Monatshefte f€ ur Chemie 134, 1311–1320 (2003) DOI 10.1007/s00706-003-0066-5
Three New 1D Polymeric Zinc(II) and Cadmium(II) Azido Complexes Containing Noncoordinated Pyridine-N-oxide or 3-Picoline-N-oxide Franz A. Mautner1;, Christian Gspan1 , Mohamed A. S. Goher2, and Morsy A. M. Abu-Youssef2 1
2
Institut f€ ur Physikalische und Theoretische Chemie, Technische Universit€at Graz, A-8010 Graz, Austria Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426 Ibrahimia, 21321 Alexandria, Egypt
Received March 5, 2003; accepted May 15, 2003 Published online September 11, 2003 # Springer-Verlag 2003 Summary. The interaction of pyridine-N-oxide (pyNO) and 3-picoline-N-oxide (3picNO) with zinc(II) and cadmium(II) azides afforded complexes with empirical formulae Zn(N3)2(pyNO)(H2O)2, Zn(N3)2(3picNO)2(H2O)2 and Cd(N3)2(3picNO)2(H2O)2. The IR spectra of these complexes are measured and discussed. X-Ray single crystal diffraction showed for the first complex, which should be formulated as {[Zn(N3)2(H2O)2](pyNO)}n, to consist of 1D chains of trans-[Zn(N3)2(H2O)2]n, double end-on (-1,1) azido bridges and noncoordinated pyNO molecules. The other two complexes are isomorphous containing 1D trans-[M(N3)2(H2O)2]n, double (-1,1) azido bridges, and hydrogen bonded noncoordinated 3picNO molecules. Each pyridine-N-oxide molecule forms three hydrogen bonds, whereas the 3-picoline-N-oxides form two hydrogen bonds. The metal centers exhibit distorted octahedral geometry. Keywords. IR spectroscopy; 1D zinc(II) and cadmium(II) azido complexes; Pyridine-N-oxide derivatives; Synthesis; X-Ray structure determination.
Introduction The importance of coordination polymers manifests itself in the great deal of interest in the synthesis and characterization of such polymers in the last decade [1]. These coordination compounds afford a variety of assembled structures and cavities and also provide a reaction environment for guest molecules [2]. Although various metal ions are used for constructing coordination polymers, zinc(II) and cadmium(II) ions Corresponding author. E-mail:
[email protected]
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permit a variety of structures due to the d10 configuration [3–7]. Previously we have shown that although cadmium(II) forms 2D polymeric azido complexes with 2-acetyl-, 4-acetyl, and 4-bromopyridine, the mode of bonding of azido groups as well as the cadmium(II) azide topologies are different in the three compounds [8]. When we used 2-picoline-N-oxide (2picNO), to interact with zinc(II) azide or cadmium(II) azide, however, other types of azido complexes were isolated [9]. Although both complexes have general formula [ML(N3)2]n, the zinc(II) complex possesses 1D chain of di--1,1 azido bridges and each zinc atom is pentacoordinated, with monodentate 2picNO, whereas the corresponding cadmium(II) complex features a distorted sixcoordinate geometry, bridging 2picNO ligand cis-di--1,1, di--1,3 azides, and 2D honeycomb structure [9]. Now, we extend our work to the reaction between pyridineN-oxide (pyNO) and 3-picoline-N-oxide (3picNO) and zinc(II) and cadmium(II) azide. This paper describes the synthesis and structural characterization of the isolated complexes as elucidated by spectroscopic and crystallographic methods. Results and Discussions Crystal Structures Figures 1 and 2 illustrate the principle structural features of {[Zn(N3)2(H2O)2] (pyNO)}n (1) and selected bond distances and bond angles are collected in Table 1.
Fig. 1. Perspective view of 1 with atom labelling scheme; broken lines indicate hydrogen bonds; symmetry codes according Table 1
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Fig. 2. Packing plot of 1 along b-axis of unit cell; broken lines indicate hydrogen bonds Table 1. Selected bond lengths=pm and angles= of 1 Zn(1) Zn(1A) Zn(1)–N(21) Zn(1)–O(1) Zn(1)–O(2) N(11)–N(12) N(21)–N(22) O(3)–N(1) Zn(1A) Zn(1) Zn(1B) N(21)–Zn(1)–O(1) N(21)–Zn(1)–N(11B) O(1)–Zn(1)–N(11B) N(21B)–Zn(1)–O(2) N(11B)–Zn(1)–O(2) N(21B)–Zn(1)–N(11) N(11B)–Zn(1)–N(11) N(12)–N(11)–Zn(1) N(13)–N(12)–N(11) N(22)–N(21)–Zn(1A) N(23)–N(22)–N(21) N(22)–N(21)–N(11)
315.21(10) 211.6(2) 212.2(2) 215.7(2) 121.6(3) 121.1(3) 134.1(3) 176.96(2) 91.90(8) 96.04(9) 91.24(8) 89.09(8) 89.54(8) 95.95(9) 177.84(2) 117.2(2) 179.5(3) 122.4(2) 178.8(3) 150.8(2)
Hydrogen bonds: O(1) O(2A) O(2) O(3) O(3) O(1D) O(1) O(3E) H(7) O(2A)
275.2(3) 265.3(3) 273.0(3) 273.0(3) 193(1)
Zn(1) Zn(1B) Zn(1)–N(21B) Zn(1)–N(11B) Zn(1)–N(11) N(12)–N(13) N(22)–N(23)
315.21(10) 212.0(2) 213.0(2) 215.9(2) 115.5(3) 115.1(3)
N(21)–Zn(1)–N(21B) N(21B)–Zn(1)–O(1) N(21B)–Zn(1)–N(11B) N(21)–Zn(1)–O(2) O(1)–Zn(1)–O(2) N(21)–Zn(1)–N(11) O(1)–Zn(1)–N(11) O(2)–Zn(1)–N(11) Zn(1A)–N(11)–Zn(1) N(22)–N(21)–Zn(1) Zn(1)–N(21)–Zn(1A) N(12)–N(11)–N(21)
177.74(2) 90.33(8) 84.27(9) 88.67(8) 178.98(7) 83.65(9) 90.90(8) 88.32(8) 94.60(9) 123.3(2) 96.16(9) 138.7(2)
O(1) O(2) O(3) H(6) H(8)
355.1(3) 268.2(3) 378.6(4) 191(2) 185(2)
O(2B) O(3C) O(3C) O(3E) O(3C)
(continued)
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Table 1 (continued) H(9) O(3) O(3) O(2) O(3C) O(2A) O(1) O(3E) O(2) O(3) O(2C) O(1)–H(6) O(3E) O(2)–H(8) O(3C)
185(2) 90.40(8) 133.47(9) 89.60(8) 162(2) 166(2)
H(8)–O(2)–H(9) O(2) O(3) O(1D) H(6)–O(1)–H(7) O(3C) O(3) O(1D) O(1)–H(7) O(2A) O(2)–H(9) O(3)
113.1(5) 77.57(8) 113.2(5) 75.56(7) 163(2) 156(2)
Symmetry codes: (A) x þ 1, y 1=2, z þ 3=2; (B) x þ 1, y þ 1=2, z þ 3=2; (C) x þ 1, y, z þ 1; (D) x, y þ 1=2, z 1=2; (E) x, y þ 1=2, z þ 1=2
The structure of 1 features 1D [Zn(N3)2(H2O)2]n chains extended along the b-axis of the unit cell. Each zinc atom in the chain is coordinated by four nitrogen atoms from double -1,1 azido bridges [Zn–N from 211.6(2) to 215.9(2) pm] and two oxygen atoms from two aqua molecules [Zn–O 212.2(2) and 215.7(2) pm]. Thus, each zinc(II) atom is six-coordinated in a distorted octahedral ZnN4O2 geometry. Hydrogen bonds of type O–H O consolidate the structure to form a 2D layer extended along the c-axis of unit cell. The oxygen atom O(3) of the noncoordinated pyridine-N-oxide acts as acceptor for three hydrogen bonds from different aqua molecules O(1D), O(2), and O(2C). O(1) forms a further hydrogen bond to O(2A). As a consequence of this intrachain hydrogen bond the Zn(II) octahedra are alternatively tilted to allow a matching O(1) O(2A) distance of 275.2(3) pm, whereas the O(1) O(2B) distance is elongated to 355.1(3) pm. A fragment of the crystal structure of 2 is shown in Fig. 3, a packing plot is given in Fig. 4, bond lengths and bond angles are listed in Table 2. All nonhydrogen atoms are located at special positions of space group Ibam (no. 72): Zn(1) at 4b with site symmetry 222, water oxygen atom O(1) at 8g with site symmetry 2, azide group and 3-picoline-N-oxide at 8j with site symmetry m. The single crystal structure determination revealed that complex 2 should be formulated as {[Zn(N3)2(H2O)2](3picNO)2}n in which the 3picNO molecules are noncoordinated and serve as stabilizers of the lattice. The structure of 2 consists of a 1D [Zn(N3)2(H2O)2)]n chain running along the c-axis. Each zinc atom in the chain is linked to the two of each neighboring symmetry related counter parts by two azido ligands, i.e. each zinc(II) is ligated with four bridging azido ligands [Zn–N ¼ 216.0(2) pm] forming a cyclic four-membered Zn2N2 unit. The remaining two coordination sites are occupied by oxygen atoms of two trans aqua molecules [Zn–O ¼ 209.4(2) pm]. The coordination environment of each zinc(II) is best described as a distorted octahedron with ZnN4O2 chromophore. The azido groups function in the -1,1 bridging fashion and both of them are asymmetric [N(11)– N(12) ¼ 121.1(4), N(12)–N(13) ¼ 115.4(4), Dd ¼ 5.7 pm]. The out of plane angle of the azido group from the Zn2N2 ring is 41.7(3) . Each noncoordinated 3picNO molecule forms two hydrogen bonds of the type O H–O with oxygen atoms of two adjacent aqua molecules in the chain (Figs. 3 and 4). The Zn Zn separation value of 323.8(2) pm within four-membered Zn2N2 units is slightly longer than 315.21(10) pm found in 1. Both values in 1 and 2, however, fall very well within the range of 303–331 pm, found for other zinc(II) azide complexes [9–13]. The
New 1D Polymeric Zinc(II) and Cadmium(II) Azido Complexes
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Fig. 3. Perspective view of 2 with atom labelling scheme; broken lines indicate hydrogen bonds; symmetry codes according Table 2
Fig. 4. Packing view of 2 along c-axis of unit cell
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Table 2. Selected bond lengths=pm and angles= of 2 Zn(1)–O(1A) Zn(1)–N(11B) Zn(1)–N(11D) O(2)–N(1) N(12)–N(13) O(1A)–Zn(1)–O(1) N(11B)–Zn(1)–N(11C) N(12)–N(11)–Zn(1B) N(13)–N(12)–N(11)
209.4(2) 216.0(2) 216.0(2) 133.2(3) 115.4(4) 180.0 97.24(9) 119.63(13) 178.5(3)
Zn(1)–O(1) Zn(1)–N(11C) Zn(1)–N(11) N(11)–N(12) Zn(1) Zn(1E) O(1)–Zn(1)–N(11) N(11)–Zn(1)–N(11C) Zn(1B)–N(11)–Zn(1) N(12)–N(11)–N(11B)
209.4(2) 216.0(2) 216.0(2) 121.1(4) 323.8(1) 91.95(8) 176.1(2) 97.11(9) 138.3(3)
Hydrogen bonds: O(1) O(2) H(2) O(2) O(1)–H(2) O(2) O(1) O(2) O(1F)
269.5(2) 186(2) 164(3) 73.84(7)
O(1)–H(2) H(2)–O(1)–H(2C) O(2) O(1) O(2C)
85.5(14) 115(4) 101.66(11)
Symmetry codes: (A) x, y þ 1, z; (B) x, y þ 1, z; (C) x, y, z þ 1=2; (D) x, y þ 1, z þ 1=2; (E) x, y þ 1, z þ 1; (F) x, y, z þ 1
Zn–N bond distance in 2 matches very well those found in complex 1, as well as those reported [202–222 pm] for other zinc(II) azido complexes [9–13]. Complex 3 is isomorphous with complex 2. Thus, the coordination geometry and structural features are similar. Due to larger ionic radius of cadmium(II) as compared to that of zinc(II), the metal-ligand (Cd–N and Cd–O) bond lengths in 3 are significantly longer than corresponding ones in 2 (Table 3). The Cd–N bonds, however, are comparable with those reported for the structures of [Cd(N3)(4-aba)(H2O)]n (4-aba ¼ 4-amino benzoic acid) (from 240.4(3) to 247.4(3) pm] [6] and other cadmium(II) azide complexes (226–237 pm) [8, 9]. The Cd Cd separation within the cyclic Cd2N2 units Table 3. Selected bond lengths=pm and angles= for 3 Cd(1)–O(1A) Cd(1)–N(11B) Cd(1)–N(11D) Cd(1) Cd(1E) N(11)–N(12) O(1A)–Cd(1)–O(1) O(1)–Cd(1)–N(11) N(12)–N(11)–Cd(1B) N(13)–N(12)–N(11)
228.5(2) 231.3(2) 231.3(2) 340.3(1) 120.8(4) 180.0 91.28(6) 119.71(12) 177.7(3)
Cd(1)–O(1) Cd(1)–N(11C) Cd(1)–N(11) O(2)–N(1) N(12)–N(13) N(11B)–Cd(1)–N(11C) N(11C)–Cd(1)–N(11) Cd(1B)–N(11)–Cd(1) N(12)–N(11)–N(11B)
228.5(2) 231.3(2) 231.3(2) 133.7(3) 115.0(4) 94.77(10) 177.45(13) 94.71(10) 137.0(2)
Hydrogen bonds: O(1) O(2) H(2) O(2) O(1)–H(2) O(2) O(1) O(2) O(1F)
2.674(2) 1.832(11) 173(4) 79.02(8)
O(1)–H(2) H(2)–O(2)–H(2C) O(2) O(1) O(2C)
84.6(10) 110(5) 106.05(11)
Symmetry codes: (A) x, y þ 1, z; (B) x, y þ 1, z; (C) x, y, z þ 1=2; (D) x, y þ 1, z þ 1=2; (E) x, y þ 1, z þ 1; (F) x, y, z þ 1
New 1D Polymeric Zinc(II) and Cadmium(II) Azido Complexes
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of 340.3(1) pm is a little shorter than corresponding values found in the structures of [Cd(2-Acpy)2(N3)2]n [356.0(1) pm] and [Cd3(N3)6(4-Brpy)4]n [370.5(1) pm] [8]. Similar to those of 2, each noncoordinated 3picNO molecule forms two hydrogen bonds of the type O H–O with two adjacent aqua molecules in the chain. IR Spectra It was pointed out that the (NO) mode is shifted to lower frequencies with D ¼ 70–30 cm1 upon complexation of pyNO via its oxygen atom [14–17]. The (NO) band which appeared at 1240 cm1 in the IR spectrum of free pyNO appeared at 1218 cm1 in complex 1. The observed shift of 22 cm1 to a lower frequency may reflect the influence of the fact that the oxygen atom of pyNO is involved in the formation of three hydrogen bonds (see structures). The situation for the other 3picNO is very similar. The medium to strong and very broad band in the region ¼ 2800–3500 cm1 with different satellites indicates the hydrogen bonded aqua molecules in the three complexes. The IR spectra of these complexes exhibit very strong bands at ¼ 2166, 2070 for complex 1, at 2068, 2049 for 2, and at 2061, 2044 cm1 for 3, respectively. These bands are associated with the as(N3) mode. The weak to medium band at ¼ 2166 cm1 in complex 1 is not consistent with its crystal structural data, and suggests a very asymmetric -1,1 azido bridge [18, 19]. A careful remeasurement of the IR spectrum of this compound with freshly prepared sample has shown that this band is reproduced at the same position and therefore it is not due to contamination with some [Zn(N3)2]n. The position of the other band at ¼ 2070 cm1 , however, is consistent with a moderate asymmetric -1,1 azide bridge. As the Dd’s for both azide groups are equal (Dd ¼ 6.1 pm), it is possible that coupling between their asymmetric vibrations is the reason for such high position. The Dd values are 5.7 pm for azide group in complex 2 and 5.8 pm for azide group in complex 3. According to the Dd vs. as(N3) relationship mentioned earlier [18, 19], the as(N3) are expected to appear at 2057 and 2058 cm1 , for 2 and 3, respectively. Two bands, however, are observed at ¼ 2068, 2049 and 2061, 2044 cm1 for 2 and 3, respectively, indicating also vibrational coupling. The results given here for the three complexes, suggest that it is difficult to predict the nature of the mode of bonding of azido groups on the basis of their IR spectral data, as the absorption in the region below ¼ 2055 cm1 has been taken as indication of -1,3 bridging azides [20–23]. Nevertheless, the position of the higher frequency band at ¼ 2069 for 2 and 2061 cm1 for 3 indicates -1,1 azide bridges and is confirmed by the appearance of a medium band at ¼ 1333 and 1328 cm1 due to s(N3), for 2 and 3, respectively. Conclusion Three new polymeric zinc(II) and cadmium(II) azido complexes have shown by X-ray crystallography to possess 1D trans-[M(N3)2(H2O)2]n chain and hydrogen bonded noncoordinated pyridine-N-oxide or 3-picoline-N-oxide molecules. Thus, the present azido complexes differ significantly from corresponding complexes derived from pyridine derivative ligands [8, 10–13, 24, 25] or those of 2-picolineN-oxide [9].
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Experimental Materials and Instrumentations Elemental analyses of C, H, N were carried out using a Perkin Elmer analyzer, Zn and Cd by complexometric titration [26]. All results were in good agreement with calculated values. IR spectra were recorded on a Bruker IFS-125 model FT-IR spectrophotometer as KBr pellets. Pyridine-N-oxide and 3-picoline-N-oxide have been purchased from Aldrich company and other chemicals were of analytical grade quality and used as received. Caution: Metal azide complexes are potentially explosives. Only a small amount of material should be prepared and should be handled with caution.
[Zn(N3)2(H2O)2](pyridine-N-oxide) (1, C5H9N7O3Zn) To 10 cm3 of an aqueous solution of zinc azide [26] (8.9 mmol Zn) saturated with hydrazoic acid pyridine-N-oxide (0.84 g, 8.9 mmol) is added. Irregular shaped crystals of complex 1 are separated upon cooling within several days. Yield: 1.50 g, 60%.
[Zn(N3)2(H2O)2](3-picoline-N-oxide)2 (2, C12H18N8O4Zn) Complex 2 was obtained by the same preparation procedure as 1, by use of 3-picoline-N-oxide (0.60 g, 5.5 mmol) as ligand in form of needle shaped, colorless transparent crystals. Yield: 0.72 g, 65%.
[Cd(N3)2(H2O)2](3-picoline-N-oxide)2 (3, C12H18CdN8O4) To an aqueous solution (25 cm3) of CdSO4 8=3H2O (0.50 g, 1.95 mmol) NaN3 (0.32 g, 5 mmol) was added followed by tropwise addition of 3-picoline-N-oxide (0.43 g, 3.9 mmol) dissolved in 3 cm3 of water. From the clear solution complex 3 was separated as colorless transparent needles after 2 days. Yield: 0.59 g, 67%.
X-Ray Crystallography Single crystal X-ray data were measured on a modified STOE four circle diffractometer at 90(2) K using graphite crystal-monochromatized Mo-K radiation ( ¼ 71.069 pm). The intensities were corrected for Lorentz-polarisation effects and for absorption [range of normalized transmission factors: 1.000–0.568, 1.000–0.717, and 1.000–0.566, respectively]. Crystallographic data and processing parameters are given in Table 4. The structures were solved by direct methods and subsequent Fourier analyses. Anisotropic displacement parameters were applied to nonhydrogen atoms in full-matrix least-squares refinements based on F 2 . Analytical expressions of neutral-atom scattering factors were employed, and anomalous dispersion corrections were incorporated. The program DIFABS [27] and SHELXTL=PC program package [28] were used for computations. The hydrogen atoms of substituted pyridines were included on calculated positions by use of the HFIX utility [28]. Hydrogen atoms of the water molecules were located from difference-Fourier maps, assigned with isotropic displacement factors and included in the final refinement cycles with O–H distance restraints. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre, as supplementary publication Nos. CCDC-205005, CCDC-205006, and CCDC-2005007. Copies of the data can be obtained free of
New 1D Polymeric Zinc(II) and Cadmium(II) Azido Complexes
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Table 4. Crystallographic data and processing parameters Compound
1
2
3
Formula Formula weight Crystal system Space group Cell parameter
C5H9N7O3Zn 280.56 Monoclinic P21=c (no. 14) a ¼ 1232.9(5) pm b ¼ 630.2(2) pm c ¼ 1456.2(6) pm ¼ 90 ¼ 106.29(3) ¼ 90 1086.0(7) 106 4 2.268 1.716 0.20 0.11 0.10 2.91–25.00 2544 1914=0.0276 158 1.086 0.0293=0.0697 0:273=0:357
C12H18N8O4Zn 403.71 Orthorhombic Ibam (no. 72) a ¼ 1314.7(4) pm b ¼ 1960.6(5) pm c ¼ 647.5(2) pm ¼ 90 ¼ 90 ¼ 90 1669.0(8) 106 4 1.509 1.607 0.35 0.15 0.14 3.10–29.47 1455 1245=0.0270 80 1.087 0.0361=0.0824 0:612=0:430
C12H18CdN8O4 450.74 Orthorhombic Ibam (no. 72) a ¼ 1306.2(4) pm b ¼ 1984.6(5) pm c ¼ 680.6(2) pm ¼ 90 ¼ 90 ¼ 90 1764.3(9) 106 4 1.273 1.697 0.45 0.16 0.14 3.12–30.01 2894 1394=0.0370 85 1.086 0.0278=0.0719 0:603=0:713
V=pm3 Z (MoK)=mm1 Dcalc=Mg m3 Crystal size=mm Theta range= Refl. collected Indep. refl.=Rint Parameters GooF on F 2 R1=wR2 ˚ 3) Residuals (e=A
charge upon application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (FAX: þ44(1223)336033; E-mail:
[email protected].
Acknowledgments The authors thank Prof. Kratky, Prof. Belaj (Univ. Graz), and Prof. Gatterer (TU-Graz) for use of experimental equipment.
References [1] e.g. (a) Swiegers GM, Malefetse TJ (2000) Chem Rev 100: 3483; (b) Zaworotko MJ (2001) J Chem Soc Chem Commun 1; (c) Munakata M, Wu LP, Kuroda T (1999) Adv Inorg Chem 46: 173 and refs therein [2] e.g. (a) Leininger BO, Lenvyk J (2000) Chem Rev 100: 853; (b) Fujita M (1998) Chem Soc Rev 27: 417 and refs therein [3] Mondal A, Chaudhuri S, Ghosh A, Laskar IR, Chaudhuri NR (1998) Acta Chem Scand 52: 1202 [4] Mondal A, Saha MK, Mitra S, Gramlich V (2000) Chem Soc Dalton Trans 3218 [5] Sun D, Cao R, Liang Y, Shi Q, Su W, Hong M (2001) J Chem Soc Dalton Trans 2335 [6] Chen HJ, Chen X-M (2002) Inorg Chim Acta 329: 13 [7] Mautner FA, Abu-Youssef MAM, Goher MAS (1997) Polyhedron 16: 235 [8] Goher MAS, Mautner FA, Abu-Youssef MAM, Hafez AK, Badr AM-A (2002) J Chem Soc Dalton Trans 3309 [9] Mautner FA, Gspan C, Hafez AK, Goher MAS (2003) Inorg Chim Acta: submitted
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F. A. Mautner et al.: New 1D Polymeric Zinc(II) and Cadmium(II) Azido Complexes Mautner FA, Kratky C (1988) Cryst Res Technol 23: 1477 Mautner FA, Krischner H, Kratky C (1987) Z Kristallogr 180: 219 Mautner FA, Krischner H, Kratky C (1988) Z Naturforsch 43B: 253 Mautner FA, Krischner H (1992) Monatsh Chem 123: 325 Prabhakaran CP, Patel CC (1972) J Inorg Nucl Chem 34: 3485 Muto Y, Jonassen HB (1966) Bull Chem Soc Jpn 39: 58 Ahuja IS, Rastogi P (1970) J Chem Soc (A) 378 Nakamoto K (1978) Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley, New York Agrell I (1971) Acta Chem Scand 25: 2965 Goher MAS (1990) Acta Chim Hung 127: 213 Manson JL, Arif AM, Miller JS (1999) J Chem Soc Chem Commun 1479 Hao X, Wei Y, Zhany S-W (2000) J Chem Soc Chem Commun 1271 Ribas J, Monfort M, Ghosh BK, Solans X (1994) Angew Chem Int Ed Engl 33: 2087 Shen Z, Zuo J-L, Gao S, Song Y, Che C-M, Fun H-K, You X-Z (2000) Angew Chem Int Ed Eng 39: 3633 Agrell I (1970) Acta Chem Scand 24: 1247 Agrell I (1970) Acta Chem Scand 24: 3575 Mautner FA (1988) Thesis, TU-Graz Walker N, Stuart D (1983) Acta Crystallogr A39: 158 SHELXTL=PC 5.03 (PC-Version), (1995) Siemens Analytical Instruments Division, Madison, WI
