Stoichiometry of N-Donor Ligand Mediated Assembly in the ZnII

ARTICLE pubs.acs.org/crystal

Stoichiometry of N-Donor Ligand Mediated Assembly in the ZnII-Hfipbb System: From a 2-Fold Interpenetrating Pillared-Network to Unique (3,4)-Connected Isomeric Nets Ya-Pan Wu,†,‡ Dong-Sheng Li,*,†,§ Feng Fu,‡ Wen-Wen Dong,†,§ Jun Zhao,† Kun Zou,† and Yao-Yu Wang*,§ †

College of Mechanical & Material Engineering, Research Institute of Materials, China Three Gorges University, Yichang 443002, China Department of Chemistry and Chemical Engineering, Shaanxi Key Laboratory of Chemical Reaction Engineering, Yan0 an University, Yan0 an, Shaanxi 716000, China § Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Department of Chemistry, Northwest University, Xi'an 710069, China ‡

bS Supporting Information ABSTRACT: In this contribution, we devote our effort to explore the effect of stoichiometry of the 4,40 -dipyridylsulfide (dps) ligand on the final structures in the ZnII-hfipbb binary system (H2hfipbb = 4,40 -(hexafluoroisopropylidene)bis(benzoic acid)). The solvothermal reaction of zinc acetate and H2hfipbb with the different stoichiometries of dps from 0.1 to 0.4 mmol has resulted in three new coordination polymers, [Zn(hfipbb)(H2hfipbb)0.5]n (1) and [Zn2(hfipbb)2(dps)(H2O)]n (2a and 2b). The structure determination reveals that complex 1 displays a three-dimensional (3D) 2-fold parallel interpenetrating pillared-layer network with one-dimensional double leftand right-handed helical tubes. Complexes 2a and 2b are framework-isomeric as two unusual (3,4)-connected 3D coordination networks, i.e., a 4-nodal (7 3 82)(4 3 7 3 9)(72 3 84)(4 3 72 3 8 3 92) net and 2-fold interpenetrating (83)2(85 3 10) net. In addition, the properties of thermogravimetric analysis, X-ray powder diffraction, and photoluminescent behaviors of the complexes have been also discussed.

’ INTRODUCTION The crystal engineering of coordination polymers and metallosupramolecular architectures has not only gained great recognition as an important interface between synthetic chemistry and materials science but also provides a solid foundation to understand how molecules can be organized and how functions can be achieved.1,2 Recently, an important motivation for crystal engineering is the rational design and preparation of crystalline solid material with peculiar topology and desired functions. Thus, much effort has been directed toward the investigation of their controllable synthesis.3 Although the earlier predesign and assembly of novel crystalline material by structure-directing factors, such as central metal ions, positional isomeric ligands, metalligand ratio, solvents, temperature, pH value, counterions, and templates, have been validated and summarized,46 there have been few reports about the single factor of stoichiometry of N-donor ligand mediating structure variability in a binary system so far. With this understanding, one crucial aim of this work is to explore the essential factors of the stoichiometry of the N-donor ligand for regulating the structural assembly, which might provide further insights in designing new hybrid crystalline materials. In general, the effective strategy for the assembly of variable topological networks is to use metal centers with suitable geometry and connectivity as the nodes in virtue of a rational r 2011 American Chemical Society

design of organic spacers.7 In this regard, the organic building blocks with special geometry, such as T-shaped,8 tripodal shape,9 and rectangular ligands,10 can serve as excellent candidates to construct such frameworks. Very recently, by using the V-shaped polycarboxylates tectons, we have successfully obtained the first armed-polyrotaxane one-dimensional (1D) array based on loop chains with side arms,11 a series of Co(II) or Mn(II) supramolecular complexes, one three-dimensional (3D) (4,5)-connected Pb(II) coordination network, and unique 3D 6-connected and 8-connected self-catenated coordination networks.12 As an extension of our previous work, herein, we choose the combination of V-shaped H2hfipbb and zinc acetate as a precursory binary system, and focus on the effect of stoichiometry of 4,40 -dipyridylsulfide (dps) on mediating the conditions of crystallization and further influencing the superstructures of the crystal seeds under solvothermal synthesis conditions. Utilizing this strategy, three new coordination polymers [Zn(hfipbb)(H2hfipbb)0.5]n (1) and [Zn2(hfipbb)2(dps) (H2O)]n (2a and 2b) were obtained, which display a 3D 2-fold parallel interpenetrating pillared-layer framework (for 1) and the unique (3,4)-connected isomeric nets, i.e., 4-nodal (7 3 82)(4 3 7 3 9)(4 3 72 3 8 3 92)(72 3 84) net and 2-fold Received: March 27, 2011 Revised: June 23, 2011 Published: July 15, 2011 3850

dx.doi.org/10.1021/cg200389q | Cryst. Growth Des. 2011, 11, 3850–3857

Crystal Growth & Design

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Table 1. Crystal Data and Structure Refinement Parameters of the Complexes 12b complex

a

1

2a

2b

empirical formula

C25.50H13F9O6Zn

C44H26F12N2O9SZn2

C44H26F12N2O9SZn2

formula weight

651.73

1117.47

1117.47

crystal system

monoclinic

monoclinic

monoclinic

space group

P2/c

P21/n

C2/c

a/Å

18.820(16)

12.3826(5)

24.768(4)

b/Å

7.292(6)

13.7119(5)

13.071(2)

c/Å

23.444(15)

26.2216(10)

27.906(4)

R/° β/°

90 123.17(5)

90 92.0750(10)

90 97.138(2) 90

γ/°

90

90

V/Å3

2693(4)

4449.2(3)

8964(2)

Z

4

4

8

T/K

293(2)

296(2)

296(2)

F(000)

1312

2240

4480

Dc/Mg m3

1.607

1.668

1.656

μ/mm1 reflections collected/unique

1.013 22295/4726

1.234 22492/7920

1.225 23473/7993

data/restraints/parameters

9039/0/775

7920/16/647

7993/939/612

goodness-of-fit on F2

1.031

1.044

0.998

R1a, wR2b [I > 2σ(I)]

0.0987, 0.2914

0.0511,0.1576

0.0528, 0.1254

R1 = Σ(|Fo||Fc|)/Σ|Fo|. b wR2 = [Σw(Fo2 Fc2)2/Σw(Fo2)2]1/2.

interpenetrating (83)2(85 3 10) net (for 2a and 2b), respectively. Moreover, X-ray powder diffraction (XRPD), thermogravimetric analysis (TG), and photoluminescent behaviors for three complexes have also been studied.

’ EXPERIMENTAL SECTION Materials and General Methods. All the solvents and reagents for synthesis were commercially available and used without further purification. All syntheses were carried out in 25 mL Teflon-lined autoclaves under autogenous pressure. Elemental analyses (C, H, and N) were recorded on an Elementar model VarioEL III instrument. Infrared spectra of KBr pellets were recorded with a BRUKER EQUINOX-55 spectrometer in the range 4000400 cm1. Thermal analysis were determined with a Netzsch STA 449C microanalyzer under a flowing N2 atmosphere at a heating rate of 10 °C min1. The powder X-ray diffraction (PXRD) patterns were recorded with a Rigaku D/MAX-3C diffractometer. Luminescence spectra for the solid samples were recorded with a Hitachi F-4500 fluorescence spectrophotometer at room temperature. Preparation of Complexes 12b. [Zn(hfipbb)(H2hfipbb)0.5]n (1). A mixture of Zn(OAc)2 3 2H2O (0.4 mmol, 0.0880 g), H2hfipbb (0.4 mmol, 0.1570 g), dps (0.1 mmol, 0.0190 g), H2O (12 mL), CH3OH (4 mL), and 2.0 M KOH (0.4 mL) solution was stirred under air atmophere for half an hour. The solution was placed in a Teflon-lined stainless steel vessel (25 mL), the vessel was sealed, and the mixture was heated to 140 °C and held at that temperature for 72 h. By slow cooling of the reaction mixture to room temperature, colorless block crystals were obtained with a yield of 53% based on ZnII. Elemental analysis (%): Calcd. for C25.5H13F9O6Zn: C, 46.99; H, 2.01. Found: C, 46.75; H, 2.11%. IR (KBr pellet, cm1): 1725w, 1618s, 1562m, 1506w, 1429w, 1375s, 1249s, 1211s, 1169s, 935m, 845s, 781m, 723s, 656w, 572m. [Zn2(hfipbb)2(dps) (H2O)]n (2a and 2b). The same synthetic method as that of 1 was used except that the amounts of dps ligand are 0.2 and 0.4 mmol, respectively. Yield: 52% (for 2a) and 55% (for 2b) based on ZnII. Anal. Calc. for 2a C44H26F12N2O9SZn2: C, 53.41; H,

4.48; N, 6.23. Found: C, 53.01; H, 4.89; N, 6.07%. IR KBr pellet, cm1): 3383s, 3037m, 2937m, 1953w, 1864w, 1645m, 1603s, 1566s, 1487m, 1400s, 1378s, 1291m, 810m, 719m, 584m. Anal. Calc. for 2b C44H26F12N2O9SZn2: C, 53.41; H, 4.48; N, 6.23. Found: C, 53.15; H, 4.75; N, 6.06%. IR KBr pellet, cm1): 3400s, 3020m, 2850m, 1935w, 1858w, 1640m, 1600s, 1558s, 1480m, 1395s, 1370s, 1285m, 800m, 725m, 580m. X-ray Crystallography. Single crystal X-ray diffraction analyses of 12b were carried out on a Bruker SMART APEX II CCD diffractometer equipped with a graphite monochromated MoKR radiation (λ = 0.71073 Å) by using j/ω scan technique at 293(2) K (for 1) and 296(2) K (for 2a and 2b). The structures were solved by the direct method using SHELXTL and refined by a full-matrix least-squares method on F2 with the SHELXL-97 program.13 Absorption corrections were applied by using multiscan program SADABS.13d All the non-hydrogen atoms were refined anisotropically. The hydrogen atoms of the carbons were generated theoretically onto the specific atoms and refined isotropically with fixed thermal factors. Other hydrogen atoms of water molecules and hydroxyl hydrogen atoms were located directly from difference Fourier maps and refined with isotropic displacement parameters. As for complex 1, PLATON reveals the presence of solvent accessible voids in the crystal lattice, indicating solvent occupancy. However, the highly disordered lattice water molecules were not located and included in structure refinements. Additionally, the crystal data of 1 show a higher residual electron density peak (more than 3.0 e Å3). Thus, we tried absorption correction but without obvious improvement. The final cycle of full-matrix least-squares refinement made the highest residual electron density peak decrease to 2.964 e Å3 with a completeness of 99.2%, R1 = 0.0987, and wR2 = 0.2914. Checking the resulting .cif file by the checkCIF program shows no A alerts but suggested that this treatment has an effect on the precision of bond lengths and angles, leading to the low bond precision on CC bonds. The slightly higher R value of 1 may be attributed to the small measurable crystals and the relatively bad quality of data. As for complexes 2a and 2b, the disordered S1 atom of complex 2a and disordered O5 atom of complex 2b were refined using S and O atoms split over two sites, with a total occupancy of no more than 3851

dx.doi.org/10.1021/cg200389q |Cryst. Growth Des. 2011, 11, 3850–3857


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Scheme 1. Series of Comparable Reactions Adjusted by Different Stoichiometries of the dps Ligand

1. The crystallographic data and selected bond lengths and angles for 12b are listed in Tables 1 and S1S3, Supporting Information. Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Center, CCDC reference numbers: 814772814774.

’ RESULTS AND DISCUSSION Synthesis and General Characterization. Complexes 12b were obtained as polymeric substances in methanol/distilled water (V/V = 1:3) mixed solution by a combination of H2hfipbb/ Zn(OAc)2 3 2H2O in the presence of dps ligand via a solvothermal approach. Try to explore different stoichiometries of N-donor ligand mediation on the assembly and structural variability, a series of solvothermal reactions as shown in Scheme 1 were attempted to disclose the crucial factor from it. When the molar ratios of Zn/H2hfipbb/dps are adjusted to 1:1:0, 1:1:0.75, and 1:1:1.5 or much higher, only the precipitates were obtained. For further determine these precipitates, the powder X-ray diffraction (PXRD) of three unknown deposits were recorded at room temperature. Compared to the simulated diffraction patterns of crystalline 1, 2a, and 2b, the PXRD patterns of these precipitates show a distinct difference; moreover, the peak shape and intensity of the deposits i and ii are similar but different from iii (Figure S1, Supporting Information). Meantime, the solid UVvis absorption spectra of these precipitates show that the deposits i and ii appear to have a similar wide absorption band and iii occurs with a relatively strong absorption band in the range of 240340 nm (Figure S2, Supporting Information). The above facts imply that three unknown deposits i, ii, and iii display two new phases different from complexes 1, 2a, and 2b. In addition, varying the reaction parameters such as the temperature, the cooling speed, and the solvent system has not succeeded in the formation of product suitable for single crystal X-ray diffraction analysis. Noteworthy is that the use of Zn(NO3)2 3 6H2O or ZnCl2 3 4H2O instead of Zn (OAc)2 3 2H2O, employing the same synthetic strategy as for preparation of 1, 2a, and 2b, also results in a crystalline substance for single-crystal X-ray diffraction. Their crystallographic cell data (a, b, c, R, β, γ) are identical to that for complexes 1, 2a, and 2b. The results indicate that the product structures weakly depend on the nature of the zinc counteranions. So we could conclude here that the dps ligand might act as buffering additives to the metal ions and influence the superstructures of the crystal seeds, which lead to the formation of different topological networks. The IR spectra of all complexes were performed by KBr pellets in the range of 4000400 cm1. The spectra show characteristic

absorption bands mainly attributable to the carboxylate groups stretching vibrations. The spectrum of complex 1 exhibits a strong band at ∼1720 cm1, assignable to the protonated carboxylate group of H2hfipbb ligand, which can also be validated by the crystal structures. The broad bands centered at ca. 3400 cm1 indicate the OH stretching of water for complexes 2a and 2b. The spectra show characteristic absorption bands mainly attributable to the carboxylate groups stretching vibrations. The samples all display a strong absorption in the range of ∼1600 1550 cm1, which may be assigned to the asymmetric stretching vibrations of the carboxylate group, and the strong bands at about ∼14201370 cm1 are attributed to the symmetric stretching vibrations. Description of Crystal Structures. [Zn(hfipbb)(H2hfipbb)0.5]n (1). Single-crystal X-ray crystallography reveals that 1 is a 3D 2-fold interpenetrating pillared network based on paddle-wheel [Zn2(COO)4] SUB, and its asymmetric unit contains one ZnII ion with an inversion center, one complete deprotonated hfipbb2 ligand, and half of a protonated H2hfipbb ligand. As shown in Figure 1a, two five-coordination ZnII ions are engaged by four carboxyate groups (μ2-η1:η1-C(10)OO/C(10A)OO/C(24B)OO/C(24C)OO, symmetry codes: A 1 x, 1 y, z; B x, y, 0.5 + z; C 1 x, 1 + y, 0.5 z) from two hfipbb2 ligands into the binuclear paddle-wheel [Zn2(COO)4] SUB, with an average ZnO/nonbonding Zn 3 3 3 Zn distance of 1.964(3)/2.649(3) Å, respectively. Whereas the axial positions of the paddlewheel are occupied by the O (η1-O(1) of μ1η1:η0-C(1)OO) atom of H2hfipbb ligands with a ZnO distance of 2.223(4) Å. All these structural parameters fall into the normal range.14 In 1, two crystallographically independent hfipbb2/H2hfipbb ligands display two different coordination modes: μ4-η1:η1:η1:η1 (Scheme 2a) and μ2-η1:η1:η0:η0 (Scheme 2b), respectively. First, μ4-hfipbb2 anions (μ2-η1:η1-C(10)OO/μ2-η1:η1-C(24)OO) link these paddlewheel ZnIISUBs into an undulating (4,4) layered network along the (010) plane with alternant helical chains by sharing the paddlewheel SBUs (Figure 1b), in which the pitch of helix is about 14.584 Å based on paddlewheel cores. Second, μ2-H2hfipbb ligands extend such a helical layer to yield a 3D pillared framework (Figure 1c). Remarkably, owing to the presence of enough space, two such frameworks are interweaved into a 2-fold interpenetrating array (Figure 1d). Despite interpenetration, the framework of 1 remains 1D open helical channels with the dimensions of the quadrate window 11.193 Å 13.805 Å (Figure 2a), which are formed by intertwining hetero helical chains from two different 3D frameworks (Figure 1d). The potential solvent-accessible volume is as large as 325.2 Å3, 3852



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Figure 1. (a) Coordination environment of the ZnII center of 1 (symmetric codes: A, 1 x, 1 y, z; B, x, y, 0.5 + z; C, 1 x, 1 + y, 0.5 z). (b) View the undulating (4,4) layered network along the (010) plane with alternant helical chains by sharing the paddlewheel SBUs. (c) View of the 3D pillared-layer network sustained by μ2-H2hfipbb ligands. (d) View of the simplified 3D 2-fold interpenetrating array.

which approximately corresponds to 12.1% of the crystal volume (2693.0 Å3), as calculated by the PLATON software.15 Topologically, by regarding each paddle-wheel [Zn2(COO)4] cluster as a 6-connected node, the overall 3D framework can be rationalized as 2-fold interpenetrating 6-connected pcu nets (Figure 2b). Although we have noticed that most examples of pcu nets are constructed by a paddle-wheel unit, which is always formed by four μ2-bridging carboxylate linkers and linear Ndonor ligands,16 complex 1 is the novel example that has the classical pcu topology generated by six μ2-bridging carboxylate linkers furnishing a paddle-wheel [Zn2(COO)4] unit. [Zn2(hfipbb)2(dps) (H2O)]n (2a and 2b). When the molar ratios of Zn/H2hfipbb/dps are adjusted to 1:1:0.5 and 1:1:1, two isomeric coordination frameworks 2a and 2b were obtained. Structural analysis reveals that two complexes crystallize in different space groups and display isomerical (3,4)-connected topological skeletons, viz. P21/n space group and 4-nodal net for 2a vs C2/c space group and 2-nodal net for 2b. The asymmetric unit of 2a and 2b contains two crystallographically unique ZnII ions, two hfipbb2 anions, one dps ligand, and one coordinated water molecule (Figure 3). In 2a, each Zn1 atom locates in a distorted octahedral coordination environment [ZnO5N], while the Zn2 atom affords a trigonalbipyramidal coordination geometry [ZnO4N] (Figure 3a); in contrast, within 2b, the Zn1 and Zn2 centers bear a similar tetrahedral coordination environment [ZnO3N], in which all ZnII ions are surrounded by hfipbb2, dps and water molecules (Figure 3b). All the ZnO (1.904(3)1.982(3) Å for 2a; 1.965(3)2.094(2) Å for 2b) and ZnN (2.044(4)2.050(5) Å for 2a; 2.084(3)2.162(3) Å

for 2b) lengths and bond angles around ZnII (94.11(2) 132.53(16) for 2a; 60.95(10)169.60(11) for 2b) fall into the normal range (Tables S2 and S3, Supporting Information). In 2a and 2b, the hfipbb2 ligands are completely deprotonated, showing three kinds of coordination modes, μ3-hfipbb22a1: μ1-η1:η1-C(1)OO/μ2-η1:η1-C(17)OO; μ3-hfipbb2-2a2: μ1- η1:η1-C(34)OO/μ2-η1:η1-C(18)OO for 2a (Scheme 2c) and μ2-hfipbb2: μ1-η1:η0-C(18)OO/μ1- η1:η0-C(32)OO; μ3-hfipbb2:μ1-η1:η0-C(1)OO/μ2-η1:η1-C(15)OO for 2b (Scheme 2d,e). While the secondary dps ligand of 2a and 2b both act as the head-to-end 2-connected spacer. In such a ligating manner, the ZnII centers of 2a and 2b are connected by the hfipbb2 and dps ligands to generate two complicated 3D isomeric frameworks (Figure 4). Recently, many reported complexes have been claimed as supramolecular isomers, but, in fact, a large number of them are based on the coexistence of different guest molecules; thus, it would be more suitable to categorize these coordination polymers as pseudopolymorphs rather than true isomers (i.e., polymorphs).17,18 Therefore, different classes of supramolecular isomers have been envisaged: terms such as “structural isomers”,1,19 “conformational isomers”,1 “catenane isomers”,1 “topological isomers”,20 “ring-opening isomers”21 and others have been adopted to describe specific situations. In this regard, complexes 2a and 2b display a pair of genuine structural isomers. The most remarkably structural feature in 2a and 2b is that they both possess the 3D complicated frameworks but display two new (3,4)-connected topologies. In 2a, the network topology can be derived by considering each μ3-hfipbb2 ligand as a 3-connected node (Zn1 + 2Zn2 for μ3-hfipbb2-2a1; 3853



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Scheme 2. The Coordination Modes of H2hfipbb Ligand in Complexes 12b

Figure 2. (a) View of 2-fold parallel interpenetration containing 1D double left- and right-handed helical tubes with a quadrate window of 1. (b) Schematic representation of the six-connected 2-fold interpenetrating pcu nets of 1 (the single networks are shown by yellow and blue lines).

2Zn1 + Zn2 for μ3-hfipbb2-2a2) and each ZnII atom as a 4-connected node. The resulting (3,4)-connected 4-nodal lattice

has a (4 3 7 3 9)(7 3 82)(72 3 84) (4 3 72 3 8 3 92) topology (Figure 5a), with an extended point symbol of (4.72.92 for μ3-hfipbb2-2a2) (7.8.82 for μ3-hfipbb2-2a1)(7.7.8.8.8.8 for Zn1)(4.7.7.82.9.9 for Zn2). Different from 2a, for 2b, topological analysis with TOPOS revealed a doubly interpenetrated (3,4)-connected binodal lattice with (83)2(85 3 10) topology, based only on 8- and 10-membered circuits (Figure S3, Supporting Information, Figure 5b). Although many (3,4)-connected networks in coordination polymers have been reported,3f,g,22 to the best of our knowledge, 2a and 2b define two new (3, 4)-connected network topologies but also represent the first example of two real topological isomers mediated by the stoichiometry of an N-donor ligand in a metal-carboxylate binary system. For inspecting the “voids” of 2a and 2b, considerable void space is evaluated for 2a with a volume of 102.0 Å (2.3% of the unit cell volume) and 2b with a volume of 148.6 Å (1.7% of the unit cell volume) using PLATON,15 which indicates interpenetrating occurrence could obviously reduce the accessible volumes of the crystalline materials. As discussed above, we found that, in the ZnII-hfipbb system, the coordination modes of the hfipbb2 ligands and the final topological networks are determined by the different stoichiometries of the dps N-donor ligand: in complex 1, when the molar ratios of Zn/H2hfipbb/dps are adjusted to 1:1:0.25, the H2hfipbb 3854



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Figure 3. (a) Coordination environment of ZnII center of 2a. (symmetric codes: A, 0.5 x, 0.5 + y, 1.5 z; B, 0.5 + x, 0.5 y, 0.5 + z; C, x, 1 + y, z; D, 0.5 + x, 0.5 y, 0.5 + z). (b) Coordination environment of ZnII center of 2b. (symmetric codes: A, 0.5 + x, 0.5 + y, z; B, 0.5 + x, 1.5 + y, z; C, x, y, 0.5 + z).

Figure 4. (a, b) View of the complicated 3D isomeric frameworks of 2a and 2b along the b axis. All the hydrogen atoms and fluorin-substitute methyl’s groups were omitted for clarity.

ligands are partially deprotonated and take μ4-η1:η1:η1:η1 and μ2-η1:η1:η0:η0 coordination modes (Scheme 2a,b), resulting in the 2-fold interpenetrating 6-connected pcu net, while in 2a and 2b, the stoichiometry of the dps ligand was successively twice as much; the H2hfipbb ligands are completely deprotonated and adopt three kinds of coordination modes, μ3-η2:η1:η1:η0 for 2a (Scheme 2c) and μ2-η1:η1:η0:η0, μ3-η1:η1:η1:η0 for 2b (Scheme 2d,e), respectively, leading to the unique isomeric (3,4)-connected nets, i.e., 4-nodal (7 3 82)(4 3 7 3 9)(4 3 72 3 8 3 92)(72 3 84) net and 2-fold interpenetrating (83)2(85 3 10) net. Although the earlier predesign and assembly of factors-controlled structural diversities (such as central metal ions, positional isomeric ligands, metalligand ratio, solvents, temperature, pH value, and counterions) have been investigated, its studies are still relatively less developed, and to our best knowledge, there are few reports about the single factor of stoichiometry of N-donor ligand mediated structure variability in the binary system, so far. Photoluminescence Spectroscopy. Currently, luminescent inorganicorganic hybrid complexes are of great interest because of their various potential applications in chemical sensors, photochemistry, electroluminescent (EL) displays, and light-emitting

diodes (LEDs).2325 Therefore, the solid-state photoluminescent spectra of complexes 1, 2a, and 2b, as well as free ligand were measured at room temperature, as depicted in the Supporting Information (Figures S4S7, Supporting Information). The free ligand H2hfipbb exhibits an emission maximum at 362 nm upon excitation at 321 nm (Figure S7, Supporting Information), while no clear luminescence was detected for dps ligand at room temperature. As shown in Figure 6, the main emission peaks of complexes 1, 2a, and 2b were observed at 468 nm (λex = 330 nm) for 1, 451 nm (λex = 345 nm) for 2a, and 439 nm (λex = 340 nm) for 2b. The emissions of complexes 1, 2a, and 2b show a small red shift compared with that of the H2hfipbb ligand, and they are all probably attributed to the ligand-to-metal charge transfer (LMCT).26 Accordingly, the spectral differences between 2a and 2b are intrinsic and could plausibly be due to the aforementioned structural variation. The red shift of emission in 2a can be tentatively rationalized by its robust 3D framework compared to 2b.27 This result might indicate that structural isomerism could not only affect the rigidity of structures but also modulate the transfer of energy effectively from ligands to the metal centers. Thermal Gravimetric Analysis and XRPD Measurement. Powder X-ray diffraction (PXRD) was used to confirm the phase 3855



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Figure 5. (a) Schematic description of the 4-nodal (3, 4)-connected net with the (4 3 7 3 9) (7 3 82) (72 3 84)(4 3 72 3 8 3 92) topological notation, constructed from the 3-connected hfipbb2 and 4-connected center nodes (green: Zn1 nodes; cyan: Zn2 nodes; orange: μ3-hfipbb2-2a1 nodes and fawn: μ3-hfipbb2-2a2 nodes). (b) Schematic representation of the 3D 2-fold interpenetrating (3,4)-connected network of with the (83)2(85 3 10) topology of 2b (the single network are shown by green and blue lines).

presented, which show a 3D 2-fold parallel interpenetrating pillared network and two unique (3,4)-connected 3D isomeric nets. Their structural variability should originate from the intrinsic characterization of zinc ions as well as the organic ligands with adaptable existing forms, coordination fashions, and conformations. Of further importance, the ZnII-hfipbb binary system is observed to show the specific sensitivity to the stoichiometry of the N-donor ligand. This interesting observation prompts us to further develop the rational synthetic strategy to obtain new crystalline materials via an appropriate external stimulus.

’ ASSOCIATED CONTENT Figure 6. The emission spectra of 1, 2a, and 2b in the solid state at room temperature.

purity of bulk materials of 12b at room temperature (see Figures S8S10, Supporting Information). Although the experimental patterns show several un-indexed or slightly broadened diffraction peaks in comparison to those simulated from the single-crystal data, it can still be regarded that the bulk of the assynthesized materials represent the pure phases of complexes 12b. There was no evidence of crystal decay during X-ray data collection for complexes 12b, which is stable at ambient conditions. Thus, thermogravimetric analyses (TGA) were carried out under N2 atmosphere to examine the thermal stability of complexes 12b (see Figures S11 and S12, Supporting Information). For 1, there are no lattice and coordination water molecules, and decomposition of the organic components occurs at about 300 °C. For 2a, the weight loss attributed to the gradual release of coordinated water molecules is observed in the range 80120 °C (obsd: 1.55% and calcd: 1.61%). For 2b, it loses coordination water molecules from 85 to 130 °C (obsd: 1.57% and calcd: 1.61%), and the anhydrous composition is stable up to 250 °C.

’ CONCLUSIONS In summary, three new ZnII coordination polymers based on fluorinated carboxylicate tecton, in the presence of different stoichiometries of 4,40 -dipyridylsulfide(dps) ligand, have been

bS

Supporting Information. X-ray crystallographic files in CIF format, selected bond lengths and bond angles, solid-state luminescent spectra, TGA curves, experimental and calculated powder XRD patterns, and other supplementary figures for free ligand, complexes 1, 2a, and 2b. This material is available free of charge via the Internet at http://pubs.acs.org/.

’ AUTHOR INFORMATION Corresponding Author

*(D.-S.L.) E-mail: [email protected]. Tel./Fax: +86-7176397516. (Y.-Y.W.) E-mail: [email protected]. Tel./Fax: +86-29-88303098.

’ ACKNOWLEDGMENT This work was financially supported by the NSF of China (20773104, 21073106), the NSRF of Shaanxi Provincial Education Office of China (2010JK903), and the IPHPEO (Z20091301 and Q20101203). ’ REFERENCES (1) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101, 1629. (2) (a) Morsali, A.; Masoumi, M. Y. Coord. Chem. Rev. 2009, 253, 1882. (b) Zeng, M. H.; Wang, Q. X.; Tan, Y. X.; Hu, S.; Zhao, H. X.; Long, L. S.; Kurmoo, M. J. Am. Chem. Soc. 2010, 132, 2561. (3) (a) Min, K. S.; Suh, M. P. J. Am. Chem. Soc. 2000, 122, 6834. (b) Kondo, S.; Kitagawa, M.; Seki, K. Angew. Chem., Int. Ed. 2000, 39, 414. 3856


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