pH-Controlled Assembly of Two Unusual Entangled Motifs Based on

Article pubs.acs.org/crystal

pH-Controlled Assembly of Two Unusual Entangled Motifs Based on a Tridentate Ligand and Octamolybdate Clusters: 1D + 1D → 3D Poly-Pseudorotaxane and 2D → 2D → 3D Polycatenation Hua Wu,†,‡ Jin Yang,*,† Ying-Ying Liu,† and Jian-Fang Ma*,† †

Key Lab of Polyoxometalate Science, Department of Chemistry, Northeast Normal University, Changchun 130024, People’s Republic of China ‡ Heilongjiang Agricultural College of Vocational Technology, Jiamusi 154007, People’s Republic of China S Supporting Information *

A B S T R A C T : T w o u n u s u al en t a n g l e d m o t i f s o f [Ag 0.52 Na 0.48 (β-Mo 8 O 26 )(H 2 O)][Ag 3 (Tipa) 2 ] (1) and [Ag6(Tipa)4(β-Mo8O26)][H2(β-Mo8O26)]·5H2O (2) based on a tri(4-imidazolylphenyl)amine (Tipa) ligand and octamolybdate clusters have been successfully synthesized at different pH values. In compound 1, the 1D inorganic chains and 1D ladders are entangled to give a highly novel 1Dladder +1Dchain → 3D poly-pseudorotaxane framework. The unusual topological feature of 2 consists of the 2-fold interpenetrated layer, which is further catenated to the two adjacent such sheets in parallel fashion to give an overall unique (2D → 3D) polycatenated framework. The luminescent properties of the compounds have also been investigated.

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INTRODUCTION Entangled systems are a unique subset of the supramolecular chemistry as seen in interpenetrated, polycatenated, polythreaded, and other species.1 The intense interest in entangled system is rapidly increasing not only for the fact that these entangled nets can lead to synthetic supramolecular arrays with potential functional applications in asymmetric catalysis, drugdelivery vehicles, and sensor devices, but also for their indisputable aesthetic and complicated topological architectures.2 Of the many reported types of entangled architectures, the polythreaded system which can be considered as extended periodic analogues of the molecular rotaxanes or pseudorotaxanes has attracted much attention in recent times.3 The polyrotaxane is the different motif that cannot be disentangled without breaking links, while the poly-pseudorotaxane is the infinite chains or finite components that can be slipped off from the threaded motifs.3 Until now, polythreading networks, as a special entangled system, have become a challenging issue in polyoxometalate-based (POM) coordination polymers, and only several polythreaded architectures based on POMs have been investigated.4 Currently, the design and synthesis of inorganic−organic hybrid materials based on POMs through crystal engineering has become a significant research area for chemists due to their versatile inorganic−organic hybrid supramolecular arrays with various organic ligands or metal−organic coordination fragments, and their potential biological applications.5 In this regard, different pH values may induce the formation of various structural types and conformational changes in organic ligand © 2012 American Chemical Society

or POMs to generate different but often related final architectures.4b,6 In this paper, two fascinating entangled motifs [Ag 0.52 Na 0.48 (β-Mo 8 O 26 )(H 2 O)][Ag 3 (Tipa) 2 ] (1) and [Ag6(Tipa)4(β-Mo8O26)][H2(β-Mo8O26)]·5H2O (2) have been synthesized at different pH values (Tipa = tri(4imidazolylphenyl)amine). In the system of POMs, compound 1 represents an unusual 1D + 1D → 3D poly-pseudorotaxane motif, while compound 2 is a very rare example of 2D → 2D → 3D polycatenation.

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EXPERIMENTAL SECTION

Materials. The Tipa ligand was synthesized in accordance with the previous report.2j Other reagents and solvents employed were commercially available and used as received without further purification. Physical Measurements. Elemental analyses were carried out with a Carlo Erba 1106 elemental analyzer, and the FT-IR spectra were recorded from KBr pellets in the range 4000−400 cm−1 on a Mattson Alpha-Centauri spectrometer. The solid-state emission/excitation spectra were recorded on a Varian Cary Eclipse spectrometer at room temperature. The inductively coupled plasma (ICP) analysis was performed on a Leeman Laboratories Prodigy inductively coupled plasma-optical atomic emission spectrometer (ICP-AES). Syntheses of [Ag0.52Na0.48(β-Mo8O26)(H2O)][Ag3(Tipa)2] (1) and [Ag6(Tipa)4(β-Mo8O26)][H2(β-Mo8O26)]·5H2O (2). A mixture of AgNO3 (0.068 g, 0.4 mmol), Tipa (0.088 g, 0.2 mmol), (NH4)6Mo7O24·4H2O (0.24 g, 0.2 mmol), and water (10 mL) was Received: November 24, 2011 Revised: March 8, 2012 Published: April 4, 2012 2272

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mixed and stirred at room temperature for 30 min. The mixture was adjusted with 1 M HNO3 to pH ≈ 1 and then sealed in a Teflon-lined autoclave and heated at 170 °C for three days. Then the mixture was cooled to room temperature, and colorless crystals of 1 were obtained in 56% yield based on Ag(I). ICP Anal. for C54H44Ag3.52Na0.48Mo8N14O27 Calcd (%): 0.45. Found (%): 0.49. FTIR (KBr pellet, cm−1): 3444 (m), 3113 (m), 1648 (w), 1514 (s), 1273 (s), 1066 (s), 943 (m), 905 (s), 836 (m), 698 (w), 543 (m), 472 (w). The preparation of compound 2 was similar to that of 1 except that the pH value was adjusted to about 3. Colorless crystals were obtained in 48% yield based on Ag(I). For C108H91Ag6Mo16N28O57, FTIR (KBr pellet, cm−1): 3443 (m), 3114 (m), 1604 (w), 1515 (s), 1307 (m), 1263 (m), 1123 (m), 1065 (s), 943 (s), 908 (s), 833 (s), 705 (m), 545 (m), 473 (w).

Table 1. Crystal Data and Structure Refinements for Compounds 1 and 2 empirical formula fw cryst system space group a [Å] b [Å] c [Å] α [deg] β [deg] γ [deg] V [Å3] Z Rint R1 [I > 2σ(I)] wR2 (all data)

1

2

C54H44Ag3.52Mo8N14Na0.48O27

C108H91Ag6Mo16N28O57

2479.29 triclinic P1̅ 11.0529(10) 13.3248(10) 13.3632(8) 100.674(6) 94.942(6) 99.900(7) 1891.0(2) 1 0.1029 0.0657 0.1774

4875.35 triclinic P1̅ 13.0784(3) 15.6015(6) 18.7501(7) 69.258(3) 85.174(2) 73.439(2) 3428.8(2) 1 0.0460 0.0363 0.0663

Figure 1. ORTEP figure of 1 (displacement ellipsoids drawn at the 30% probability level). (Symmetry codes: #1, −x + 1, −y + 1, −z + 2; #2, x + 1, y + 1, z + 1; #4, −x, −y + 2, −z.)

from two β-[Mo8O26]4‑ polyoxoanions and one water O atom in a slightly distorted tetragonal-pyramidal geometry. Ag2 ion is coordinated by two N atoms from two different Tipa ligands, displaying a distorted linear coordination geometry [N3−Ag2− N5#2 = 156.5(4)°]. Ag3 ion is also two-coordinated by two N atoms in a linear geometry [N7−Ag3−N7#4 = 180°]. The β-[Mo8O26]4‑ cluster consists of two [Mo4O13] subunits in which each exhibits an [O4] unit of four terminal oxygen atoms in a square planar arrangement. As shown in Figure 2a, each crystallographically half-occupied Ag1 ion binds two adjacent β-[Mo8O26]4‑ clusters through four Ag−O bonds from two [O4] faces of two Mo8 clusters, resulting in an infinite inorganic anion chain of [Ag0.52Na0.48(β-Mo8O26)(H2O)]3‑. Each Tipa ligand links the adjacent Ag2 and Ag3 atoms to generate a cationic 1D ladder of [Ag3(Tipa)2]3+ with the rectangular windows of 18.34 × 23.77 Å2 (Figure 2b). The rectangular opening is divided into two infinite rectangular channels by the ladders located above and below. These channels in turn are occupied by the inorganic chains, in which one rectangular opening is filled by two cationic chains to generate a highly novel 1Dladder + 1Dchain → 3Dpoly‑pseudorotaxane framework (Figure 2c,d). So far, although a few poly-pseudorotaxane coordination polymers have been reported, only one fascinating example of 1Dladder + 1Dchain → 3Dpoly‑pseudorotaxane framework, [Cu(L)(solv)(NO 3 ) 2 ][Cu(L) 1.5 (NO 3 ) 2 ]·2solv (L = 1,4-bis[(4′pyridylethynyl)benzene; solv = EtOH or MeOH) (3), has been documented.7−9 It should be pointed out that although both 1 and the reported compound (3) show 1D + 1D → 3D poly-pseudorotaxane frameworks, their entangled modes are entirely different. In that reported compound (3), the windows between the rungs were threaded by four neutral chains; however, in 1, only two cationic chains pass through one window between the rungs (Scheme 1). [Ag6(Tipa)4(β-Mo8O26)][H2(β-Mo8O26)]·5H2O (2). The preparation of compound 2 was similar to that of 1 except that the pH value was adjusted to about 3. Single-crystal X-ray analysis reveals that the asymmetric unit of 2 contains three kinds of Ag(I) ions, two kinds of Tipa ligands, two kinds of β[Mo8O26]4‑ anions, and three kinds of water molecues (Figure 3). Both Ag1 and Ag2 ions display similar distorted linear coordination geometries, which are completed by two N atoms from two different Tipa ligands, with the N4−Ag1−N12 and

X-ray Crystallography. Experimental details of the X-ray analyses are provided in Table 1. Single-crystal X-ray diffraction data for complex 1 was recorded on a Oxford Diffraction Gemini R Ultra diffractometer at a temperature of 293(2) K, using a ω scan technique with Cu Kα radiation (λ = 1.541 84 Å). Complex 2 was recorded on a Oxford Diffraction Gemini R Ultra diffractometer at a temperature of 293(2) K, using a ω scan technique with Mo Kα radiation (λ = 0.710 73 Å). The structures of 1 and 2 were solved by the direct method of SHELXS-977 and refined by full-matrix least-squares techniques using the SHELXL-97 program.8 Non-hydrogen atoms were refined with anisotropic temperature parameters, and hydrogen atoms of the ligands were refined as rigid groups. The hydrogen atoms of the water molecules O1W in 1 and O1W and O3W in 2 were not located from the difference Fourier maps. The Ag1 and Na1 atoms of 1 were refined with the same site, xyz and Uij parameters by using the EXYZ, EADP, and FVAR constraints, and their occupancies were refined freely. In the final refinement, the occupancies for Ag1 and Na1 are 0.516(11) and 0.484(11), respectively. The refinement was further suggested by the ICP analysis.

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RESULTS AND DISCUSSION [Ag0.52Na0.48(β-Mo8O26)(H2O)][Ag3(Tipa)2] (1). Single crystal X-ray analysis reveals that 1 is made up of two kinds of species: 1D chain and 1D ladder. The asymmetric unit of 1 contains one and two halves of Ag(I) ions, one Tipa ligand, half a β-[Mo8O26]4‑ polyoxoanion, and half a coordinated water molecule (Figure 1). Interestingly, there are two types of coordination environments around the Ag(I) ions in the crystal structure. The unique Ag1 is five-coordinated by four O atoms 2273

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Figure 3. ORTEP figure of 2 (displacement ellipsoids drawn at the 30% probability level). (Symmetry codes: #1, −x + 1, −y + 1, −z + 2; #2, x, y − 2, z + 1; #4, −x, −y + 2, −z.)

N1−Ag2−N14 angles being 176.74° and 164.92 o, respectively. Nevertheless, the Ag3 ion is four-coordinated by two N atoms from two Tipa ligands, and two O atoms from one β[Mo8O26]4‑ polyanion in a distorted tetrahedral geometry. It is worth noting that there is a long, weak interaction between Ag3 and OW3 (3.106 Å). The distortion of the tetrahedral geometry is likely attributed to this long, weak interaction. The Ag(I) atoms are linked by the two Tipa ligands into a 2D Ag-Tipa sheet (Figure 4). Further, the β-[Mo8O26]4‑ polyanions

Figure 2. (a) View of the single inorganic anion chain in 1. (b) View of the cationic 1D ladder of [Ag3(Tipa)2]3+. (c) View of the 1Dchain + 1Dladder → 3Dpoly‑pseudorotaxane framework. (d) Schematic representation of the 1Dchain + 1Dladder → 3Dpoly‑peseudorotaxane framework.

Figure 4. View of the 2D Ag-Tipa sheet of 2.

Scheme 1. Different Entangled Modes of Compounds 1 (Left) and 3 (Right)

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entanglement of 3D motifs is rarely observed in the area of POMs. Up until now, although three 2D → 2D → 3D examples have been reported, their frameworks are constructed from 44 or 63 layers.8−10 Therefore, compound 2 is a unique 2D → 2D → 3D polycatenated motif containg simple 83 layer. On the other hand, compounds 1 and 2 are entirely different from our just reported compound [Ag3(OH)(H2O)2(Tipa)2.5][Mo2O7]·4.5H2O (4).2a That reported compound 4 contains a record 54 interpenetrating 103-srs networks.2a Although the reaction compositions of these three compounds are the same, their ratios and pH values are completely different, which are the key factors for the formation of these three diverse frameworks. Luminescent Properties. The emission spectrum of 1 exhibits an emission at 416 nm upon excitation at 330 nm, which is slightly blue-shifted 4 nm compared with the Tipa ligand (λex = 365 nm and λem = 420 nm)2j (Figure 6).

pillar two adjacent Ag-Tipa layers through Ag−O interactions to generate a 2D double undulating layers with the thickness of 13.928 Å (Figures 5a and S1). The layer exhibits rectanglar

Figure 6. Emission spectrum of 1 at room temperature.

Therefore, the emission peak of 1 may be assigned to the intraligand fluorescent emission. The small blue shift of luminescence is likely to be from electronic energy level changes upon coordination to the metal.

Figure 5. (a) View of the 2D double undulating layer of 2. (b) Schematic representation of the 2D 3-connected 83 net of 2. (c) Schematic representation of 2-fold 2D → 2D interpenetrating layer. (d) View of the 2D → 2D → 3D framework of 2.

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CONCLUSION

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ASSOCIATED CONTENT

In conclusion, two unusual POMs-based entangled motifs, 1D + 1D → 3D poly-pseudo-rotaxane and 2D → 2D → 3D polycatenation, have been synthesized at different pH values. The completely different topological features of 1 and 2 indicate that the different pH values play a crucial role in the formation of their final architectures. The successful preparation of 1 and 2 may provide a valuable clue in entangled systems.

windows (25.28 × 34.53 Å2) built up by six Ag atoms and six Tipa ligands. These windows are very large, which allows the adjacent layers to interpenetrate and catenate in an unusual parallel fashion. Each isolated β-[H2Mo8O26]2‑ polyanion acts as a counterion. If the Ag1 ion, Ag3 ion, and [Mo8O26]4‑ anion are considered as connecters, and Tipa ligand and Ag2 ion are considered as 3connected nods, the topology of the double layer can be simplified as a 3-connected 83 net (Figure 5b). Pairs of sheets interpenetrate each other in a parallel fashion, and the mean planes of them are parallel and coincident to result in a 2-fold 2D → 2D interpenetrating layer (defined as basic 2-fold layer as shown in Figure 5c). The unusual topological feature of 2 consists of the 2-fold interpenetrated layer, which is further catenated to the two adjacent such sheets in parallel fashion (average planes diplaced about 5 Å in the normal direction) to give an overall unique (2D → 3D) polycatenated framework (Figure 5d). In the resulting array, each layer is interlocked with five others, with one on the same average plane, plus two of the four interpenetrated “above” and two “below” layers. This type of

S Supporting Information *

X-ray crystallographic data (CIF). Selected bond lengths and angles. Figure for the structure of 2. 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] (J.Y.); jianfangma@ yahoo.com.cn (J.-F.M.). Notes

The authors declare no competing financial interest. 2275

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Ciani, G.; Proserpio, D. M. Cryst. Growth Des. 2004, 4, 29. (c) Guo, H.; Qiu, D.; Guo, X.; Batten, S. R.; Zhang, H. CrystEngComm 2009, 11, 2611.

ACKNOWLEDGMENTS We thank the National Natural Science Foundation of China (Grant 21071028, 21001023), the Science Foundation of Jilin Province (20090137, 20100109), the Fundamental Research Funds for the Central Universities, and the Specialized Research Fund for the Doctoral Program of Higher Education for support.

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