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Structural, spectral and thermal properties of a polymeric nickel(II) complex containing two-dimensional network
Journal of Molecular Structure 520 (2000) 259–263 www.elsevier.nl/locate/molstruc
Structural, spectral and thermal properties of a polymeric nickel(II) complex containing two-dimensional network Y. Zhang a, b,*, J. Li a, M. Nishiura c, T. 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, Faculty of Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan Received 14 June 1999; received in revised form 20 July 1999; accepted 29 July 1999
Abstract The structure of the complex [Ni(hmt)(NCS)2(H2O)2]n, assembled by hexamethylenetetramine (hmt) and octahedral Ni(II), is b 12:06 1 A; c 12:505 8 A; b 114:41 48; V 1357 1 A 3 ; Z reported. Crystal data: Fw 351:07; a 9:885 10 A; 21 4; space group C2=c; T 173 K; l Mo 2 K a 0:71070 A; rcalc 1:718 g cm ; m 17:44 cm21 ; R 0:099; Rw 0:145: The tetrahedral assembling template effect of the hmt molecule is completed by two coordination bonds and two hydrogen interactions. The UV–vis absorption spectrum of this complex [Ni(hmt)(NCS)2(H2O)2]n with a two-dimensional network is determined in the range of 5000–35000 cm 21 at room temperature. The observed spectrum is discussed and explained perfectly by the scaling radial theory proposed by us. The two-dimensional structure has no apparent effects on the d–d transitions of the central Ni(II) ion. The IR spectrum and the GT curve of the complex were also measured and clearly reflect its structural properties. q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Network; Hydrogen bond; X-ray structure; Spectroscopy; d–d transition
1. Introduction The design of new nanoporous materials based on polymeric coordination compounds is a most attractive topic in 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), as a possible tetradentate ligand, has attracted much attention for assembly of new ligand–metal–ligand type supramolecular architectures [11–19]. Hexamethylenetetramine is widely used industrially as a crosslinking agent [20]. It can * Corresponding author. Tel.: 1 86-551-360-3018; fax: 1 86551-363-1760. E-mail address: [email protected] (Y. Zhang).
form a variety of crystalline complexes with phenol and substituted phenols by N–H–O hydrogen bonds [21–23]. Combining both coordination and hydrogen bonding motifs in the tetrahedral template of hmt is also an attractive assembling model in the construction of new supramolecular architectures [16–19]. Here, we report syntheses and X-ray structures of a new complex [Ni(hmt)(NCS)2(H2O)2]n, assembled by hmt and octahedral Ni(II) metal ions. Contrary to thousands of novel and interesting supramolecular architectures which have been designed and synthesized, studies of spectroscopic properties of supramolecules and their relations to molecular structures are very limited. However, the study of spectral properties of supramolecular assemblies will help us to understand the molecular structures and to discover
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wider applications of these assemblies. As a bridge that links the crystal structure and the electronic structure, study of spectroscopic properties is strongly attractive to us. Here, the spectral and thermal properties of a Ni(II) polymeric complex are also reported. 2. Experiment Synthesis. All starting materials were purchased from Aldrich or other companies and were used without further purification. [Ni(hmt)(NCS)2(H2O)2]n (hmt hexamethylenetetramine) (I). To an aqueous solution of Ni(NO3)26H2O (1 mmol) and NaNCS (2 mmol) was added an aqueous solution of hexamethylenetetramine (0.5 mmol) at room temperature with stirring. It was allowed to stand for several days, and the green crystals were isolated to yield (I) 161.5 mg (0.46 mmol, 92% based on hmt). Anal. Calc. for C8H16N6O2S2Ni: C, 27.34; H, 4.56; N, 23.93%. Found. C, 27.21; H, 4.55; N, 23.87%. Characterizations. The UV–vis spectrum of complex (I) was determined at room temperature in the region 6000–35 000 cm 21 using a diffuse reflection spectrograph (Hitachi V-34100) at The Anhui Institute of Optics and Fine Mechanics of ACS. A TGA investigation 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. Elemental analyses and measurement of the IR spectrum were carried out by the Structure Research Laboratory, University of Science & Technology of China. A single crystal of I was set up on a R-AXISII
diffractometer with graphite monochromated Mo-Ka radiation. The data were collected at 173 K to a maximum 2u value of 508. A laser-stimulated 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 direct methods using SIR92 and expanded using Fourier techniques, and refined by full-matrix least-squares calculation. The non-hydrogen atoms were refined. Hydrogen atoms were included, but their positions were not refined. All calculations were performed using the teXsan crystallographic software package of the Molecular Structure Corporation. For (I) [Ni(hmt)(NCS)2(H2O)2]n: A total of 1206 reflections were collected, of which 1083 had I . 3s I with 89 parameters. Final R 0:099; Rw 0:145; goodness of fit 3:09; max: shift=e:s:d: 0:02: Details of crystal data, collection and refinement are listed in Table 1. Selected bond distances and angles are listed in Table 2. 3. Results and discussion Description of the structure of [Ni(hmt)(NCS)2(H2O)2]n (I). The X-ray analysis reveals that complex I contains a six coordinate Ni(II) center which is coordinated by two terminal NCS groups, two water molecules and two hmt molecules, Fig. 1a. Locally, Ni is in a distorted octahedron with two ˚ ), two short Ni– short Ni–O (H2O) bonds (2.011(4) A ˚ N (NCS) bonds (2.090(6) A) and two long Ni–N ˚ ). The NCS groups are almost (hmt) bonds (2.294(4) A
Table 1 Crystallographic data for complex I Empirical space group Space group ˚) a (A ˚) c (A ˚ 3) V (A r calc (g cm 23) m (cm 21) RwF02 . 2s F02 b a b
C8H16N6O2S2Ni C2=c 9.885(10) 12.505(8) 1357(1) 1.718( 17.44 0.145
P R iiF0 i 2 iFc ii=iF0 i: P P Rw w F02 2 Fc2 2 = w F02 2 1=2 :
Formula weight T (8C) ˚) b (A b (8) Z ˚) l (Mo-Ka) (A RF02 . 2s F02 a
351.07 2 100 12.06(1) 114.41(4) 4 0.71070 0.099
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Table 2 ˚ ) and angles (8) Selected bond length (A Ni(1) O(1) 2.090(4) Ni(1) N(1) 2.011(6) Ni(1) N(2) 2.294(4) O(1) Ni(1) O(1) 180.0 O(1) Ni(1) N(1) 90.1(2) O(1) Ni(1) N(2) 88.1(1) O(1) Ni(1) N(1) 89.9(2) O(1) Ni(1) N(2) 91.9(2) N(1) Ni(1) N(2) 89.0(2) N(1) Ni(1) N(2) 91.0(2) N(2) Ni(1) N(2) 180.0
Ni(1) O(1) 2.090(4) Ni(1) N(1) 2.011(6) Ni(1) N(2) 2.294(4) O(1) Ni(1) N(1) 89.9(2) O(1) Ni(1) N(2) 91.9(1) O(1) Ni(1) N(1) 90.1(2) O(1) Ni(1) N(2) 88.1(1) N(1) Ni(1) N(1) 180.0 N(1) Ni(1) N(2) 91.0(2) N(1) Ni(1) N(2) 89.2(2) Ni(1) N(1) C(1) 170.0(4)
Fig. 2. Extended crystal structure of complex I: (a) hydrogen bonded two-dimensional network in the bc-plane; (b) packing diagram of the 2D layers along the b-axis.
Fig. 1. (a) ORTEP diagram of I with labeling scheme; (b) coordination of Ni 21 ions in complex I.
linear with N–C–S angles of 176.98. The connection between Ni atoms and NCS groups is slightly bent with a C1–N1–Ni angle of 170.08. Each hmt molecule acts as a bidentate ligand bridged to two Ni(II) ions to form a one-dimensional zigzag chain structure. Here, the Ni(II) atoms act as linear spacers by coordinating two NCS and two H2O molecules in one plane to connect with two hmt molecules forming this chain structure, Fig. 2. The hmt molecule is a good assembling tetrahedral template with constant bite angle—an important factor in construction of ordered supramolecular architectures. An extended two-dimensional network is assembled via hydrogen interactions in complex I. Two coordinated water molecules of adjacent Ni atoms in one chain connect with two nitrogen atoms of the same hmt molecule of the adjacent chain by a hydrogen bond (N–H–O,
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˚ ) in the bc plane. This hydrogen-bonding 2.860(7) A motif can be described in Etter’s graph set notation as R22(12) [24,25]. All water molecules and uncoordinated N atoms of hmt molecules in I are involved in an intermolecular hydrogen bond system that makes hmt molecules act as tetrahedral templates. The ˚ in distances between adjacent Ni atoms are 6.163 A ˚ in the H-bonded layer and its chain structure, 6.03 A ˚ between different layers. 6.23 A Infrared spectroscopy. The IR spectrum of complex I was recorded within the frequency range 4000– 400 cm 21. The sample was studied as powder dispersed in KBr pellets. The IR spectrum can be divided into three distinctive regions. High energy bands, in the range of 3460– 2700 cm 21, correspond to n CH2 of the coordination water molecules 3453.2 cm 21 and n CH2 of methylene groups in hmt molecules 2919.3 cm 21. In the middle energy range, the typical IR absorption of n CN is observed at 2111.2 cm 21 as a singlet peak. On the low energy side of the spectrum, a series of bands are observed, 1641.7 d OH, 1461.7, 1380.3 d CH2, 1229.4, 1020.1 and 1001.6 cm 21 d CN [26]. Thermal treatment. TGA and GT curves are shown in Fig. 3. The weight losses during the TGA experiment are: 211.88C, 10.51%; 222.28C, 16.0%; 237– 3408C, about 30%. They clearly indicate the steps of the thermal decomposition mechanism. Two water molecules are lost at 211.88C (2H2O, 10.25% in calc.). This decomposition temperature is very high for water molecules because of the strong hydrogen bond network. The weight loss at 222.28C corresponds to decomposition of NCS groups. And then, the anhydrous complex is gradually decomposed. UV–vis spectrum. In ligand field theory, the wave function scaling radial theory of non-free ions has been set up and double-z radial wave functions of some transition metal ions have been proposed by us [27,28]. The radial wave function of Ni(II) can be written as, [29] R3d r; V C21=2 0:534855 STO z1 1 0:62500 STO z2 a1 STO z1 1 a2 STO z2
z1 6:1282 1 2 0:351045V 2 0:28760V2
Fig. 3. TG-DTG chart of complex I.
z2 2:4250 1 2 1:584119V 1 0:322824V2 ( C 1 2 0:668569 0:483577 2
"
2 z1 z2 1=2 z1 1 z2
#7 )
where V is the so-called scale of non-freedom, which is a variable parameter to describe the deviation of free ion. In complex I, the Ni(II) ion has an octahedral geometry with slight distortion, and the symmetry is considered as D2h : According to the environment of Ni(II) and the coordinate system we have taken (Fig. 1b), the parameters of the crystal field and the electronic energy of the crystal can be calculated by using a Program Package for the calculation of the Ligand Field Theory. The values calculated are listed in Tables 3 and 4. In the UV–vis spectrum of complex I (Table 4), the strong and broad absorption bands that occurred at 8530, 15 575, 24 985 cm 21, are typical absorptions of d–d transitions of an Ni(II) ion [30,31] They are assigned as d–d transitions of an Ni(II) ion in an octahedral field: 3
A2g ! 3 T2ga 1 3 T2gb 1 3 T2gc ;
3
A2g ! 3 T1gz 1 3 T1gy 1 3 T1gx ;
3
A2g ! 3 T1gz 1 3 T1gy 1 3 T1gx :
The strong absorption peak observed at the position higher than 30 000 cm 21 is due to the p ! pp
Y. Zhang et al. / Journal of Molecular Structure 520 (2000) 259–263 Table 3 The crystal field parameters of complex I
m (debye) V (hartree) N P (2) P (4) z1 z2 t
1.2267 0.17122 0.9600 1.55143 1.94739 5.72236 1.79022 0.04669
a1 a2 kr 2 l (a.u.) kr 4 l (a.u.) kr 23 l (a.u.) B (cm 21) C (cm 21) z 3d (cm 21)
0.56545 0.66075 2.28563 13.86864 5.02210 942 3238 473
Table 4 The d–d transition energy levels of complex I (cm 21) Assignment
Calc.
3
A2g (e2) T2ga,b (te) 3 T2gc (te) 3 T1gz (te) 3 T1gy,x (te) 3 T1gz (t2) 3 T1gy,x (t2) 3
10 10 16 16 26 27
0 255 649 734 846 854 100
Obs. 0 10 433 16 830 26 956
transitions [32–34] The d–d transition energy levels of complex I are calculated and listed in Table 4. According to the results in Table 4, the calculated results of the d–d transition energy levels agree well with the experimental values. The network structure has no apparent special effects on the electron absorption. Acknowledgements We thank the National Nature Science Foundation, Grant No. 29871027, the Ministry of Education, for financial support. References [1] R. Robson, B.F. Abrahams, S.R. Baten, R.W. Gable, B.F. Hoskins, J. Liu, Supramolecular Architecture, ACS, Washington, 1992, chap. 19.
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[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) 12861. [13] A. Michelet, B. Viossat, P. Khodadad, N. Rodier, Acta Crystallogr. B 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., B: 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., B: Chem. Sci. 49 (1994) 325. [19] J. Pickardt, G. Gong, Z. Kristallogr. 210 (1995) 717. [20] M.G. Looney, D.H. Solomon, Aust. J. Chem. 48 (1995) 323. [21] P.J. Bruyn, R.W. Gable, A.C. Potter, D.H. Solomon, Acta Cryst. C 52 (1996) 466. [22] T.C.W. Mak, J. Chem. Phys. 43 (1965) 2799. [23] C.S. Tse, Y.S. Wong, T.C.W. Mak, J. Appl. Cryst. 10 (1977) 68. [24] M.C. Etter, Acc. Chem. Res. 23 (1990) 120. [25] M.C. Etter, J. Phys. Chem. 95 (1991) 4601. [26] Y. Zhang, J. Li, H. Xu, H. Hou, M. Nishiura, T. Imamoto, J. Mol. Struc. (1999) 5. [27] Y. Zhang, J. Li, Inorg. Chim. Acta. 87 (1984) L25. [28] Y. Zhang, J. Li, J. Mol. Sci. 2 (1982) 165. [29] J. Li, Y. Zhang, Cryst. Res. Technol. 26 (1990) 193. [30] Y. Zhang, J. Li, Q. Su, G. Zhao, Spectrochimica Acta 48A (1992) 175. [31] M. Linhard, M. Weigel, Z. Anorg. Allg. Chem. 226 (1951) 64. [32] J. Li, Y. Zhang, W. Lin, S. Liu, J. Huang, Polyhedron 11 (1992) 419. [33] Y. Zhang, J. Li, W. Lin, S. Liu, J. Huang, J. Cryst. Spec. Res. 22 (1992) 433. [34] Y. Zhang, J. Li, M. Xu, Transition Met. Chem. 20 (1995) 115.
Structural, spectral and thermal properties of a polymeric nickel(II) complex containing two-dimensional network Y. Zhang a, b,*, J. Li a, M. Nishiura c, T. 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, Faculty of Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan Received 14 June 1999; received in revised form 20 July 1999; accepted 29 July 1999
Abstract The structure of the complex [Ni(hmt)(NCS)2(H2O)2]n, assembled by hexamethylenetetramine (hmt) and octahedral Ni(II), is b 12:06 1 A; c 12:505 8 A; b 114:41 48; V 1357 1 A 3 ; Z reported. Crystal data: Fw 351:07; a 9:885 10 A; 21 4; space group C2=c; T 173 K; l Mo 2 K a 0:71070 A; rcalc 1:718 g cm ; m 17:44 cm21 ; R 0:099; Rw 0:145: The tetrahedral assembling template effect of the hmt molecule is completed by two coordination bonds and two hydrogen interactions. The UV–vis absorption spectrum of this complex [Ni(hmt)(NCS)2(H2O)2]n with a two-dimensional network is determined in the range of 5000–35000 cm 21 at room temperature. The observed spectrum is discussed and explained perfectly by the scaling radial theory proposed by us. The two-dimensional structure has no apparent effects on the d–d transitions of the central Ni(II) ion. The IR spectrum and the GT curve of the complex were also measured and clearly reflect its structural properties. q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Network; Hydrogen bond; X-ray structure; Spectroscopy; d–d transition
1. Introduction The design of new nanoporous materials based on polymeric coordination compounds is a most attractive topic in 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), as a possible tetradentate ligand, has attracted much attention for assembly of new ligand–metal–ligand type supramolecular architectures [11–19]. Hexamethylenetetramine is widely used industrially as a crosslinking agent [20]. It can * Corresponding author. Tel.: 1 86-551-360-3018; fax: 1 86551-363-1760. E-mail address: [email protected] (Y. Zhang).
form a variety of crystalline complexes with phenol and substituted phenols by N–H–O hydrogen bonds [21–23]. Combining both coordination and hydrogen bonding motifs in the tetrahedral template of hmt is also an attractive assembling model in the construction of new supramolecular architectures [16–19]. Here, we report syntheses and X-ray structures of a new complex [Ni(hmt)(NCS)2(H2O)2]n, assembled by hmt and octahedral Ni(II) metal ions. Contrary to thousands of novel and interesting supramolecular architectures which have been designed and synthesized, studies of spectroscopic properties of supramolecules and their relations to molecular structures are very limited. However, the study of spectral properties of supramolecular assemblies will help us to understand the molecular structures and to discover
0022-2860/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S0022-286 0(99)00343-9
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wider applications of these assemblies. As a bridge that links the crystal structure and the electronic structure, study of spectroscopic properties is strongly attractive to us. Here, the spectral and thermal properties of a Ni(II) polymeric complex are also reported. 2. Experiment Synthesis. All starting materials were purchased from Aldrich or other companies and were used without further purification. [Ni(hmt)(NCS)2(H2O)2]n (hmt hexamethylenetetramine) (I). To an aqueous solution of Ni(NO3)26H2O (1 mmol) and NaNCS (2 mmol) was added an aqueous solution of hexamethylenetetramine (0.5 mmol) at room temperature with stirring. It was allowed to stand for several days, and the green crystals were isolated to yield (I) 161.5 mg (0.46 mmol, 92% based on hmt). Anal. Calc. for C8H16N6O2S2Ni: C, 27.34; H, 4.56; N, 23.93%. Found. C, 27.21; H, 4.55; N, 23.87%. Characterizations. The UV–vis spectrum of complex (I) was determined at room temperature in the region 6000–35 000 cm 21 using a diffuse reflection spectrograph (Hitachi V-34100) at The Anhui Institute of Optics and Fine Mechanics of ACS. A TGA investigation 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. Elemental analyses and measurement of the IR spectrum were carried out by the Structure Research Laboratory, University of Science & Technology of China. A single crystal of I was set up on a R-AXISII
diffractometer with graphite monochromated Mo-Ka radiation. The data were collected at 173 K to a maximum 2u value of 508. A laser-stimulated 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 direct methods using SIR92 and expanded using Fourier techniques, and refined by full-matrix least-squares calculation. The non-hydrogen atoms were refined. Hydrogen atoms were included, but their positions were not refined. All calculations were performed using the teXsan crystallographic software package of the Molecular Structure Corporation. For (I) [Ni(hmt)(NCS)2(H2O)2]n: A total of 1206 reflections were collected, of which 1083 had I . 3s I with 89 parameters. Final R 0:099; Rw 0:145; goodness of fit 3:09; max: shift=e:s:d: 0:02: Details of crystal data, collection and refinement are listed in Table 1. Selected bond distances and angles are listed in Table 2. 3. Results and discussion Description of the structure of [Ni(hmt)(NCS)2(H2O)2]n (I). The X-ray analysis reveals that complex I contains a six coordinate Ni(II) center which is coordinated by two terminal NCS groups, two water molecules and two hmt molecules, Fig. 1a. Locally, Ni is in a distorted octahedron with two ˚ ), two short Ni– short Ni–O (H2O) bonds (2.011(4) A ˚ N (NCS) bonds (2.090(6) A) and two long Ni–N ˚ ). The NCS groups are almost (hmt) bonds (2.294(4) A
Table 1 Crystallographic data for complex I Empirical space group Space group ˚) a (A ˚) c (A ˚ 3) V (A r calc (g cm 23) m (cm 21) RwF02 . 2s F02 b a b
C8H16N6O2S2Ni C2=c 9.885(10) 12.505(8) 1357(1) 1.718( 17.44 0.145
P R iiF0 i 2 iFc ii=iF0 i: P P Rw w F02 2 Fc2 2 = w F02 2 1=2 :
Formula weight T (8C) ˚) b (A b (8) Z ˚) l (Mo-Ka) (A RF02 . 2s F02 a
351.07 2 100 12.06(1) 114.41(4) 4 0.71070 0.099
Y. Zhang et al. / Journal of Molecular Structure 520 (2000) 259–263
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Table 2 ˚ ) and angles (8) Selected bond length (A Ni(1) O(1) 2.090(4) Ni(1) N(1) 2.011(6) Ni(1) N(2) 2.294(4) O(1) Ni(1) O(1) 180.0 O(1) Ni(1) N(1) 90.1(2) O(1) Ni(1) N(2) 88.1(1) O(1) Ni(1) N(1) 89.9(2) O(1) Ni(1) N(2) 91.9(2) N(1) Ni(1) N(2) 89.0(2) N(1) Ni(1) N(2) 91.0(2) N(2) Ni(1) N(2) 180.0
Ni(1) O(1) 2.090(4) Ni(1) N(1) 2.011(6) Ni(1) N(2) 2.294(4) O(1) Ni(1) N(1) 89.9(2) O(1) Ni(1) N(2) 91.9(1) O(1) Ni(1) N(1) 90.1(2) O(1) Ni(1) N(2) 88.1(1) N(1) Ni(1) N(1) 180.0 N(1) Ni(1) N(2) 91.0(2) N(1) Ni(1) N(2) 89.2(2) Ni(1) N(1) C(1) 170.0(4)
Fig. 2. Extended crystal structure of complex I: (a) hydrogen bonded two-dimensional network in the bc-plane; (b) packing diagram of the 2D layers along the b-axis.
Fig. 1. (a) ORTEP diagram of I with labeling scheme; (b) coordination of Ni 21 ions in complex I.
linear with N–C–S angles of 176.98. The connection between Ni atoms and NCS groups is slightly bent with a C1–N1–Ni angle of 170.08. Each hmt molecule acts as a bidentate ligand bridged to two Ni(II) ions to form a one-dimensional zigzag chain structure. Here, the Ni(II) atoms act as linear spacers by coordinating two NCS and two H2O molecules in one plane to connect with two hmt molecules forming this chain structure, Fig. 2. The hmt molecule is a good assembling tetrahedral template with constant bite angle—an important factor in construction of ordered supramolecular architectures. An extended two-dimensional network is assembled via hydrogen interactions in complex I. Two coordinated water molecules of adjacent Ni atoms in one chain connect with two nitrogen atoms of the same hmt molecule of the adjacent chain by a hydrogen bond (N–H–O,
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˚ ) in the bc plane. This hydrogen-bonding 2.860(7) A motif can be described in Etter’s graph set notation as R22(12) [24,25]. All water molecules and uncoordinated N atoms of hmt molecules in I are involved in an intermolecular hydrogen bond system that makes hmt molecules act as tetrahedral templates. The ˚ in distances between adjacent Ni atoms are 6.163 A ˚ in the H-bonded layer and its chain structure, 6.03 A ˚ between different layers. 6.23 A Infrared spectroscopy. The IR spectrum of complex I was recorded within the frequency range 4000– 400 cm 21. The sample was studied as powder dispersed in KBr pellets. The IR spectrum can be divided into three distinctive regions. High energy bands, in the range of 3460– 2700 cm 21, correspond to n CH2 of the coordination water molecules 3453.2 cm 21 and n CH2 of methylene groups in hmt molecules 2919.3 cm 21. In the middle energy range, the typical IR absorption of n CN is observed at 2111.2 cm 21 as a singlet peak. On the low energy side of the spectrum, a series of bands are observed, 1641.7 d OH, 1461.7, 1380.3 d CH2, 1229.4, 1020.1 and 1001.6 cm 21 d CN [26]. Thermal treatment. TGA and GT curves are shown in Fig. 3. The weight losses during the TGA experiment are: 211.88C, 10.51%; 222.28C, 16.0%; 237– 3408C, about 30%. They clearly indicate the steps of the thermal decomposition mechanism. Two water molecules are lost at 211.88C (2H2O, 10.25% in calc.). This decomposition temperature is very high for water molecules because of the strong hydrogen bond network. The weight loss at 222.28C corresponds to decomposition of NCS groups. And then, the anhydrous complex is gradually decomposed. UV–vis spectrum. In ligand field theory, the wave function scaling radial theory of non-free ions has been set up and double-z radial wave functions of some transition metal ions have been proposed by us [27,28]. The radial wave function of Ni(II) can be written as, [29] R3d r; V C21=2 0:534855 STO z1 1 0:62500 STO z2 a1 STO z1 1 a2 STO z2
z1 6:1282 1 2 0:351045V 2 0:28760V2
Fig. 3. TG-DTG chart of complex I.
z2 2:4250 1 2 1:584119V 1 0:322824V2 ( C 1 2 0:668569 0:483577 2
"
2 z1 z2 1=2 z1 1 z2
#7 )
where V is the so-called scale of non-freedom, which is a variable parameter to describe the deviation of free ion. In complex I, the Ni(II) ion has an octahedral geometry with slight distortion, and the symmetry is considered as D2h : According to the environment of Ni(II) and the coordinate system we have taken (Fig. 1b), the parameters of the crystal field and the electronic energy of the crystal can be calculated by using a Program Package for the calculation of the Ligand Field Theory. The values calculated are listed in Tables 3 and 4. In the UV–vis spectrum of complex I (Table 4), the strong and broad absorption bands that occurred at 8530, 15 575, 24 985 cm 21, are typical absorptions of d–d transitions of an Ni(II) ion [30,31] They are assigned as d–d transitions of an Ni(II) ion in an octahedral field: 3
A2g ! 3 T2ga 1 3 T2gb 1 3 T2gc ;
3
A2g ! 3 T1gz 1 3 T1gy 1 3 T1gx ;
3
A2g ! 3 T1gz 1 3 T1gy 1 3 T1gx :
The strong absorption peak observed at the position higher than 30 000 cm 21 is due to the p ! pp
Y. Zhang et al. / Journal of Molecular Structure 520 (2000) 259–263 Table 3 The crystal field parameters of complex I
m (debye) V (hartree) N P (2) P (4) z1 z2 t
1.2267 0.17122 0.9600 1.55143 1.94739 5.72236 1.79022 0.04669
a1 a2 kr 2 l (a.u.) kr 4 l (a.u.) kr 23 l (a.u.) B (cm 21) C (cm 21) z 3d (cm 21)
0.56545 0.66075 2.28563 13.86864 5.02210 942 3238 473
Table 4 The d–d transition energy levels of complex I (cm 21) Assignment
Calc.
3
A2g (e2) T2ga,b (te) 3 T2gc (te) 3 T1gz (te) 3 T1gy,x (te) 3 T1gz (t2) 3 T1gy,x (t2) 3
10 10 16 16 26 27
0 255 649 734 846 854 100
Obs. 0 10 433 16 830 26 956
transitions [32–34] The d–d transition energy levels of complex I are calculated and listed in Table 4. According to the results in Table 4, the calculated results of the d–d transition energy levels agree well with the experimental values. The network structure has no apparent special effects on the electron absorption. Acknowledgements We thank the National Nature Science Foundation, Grant No. 29871027, the Ministry of Education, for financial support. References [1] R. Robson, B.F. Abrahams, S.R. Baten, R.W. Gable, B.F. Hoskins, J. Liu, Supramolecular Architecture, ACS, Washington, 1992, chap. 19.
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