Paratactic Assembly of Two Distinct Units into a Unique 3D Architecture Yu-Mei Dai,†,‡,§ En Ma,† En Tang,† Jian Zhang,† Zhao-Ji Li,† Xu-Dong Huang,# and Yuan-Gen Yao*,† State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, The Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China, College of Chemistry & Material Science, Fujian Normal University, Fuzhou 350007, P. R. China, College of Chemistry & Chemical Engineering, Fuzhou University, Fuzhou 350002, P. R. China, and Genetics & Aging Research Unit, Massachusetts Institute of Neurodegenerative Diseases and Department of Psychiatry, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129 Received February 1, 2005;
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Revised Manuscript Received April 4, 2005
ABSTRACT: The hydrothermal reaction of zinc acetate with isophthalate (ip) and 4,4-bipyridine (4,4-bipy) in alkaline solution yielded a novel coordination polymer [Zn(ip)(4,4-bipy)2][Zn(ip)(4,4-bipy)]‚0.25H2O, whose three-dimensional network was constructed by the paratactic assembly of two distinct units in an ABCD array. A large family of coordination polymers have been developed during this decade because of their potential applications as functional solid materials and their intriguing architectures or topologies.1-4 The development of molecular assembly techniques allows chemists to rationally design new metal-organic coordination polymers based on covalent and noncovalent contacts between metals and donors, such as hydrogen bond, π-π stacking interactions. An impressive literature of various structural motifs with one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) networks (such as helical, brick wall, ladder, honeycomb, square grid, parquet, and diamondoid structures) has been reported to date. Several examples of interpenetration types of different structural motifs have been reported, such as “1D+1D”, “1D+2D”, “1D+3D”, “2D+3D”, and “1D+1D+2D” types.5 However, examples of the coexistence of two or more independent motifs in one framework, especially those without interpenetration, are still very rare. In this communication, we report an unprecedented noninterpenetrated 2D+2D network [Zn(ip)(4,4-bipy)2][Zn(ip)(4,4-bipy)]‚0.25H2O, which is paratactically assembled by two distinct 2D motifs in an ABCD sequence. The hydrothermal reaction of zinc acetate with H2ip, 4,4-bipyridine, and KOH led to the formation of the crystalline complex.6 The structure was identified by satisfactory elemental analysis, IR, and X-ray diffraction.7 The IR spectrum of the complex showed the typical antisymmetric (1615 cm-1) and symmetric (1555, 1479 and 1400 cm-1) stretching bands of carboxylate groups. The respective values of [νasym(CO2)-νsym(CO2)] clearly indicate the presence of chelating (60 cm-1), bridging (136 cm-1), and monodentating coordination modes (215 cm-1) of the carboxylate groups.8 This is consistent with the X-ray structural analytical results. The absence of the expected vibration at 1730-1690 cm-1 for the protonated carboxylate groups means the complete deprotonation of the ip ligand.9 To our amazement, the X-ray diffraction structural analysis reveals that the complex, in acentric space group * Corresponding Author: E-mail:
[email protected]. Fax: (+86)-591-83714946. † Fujian Institute of Research on the Structure of Matter, The Chinese Academy of Sciences. ‡ Fujian Normal University. § Fuzhou University. # Massachusetts General Hospital and Harvard Medical School.
Figure 1. Schematic representation of (A) the basic 2D grid; (B) the boxlike polymer 1; (C) the tablelike polymer 2 via the different linking styles.
Pnn2, contains two kinds of independent polymers: [Zn(ip)(4,4-bipy)]‚0.25H2O (1) and [Zn(ip)(4,4-bipy)2] (2). As shown in Figure 1, these two polymers are constructed from a basic 2D rectangle grid (dimension: ca. 10.419 × 11.955 Å2), in which Zn-ip chains are interlinked by 4,4-bipy ligands. The boxlike polymer 1 is formed when the Zn centers in the basic 2D grid are coordinated to O atoms of ip ligands from the neighboring 2D rectangle grid. As a contrast, the tablelike polymer 2 is formed when the Zn centers in the 2D grid are coordinated to N atoms of the terminal 4,4-bipy ligands. The box of polymer 1 has a dimension of ca. 10.419 × 4.263 × 11.955 Å3, in which water molecules are encapsulated as the guest molecules. Each Zn atom is octahedrally coordinated by four oxygen atoms (two of them are chelating, the other two are monodentating) of three ip ligands and two µ2-bridging N atoms of two 4,4-bipy. Zn-O bond lengths are in the range of 2.140(4)-2.493(4) Å, and Zn-N bond lengths are in the range of 2.264(6)-2.271(6) Å (Figure S1, Supporting Information). Similar to polymer 1, each Zn atom in polymer 2 is also octahedrally coordinated by three O atoms of two ip and three N atoms from two µ2-bridging 4,4-bipy and one terminate 4,4-bipy (the table leg). Zn-O bond lengths are in the range of 2.090(4)-2.225(4) Å, and Zn-N bond lengths are in the range of 2.247(6)-2.361(6) Å. The packing style of polymer 1 and 2 inside the framework is very interesting. As shown in Figure 2, polymer 1 is arranged in an ACAC sequence as C is the ca. 4.5 Å slip of A along the c axis. Owing to its large dimension of 10.30 × 11.37 Å2 and the fact that one tenminal N of one of the three 4,4-bipyridine ligands is free, two tablelike polymer 2 molecules are embedded in each other in a face-
10.1021/cg0500425 CCC: $30.25 © 2005 American Chemical Society Published on Web 05/27/2005
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Figure 2. The assembly sequence ABCD of polymers 1 and 2 in the crystal. C is the consequence of ca. 4.5 Å slip of A along the c axis, while D is the result of rotation of 180° along the c axis of B. (The right panel is the schematic representation of the assembly.)
to-face manner. Between them, an offset of ca. one-half the layer width along the c axis and the closest interlayer separation of 4.432 Å are observed (Figure S1, Supporting Information). These embeding segments adopt a BDBD sequence along the a axis as D is the 180° rotation of B. Consequently, polymers 1 and 2 are paratactically assembled in a ABCD sequence along the a axis. To our knowledge, it is the first example that two independent 2D polymers coexist in one crystal without mutual interpenetration. The supramolecular interactions between the structural motifs in the form of π-π interactions and C-H‚‚‚O hydrogen bonds10 play a crucial role in the construction of such a 2D+2D architecture. Between the two embedded tables of 2, the interlayer π-π stacking interactions are observed between the phenyl rings of ip and 4,4-bipy with a center-center distance of 3.722(3) Å (Figure S2, Supporting Information). The interactions between 1 and 2 include: (i) weak π-π interactions between the tilted bipyridyl rings (of table leg) of 2 and the bipyridyl or ip phenyl rings of 1 with the center-center distance of 4.020(3) Å (the shortest is 3.596 Å); (ii) two sets of C-H‚‚‚O hydrogen bonds: the first is formed between the C atoms of bipy of 1 and the carboxyl O atoms of 2; the second is formed between the carboxyl O atoms of 1 and the bipy C atoms of 2. The C‚‚‚O distances are 3.268 and 3.430(8) Å, respectively. The complex exhibits intense blue photoluminescence in the solid state. The excitation and emission spectra at room temperature are shown in Figure 3. The excitation spectrum consists of two bands at 338 and 384 nm, respectively. The emission spectrum excited by 338 nm radiation is somewhat different from that excited by 384 nm radiation, implying that the excitation at the 338 nm band is favorable to improve the intensity of short wavelength emission, while the excitation at the 384 nm band is favorable to improve the intensity of the long wavelength emission. According to the literature reports,11,12 the 4,4-bipy ligand has a weak emission at λem ) 424 nm (λex ) 350 nm) and H2ip has a weak emission at λem ) 408 nm (λex ) 348 nm); we consider that they are the intraligand fluorescent emissions of the complex. Furthermore, the lifetime measurement at λem ) 450 nm (λex ) 397 nm) with a result of 4.2 and 12.3 ns can also support the above viewpoint. The similar spectrum shape of free 4,4-bipy ligand when excited at 338 nm indicates that the emission at λem ) 445 nm (λex ) 3 38 nm) could be assigned as the π-π* transition of µ2-bridging 4,4-bipy ligands, while the emission at λem ) 467 nm (λex ) 384 nm) can be mostly
Figure 3. Solid-state fluorescence emission and excitation spectra of the complex at room temperature. The blue and red lines correspond to the 384 and 338 nm excited scans (inset), respectively.
derived from the π-π* transition of dangling 4,4-bipy ligands due to the wider shape. Along with the fact that the complex is virtually insoluble in most solvents such as ethanol, chloroform, ethyl acetate, acetone, acetonitrile, benzene, and water, the blue fluorescent emission property makes the complex a potential new material used in blue LED devices. In conclusion, we synthesized and characterized a novel acentric complex with two distinct 2D polymers paratactically assembled in an ABCD sequence without interpenetration. The characteristic architecture may result in its interesting photoluminescent behavior. The new design idea reported here may be a promising technique to obtain a fascinating polymeric architecture with good photoelectronic properties. Acknowledgment. Based on work supported by the National Natural Science Foundation of China under project No. 20173063, the State Key Basic Research and Development Plan of China (001CB108906), and the NSF of Fujian Province (E0020001). Supporting Information Available: Figures of polymer 1 with the guest water encapsulated inside the boxlike cavity and the tablelike polymer 2; and π-π interactions between phenyl rings of ip and 4,4-bipy between the two embedded tables of polymer 2, and the supramolecular interactions between 1 and 2. Crystallographic data in CIF. This material is available free of charge via the Internet at http://pubs.acs.org.
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(7)
(8)
(9) (10) (11) (12)
based on Zn). Elemental analysis: calc. for C46H32.50N6O8.25Zn2: C, 59.28; H, 3.51; N, 9.02. Found: C, 59.16; H, 3.39; N, 8.96; IR (KBr, cm-1) 3131(s), 2346(w), 1615(s), 1555(m), 1479(m), 1400(s), 1133(m), 1097(m), 741(m), 723(m), 631(m). Crystal data for 1: C46H32.50N6O8.25Zn2, fw ) 932.02, orthorhombic, Pnn2; a ) 36.81(3), b ) 10.419(9), c ) 11.955(10) Å, R ) β ) γ ) 90.00°; V ) 4585(7) Å3, Z ) 4, Dc ) 1.367 g/cm3, µ(Mo KR)) mm-1, T ) 293(2) K, final R1 ) 0.0490, wR2 ) 0.1074 for 6632 observed reflections with I >2σ(I) from 9387 independent reflections. The data set was collected on a Siemens Smart CCD diffractometer equipped with graphite-monochromated Mo KR radiation (λ ) 0.7013 Å) at room temperature. The structure was solved by direct methods and refined by full matrix leastsquares techniques. (a) Deacon, G. B.; Phillips, R. J. Coord. Chem. Rev. 1980, 33, 227. (b) Nakamoto, K. Infrared Spectra and Raman Spectra of Inorganic and Coordination Compound; John Wiley & Sons: New York, 1986. Bellamy, L. J. The Infrared Spectra of Complex Molecules; Wiley: New York, 1958. Desiraju, G. R. Acc. Chem. Res. 1991, 24, 290; Desiraju, G. R. Acc. Chem. Res. 1996, 29, 441. Xu, L.; Guo, G.-C.; Liu, B.; Wang, M.-S.; Huang, J.-S. Inorg. Chem. Commun. 2004, 7, 1145. Wang, M.-S.; Guo, G.-C.; Cai, L.-Z.; Chen, W.-T.; Liu, B.; Wu, A.-Q.; Huang, J.-S. Dalton Trans. 2004, 2230.
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