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CRYSTAL STRUCTURES AND LUMINESCENCE OF A SERIES OF CADMIUM(II) COMPLEXES BASED ON ISOPHORONE DERIVATIVE CONTAINING IMIDAZOLYL © 2014 W. G. Xi1, M. D. Yang1, L. P. Wang2, H. J. Li1, H. P. Zhou1, *, and Z. C. Wu1
1College of Chemistry and Chemical Engineering, Key Laboratory of Functional Inorganic Materials Chemistry of Anhui Province, Anhui University, Hefei, 230601 P.R. China 2School of Materials and Chemical Engineering, Anhui Jianzhu University, Hefei, 230601 P.R. China
*E-mail: zhpzhp@263.net Received March 22, 2014
Three new complexes, [CdL2(CH3COO)2(H2O)2] (I), Cd^Br2 (II), CdL^2 (III), have been successfully synthesized by self-assembly of corresponding metal salts with (E)-2-(3-(4-(1H-imidazole-1-yl)styryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (L). The structures of the complexes were determined by single crystal X-ray diffraction analysis (CIF file CCDC nos. 957831 (I), 957792 (II), 957832 (III)). In complex I, central metal is six-coordinated and the crystal packing shows a 3D supramolecular framework. Complexes II and III display the similar 2D supramolecular structures in which the central metals are four-coordination. The luminescent properties were investigated.
DOI: 10.7868/S0132344X14100119
INTRODUCTION
Over the past decade, the design and synthesis of supramolecular complexes have attracted great interest due to their intriguing structural architectures and potential applications in catalysis, gas storage, chemical separation, photoluminescence, and so on [1—6]. Up to now, a number of supramolecular complexes with specific topologies and excellent properties have been synthesized by assembly of metal salts and organic ligands [7, 8]. The structural types of the resulting supramolecular complexes are affected by factors such as organic linkers, pH value, solvent, temperature, and so on [9—14]. Among them, the metal ions and anions are based-control factors. It is well known that different metal ions possess different properties and coordination modes, which play key roles in the formation of both molecular structures and packing structures of complexes [15, 16]. Plenty of studies have shown that Cd2+ ion may adopt different coordination modes, such as four-, five- or six-coordination modes according to the specific structures of the different ligands [17, 18]. The introduction of different small anions can also have a significant effect on the structural construction of complexes and their properties [18, 19]. It is important for synthesizing target materials to understand the role of the above factors in self-assembly process.
Without a doubt, the organic ligands can control the properties and topology of coordination complexes. The multidentate n-conjugated ligands have been most extensively used due to their good optical properties and coordinating with metal centres in various
modes. We designed and synthesized the ligand (E)-2-(3-(4-(1H-imidazole-1-yl)styryl)-5,5-dimethylcyclo-hex-2-enylidene)malononitrile (L) which contain a n-conjugated system and imidazolyl as well as dicy-anoisophorone groups. Schematic drawing of the ligand is shown below:
CN
NC
(L)
In order to evaluate the role of anions in the self-assembly process and the optical properties, we prepared three new complexes [CdL2(CH3COO)2(H2O)2] (I), CdL2Br2 (II), CdL2I2 (III). The crystal structures and solid state luminescent properties were investigated in detail.
EXPERIMENTAL
General methods. All the reagents and solvents were commercially available and used without further purification. IR spectra were recorded from KBr discs in the 4000—40 cm-1 range on a Nicolet Nexus 870 spec-trophotometer. Elemental analyses were carried out on Vario EL analyzer. The solid state luminescence spectra were measured on the Hitachi F-7000 fluores-
cence spectrophotometer. In the measurements of emission and excitation spectra, the pass width is 5 nm for complexes I, II, and III. For time-resolved fluorescence measurements, the fluorescence signals were collimated and focused onto the entrance slit of a monochromator with the output plane equipped with a photomultiplier tube (HORIB FluoroMax-4P). The decays were analyzed by least-squares. The quality of the exponential fits was evaluated by the goodness of
fit (x2).
Synthesis of L was carried out as described in [20].
Synthesis of complex I. A methanol solution (10 mL) of Cd(CH3COO)2 (0.051 g, 0.22 mmol) was carefully layered onto a solution of L (0.15 g, 0.44 mmol) in chloroform (10 mL). Yellow, block crystals were obtained by diffusing the methanol solution into chloroform solution for a week at room temperature. The yield was 0.14 g (69%).
For C48H5oN8O6Cd
anal. calcd., %: Found, %:
C, 60.85; C, 60.47;
H, 5.32; H, 5.28;
N, 11.83. N, 11.59.
IR bands (v, cm-1): 3339 s, 3125 s, 2950 s, 2221 v.s, 1569 v.s, 1522 v.s, 1392 s, 1337 s, 1307 s, 1271 s, 1186 s, 1159 s, 1124 s, 1064 s, 982 s, 962 s, 853 s, 819 s, 738 m, 653 m, 550 m, 496 m.
Synthesis of complex II was carried out by the same procedure used for preparing I except that CdBr2 (0.06 g, 0.22 mmol), instead of Cd(CH3COO)2 (0.051 g, 0.22 mmol), was used as the starting material. Saffron yellow, block crystals were obtained. The yield was 0.15 g (71%).
For C44H40N8Br2Cd
anal. calcd., %: C, 55.45; H, 4.23; N, 11.76. Found, %: C, 55.36; H, 4.20; N, 11.51.
IR bands (v, cm-1): 3426 s, 3131 s, 2928 m, 2220 s, 1796 m, 1568 v.s, 1523 v.s, 1501 s, 1399 s, 1367 s, 1331 s, 1308 s, 1269 s, 1190 s, 1129 s, 1066 s, 975 s, 962 s, 876 m, 853 m, 817 m, 741 m, 642 m, 549 m.
Synthesis of complex III was fabricated by the same procedure used for the preparation of I except that Cd(CH3COO)2 was replaced with CdI2 (0.08 g, 0.22 mmol). Yellow, block crystals were obtained. The yield was 0.15 g (65%).
For C44H40N8I2Cd
anal. calcd., %: C, 50.47; H, 3.85; N, 10.70. Found, %: C, 50.57; H, 3.93; N, 10.61.
IR bands (v, cm-1): 3406 s, 3129 s, 2953 s, 2926 m, 2220 v.s, 1566 v.s, 1523 v.s, 1501 s, 1398 s, 1367 s, 1332 s, 1308 s, 1268 s, 1190 s, 1161 s, 1128 s, 1065 s, 975 s, 962 s, 939 s, 877 s, 852 s, 817 s, 736 m, 642 m, 549 m.
X-ray crystallography. The X-ray diffraction measurements were performed on Bruker SMART CCD area detector using graphite monochromated Mo^a radiation (A = 0.71069 A) at 298(2) K. Intensity data were collected in the variable «-scan mode. The structures were solved by direct methods and difference Fourier syntheses. The non-hydrogen atoms were refined anisotropically and hydrogen atoms were introduced geometrically. Calculations were performed with SHELXTL program package [21]. Details of the crystal parameters, data collections and refinements are listed in Table 1, and selected bond distances and angles are given in Table 2.
Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication (no. 957831 (I), 957792 (II), 957832 (III): deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac. uk/data_request/cif).
RESULTS AND DISCUSSION
In complex I, Cd2+ ion is six-coordinated two O atoms of acetate anions, two N atoms of the imidazolyl groups from two ligands and two coordinated water molecules, to form a slightly distorted octahedral geometry (Fig. 1a). The bond angles around the Cd2+ ion are in the range of 87.56(8)°-180.00(9)°.
As shown in Fig. 1b, the neighboring molecules are linked by intermolecular O(3)#1-H(3£)#1-O(2), C(22)-H(22)-"O(2) hydrogen bonding interactions and C(5)—H(5^)-"TC interactions into one-dimensional chains along the x axis. The distances of H(3^)#1-O(2), H(22)-O(2) and H(5^)-centroid are 2.14, 2.48, and 2.76 Á, respectively. In addition, the intramolecular hydrogen bonding interactions occur between O(1) and H(3^), the distance of H(3A)-O(1) is 1.81 Á and the angle of O(3)-H(3A)-O(1) is 156°, which form a coplanar six-member ring with C(23), O(2), Cd(1), and O(3). Two nitrogen atoms of cyano in one ligand are not directly involved in coordination, but play an important role in the formation of 2D and 3D structures through C—H—N hydrogen bonding interactions. As shown in Fig. 1c, the C(5)-H(5^)-N(1)#1 interactions with 2.59 Á of H(5^)-N(1)#1 and 162° of C(5)-H(5B)--N(1)#1 based on the cyano-group link the neighboring chains to form a 2D supramolecular structure. The adjacent layers are stacked through C(12)-H(12)-N(2) and C(18)-H(18)-N(2) hydrogen bonding interactions to form a 3D structures. The distances of H(12)-N(2) and H(18)-N(2) are 2.72 and 2.66 Á, respectively.
In complex II, the Cd2+ ion is coordinated with two terminal bromine ions and two N atoms of imidazolyl groups (Fig. 2a). The bond angles around the Cd2+ ions are in the range of 98.79(8)°-123.26(8)°.
588 XI et al.
Table 1. Crystallographic data and structure refinement for complexes I—III
Parameter Value
I II III
Formula weight 947.36 953.06 1047.04
Crystal system Triclinic Monoclinic Monoclinic
Space group P1 P2/c P2/c
a, A 5.553(5) 18.837(9) 18.656(5)
b, A 11.269(5) 6.467(3) 6.473(5)
c, A 18.858(5) 18.193(9) 18.578(5)
a, deg 83.281(5) 90 90
P, deg 85.768(5) 103.025(6) 103.729(5)
Y, deg 85.061(5) 90 90
V, A3 1165.2(12) 2159.2(18) 2179.4(19)
Z 1 2 2
Pcalcd g cm-3 1.350 1.466 1.596
p., mm-1 0.525 2.396 1.957
9 Range, deg 1.09-25.94 1.11-25.00 1.12-25.00
/(000) 490 956 1028
Reflections collected/unique 8757/4395 14702/3808 13433/3732
Rint 0.0167 0.0355 0.0301
GOOF on F 2 1.151 1.122 1.046
Rh wR2 (I> 2ct(I)) 0.0291, 0.0872 0.0325, 0.0858 0.0358, 0.1162
R1, wR2 (all data) 0.0307, 0.0939 0.0479, 0.1025 0.0488, 0.1389
^max^mim « A~3 0.515/-0.326 0.975/-0.820 1.726/—1.303
The neighboring molecules are linked in "face to face" mode by C(9)—H(9)---Br hydrogen bonding (the distance of H-Br is 2.97 A and the angle of C-H-Br is 144.37°) and C(17)-H(17^)-n interaction (the distance of H---centroid is 2.70 A and the angle of C-H-'-centroid is 1
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