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Synthesis, structure and anion-exchange property of the first example of self-penetrated three-dimensional metal-organic framework with flexible three-connecting ligand and nickel(II) perchlorate
Microporous and Mesoporous Materials 73 (2004) 101–108 www.elsevier.com/locate/micromeso
Synthesis, structure and anion-exchange property of the first example of self-penetrated three-dimensional metal-organic framework with flexible three-connecting ligand and nickel(II) perchlorate Shuang-Yi Wan, Yu-Ting Huang, Yi-Zhi Li, Wei-Yin Sun
*
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China Received 19 April 2003; received in revised form 16 December 2003; accepted 22 December 2003 Available online 8 June 2004
Abstract Novel polymeric coordination complex [Ni(timpt)2 ](ClO4 )2 1 was synthesized by solvothermal reaction of 2,4,6-tris[4-(imidazol1-ylmethyl)phenyl]-1,3,5-triazine (timpt) ligand with Ni(ClO4 )2 Æ 6H2 O and characterized by X-ray crystallography. Each Ni(II) is coordinated by six imidazolyl N atoms from six different timpt ligands with an octahedral geometry and each timpt ligand connects three metal atoms to generate a three-dimensional (3D) metal-organic framework with self-penetration. The uncoordinated perchlorate anions are located within the voids of the 3D structure through C–H O hydrogen bonds, which enable the complex to show anion-exchange property. 2004 Elsevier Inc. All rights reserved. Keywords: Anion exchange; Metal-organic framework; Self-penetration; Nickel(II) complex; Three-connecting ligand
1. Introduction Construction of metal-organic frameworks (MOFs) are of great current attention not only for their interesting structures and topologies, but also for their potential applications as new zeolite-like materials for molecular selection, ion exchange and catalysis [1]. One of the efficient approaches to get such kind of MOFs is employing multidentate organic ligands to link the metal atoms with definite coordination geometry to give coordination frameworks [1]. Up to now, various MOFs with specific topology and structures have been obtained by assembly reactions of suitable metal ions with rationally designed three-connecting ligands, for example 2,4, 6-tris(4-pyridyl)-1,3,5-triazine (tpt) [2], 1,3,5-tricyanobenzene (tcb) [3,4], 1,3,5-tris(4-ethynylbenzonitrile)benzene (teb) [4], 1,3,5-benzenetricarboxylate (BTC) [5], 1,3,5-benzenetribenzoate (BTB) [6], 2,4,6-tris[(4-pyridyl)methylsulfulyl]-1,3,5-triazine (tpst) [7]. A three*
Corresponding author. Tel.: +86-25-83593485; fax: +86-2583314502/3317761. E-mail address: [email protected] (W.-Y. Sun). 1387-1811/$ - see front matter 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2003.12.029
dimensional (3D) self-entangled (12,3)-a net was obtained by the reaction of tpt with Ni(NO3 )2 [2b]. While the reaction of tpt with ZnSiF6 gave a 3D interpenetrating (10,3)-a net [2c]. Two 2D MOFs with honeycomb-like structures and exchange properties of guest species were obtained by the reactions of teb and tcb with silver(I) trifluoromethanesulfonate, respectively [3,4]. Most recently, Yaghi et al. reported a 3D interwoven framework constructed from H3 BTB with Cu(NO3 )2 , showing reversible sorption properties towards gases and organic solvents [6]. Kitagawa and his co-workers have reported methane gas adsorption properties of coordination polymers with large porosity by using pyrazine-2,3-dicarboxylate etc. [8]. However most of these reported MOFs are formed by reactions of the rigid multidentate organic ligands with metal ions, the reported flexible three-connecting ligands with aromatic core in this field are relatively rare up to now [9–12]. In the case of flexible ligands, the possible coordination modes are much more abundant than those of the rigid one due to the flexibility and low symmetry of the ligands since the flexible ligands can adopt different conformations when they interact with metal atoms
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according to the different geometric requirements of the metal ions. We focus our attentions on the construction, structures and properties of MOFs using flexible multidentate ligands containing imidazole groups, e.g. 1,3, 5-tris(imidazol-1-ylmethyl)benzene (tib) [11], 1,3,5tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (titmb) [12]. Due to the presence of methylene group between the imidazole and central benzene ring groups, tib and titmb are flexible divergent ligands. There are at least two different conformations (cis, cis, cis and cis, trans, trans) (Scheme 1) when they interact with metal ions as demonstrated in the previous studies [10–12]. Most recently, we extended this system and synthesized a nanometer sized flexible three-connecting ligand 2,4,6tris[4-(imidazol-1-ylmethyl)phenyl]-1,3,5-triazine (timpt) (Scheme 1) [13]. Introduction of an aromatic phenyl group between the terminal imidazol-1-ylmethyl and central triazine groups not only enlarges the size of the ligand but also increases possibility of p–p interactions between the aromatic groups which may favor penetrating structures. The reaction of timpt with lead(II) nitrate afforded a novel 2D threefold polycatenated network with rare 4.82 topology [13]. Herein, we report
the synthesis, crystal structure and anion-exchange property of a new 3D self-penetrating framework constructed from timpt and Ni(ClO4 )2 .
2. Experimental section 2.1. Materials and measurements All commercially available chemicals were used as received without further purification. Ligand timpt was prepared by the previously reported method [13]. Solvents were purified according to standard methods. Elemental analyses for C, H and N were made on a Perkin-Elmer 240C elemental analyzer at the Analysis Center of Nanjing University. Infrared (IR) spectra were recorded on a Bruker Vector22 FT-IR spectrophotometer by using KBr discs. 2.2. Synthesis A mixture of timpt (16.5 mg, 0.030 mmol) and Ni(ClO4 )2 Æ 6H2 O (11.9 mg, 0.032 mmol) in water/ethanol (6:1, v/v, 14 ml) was stirred for 15 min at room
Scheme 1.
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temperature. Then the mixture was transferred and kept in a Teflon lined autoclave at 160 C for three days. After cooling to the room temperature, plate light blue crystals were obtained in 47% yield (based on ligand). Anal. Found: C, 58.48; H, 4.24; N, 18.37%. Calcd. for C66 H54 Cl2 N18 NiO8 : C, 58.42; H, 4.01; N, 18.58%. Safety note: Perchlorate salt of metal complex with organic ligand is potentially explosive and should be handled with care. 2.3. General procedures for anion exchange Well-ground powder of [Ni(timpt)2 ](ClO4 )2 1 (15.0 mg) was suspended in an aqueous solution of NaNO3
Table 1 Crystallographic data for complex 1 C66 H54 Cl2 N18 NiO8 1356.88 Triclinic P -1 13.987(2) 16.153(2) 17.299(2) 70.010(10) 79.690(10) 66.100(10) 3354.3(7) 2 1.343 0.437 55.00 16,844 11,610 0.0127 6233 856 0.0688 0.1816a 0.1139 0.1908 1.211 0.652; )0.963
Empirical formula Formula weight Crystal system Space group a [A] b [A] c [A] a [] b [] c [] 3 ] V [A Z Dc [g cm3 ] l [mm1 ] 2h max () Reflns. collected Independent reflns. Rint Obsd. reflns. [I > 2rðIÞ] Parameters refined R1 (obsd. data) WR2 (obsd. data) R1 (all data) WR2 (all data) Goodness of fit 3 ] Residual electron density [e A a
x ¼ 1=½r2 ðF0 Þ2 þ ð0:0800P Þ2 þ 1:9900P , where P ¼ ðF02 þ 2Fc2 Þ=3.
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(0.10 mol l1 , 5 ml). The mixture was stirred for three days at room temperature, then filtrated, washed with water for several times, and dried in air to give light blue powder. 2.4. Crystal structure determination The data collection for complex 1 was performed on a Smart Apex CCD diffractometer at 293 K, using graphite-monochromated Mo-Ka radiation (k ¼ The structure was solved by direct method 0:71073 A). with SHELXTL-97 and expanded using Fourier technique [14]. The absorption correction for the complex was performed by empirical method. All non-hydrogen atoms were refined anisotropically by the full-matrix least-squares method on F 2 using SHELXL-97 [15]. Hydrogen atoms were generated geometrically assigned fixed isotropic thermal parameters at 1.2 times the equivalent isotropic U of the atoms to which they are attached and allowed to ride on their respective parent atoms. Details of the crystal parameters, data collection and refinement for the complex are summarized in Table 1, and selected bond lengths and angles with their estimated standard deviations are given in Table 2.
3. Results and discussion 3.1. Structure description The X-ray crystallographic structural analysis of 1 reveals that it crystallizes in triclinic with space group P 1 and the asymmetric unit consists of one unique Ni(II) atom, two timpt ligands and two perchlorate anions. Each Ni(II) atom is coordinated by six imidazolyl N atoms from six different timpt ligands, as illustrated in Fig. 1, with a slight distorted octahedral geometry. The Ni1 atom lies in the plane defined by N1, N5, N11 and N7 atoms with the Ni–N bond distances ranging from which are similar to those ob2.097(5) to 2.151(4) A, served in the reported Ni(II) complexes with imidazole
Table 2 and angles () for 1 Selected bond distances (A) Ni1–N1 Ni1–N5 Ni1–N9 N1–Ni1–N9 N9–Ni1–N3 N9–Ni1–N7 N1–Ni1–N11 N3–Ni1–N11 N1–Ni1–N5 N3–Ni1–N5 N11–Ni1–N5
2.097(5) 2.151(4) 2.110(5) 90.3(2) 178.77(19) 91.36(18) 178.11(19) 88.66(19) 90.78(17) 91.80(17) 87.48(18)
Ni1–N3 Ni1–N7 Ni1–N11 N1–Ni1–N3 N1–Ni1–N7 N3–Ni1–N7 N9–Ni1–N11 N7–Ni1–N11 N9–Ni1–N5 N7–Ni1–N5
2.112(5) 2.116(4) 2.122(5) 90.65(19) 89.97(18) 89.38(18) 90.34(19) 91.78(19) 87.45(17) 178.60(19)
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Fig. 1. Crystal structure of 1, the thermal ellipsoids were drawn at 30% probability. The carbon atoms are unlabeled and the hydrogen atoms are omitted for clarity.
and pyridine N donors [16]. All the N–Ni1–N angles are close to either 90 or 180 as listed in Table 2. It should be noticed that there are two distinct timpt ligands in the asymmetric unit of 1 as mentioned above. First, if we ignore one of the two timpt ligands containing triazine group with N16, N17 and N18 (hereafter we called it as timpt2, Fig. 1) and only consider the connections between the nickel(II) atoms and timpt ligand containing triazine group involving N13, N14 and N15 (it was called as timpt1 hereafter, Fig. 1), an infinite 2D network structure is obtained and the result is exhibited in Fig. 2. In this 2D network, each Ni(II) atom is coordinated by three N atoms from three different timpt1 ligands and each timpt1 ligand in turn connects three nickel(II) atoms to form a triangle with edge lengths (i.e. Ni Ni separation) of 19.21 (e.g. Ni1A– Ni1B in Fig. 2a), 17.30 (e.g. Ni1–Ni1A) and 16.15 (e.g. Such unit repeated in the bc plane to give Ni1–Ni1B) A. a 2D honeycomb network. It is noteworthy that such 2D network can be regarded as a (6,3)-net topology, as schematically exhibited in Fig. 2b, since both each timpt1 ligand and each Ni(II) atom act as three-connecting nodes. Next, without consideration of the timpt1 ligand, the coordination mode of the timpt2 ligand with nickel(II) atoms is shown in Fig. 3. It is obvious that the structure shown in Fig. 3a is 1D ribbon, rather than 2D network in Fig. 2a, although each Ni(II) atom is also coordinated by three N atoms and each timpt2 ligand connects three Ni(II) atoms (Fig. 3a) which are the same as those of Ni(II) and timpt1 shown in Fig. 2a. The Ni Ni separations between each two of three Ni(II) atoms coordinated to the same timpt2 ligand are 20.05 (e.g. Ni1B–Ni1C in Fig. 3a), 16.54 (e.g. Ni1–Ni1C) and respectively. 13.27 (e.g. Ni1–Ni1B) A, Due to the flexibility of timpt ligand (vide supra), it can adopt different conformations when it interacts with
(a)
(b) Fig. 2. (a) The perspective view of the 2D sheet with the honeycomb structure (dashed lines) formed by Y-shaped timpt1 ligands and Ni(II) atoms. (b) Schematic drawing of 2D honeycomb network in which the timpt1 ligands are represented by three spokes radiating from a point (i.e. the centroid of triazine) and Ni centers by circles.
metal ions. It can be seen that the conformation of timpt1 in the 2D network of 1 (Fig. 2a) is near a Y-shaped
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(a)
(b) Fig. 3. (a) The perspective view of the 1D ribbon formed by y-shaped timpt2 ligands and Ni(II) atoms. (b) Schematic drawing of the 1D ribbon in which the timpt2 ligands are represented by three spokes radiating from a point (i.e. the centroid of triazine) and Ni centers by circles.
propeller-type, rather than cis, cis, cis or cis, trans, trans as observed in complexes of titmb (Scheme 1) [10–12]. The angles of Ni1–X1A–Ni1A, Ni1–X1A–Ni1B and Ni1A–X1A–Ni1B are 119.1, 115.4 and 124.0, respectively (X1A is the centriod of the triazine group of the timpt1 ligand, Fig. 2a), which are close to 120. While in the case of 1D ribbon part of 1 (Fig. 3a), the conformation of timpt2 is clearly different from that of timpt1 in 2D network and can be described as a y-shape (Scheme 1). The angles of Ni1–X1B–Ni1B, Ni1–X1B– Ni1C and Ni1B–X1B–Ni1C are 74.7, 112.1 and 158.9, respectively (X1B is the centriod of the triazine group of the timpt2 ligand, Fig. 3a), which are quite different from those of timpt1. The remarkable structure feature of complex 1 is that the hexagonal voids in the 2D network are large enough to include another timpt ligand to generate a penetration structure. It is easy to understand the whole structure of complex 1, by combination of 2D network (Fig. 2a) and 1D ribbon (Fig. 3a) structures. The three neighboring 2D sheets are linked by one timpt2 ligand from the 1D ribbon, which uses two of three arms to connect two Ni(II) atoms of the first two layers, and uses the remaining third arm to pass the hexagon of the second 2D layer and to connect the Ni(II) atom from the third layer. Thus a 3D framework with self-penetration is formed as schematically shown in Fig. 4, in which the two types of timpt1 and timpt2 ligands are represented by solid and open lines, respectively. This is, to the best of our knowledge, the first example of self-penetrating MOF constructed from flexible three-connecting ligand, although there is an example of self-penetrating framework from a rigid three-connecting ligand tpt with Ni(NO3 )2 [2b] and a few other examples from twoconnecting ligands [17]. In the 3D structure of complex 1, the distance be and the ones tween two adjacent 1D ribbons is 11.81 A as between two adjacent 2D sheets are 5.42 and 7.36 A schematically shown in Fig. 4. Perchlorate anions are
located within the voids of the 3D framework. It is interesting that one perchlorate anion is loosely bound to the framework through only one C–H O hydrogen bond while the other one has four C–H O hydrogen bonds using its four O atoms as illustrated in Fig. 6. The hydrogen bonding data are summarized in Table 3. In addition to the C–H O hydrogen bonding interactions, there are face-to-face p–p interactions in complex 1 as expected, since there are triazine and benzene ring planes in timpt ligand. The nearest centroid–centroid distance between the triazine and benzene rings is 3.77 A with a dihedral angle of 9.1, and the one between two with a dihedral angle of triazine ring planes is 3.53 A 1.7 (Fig. 7). 3.2. Anion exchange The crystal structural analysis showed that the perchlorate anions in 1 are bound to the 3D framework through C–H O hydrogen bonds, the framework is expected to have anion-exchange property [12b,12c,18]. The powdered complex 1 which is insoluble in water and common organic solvents such as methanol, acetonitrile etc., was suspended in an aqueous solution of NaNO3 to allow possible anion exchange. The solid was filtered off, washed with water (8 ml · 5) and dried in air. The IR spectrum of the anion-exchanged product showed the 1 characteristic band of NO and the 3 at 1384 cm characteristic bands of ClO4 at 1088 and 1120 cm1 as exhibited in Fig. 5. Both bands of NO 3 and ClO4 anions have similar intensities. The anion-exchange procedure was repeated and the IR spectrum of the anion-exchanged product showed no further change of the bands at 1384 cm1 and at 1088 and 1120 cm1 . The above results indicate that the ClO 4 anions in complex 1 can be partially exchanged by NO 3 anions, which is similar to the previously reported Cd(II) framework with imidazole-containing ligand [19]. The anion exchange was also carried out by using NaBF4 , instead of
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Fig. 4. (a) Schematic view of the 3D framework of the cationic part of 1. The Ni(II) atoms are represented by circles and the two types of timpt ligands (solid and open lines) are represented by three spokes radiating from a point (i.e. the centroid of triazine); (b) schematically a visualization of the relative positions of the two interpenetrating components.
Table 3 Hydrogen bonding data for complex 1 D–H A
Distance of D A [A]
Angles of D–H–A []
C4–H4B O22#1 C41–H41A O21#2 C50–H50B O23#3 C54–H54A O24#4 C63–H63A O14#4
3.459(11) 3.259(10) 3.308(8) 3.327(10) 3.503(13)
165 156 143 140 176
Symmetry code: (#1) 1 þ x; y; z; (#2) 1 x; 1 y; 2 z; (#4) 1 x; 1 y; 1 z.
1 x; y; 2 z;
a
b
(#3)
NaNO3 , and it is the same that partial anion exchange was observed. This agrees well with the results of structural analysis: the perchlorate anion bound to the framework via only one hydrogen bond could be exchanged while the other one could not since it was
2000
1500
1000
wavelength / cm-1
500
Fig. 5. FT-IR spectra of (a) complex 1 treated with aqueous solution of NaNO3 ; (b) complex 1 in the solid state at room temperature.
S.-Y. Wan et al. / Microporous and Mesoporous Materials 73 (2004) 101–108
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strongly bound to the framework by formation of four hydrogen bonds as mentioned above.
4. Conclusion In conclusion, the present work provides the first example of self-penetrating metal-organic framework from flexible three-connecting ligand. The flexibility and different conformations of timpt ligands play important role in formation of such kind of self-penetrating 3D structure. The framework shows partial anion-exchange property.
Acknowledgement Fig. 6. Crystal packing diagram of 1 in color. The hydrogen bonds were shown with dashed lines and the hydrogen atoms are partially omitted for clarity.
This work was supported by National Natural Science Foundation of China (Grant No. 20231020).
Fig. 7. The face-to-face p–p interactions in complex 1 are indicated by dashed lines. The centroid–centroid distance between the triazine and benzene rings with a dihedral angle of 9.1 (a), and the one between two triazine rings A and E is 3.53 A with a dihedral angle of 1.7 (b). Q and R (or R0 and Q0 ) is 3.77 A
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Synthesis, structure and anion-exchange property of the first example of self-penetrated three-dimensional metal-organic framework with flexible three-connecting ligand and nickel(II) perchlorate Shuang-Yi Wan, Yu-Ting Huang, Yi-Zhi Li, Wei-Yin Sun
*
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China Received 19 April 2003; received in revised form 16 December 2003; accepted 22 December 2003 Available online 8 June 2004
Abstract Novel polymeric coordination complex [Ni(timpt)2 ](ClO4 )2 1 was synthesized by solvothermal reaction of 2,4,6-tris[4-(imidazol1-ylmethyl)phenyl]-1,3,5-triazine (timpt) ligand with Ni(ClO4 )2 Æ 6H2 O and characterized by X-ray crystallography. Each Ni(II) is coordinated by six imidazolyl N atoms from six different timpt ligands with an octahedral geometry and each timpt ligand connects three metal atoms to generate a three-dimensional (3D) metal-organic framework with self-penetration. The uncoordinated perchlorate anions are located within the voids of the 3D structure through C–H O hydrogen bonds, which enable the complex to show anion-exchange property. 2004 Elsevier Inc. All rights reserved. Keywords: Anion exchange; Metal-organic framework; Self-penetration; Nickel(II) complex; Three-connecting ligand
1. Introduction Construction of metal-organic frameworks (MOFs) are of great current attention not only for their interesting structures and topologies, but also for their potential applications as new zeolite-like materials for molecular selection, ion exchange and catalysis [1]. One of the efficient approaches to get such kind of MOFs is employing multidentate organic ligands to link the metal atoms with definite coordination geometry to give coordination frameworks [1]. Up to now, various MOFs with specific topology and structures have been obtained by assembly reactions of suitable metal ions with rationally designed three-connecting ligands, for example 2,4, 6-tris(4-pyridyl)-1,3,5-triazine (tpt) [2], 1,3,5-tricyanobenzene (tcb) [3,4], 1,3,5-tris(4-ethynylbenzonitrile)benzene (teb) [4], 1,3,5-benzenetricarboxylate (BTC) [5], 1,3,5-benzenetribenzoate (BTB) [6], 2,4,6-tris[(4-pyridyl)methylsulfulyl]-1,3,5-triazine (tpst) [7]. A three*
Corresponding author. Tel.: +86-25-83593485; fax: +86-2583314502/3317761. E-mail address: [email protected] (W.-Y. Sun). 1387-1811/$ - see front matter 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2003.12.029
dimensional (3D) self-entangled (12,3)-a net was obtained by the reaction of tpt with Ni(NO3 )2 [2b]. While the reaction of tpt with ZnSiF6 gave a 3D interpenetrating (10,3)-a net [2c]. Two 2D MOFs with honeycomb-like structures and exchange properties of guest species were obtained by the reactions of teb and tcb with silver(I) trifluoromethanesulfonate, respectively [3,4]. Most recently, Yaghi et al. reported a 3D interwoven framework constructed from H3 BTB with Cu(NO3 )2 , showing reversible sorption properties towards gases and organic solvents [6]. Kitagawa and his co-workers have reported methane gas adsorption properties of coordination polymers with large porosity by using pyrazine-2,3-dicarboxylate etc. [8]. However most of these reported MOFs are formed by reactions of the rigid multidentate organic ligands with metal ions, the reported flexible three-connecting ligands with aromatic core in this field are relatively rare up to now [9–12]. In the case of flexible ligands, the possible coordination modes are much more abundant than those of the rigid one due to the flexibility and low symmetry of the ligands since the flexible ligands can adopt different conformations when they interact with metal atoms
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according to the different geometric requirements of the metal ions. We focus our attentions on the construction, structures and properties of MOFs using flexible multidentate ligands containing imidazole groups, e.g. 1,3, 5-tris(imidazol-1-ylmethyl)benzene (tib) [11], 1,3,5tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (titmb) [12]. Due to the presence of methylene group between the imidazole and central benzene ring groups, tib and titmb are flexible divergent ligands. There are at least two different conformations (cis, cis, cis and cis, trans, trans) (Scheme 1) when they interact with metal ions as demonstrated in the previous studies [10–12]. Most recently, we extended this system and synthesized a nanometer sized flexible three-connecting ligand 2,4,6tris[4-(imidazol-1-ylmethyl)phenyl]-1,3,5-triazine (timpt) (Scheme 1) [13]. Introduction of an aromatic phenyl group between the terminal imidazol-1-ylmethyl and central triazine groups not only enlarges the size of the ligand but also increases possibility of p–p interactions between the aromatic groups which may favor penetrating structures. The reaction of timpt with lead(II) nitrate afforded a novel 2D threefold polycatenated network with rare 4.82 topology [13]. Herein, we report
the synthesis, crystal structure and anion-exchange property of a new 3D self-penetrating framework constructed from timpt and Ni(ClO4 )2 .
2. Experimental section 2.1. Materials and measurements All commercially available chemicals were used as received without further purification. Ligand timpt was prepared by the previously reported method [13]. Solvents were purified according to standard methods. Elemental analyses for C, H and N were made on a Perkin-Elmer 240C elemental analyzer at the Analysis Center of Nanjing University. Infrared (IR) spectra were recorded on a Bruker Vector22 FT-IR spectrophotometer by using KBr discs. 2.2. Synthesis A mixture of timpt (16.5 mg, 0.030 mmol) and Ni(ClO4 )2 Æ 6H2 O (11.9 mg, 0.032 mmol) in water/ethanol (6:1, v/v, 14 ml) was stirred for 15 min at room
Scheme 1.
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temperature. Then the mixture was transferred and kept in a Teflon lined autoclave at 160 C for three days. After cooling to the room temperature, plate light blue crystals were obtained in 47% yield (based on ligand). Anal. Found: C, 58.48; H, 4.24; N, 18.37%. Calcd. for C66 H54 Cl2 N18 NiO8 : C, 58.42; H, 4.01; N, 18.58%. Safety note: Perchlorate salt of metal complex with organic ligand is potentially explosive and should be handled with care. 2.3. General procedures for anion exchange Well-ground powder of [Ni(timpt)2 ](ClO4 )2 1 (15.0 mg) was suspended in an aqueous solution of NaNO3
Table 1 Crystallographic data for complex 1 C66 H54 Cl2 N18 NiO8 1356.88 Triclinic P -1 13.987(2) 16.153(2) 17.299(2) 70.010(10) 79.690(10) 66.100(10) 3354.3(7) 2 1.343 0.437 55.00 16,844 11,610 0.0127 6233 856 0.0688 0.1816a 0.1139 0.1908 1.211 0.652; )0.963
Empirical formula Formula weight Crystal system Space group a [A] b [A] c [A] a [] b [] c [] 3 ] V [A Z Dc [g cm3 ] l [mm1 ] 2h max () Reflns. collected Independent reflns. Rint Obsd. reflns. [I > 2rðIÞ] Parameters refined R1 (obsd. data) WR2 (obsd. data) R1 (all data) WR2 (all data) Goodness of fit 3 ] Residual electron density [e A a
x ¼ 1=½r2 ðF0 Þ2 þ ð0:0800P Þ2 þ 1:9900P , where P ¼ ðF02 þ 2Fc2 Þ=3.
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(0.10 mol l1 , 5 ml). The mixture was stirred for three days at room temperature, then filtrated, washed with water for several times, and dried in air to give light blue powder. 2.4. Crystal structure determination The data collection for complex 1 was performed on a Smart Apex CCD diffractometer at 293 K, using graphite-monochromated Mo-Ka radiation (k ¼ The structure was solved by direct method 0:71073 A). with SHELXTL-97 and expanded using Fourier technique [14]. The absorption correction for the complex was performed by empirical method. All non-hydrogen atoms were refined anisotropically by the full-matrix least-squares method on F 2 using SHELXL-97 [15]. Hydrogen atoms were generated geometrically assigned fixed isotropic thermal parameters at 1.2 times the equivalent isotropic U of the atoms to which they are attached and allowed to ride on their respective parent atoms. Details of the crystal parameters, data collection and refinement for the complex are summarized in Table 1, and selected bond lengths and angles with their estimated standard deviations are given in Table 2.
3. Results and discussion 3.1. Structure description The X-ray crystallographic structural analysis of 1 reveals that it crystallizes in triclinic with space group P 1 and the asymmetric unit consists of one unique Ni(II) atom, two timpt ligands and two perchlorate anions. Each Ni(II) atom is coordinated by six imidazolyl N atoms from six different timpt ligands, as illustrated in Fig. 1, with a slight distorted octahedral geometry. The Ni1 atom lies in the plane defined by N1, N5, N11 and N7 atoms with the Ni–N bond distances ranging from which are similar to those ob2.097(5) to 2.151(4) A, served in the reported Ni(II) complexes with imidazole
Table 2 and angles () for 1 Selected bond distances (A) Ni1–N1 Ni1–N5 Ni1–N9 N1–Ni1–N9 N9–Ni1–N3 N9–Ni1–N7 N1–Ni1–N11 N3–Ni1–N11 N1–Ni1–N5 N3–Ni1–N5 N11–Ni1–N5
2.097(5) 2.151(4) 2.110(5) 90.3(2) 178.77(19) 91.36(18) 178.11(19) 88.66(19) 90.78(17) 91.80(17) 87.48(18)
Ni1–N3 Ni1–N7 Ni1–N11 N1–Ni1–N3 N1–Ni1–N7 N3–Ni1–N7 N9–Ni1–N11 N7–Ni1–N11 N9–Ni1–N5 N7–Ni1–N5
2.112(5) 2.116(4) 2.122(5) 90.65(19) 89.97(18) 89.38(18) 90.34(19) 91.78(19) 87.45(17) 178.60(19)
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Fig. 1. Crystal structure of 1, the thermal ellipsoids were drawn at 30% probability. The carbon atoms are unlabeled and the hydrogen atoms are omitted for clarity.
and pyridine N donors [16]. All the N–Ni1–N angles are close to either 90 or 180 as listed in Table 2. It should be noticed that there are two distinct timpt ligands in the asymmetric unit of 1 as mentioned above. First, if we ignore one of the two timpt ligands containing triazine group with N16, N17 and N18 (hereafter we called it as timpt2, Fig. 1) and only consider the connections between the nickel(II) atoms and timpt ligand containing triazine group involving N13, N14 and N15 (it was called as timpt1 hereafter, Fig. 1), an infinite 2D network structure is obtained and the result is exhibited in Fig. 2. In this 2D network, each Ni(II) atom is coordinated by three N atoms from three different timpt1 ligands and each timpt1 ligand in turn connects three nickel(II) atoms to form a triangle with edge lengths (i.e. Ni Ni separation) of 19.21 (e.g. Ni1A– Ni1B in Fig. 2a), 17.30 (e.g. Ni1–Ni1A) and 16.15 (e.g. Such unit repeated in the bc plane to give Ni1–Ni1B) A. a 2D honeycomb network. It is noteworthy that such 2D network can be regarded as a (6,3)-net topology, as schematically exhibited in Fig. 2b, since both each timpt1 ligand and each Ni(II) atom act as three-connecting nodes. Next, without consideration of the timpt1 ligand, the coordination mode of the timpt2 ligand with nickel(II) atoms is shown in Fig. 3. It is obvious that the structure shown in Fig. 3a is 1D ribbon, rather than 2D network in Fig. 2a, although each Ni(II) atom is also coordinated by three N atoms and each timpt2 ligand connects three Ni(II) atoms (Fig. 3a) which are the same as those of Ni(II) and timpt1 shown in Fig. 2a. The Ni Ni separations between each two of three Ni(II) atoms coordinated to the same timpt2 ligand are 20.05 (e.g. Ni1B–Ni1C in Fig. 3a), 16.54 (e.g. Ni1–Ni1C) and respectively. 13.27 (e.g. Ni1–Ni1B) A, Due to the flexibility of timpt ligand (vide supra), it can adopt different conformations when it interacts with
(a)
(b) Fig. 2. (a) The perspective view of the 2D sheet with the honeycomb structure (dashed lines) formed by Y-shaped timpt1 ligands and Ni(II) atoms. (b) Schematic drawing of 2D honeycomb network in which the timpt1 ligands are represented by three spokes radiating from a point (i.e. the centroid of triazine) and Ni centers by circles.
metal ions. It can be seen that the conformation of timpt1 in the 2D network of 1 (Fig. 2a) is near a Y-shaped
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(a)
(b) Fig. 3. (a) The perspective view of the 1D ribbon formed by y-shaped timpt2 ligands and Ni(II) atoms. (b) Schematic drawing of the 1D ribbon in which the timpt2 ligands are represented by three spokes radiating from a point (i.e. the centroid of triazine) and Ni centers by circles.
propeller-type, rather than cis, cis, cis or cis, trans, trans as observed in complexes of titmb (Scheme 1) [10–12]. The angles of Ni1–X1A–Ni1A, Ni1–X1A–Ni1B and Ni1A–X1A–Ni1B are 119.1, 115.4 and 124.0, respectively (X1A is the centriod of the triazine group of the timpt1 ligand, Fig. 2a), which are close to 120. While in the case of 1D ribbon part of 1 (Fig. 3a), the conformation of timpt2 is clearly different from that of timpt1 in 2D network and can be described as a y-shape (Scheme 1). The angles of Ni1–X1B–Ni1B, Ni1–X1B– Ni1C and Ni1B–X1B–Ni1C are 74.7, 112.1 and 158.9, respectively (X1B is the centriod of the triazine group of the timpt2 ligand, Fig. 3a), which are quite different from those of timpt1. The remarkable structure feature of complex 1 is that the hexagonal voids in the 2D network are large enough to include another timpt ligand to generate a penetration structure. It is easy to understand the whole structure of complex 1, by combination of 2D network (Fig. 2a) and 1D ribbon (Fig. 3a) structures. The three neighboring 2D sheets are linked by one timpt2 ligand from the 1D ribbon, which uses two of three arms to connect two Ni(II) atoms of the first two layers, and uses the remaining third arm to pass the hexagon of the second 2D layer and to connect the Ni(II) atom from the third layer. Thus a 3D framework with self-penetration is formed as schematically shown in Fig. 4, in which the two types of timpt1 and timpt2 ligands are represented by solid and open lines, respectively. This is, to the best of our knowledge, the first example of self-penetrating MOF constructed from flexible three-connecting ligand, although there is an example of self-penetrating framework from a rigid three-connecting ligand tpt with Ni(NO3 )2 [2b] and a few other examples from twoconnecting ligands [17]. In the 3D structure of complex 1, the distance be and the ones tween two adjacent 1D ribbons is 11.81 A as between two adjacent 2D sheets are 5.42 and 7.36 A schematically shown in Fig. 4. Perchlorate anions are
located within the voids of the 3D framework. It is interesting that one perchlorate anion is loosely bound to the framework through only one C–H O hydrogen bond while the other one has four C–H O hydrogen bonds using its four O atoms as illustrated in Fig. 6. The hydrogen bonding data are summarized in Table 3. In addition to the C–H O hydrogen bonding interactions, there are face-to-face p–p interactions in complex 1 as expected, since there are triazine and benzene ring planes in timpt ligand. The nearest centroid–centroid distance between the triazine and benzene rings is 3.77 A with a dihedral angle of 9.1, and the one between two with a dihedral angle of triazine ring planes is 3.53 A 1.7 (Fig. 7). 3.2. Anion exchange The crystal structural analysis showed that the perchlorate anions in 1 are bound to the 3D framework through C–H O hydrogen bonds, the framework is expected to have anion-exchange property [12b,12c,18]. The powdered complex 1 which is insoluble in water and common organic solvents such as methanol, acetonitrile etc., was suspended in an aqueous solution of NaNO3 to allow possible anion exchange. The solid was filtered off, washed with water (8 ml · 5) and dried in air. The IR spectrum of the anion-exchanged product showed the 1 characteristic band of NO and the 3 at 1384 cm characteristic bands of ClO4 at 1088 and 1120 cm1 as exhibited in Fig. 5. Both bands of NO 3 and ClO4 anions have similar intensities. The anion-exchange procedure was repeated and the IR spectrum of the anion-exchanged product showed no further change of the bands at 1384 cm1 and at 1088 and 1120 cm1 . The above results indicate that the ClO 4 anions in complex 1 can be partially exchanged by NO 3 anions, which is similar to the previously reported Cd(II) framework with imidazole-containing ligand [19]. The anion exchange was also carried out by using NaBF4 , instead of
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Fig. 4. (a) Schematic view of the 3D framework of the cationic part of 1. The Ni(II) atoms are represented by circles and the two types of timpt ligands (solid and open lines) are represented by three spokes radiating from a point (i.e. the centroid of triazine); (b) schematically a visualization of the relative positions of the two interpenetrating components.
Table 3 Hydrogen bonding data for complex 1 D–H A
Distance of D A [A]
Angles of D–H–A []
C4–H4B O22#1 C41–H41A O21#2 C50–H50B O23#3 C54–H54A O24#4 C63–H63A O14#4
3.459(11) 3.259(10) 3.308(8) 3.327(10) 3.503(13)
165 156 143 140 176
Symmetry code: (#1) 1 þ x; y; z; (#2) 1 x; 1 y; 2 z; (#4) 1 x; 1 y; 1 z.
1 x; y; 2 z;
a
b
(#3)
NaNO3 , and it is the same that partial anion exchange was observed. This agrees well with the results of structural analysis: the perchlorate anion bound to the framework via only one hydrogen bond could be exchanged while the other one could not since it was
2000
1500
1000
wavelength / cm-1
500
Fig. 5. FT-IR spectra of (a) complex 1 treated with aqueous solution of NaNO3 ; (b) complex 1 in the solid state at room temperature.
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strongly bound to the framework by formation of four hydrogen bonds as mentioned above.
4. Conclusion In conclusion, the present work provides the first example of self-penetrating metal-organic framework from flexible three-connecting ligand. The flexibility and different conformations of timpt ligands play important role in formation of such kind of self-penetrating 3D structure. The framework shows partial anion-exchange property.
Acknowledgement Fig. 6. Crystal packing diagram of 1 in color. The hydrogen bonds were shown with dashed lines and the hydrogen atoms are partially omitted for clarity.
This work was supported by National Natural Science Foundation of China (Grant No. 20231020).
Fig. 7. The face-to-face p–p interactions in complex 1 are indicated by dashed lines. The centroid–centroid distance between the triazine and benzene rings with a dihedral angle of 9.1 (a), and the one between two triazine rings A and E is 3.53 A with a dihedral angle of 1.7 (b). Q and R (or R0 and Q0 ) is 3.77 A
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