Article pubs.acs.org/crystal
Two Unusual Chiral Lanthanide−Sulfate Frameworks with Helical Tubes and Channels Constructed from Interweaving Two DoubleHelical Chains Wen-Hua Wang, Han-Rui Tian, Zhi-Chao Zhou, Yun-Long Feng, and Jian-Wen Cheng* Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical Chemistry, Zhejiang Normal University, Jinhua, Zhejiang, 321004, People's Republic of China S Supporting Information *
ABSTRACT: Two novel chiral lanthanide−sulfate frameworks, Ln4(OH)4(SO4)4(H2O)3 [Ln = Y (1) and Er (2)], have been synthesized under hydrothermal reactions. X-ray crystal structure analyses reveal that 1 and 2 are isomorphous and crystallize in the orthorhombic space group P2(1)2(1)2(1). Both compounds are isostructural and contain helical tubes and channels constructed from double left- and right-handed helical chains. Further structural analysis reveals that compound 1 is a high connected binodal net by assigning the SO42− anion as a three-connected node and the {Y4} cluster as a 12connected node. Furthermore, the infrared, thermogravimetric analysis, and powder X-ray diffraction properties were also studied.
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INTRODUCTION The synthesis and characterization of zeolites and zeolite-like materials have been of great interest due to their intriguing variety of topologies and potential applications in catalysis, separation, and host−guest assemblies.1−3 As a result, a large number of microporous inorganic frameworks such as silicates,4 phosphates,5 borates,6 and germanates7 have been reported. Recent interests have been focused on the sulfates to examine its difference between silicates and phosphates.8,9 Among these reported compounds, the chiral solids are relatively scarce. One of the strategies used for the design of such chiral solids materials is the selection of chiral structure-directing agents (SDAs), because the chirality of the SDAs can be transferred into the inorganic frameworks.10 Polynuclear lanthanide clusters have been used as connectors for high-connected lanthanide−organic frameworks.11,12 A common synthetic strategy toward higher polynuclear lanthanide clusters is to introduce auxiliary organic ligands to control the hydrolysis of lanthanide ions at “high” pH.13,14 In the absence of any organic supporting ligands, several examples of inorganic lanthanide clusters compounds have also been obtained.15 However, lanthanide clusters bridged by simple inorganic ions to form 3D inorganic networks remain largely unexplored.15 Accordingly, our aim is to synthesize 3D chiral lanthanide sulfate frameworks by using lanthanide clusters as building blocks. Here, we report the syntheses and structures of two novel chiral lanthanide−sulfate compounds of Ln4(OH)4(SO4)4(H2O)3 [Ln = Y (1) and Er (2)]. The structures of 1 and 2 not only contain helical tubes and channels constructed from double left- and right-handed helical © 2012 American Chemical Society
chains but also display high-connected binodal networks. To date, only a few 3D lanthanide sulfates have been structurally characterized as compared to the number of low dimensional lanthanide sulfates.8,9,16 These compounds represent good examples of using lanthanide clusters to construct fascinating chiral lanthanide−sulfate frameworks.
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EXPERIMENTAL SECTION
Materials and Methods. All chemicals were available commercially and used without further purification. The Fourier transform infrared (FT-IR) spectra (KBr pellets) were recorded on an Nicolet NEXUS670 spectrometer. Thermogravimetric analyses (TGA) were performed on a Netzsch STA 449C analyzer with a heating rate of 10 °C/min under an air atmosphere. Powder X-ray diffraction (PXRD) data were obtained using a Philips PW3040/60 diffractometer with Cu Ka radiation (λ = 1.54056 Å). Ln4(SO4)4(OH)4(H2O)3 [Ln = Y (1) and Er (2)]. A mixture of Ln2O3 (Y2O3, 0.5 mmol, 0.113 g; Er2O3, 0.5 mmol, 0.191 g), H2SO4 (0.7 mmol), D-camphoric acid (0.15 mmol, 0.03 g), and H2O (10 mL) was sealed in a 30 mL Telfon-lined bomb at 170 °C for 6 days and then slowly cooled to room temperature. Colorless prismatic crystals of 1 and pink prismatic crystals of 2 were obtained (yield, 42 and 36% based on H2SO4) (Figure S1 in the Supporting Information). The experimental PXRD patterns of compounds 1 and 2 match well with the simulated PXRD patterns of 1 and 2, and the difference in reflection intensities between the simulated and the experimental patterns was due to the variation in the preferred orientation of the powder sample during collection of the experimental PXRD data (Figure 1). Anal. calcd for Y4S4O23H10 (1): Energy-dispersive Received: February 5, 2012 Revised: March 20, 2012 Published: March 23, 2012 2567
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on the crystallographic data are given in the CIF (see the Supporting Information).
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RESULTS AND DISCUSSION Single crystals of 1 and 2 were obtained by hydrothermal reactions of Ln2O3, H2SO4, and D-camphoric acid (D-H2cam) in water at pH 1 and 170 °C. X-ray crystallographic studies revealed that 1 and 2 exhibit 3D chiral lanthanide−sulfate Table 2. Selected Bond Lengths (Å) for Compounds 1 and 2a Ln(1)−O(1) Ln(1)−O(18) Ln(1)−O(14A) Ln (1)−OW1 Ln (1)−O(2B) Ln(1)−O(15C) Ln(1)−O(17) Ln(1)−O(19) Ln(2)−O(12D) Ln(2)−O(5) Ln(2)−O(20) Ln(2)−O(9) Ln(2)−O(17) Ln(2)−O(8D) Ln(2)−O(18) Y(2)−-OW2 Ln(3)−O(11A) Ln(3)−O(17) Ln(3)−O(19) Ln(3)−O(10) Ln(3)−O(13) Ln(3)−O(20) Ln(3)−O(16A) Ln(4)−O(3E) Ln(4)−O(7E) Ln(4)−O(4B) Ln(4)−O(6D) Ln(4)−O(20) Ln(4)−O(19) Ln(4)−O(18) Ln(4)−OW3 S(1)−O(1) S(1)−O(3) S(1)−O(4) S(1)−O(2) S(2)−O(7) S(2)−O(5) S(2)−O(8) S(2)−O(6) S(3)−O(12) S(3)−O(11) S(3)−O(9) S(3)−O(10) S(4)−O(15) S(4)−O(13) S(4)−O(14) S(4)−O(16)
Figure 1. Simulated and experimental PXRD patterns of compounds 1 and 2. spectrometry (EDS) gives the Y/S molar ratio in 1 as 1.1:1 (calcd Y/S = 1:1). IR bands (cm−1) for 1: 3600 (vs), 3512 (w), 3325 (m), 1620 (m), 1149 (vs), 715 (s), 604 (s), 480 (w). Anal. calcd for Er4S4O23H10 (2): EDS gives the Er/S molar ratio in 2 as 1.1:1 (calcd Er/S = 1:1). IR bands (cm−1) for 2: 3600 (vs), 3504 (w), 3313 (w), 1627 (m), 1149 (vs), 722 (s), 612 (s), 479 (w). Single-Crystal Structure Determination. The intensity data were collected on a Bruker APEX II (1 and 2) with graphitemonochromated Mo Kα radiation (λ = 0.71073 Å) at room temperature. All absorption corrections were performed using the multiscan program. The structures were solved by direct methods and refined by full-matrix least-squares on F2 with the SHELXTL-97 program.17 The H atoms of water molecules and hydroxy H atoms in 1 and 2 have not been included in the final refinement. All atoms except H atoms were refined anisotropically. Further details for structural 1 and 2 analyses are summarized in Table 1, and selected bond lengths of compounds 1 and 2 are listed in Table 2. More details
Table 1. Crystal Data and Structure Refinement for Compounds 1 and 2 formula Mr crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (g cm−3) μ (mm−1) F(000) GOF collected reflns unique reflns (Rint) observed reflns [I > 2σ(I)] refined params R1a/wR2b [I > 2σ(I)] R1a/wR2b (all data) a
1
2
Y4S4O23H10 861.96 orthorhombic P2(1)2(1)2(1) 10.2608(4) 10.7516(4) 16.5684(6) 90.00 90.00 90.00 1827.83(12) 4 3.132 13.148 1656 1.092 15545 4246 (0.0484) 3820 282 0.0468/0.1112 0.0545/0.1151
Er4S4O23H10 1175.36 orthorhombic P2(1)2(1)2(1) 10.23400(10) 10.7014(2) 16.5476(3) 90.00 90.00 90.00 1812.26(5) 4 4.308 18.912 2120 1.240 13613 3347 (0.0382) 3304 281 0.0275/0.0615 0.0279/0.0616
1
2
2.292(6) 2.293(6) 2.330(7) 2.338(8) 2.342(7) 2.363(7) 2.411(6) 2.491(6) 2.251(7) 2.314(7) 2.318(6) 2.336(7) 2.345(6) 2.361(7) 2.379(6) 2.555(7) 2.251(7) 2.278(6) 2.293(6) 2.317(7) 2.341(7) 2.352(7) 2.459(7) 2.281(6) 2.288(6) 2.310(7) 2.339(6) 2.344(7) 2.372(6) 2.431(6) 2.501(7) 1.454(6) 1.456(7) 1.470(7) 1.478(7) 1.445(7) 1.450(7) 1.454(8) 1.491(7) 1.444(7) 1.454(7) 1.458(7) 1.469(7) 1.455(7) 1.469(6) 1.477(8) 1.486(7)
2.287(2) 2.2773(17) 2.331(2) 2.332(2) 2.345(2) 2.344(2) 2.3989(17) 2.4879(18) 2.247(2) 2.298(2) 2.3110(17) 2.329(2) 2.3432(18) 2.338(2) 2.3593(17) 2.5404(19) 2.241(2) 2.2673(19) 2.2870(17) 2.3070(19) 2.3311(19) 2.3401(18) 2.440(2) 2.260(2) 2.2770(18) 2.2979(19) 2.3470(19) 2.3369(18) 2.3530(18) 2.4205(19) 2.499(2) 1.458(2) 1.469(2) 1.4723(19) 1.469(2) 1.446(2) 1.455(2) 1.455(2) 1.4790(19) 1.444(2) 1.454(2) 1.459(2) 1.4728(19) 1.468(2) 1.469(2) 1.467(2) 1.484(2)
a Symmetry codes: (A) x + 1/2, −y + 1/2, −z; (B) −x + 1, y − 1/2, −z + 1/2; (C) −x + 1/2, −y, z + 1/2; (D) −x, y − 1/2, −z + 1/2; and (E) −x + 1/2, −y, z − 1/2.
R1 = Σ||Fo| − |Fc||/Σ|Fo|. bwR2 = {Σ[w(Fo2 − Fc2)2]/ Σ[w(Fo2)2]}1/2. 2568
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structures by incorporating {Ln4} clusters as building blocks. Compounds 1 and 2 are air-stable and insoluble in water and common organic solvents. After compounds 1 and 2 were obtained, we tried to make isomorphous compounds with other lanthanide ions under the same condition, but this was fruitless, which indicates that the ionic radius of the lanthanide ion seems to be the predominant factor governing the obtained structure. It is noteworthy that the addition of a small amount of D-H2cam is very important to obtain the chiral lanthanide− sulfate frameworks, although D-H2cam was not present in 1 and 2. When D-H2cam was removed from the reaction system, attempts to make 1 and 2 were unsuccessful under the same conditions, which may be attributed to the chirality induction effect in the chiral crystallization.18 Compounds 1 and 2 are isomorphous; therefore, only the structure of 1 is described in detail. The asymmetric unit of 1 contains four Y3+ ions, four μ3-OH− ions, four SO42− ions with the same coordination mode, and three coordinated water molecules. The Y(1), Y(2), and Y(4) ions are eight-coordinated and have the same bicapped trigonal-prism coordination environment: four O atoms from four SO42− ligands, three μ3-OH, and one terminal water molecules. The Y(3) ion is seven-coordinated and has a capped trigonal-prism coordination environment: four O atoms from four SO42− ligands and three μ3-OH (Figure 2). The Y−O distances range from
Figure 3. (a) Framework of 1 viewed along the c-axis, showing helical tubes and channels arranged alternately, the coordinated water molecules are pointed to the channels. (b and c) View of the helical tubes (b) and channels (c) constructed from double left-helical chains weaved by double right-helical chains along the c-axis. The double lefthelical chains are marked green and cyan, and the double right-helical chains are displayed with blue and yellow. Figure 2. Coordination environment of Y atoms in 1. Symmetry codes for the generated atoms are the same as those in Table 2.
the 4,5-imidazoledicarboxylic acid,19 and the compounds 1 and 2 represent good examples of using inorganic SO42− anions to construct fascinating 3D lanthanide−sulfate frameworks with helical tubes and channels that consist of interweaving two double-helical chains. As shown in Figure 4a,b, each SO42− anion is linked to three {Y4} clusters, while each {Y4} cluster is linked to twelve nearest SO42− ions. Therefore, the framework can be rationalized as a binodal (3,12)-connected net by assigning the SO42− anion as a three-connected node and the {Y4} cluster as an 12-connected node with schläfli symbol of (43)4(420·628·818) (Figure 4c). To date, examples of high-connected binodal networks, such as (3,12), (3,13), (4,12), and (5,12) are relatively rare;20,21 the reported (3,12) network here is a good example of using Ln clusters to construct high-connected chiral lanthanide−sulfate frameworks.11 According to approaches to the analysis of highly connected frameworks based on the visualization of the structures as combinations of interconnected layered 2D sheets or subnet tectons proposed by Hill et al.,22 the (3,12)connected net of 1 can be described as the parallel (3,6)connected nets are cross-linked by zigzag chains in the two adjacent layers, and the zigzag chains cross the diagonal of windows.
2.251(7) to 2.555(7) Å, and the Er−O bonds in 2 are similar to the corresponding Y−O bonds in 1 (Table 2). The Y3+ ions are linked by hydroxo bridges to give cubane [Y4(OH)4]8+ ({Y4}) cluster cores that contain Y(1), Y(2), Y(3), and Y(4) atoms, which are common in Ln cluster chemistry.11 The most striking features of 1 are the linkages between Y3+ and SO42− ions that form an unprecedented chiral 3D framework with helical tubes and channels (Figures 3a S2 in the Supporting Information). The helical tubes consist of double left-helical chains and double right-helical chains with a pitch of 16.57 Å running along the 21-axis; the double lefthelical chains and double right-helical chains are interweaved to make the tubular walls with the same chirality (Figure 3b). These adjacent tubular walls are further bridged together by SO42− anions through their remaining μ-O atoms to form the helical channels. It is interesting to note that the 1D channels are also contain the interweaved double left-helical chains and double right-helical chains along the c-axis with a pitch of 16.57 Å (Figure 3c), and the coordinated water molecules are located in channels. Recently, two lanthanide−organic open frameworks with helical tubes constructed from interweaving triplehelical and double-helical chains have been reported by using 2569
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ASSOCIATED CONTENT
S Supporting Information *
X-ray crystallographic files in CIF format for structures 1 and 2, morphologies, TGA, and IR spectra. 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 Financial support from the NNSF of China (21001094 and 21173197) is greatly appreciated.
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Figure 4. (a and b) Coordination environments of SO42− and {Y4} cluster in 1. (c) Schematic representation of (3,12)-connected net. Yellow, SO42−; green, {Y4} cluster.
The thermal stabilities of 1 and 2 were examined by TG analysis in dry air atmosphere from 30 to 800 °C. These compounds show a similar thermal behavior and undergo two steps of weight loss. The coordinated water molecules were gradually lost before 390 °C for 1 (calcd/found, 6.3/5.3%) and 2 (calcd/found, 4.6/4.3%), respectively. Above that temperature, the weight loss is due to the decomposition and the collapse of the whole framework (Figure S3 in the Supporting Information). The solid-state luminescent spectra of compound 2 were investigated at room temperature. Compound 2 did not show characteristic emission bands of the erbium(III) in the near-IR region, which may be ascribed to the “quenching effect” of the water molecules.23 The IR spectra of 1 and 2 are similar; the strong and broad absorption bands in the range of 3000−3700 cm−1 in 1 and 2 are assigned as characteristic peaks of OH vibration. The band at around 1627 cm−1 is due to the bending modes of water molecules coordinated to metal ions. The characteristic bands around 1149 cm−1 are due to the sulfate ions. The bands in the 612−715 cm−1 are associated with Y−O vibration (Figure S4 in the Supporting Information). The assignments are consistent with those previously reported.16c
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CONCLUSIONS
In summary, two 3D chiral lanthanide−sulfate compounds are prepared under hydrothermal conditions by incorporating {Ln4} as building blocks. The linkage between {Ln4} and SO42− gives an unusual high connected binodal network. Interestingly, the architectures contain helical tubes and channels constructed from double left- and right-handed helical chains. The successful isolation of these compounds demonstrates that using lanthanide clusters as building blocks is a feasible route to synthesize high-connected lanthanide sulfate. 2570
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