Synthesis and Structural Characterization of Open-Framework Copper

Nov 14, 2008 - Under a water-poor solvothermal condition, the terminal-ligand-avoid three-dimensional open frameworks (including one- and two-dimensio...
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CRYSTAL GROWTH & DESIGN

Synthesis and Structural Characterization of Open-Framework Copper (II) Sulfates Jian Lin, Dong-Wei Guo, and Yun-Qi Tian* Institute of Chemistry for Functionalized Materials, College of Chemistry and Chemical Engineering Liaoning Normal UniVersity, Dalian 116029, P. R. China

2008 VOL. 8, NO. 12 4571–4575

ReceiVed June 16, 2008; ReVised Manuscript ReceiVed August 24, 2008

ABSTRACT: A series of novel ammonium copper sulfates, (NH4)4[Cu2(SO4)4] (1), (NH4)3[Cu2(OH)(SO4)3] (2), (NH4)1.5[Cu1.25(SO4)2] (3), [Cu0.5(NH4)][Cu(SO4)2] (4), and (NH4)[Cu1.5(SO4)2] (5), have been synthesized under solvothermal conditions. X-ray singlecrystal analyses reveal that compound 1 has a structure of one-dimensional (1D) chain; compounds 2 and 3 have two-dimensional (2D) layer structures; and compounds 4 and 5 demonstrate the structures of three-dimensional (3D) open frameworks with 12- and 10-ring channels, respectively. Introduction Inorganic open-framework compounds, as an important class of materials, have attracted much attention in the past few years.1 A large number of metal silicates, phosphates, selenates, germanates, and arsenates with open frameworks2-9 have been extensively synthesized and characterized, in which anions are often involved as [TO4] units (T ) tetrahedrally coordinated atoms) of inorganic frameworks. Similarly, metal sulfates involve also the [TO4] units that are known to promote a wide range of structural arrangements in inorganic solids.10 However they seems hard to generate the architectures with openframeworks. Due to the pioneering works of Rao and his coworkers in this direction, many metal sulfates involving those of three-dimensional (3D) structures with open-frameworks11-28 have been realized. Nevertheless, low-dimensional architectures still predominate the metal sulfate compounds, for example, the sulfates involving copper atoms are few reported with 3D architectures.29,30 Accordingly, finding out the key points that obstruct the formation of 3D metal sulfates is the first important step in paving the way for realizing the substances with open frameworks. Different from the water-insolubility of silicates, phosphates, selenates, germanates, and arsenates, most of metal sulfates are water-soluble that indicates water molecules are the terminal ligands and most competitive with the sulfate groups in bonding the metal cations. Thus, the hydrothermal method for synthesis of above-mentioned silicates etc is obviously not yet available in realizing the metal sulfate 3D architectures since the water molecules will terminate the 3D polymerization. Thus, getting rid of the various terminal ligands (especially water molecules) from the reaction system should be an effective synthetic strategy for realizing the 3D structures that are essential for the open frameworks. Even though cross-linking a low-dimensional metal sulfate by thermal elimination of water molecules from the metal coordination spheres may generate the 3D framework of metal sulfates (for example, an heretofore only 3D framework of copper sulfate, the anhydrous copper sulfate,31 was prepared by dehydration of CuSO4 · 5H2O), this method usually generates close-packed architectures because dehydration is usually performed at a rather higher temperature. Accordingly, if we prepared a metal sulfate under an anhydrous or a water-poor * Corresponding author. E-mail: [email protected]. Fax: 86-411-82156858. Tel: 86-411-82159141.

environment, the open framework of the 3D metal sulfate could be realized at a relatively lower temperature. By virtue of this consideration, we choose a solvothermal synthesis of copper sulfates in glacial acetic that has afforded five novel ammonium copper sulfates: [NH4]4[Cu2(SO4)4] (1), [NH4]3[Cu2(OH)(SO4)3] (2), [NH4]1.5[Cu1.25(SO4)2] (3), [NH4][Cu1.5(SO4)2] (4), and [NH4][Cu1.5(SO4)2] (5) (Table 1), of which 4 and 5 are the open frameworks of 3D structures. In this paper, we will report the synthesis and characterization of these novel compounds. Experimental section Materials and Measurements. All chemicals were obtained commercially and used as received without further purification. The IR spectra were recorded (400-4000 cm-1) on a FT-IR spectrometer TENSOR 27. The XRD analyses were carried out on a Bruker D8 Advance and the TGA was performed under nitrogen stream with a heating rate of 5 /min by using a Perkin-Elmer Diamond Thermogravimetric Analyzer. X-ray Single-Crystal Analyses. X-ray single-crystal diffraction data for 1-5 were collected on a Bruker SMART CCD diffractometer with graphite-monochromatized Mo KR radiation (λ ) 0.71073 Å) at 293(2) K. The structures were solved by direct methods and refined by fullmatrix least-squares techniques on F2 using the SHELX program package.32 All non-hydrogen atoms of the ammonium copper sulfates were refined anisotropically. The selected crystallographic data and information are presented in Table 1. Preparation of Ammonium Copper Sulfates. The Compounds 1 and 3-5 were typically prepared by mixing and grinding Cu(OOCCH3)2 · H2O (0.2 g, 1.0 mmol) and (NH4)2SO4 (0.132 g, 1.0 mmol) in an agate mortar. The powdered reactant mixture and 15 mL of glacial acetic acid were subsequently added into a Teflon-lined autoclave (30 mL) that was then sealed. As we heated the autoclave at 150 for 2 days, a yielding mixture of ammonium copper sulfates containing blue blocks of [NH4]2[Cu(SO4)2] (1), brown plates of [NH4]1.5[Cu1.25(SO4)2] (3), pale blue polyhedra of [NH4][Cu1.5(SO4)2] (4), and colorless plates of [NH4][Cu1.5(SO4)2] (5) was obtained. [NH4]3[Cu2(OH)(SO4)3] (2) of pale-blue crystalline blocks was prepared in a procedure almost as same as the above. The only difference is that the reactants of Cu(OOCCH3)2 · H2O (0.2 g, 1.0 mmol) and (NH4)2SO4 (0.132 g, 1.0 mmol) were simply mixed without grinding that affords 2 companied with a large amount of the reactants.

Results and Discussion The ammonium copper sulfates 1-5 are the products of the heterogeneous reactions. Thereby, any single phase of the polymorphs has not yet been obtained from one synthetic batch. For the X-ray single crystal analyses, individual single crystals

10.1021/cg8006316 CCC: $40.75  2008 American Chemical Society Published on Web 11/14/2008

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Table 1. Crystallographic Data and Structure Refinement Summary for Complexes 1-5

formula fw space group cryst syst a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z Dcalcd µ (mm-1) T (K) F(000) GOF R1 [I > 2σ(I)] wR2 (F2 all data)

1

2

3

4

5

(NH4)4[Cu2(SO4)4] 583.5 triclinic P1j 9.313(3) 9.375(3) 10.034(4) 91.358(5) 114.465(5) 91.200(5) 796.7(5) 2 2.432 3.288 293(2) 588 1.019 0.063 0.145

(NH4)3[Cu2(OH)(SO4)3] 486.39 triclinic P1j 7.6653(6) 10.2169(8) 10.2721(8) 61.2420(10) 84.7140(10) 69.5680(10) 658.05(9) 2 2.455 3.782 293(2) 488 1.019 0.0378 0.101

(NH4)1.5[Cu1.25(SO4)2] 298.61 monoclinic C2/c 17.761(3) 5.1952(10) 19.314(5) 90 115.351(2) 90 1610.6(6) 8 2.463 3.89 293(2) 1190 1.03 0.0685 0.1875

(NH4)[Cu1.5(SO4)2] 305.47 monoclinic C2/c 16.070(3) 9.6813(15) 9.1411(14) 90 92.916(2) 90 1420.3(4) 8 2.857 5.135 293(2) 1204 1.034 0.0564 0.1468

(NH4)[Cu1.5(SO4)2] 305.47 orthorhombic Pnma 9.3244(10) 16.0720(17) 9.0726(10) 90 90 90 1359.6(3) 8 2.985 5.364 293(2) 1204 1.076 0.0352 0.0754

Table 2. Selected Bond Lengths (Å) and Angles (deg) of Compounds 1-5 moiety

bond length (Å)

moiety

bond length (Å)

moiety

angle (deg)

moiety

angle (deg)

a

Complex 1 Cu(1)-O(4) Cu(1)-O(9) Cu(1)-O(3) Cu(1)-O(5)

1.922(5) 1.939(5) 1.943(6) 1.950(5)

Cu(2)-O(13) Cu(2)-O(14) Cu(2)-O(8) Cu(2)-O(12)

1.920(5) 1.954(5) 1.966(5) 1.972(6)

S(1)-O(3)-Cu(1) S(1)#1-O(4)-Cu(1) S(2)-O(5)-Cu(1) S(2)-O(8)-Cu(2)

116.3(3) 135.8(4) 140.2(3) 116.3(3)

S(3)-O(9)-Cu(1) S(3)-O(12)-Cu(2) S(4)#2-O(13)-Cu(2) S(4)-O(14)-Cu(2)

119.0(3) 140.5(4) 134.7(3) 126.2(3)

117.37(12) 113.40(13) 134.51(15) 129.08(14) 136.75(16)

S(3)-O(11)-Cu(1) S(3)-O(12)-Cu(2) Cu(2)-O(13)-Cu(1) Cu(2)-O(13)-Cu(2)#2 Cu(1)-O(13)-Cu(2)#2

118.32(13) 133.16(15) 106.68(10) 97.95(10) 118.05(11)

136.0(4) 123.2(3) 129.6(3) 125.3(3)

S(2)-O(5)-Cu(2)#5 S(2)-O(7)-Cu(1)#3 S(2)-O(8)-Cu(2) Cu(1)-O(5)-Cu(2)#5

119.8(2) 134.5(3) 126.1(3) 109.4(2)

123.5(3) 109.7(3) 134.1(3) 143.0(4)

S(2)#6-O(5)-Cu(2) S(1)#1-O(6)-Cu(2) S(2)-O(7)-Cu(2) Cu(2)-O(3)-Cu(1)

143.0(4) 134.4(4) 128.9(4) 105.1(2)

129.53(18) 136.16(18) 144.2(2) 125.70(17)

S(3)#5-O(5)-Cu(1) S(1)-O(7)-Cu(2) S(2)-O(8)-Cu(2)

122.52(18) 128.0(3) 140.17(19)

Complex 2b Cu(1)-O(8)#1 Cu(1)-O(7) Cu(1)-O(13) Cu(1)-O(2)#2 Cu(1)-O(11)

1.943(2) 1.945(2) 1.969(2) 1.994(2) 2.354(2)

Cu(2)-O(9)#3 Cu(2)-O(12) Cu(2)-O(13) Cu(2)-O(13)#2 Cu(2)-O(4)

1.909(2) 1.962(2) 1.965(2) 2.015(2) 2.345(2)

S(1)-O(2)-Cu(1)#2 S(1)-O(4)-Cu(2) S(2)-O(7)-Cu(1) S(2)-O(8)-Cu(1)#1 S(3)-O(9)-Cu(2)#3 Complex 3c

Cu(1)-O(3)#1 Cu(1)-O(2)#2 Cu(1)-O(5) Cu(1)-O(7)#3

1.936(5) 1.955(5) 1.980(5) 1.981(5)

Cu(1)-O(4) Cu(2)-O(8) Cu(2)-O(5)#1

2.281(5) 2.038(5) 2.352(5)

S(1)-O(2)-Cu(1)#2 S(1)-O(3)-Cu(1)#5 S(1)-O(4)-Cu(1) S(2)-O(5)-Cu(1) Complex 4d

Cu(1)-O(3) Cu(1)-O(1)#2 Cu(2)-O(4) Cu(2)-O(7)

2.310(5) 2.313(6) 1.955(6) 1.959(6)

Cu(2)-O(3) Cu(2)-O(6) Cu(2)-O(5)

1.988(5) 2.024(5) 2.230(6)

S(1)-O(1)-Cu(1)#2 S(1)-O(3)-Cu(2) S(1)-O(3)-Cu(1) S(2)#5-O(4)-Cu(2) Complex 5e

Cu(1)-O(5) Cu(1)-O(1) Cu(1)-O(3) Cu(1)-O(2)

1.917(3) 1.925(3) 1.976(3) 2.011(3)

Cu(1)-O(4) Cu(2)-O(9) Cu(2)-O(7) Cu(2)-O(8)

2.232(3) 1.908(4) 1.920(4) 2.000(3)

S(2)#3-O(1)-Cu(1) S(2)#5-O(2)-Cu(1) S(1)-O(3)-Cu(1) S(2)-O(4)-Cu(1)

a Symmetry transformations used to generate equivalent atoms. #1: -x + 1, -y, -z; #2: -x, -y + 1, -z + 1. b Symmetry transformations used to generate equivalent atoms. #1: -x, -y, -z + 1; #2: -x, -y, -z; #3: -x + 1, -y, -z. c Symmetry transformations used to generate equivalent atoms. #1: x, y + 1, z; #2: -x + 1, -y + 1, -z + 2; #3: -x + 3/2, -y + 3/2, -z + 2; #4: -x + 3/2, -y + 5/2, -z + 2; #5: x, y - 1, z. d Symmetry transformations used to generate equivalent atoms. #1: -x, y, -z + 1/2; #2: -x, -y, -z; #3: x, -y, z + 1/2; #4: -x + 1/2, y + 1/2, -z + 1/2; #5: -x + 1/2, -y + 1/2, -z; #6: -x + 1/2, y - 1/2, -z + 1/2. e Symmetry transformations used to generate equivalent atoms. #1: x, -y + 3/2, z; #2: x - 1/2, y, -z + 1/2; #3: -x, -y + 1, -z #4: x - 1/2, -y + 3/2, -z + 1/2; #5: x + 1/2, y, -z + 1/2.

of the above-mentioned polymorphous compounds were carefully selected. But for the XRD, IR and TGA measurements (see the Supporting Information), only the compound 3 was isolated because of its relatively large size and special brown color of the crystals that make the manual separation of the crystals under microscope available. X-ray single crystal analyses on compounds 1-5 reveal series of 1D, 2D and 3D architectures of the negative copper sulfate aggregates that were charge-balanced with ammonium cations residing in the interlamination or holes. In the compounds 1-5, the Cu atoms show tetragonal or square pyramid geometries where the Cu-O distances fall in the range 1.908(4) to 2.354(2) Å (Table 2). The tetrahedral sulfate groups display three

coordination models of A, B and C (Figure 1) in which the sulfate groups provide two, three, or all four of their oxygen atoms, respectively, in coordination with the Cu atoms. Compound 1 is formulated as [NH4]2[Cu(SO4)2]. It crystallizes in triclinic with a space group P1j. In the asymmetric unit (Figure 2a) of 1, there are four S and two Cu crystallographically distinct atoms: the Cu atoms are coordinated with four oxygen atoms from four separate sulfate groups in distorted tetragonal geometries; The sulfate groups display the coordination style of model A, providing two of its four oxygen for coordination with Cu atoms. The compound 1 demonstrates a 1D kro¨hnkitelike33,34 chain structure (b and c in Figure 2) that is similar to the [C3N2H12][Zn(SO4)2] reported by Rao et al.27

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Figure 1. Coordination models of sulfate groups in the ammonium copper sulfates.

Figure 3. (a) ORTEP drawing of the asymmetric unit of 2 (30% probability level thermal ellipsoids); (b) polyhedral diagram of 2D framework of 2 in the ac-plane; (c) chain formed by [Cu4(OH)2(SO4)2] units along the c-axis direction; (d) [Cu4(OH)2(SO4)2] unit of 2.

Figure 2. (a) ORTEP drawing of the asymmetric unit of 1 (30% probability level thermal ellipsoids); (b) the ball-and-stick and (c) polyhedral diagram of 1 with one-dimensional structure.

Compound [NH4]3[Cu2(OH)(SO4)3] (2) crystallizes in a triclinic structure with space group P1j. The asymmetric unit of 2 contains two Cu and three S crystallographically distinct atoms where each Cu atom is coordinated with five oxygen atoms in a square-pyramid geometry (CuO5) and two sulfate groups present the coordination model A, whereas the other one presents model B (Figure 3a). There is a hydroxyl (OH-) group in the asymmetric unit of 2 that serves as the µ3-O bridge of copper atoms. Two of the hydroxyl (OH-) groups combine four Cu atoms into a [Cu4(OH)2(SO4)2] unit (Figure 3d). Every two of the [Cu4(OH)2(SO4)2] unit are bridged by a pair of sulfate groups into a double-stranded [Cu4(OH)2(SO4)2]n chains running along the c-axis (Figure 3c). These chains are then linked with sulfate groups on the CuO5 square-pyramids by sharing the oxygen atoms that forms a 2D sheet with 10-rings parallel to the acplane (Figure 3b). The framework of 3 consists of CuO5 square-pyramids, CuO4 tetragons and SO4 tetrahedra by sharing the vertices of oxygen atoms (Figure 4). In compound 3, the numbers of sulfate groups in model A and B are equal. Two CuO5 square-pyramid and one CuO4 tetragon are connected alternately by sharing the corners to generate the Cu3O12 units, which are connected by a pair of SO4 tetrahedra alternatively, forming an one-dimensional chain along the [11j0] direction. These chains parallel running in b-axis are arranged by connecting the sulfate groups with the CuO5 and CuO4 polyhedra giving rise to a 2D sheet. Both compounds 4 and 5 are formulated as [NH4][Cu1.5(SO4)2], but they crystallize in different crystalline systems.

Figure 4. (a) ORTEP drawing of the asymmetric unit of 3 (30% probability level thermal ellipsoids); (b) polyhedral diagram of 2D plane of 3 in the ab-plane; (c) chain formed by CuO5, CuO4, and SO4 along the [11j0] direction.

Compound 4 is monoclinic with space group C2/c, whereas compound 5 is orthorhombic with space group Pnma. In compound 4, there are three kinds of Cu (Cu1, Cu2, and Cu3) and two kinds of S (S1 and S2) crystallographically distinct atoms (Figure 5a): The Cu1 and Cu2 are coordinated by oxygen atoms of the sulfate groups in the tetragonal and square-pyramid

4574 Crystal Growth & Design, Vol. 8, No. 12, 2008

Figure 5. (a) ORTEP drawing of the asymmetric unit of 4 (30% probability level thermal ellipsoids); (b) polyhedral diagram of 4 (blue, Cu atoms in the framework; yellow, S atoms; red, O atoms; pink, Cu atoms charge-balanced the framework) of the 3D framework viewing in the [001] direction; (c) 2D layer parallel to the (11j0) plane; (d) 1D chain along the c-axis direction; (e) ball-and-stick diagram of SBU of [Cu5(SO4)8].

geometries respectively (the Cu1-O bond lengths from 2.310(5) to 2.313(6) Å and Cu2-O bond lengths from 1.955(6) to 2.230(6) Å), whereas the Cu3 atoms with all of the distances between Cu and O beyond 2.35 Å (Table 2), the Cu-O bonds on the Cu3 are, therefore, not regarded to have formed. They serve only as the cations to charge-balance the negative framework of the compound 4 that should be reformulated as [(NH4)(Cu0.25)][Cu1.25(SO4)2]. The sulfate groups in compound 4 serve as oxygen-bridge supplier of the copper atoms in a style of model B that promotes the copper sulfate into a 3D framework. The 3D framework of 4 can be described with a secondary building unit (SBU) of [Cu5(SO4)8] (Figure 5e) that consists of five Cu atoms (one tetragonal and four square-pyramid) and eight sulfate groups. This SBU is repeating along the c-axis by common using the end-sulfate-groups of the SBU forming a 1D chain (Figure 5d). Such chains connect each other in [1 1 0] direction producing a 2D layer (Figure 5c) which then joint together running in [1 -1 0] direction to complete an elegant 3D open framework of 12-ring channels running along the c-axis (Figure 5b). Compound 5 has two kinds of Cu (square-pyramid Cu1 and tetragonal Cu2) and three kinds of crystallographically distinct S (S1, S2 and S3) atoms (Figure 6a). The SBU of 5 is a [Cu6(SO4)8] cluster that contains six Cu (two tetragonal and four square-pyramid) atoms and eight sulfate groups, which demonstrate two coordination styles of models B and C in a proportion of 1:1 (Figure 6e). Similarly to the SBU of compound 4, the [Cu6(SO4)8] cluster repeats along the a-axis by common using the end-sulfate-groups of the cluster forming a 1D chain (Figure 6d); Such chains are then connected along the [0 1 0] direction giving rise a 2D sheet (Figure 6c); Those sheets parallel to the (001) plane are linked together by the oxygen atoms producing a 3D framework with 10-ring channels that are blocked by some sulfate groups of model B (Figure 6b).

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Figure 6. (a) ORTEP drawing of the asymmetric unit of 5 (30% probability level thermal ellipsoids); (b) polyhedral diagram of 5 (blue, Cu atoms in the framework; yellow, S atoms; red, O atoms) of the 3D framework viewing in the [100] direction; (c) 2D layer parallel to the (001) plane; (d) 1D chain along the a-axis direction; (e) ball-and-stick diagram of SBU of [Cu6(SO4)8].

With the same chemical composition, the compound 4 demonstrates the larger channels than the compound 5. This difference arises from the coordination model of the sulfate groups: one-half of the sulfate groups of 5 in model C have bonded one-sixth more Cu atoms that serve as the guest chargebalancer accommodated in the holes of compound 4. Conclusion 1D, 2D, and 3D copper sulfates have been synthesized under a solvothermal condition in glacial acetic acid. Although this synthetic strategy can afford series of anhydrous copper sulfates, however, an anhydrous metal sulfate is not definitely the 3D architecture that depends on the coordination model of the sulfate groups: (i) model A favors low-dimensional 1D structure; (ii) the coexistence model A and B in one structure promotes the formation of 2D structure; (iii) both models B and C will complete the construction of a 3D architecture; however, the model B is more likely to generate the architectures with open framework. Moreover, because of the heterogeneous reaction, any bulk single phase of the ammonium copper sulfates was not obtained and an investigation on the properties such as the thermostability and gas adsorption has not yet been performed. Further research in this direction is still in progress. Acknowledgment. We thank the National Science Foundation of PR China (NSFC) (2003034003), The Foundation for the Author of National Excellent Doctoral Dissertation of PR China (FANEDD) (200733), and the Education Foundation of Liaoning Province of PR China (EFLPC) (20060470) for the financial support. Supporting Information Available: XRD, TGA, and IR for compound 3 and table (PDF); CIF files of compounds 1-5. This material is available free of charge via the Internet at http://pubs.acs.org.

Open-Framework Copper Sulfates

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