Citation: LI Xiu-Mei, Yang Jia-Qi, PAN Ya-Ru, LIU Bo, ZHOU Shi. Syntheses, Crystal Structures and Photoluminescent Properties of Two Co(Ⅱ)/Cu(Ⅰ) Coordination Polymers Based on Bis(imidazol) Ligands[J]. Chinese Journal of Inorganic Chemistry, 2020, 36(4): 730-736. doi: 10.11862/CJIC.2020.076
两个基于双咪唑基配体的Co(Ⅱ)/Cu(Ⅰ)配合物的合成、晶体结构及荧光性质
English
Syntheses, Crystal Structures and Photoluminescent Properties of Two Co(Ⅱ)/Cu(Ⅰ) Coordination Polymers Based on Bis(imidazol) Ligands
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Key words:
- hydrothermal synthesis
- / crystal structure
- / Co(Ⅱ) complex
- / Cu(Ⅰ) complex
- / luminescence
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0. Introduction
The design and synthesis of metal-organic coordination polymers relied on the selection of ligands and metal ions has become a very attractive research field. This is motivated not only by the intriguing structural diversity but also by the demand of applying functional materials into the fields of catalysis, porosity, magnetism, luminescence and nonlinear optics[1-3]. In general, grids with various sizes and shapes can be synthesized by choosing suitable single metal ions and organic ligands such as carboxylates and N-donor groups[4-6]. Self-assembly is a complex process, highly influenced by many factors, such as the coordination geometry of metal ions, the nature of organic ligands, solvent system, temperature, pH value of the solution, the ratio between metal salt and ligand, the templates and the counter anions[7-14]. These factors have been well-studied, but there are other forces such as hydrogen-bonding, π-π interac-tions, metal-metal interactions that can greatly influence the supramolecular topology and its dimensionality[15-17]. Therefore, these considerations made us investigate new coordination structures with 4, 4'-(1, 3-phenylene-bis(methyleneoxy)) dibebzoic acid (H2pmda), and brid-ging ligands (bib/bix). In this manuscript, we reported the syntheses, crystal structures, IR and fluorescence properties of two new complexes, namely {[Co(bib)3](ClO4)2}n (1) and {[Cu3(bix)4.5](ClO4)3}n (2). Complexes 1 and 2 all exhibit intense purple luminescence, and appears to be good candidates for novel hybrid inorganic-organic photoactive materials.
1. Experimental
1.1 General procedures
All reagents were purchased commercially and used without further purification. Elemental analyses (C, H and N) were measured on a Vario EL(Ⅲ) Elemental Analyzer. IR spectrum was recorded in a range of 4 000~400 cm-1 on a Nicolet 6700 spectro-meter using a KBr pellet. The fluorescence spectra were performed on an F-7000 photospectrometer (Hitachi, High-Tech, Science, Japan). The powder X-ray diffraction (PXRD) studies were performed with a Bruker D8 Discover instrument (Cu Kα radiation, λ=0.154 184 nm, U=40 kV, I=40 mA) over the 2θ range of 5°~50° at room temperature.
1.2 Synthesis
{[Co(bib)3](ClO4)2}n (1):H2pmda (0.075 6 g, 0.2 mmol), Co(ClO4)2·6H2O (0.2 mmol, 0.075 g), bib (0.038 g, 0.2 mmol) and 18 mL H2O were mixed, and the pH value of the mixture was adjust to about 8 with 40% NaOH. Then it was sealed in a Teflon-lined stainless steel vessel, heated to 120℃ for 7 days, and followed by slow cooling to room temperature. Pink block crystals were obtained. Unfortunately, H2pmda ligand did not participate in the coordination. Yield:34%. Anal. Calcd. for C30H42Cl2CoN12O8(%):C, 43.49; H, 5.11; N, 20.29. Found(%):C, 43.00; H, 4.99; N, 19.95. IR (cm-1):3 126m, 2 952w, 1 657w, 1 605w, 1 521s, 1 465w, 1 443w, 1 404w, 1 373m, 1 303w, 1 280m, 1 236s, 1 096s, 936m, 870w, 834m, 772m, 743w, 729w, 667m, 623m.
{[Cu3(bix)4.5](ClO4)3}n (2):H2pmda (0.075 6 g, 0.2 mmol), Cu(ClO4)2·6H2O (0.2 mmol, 0.08 g), bix (0.048 g, 0.2 mmol) and 18 mL H2O were mixed, and the pH value of the mixture was adjust to about 6 with 40% NaOH, Then it was sealed in a Teflon-lined stainless steel vessel, heated to 120℃ for 7 days, and followed by slow cooling to room temperature. Pale yellow block crystals were obtained. Unfortunately, H2pmda ligand did not participate in the coordination. Yield:23%. Anal. Calcd. for C63H63Cl3Cu3N18O12(%):C, 48.46; H, 4.07; N, 16.15. Found(%):C, 48.01; H, 3.71; N, 15.85. IR (cm-1):3 448w, 3 128m, 2 948w, 1 655w, 1 618w, 1 521s, 1 450m, 1 430w, 1 401w, 1 351w, 1 302w, 1 279m, 1 237s, 1 181w, 1 126w, 1 081s, 1 023w, 978w, 942w, 869w, 824w, 815w, 764w, 742m, 714s, 653m, 624s, 517w, 436w.
1.3 Structure determination
Single-crystal X-ray diffraction data for 1 with dimensions of 0.45 mm×0.35 mm×0.34 mm and 2 with dimensions of 0.30 mm×0.22 mm×0.18 mm were recorded on a Bruker D8 QUEST CMOS diffractometer with graphite-monochromated Mo Kα radiation (λ=0.071 073 nm) at 293 K. The structures were solved with the direct method of SHELXS-97 and refined with full-matrix least-squares techniques using the SHELXL-97 program[18-19]. The non-hydrogen atoms of the complexes were refined with anisotropic temperature parameters. The hydrogen atoms attached to carbons were generated geometrically. Selected bond lengths and bond angles are listed in Table 1.
表 1
1 Co(1)-N(1) 0.218 2(2) Co(1)-N(1A) 0.218 2(2) Co(1)-N(1B) 0.218 2(2) Co(1)-N(1C) 0.218 2(2) Co(1)-N(1D) 0.218 2(2) Co(1)-N(1E) 0.218 2(2) N(1)-Co(1)-N(1B) 90.82(9) N(1)-Co(1)-N(1E) 89.18(9) N(1B)-Co(1)-N(1E) 180.000(1) N(1)-Co(1)-N(1C) 180.0 N(1B)-Co(1)-N(1C) 89.18(9) N(1E)-Co(1)-N(1C) 90.82(9) N(1)-Co(1)-N(1A) 90.82(9) N(1B)-Co(1)-N(1A) 90.82(9) N(1E)-Co(1)-N(1A) 89.18(9) N(1C)-Co(1)-N(1A) 89.18(9) N(1)-Co(1)-N(1D) 89.18(9) N(1C)-Co(1)-N(1D) 89.18(9) N(1E)-Co(1)-N(1D) 90.82(9) N(1C)-Co(1)-N(1D) 90.82(9) N(1A)-Co(1)-N(1D) 180.00(9) 2 Cu(1)-N(5) 0.196 5(2) Cu(1)-N(5A) 0.196 5(2) Cu(1)-N(5B) 0.196 5(2) Cu(2)-N(1) 0.196 4(3) Cu(2)-N(1C) 0.196 4(3) Cu(2)-N(1D) 0.196 4(3) Cu(3)-N(4) 0.197 4(2) Cu(3)-N(4E) 0.197 4(2) Cu(3)-N(4F) 0.197 4(2) N(5A)-Cu(1)-N(5B) 119.955(7) N(5A)-Cu(1)-N(5) 119.955(7) N(5B)-Cu(1)-N(5) 119.955(6) N(1C)-Cu(2)-N(1) 119.819(14) N(1D)-Cu(2)-N(1C) 119.819(14) N(1)-Cu(2)-N(1C) 119.819(14) N(4)-Cu(3)-N(4E) 119.990(3) N(4)-Cu(3)-N(4F) 119.990(3) N(4E)-Cu(3)-N(4F) 119.990(3) Symmetry codes:A: 1-y, x-y-1, z; B: 2-x+y, 1-x, z; C: 2-x, -y, 2-z; D: 1+y, 1-x+y, 2-z; E: x-y, x-1, 2-z for 1; A: 1-y, x-y, z; B: 1-x+y, 1-x, z; C: -y, x-y, z; D: -x+y, -x, z; E: -y, x-y-1, z; F: 1-x+y, -x, z for 2. CCDC:1950200, 1; 1950184, 2.
2. Results and discussion
2.1 Description of the structure
Single crystal X-ray analysis reveals that complex 1 crystalizes in trigonal system with P
$\bar 3$ space group. The asymmetric unit of complex 1 is composed of one-sixth crystallographically Co(Ⅱ) ion, half bib ligand, and one-third free ClO4- (Fig. 1). Each Co(Ⅱ) ion is six-coordinated and attach to six nitrogen atoms from six different bib ligands, forming the cation[Co(bib)3]2+, while the two ClO4- anions play the role of balancing the charge. The geometry around each Co(Ⅱ) center is slightly distorted octahedron coordination sphere because the angles in a range of 89.18(9)°~180.00(9)°. The Co-N bond distance is 0.218 2(2) nm and similar to those in analogous complexes[20-21].图 1
In complex 1, the bib ligand takes trans-conformation bridging mode with a dihedral angle between the two imidazole rings of 0°. As depicted in Fig. 2, three Co(Ⅱ) ions are bridged by six nitrogen atoms of bib ligands to give crystallographically isosceles triangle trimers with Co…Co distance of 1.411 9 nm, which are further connected to a two-dimensional network with a 36-membered ring, and to the best of our knowledge, this structure is relatively rare. Single crystal X-ray diffraction reveals that [Co(bib)3]2+ and ClO4- units form 3D supramolecular architectures (Fig. 3) through two hydrogen bonds:C(1)-H(1)…O(2) (C(1)…O(2) 0.323 5(17) nm) and C(3)-H(3)…O(1) (C(3)…O(1) 0.315 6(8) nm), undoubtedly stabilizing the 3D structure of complex 1.
图 2
图 3
A single-crystal X-ray diffraction study reveals that complex 2 crystallizes in trigonal system with R
$\bar 3$ space group and features a 2D network structure. The coordination environment of Cu(Ⅰ) ion in 2 is shown in Fig. 4. The Cu(Ⅰ) ion is three-coordinated by three nitrogen atoms from three different bix ligands to furnish a slightly distorted plane triangle coordination architecture, which has been reported relatively rarely[22]. The bond distances of Cu-N in complex 2 are in a range of 0.196 4(3)~0.197 4(2) nm and the coor-dination angles around the Cu(Ⅰ) ion are in a range of 119.819(14)°~119.990(3)°, which further proves that the plane triangle structure of Cu(Ⅰ) ion. It is worth pointing out that Cu(Ⅱ) ion took place redox reaction, and turned into Cu(Ⅰ) ion, which may be the magic of hydrothermal reactions.图 4
In the crystal structure of complex 2, the bix ligand adopts a trans-conformation bridging mode with a dihedral angle between two imidazole rings of 28.81° and link the Cu(Ⅰ) ions to form a two-dimensional network structure with 84-membered ring, as shown in Fig. 5.
图 5
Hydrogen bonding interactions are frequently chief in the synthesis of supramolecular structure. Single crystal X-ray reveals that[Cu3(bix)4.5]3+ and ClO4- units form 3D supramolecular architectures through two hydrogen bonds:C(12)-H(12A)…O(1) (C(12)… O(1) 0.334 9(7) nm) and C(20)-H(20A)…O(4) (C(20)…O(4) 0.348 4(5) nm). In addition, there are π-π interactions (Fig. 6) in complex 2 between imidazole rings of bix ligands. The centroid-to-centroid distance between adjacent ring is 0.366 82(17) nm for N(3)C(12)N(4)C(13)C(14) and N(5)C(15)C(16)N(6)C(17) (Sym-metry code:y, -x+y, 1-z) imidazole rings. The perpendicular distance is 0.338 23(12) nm and the dihedral angle is 0.00(17)°. Thus, through hydrogen bonds and π-π interactions, a three-dimensional supramolecular architecture is formed and plays an important role in stabilizing complex 2.
图 6
To investigate whether the analyzed crystal structure is truly representative of the bulk materials, X-ray powder diffraction (PXRD) analysis has been performed for the complex at room temperature (Fig. 7). The main peak positions observed are in good agreement with the simulated ones. Although minor differences can be found in the positions, widths, and intensities of some peaks, the bulk synthesized materials and analyzed crystal can still be considered as homogeneous. The differences may be due to the preferred orientation of the powder samples[23-24].
图 7
2.2 Photoluminescent properties
Metal-organic coordination polymers and conjugated organic linker have been studied because of their fluorescent properties and potential applications as fluorescent-emitting materials, chemical sensors and electroluminescent displays[25]. Therefore, in the present work, the photoluminescent properties of bib, bix, complexes 1 and 2 have been investigated in the solid state at room temperature, as depicted in Fig. 8. The free ligands bib and bix showed photoluminescence with the emission maximum at 408 nm(λex=348 nm) and 450 nm (λex=350 nm), respe-ctively, which can be assigned to intraligand (π→π*) transition[26]. Compared with the free bib ligand, a wide range of the emission with maximum peaks at ca. 438 nm upon excitation at ca. 350 nm for complex 1 was observed, which was red-shift. This emission band can be tentatively attributed to a ligand-to-metal charge transfer (LMCT)[27]. While the emission peak of complex 2 (λem=434 nm, λex=350 nm) was blue-shift as compared to the free ligand bix. Therefore, this emission band may be assigned as ligand-to-ligand charge transfer (LLCT) transitions[28-29]. The fluorescence emissions of the complexes make them potentially useful photoactive materials.
图 8
3. Conclusions
In general, we have prepared two new complexes with bib/bix ligands. The bib/bix ligands adopt bridging mode, and link neighboring Co(Ⅱ)/Cu(Ⅰ) ions to generate 2D network structure. Furthermore, the 3D supramolecular architectures are formed by hydrogen bonding or π-π interactions. They all exhibit intense purple luminescence. These materials will give new impetus to the construction of novel functional material with potentially useful physical properties.
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表 1 Selected bond lengths (nm) and bond angles (°) for 1 and 2
1 Co(1)-N(1) 0.218 2(2) Co(1)-N(1A) 0.218 2(2) Co(1)-N(1B) 0.218 2(2) Co(1)-N(1C) 0.218 2(2) Co(1)-N(1D) 0.218 2(2) Co(1)-N(1E) 0.218 2(2) N(1)-Co(1)-N(1B) 90.82(9) N(1)-Co(1)-N(1E) 89.18(9) N(1B)-Co(1)-N(1E) 180.000(1) N(1)-Co(1)-N(1C) 180.0 N(1B)-Co(1)-N(1C) 89.18(9) N(1E)-Co(1)-N(1C) 90.82(9) N(1)-Co(1)-N(1A) 90.82(9) N(1B)-Co(1)-N(1A) 90.82(9) N(1E)-Co(1)-N(1A) 89.18(9) N(1C)-Co(1)-N(1A) 89.18(9) N(1)-Co(1)-N(1D) 89.18(9) N(1C)-Co(1)-N(1D) 89.18(9) N(1E)-Co(1)-N(1D) 90.82(9) N(1C)-Co(1)-N(1D) 90.82(9) N(1A)-Co(1)-N(1D) 180.00(9) 2 Cu(1)-N(5) 0.196 5(2) Cu(1)-N(5A) 0.196 5(2) Cu(1)-N(5B) 0.196 5(2) Cu(2)-N(1) 0.196 4(3) Cu(2)-N(1C) 0.196 4(3) Cu(2)-N(1D) 0.196 4(3) Cu(3)-N(4) 0.197 4(2) Cu(3)-N(4E) 0.197 4(2) Cu(3)-N(4F) 0.197 4(2) N(5A)-Cu(1)-N(5B) 119.955(7) N(5A)-Cu(1)-N(5) 119.955(7) N(5B)-Cu(1)-N(5) 119.955(6) N(1C)-Cu(2)-N(1) 119.819(14) N(1D)-Cu(2)-N(1C) 119.819(14) N(1)-Cu(2)-N(1C) 119.819(14) N(4)-Cu(3)-N(4E) 119.990(3) N(4)-Cu(3)-N(4F) 119.990(3) N(4E)-Cu(3)-N(4F) 119.990(3) Symmetry codes:A: 1-y, x-y-1, z; B: 2-x+y, 1-x, z; C: 2-x, -y, 2-z; D: 1+y, 1-x+y, 2-z; E: x-y, x-1, 2-z for 1; A: 1-y, x-y, z; B: 1-x+y, 1-x, z; C: -y, x-y, z; D: -x+y, -x, z; E: -y, x-y-1, z; F: 1-x+y, -x, z for 2. -
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