ. After checking their presence in the dif-
Empirical
C8 H8 O6 Zn
Formula weight Crystal system Space group ) a (A ) b (A ) c (A b(°) 3 ) V ðA Z F (0 0 0) qcalcd (g cm3 ) l; ðmm1 ) R1 a ½I > 2rðIÞ wR2 b ½I > 2rðIÞ R1 a [all data] wR2 b [all data] GOF
265.51 monoclinic C2/c 15.09(2) 5.058(7) 12.196(16) 103.62(2) 904(2) 4 536 1.950 2.721 0.0225 0.0572 0.0244 0.0580 1.134
a b
R1 ¼ RkFo j j Fc k=R j Fo j. wR2 ¼ fR½wðFo2 Fc2 Þ2 =R½wðFo2 Þ2 g1=2 .
Table 2 ) and angles (°) for [Zn(BDC)(H2 OÞ Selected bond lengths (A 2 n Lengths (A) Zn(1)–O(1A) Zn(1)–O(1) Zn(1)–O(3) Zn(1)–O(3A) O(1)–H(2) O(1)–H(1) O(2)–C(1) O(3)–C(1) C(1)–C(2)
1.993(2) 1.993(2) 2.011(2) 2.011(2) 0.840(10) 0.836(10) 1.246(3) 1.291(3) 1.507(3)
Angle (°) O(1A)–Zn(1)–O(1) O(1A)–Zn(1)–O(3) O(1)–Zn(1)–O(3) O(1A)–Zn(1)–O(3A) O(1)–Zn(1)–O(3A) O(3)–Zn(1)–O(3A) Zn(1)–O(1)–H(2) Zn(1)–O(1)–H(1) H(2)–O(1)–H(1) C(1)–O(3)–Zn(1) O(2)–C(1)–O(3) O(2)–C(1)–C(2) O(3)–C(1)–C(2) C(4)–C(2)–C(1) C(3)–C(2)–C(1)
91.12(14) 100.76(11) 135.83(8) 135.83(8) 100.76(11) 99.59(14) 123(2) 126(2) 111(3) 103.16(14) 120.8(2) 122.2(2) 117.0(2) 120.5(2) 120.2(2)
Symmetry transformations used to generate equivalent atoms: (a) x; y; z þ 1=2; (b) x þ 1=2, y þ 3=2; z þ 1.
L.-N. Zhu et al. / Inorganic Chemistry Communications 5 (2002) 1017–1021
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3. Result and discussion The molecular structure and atom-labeling scheme of 1 is given in Fig. 1. The local coordination environment of the zinc(II) ion can be described as a distorted tetrahedron completed by two oxygen atoms from two water molecules and two oxygen atoms from two BDC ligands. Each BDC in 1 adopts the bis-monodentated (syn–anti) coordination mode to connect two adjacent zinc(II) ions forming a 1-D zigzag chain. The Zn(1)– , which is slightly OðH2 OÞ bond length is 1.993(2) A shorter than 2.011(2) Aof the Zn(1)–O(BDC) bond length. The O(1)–Zn(1)–O(1A) and O(3)–Zn(1)–O(3A) bond angles are 91.12(14)° and 99.59(14)°, respectively, indicating a slight distortion.
Fig. 2. The molecular structure diagram of 1 showing intermolecular hydrogen bonds (phenyl ring omitted for clarity).
The most striking feature of 1 is that it consists of a high-dimensional network structure constructed from BDC-bridged 1-D chains via interchain hydrogen bonds. As shown in Fig. 2 (phenyl ring omitted for
Fig. 1. The molecular structure and atom-labeling scheme of 1 (30% thermal ellipsoids).
clarity), the intermolecular hydrogen bond plays an important role in creating such a high-dimensional structure. These hydrogen bonds involve the coordinated oxygen atoms of water molecules and the coordinated and uncoordinated oxygen atoms of BDC , O2–O1i ¼ 2:730 A , O3– ligands [O1–O2i ¼ 2:730 A ii O1 ¼ 2:801 A; symmetry codes: (i) x; y; z þ 1, (ii) x; y þ 1; z þ 0:5]. Obviously, there are two types of intermolecular hydrogen bonding linking the paralleling chains into a high-dimensional structure. In one type both oxygen atoms are coordinated to the zinc(II) ions, while in the other type the oxygen atom from BDC is uncoordinated. That is, the difference in hydrogen bonding derives from the two oxygen atoms of the carboxylate group, an example of which may be seen from the O(2A) and O(3A) atoms of the carboxylate group O(2A)–C(1A)–O(3A). As a result, the 1-D zinc(II) complex chains are linked by interchain hydrogen bonds forming a network structure (Fig. 3). Parallel zigzag chains are easy to notice in this figure, while two kinds of channels are also identified. The dimension of the 9.870 large channel involving phenyl rings is 2.730 A , while the dimension of the small one involving zinA 3.044 A . No solvent molecules are c(II) ions is 2.730 A encapsulated in these channels. The excitation and emission spectra of pure 1 in the aqueous solution at room temperature are shown in Fig. 4. The fluorescence maximum (417 nm, 23 981 cm1 ) is redshifted ca. 2900 cm1 from the 0–0 transition band (372 nm, 26 882 cm1 ). The emission of 1 excited at 321 nm UV light is neither metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge transfer (LMCT) in nature, and can probably be assigned to the fluorescence from the intraligand emission excited state [30]. On the other hand, the excitation spectrum of 1, monitored at
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from BDC-bridged 1-D chains via interchain hydrogen bonds. The luminescence studies of the compound show strong blue photoluminescence as the result of the fluorescence from the intraligand emission excited state. Efforts to further investigate other luminescent metal complexes and coordination polymers are underway in our laboratory.
Supplementary material X-ray crystallographic file in CIF format for 1 is available from Prof. D.-Z. Liao.
Fig. 3. A perspective view of 1 along the c-axis (hydrogen omitted for clarity).
Acknowledgements This work was supported by the National Natural Science Foundation of China (Nos. 20071019, 50172021 and 90101028).
References
Fig. 4. The excitation and emission spectra of pure 1 in the aqueous solution at room temperature.
417 nm light, is dominated by a strong absorption peak at 325 nm. The most attractive luminescent behavior of 1 is that its high-dimensional condensed polymeric structure leads to significant enhancement of fluorescence intensity compare to the free BDC ligand, since the latter is nearly non-fluorescent. The enhanced luminescence efficiency is therefore attributed to the chelating of the BDC ligands to zinc ions that effectively increases the rigidity of the ligand and reduces the loss of energy via radiationless decay of the intraligand emission excited state [25,26,31]. Thus, results from the present investigation indicate that the compound 1 is capable of producing a blue light in electroluminescent devices. Also, this condensed polymeric material may be an excellent candidate for highly thermally stable blue fluorescent material. In summary, we have successfully synthesized a novel coordination polymer ½ZnðBDCÞðH2 OÞ2 n constructed
[1] C. Piguet, G. Bernardinelli, G. Hopfgartner, Chem. Rev. 97 (1997) 2005. [2] G.F. Swiegers, T.J. Malefetse, Chem. Rev. 100 (2000) 3483. [3] A. Caneschi, D. Gatteschi, L. Pardi, R. Sessoli, in: A.F. Williams (Ed.), Clusters, Chains and Layered Molecules: the ChemistÕs Way to Magnetic Materials; Perspectives in Coordination Chemistry, VCH, Weinheim, 1992. [4] D. Philp, J.F. Stoddart, Angew. Chem. Int. Ed. 35 (1996) 1154. [5] P.D. Beer, P.A. Gale, Angew. Chem. Int. Ed. 40 (2001) 486. [6] P. Chaudhuri, K. Oder, K. Wieghardt, S. Gehring, W. Haase, B. Nuber, J. Weiss, J. Am. Chem. Soc. 110 (1988) 3657. [7] Z.-L. Deng, J. Shi, Z.-H. Jiang, D.-Z. Liao, S.-P. Yan, G.-L. Wang, H.-G. Wang, R.-J. Wang, Polyhedron 11 (1992) 885. [8] K.S. B€ urger, P. Chaudhuri, K. Wieghardt, B. Nuber, Chem. Eur. J. 1 (1995) 583. [9] J. Cano, G.D. Munno, J.L. Sanz, R. Ruiz, J. Faus, F. Lloret, M. Julve, A. Caneschi, J. Chem. Soc., Dalton Trans. (1997) 1915. [10] E. Bakalbassis, C. Tsipis, A. Bozopoulos, W. Dreissig, H. Hartl, J. Mrozinski, Inorg. Chim. Acta 186 (1991) 113. [11] J. Cano, G.D. Munno, J.L. Sanz, R. Ruiz, F. Lloret, J. Faus, M. Julve, J. Chem. Soc., Dalton Trans. (1994) 3465. [12] R.H. Groeneman, L.R. MacGillvrey, J.L. Atwood, Inorg. Chem. 38 (1999) 208. [13] L. Deakin, A.M. Arif, J.S. Miller, Inorg. Chem. 38 (1999) 5272. [14] E. Bakalbassis, P. Bergerat, O. Kahn, S. Jeannin, Y. Jeannin, Y. Dromzee, M. Guillot, Inorg. Chem. 31 (1992) 625. [15] C.S. Hong, Y. Do, Inorg. Chem. 36 (1997) 5684. [16] H.J. Choi, M.P. Suh, Inorg. Chem. 38 (1999) 6309. [17] H.-K. Fun, S.S.S. Raj, R.-G. Xiong, J.-L. Zuo, Z. Yu, X.-Z. You, J. Chem. Soc., Dalton Trans. (1999) 1915. [18] H. Li, M. Eddaoudi, M. OÕKeeffe, O.M. Yaghi, Nature 402 (1999) 276. [19] H. Li, C.E. Davis, T.L. Groy, D.G. Kelly, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 2186. [20] H. Li, M. Eddaoudi, T.L. Groy, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 8571. [21] J. Zyss, I. Ledoux, J.F. Nicoud, in: J. Zyss (Ed.), Molecular Nonlinear Optics, Academic Press, Boston, 1993.
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½ZnðBDCÞðH2OÞ2n: a novel blue luminescent coordination polymer constructed from BDC-bridged 1-D chains via interchain hydrogen bonds (BDC ¼ 1,4-benzenedicarboxylate) Li-Na Zhu a, Lei Z. Zhang a, Wen-Zhen Wang a, Dai-Zheng Liao Peng Cheng a, Zong-Hui Jiang a,b, Shi-Ping Yan a b
a,*
,
a Department of Chemistry, Nankai University, Tianjin 300071, PR China State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing University, Nanjing 210093, PR China
Received 28 May 2002; Accepted 16 September 2002
Abstract A novel coordination polymer ½ZnðBDCÞðH2 OÞ2 n 1 (where BDC ¼ 1,4-benzenedicarboxylate), has been synthesized and , b ¼ 5:058ð7Þ A , c ¼ 12:196ð16Þ characterized by X-ray diffraction. 1 crystallizes in the monoclinic space group C2/c, a ¼ 15:09ð2Þ A 3 A, b ¼ 103:62ð2Þ°, V ¼ 904ð2Þ A , Z ¼ 4. The most striking feature of 1 is that it consists of a high-dimensional network structure constructed from BDC-bridged 1-D chains via interchain hydrogen bonds. The coordination sphere of the zinc(II) ion is a distorted tetrahedron completed by four oxygen atoms from two water molecules and two BDC ligands. BDC adopts the bis-monodentated (syn–anti) coordination mode linking two adjacent zinc(II) ions. 1 shows strong blue photoluminescence as the result of the fluorescence from the intraligand emission excited state. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Zinc; Coordination polymer; Crystal structure; Luminescence
1. Introduction In recent years, much attention has been paid to the design and synthesis of high-dimensional coordination polymers with specific properties [1,2]. Molecular materials constructed by robust covalent bonds and/or weak intermolecular interaction have become an important kind of advanced materials, which motivated the studies of magnetic materials, electronic devices, catalysis and separation science to the molecular level [3–5]. 1,4-Benzenedicarboxylate (BDC) is a versatile bridging ligand, able to be manifested by the formation of binuclear metal complexes [6–9], 1-D [10–13], 2-D [14,15], and 3-D [16,17] coordination polymers. One remarkable example of BDC-bridged metal complex is Zn4 OðBDCÞ6 ðDMFÞ8 ðC6 H5 ClÞ, a three-dimensional coordinatively saturated framework resulting in a *
Corresponding author. Fax: +86-22-23502779. E-mail address: [email protected] (D.-Z. Liao).
structure with higher apparent surface area and pore volume than most porous crystalline zeolites [18]. Coordinatively unsaturated metal centers in the extended porous framework of Zn3 ðBDCÞ3 6CH3 OH and Zn(BDC)(DMF)ðH2 OÞ have also been addressed and show a clear preference for the inclusion of alcohol and gas sorption properties [19,20]. Apart from the aesthetically attractive structural aspect of these novel compounds, high-dimensional coordination polymer offers the opportunity for potential applications in many areas of optoelectronics [21,22]. On the other hand, blue luminescent metal complexes and coordination polymers have been of our particular interest because they are one of the key color components required for fullcolor electroluminescent displays [23,24]. In our previous works, we have performed spectroscopic studies of a zinc(II) complex within the 1-D nanoporous channels host [25] and a 2-D sheet-like zinc(II) coordination polymer [26], both of which show strong blue luminescence. In this present contribution, we have obtained
1387-7003/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 ( 0 2 ) 0 0 6 3 4 - 2
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L.-N. Zhu et al. / Inorganic Chemistry Communications 5 (2002) 1017–1021
[Zn(BDC)ðH2 OÞ2 n 1, a high-dimensional coordination polymer constructed from BDC-bridged 1-D zigzag chains via interchain hydrogen bonds. Moreover, 1 displays a very strong blue emission in the aqueous solution. Herein we report the synthesis and the structure of 1, together with its photoluminescence behavior, which forms the subject of this communication.
ference map, the positions of all H atoms were geometrically idealized and allowed to ride on their parent atoms. The largest peak and hole on the final difference3 , reFourier map had values of 0.204 and )0.360 e A spectively. Other relevant parameters of the crystal structures are listed in Table 1. Selected bond lengths and angles are given in Table 2.
2. Experimental
Table 1 Crystallographic data and structure refinement for ½ZnðBDCÞðH2 OÞ2 n
All the solvents and chemicals were reagent grade and used without further purification. Elemental analyses of carbon and hydrogen were carried out with a Perkin– Elmer analyzer model 240. The infrared spectra were recorded as KBr discs on a Shimadzu IR-408 infrared spectrophotometer in the 4000–600 cm1 region. Both the excitation and emission spectra were measured on Acton Research SpectroPro-300i spectrophotometer with a xenon arc lamp as the excitation light source. 2.1. Preparation of 1 A methanol solution (10 ml) of 1,4-benzenedicarboxylate piperidine salt (0.1 mmol) was added to an aqueous solution (10 ml) of Zn ðClO4 Þ2 6H2 O (0.1 mmol). White precipitates were obtained rapidly. After stirring for half an hour, the white precipitates were filtered in 80% overall yield. Colorless single crystals suitable for X-ray diffraction were obtained by slow evaporation from the filtrate, which was the same as the white power. Anal. Calc. for C8 H8 O6 Zn: C, 36.25; H, 3.04; found: C, 36.20; H, 3.10. IR spectrum (cm1 ): 1570 (CO 2 ; ma ), 1405 (CO2 ; ms ), 1360 (CO2 ; ms ). 2.2. X-ray structure determination for 1 A colorless cuboid crystal with dimensions of 0:30 0:25 0:20 mm3 was mounted on a computercontrolled Bruker SMART 1000 CCD diffractometer equipped with graphite-monochromatized Mo Ka ra at 293(2) diation with radiation wavelength 0.71073 A K. Cell parameters were determined by a least-squares calculations with h angle ranging from 2.78° to 25.02°. The intensities were collected using multi-scans mode. Empirical absorption corrections, following the procedure SADABS were applied [27]. 1496 reflections measured in the hkl range )17 to 15, )6 to 5, and )14 to 10. A total of 768 independent reflections were collected giving 418 observed reflections with I > 2rðIÞ. The structures were solved by direct-methods using SHELXS-97 [28] and refined using SHELXL-97 [29]. 768 reflections and 77 parameters using 2 restraints were refined by a full-matrix least-squares method on F 2 ðw ¼ 1=½r2 ðFo2 Þ þ ð0:0369P Þ2 þ 0:0000P ] where P ¼ ðFo2 þ 2Fc2 Þ=3Þ. After checking their presence in the dif-
Empirical
C8 H8 O6 Zn
Formula weight Crystal system Space group ) a (A ) b (A ) c (A b(°) 3 ) V ðA Z F (0 0 0) qcalcd (g cm3 ) l; ðmm1 ) R1 a ½I > 2rðIÞ wR2 b ½I > 2rðIÞ R1 a [all data] wR2 b [all data] GOF
265.51 monoclinic C2/c 15.09(2) 5.058(7) 12.196(16) 103.62(2) 904(2) 4 536 1.950 2.721 0.0225 0.0572 0.0244 0.0580 1.134
a b
R1 ¼ RkFo j j Fc k=R j Fo j. wR2 ¼ fR½wðFo2 Fc2 Þ2 =R½wðFo2 Þ2 g1=2 .
Table 2 ) and angles (°) for [Zn(BDC)(H2 OÞ Selected bond lengths (A 2 n Lengths (A) Zn(1)–O(1A) Zn(1)–O(1) Zn(1)–O(3) Zn(1)–O(3A) O(1)–H(2) O(1)–H(1) O(2)–C(1) O(3)–C(1) C(1)–C(2)
1.993(2) 1.993(2) 2.011(2) 2.011(2) 0.840(10) 0.836(10) 1.246(3) 1.291(3) 1.507(3)
Angle (°) O(1A)–Zn(1)–O(1) O(1A)–Zn(1)–O(3) O(1)–Zn(1)–O(3) O(1A)–Zn(1)–O(3A) O(1)–Zn(1)–O(3A) O(3)–Zn(1)–O(3A) Zn(1)–O(1)–H(2) Zn(1)–O(1)–H(1) H(2)–O(1)–H(1) C(1)–O(3)–Zn(1) O(2)–C(1)–O(3) O(2)–C(1)–C(2) O(3)–C(1)–C(2) C(4)–C(2)–C(1) C(3)–C(2)–C(1)
91.12(14) 100.76(11) 135.83(8) 135.83(8) 100.76(11) 99.59(14) 123(2) 126(2) 111(3) 103.16(14) 120.8(2) 122.2(2) 117.0(2) 120.5(2) 120.2(2)
Symmetry transformations used to generate equivalent atoms: (a) x; y; z þ 1=2; (b) x þ 1=2, y þ 3=2; z þ 1.
L.-N. Zhu et al. / Inorganic Chemistry Communications 5 (2002) 1017–1021
1019
3. Result and discussion The molecular structure and atom-labeling scheme of 1 is given in Fig. 1. The local coordination environment of the zinc(II) ion can be described as a distorted tetrahedron completed by two oxygen atoms from two water molecules and two oxygen atoms from two BDC ligands. Each BDC in 1 adopts the bis-monodentated (syn–anti) coordination mode to connect two adjacent zinc(II) ions forming a 1-D zigzag chain. The Zn(1)– , which is slightly OðH2 OÞ bond length is 1.993(2) A shorter than 2.011(2) Aof the Zn(1)–O(BDC) bond length. The O(1)–Zn(1)–O(1A) and O(3)–Zn(1)–O(3A) bond angles are 91.12(14)° and 99.59(14)°, respectively, indicating a slight distortion.
Fig. 2. The molecular structure diagram of 1 showing intermolecular hydrogen bonds (phenyl ring omitted for clarity).
The most striking feature of 1 is that it consists of a high-dimensional network structure constructed from BDC-bridged 1-D chains via interchain hydrogen bonds. As shown in Fig. 2 (phenyl ring omitted for
Fig. 1. The molecular structure and atom-labeling scheme of 1 (30% thermal ellipsoids).
clarity), the intermolecular hydrogen bond plays an important role in creating such a high-dimensional structure. These hydrogen bonds involve the coordinated oxygen atoms of water molecules and the coordinated and uncoordinated oxygen atoms of BDC , O2–O1i ¼ 2:730 A , O3– ligands [O1–O2i ¼ 2:730 A ii O1 ¼ 2:801 A; symmetry codes: (i) x; y; z þ 1, (ii) x; y þ 1; z þ 0:5]. Obviously, there are two types of intermolecular hydrogen bonding linking the paralleling chains into a high-dimensional structure. In one type both oxygen atoms are coordinated to the zinc(II) ions, while in the other type the oxygen atom from BDC is uncoordinated. That is, the difference in hydrogen bonding derives from the two oxygen atoms of the carboxylate group, an example of which may be seen from the O(2A) and O(3A) atoms of the carboxylate group O(2A)–C(1A)–O(3A). As a result, the 1-D zinc(II) complex chains are linked by interchain hydrogen bonds forming a network structure (Fig. 3). Parallel zigzag chains are easy to notice in this figure, while two kinds of channels are also identified. The dimension of the 9.870 large channel involving phenyl rings is 2.730 A , while the dimension of the small one involving zinA 3.044 A . No solvent molecules are c(II) ions is 2.730 A encapsulated in these channels. The excitation and emission spectra of pure 1 in the aqueous solution at room temperature are shown in Fig. 4. The fluorescence maximum (417 nm, 23 981 cm1 ) is redshifted ca. 2900 cm1 from the 0–0 transition band (372 nm, 26 882 cm1 ). The emission of 1 excited at 321 nm UV light is neither metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge transfer (LMCT) in nature, and can probably be assigned to the fluorescence from the intraligand emission excited state [30]. On the other hand, the excitation spectrum of 1, monitored at
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from BDC-bridged 1-D chains via interchain hydrogen bonds. The luminescence studies of the compound show strong blue photoluminescence as the result of the fluorescence from the intraligand emission excited state. Efforts to further investigate other luminescent metal complexes and coordination polymers are underway in our laboratory.
Supplementary material X-ray crystallographic file in CIF format for 1 is available from Prof. D.-Z. Liao.
Fig. 3. A perspective view of 1 along the c-axis (hydrogen omitted for clarity).
Acknowledgements This work was supported by the National Natural Science Foundation of China (Nos. 20071019, 50172021 and 90101028).
References
Fig. 4. The excitation and emission spectra of pure 1 in the aqueous solution at room temperature.
417 nm light, is dominated by a strong absorption peak at 325 nm. The most attractive luminescent behavior of 1 is that its high-dimensional condensed polymeric structure leads to significant enhancement of fluorescence intensity compare to the free BDC ligand, since the latter is nearly non-fluorescent. The enhanced luminescence efficiency is therefore attributed to the chelating of the BDC ligands to zinc ions that effectively increases the rigidity of the ligand and reduces the loss of energy via radiationless decay of the intraligand emission excited state [25,26,31]. Thus, results from the present investigation indicate that the compound 1 is capable of producing a blue light in electroluminescent devices. Also, this condensed polymeric material may be an excellent candidate for highly thermally stable blue fluorescent material. In summary, we have successfully synthesized a novel coordination polymer ½ZnðBDCÞðH2 OÞ2 n constructed
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