Two Unprecedented Transition-Metal–Organic Frameworks Showing

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Two Unprecedented Transition-Metal−Organic Frameworks Showing One Dimensional-Hexagonal Channel Open Network and Two-Dimensional Sheet Structures Chengjie Wang, Tao Wang, Wan Zhang, Huijie Lu, and Gang Li* Department of Chemistry, Zhengzhou University, Henan 450052, P. R. China S Supporting Information *

ABSTRACT: Two new metal−organic frameworks, {[Co3(μ3DMPhIDC)2(H2O)6]·2H2O}n (1) and {[Mn5(μ3-DMPhIDC)2(μ2-HDMPhIDC)2(Phen)5]·2CH3OH·3H2O}n (2) (H3DMPhIDC = 2-(3,4-dimethylphenyl)-1H-imidazole-4,5-dicarboxylic acid, Phen = 1,10-phenanthroline), have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, elemental analyses, X-ray powder diffraction (XRPD), thermal analyses, and IR spectra. Polymer 1 is an enchanting threedimensional network containing infinite one-dimensional-hexagonal channels and [Co2(DMPhIDC)]6 cages, which have two interpenetrating nets topology. Polymer 2 exhibits a two-dimensional framework, which is composed of left- and right-handed helices pillared by Mn2+ linkages. Antiferromagnetic coupling exists between the Co(II) ions or Mn(II) ions in 1 or 2, respectively.

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distributions of the designed ligand by us, 2-(3,4-dimethylphenyl)-1H-imidazole-4,5-dicarboxylic acid (H3DMPhIDC). The theoretical calculation result indicates H3DMPhIDC may have pretty good coordination features (Supporting Information, Scheme S1). The computed results reveal that the negative NBO charges mainly distribute on the oxygen and nitrogen atoms in the free ligand H3DMPhIDC. The NBO charges are −0.636 for O1, −0.648 for O2, −0.666 for O3, −0.599 for O4, −0.462 for N5, and −0.498 for N6. These values indicate that the oxygen and nitrogen atoms of the H3DMPhIDC ligand have potential coordination ability and may show various coordination modes under the appropriate reaction conditions. Thus, we introduce the methyl groups into the phenyl unit to modify the H3PhIDC ligand. Consequently, an unprecedented 3D architecture, {[Co3(μ3-DMPhIDC)2(H2O)6]·2H2O}n (1) and a fascinating two-dimensional (2D) framework, {[Mn 5 (μ 3 -DMPhIDC) 2 (μ 2 -HDMPhIDC) 2 (Phen)5]·2CH3OH·3H2O}n (Phen = 1,10-phenanthroline) (2), have been first synthesized. Herein, we show the outstanding reactivity of the H3DMPhIDC linker with a source of chloride salt under hydro(solvo)thermal conditions, which confirms our predication of coordination characteristics about the H3DMPhIDC ligand. Plum cubic crystals of 1 and light-yellow cuboid crystals of 2 were synthesized by employing the hydro(solvo)thermal route in a 25 mL Teflon-lined bomb from the reaction of H3DMPhIDC

or the last two decades, the rational design and construction of metal−organic frameworks (MOFs) continue to be a productive research area, not only owing to their fascinating architectures, but also due to their explosive growth for possible applications in magnetism, gas separation/storage, catalysts, drug delivery, etc.1 Generally, to get such intriguing functional materials, the crucial step is to design and prepare multifunctional organic ligands containing appropriate coordination sites linked by a proper spacer with a specific positional orientation. To some extent, obtaining an excellent organic ligand is half of the success for the construction of MOFs. In this context, imidazole-4,5-dicarboxylic acid (H3IDC) and its 2-position substituted derivatives have recently attracted much attention because of their strong coordination abilities and outstanding features of various coordination fashions.2 Although there are a great number of MOFs from H3IDC and its 2-position aliphatic hydrocarbons substituted derivatives reported in the literature,2a−e the MOFs built by 2-position aromatic phenyl group substituted imidazole dicarboxylate ligands are very limited.2f−h Indeed, to the best of our knowledge, only five threedimensional (3D) and three one-dimensional (1D) MOFs bearing 2-phenyl-1H-imidazole-4,5-dicarboxylate (H3PhIDC) ligand have been reported by our laboratory.2f−h Through our preliminary research, we found that the imidazole dicarboxylate ligand bearing 2-position bulky conjugate groups can indicate strong coordination ability and diverse coordination modes. This prompted us to prepare more similar ligands to explore their coordination features. To get a promising candidate for obtaining useful MOFs, we first calculated the natural bond orbital (NBO) charge © 2012 American Chemical Society

Received: January 9, 2012 Revised: January 30, 2012 Published: February 6, 2012 1091

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with CoCl2·6H2O in DMF/H2O, with MnCl2·4H2O in CH3OH/ H2O, respectively (see the Supporting Information). They were formulated on the basis of single-crystal X-ray diffraction, elemental analyses, IR spectra, and thermogravimetric analyses. Both 1 and 2 are very stable in air at ambient temperature and insoluble in common solvents, such as methanol, acetonitrile, and water. Compound 1 crystallizes in the trigonal R3̅ space group and exhibits a 1D-hexagonal or tetragonum channel open network with windmill-like 3D topology (Figure 1a). As depicted in

[CoN2O4] or [CoO6]. The Co1 center displays a distorted octahedron, which is provided by two imidazolate N atoms and two carboxylate O atoms from two individual μ3-DMPhIDC3− ions; the other two O atoms come from two coordinated water molecules. Co2 is also six-coordinated by four carboxylate O atoms from two individual μ3-DMPhIDC3− in the equatorial plane, and two oxygen atoms from two coordinated water molecules in axial positions. The Co−L (L = N or O) distances are in the range of 1.996(3)−2.187(4) Å, and the trans L−Co−L bond angles range from 78.00(13)° to 179.999(1)° which are normal values.3 Each DMPhIDC3− ligand adopts the same coordination mode, namely, μ3-kN,O: kN′,O′: kO,O′ (Supporting Information, Scheme S2a). Six DMPhIDC3− anions are connected by six Co1 cations to construct a chair conformational [Co6(DMPhIDC3−)6] hexagonal ring. The ring diameters, defined as the distance between two symmetryrelated opposing Co1 ions, range from 12.7402(13) to 12.7402(20) Å. To our astonishment, six Co1II almost are in the same circumference. Every [Co6(DMPhIDC3−)6] ring is pillared by Co2 linkages from a infinite chain (Figure 1d). For simplicity, adjacent chains share edges and Co2 to form a 2D flower-like layer (Figure 1e). It is noteworthy that 12 CoII ions are linked by 6 DMPhIDC3− ligands to form one [Co2(DMPhIDC)]6 cage (Figure 1c); moreover, these cages are further connected through the Co2 atoms to yield a 3D framework with 1D channels (Figure 1b). The guest water molecules occupy the void interspace region and by O−H···O hydrogen-bonding interact with the coordinated water molecules and DMPhIDC3− units. From a topological viewpoint, the DMPhIDC3− and the two cobalt ions can be viewed a 3-connected node (Supporting Information, Figure S1b,c), respectively. Thus, the 3D framework of 1 can be described as a (3,3)-connected topology with the point symbol of (4·122) (Figure 1a), and there are two interpenetrating nets, full interpenetration vectors [0,0,1]. The crystal structure determination reveals that compound 2 crystallizes in the orthorhombic crystal system Pccn. The asymmetric unit contains five crystallographically independent Mn(II) ions, five Phen units, two μ3-DMPhIDC3− and two μ2-HDMPhIDC2− anions, two free CH3OH molecules, and three lattice water molecules (Supporting Information, Figure S2a). The Mn1 and Mn3 ions are both six-coordinated, with each forming a distorted octahedron [MnN4O2] unit. The Mn1 atom is surrounded by two nitrogen atoms from one Phen, two carboxylate oxygen atoms, and the other two nitrogen atoms from two individual μ3-DMPhIDC3− and μ2-HDMPhIDC2− ligands. The surrounding of atom Mn3 is similar to that of Mn1. The Mn2 is also six-coordinated; the coordination environment around the Mn2 center is best portrayed as a slightly distorted [MnN2O4] octahedron, ligated by four carboxylate oxygen atoms (O3, O3A, O2, and O2A) from two individual μ3-DMPhIDC3−, and two nitrogen atoms (N9, N9A) from one Phen. The Mn−L distances are in the range of 2.068(3)− 2.328(3) Å, and the trans L−Mn−L bond angles range from 69.72(16) to 159.41(14)°, all of which are comparable to those reported for other imidazole dicarboxylate Mn(II) complexes.4 The DMPhIDC3− and HDMPhIDC2− units in the compound 2 adopt two different coordination modes: one as μ3-kN,O: kN′,O′: kO, O′ mode (Supporting Information, Scheme S2a) and the other one as μ2-kN,O: kN′,O′ mode (Supporting Information, Scheme S2b) and links neighboring Mn1 and Mn3 atoms from a 1D left-handed helix and a 1D right-handed helix (Figure 2a) and are further pillared by [Mn(Phen)] linkages to form a 2D

Figure 1. (a) The (3,3)-connected topology observed in 1. (b) View of the 3D framework of 1 with 1D channels (partly atoms omitted for clarity). (c) View of the [Co2(DMPhIDC)]6 cage. (d) View the 1D chains of 1 (the Co1 octahedral coordination polyhedrons are turquoise, the Co2 octahedral coordination polyhedrons are pink). (e) View of the 2D layer of 1 perpendicular to the c axis.

Figure S1a (see the Supporting Information), two crystallographically independent Co(II) atoms are located in two different distorted octahedral coordination environments, 1092

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642.5 °C corresponding to the removal of two free water molecules, two HDMPhIDC2−, two DMPhIDC3−, and five Phen units (observed 77.39%, calculated 77.74%). Subsequently, a plateau region is observed from 642.5 to 850 °C. A black amorphous residue is 5MnO2 (observed 19.13%, calculated 18.73%). In order to see whether they may be a potential candidate as magnetic material, we investigated their variable-temperature magnetism. Variable-temperature magnetic study on 1 or 2 is carried out over the temperature range of 2.0−300 K. The variation of the inverse of the magnetic susceptibility χM−1 and χMT of 1 or 2 are shown in Figure 4, panels a and b, respectively. For 1: at

Figure 2. (a) The 1D left-handed helical chain and 1D right-handed helical chain (the Mn1 and Mn3 octahedral coordination polyhedrons are purple, the Mn2 octahedral coordination polyhedrons are lime). (b) The 2D sheet comprising infinite helical chains bridged by [Mn(Phen)] linkages.

layer (Figure 2b). The 2D sheets are interlinked to produce a 3D supramolecular framework (Supporting Information, Figure S2b) through O−H···O hydrogen-bonding interactions that further stabilize the crystal structure. The X-ray powder diffraction (XRPD) was used to check the purity of compounds 1 and 2. Most peak positions of simulated and experimental patterns are in good agreement with each other. The dissimilarities in intensity may be due to the preferred orientation of the crystalline powder samples (Supporting Information, Figures S3 and S4). The TG curves have been obtained under flowing air for crystalline samples of 1 and 2 in the temperature range 20−850 °C, which show the thermal stabilities of 1 and 2 (Figure 3).

Figure 3. The TG analysis profiles of compounds 1 and 2.

Figure 4. Plots of experimental χMT vs. T and 1/χM vs. T of (a) 1 and (b) 2.

Compound 1 reveals a weight loss of 12.76% (calculated 12.93%) from 30 to 162.5 °C corresponding to the release of two lattice water molecules and four coordinated water molecules, and then, another two coordinated water molecules decompose from 162.5 to 255.0 °C (observed 4.05%, calculated 4.31%). It keeps losing weight from 255.0 to 637.0 °C corresponding to the removal of the organic ligands (observed 54.21%, calculated 52.94%). Finally, a plateau region is observed from 637.0 to 850 °C. The remaining weight of 28.98% corresponds to the percentage (calculated 29.82%) of the Co and O components, indicating that the final product is 1.5Co2O3. Compound 2 is stable up to 55.0 °C and then loses weight from 55.0 to 322.5 °C (observed 3.48%, calculated 3.53%) corresponding to losses of two free methanol molecules and one free water molecule. It keeps losing weight from 322.5 to

300 K, the effective magnetic moment (μeff) per cobalt(II) is 4.425 μB for 1 and is higher than the expected value for the spin-only S = 3/2 system (3.87 μB) due to the orbital contribution.5 The thermal evolution of χM−1 obeys Curie−Weiss law, χM = C/(T −θ) in the temperature range of 300− 2.0 K with Weiss constant, θ, of −8.35 K and Curie constant, CM, of 2.52 cm3 K mol−1. On lowering the temperature, the χMT value decreases smoothly, and below 42 K it decreases abruptly to a minimum of 0.359 cm3 K mol−1 at 2 K. For 2: the thermal evolution of χM−1 obeys Curie−Weiss law in the range of 2.0−300 K with a Weiss constant, θ, of −28.39 K and a Curie constant, CM, of 4.99 cm3 K mol−1, respectively. At 300 K, the χMT value is 4.62 cm3 K mol−1 (6.079 μB), which is slightly larger than the value of 4.38 cm3 K mol−1 (5.92 μB) 1093

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Y.-Y.; Guo, Y.; Jin, C.; Shi, Q.-Z. Chem. Commun. 2011, 47, 5464. (f) Lu, Z.-Z.; Zhang, R.; Li, Y.-Z.; Guo, Z.-J.; Zheng, H.-G. J. Am. Chem. Soc. 2011, 133, 4172. (2) (a) Zheng, S. R.; Cai, S. L.; Fan, J.; Xiao, T. T.; Zhang, W. G. Inorg. Chem. Commun. 2011, 14, 1097. (b) Gu, Z. G.; Fang, H. C.; Yin, P. Y.; Tong, L.; Ying, Y.; Hu, S. J.; Li, W. S.; Cai, Y. P. Cryst. Growth Des. 2011, 11, 2220. (c) Zhang, F. W.; Li, Z. F.; Ge, T. Z.; Yao, H. C.; Li, G. Inorg. Chem. 2010, 49, 3776. (d) Li, Z. F.; Chen, C. J.; Yan, L. H.; Li, G.; Wu, C. J.; Lu, H. J. Inorg. Chim. Acta 2011, 377, 42. (e) Ghosh, A.; Prabhakara, R. K.; Sanguramath., R. A.; Rao, C. N. R. J. Mol. Struct. 2009, 927, 37. (f) Wang, W. Y.; Niu, X. L.; Gao, Y. C.; Zhu, Y. Y.; Li, G.; Lu, H. J. Cryst. Growth Des. 2010, 10, 4050. (g) Wang, W. Y.; Yang, Z. L.; Wang, C. J.; Lu, H. J.; Zang, S. Q.; Li, G. CrystEngComm 2011, 13, 4895. (h) Zhu, Y.; Wang, W. Y.; Guo, M. W.; Li, G.; Lu, H. J. Inorg. Chem. Commun. 2011, 14, 1432. (i) Li, Z.-F.; Luo, X.-B.; Gao, Y-C.; Lu, H.-J.; Li, G. Inorg. Chim. Acta 2012, in press. doi: 10.1016/j.ica, and references therein. (3) (a) Li, J. X.; Du, Z. X.; Wang, L. Z.; Huang, W. P. Inorg. Chim. Acta 2011, 376, 479. (b) Cheng, A. L.; Liu, N.; Zhang, J. Y.; Gao, E. Q. Inorg. Chem. 2007, 46, 1034. (c) Li, X. X.; Yue, S. T.; Wang, N.; Li, Z. Y.; Liu, Y. L. Z. Anorg. Allg. Chem. 2010, 636, 2481. (d) Wu, H. X.; Han, M. L. Z. Kristallogr.New Cryst. Struct. 2011, 226, 217. (e) Luo, Z. R.; Zhuang, J. C.; Wu, Q. L.; Yin, X. H.; Tan, S. W.; Liu, J. Z. J. Coord. Chem. 2011, 64, 1054. (4) (a) Zhang, M. B.; Chen, Y. M.; Zheng, S. T.; Yang, G. Y.; Eur., J. Inorg. Chem. 2006, 7, 1423. (b) Lu, W. G.; Gu, J. Z.; Jiang, L.; Tan, M. Y.; Lu, T. B. Cryst. Growth Des. 2008, 8, 192. (c) Song, J. F.; Zhou, R. S.; Hu, T. P.; Chen, Z.; Wang, B. B. J. Coord. Chem. 2010, 63, 4201. (d) Li, S. J.; Miao, D. L.; Song, W. D.; Li, S. H.; Yan, J. B. Acta Crystallogr. Sect. E: Struct. Rep. Online 2010, E66, 1096. (e) Yan, J. B.; Li, S. J.; Song, W. D.; Wang, H.; Miao, D. L. Acta Crystallogr. Sect. E: Struct. Rep. Online 2010, E66, 99. (f) Zhang, G.; Wang, Y. Acta Crystallogr. Sect. E: Struct. Rep. Online 2011, E67, 828. (g) Fang, R. Q.; Zhang, X. M. Cryst. Growth Des. 2006, 6, 4801. (5) Mao, H. Y.; Zhang, C. Z.; Li, G.; Zhang, H. Y.; Hou, H. W.; Li, L. K.; Wu, Q. A.; Zhu, Y.; Wang, E. B. Dalton Trans. 2004, 3918. (6) Kahn, O. Molecular Magnetism; New York: VCH, 1993. (7) (a) Huang, Y. Q.; Cheng, P. Inorg. Chem. Commun. 2008, 11, 66. (b) Yao, Y. L.; Che, Y. X.; Zheng, J. M. Cryst. Growth Des. 2008, 8, 2299. (c) Liu, B. L.; Xiao, H.-P.; Nfor, E. N.; Song, Y.; You, X. Z. Inorg. Chem. Commun. 2009, 12, 8. (8) Fisher, M. E. Am. J. Phys. 1963, 32, 343. (9) Wagner, G. R.; Friedberg, S. A. Phys. Lett. 1964, 9, 11. (10) McElearney, J. N.; Merchant, S.; Carlin, R. L. Inorg. Chem. 1973, 12, 906.

expected for magnetically isolated high-spin Mn(II) (SMn = 5/2, g = 2.0).6 On lowering the temperature, the χMT value decreases smoothly, to a minimum of 0.411 cm3 K mol−1 at 2 K. Such χMT vs T curves and the negative values can referred to the presence of typical antiferromagnetic exchange interactions between neighbor Co(II) or Mn(II) ions in polymers 1 or 2, respectively. According to the structural data, the μ3-DMPhIDC3− units link the Co(II) ions into a 3D network, and the μ3DMPhIDC3−and μ2-HDMPhIDC2− units link the Mn(II) ions into a 2D sheet. Until now, no appropriate theory model has been established to determine the magnetic coupling constant between metal ions for a 2D layer or 3D net polymeric complexes. In order to evaluate the magnetic interactions in 2, we employ an approximate approach that has been used for similar cases.7 The magnetic susceptibility of 2 has been fitted to the Fisher model8 of the isotropic Heisenberg antiferromagnet, and later modified by Wagner and Friedberg9 for a Mn2+ system of spin 5/2.10 Unfortunately, we could not get a satisfactory result. The similar case could be found in polymer 1. Obviously, the magnetic pathways between neighbor Mn(II) or Co(II) ions of 2 or 1 are complicated, which could not be simply dealt with. However, compared with the Weiss constant of 1 (θ: −8.35 K) and 2 (θ: −28.39 K), it is obvious that the antiferromagnetic coupling in 2 is stronger than that in 1. In conclusion, the beautiful extended architectures of polymers 1 and 2 show that the H3DMPhIDC ligand is a promising candidate for construction of novel MOFs. It is an effective way to modify organic ligands to get different structural target complexes, and the quantum-chemical calculation method is also a valuable tool to predicate the coordination ability of different organic ligands, by which the NBO charges of the organic ligands can be calculated and show the coordination ability of potential coordination atoms. Finally, further work about H3DMPhIDCbased MOFs is underway in our laboratory.

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ASSOCIATED CONTENT

* Supporting Information S

Experimental procedures, additional figures, tables, and crystallographic data in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the financial support by the National Natural Science Foundation of China (21071127, 20501017, and J0830412), and Program for New Century Excellent Talents in University (NCET-10-0139) and the Natural Science Foundation of Henan Education Department (2009A150028 and 2011A150029).

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REFERENCES

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dx.doi.org/10.1021/cg300027h | Cryst. Growth Des. 2012, 12, 1091−1094