Bimetallic Clusters of Pyridine-Appended Ethylenediaminetetraacetic Acid (EDTA)-amides in Designing 1D and 2D Coordination Frameworks Lalit Rajput and Kumar Biradha*
CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 12 2376–2379
Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India ReceiVed March 26, 2007; ReVised Manuscript ReceiVed August 21, 2007
ABSTRACT: A new ligand containing an ethylenediaminetetraacetic acid (EDTA) core and four amidopyridines was synthesized for the first time and was shown capable of forming bimetallic species (MnII/ZnII/CoII), which were further assembled into one- and two-dimensional coordination frameworks. The bimetallic cluster contains six uncoordinated pyridine units for the propagation of coordination networks. These clusters have shown the ability to form one- and two-dimensional coordination networks by linking up with additional transitionmetal centers. Crystal engineering of metal organic frameworks is a very fast growing area of research because of the creation of new materials with the properties as diverse as gas adsorption, separation, host–guest chemistry, optics, magnetism, catalysis, and photoluminescence.1 There is a continuous quest for new ligands and therefore new topological architectures. On the other hand, the complexing powers of ethylenediaminetetraacetic acid (EDTA) have been well-explored with numerous transition metals; its use in the generation of coordination polymers is very limited.2 Accordingly, to prepare the coordination polymers containing an EDTA core, here, we have employed the strategy of appending pyridine moieties to EDTA via amide linkages.3 A search in the Cambridge Structural Database shows that only two EDTA amides (1) have been explored (R ) H and Ph) to date, to form coordination complexes with transition-metal ions.4 The coordination geometries of these amides were found to have similar geometries as in EDTA complexes. Further, the EDTA amide ligands were also shown to be good ion transporters for curing tumor disease.5 In this contribution, we have explored the coordination abilities of newly synthesized ligand 1 with transition-metal salts and found that 1 is indeed capable of forming bimetallic clusters, which can be further linked into 1D and 2D coordination polymers.6 The ligand 1 has been synthesized by reacting EDTA with 3-aminopyridine in pyridine. The treatment of the ligand 1 with the corresponding metal salts in MeOH resulted in the crystals of complexes 2–6.7 The crystal structure analyses of these complexes reveal that 2 and 3 form a bimetallic species, 4 forms a one-dimensional ladder-like network, and complexes 5 and 6 form two-dimensional layers. Interestingly, the complexes 4–6 also contain a bimetallic species that is observed in 2 and 3, implying that it can be considered as SBU in designing coordination polymeric networks. The crystal structures of 2 and 3 reveal the formation of a discrete
bimetallic species in which the metal has hepta coordination.8 The coordination sphere of metal is best approximated as a distorted pentagonal bipyramid (pbp). Each metal center is coordinated to the two N atoms and four O atoms of amide groups of ligand 1 and one pyridyl group from the neighboring moiety of 1. Two O atoms of amide groups occupy the axial positions [Mn–O, 2.182(3) * To whom correspondence should be addressed. Fax: +91-3222-282252. Telephone: +91-3222-283346. E-mail:
[email protected].
and 2.208(3) Å; Co–O, 2.207(3) and 2.294(3) Å]. The two N atoms of en core [Mn–N, 2.356(3) and 2.515(2) Å; Co–N, 2.238(3) and 2.318(3) Å] and two O atoms of the different amide groups [Mn–O, 2.177(3) and 2.473(3) Å; Co–O, 2.086(3) and 2.120(3) Å] and N atom of the pyridyl group [Mn–N, 2.263(2) Å; Co–N, 2.162(3) Å] occupy the pentagonal plane. The pentagonal plane is distorted in an alternating up and down relationship with the mean deviation of 0.41 Å in 2 and 0.38 Å in 3. The average bond angles in pentagonal planes are 74.8° (69.7–81.8°) and 74.46° (67.2–79.6°, with an ideal angle of 72°) in 2 and 3, respectively. Two of the amide oxygen atoms coordinate at epical positions with the O–Tr–O bond angle close to linearity (174.5° in 2 and 173° in 3). Two of these metal centers are connected via pyridine moieties such that there exist an inversion symmetry. The intermetallic distances in the bimetallic cluster are 6.8 and 6.9 Å for 2 and 3, respectively. The SO4- anion and H2O molecules in 2 were successfully located and refined. The sulfate ion forms a two-dimensional layer via hydrogen bonds with water molecules. This layer comprises several rings, in which the six-membered rings with six hydrogen bonds between four water molecules and two sulfate ions are worth mentioning. Both of these rings exist in the chair conformation of cyclohexane and have an inversion center [O · · · O, 2.813(10), 2.832(12), and 3.100(9) Å for ring I and 2.751(6), 2.805(6), and 2.842(6) Å for ring II] (Figure 1). Whereas in complex 3, half of PF6 ions and H2O molecules exhibited high thermal motions and disorder. Therefore, the final structure was refined using the Platon squeeze option.9 Similar to the above complexes, complex 4 also contains a bimetallic species.10 In the asymmetric unit, it contains three CoII centers, which perform different roles: two involve (Co1 and Co2) in the formation of a unsymmetrical bimetallic cluster, and the remaining one (Co3) is involved in the propagation of the coordination network (Figure 2). The Co1 and Co2 atoms, similar to the above complexes, contain a distorted pbp coordination. The mean deviations from the pentagonal planes are 0.42 and 0.41 Å, and the mean angles in the planes are 75.10° (67.51–80.80°) and 74.77° (67.38–80.26°). The trans O–Co–O angles are closer to linearity (177.80° and 175.24°) compared to that of complexes 2 and 3. The Co1 and Co2 atoms are separated by a distance of 7.13 Å. These bimetallic clusters are interconnected by the third CoII atom (Co3) and propagate the one-dimensional coordination framework. Three H2O and three pyridyl moieties coordinate to Co3 such that it has an octahedral geometry [Co–N, 2.066(5), 2.219(5), and 2.221(5) Å; Co-O, 1.980(4), 2.134(5), and 2.179(5) Å]. The Co3 adopts T-shape geometry with respect to the coordination of pyridyl units. Interestingly, the pyridyl groups that are coordinated to Co3 are originated from the ligand that is coordinated to Co1 only. This type of coordination generates a one-
10.1021/cg070289x CCC: $37.00 2007 American Chemical Society Published on Web 11/03/2007
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Figure 1. Illustrations for 2. (a) Bimetallic species. Notice that the MnII is seven-coordinated with pbp geometry. (b) Hydrogen-bonded layer. The six-membered rings with six hydrogen bonds are represented as I and II.
Figure 2. Illustrations for crystal structure 4. (a) Bimetallic clusters. (b) One-dimensional ladder network. The metal atoms in the bimetallic cluster were shown in magenta (Co1 and Co2), and the ones that are involved in framework formation were shown in green (Co3).
Figure 3. Bimetallic clusters observed in complexes (a) 5 and (b) 6.
dimensional ladder network, which is well-known with coordination polymers of linear exobidentate ligands.11 However, in those complexes, the network is formed by a linear spacer and T node of the metal. Whereas, in the network reported here, both the metal and ligand (bimetallic cluster) adopt T-shape geometries. The framework has rhomboidal cavities of dimensions 9.23 × 8.23 Å and a diagonal distance of 14.60 Å. In contrast to the above results, the treatment of ZnII with ligand 1 resulted in complexes 5 and 6, both of which contain twodimensional networks with subtle differences.12 Although both exhibit a bimetallic species, the ZnII centers in the cluster do not
exhibit PBP coordination but exhibit an octahedral coordination geometry (Figure 3). This is due to the fact that one of the four amide groups of the ligand faces away from the metal center, and hence, the three O atoms of the amide units [Zn–O, 1.110(2), 2.130(2), and 2.151(2) Å in 5 and 2.084(4), 2.124(4), and 2.139(4) Å in 6], two N atoms of en core [Zn–N, 2.185(2) and 2.227(2) Å in 5 and 2.173(5) and 2.223(5) Å in 6], and one N atom from the pyridine unit [Zn–N, 2.053(2) Å in 5 and 2.040(5) Å in 6] of the neighboring ligand complete octahedral coordination. In the asymmetric units, both contain two independent ZnII centers: one of which (Zn1) participates in the bimetallic cluster formation, while
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Figure 4. Illustrations for 5 and 6. Two-dimensional layers in complexes 5 (a and c) and 6 (b and d). a and b are top views of the layers, and c and d are side views of the layers along the b axis for 5 and along the a axis for 6. For the sake of clarity, the rectangular nature of bimetallic clusters were shown by dotted lines.
the other (Zn2) participates in the propagation of the coordination network (Figure 4). The Zn2 also contains an octahedral coordination with four pyridine units in equatorial positions [Zn–N, 2.167(2) and 2.165(2) Å in 5 and 2.132(5) and 2.173(4) Å in 6] and two H2O molecules in axial positions [Zn–O, 2.185(2) Å in 5 and 2.146(5) Å in 6]. Each of the two ligands in the bimetallic cluster has three pyridine units; two of the three pyridine units participate in the formation of the two-dimensional coordination network with Zn2. As a result, the layers can be viewed as joining the rectangular building units by square planar nodes. Although the layers in 5 and 6 are having similar topological connections, they have some interesting differences. In 5, the rectangular building units, which have a 19.1 × 12.6 Å dimension, are joined in the plane to result in a coplanar layer, while in 6, they have a 18.9 × 12.7 Å dimension and are joined such that corrugated layers are formed. This difference could be attributed to the difference in size and shape of anions.13 The nitrate anion being small in size and planar in shape generated a flat network. Whereas ClO4 is relatively large in size and tetrahedral in shape, the layers maintain nonplanarity to provide spherical cavities between the layer for its inclusion. Here, it is interesting to note that all five complexes have a plethora of water molecules. The anions and uncoordinated water molecules occupy 37, 36, 47.2, 40.9, and 47.9% of crystal volumes in 2, 3, 4, 5, and 6, respectively.10 In summary, the ethylenediamine moiety of the ligand 1 exhibited a tendency for chelation with CoII/MnII/ZnII, similar to the parent EDTA anion. These chelated metal centers are assembled into bimetallic aggregates (SBU) by the appended pyridine groups. As a result, each SBU contains six free pyridine units, which were used to assemble SBUs into coordination networks. The SBUs were crystallized as such in the complexes 2 and 3, whereas they are assembled into one- and two-dimensional networks in complexes 4 and 5/6, respectively. Further works are underway in our laboratory on the exploration of coordination networks of 1 and related ligands.
Acknowledgment. We gratefully acknowledge financial support from the Department of Science and Technology (DST, SR/S1/ OC-36/2002), Indian Institute of Technology (IIT), Kharagpur, and IIT, Guwahati, for the single-crystal X-ray facility. L.R. thanks IIT (Kharagpur) for a research fellowship.
Supporting Information Available: Synthetic details of 1, IR, TGA spectra, and crystallographic tables of 2–6. This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) (a) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460. (b) O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319. (c) Moulton, B.; Zaworotko, M. J. Chem. ReV. 2001, 101, 1629. (d) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43, 2334. (e) Lin, W.; Evans, O. R. Acc. Chem. Res. 2002, 35, 511. (f) Papaefstathiou, G. S.; MacGillivray, L. R. Coord. Chem. ReV. 2003, 246, 169. (g) Belanger, S.; Hupp, J. T.; Stern, C. L.; Slone, R. V.; Watson, D. F.; Carell, T. M. J. Am. Chem. Soc. 1999, 121, 557. (h) Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim, K. Nature 2000, 404, 982. (i) Lahav, M.; Gabai, R.; Shipway, A. N.; Willner, I. Chem. Commun. 1999, 1937. (j) Biradha, K. CrystEngComm 2003, 5, 374. (k) Biradha, K.; Fujita, M. Angew. Chem., Int. Ed. 2002, 41, 3392. (l) Ohmori, O.; Kawano, M.; Fujita, M. J. Am. Chem. Soc. 2004, 126, 16292. (2) (a) Kaplun, M.; Sandstorm, M.; Bostrom, D.; Shchukarev, A.; Persson, P. Inorg. Chim. Acta 2005, 358, 527. (b) Stavila, V.; Gulea, A.; Popa, N.; Shova, S.; Merbach, A.; Simonov, Y. A.; Lipkowski, J. Inorg. Chem. Commun. 2004, 7, 634. (c) Wang, C. C.; Yang, C. H.; Lee, C. H.; Lee, G. H. Inorg. Chem. 2002, 41, 429. (d) Shi, Z.; Feng, S.; Sun, Y.; Hua, J. Inorg. Chem. 2001, 40, 5312. (e) Musso, S.; Anderegg, G.; Ruegger, H.; Schlapfer, C. W.; Gramlich, V. Inorg. Chem. 1995, 34, 3329. (3) Some recent references on coordination networks with the ligand containing multiple amidopyrdine units: (a) Sarkar, M.; Biradha, K. Cryst. Growth Des. 2006, 6, 1742. (b) Sarkar, M.; Biradha, K. Chem. Commun. 2005, 2229. (c) Uemura, K.; Kitagawa, S.; Fukui, K.; Saito, K. J. Am. Chem. Soc. 2004, 126, 3817. (d) Tzeng, B. C.; Chen, B. S.; Yeh, H. T.; Lee, G. H.; Peng, S. M. New J. Chem. 2006, 30, 1087. (e) Noveron, J. C.; Lah, M. S.; Del Sesto, R. E.; Arif, A. M.; Miller, J. S.; Stang, P. J. J. Am. Chem. Soc. 2002, 124, 6613. (f) Qin, Z.; Jennings, M. C.; Puddephatt, R. J. Chem.—Eur. J. 2002, 8, 735. (g) Muthu, S.; Yip, J. H. K.; Vittal, J. J. J. Chem. Soc., Dalton Trans. 2001, 3577. (4) (a) Danil de Namor, A. F.; Cardenas, J. D.; Bullock, J. I.; Garcia, A. A.; Brianso, J. L.; Rius, J.; Whitaker, C. R. Polyhedron 1997, 16, 4323. (b) Ryan, L. P.; Nolan, K. B. Inorg. Chim. Acta 1993, 206, 23. (c) Clapp, L. A.; Siddons, C. J.; Whitehead, J. R.; VanDerveer, D. G.; Rogers, R. D.; Griffin, S. T.; Jones, S. B.; Hancock, R. D. Inorg. Chem. 2005, 44, 8495. (5) (a) Ryan, L. P.; Nolan, K. B. Inorg. Chim. Acta 1993, 206, 23. (b) Nolan, K. B.; Murphy, T.; Hermanns, R. D.; Rahoo, H.; Creighton, A. M. Inorg. Chim. Acta 1990, 168, 283. (c) Claudio, E. S.; ter Horst,
Communications M. A.; Forde, C. E.; Stern, C. L.; Zart, M. K.; Godwin, H. A. Inorg. Chem. 2000, 39, 1391. (6) Several derivatives of 1 (R ) 4-pyridyl and substututed phenyl) were prepared in our laboratory. Their crystal structures, cocrystals, coordination polymers, and other properties are under study. (7) A total of 50 mg (0.083 mmol) of ligand was dissolved in 25 mL of methanol with the addition of MeOH solution (10 mL) of the corresponding metal salt (0.3355 mmol). Clear solutions with pink color in the case of cobalt and colorless solutions in case of ZnII and MnII were obtained. Slow evaporation of these solutions at room temperature resulted in crystals suitable for single-crystal X-ray diffraction. Further, the usage of excess metal salt (M/L ) 6:1) in the reaction also resulted in similar crystals, implying that the complex formation/composition has no dependency on the metal/ligand ratios present in the reaction. (8) The X-ray diffraction data were collected on a Bruker SMART Apex diffractometer with CCD detectors, and structures were solved using SHELXTL software. Crystal data 2: triclinic, P1, a ) 13.453(3) Å, b ) 14.200(3) Å, c ) 14.372(3) Å, R ) 102.34(3)°, β ) 91.96(3)°, γ ) 116.04(3)°, V ) 2118.9(15) Å3, Z ) 1, Dc ) 1.426 g cm–3, 4720 reflections of 7074 unique reflections with I > 2σ(I), 1.76° < θ < 28.35°, final R factors R1 ) 0.0515, wR2 ) 0.1625. Elemental analysis: C, 39.68%; H, 5.40%; N, 15.34%; calcd: C, 39.60%; H, 5.50%; N, 15.40%, yield: 70%. Crystal data 3: triclinic, P1, a ) 13.269(3) Å, b ) 13.674(3) Å, c ) 14.545(3) Å, R ) 92.93(1)°, β ) 108.24(1)°, γ ) 118.68(1)°, V ) 2133.9(15) Å3, Z ) 1, Dc ) 1.956 g cm–3, 4643 reflections of 10 442 unique reflections with I > 2σ(I), 1.52° < θ < 28.56°, final R factors R1 ) 0.0743, wR2 ) 0.2127. The peaks corresponding to half PF6 ion and water molecules exhibited high thermal motions and disorder. Therefore, the Platon squeeze option
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(9) (10)
(11) (12)
(13)
was applied for the final refinement. Elemental analysis: C, 29.75%; H, 3.65%; N, 12.09%; calcd: C, 30.07%; H, 4.59%; N, 11.69%, yield: 91%. Spek, A. L. PLATON—A Multi Purpose Crystallographic Tool; Utrecht University: Utrecht, The Netherlands, 2002. Crystal data 4: triclinic, P1, a ) 13.198(1) Å, b ) 13.589(2) Å, c ) 24.985(3) Å, R ) 105.433(5)°, β ) 96.685(5)°, γ ) 104.462(3)°, V ) 5007.0(10) Å3, Z ) 2, Dc ) 1.442 g cm–3, 4735 reflections of 21602 unique reflections with I > 2σ(I), 0.86° < θ < 30.62°, final R factors R1 ) 0.0868, wR2 ) 0.2470. In structures 4–6, the peaks corresponding to anions and free water molecules exhibited high thermal motions and heavy disorder. Therefore, the Platon squeeze option was applied to refine the final structures. Elemental analysis: C, 32.37%; H, 5.16%; N, 16.26%; calcd: C, 33.13%; H, 5.15%; N, 16.75%, yield: 82%. Biradha, K.; Sarkar, M.; Rajput, L. Chem. Commun., 2006, 4169. Crystal data 5: monoclinic, C2/c, a ) 27.096(3) Å, b ) 12.639(1) Å, c ) 26.681(2) Å, β ) 92.178(2)°, V ) 9131.2(15) Å3, Z ) 4, Dc ) 1.543 g cm–3, 5346 reflections of 7779 unique reflections with I > 2σ(I), 1.50° < θ < 25.00°, final R factors R1 ) 0.0354, wR2 ) 0.1417. Elemental analysis: C, 34.72%, H, 4.24%, N, 17.21%; calcd: C, 34.61%, H, 5.00%, N, 17.50%, yield: 86%. Crystal data 6: monolinic, P2/n, a ) 12.733(3) Å, b ) 12.197(1) Å, c ) 32.286(7) Å, β ) 96.62(2)°, V ) 4980.4(17) Å3, Z ) 2, Dc ) 1.565 g cm–3, 3874 reflections of 8766 unique reflections with I > 2σ(I), 1.27° < θ < 25.00°, final R factors R1 ) 0.0874, wR2 ) 0.1976. Elemental analysis: C, 30.28%, H, 4.32%, N, 11.53%; calcd: C, 30.70%; H, 4.43%; N, 11.94%, yield: 84%. The distances between metal atoms of the two sides of a rectangle were considered as dimensions of SBU.
CG070289X
