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Structural, spectral and thermal properties of a new anion zinc(II) hexamethylenetetramine complex
Journal of Molecular Structure 523 (2000) 257–260 www.elsevier.nl/locate/molstruc
Structural, spectral and thermal properties of a new anion zinc(II) hexamethylenetetramine complex Yugen Zhang a,b,*, Jianmin Li a, Masayoshi Nishiura c, Tsuneo Imamoto c a
Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China b Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China c Department of Chemistry, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan Received 12 July 1999; accepted 19 October 1999
Abstract The structure of complex [Hhmt]2[Zn2(hmt)(NCS)6], where hmt hexamethylenetetramine, is reported. Crystal data: Fw a 67:11 3; V 1900 1 A 3 ; Z 2; space group P-1; T 173 K; 901.80, a 13:87 1; b 17:18 1; c 9:125 7 A; 21 21 l Mo-Ka 0:71070 A; rcalc 1:576 g cm ; m 16:73 cm ; R 0:073; Rw 0:110: The ligand hmt is bridged by two Zn ions, forming a novel structure motif. Two protonated hmt groups per formula unit act as counter ions. The IR spectrum and the GT curve of the complex are also measured and clearly reflect its structural properties. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Cationic complex; X-ray structure; IR spectroscopy
1. Introduction The design of new nanoporous materials based on polymeric coordination compounds has been an attractive topic in the recent years [1–5]. The assembly of these complexes strongly depends on the selection of both the metallic centers and the ligands [6–10]. Hexamethylenetetramine (hmt), a possible tetradentate ligand, has been used to assemble new ligand–metal–ligand type supramolecular architectures [11–19]. Several M-hmt (M Zn,Ni) structural motifs have been reported [16–19]. Here, we report the synthesis and X-ray structure of a new complex [Zn2(hmt)(NCS)6][Hhmt]2, which contains a * Corresponding author. Department of Chemistry, University of Science and Technology of China, Anhui, People’s Republic of China. Tel.: 186-551-360-1113; fax: 186-551-363-1760. E-mail address: [email protected] (Y. Zhang).
new interesting hmt bridged binuclear anion group and two protonated hmt cations. We also report the IR and thermal properties of this complex.
2. Experiment 2.1. Synthesis All starting materials were purchased from Aldrich or other suppliers and were used without further purification. [Zn2(hmt)(NCS)6][(Hhmt)2] (hmt Hexamethylenetetramine) (1). To an aqueous solution of ZnSO4·7H2O (1 mmol) and NaNCS (2 mmol) was added an aqueous solution of hexamethylenetetramine (0.5 mmol) at room temperature with stirring. The mixture was allowed to stand for several days to yield (1) as colourless crystals (0.158 mmol, 95%
0022-2860/00/$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(99)00400-7
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Y. Zhang et al. / Journal of Molecular Structure 523 (2000) 257–260
Table 1 Crystallographic data for complex 1 Empirical formula Space group ˚) a (A ˚) c (A b (8) ˚ 3) V (A r calc (g cm 23) m (cm 21) RwFo2 . 2s Fo2 b Largest diff. peak a b
C24H38N18S6Zn2 P-1 13.87(1) 9.125(7) 108.45(7) 1900(1) 1.576 16.39 0.110 ˚ 23) 2.68 (e A
Formula weight T (8C) ˚) b (A a (8) g (8) Z ˚) l (Mo-Ka) (A RFo2 . 2s Fo2 a GOF Largest diff. Hole
901.80 2100 17.18(1) 96.82(3) 67.11(3) 2 0.71070 0.073 3.63 ˚ 23) 21.32 (e A
P R iFo u 2 uFc i=uFo u: P P Rw w Fo2 2 Fc2 2 = w Fo2 2 1=2 :
based on hmt). Anal. Calcd for C24H38N18S6Zn2: C, 31.94; H, 4.21; N, 27.94%. Found C, 31.90; H, 4.22; N, 27.89%.
2.2. Characterizations TGA experiment was performed on a WRT-3 thermal analyzer under a 80 ml/min air atmosphere. The final temperature was 5008C with a heating rate of 108C/min. The sample was gradually decomposed above 2318C. Elemental analyses and IR spectrum were carried Table 2 ˚ ) and angles (8) Selected bond lengths (A Zn(1)–N(1) Zn(1)–N(3) Zn(2)–N(5) Zn(2)–N(7) S(1)–C(1) S(3)–C(3) S(5)–C(5) N(1)–C(1) N(3)–C(3) N(7)–C(5) N(1)–Zn(1)–N(2) N(1)–Zn(1)–N(4) N(2)–Zn(1)–N(4) N(5)–Zn(2)–N(6) N(5)–Zn(2)–N(8) N(6)–Zn(2)–N(8) Zn(1)–N(1)–C(1) Zn(1)–N(3)–C(3) Zn(2)–N(7)–C(5)
1.953(5) 1.970(5) 2.096(4) 1.938(6) 1.649(6) 1.613(5) 1.610(6) 1.162(8) 1.183(7) 1.201(8) 112.5(2) 112.2(2) 106.3(2) 110.8(2) 101.8(2) 113.5(2) 152.5(5) 147.9(4) 168.6(5)
Zn(1)–N(2) Zn(1)–N(4) Zn(2)–N(6) Zn(2)–N(8) S(2)–C(2) S(4)–C(4) S(6)–C(6) N(2)–C(2) N(6)–C(4) N(8)–C(6) N(1)–Zn(1)–N(3) N(2)–Zn(1)–N(3) N(3)–Zn(1)–N(4) N(5)–Zn(2)–N(7) N(6)–Zn(2)–N(7) N(7)–Zn(2)–N(8) Zn(1)–N(2)–C(2) Zn(2)–N(6)–C(4) Zn(2)–N(8)–C(6)
1.962(5) 2.085(4) 1.942(6) 1.946(6) 1.632(5) 1.614(7) 1.628(6) 1.158(7) 1.183(9) 1.161(8) 111.9(2) 109.7(2) 103.8(2) 104.5(2) 113.1(2) 112.2(2) 163.7(5) 167.7(5) 172.3(5)
out by Structure Research Laboratory at The University of Science & Technology of China. A single crystal of complex 1 was set up on a R-AXISII diffractometer with graphite monocromated Mo-Ka radiation. The data were collected at 173 K to a maximum 2u value of 508. A laserstimulated fluorescence image plate was used as a two-dimensional area detector. The distance between the crystal and the detector was 80 mm. Thus, 43 frames were recorded at intervals of 38 and each exposure lasted for 5 min. The data were corrected for Lorentz-polarization effects. The structure was solved by Patterson methods using DIRDIF92 and expanded using Fourier techniques, and refined by full-matrix least-squares calculation. The nonhydrogen atoms were refined. Hydrogen atoms were included, but their positions were not refined. All calculations were performed using the teXsan crystallographic software package of Molecular Structure Corporation. A total of 5974 reflections were collected, of which 5612 had I . 3s I with 451 parameters. Final R 0:073; Rw 0:110; goodness of fit 3.63, max. shift/e.s.d. 0.09. Details of crystal data, collection and refinement are listed in Table 1. The selected bond distances and angles are listed in Table 2.
3. Results and discussion 3.1. Description of the structure of [Zn2(hmt)(NCS)6][(Hhmt)2] (1) The X-ray analysis reveals that complex 1 contains
Y. Zhang et al. / Journal of Molecular Structure 523 (2000) 257–260
Fig. 1. ORTEP diagram of 1 with labelling scheme.
one coordination anion group of [Zn2(hmt)(NCS)6] 22 and two Hhmt 1 cations, Fig. 1. The anion group contains two zinc(II) atoms bridged by one hmt molecule, and coordinated by three terminal NCS 2 groups for each Zn(II) ion. Zn(II) atoms form slightly distorted tetrahedral arrangement by getting coordinated to three nitrogen atoms from NCS group and one nitrogen atom from bridged hmt molecule with angles ranging between 103.8(2) and 112.5(2) for Zn1, and 101.8(2) and 113.1(2) for Zn2 center. Here, two Zn(II) tetrahedrons which were bridged by the hmt are asymmetric, possibly due to the push effect of two cation groups, Fig. 2. The Zn(II) coordination spheres and Hhmt cations are arranged in a layer formation in
Fig. 2. Extended crystal structure of complex 1.
259
the extended structure, Fig. 2. Average Zn–N (NCS) ˚ and that of Zn2 bond length of Zn1 center is 1.962 A ˚ . The longer Zn–N bond length center is 1.942 A corresponding to the shorter CN bond length (ranged ˚ ) of NCS groups. The NCS from 1.158 to 1.201 A groups are almost linear in two tetrahedrons with an average N–C–S angle of 178.48. The connection between Zn atoms and NCS groups are slightly bent in Zn2 tetrahedron with average C–N–Zn angle of 169.58, and that of Zn1 tetrahedron are more bent with an average C–N–Zn angle 154.68 [20–22]. The distance between two Zn atoms is ˚ . It is interesting that one hmt molecule 5.941(4) A acts as bidentate ligand to link two Zn(II) atoms forming a binuclear structure, and two protonated hmt molecules worked as cations crystallize in this structure. It is a new cationic coordination motif of hmt ligand.
3.2. Infrared spectroscopy The IR spectroscopy of complex 1 was recorded in the 4000–400 cm 21 range, Fig. 3. The sample was studied as powders dispersed in KBr pellets. The IR spectrum can be divided into three distinctive regions. High energy bands, in the range higher than 2700 cm 21, no absorption of water molecules was observed, even this sample was synthesized from aqueous solution. n CH2 of methylene groups of hmt molecules occurred at 2929.8 cm 21. This peak is a little broad corresponding to the different surroundings of methylene in hmt and also hmt itself. In the middle energy range, the typical IR absorption of n CN is observed at 2113.6 and 2073.9 cm 21 as a double peak. It means that the IR absorptions of NCS groups in two different coordination metal spheres have a shift Dn 39:7 cm21 : This shift corresponds to the variety of CN bond lengths of NCS groups in two Zn(II) tetrahedrons. On the low energy side of the spectrum, a series of bands are observed, 1458.4, 1401.0, 1361.5 n CH2, 1256.7 (triplet) n C – S, 1061.6, 1013.0 and 978.9 n C – N cm 21 [20–22]. All these absorptions split into multi-peaks in Fig. 3 corresponding to the asymmetric binuclear structure. Supplementary Data relating to this article are deposited with the B.L.D.D. as Supplementary Publication No. SUP 26633.
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Y. Zhang et al. / Journal of Molecular Structure 523 (2000) 257–260
Fig. 3. IR spectrum of complex 1.
Acknowledgements This work was financially supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences. References [1] R. Robson, B.F. Abrahams, S.R. Baten, R.W. Gable, B.F. Hoskins, J. Liu, Supramolecular Architecture, ACS Publications, Washington, DC, 1992, chap. 19. [2] C.L. Bowes, G.A. Ozin, Adv. Mater. 8 (1996) 13. [3] P. Feng, X. Bu, G.D. Stucky, Nature 388 (1997) 735. [4] Y. Zhang, M. Nishiura, J. Li, W. Deng, T. Imamoto, Inorg. Chem. 38 (1999) 825. [5] Y. Zhang, J. Li, M. Zhu, Q. Wang, X. Wu, Chem. Lett. (1998) 1803. [6] S.R. Baten, B.F. Hoskins, R. Robson, J. Am. Chem. Soc. 117 (1995) 5385. [7] B.F. Hoskins, R. Robson, J. Am. Chem. Soc. 112 (1990) 1546. [8] G.B. Gardner, D. Venkataraman, J.S. Moore, S. Lee, Science 374 (1995) 792.
[9] G.D. Desiraju, Angew. Chem., Int. Ed. Engl. 34 (1995) 2311. [10] O. Ermer, J. Am. Chem. Soc. 110 (1988) 3747. [11] L. Carlucci, G. Ciani, D.M. Proserpio, A. Sironi, Inorg. Chem. 36 (1997) 1736. [12] L. Carlucci, G. Ciani, D.M. Proserpio, A. Sironi, J. Am. Chem. Soc. 117 (1995) 12 861. [13] A. Michelet, B. Viossat, P. Khodadad, N. Rodier, Acta Crystallogr. B37 (1981) 2171. [14] L. Carlucci, G. Ciani, D.W.v. Gudenberg, D.M. Proserpio, A. Sironi, Chem. Commun. (1997) 631. [15] O. Ermer, A. Eling, J. Chem. Soc., Perkin Trans. (1994) 925. [16] J. Pickardt, G. Gong, Z. Naturforsch., Chem. Sci. 48 (1993) 23. [17] J. Pickardt, G. Gong, Z. Anorg. Allg. Chem. 602 (1994) 183. [18] J. Pickardt, G. Gong, S. Wischnack, C. Steinkopff, Z. Naturforsch., Chem. Sci. 49 (1994) 325. [19] J. Pickardt, G. Gong, Z. Kristallogr. 210 (1995) 717. [20] Y. Zhang, J. Li, H. Xu, H. Hou, M. Nishiura, T. Imamoto, J. Mol. Struc. 510 (1999) 191–196. [21] Y. Zhang, J. Li, M. Nishiura, T. Imamoto, J. Mol. Struc. 520 (2000) 259–263. [22] J. Lu, T. Paliwala, S.C. Lim, C. Yu, T. Niu, A.J. Jacobson, Inorg. Chem. 36 (1997) 923.
Structural, spectral and thermal properties of a new anion zinc(II) hexamethylenetetramine complex Yugen Zhang a,b,*, Jianmin Li a, Masayoshi Nishiura c, Tsuneo Imamoto c a
Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China b Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China c Department of Chemistry, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan Received 12 July 1999; accepted 19 October 1999
Abstract The structure of complex [Hhmt]2[Zn2(hmt)(NCS)6], where hmt hexamethylenetetramine, is reported. Crystal data: Fw a 67:11 3; V 1900 1 A 3 ; Z 2; space group P-1; T 173 K; 901.80, a 13:87 1; b 17:18 1; c 9:125 7 A; 21 21 l Mo-Ka 0:71070 A; rcalc 1:576 g cm ; m 16:73 cm ; R 0:073; Rw 0:110: The ligand hmt is bridged by two Zn ions, forming a novel structure motif. Two protonated hmt groups per formula unit act as counter ions. The IR spectrum and the GT curve of the complex are also measured and clearly reflect its structural properties. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Cationic complex; X-ray structure; IR spectroscopy
1. Introduction The design of new nanoporous materials based on polymeric coordination compounds has been an attractive topic in the recent years [1–5]. The assembly of these complexes strongly depends on the selection of both the metallic centers and the ligands [6–10]. Hexamethylenetetramine (hmt), a possible tetradentate ligand, has been used to assemble new ligand–metal–ligand type supramolecular architectures [11–19]. Several M-hmt (M Zn,Ni) structural motifs have been reported [16–19]. Here, we report the synthesis and X-ray structure of a new complex [Zn2(hmt)(NCS)6][Hhmt]2, which contains a * Corresponding author. Department of Chemistry, University of Science and Technology of China, Anhui, People’s Republic of China. Tel.: 186-551-360-1113; fax: 186-551-363-1760. E-mail address: [email protected] (Y. Zhang).
new interesting hmt bridged binuclear anion group and two protonated hmt cations. We also report the IR and thermal properties of this complex.
2. Experiment 2.1. Synthesis All starting materials were purchased from Aldrich or other suppliers and were used without further purification. [Zn2(hmt)(NCS)6][(Hhmt)2] (hmt Hexamethylenetetramine) (1). To an aqueous solution of ZnSO4·7H2O (1 mmol) and NaNCS (2 mmol) was added an aqueous solution of hexamethylenetetramine (0.5 mmol) at room temperature with stirring. The mixture was allowed to stand for several days to yield (1) as colourless crystals (0.158 mmol, 95%
0022-2860/00/$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(99)00400-7
258
Y. Zhang et al. / Journal of Molecular Structure 523 (2000) 257–260
Table 1 Crystallographic data for complex 1 Empirical formula Space group ˚) a (A ˚) c (A b (8) ˚ 3) V (A r calc (g cm 23) m (cm 21) RwFo2 . 2s Fo2 b Largest diff. peak a b
C24H38N18S6Zn2 P-1 13.87(1) 9.125(7) 108.45(7) 1900(1) 1.576 16.39 0.110 ˚ 23) 2.68 (e A
Formula weight T (8C) ˚) b (A a (8) g (8) Z ˚) l (Mo-Ka) (A RFo2 . 2s Fo2 a GOF Largest diff. Hole
901.80 2100 17.18(1) 96.82(3) 67.11(3) 2 0.71070 0.073 3.63 ˚ 23) 21.32 (e A
P R iFo u 2 uFc i=uFo u: P P Rw w Fo2 2 Fc2 2 = w Fo2 2 1=2 :
based on hmt). Anal. Calcd for C24H38N18S6Zn2: C, 31.94; H, 4.21; N, 27.94%. Found C, 31.90; H, 4.22; N, 27.89%.
2.2. Characterizations TGA experiment was performed on a WRT-3 thermal analyzer under a 80 ml/min air atmosphere. The final temperature was 5008C with a heating rate of 108C/min. The sample was gradually decomposed above 2318C. Elemental analyses and IR spectrum were carried Table 2 ˚ ) and angles (8) Selected bond lengths (A Zn(1)–N(1) Zn(1)–N(3) Zn(2)–N(5) Zn(2)–N(7) S(1)–C(1) S(3)–C(3) S(5)–C(5) N(1)–C(1) N(3)–C(3) N(7)–C(5) N(1)–Zn(1)–N(2) N(1)–Zn(1)–N(4) N(2)–Zn(1)–N(4) N(5)–Zn(2)–N(6) N(5)–Zn(2)–N(8) N(6)–Zn(2)–N(8) Zn(1)–N(1)–C(1) Zn(1)–N(3)–C(3) Zn(2)–N(7)–C(5)
1.953(5) 1.970(5) 2.096(4) 1.938(6) 1.649(6) 1.613(5) 1.610(6) 1.162(8) 1.183(7) 1.201(8) 112.5(2) 112.2(2) 106.3(2) 110.8(2) 101.8(2) 113.5(2) 152.5(5) 147.9(4) 168.6(5)
Zn(1)–N(2) Zn(1)–N(4) Zn(2)–N(6) Zn(2)–N(8) S(2)–C(2) S(4)–C(4) S(6)–C(6) N(2)–C(2) N(6)–C(4) N(8)–C(6) N(1)–Zn(1)–N(3) N(2)–Zn(1)–N(3) N(3)–Zn(1)–N(4) N(5)–Zn(2)–N(7) N(6)–Zn(2)–N(7) N(7)–Zn(2)–N(8) Zn(1)–N(2)–C(2) Zn(2)–N(6)–C(4) Zn(2)–N(8)–C(6)
1.962(5) 2.085(4) 1.942(6) 1.946(6) 1.632(5) 1.614(7) 1.628(6) 1.158(7) 1.183(9) 1.161(8) 111.9(2) 109.7(2) 103.8(2) 104.5(2) 113.1(2) 112.2(2) 163.7(5) 167.7(5) 172.3(5)
out by Structure Research Laboratory at The University of Science & Technology of China. A single crystal of complex 1 was set up on a R-AXISII diffractometer with graphite monocromated Mo-Ka radiation. The data were collected at 173 K to a maximum 2u value of 508. A laserstimulated fluorescence image plate was used as a two-dimensional area detector. The distance between the crystal and the detector was 80 mm. Thus, 43 frames were recorded at intervals of 38 and each exposure lasted for 5 min. The data were corrected for Lorentz-polarization effects. The structure was solved by Patterson methods using DIRDIF92 and expanded using Fourier techniques, and refined by full-matrix least-squares calculation. The nonhydrogen atoms were refined. Hydrogen atoms were included, but their positions were not refined. All calculations were performed using the teXsan crystallographic software package of Molecular Structure Corporation. A total of 5974 reflections were collected, of which 5612 had I . 3s I with 451 parameters. Final R 0:073; Rw 0:110; goodness of fit 3.63, max. shift/e.s.d. 0.09. Details of crystal data, collection and refinement are listed in Table 1. The selected bond distances and angles are listed in Table 2.
3. Results and discussion 3.1. Description of the structure of [Zn2(hmt)(NCS)6][(Hhmt)2] (1) The X-ray analysis reveals that complex 1 contains
Y. Zhang et al. / Journal of Molecular Structure 523 (2000) 257–260
Fig. 1. ORTEP diagram of 1 with labelling scheme.
one coordination anion group of [Zn2(hmt)(NCS)6] 22 and two Hhmt 1 cations, Fig. 1. The anion group contains two zinc(II) atoms bridged by one hmt molecule, and coordinated by three terminal NCS 2 groups for each Zn(II) ion. Zn(II) atoms form slightly distorted tetrahedral arrangement by getting coordinated to three nitrogen atoms from NCS group and one nitrogen atom from bridged hmt molecule with angles ranging between 103.8(2) and 112.5(2) for Zn1, and 101.8(2) and 113.1(2) for Zn2 center. Here, two Zn(II) tetrahedrons which were bridged by the hmt are asymmetric, possibly due to the push effect of two cation groups, Fig. 2. The Zn(II) coordination spheres and Hhmt cations are arranged in a layer formation in
Fig. 2. Extended crystal structure of complex 1.
259
the extended structure, Fig. 2. Average Zn–N (NCS) ˚ and that of Zn2 bond length of Zn1 center is 1.962 A ˚ . The longer Zn–N bond length center is 1.942 A corresponding to the shorter CN bond length (ranged ˚ ) of NCS groups. The NCS from 1.158 to 1.201 A groups are almost linear in two tetrahedrons with an average N–C–S angle of 178.48. The connection between Zn atoms and NCS groups are slightly bent in Zn2 tetrahedron with average C–N–Zn angle of 169.58, and that of Zn1 tetrahedron are more bent with an average C–N–Zn angle 154.68 [20–22]. The distance between two Zn atoms is ˚ . It is interesting that one hmt molecule 5.941(4) A acts as bidentate ligand to link two Zn(II) atoms forming a binuclear structure, and two protonated hmt molecules worked as cations crystallize in this structure. It is a new cationic coordination motif of hmt ligand.
3.2. Infrared spectroscopy The IR spectroscopy of complex 1 was recorded in the 4000–400 cm 21 range, Fig. 3. The sample was studied as powders dispersed in KBr pellets. The IR spectrum can be divided into three distinctive regions. High energy bands, in the range higher than 2700 cm 21, no absorption of water molecules was observed, even this sample was synthesized from aqueous solution. n CH2 of methylene groups of hmt molecules occurred at 2929.8 cm 21. This peak is a little broad corresponding to the different surroundings of methylene in hmt and also hmt itself. In the middle energy range, the typical IR absorption of n CN is observed at 2113.6 and 2073.9 cm 21 as a double peak. It means that the IR absorptions of NCS groups in two different coordination metal spheres have a shift Dn 39:7 cm21 : This shift corresponds to the variety of CN bond lengths of NCS groups in two Zn(II) tetrahedrons. On the low energy side of the spectrum, a series of bands are observed, 1458.4, 1401.0, 1361.5 n CH2, 1256.7 (triplet) n C – S, 1061.6, 1013.0 and 978.9 n C – N cm 21 [20–22]. All these absorptions split into multi-peaks in Fig. 3 corresponding to the asymmetric binuclear structure. Supplementary Data relating to this article are deposited with the B.L.D.D. as Supplementary Publication No. SUP 26633.
260
Y. Zhang et al. / Journal of Molecular Structure 523 (2000) 257–260
Fig. 3. IR spectrum of complex 1.
Acknowledgements This work was financially supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences. References [1] R. Robson, B.F. Abrahams, S.R. Baten, R.W. Gable, B.F. Hoskins, J. Liu, Supramolecular Architecture, ACS Publications, Washington, DC, 1992, chap. 19. [2] C.L. Bowes, G.A. Ozin, Adv. Mater. 8 (1996) 13. [3] P. Feng, X. Bu, G.D. Stucky, Nature 388 (1997) 735. [4] Y. Zhang, M. Nishiura, J. Li, W. Deng, T. Imamoto, Inorg. Chem. 38 (1999) 825. [5] Y. Zhang, J. Li, M. Zhu, Q. Wang, X. Wu, Chem. Lett. (1998) 1803. [6] S.R. Baten, B.F. Hoskins, R. Robson, J. Am. Chem. Soc. 117 (1995) 5385. [7] B.F. Hoskins, R. Robson, J. Am. Chem. Soc. 112 (1990) 1546. [8] G.B. Gardner, D. Venkataraman, J.S. Moore, S. Lee, Science 374 (1995) 792.
[9] G.D. Desiraju, Angew. Chem., Int. Ed. Engl. 34 (1995) 2311. [10] O. Ermer, J. Am. Chem. Soc. 110 (1988) 3747. [11] L. Carlucci, G. Ciani, D.M. Proserpio, A. Sironi, Inorg. Chem. 36 (1997) 1736. [12] L. Carlucci, G. Ciani, D.M. Proserpio, A. Sironi, J. Am. Chem. Soc. 117 (1995) 12 861. [13] A. Michelet, B. Viossat, P. Khodadad, N. Rodier, Acta Crystallogr. B37 (1981) 2171. [14] L. Carlucci, G. Ciani, D.W.v. Gudenberg, D.M. Proserpio, A. Sironi, Chem. Commun. (1997) 631. [15] O. Ermer, A. Eling, J. Chem. Soc., Perkin Trans. (1994) 925. [16] J. Pickardt, G. Gong, Z. Naturforsch., Chem. Sci. 48 (1993) 23. [17] J. Pickardt, G. Gong, Z. Anorg. Allg. Chem. 602 (1994) 183. [18] J. Pickardt, G. Gong, S. Wischnack, C. Steinkopff, Z. Naturforsch., Chem. Sci. 49 (1994) 325. [19] J. Pickardt, G. Gong, Z. Kristallogr. 210 (1995) 717. [20] Y. Zhang, J. Li, H. Xu, H. Hou, M. Nishiura, T. Imamoto, J. Mol. Struc. 510 (1999) 191–196. [21] Y. Zhang, J. Li, M. Nishiura, T. Imamoto, J. Mol. Struc. 520 (2000) 259–263. [22] J. Lu, T. Paliwala, S.C. Lim, C. Yu, T. Niu, A.J. Jacobson, Inorg. Chem. 36 (1997) 923.