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Three new complexes synthesized from an imidazole-based dicarboxylate ligand containing hydroxymethyl group
Inorganic Chemistry Communications 14 (2011) 1097–1101
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Inorganic Chemistry Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i n o c h e
Three new complexes synthesized from an imidazole-based dicarboxylate ligand containing hydroxymethyl group Sheng-Run Zheng, Song-Liang Cai, Jun Fan, Tian-Tian Xiao, Wei-Guang Zhang ⁎ Institute of Special Materials & School of Chemistry and Environment, South China Normal University, Guangzhou 510006, PR China
a r t i c l e
i n f o
Article history: Received 5 March 2011 Accepted 31 March 2011 Available online 7 April 2011 Keywords: Imidazole-based dicarboxylate ligand In situ reaction
a b s t r a c t Three new complexes, [Cd(H2hmIDC)(bpy)]n (1), {[Co4(HIDC)4(bpy)4]·14H2O}n (2) and {[Co5(IDC)2(HIDC)2 (phen)4(H2O)2]·12H2O}n (3) (H4hmIDC = 2-(hydroxymethyl)-1 H-imidazole-4,5-dicarboxylic acid, H3IDC = imidazole-4,5-dicarboxylic acid, bpy = 2,2’-bipyridyl, phen = 1,10-phenanthroline), were obtained under hydrothermal conditions by using H4hmIDC as initial reactant. Complex 1 is a zigzag chain containing angular [Cd(phen)]2+ node and H2hmIDC2- linker, compound 2 is a discrete Co4 square, while 3 is a 1D chain based on Co4 square motifs similar to that in complex 2. In complex 1, the hydroxymethyl group of the H4hmIDC molecule retains integrated and acts as effective hydrogen bonding interaction site, while in complexes 2 and 3, all the hydroxymethyl groups are lost in situ. The hydroxymethyl groups undergo different reactions directed by metal ions. © 2011 Elsevier B.V. All rights reserved.
Most recently, the design of coordination polymers with potential applications in catalysis, conductivity, luminescence, magnetism, sensors, nonlinear optics, porosity and so on has been one of the most attractive topics [1–3]. However, the structure diversity of coordination polymers is still a puzzle for chemists due to the fact that effect factors in self-assembly process are indeed complicated and the final product is difficult to be predicted [4,5]. Undoubtedly, the choice of organic ligands and metal ions can affect the final structure in great extent, and the interactions between them are important for deliberate design of functional complexes. In general, the choice of metal ions affects the organic ligands in two ways: (i) to regulate the coordination mode of the ligands according to their different coordination geometries and coordination abilities to different donor groups [6]. At this time, all the covalent bonds in the ligand are not changed, the difference by introducing different metal ions is just to affect the supramolecular interactions (coordination bonds, hydrogen bonds and so on) around the ligand. Thus, we can say that the metal ions affect the organic ligand at supramolecular level. (ii) to induce in situ synthesis of new ligands from the original ligand [7]. At this time, covalent bonds in the original ligands are broken off or reformed during the reactions, leading to a new ligand, thus we can say that the metal ions induce the ligand change at a molecular level. Therefore, by the careful choice of organic ligands and metal ions, we can achieve a metal–organic system directed by the synergistic metal and ligand effects at both two levels [8]. However, studies on this type of ligand are still less explored.
⁎ Corresponding author. Tel./fax: + 86 20 39310187. E-mail address: [email protected] (W.-G. Zhang). 1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2011.03.065
In addition, imidazole-4,5-dicarboxylic acid (H3IDC), a planar rigid ligand containing two nitrogen and four oxygen atoms, has attracted much interest in coordination chemistry and proven to be an excellent building block to form a series of metal-organic frameworks (MOFs) with different structures and useful properties [9,10]. Recently, introducing an additional group on 2-position of such motif has become a tendency in the chemistry of imidazole-based dicarboxylate ligand. Up to now, some imidazole-based ligands such as 2-ethyl-1 H-imidazole-4,5-dicarboxylic acid, 2-propyl-1 H-imidazole-4,5-dicarboxylic acid [11] and 2-pyridinyl1 H-imidazole- 4,5-dicarboxylic acid [12] have been designed and studied extensively. In order to further investigate the chemistry of this sort of ligands, we introduced a hydroxymethyl group on the 2-position of imidazole-4,5-dicarboxylic acid (H3IDC) and obtained a new ligand, 2(hydroxymethyl)-1 H-imidazole-4,5-dicarboxylic acid (H4hmIDC). This ligand attracted our attention mainly because the reaction behavior of the hydroxymethyl group in this ligand is various. It not only remains uncoordinated, but also become coordinated or convert to the carboxyl group in situ directed by metal ions as we reported [8]. Herein we report three new complexes assembled from this ligand. In complex 1, the hydroxymethyl group retains integrated and acts as effective hydrogen bonding interaction site in the reaction of Cd(II) ions and the H4hmIDC molecules, while in situ dehydroxymethylation reaction (the cleavage of C-C bond between hydroxymethyl group and imidazole group) took place in complexes 2 and 3 when using Co(II) ion as metal source under certain conditions (scheme 1). Reaction of Cd(II) with H4hmIDC results in complex 1. As shown in Fig. 1a, complex 1 is a 1D zigzag chain constructed by a angular [Cd(bpy)]2+ node and H4hmIDC rod. The Cd(II) ion is six-coordinated with two N atoms from two different bpy molecules, two imidazole N
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S.-R. Zheng et al. / Inorganic Chemistry Communications 14 (2011) 1097–1101
Scheme 1. Construction of three new complexes by using H4hmIDC as initial reactant.
atoms and two carboxylate O atoms from two different H2HmIDC2-. The H2hmIDC2- ligands link the neighboring Cd(II) ions via N,Ochelating and N’,O’-chelating into a 1-D zigzag chain composed of fused five-member rings along the a-axis (Fig. 1b). The angle between two adjacent H2hmIDC2- planes is 79.675(42)°, and the distance of the neighboring Cd(II) ions is 6.6673(8) Å. It is the O-H···O hydrogen bond between hydroxylmethyl group and carboxyl group (O(5)-
H(5)···O(1), H···O 2.0922(29) Å, O···O 2.741(5) Å, ∠OHO 135.844 (295)°, symmetry code: 3/2 − x, 1/2 + y, z,) assemble the zigzag chain into 2D network (Fig. 1b). Furthermore, a 3D supramolecular network is built up by π–π stacking interactions between 2, 2’-bipy rings (centre to centre, 3.4982(3) Å) as shown in Fig. 1c. Because the hydroxymethyl remains the uncoordinated state, the coordination modes of H4hmIDC is similar to H3IDC that have been
S.-R. Zheng et al. / Inorganic Chemistry Communications 14 (2011) 1097–1101
Fig. 1. (a) The coordination environment of Cd(II) and 1D zigzag chain in 1. (b) 2D hydrogen bonding network in 1. (c) 3D supramolecular network in 1.
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reported, the structures of the complexes with H4hmIDC ligands are similar to those based on H3IDC molecules [13]. However, the hydroxylmethyl group on the 2-position of H4hmIDC can participate in hydrogen bonds, further leading to a different supramolecular network. Thus, the hydrogen bonding interactions formed by hydroxylmethyl group play a key role in forming the final supramolecular networks. When using Co(II) ion as the reactant, the in situ dehydroxymethylation reaction happened and H4hmIDC was transformed into H3IDC, which is revealed by X-ray analysis. In complex 2, the asymmetry unit contains two independent Co(II) ions, which are both six-coordinated with two N atoms from two different bpy molecules, two imidazole N atoms and two carboxylate O atoms from two different HIDC2- (Fig. 2a). Thus, two [Co(bpy)]2+ ions play the roles of angular nodes, and four HIDC2- anions behave as rigid linear rods, generating a Co4 molecular square (Fig. 2b). The four metal ions are exactly coplanar, and two of the four HIDC2- planes in the ring are almost perpendicularly to the Co4 plane (the angle is 85.927(51)°), and the other two HIDC2- planes are almost parallel with the Co4 plane (the angle is 2.331(41)°). The Co(II)···Co(II) distances in the Co4 square are 5.9686(33) and 6.0109(29) Å, respectively, and the vertex angles are 91.601(18)° and 88.399(18)°, indicating only slight deviations from the ideal square geometry. In addition, free water molecules exist among the Co4 squares. The connections of the abundant hydrogen bonds between the carboxylate group and other water molecules lead to a complicated 3D supramolecular network (Fig. S1). Complex 2 is a first example of the complex with ideal square planar geometry constructed from Co(II) and HIDC2-, although it is similar to motif in the reported work [14]. This sort of Co4 square is also observed in complex 3 and the coordination environment of Co(II) ion in the square is similar to complex 2, except that bpy molecule are replaced with phen molecule (Fig. 2c). The Co(II)···Co(II) lengths of the Co4 square are 6.1030(18)
Fig. 2. (a) The coordination environment of Co(II) ions in 2. (b) The Co4 tetranuclear ring in 2. (c) The coordination environment of Co(II) ions in 3. (d) 1D chain based on Co4 tetranuclear ring in 3.
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S.-R. Zheng et al. / Inorganic Chemistry Communications 14 (2011) 1097–1101
Appendix A. Supplementary material CCDC 794914, 794917 and 794918 contain the supplementary crystallographic data for the compounds 1, 2 and 3, respectively. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data to this article can be found online at doi:10.1016/j. inoche.2011.03.065. References
Fig. 3. The photoluminescent spectra of H4hmIDC (red dash line) and complex 1 (blue line) in the solid state at room temperature.
and 6.0786(16) Å, and the vertex angles are 89.726(18)° and 90.274 (18)°, respectively, which is even more nearly to the ideal square compare to complex 2. Furthermore, the Co(3) ions, which display in distorted octahedral geometries coordinated by two water molecules and four carboxylate O atoms from two adjacent squares, connect the molecular squares into a chain along the (1 1 0) direction (Fig. 2d). Between the chains, there exist water molecules that hydrogen-bonding to the carboxylate groups or the coordinated water molecules, thus leading to a complicated supramolecular network (Fig. S2). Although complexes 2 and 3 are based on H3IDC ligands, they don't be synthesized directly by using H3IDC and Co(II) ion as initial reactant under the same or similar condition [10,14,15]. The true means for the introduction of hydroxylmethyl group may put the effects on the assembling process dramatically, although it does not appear in the final product. Previous studies have shown that the Cd(II) coordination polymers exhibit good photoluminescent properties. Hence, we investigated the photoluminescent properties of the ligand (H4hmIDC) and complex 1 (Fig. 3). In the solid state, strong photoluminescence emission bands at 452 nm (λex = 381 nm) are observed for 1 and at 461 nm (λex = 361 nm) for free ligand. Although the maximum emission wavelength of complex 1 undergoes a very slight blue-shift, its emission band is very similar to that found for the free ligand in terms of the position and the band shape. Therefore, the emission band of complex 1 is mainly due to an intraligand emission state as reported for Cd(II) or other d10 metal complexes [16]. In conclusion, an imidazole-based dicarboxylate ligand containing a hydroxymethyl group, 2-(hydroxymethyl)-1H-imidazole-4,5-dicarboxylic acid (H4hmIDC) display flexible reaction behaviors under different hydrothermal conditions. In complex 1, the hydroxymethyl group acts as hydrogen bonding donor or acceptor, while it disappeared in the reaction between the ligand H4hmIDC and Co(II) ions. It is very interesting that the reaction behavior of the hydroxymethyl group is largely dependent on the metal ions we used. The results also show that the introduction of a flexible group on the organic ligand may be an effective way to obtain some unprecedented coordination assemblies. Acknowledgement This work was financially supported by the National Natural Science Foundation of China (Grant 21003053) and the Ministry of Science and Technology of China (No. 10C26214412704).
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Contents lists available at ScienceDirect
Inorganic Chemistry Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i n o c h e
Three new complexes synthesized from an imidazole-based dicarboxylate ligand containing hydroxymethyl group Sheng-Run Zheng, Song-Liang Cai, Jun Fan, Tian-Tian Xiao, Wei-Guang Zhang ⁎ Institute of Special Materials & School of Chemistry and Environment, South China Normal University, Guangzhou 510006, PR China
a r t i c l e
i n f o
Article history: Received 5 March 2011 Accepted 31 March 2011 Available online 7 April 2011 Keywords: Imidazole-based dicarboxylate ligand In situ reaction
a b s t r a c t Three new complexes, [Cd(H2hmIDC)(bpy)]n (1), {[Co4(HIDC)4(bpy)4]·14H2O}n (2) and {[Co5(IDC)2(HIDC)2 (phen)4(H2O)2]·12H2O}n (3) (H4hmIDC = 2-(hydroxymethyl)-1 H-imidazole-4,5-dicarboxylic acid, H3IDC = imidazole-4,5-dicarboxylic acid, bpy = 2,2’-bipyridyl, phen = 1,10-phenanthroline), were obtained under hydrothermal conditions by using H4hmIDC as initial reactant. Complex 1 is a zigzag chain containing angular [Cd(phen)]2+ node and H2hmIDC2- linker, compound 2 is a discrete Co4 square, while 3 is a 1D chain based on Co4 square motifs similar to that in complex 2. In complex 1, the hydroxymethyl group of the H4hmIDC molecule retains integrated and acts as effective hydrogen bonding interaction site, while in complexes 2 and 3, all the hydroxymethyl groups are lost in situ. The hydroxymethyl groups undergo different reactions directed by metal ions. © 2011 Elsevier B.V. All rights reserved.
Most recently, the design of coordination polymers with potential applications in catalysis, conductivity, luminescence, magnetism, sensors, nonlinear optics, porosity and so on has been one of the most attractive topics [1–3]. However, the structure diversity of coordination polymers is still a puzzle for chemists due to the fact that effect factors in self-assembly process are indeed complicated and the final product is difficult to be predicted [4,5]. Undoubtedly, the choice of organic ligands and metal ions can affect the final structure in great extent, and the interactions between them are important for deliberate design of functional complexes. In general, the choice of metal ions affects the organic ligands in two ways: (i) to regulate the coordination mode of the ligands according to their different coordination geometries and coordination abilities to different donor groups [6]. At this time, all the covalent bonds in the ligand are not changed, the difference by introducing different metal ions is just to affect the supramolecular interactions (coordination bonds, hydrogen bonds and so on) around the ligand. Thus, we can say that the metal ions affect the organic ligand at supramolecular level. (ii) to induce in situ synthesis of new ligands from the original ligand [7]. At this time, covalent bonds in the original ligands are broken off or reformed during the reactions, leading to a new ligand, thus we can say that the metal ions induce the ligand change at a molecular level. Therefore, by the careful choice of organic ligands and metal ions, we can achieve a metal–organic system directed by the synergistic metal and ligand effects at both two levels [8]. However, studies on this type of ligand are still less explored.
⁎ Corresponding author. Tel./fax: + 86 20 39310187. E-mail address: [email protected] (W.-G. Zhang). 1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2011.03.065
In addition, imidazole-4,5-dicarboxylic acid (H3IDC), a planar rigid ligand containing two nitrogen and four oxygen atoms, has attracted much interest in coordination chemistry and proven to be an excellent building block to form a series of metal-organic frameworks (MOFs) with different structures and useful properties [9,10]. Recently, introducing an additional group on 2-position of such motif has become a tendency in the chemistry of imidazole-based dicarboxylate ligand. Up to now, some imidazole-based ligands such as 2-ethyl-1 H-imidazole-4,5-dicarboxylic acid, 2-propyl-1 H-imidazole-4,5-dicarboxylic acid [11] and 2-pyridinyl1 H-imidazole- 4,5-dicarboxylic acid [12] have been designed and studied extensively. In order to further investigate the chemistry of this sort of ligands, we introduced a hydroxymethyl group on the 2-position of imidazole-4,5-dicarboxylic acid (H3IDC) and obtained a new ligand, 2(hydroxymethyl)-1 H-imidazole-4,5-dicarboxylic acid (H4hmIDC). This ligand attracted our attention mainly because the reaction behavior of the hydroxymethyl group in this ligand is various. It not only remains uncoordinated, but also become coordinated or convert to the carboxyl group in situ directed by metal ions as we reported [8]. Herein we report three new complexes assembled from this ligand. In complex 1, the hydroxymethyl group retains integrated and acts as effective hydrogen bonding interaction site in the reaction of Cd(II) ions and the H4hmIDC molecules, while in situ dehydroxymethylation reaction (the cleavage of C-C bond between hydroxymethyl group and imidazole group) took place in complexes 2 and 3 when using Co(II) ion as metal source under certain conditions (scheme 1). Reaction of Cd(II) with H4hmIDC results in complex 1. As shown in Fig. 1a, complex 1 is a 1D zigzag chain constructed by a angular [Cd(bpy)]2+ node and H4hmIDC rod. The Cd(II) ion is six-coordinated with two N atoms from two different bpy molecules, two imidazole N
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Scheme 1. Construction of three new complexes by using H4hmIDC as initial reactant.
atoms and two carboxylate O atoms from two different H2HmIDC2-. The H2hmIDC2- ligands link the neighboring Cd(II) ions via N,Ochelating and N’,O’-chelating into a 1-D zigzag chain composed of fused five-member rings along the a-axis (Fig. 1b). The angle between two adjacent H2hmIDC2- planes is 79.675(42)°, and the distance of the neighboring Cd(II) ions is 6.6673(8) Å. It is the O-H···O hydrogen bond between hydroxylmethyl group and carboxyl group (O(5)-
H(5)···O(1), H···O 2.0922(29) Å, O···O 2.741(5) Å, ∠OHO 135.844 (295)°, symmetry code: 3/2 − x, 1/2 + y, z,) assemble the zigzag chain into 2D network (Fig. 1b). Furthermore, a 3D supramolecular network is built up by π–π stacking interactions between 2, 2’-bipy rings (centre to centre, 3.4982(3) Å) as shown in Fig. 1c. Because the hydroxymethyl remains the uncoordinated state, the coordination modes of H4hmIDC is similar to H3IDC that have been
S.-R. Zheng et al. / Inorganic Chemistry Communications 14 (2011) 1097–1101
Fig. 1. (a) The coordination environment of Cd(II) and 1D zigzag chain in 1. (b) 2D hydrogen bonding network in 1. (c) 3D supramolecular network in 1.
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reported, the structures of the complexes with H4hmIDC ligands are similar to those based on H3IDC molecules [13]. However, the hydroxylmethyl group on the 2-position of H4hmIDC can participate in hydrogen bonds, further leading to a different supramolecular network. Thus, the hydrogen bonding interactions formed by hydroxylmethyl group play a key role in forming the final supramolecular networks. When using Co(II) ion as the reactant, the in situ dehydroxymethylation reaction happened and H4hmIDC was transformed into H3IDC, which is revealed by X-ray analysis. In complex 2, the asymmetry unit contains two independent Co(II) ions, which are both six-coordinated with two N atoms from two different bpy molecules, two imidazole N atoms and two carboxylate O atoms from two different HIDC2- (Fig. 2a). Thus, two [Co(bpy)]2+ ions play the roles of angular nodes, and four HIDC2- anions behave as rigid linear rods, generating a Co4 molecular square (Fig. 2b). The four metal ions are exactly coplanar, and two of the four HIDC2- planes in the ring are almost perpendicularly to the Co4 plane (the angle is 85.927(51)°), and the other two HIDC2- planes are almost parallel with the Co4 plane (the angle is 2.331(41)°). The Co(II)···Co(II) distances in the Co4 square are 5.9686(33) and 6.0109(29) Å, respectively, and the vertex angles are 91.601(18)° and 88.399(18)°, indicating only slight deviations from the ideal square geometry. In addition, free water molecules exist among the Co4 squares. The connections of the abundant hydrogen bonds between the carboxylate group and other water molecules lead to a complicated 3D supramolecular network (Fig. S1). Complex 2 is a first example of the complex with ideal square planar geometry constructed from Co(II) and HIDC2-, although it is similar to motif in the reported work [14]. This sort of Co4 square is also observed in complex 3 and the coordination environment of Co(II) ion in the square is similar to complex 2, except that bpy molecule are replaced with phen molecule (Fig. 2c). The Co(II)···Co(II) lengths of the Co4 square are 6.1030(18)
Fig. 2. (a) The coordination environment of Co(II) ions in 2. (b) The Co4 tetranuclear ring in 2. (c) The coordination environment of Co(II) ions in 3. (d) 1D chain based on Co4 tetranuclear ring in 3.
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Appendix A. Supplementary material CCDC 794914, 794917 and 794918 contain the supplementary crystallographic data for the compounds 1, 2 and 3, respectively. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data to this article can be found online at doi:10.1016/j. inoche.2011.03.065. References
Fig. 3. The photoluminescent spectra of H4hmIDC (red dash line) and complex 1 (blue line) in the solid state at room temperature.
and 6.0786(16) Å, and the vertex angles are 89.726(18)° and 90.274 (18)°, respectively, which is even more nearly to the ideal square compare to complex 2. Furthermore, the Co(3) ions, which display in distorted octahedral geometries coordinated by two water molecules and four carboxylate O atoms from two adjacent squares, connect the molecular squares into a chain along the (1 1 0) direction (Fig. 2d). Between the chains, there exist water molecules that hydrogen-bonding to the carboxylate groups or the coordinated water molecules, thus leading to a complicated supramolecular network (Fig. S2). Although complexes 2 and 3 are based on H3IDC ligands, they don't be synthesized directly by using H3IDC and Co(II) ion as initial reactant under the same or similar condition [10,14,15]. The true means for the introduction of hydroxylmethyl group may put the effects on the assembling process dramatically, although it does not appear in the final product. Previous studies have shown that the Cd(II) coordination polymers exhibit good photoluminescent properties. Hence, we investigated the photoluminescent properties of the ligand (H4hmIDC) and complex 1 (Fig. 3). In the solid state, strong photoluminescence emission bands at 452 nm (λex = 381 nm) are observed for 1 and at 461 nm (λex = 361 nm) for free ligand. Although the maximum emission wavelength of complex 1 undergoes a very slight blue-shift, its emission band is very similar to that found for the free ligand in terms of the position and the band shape. Therefore, the emission band of complex 1 is mainly due to an intraligand emission state as reported for Cd(II) or other d10 metal complexes [16]. In conclusion, an imidazole-based dicarboxylate ligand containing a hydroxymethyl group, 2-(hydroxymethyl)-1H-imidazole-4,5-dicarboxylic acid (H4hmIDC) display flexible reaction behaviors under different hydrothermal conditions. In complex 1, the hydroxymethyl group acts as hydrogen bonding donor or acceptor, while it disappeared in the reaction between the ligand H4hmIDC and Co(II) ions. It is very interesting that the reaction behavior of the hydroxymethyl group is largely dependent on the metal ions we used. The results also show that the introduction of a flexible group on the organic ligand may be an effective way to obtain some unprecedented coordination assemblies. Acknowledgement This work was financially supported by the National Natural Science Foundation of China (Grant 21003053) and the Ministry of Science and Technology of China (No. 10C26214412704).
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