КООРДИНАЦИОННАЯ ХИМИЯ, 2015, том 41, № 2, с. 79-84
УДК 541.49
SYNTHESIS, CHARACTERIZATION, AND PROPERTY STUDY OF COORDINATION POLYMERS CONSTRUCTED FROM CD SALT
AND MIXED LIGANDS
© 2015 P. Zhang*, J. Tong, and C. Y. Xing
College of Chemistry, Liaoning University, Shenyang, 110036 P.R. China *E-mail: zhangpeng@lnu.edu.cn Received June 9, 2014
Two interesting new coordination polymers {[Cd(Dcbpyno)(1,4'-Bix)15] ■ 2H2O}n (I) and [Cd(1,2'-Cy)(4,4'-Bipy)]n (II) (Dcbpyno = 2,2-bipyridine-3,3-dicarboxylate-1,1'-dioxide, 1,4-Bix = 1,4-bis(imidazol-1-ylmeth-yl)benzene, 1,2'-Cy = 4-cyclohexene-1,2-dicarboxylate and 4,4'-Bipy = 4,4'-bipyridine) have been synthesized under different conditions. The X-ray crystal structures of these two complexes are presented (CIF files CCDC nos. 905357 (I), 874125 (II)). Complex I exhibits three-dimensional network, while complex II shows an interesting two-dimensional covalent layer structure. Furthermore, the photocatalytic property of complex I and the fluorescent property of complex II were reported.
DOI: 10.7868/S0132344X15010120
INTRODUCTION
During the past decades, coordination polymers have attracted considerable attention because of their interesting topologies and crystal packing modes, alongside potential applications in many areas including gas storage, catalysis, magnetism, optics, as well as conductivity [1—6]. The rational design and controllable preparation of coordination polymers are highly influenced by the coordination geometry of the central atom, the structure of the organic ligand and the reaction conditions [7—9]. Among above factors, the nature of the organic ligand plays crucial role in manipulating the network structure of the coordination polymers [10—15]. It is well known that the carboxylate ligand plays an important role in coordination chemistry, which can adopt various coordination modes and link metal ions with different manners [16—20]. In the large family of carboxylates, 2,2-bipyridine-3,3-dicar-boxylate-1,1'-dioxide (Dcbpyno) and 4-cyclohexene-1,2-dicarboxylate (1,2'-Cy) are an good organic ligands in constructing coordination polymers, because they possesses two carboxylate groups, which can be completely or partially deprotonated and may serve as potential anion groups [21].
Nowadays, studies reveal that coordination polymers built from mixed ligands of carboxylate groups and pyridyl groups not only are more adjustable through changing one of the above two organic ligands but also incorporate interesting properties of different functional groups [22—24]. Although many coordination polymers have been synthesized from Dcbpyno and 1,2'-Cy ligands, the complexes constructed from
Dcbpyno, 1,2'-Cy and nitrogen-containing ligands are still largely unexplored [25]. We can conclude that the coordination polymers constructed from these two kinds of ligands may exhibit interesting structural and physical properties.
Based on these points, to synthesize new coordination polymers based on Dcbpyno, 1,2'-Cy and nitrogen-containing ligands as well as enrich their coordination chemistry, herein, we reported the preparation and the crystal structure of two new coordination polymers: {[Cd(Dcbpyno)(1,4'-Bix)15] ■ 2H2O}„ (I) and [Cd(1,2'-Cy)(4,4'-Bipy)]„ (II) (1,4-Bix = 1,4-¿/s(imidazol-1-ylmethyl)benzene, and 4,4'-Bipy = = 4,4'-bipyridine). Furthermore, the photocatalytic property of complex I and the fluorescent property of complex II were reported.
EXPERIMENTAL
Materials and methods. All purchased chemicals were reagent grade and used without further purification. Elemental analyses (C, H, and N) were performed on a PerkinElmer 2400 CHN elemental analyzer. FT/IR spectra were recorded in the range 4000— 400 cm-1 on an Alpha Centaut FTIR spectrophotometer using a KBr pellet. TG analyses were performed on Perkin-Elmer TGA7 instrument in flowing N2 with a heating rate of 10°C min-1. The UV-visible adsorption spectrum was recorded using a Hitachi U-3010 UV-visible spectrometer. Photoluminescence spectrum was measuring using a FL-2T2 instrument
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ZHANG et al.
(SPEX, USA) with 450-W xenon lamp monochroma-tized by double grating (1200 gr/mu).
Synthesis of I. The mixture of Cd(OAc)2 • 2H2O (0.134 g, 0.5 mmol), Dcbpyno (0.138 g, 0.5 mmol), 1,4'-Bix (0.119 g, 0.5 mmol), and 8 mL H2O was stirred for 30 min, and then the pH value was adjusted to 7 with 1 M NaOH. After stirring for another 15 min, the mixture was transferred to a 25 mL Teflon-lined stainless steel bomb and kept at 130°C under autoge-nously pressure for 4 days. The reaction system was cooled to room temperature during 24 h. A large amount of colorless crystals of I were obtained. The yield was 73% (based on Cd).
For C33H31N8O8Cd
anal. calcd., %: C, 50.81; H, 4.01; N, 14.36. Found, %: C, 50.67; H, 4.08; N, 14.25.
Synthesis of II. The mixture of Cd(OAc)2 • 2H2O (0.134 g, 0.5 mmol), 1,2'-Cy (0.085 g, 0.5 mmol), 4,4'-Bipy (0.078 g, 0.5 mmol) and 8 mL H2O was stirred for 30 min, and then the pH value was adjusted to 7 with 1 M KOH. After stirring for another 30 min, the mixture was transferred to a 15 mL Teflon-lined stainless steel bomb and kept at 170°C under autoge-nously pressure for 5 days. The reaction system was cooled to room temperature during 24 h. A large amount of colorless block crystals of II were obtained. The yield was 55% based on Cd.
For C18H16N2O4Cd
anal. calcd., %: C, 49.50; H, 3.69; N, 6.41. Found, %: C, 49.42; H, 3.73; N, 6.38.
IR (v, cm-1): 1539 s, 1480 s, 1390 s, 1218 w, 1067 m, 890 s, 812 s, 661 m, 615 s, 547 w, 491 s.
Photocatalytic experiment. The photocatalytic activities of the samples were evaluated by the degradation of RhB in the aqueous solution. 70 mL RhB aqueous solution with concentration of 10-5 mol/L was mixed with 30 mg catalysts, which was exposed to illumination. Before turning on the lamp, the suspension containing RhB and photocatalyst were magnetically stirred in a dark condition for 40 min till an adsorption-desorption equilibrium was established. Samples were then taken out regularly from the reactor and centrifuged immediately for separation of any suspended solid. The transparent solution was analyzed by a UV-Vis spectrometer. An 11 W germicidal lamp (k = 254 nm) served as a UV light source. Langmuir-Hinshelwood (L-H) equation (r0 = k0c0/1 + K0c0) is employed to quantify the degradation reaction of RhB (r0 represents the initial rate, k0 represents the kinetic rate constant and K0 represents the adsorption coefficient of the reactant RhB). As the value of c0 is too
small, K0c0 ^ 1, the L-H rate expression can simply to first-order rate expression: r0 = dC0/dt = k0C0. This equation can be solved to obtain ln(c/c0) = -k0t. Based on Lambert-Beer law, c/c0= I/I0, the equation can reduce to ln(I/I0) = -k0t finally.
X-ray crystallography. Suitable single crystals of I and II were carefully selected under an optical microscope and glued on glass fibers. Structural measurements were performed on a Bruker AXS SMART APEX II CCD diffractometer at 293 K. The structures were solved by the direct method and refined by the full-matrix least-squares method on F2 using the SHELXTL-97 crystallographic software package [26, 27]. Anisotropic thermal parameters were used to refine all non-hydrogen atoms. Carbon-bound hydrogen atoms were placed in geometrically calculated positions; oxygen-bound hydrogen atoms were located in the difference Fourier maps, kept in that position and refined with isotropic temperature factors. Further details of the X-ray structural analysis are given in Table 1. Selected bond lengths are listed in Table 2.
Supplementary material for complexes has been deposited with the Cambridge Crystallographic Data Centre (nos. 905357 (I) and 874125 (II); deposit@ccdc. cam.ac.uk or http://www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
Complex I exhibits an interesting 3D network. Cd(1) atom adopts distorted octahedron coordination mode and connects with three nitrogen atoms from three Bix ligands with Cd-N bond distances 2.273(4), 2.321(5), and 2.393(4) A, respectively. The other coordination sites are occupied by three carboxylate oxygen atoms from two dcbpyno ligands with Cd-O bond distances range from 2.328(4) to 2.464(3) A as shown in Fig. 1a. Two carboxylate groups in Dcbpyno ligands adopt two kind of connection mode, one is monoden-tate and the other is chelating. Further extension of the [CdN3O3] octahedron through the Dcbpyno ligands and ¿«-bridging Bix ligands results a 3D network, as shown in Fig. 2.
Complex II exhibits an interesting wavelike two-dimensional layer structure. There exists one crystallo-graphically independent Cd atom in the fundamental unit as shown in Fig. 1b. Cd1 connects with four oxygen atoms from three 1,2'-Cy ligands with Cd-O bond distances range from 2.229(2) to 2.439(2) A. Two nitrogen atoms from two 4,4'-Bipy ligands occupy the other two coordination sites. This results a distorted octahedron coordination mode of Cd(1). In complex II, one carboxylate group adopts chelating coordination mode, the other carboxylate group adopts bridging coordination mode. With this linking mode, adjacent Cd atoms are connected and form
SYNTHESIS, CHARACTERIZATION, AND PROPERTY STUDY
Table 1. Crystallographic data and experimental details for complexes I and II
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Parameter Value
I II
Formula weight 780.06 436.73
Crystal system Monoclinic Triclinic
Space group C2/c PI
Unit cell dimensions:
a, A 25.469(2) 7.7499(16)
b, A 15.3912(12) 9.5902(19)
c, A 17.1439(13) 11.860(2)
a, deg 113.30(3)
ß, deg 98.7910(10) 99.40(3)
Y, deg 93.88(3)
V, A3 6641.4(9) 790.1(3)
Z 8 2
Pcalcd g/cm3 1.560 1.836
p., mm-1 0.722 1.409
/(000) 3176 436
9 Range, deg 1.55-25.00 3.30-25.00
Reflections collected 19379 6215
-flint 0.0312 0.0227
Reflections with I > 2o(I) 5851 2762
Max, min transmission 0.891, 0.859 0.765, 0.700
Goodness-of-fit on F 2 1.113 1.050
D ata/restr aints/p ar ameters 5851/6/453 2762/0/234
Final R indices (I >
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