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Syntheses and structures of two new 3D open-framework germanates constructed from Ge9O18(OH)4 clusters
Microporous and Mesoporous Materials 74 (2004) 205–211 www.elsevier.com/locate/micromeso
Syntheses and structures of two new 3D open-framework germanates constructed from Ge9O18(OH)4 clusters Zhi-En Lin a, Jie Zhang a, Shou-Tian Zheng a, Guo-Yu Yang
a,b,*
a
Coordination and Hydrothermal Chemistry Group, State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, 155 West Yangqiao Road, Fuzhou, Fujian 350002, China b State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, Jiangsu 210093, China Received 5 January 2004; received in revised form 30 May 2004; accepted 28 June 2004
Abstract Two new open-framework germanates, [Cd2(C2N2H8)3][Ge9O18(OH)4] (1) and (C8N4H26)[Ge9O18(OH)4] (2), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction. Compound 1 crystallizes in the orthorhombic space ˚ , V = 2736.0(9) A ˚ 3, Z = 4. The compound is the first organically temgroup, Pbca, with a = 14.318(3), b = 13.106(3), c = 14.580(3) A plated cadmium germanate. The structure of 1 is constructed from two distinct motifs, a body-centered [Ge9O18(OH)4] cluster and a cadmium complex [Cd2(C2N2H8)3O6], which integrate to generate a 3D architecture with neutral framework. The structures of 2 is closely related to that of 1 and has identical Ge9O18(OH)4 clusters. It crystallizes in the orthorhombic space group, Pbca, with ˚ , V = 2722.5(9) A ˚ 3, Z = 4. The connectivity between the Ge9 clusters result in a 3D a = 14.158(3), b = 13.213(3), c = 14.553(3) A open-framework structure. The quadruply protonated N,N 0 -bis(3-aminopropyl)ethylene diamine molecules are located in the free voids and interact with the macroanionic inorganic framework by extensive hydrogen bonds. 2004 Elsevier Inc. All rights reserved. Keywords: Open framework; Germanate; Cluster; Hydrothermal synthesis; Crystal structure
1. Introduction Open-framework inorganic solids attracted considerable attention in the past decades due to their rich structural chemistry and potential application in ionexchange, separation and catalysis [1]. Zeolites (aluminosilicates) are the most well-known family of such materials. Following the discovery of organically templated germanates in 1991 [2,3], great efforts have been
* Corresponding author. Address: Coordination and Hydrothermal Chemistry Group, State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, 155 West Yangqiao Road, Fuzhou, Fujian 350002, China. Tel./fax: +86 5913710051. E-mail address: [email protected] (G.-Y. Yang).
1387-1811/$ - see front matter 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2004.06.020
devoted to the pursuit of novel open-framework structures within this system [4–14]. Open-framework germanates are interesting for several reasons. First, in contrast to silicon, which is usually tetrahedrally coordinated, germanium can exist in a more variable and expanded coordination environment due to the relatively large Ge/O radius ratio. This implies that a large number of novel structures can be potentially accessed. Second, germanates show great tendency to form extended structures with odd-membered rings. For example, open-framework germanates with 3-, 5-, 7- and 9-rings have been synthesized and characterized [15–18]. Finally, the capacity of germanium to form cluster aggregates offers great opportunities for the design of open frameworks with large pores and channel sizes. Yaghi et al. have reported Ge7O14.5F2 Æ [(CH3)2NH2]3(H2O)0.86 (ASU-12) as a genuinely porous germanate with
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large 16-membered-ring windows [19]. The structure is constructed from Ge7 clusters and exhibits remarkable ion-exchange properties reminiscent of aluminosilicate zeolites. By using a different organic amine as structure-directing agent, a material (ASU-16) with the same building units, but with a larger 24-ring channels and much lower framework density (8.6 Ge atoms per 1000 ˚ 3), has been prepared in similar synthesis conditions A [9]. Zhao et al. have reported the synthesis and structure of another 24-membered-ring germanate (FDU-4), which is condensed from Ge9 clusters under solvothermal conditions [20]. The aim of our work is to construct new open frameworks from germanium-oxide clusters, and we have isolated several new compounds in this system [21]. Here, we report two new germanates [Cd2(C2N2H8)3][Ge9O18(OH)4] (1) and (C8N4H26)[Ge9O18(OH)4] (2), which consist of Ge9 clusters as building units connected though common vertices to form 3D framework.
2. Experimental
was recovered by filtration, washed with distilled water and dried in air (54% yield based on germanium). Elemental analysis was carried out to verify the organic content. Anal. found: C, 8.00%; H, 2.57%; N, 4.61%. Calcd: C, 8.09%; H, 2.55%; N, 4.72%. IR (KBr, cm1) for 2: 3024w, 1600m, 1506m, 1475m, 1285m, 1213m, 779vs, 717s, 583s, 492s, 417m. Preliminary thermogravimetric analyses of compound 1 and 2 were carried out under O2 atmosphere with a heating rate of 10 C/min1 from 40 to 700 C. For 1, a two-step weight loss of 15.78% was observed in the range between 360 and 670 C, corresponding to the departure of ethylenediamine molecules (observed: 13.01%; expected: 12.75%) and the dehydration process (observed: 2.77%; expected: 2.55% weight loss for two water molecules per formula unit). The post residue is CdO and GeO2. For 2, a total weight loss of 17.24% was observed in the range between 260 and 680 C, due to the release of organic amines (expected: 14.67%) from the structure and the partial dehydration process (expected: 6.06% weight loss for four water molecules per formula unit). The final product is amorphous GeO2.
2.1. Synthesis and initial characterization In a typical synthesis for 1, 0.15 g of GeO2 was dispersed in a mixed solution of 0.5 ml of H2O and 1.33 ml of ethylene glycol, and then 0.77 ml of ethylenediamine was dropwise added to get a clear solution. To this mixture, 0.082 g of CdCl2 Æ 2H2O was finally added and homogenized for 30 min. The resulting mixture of the composition GeO2:ethylenediamine:CdCl2 Æ 2H2O:H2O:ethylene glycol in a molar ratio of 1:8:0.25: 25:15 was sealed in a Teflon-lined steel autoclave, heated at 170 C for 7 days and then cooled to room temperature. The product was recovered by filtration, washed thoroughly with distilled water, dried at room temperature, and then colorless prism-like crystals were obtained (65% yield based on germanium). The ICP analysis shows that the compound contains 44.86 wt% Ge and 15.13 wt% Cd, indicating a Ge:Cd ratio of 9:2. Elemental analysis results of the bulk product are consistent with the stoichiometry of 1. Anal. found: C, 5.24%; H, 1.51%; N, 5.92%. Calcd: C, 5.09%; H, 1.71%; N, 5.94%. IR (KBr, cm1) for 1: 3318m, 3267m, 3161w, 2920m, 2457w, 1583m, 1485w, 1458w, 1283m, 1189w, 1110m, 1038m, 950w, 780s, 728s, 703s, 581s, 522s, 482s, 416m. In a typical synthesis for 2, a mixture of GeO2 (0.15 g), H2O (0.5 ml), ethylene glycol (1.33 ml) and N,N 0 bis(3-aminopropyl)ethylene diamine (2.2 ml) in a molar ratio of 1:25:15:8 was stirred under ambient conditions. The resulting gel, with a pH of 9, was sealed in a Teflon-lined steel autoclave and heated in 170 C for 7 days and then cooled to room temperature. The resulting product, which contained colorless prism-like crystals,
2.2. Crystal structure determination A suitable single crystal of as-synthesized compounds with the dimensions of 0.29 · 0.11 · 0.06 mm for 1 and 0.33 · 0.20 · 0.16 mm for 2 was carefully selected under an optical microscope and glued to a thin glass fiber with epoxy resin, respectively. Crystal structure determination by X-ray diffraction was performed on a Siemens SMART CCD diffractometer with graphite-monochro˚ ) radiation in the x and mated MoKa (k = 0.71073 A u scanning mode at room temperature. Both structures were solved by direct methods and refined on F2 by fullmatrix least-squares methods using the SHELX97 program package [22,23]. The crystal structure of 1 was solved in the orthorhombic space group Pbca (No. 61). The cadmium and germanium atoms were first located, and the carbon, nitrogen, and oxygen atoms were found in the final difference Fourier map. The cadmium atom is disorder over two positions, with the occupancies of 90% and 10%, respectively. The H atom were positioned at idealized geometry and refined using a riding model, except the hydrogen attached to O(10) and N(1) atoms. All non-hydrogen atoms were refined anisotropically. Experimental details for the structure determination are presented in Table 1. The coordinates of all non-H atoms are given in Table 2. Selected bond distances are listed in Table 3. The determination of the crystal structure of 2 followed the same procedure as outlined for 1 with location of the Ge atoms from direct methods (space
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Table 1 Crystal data and structure refinement for 1 and 2
Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
Volume Z Density (calcd) Absorption coefficient F(0 0 0) Crystal size h range for data collection Limiting indices Reflections collected Independent reflections Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)]a R indices (all data)a Largest diff. peak and hole a
1
2
C6H28Cd2Ge9N6O22 1414.45 293(2) K ˚ 0.71073 A
C8H30Ge9N4O22 1187.67 293(2) K ˚ 0.71073 A
Orthorhombic Pbca ˚ a = 14.318(3) A ˚ b = 13.106(3) A ˚ c = 14.580(3) A ˚3 2736.0(9) A
Orthorhombic Pbca ˚ a = 14.158(3) A ˚ b = 13.213(3) A ˚ c = 14.553(3) A ˚3 2722.5(9) A
4 3.434 g cm3 11.359 mm1 2664 0.29 · 0.11 · 0.06 mm 2.53–27.48 18 6 h 6 18, 16 6 k 6 17, 18 6 l 6 18 5783 3082 [R(int) = 0.0426] Full-matrix least-squares on F2 3082/0/214 1.090 R1 = 0.0591, wR2 = 0.1230 R1 = 0.0794, wR2 = 0.1291 ˚ 3 1.238 and 1.535 eA
4 2.898 g cm3 9.892 mm1 2280 0.33 · 0.20 · 0.16 mm 2.53–27.48 18 6 h 6 18, 17 6 k 6 17, 18 6 l 6 18 5782 3070 [R(int) = 0.0274] Full-matrix least-squares on F2 3070/0/166 0.947 R1 = 0.0407, wR2 = 0.0885 R1 = 0.0585, wR2 = 0.0927 ˚ 3 1.567 and 0.964 eA
R1 = RkFojjFck/R jFoj, wR2 ¼ ½R½wðF 2o F 2c Þ2 =R½wðF 2o Þ2 1=2 .
Table 2 Atomic coordinates (·104) and equivalent isotropic displacement ˚ 2 · 103) for 1 parameters (A
Cd(1) Cd(1 0 ) Ge(1) Ge(2) Ge(3) Ge(4) Ge(5) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) O(10) O(11) N(1) N(2) N(3) C(1) C(2) C(3)
x
y
z
U(eq)a
3542(1) 3266(9) 5138(1) 6564(1) 4949(1) 3609(1) 5000 6256(4) 6183(5) 6100(4) 5218(5) 5001(4) 3982(5) 2763(5) 4621(4) 4198(5) 4699(5) 2758(5) 2460(9) 2831(13) 4066(16) 1965(14) 2418(17) 4582(14)
9048(1) 8593(11) 6779(1) 6668(1) 7851(1) 7241(1) 5000 5401(5) 7210(6) 7305(5) 6925(6) 5486(5) 7856(6) 8284(5) 6302(5) 7532(6) 8888(6) 6288(6) 8419(11) 10,546(11) 10,279(15) 9299(17) 10,260(20) 10,219(18)
3404(1) 3162(9) 3565(1) 5121(1) 1504(1) 5035(1) 5000 5140(5) 4089(5) 6078(5) 2399(5) 3784(5) 6050(5) 4765(5) 5395(4) 3977(5) 2265(5) 4986(7) 2469(9) 2773(15) 4249(19) 2094(15) 1979(15) 5100(19)
27(1) 49(3) 13(1) 13(1) 14(1) 14(1) 12(1) 16(2) 19(2) 17(2) 23(2) 17(2) 20(2) 18(2) 14(1) 21(2) 22(2) 32(2) 52(3) 99(7) 144(11) 87(7) 27(5) 96(8)
a U(eq) is defined as one-third of the trace of the orthogonalized Uij tensor.
group Pbca; No. 61), and subsequent difference Fourier analysis in order to locate the carbon, nitrogen, and
Table 3 ˚ ) for 1a Selected bond lengths (A Cd(1)–N(3) Cd(1)–N(1) Cd(1)–O(9) Cd(1)–O(10) Cd(1)–N(2) Cd(1)–O(7) Ge(1)–O(4) Ge(1)–O(5) Ge(1)–O(2) Ge(1)–O(9) Ge(2)–O(1) Ge(2)–O(7)#1 Ge(2)–O(2) Ge(2)–O(3) Ge(3)–O(3)#2
2.163(19) 2.223(12) 2.352(7) 2.356(7) 2.395(16) 2.486(7) 1.715(7) 1.736(7) 1.772(7) 1.773(7) 1.719(7) 1.725(7) 1.751(7) 1.757(7) 1.772(6)
Ge(3)–O(10) Ge(3)–O(6)#2 Ge(3)–O(4) Ge(3)–O(8)#2 Ge(4)–O(11) Ge(4)–O(6) Ge(4)–O(9) Ge(4)–O(7) Ge(4)–O(8) Ge(5)–O(8) Ge(5)–O(8)#3 Ge(5)–O(5) Ge(5)–O(5)#3 Ge(5)–O(1)#3 Ge(5)–O(1)
1.791(7) 1.793(7) 1.823(7) 2.018(7) 1.747(8) 1.768(7) 1.798(7) 1.869(7) 1.972(6) 1.880(7) 1.880(7) 1.884(7) 1.884(7) 1.885(6) 1.885(6)
a
Symmetry transformations used to generate equivalent atoms: #1 x + 1/2, y + 3/2, z + 1; #2 x, y + 3/2, z1/2; #3 x + 1, y + 1, z + 1.
oxygen atoms. There is one protonated N,N 0 -bis(3aminopropyl)ethylene diamine per formula, which is disordered within the cavities of the structure. The hydrogen atoms were positioned at idealized geometry and all the framework atoms were refined anisotropically. Experimental details for the structure determination are presented in Table 1. The coordinates of all non-H atoms are given in Table 4. Selected bond distances are listed in Table 5.
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Table 4 Atomic coordinates (·104) and equivalent isotropic displacement ˚ 2 · 103) for 2 parameters (A
Ge(1) Ge(2) Ge(3) Ge(4) Ge(5) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) O(10) O(11) N(1) N(2) C(1) C(2) C(3) C(4)
x
y
z
U(eq)a
5133(1) 6596(1) 5026(1) 3639(1) 5000 6284(3) 6192(3) 6193(3) 5276(4) 4989(3) 4068(4) 2819(3) 4658(3) 4172(3) 4846(4) 2753(3) 1580(30) 3890(20) 2431(19) 2860(30) 3607(16) 4930(20)
6766(1) 6651(1) 7836(1) 7263(1) 5000 5372(3) 7219(3) 7313(3) 6882(3) 5475(3) 7880(4) 8335(3) 6325(3) 7484(3) 8859(3) 6326(4) 5010(30) 4860(20) 4756(19) 5410(30) 4855(17) 4909(19)
3559(1) 5095(1) 1507(1) 5038(1) 5000 5127(3) 4076(3) 6059(3) 2389(3) 3778(3) 6057(3) 4860(3) 5402(3) 3944(3) 2262(3) 5052(4) 3330(30) 580(20) 2650(20) 2230(30) 1619(17) 468(16)
13(1) 12(1) 16(1) 15(1) 10(1) 15(1) 21(1) 22(1) 27(1) 17(1) 29(1) 21(1) 12(1) 25(1) 35(1) 35(1) 410(20) 268(13) 211(12) 310(20) 166(9) 196(11)
a
U(eq) is defined as one-third of the trace of the orthogonalized Uij tensor.
Table 5 ˚ ) and angles (degree) for 2a Selected bond lengths (A Ge(1)–O(4) Ge(1)–O(5) Ge(1)–O(9) Ge(1)–O(2) Ge(2)–O(7)#1 Ge(2)–O(1) Ge(2)–O(3) Ge(2)–O(2) Ge(3)–O(10) Ge(3)–O(6)#2 Ge(3)–O(3)#2 Ge(3)–O(4)
1.721(4) 1.747(4) 1.750(4) 1.781(4) 1.733(5) 1.747(4) 1.749(4) 1.758(4) 1.761(4) 1.779(5) 1.787(4) 1.834(4)
Ge(3)–O(8)#2 Ge(4)–O(11) Ge(4)–O(9) Ge(4)–O(6) Ge(4)–O(7) Ge(4)–O(8) Ge(5)–O(5) Ge(5)–O(5)#3 Ge(5)–O(1) Ge(5)–O(1)#3 Ge(5)–O(8)#3 Ge(5)–O(8)
2.022(4) 1.762(5) 1.786(4) 1.799(4) 1.850(4) 1.975(4) 1.886(4) 1.886(4) 1.893(4) 1.893(4) 1.909(4) 1.909(4)
a
Symmetry transformations used to generate equivalent atoms: #1 x + 1/2, y + 3/2, z + 1; #2 x, y + 3/2, z1/2; #3 x + 1, y + 1, z + 1.
3. Results 3.1. Crystal structure of [Cd2(C2N2H8)3][Ge9O18(OH)4] 1 The asymmetric unit of 1 consists of 23 non-hydrogen atoms, as shown in Fig. 1. There are one crystallographically distinct cadmium atom and five unique germanium atoms. The cadmium atom is octahedrally coordinated, bonded to three oxygen atoms [Cd–O ˚ ] and three nitrogen atoms [Cd–N (ave.) (ave.) 2.399 A ˚ 2.260 A] from ethylenediamine ligands. Of the five independent Ge atoms, Ge(1) and Ge(2) atoms are tetrahed-
Fig. 1. ORTEP view of the asymmetric unit of 1, with 30% thermal ellipsoids and the atom-labeling scheme.
rally coordinated, with the Ge–O distances in the range ˚ (ave. 1.743 A ˚ ) and the O–Ge–O 1.715(7)–1.773(7) A angles in the range of 106.4(3)–113.2(3). Ge(3) and Ge(4) atoms are coordinated to five oxygen atoms, with the Ge–O bond distances varying from 1.747(8) to ˚ (ave. 1.836 A ˚ ). Ge(5) is located at the inver2.018(7) A sion center and is octahedrally coordinated, with Ge–O ˚ (ave. 1.883 distances between 1.880(7) and 1.885(6) A ˚ ). These geometric parameters are in accord with those A observed for open-framework germanates containing Ge9O18(OH)4 clusters [24–27]. Assuming the usual valence of Cd, Ge, and O atoms to be +2, +4, and 2, respectively, the framework stoichiometry of [CdGe4.5O11] creates a net charge of 2, which is needed to be balanced. Bond valence sum values indicate that O(10) and O(11) are hydroxyl groups. The structure of 1 is constructed from two distinct motifs, a body-centered [Ge9O18(OH)4] cluster and a cadmium complex [Cd2(C2N2H8)3O6], which integrate to generate a 3D architecture with neutral framework (Fig. 2a and b). As shown in Fig. 3a, the Ge9 building block is condensed from four GeO4 tetrahedra, four GeO4(OH) trigonal bipyramids, and one GeO6 octahedron. The GeO6 occupies the center of the cluster and links the four GeO4 and four GeO4(OH) through doubly bridging oxygen atoms and tri-bridging oxygen atoms. Each of such building units is connected to eight adjacent Ge9 units in a body-centered manner to form a three-dimensional framework. The second structural building block is a cadmium complex [Cd2(C2N2H8)3O6] containing two types of ethylenediamine molecules, one acts as chelating ligand and protrudes into the 8-ring channel and the other serves as a bridge to connect two symmetry-related cadmium atoms (Fig. 3b). In addition to the three nitrogen donors from the ethylenediamine ligands, each cadmium atom is connected to the germanate framework through O(7), O(9) and O(10) atoms.
Z.-E. Lin et al. / Microporous and Mesoporous Materials 74 (2004) 205–211
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Fig. 2. View of the structure of 1 along the (a) [0 1 0] and (b) [1 1 0] direction, respectively.
Fig. 3. The 3D framework of 1 is constructed from the building blocks of (a) Ge9O18(OH)4 clusters and (b) Cd2(C2N2H8)3O3 complexes.
Fig. 4. ORTEP view of the coordination environments of the germanium atoms in 2, with 30% thermal ellipsoids and the atomlabeling scheme.
3.2. Crystal structure of (C8N4H26)[Ge9O18(OH)4] 2 As seen in Fig. 4, the asymmetric unit of 2 contains five crystallographically distinct germanium atoms, which have three different coordination numbers. Ge(1) and Ge(2) each has typical tetrahedral coordination, with the Ge–O distances in the range 1.721(4)– ˚ (ave. 1.748 A ˚ ) and the O–Ge–O angles in 1.781(4) A the range of 105.38(19)–112.6(2). Ge(3) and Ge(4) each is coordinated to five oxygen atoms, one of them being a terminal –OH group. Ge(5) is located at the inversion center and adopts an octahedral coordination. The Ge–O distances within the trigonal bipyramidal and octahedral germanium centers are between 1.761(4) ˚ , which are markedly longer than those and 2.022(4) A found in the GeO4 tetrahedra. The connectivity of GeO4 tetrahedra, GeO5 trigonal bipyramids and GeO6 octahedra gives rise to the 3D
framework. In the structure, there are three types of channels. The smaller one has an eight-membered ring and runs along the [0 1 0] direction, as shown in Fig. 5. The diameter of the channel is approximately 5.9 · 6.1 ˚ (corresponding to the interatomic O–O distances). A Intersecting this channel are the two elliptical 10-membered windows, which have the same aperture and run along the [1 0 1] and [1 0 1] directions, respectively. The diameter of the channels is approximately 7.1 · ˚ (Fig. 6). 7.6 A The quadruply protonated N,N 0 -bis(3-aminopropyl)ethylene diamine molecules are located in the 10ring channels and interact with the inorganic framework through hydrogen bonds as N(1)–H(4) O(10) [d = ˚ ], N(1)–H(5) O(4) [d = 2.39 A ˚ ], N(2)–H(6) 2.27 A ˚ ˚ ]. O(11) [d = 2.20 A], and N(2)–H(7) O(7) [d = 2.12 A The extensive interactions between the organic moieties
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Fig. 5. Polyhedral view of the 3D framework of 2 along the [0 1 0] direction, showing the 8-ring channels. Guest molecules are omitted for clarity.
Fig. 6. Polyhedral view of the 3D framework of 2 along the [1 0 1] direction, showing the 10-ring channels. Guest molecules are omitted for clarity.
and the inorganic framework may play an important role to stabilize the structure, because attempts to remove of the organic moieties by calcination make the structure collapse.
4. Discussion Two new 3D open-framework germanates, [Cd2(C2N2H8)3][Ge9O18(OH)4] (1) and (C8N4H26)[Ge9O18(OH)4] (2), have been obtained as good-quality single crystals under similar hydrothermal conditions. The two compounds possess similar germanate framework that is assembled from Ge9O18(OH)4 clusters. Interestingly, the molecular Ge9 cluster has been successfully
isolated under hydrothermal conditions by Tripathi et al. [28]. According to the aufbau principle of building higher-dimensional structures from that of the lowerdimensional ones [29], it is conceivable that the use of this Ge9 clusters as the precursor to produce novel open frameworks may be realized either in the solid state or via a solution mediated process. The role of the metal complex in the structure of 1 is subtle and merits some attention. In previous literatures, metal complexes are usually used as structure-directing agents to direct the formation of specific inorganic frameworks [30–38]. These complexes are accommodated in the free voids of the structures and interact with the macroanionic ‘‘host’’ frameworks through H-bonding interactions. In the present compound 1 the Cd atom is bound to the host via covalent bonds. The framework ˚3 density defined as the number of polyhedra per 1000 A is 16.1 for 1, compared with the value of 16.7 for the structurally related zinc germanates ZnGe-1A(B) [39], and 16.4 for the cobalt germanate [Co2(C2N2H8)3][Ge9O18(OH)4] [40]. Compound 2 possesses a similar germanate framework constructed from Ge9O18(OH)4 clusters, however, the framework density of 13.2 for 2 makes it more of an open framework structure than 1. Another way to quantify the openness of these types of compounds is to calculate the fraction of the unit cell volume not occupied by the framework atoms, assuming typical van der Waals radii for these species. A void space analysis with PLATON indicates that the inorganic framework of 2 occupies 58.0% of the unit cell volume, leaving 42.0% ˚ 3 out of the unit cell volume of 2722.5 A ˚ 3) as (1142.2 A ‘‘solvent accessible’’ space [41]. However, only 427.9 ˚ 3 (15.6% of the unit cell volume) for compound 1 reA mains unoccupied, when the C, N, and H atoms of the ethylenediamine molecules are ignored. The decreased free space of compound 1 is due to that the cadmium complexes block the 10-ring channels along the [1 0 1] and [1 0 1] directions.
5. Conclusion Two new open-framework germanates, [Cd2(C2N2H8)3][Ge9O18(OH)4] (1) and (C8N4H26)[Ge9O18(OH)4] (2), were obtained as good quality single crystals under hydrothermal conditions. The structural analyses demonstrate that they have 3D structures assembled from the building unit of [Ge9O18(OH)4] clusters. For 1, the connectivity between the [Ge9O18(OH)4] clusters and the cadmium complexes results in a neutral inorganicorganic hybrid framework; while the structures of 2 has a macroanionic inorganic framework with 8-, 10-, and 10-ring channels along the [0 1 0], [1 0 1] and [1 0 1] directions.
Z.-E. Lin et al. / Microporous and Mesoporous Materials 74 (2004) 205–211
Acknowledgments This work was supported by the NSF of China (Grant nos. 20271050 and 20171045), the SRF for ROCS of State Education Ministry, the Ministry of Finance of China and the Talents Program of Chinese Academy of Sciences, and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry of Jilin University. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.micromeso.2004.06.020. References [1] M.E. Davis, Nature 417 (2002) 813. [2] J. Cheng, R. Xu, J. Chem. Soc., Chem. Commun. (1991) 483. [3] J. Cheng, R. Xu, G. Yang, J. Chem. Soc., Dalton Trans. (1991) 1537. [4] R.H. Jones, J. Chen, J.M. Thomas, A. George, M.B. Hursthouse, R. Xu, S. Li, Y. Lu, G. Yang, Chem. Mater. 4 (1992) 808. [5] H. Li, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 10569. [6] C. Cascales, E. Gutie´rrez-Puebla, M. Iglesias, M.A. Monge, C. Ruız-Valero, Angew. Chem. Int. Ed. 38 (1999) 2436. [7] X. Bu, P. Feng, G.D. Stucky, Chem. Mater. 11 (1999) 3025. [8] X. Bu, P. Feng, G.D. Stucky, Chem. Mater. 11 (1999) 3423. [9] H. Li, M. Eddaoudi, J. Ple´vert, M. OKeeffe, O.M. Yaghi, J. Am. Chem. Soc. 122 (2000) 12409. [10] M.S. Dadachov, K. Sun, T. Conradsson, X. Zou, Angew. Chem., Int. Ed. 39 (2000) 3674. [11] T. Conradsson, M.S. Dadachov, X. Zou, Micropor. Mesopor. Mater. 41 (2000) 183. [12] C. Cascales, E. Gutie´rrez-Puebla, M. Iglesias, M.A. Monge, C. Ruız-Valero, N. Snejko, Chem. Commun. (2000) 2145. [13] L. Beitone, T. Loiseau, G. Fe´rey, Inorg. Chem. 41 (2002) 3962. [14] D. Pitzschke, W. Bensch, Angew. Chem. Int. Ed. 42 (2003) 4389. [15] X. Bu, P. Feng, G.D. Stucky, J. Am. Chem. Soc. 120 (1998) 11204.
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Syntheses and structures of two new 3D open-framework germanates constructed from Ge9O18(OH)4 clusters Zhi-En Lin a, Jie Zhang a, Shou-Tian Zheng a, Guo-Yu Yang
a,b,*
a
Coordination and Hydrothermal Chemistry Group, State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, 155 West Yangqiao Road, Fuzhou, Fujian 350002, China b State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, Jiangsu 210093, China Received 5 January 2004; received in revised form 30 May 2004; accepted 28 June 2004
Abstract Two new open-framework germanates, [Cd2(C2N2H8)3][Ge9O18(OH)4] (1) and (C8N4H26)[Ge9O18(OH)4] (2), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction. Compound 1 crystallizes in the orthorhombic space ˚ , V = 2736.0(9) A ˚ 3, Z = 4. The compound is the first organically temgroup, Pbca, with a = 14.318(3), b = 13.106(3), c = 14.580(3) A plated cadmium germanate. The structure of 1 is constructed from two distinct motifs, a body-centered [Ge9O18(OH)4] cluster and a cadmium complex [Cd2(C2N2H8)3O6], which integrate to generate a 3D architecture with neutral framework. The structures of 2 is closely related to that of 1 and has identical Ge9O18(OH)4 clusters. It crystallizes in the orthorhombic space group, Pbca, with ˚ , V = 2722.5(9) A ˚ 3, Z = 4. The connectivity between the Ge9 clusters result in a 3D a = 14.158(3), b = 13.213(3), c = 14.553(3) A open-framework structure. The quadruply protonated N,N 0 -bis(3-aminopropyl)ethylene diamine molecules are located in the free voids and interact with the macroanionic inorganic framework by extensive hydrogen bonds. 2004 Elsevier Inc. All rights reserved. Keywords: Open framework; Germanate; Cluster; Hydrothermal synthesis; Crystal structure
1. Introduction Open-framework inorganic solids attracted considerable attention in the past decades due to their rich structural chemistry and potential application in ionexchange, separation and catalysis [1]. Zeolites (aluminosilicates) are the most well-known family of such materials. Following the discovery of organically templated germanates in 1991 [2,3], great efforts have been
* Corresponding author. Address: Coordination and Hydrothermal Chemistry Group, State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, 155 West Yangqiao Road, Fuzhou, Fujian 350002, China. Tel./fax: +86 5913710051. E-mail address: [email protected] (G.-Y. Yang).
1387-1811/$ - see front matter 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2004.06.020
devoted to the pursuit of novel open-framework structures within this system [4–14]. Open-framework germanates are interesting for several reasons. First, in contrast to silicon, which is usually tetrahedrally coordinated, germanium can exist in a more variable and expanded coordination environment due to the relatively large Ge/O radius ratio. This implies that a large number of novel structures can be potentially accessed. Second, germanates show great tendency to form extended structures with odd-membered rings. For example, open-framework germanates with 3-, 5-, 7- and 9-rings have been synthesized and characterized [15–18]. Finally, the capacity of germanium to form cluster aggregates offers great opportunities for the design of open frameworks with large pores and channel sizes. Yaghi et al. have reported Ge7O14.5F2 Æ [(CH3)2NH2]3(H2O)0.86 (ASU-12) as a genuinely porous germanate with
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large 16-membered-ring windows [19]. The structure is constructed from Ge7 clusters and exhibits remarkable ion-exchange properties reminiscent of aluminosilicate zeolites. By using a different organic amine as structure-directing agent, a material (ASU-16) with the same building units, but with a larger 24-ring channels and much lower framework density (8.6 Ge atoms per 1000 ˚ 3), has been prepared in similar synthesis conditions A [9]. Zhao et al. have reported the synthesis and structure of another 24-membered-ring germanate (FDU-4), which is condensed from Ge9 clusters under solvothermal conditions [20]. The aim of our work is to construct new open frameworks from germanium-oxide clusters, and we have isolated several new compounds in this system [21]. Here, we report two new germanates [Cd2(C2N2H8)3][Ge9O18(OH)4] (1) and (C8N4H26)[Ge9O18(OH)4] (2), which consist of Ge9 clusters as building units connected though common vertices to form 3D framework.
2. Experimental
was recovered by filtration, washed with distilled water and dried in air (54% yield based on germanium). Elemental analysis was carried out to verify the organic content. Anal. found: C, 8.00%; H, 2.57%; N, 4.61%. Calcd: C, 8.09%; H, 2.55%; N, 4.72%. IR (KBr, cm1) for 2: 3024w, 1600m, 1506m, 1475m, 1285m, 1213m, 779vs, 717s, 583s, 492s, 417m. Preliminary thermogravimetric analyses of compound 1 and 2 were carried out under O2 atmosphere with a heating rate of 10 C/min1 from 40 to 700 C. For 1, a two-step weight loss of 15.78% was observed in the range between 360 and 670 C, corresponding to the departure of ethylenediamine molecules (observed: 13.01%; expected: 12.75%) and the dehydration process (observed: 2.77%; expected: 2.55% weight loss for two water molecules per formula unit). The post residue is CdO and GeO2. For 2, a total weight loss of 17.24% was observed in the range between 260 and 680 C, due to the release of organic amines (expected: 14.67%) from the structure and the partial dehydration process (expected: 6.06% weight loss for four water molecules per formula unit). The final product is amorphous GeO2.
2.1. Synthesis and initial characterization In a typical synthesis for 1, 0.15 g of GeO2 was dispersed in a mixed solution of 0.5 ml of H2O and 1.33 ml of ethylene glycol, and then 0.77 ml of ethylenediamine was dropwise added to get a clear solution. To this mixture, 0.082 g of CdCl2 Æ 2H2O was finally added and homogenized for 30 min. The resulting mixture of the composition GeO2:ethylenediamine:CdCl2 Æ 2H2O:H2O:ethylene glycol in a molar ratio of 1:8:0.25: 25:15 was sealed in a Teflon-lined steel autoclave, heated at 170 C for 7 days and then cooled to room temperature. The product was recovered by filtration, washed thoroughly with distilled water, dried at room temperature, and then colorless prism-like crystals were obtained (65% yield based on germanium). The ICP analysis shows that the compound contains 44.86 wt% Ge and 15.13 wt% Cd, indicating a Ge:Cd ratio of 9:2. Elemental analysis results of the bulk product are consistent with the stoichiometry of 1. Anal. found: C, 5.24%; H, 1.51%; N, 5.92%. Calcd: C, 5.09%; H, 1.71%; N, 5.94%. IR (KBr, cm1) for 1: 3318m, 3267m, 3161w, 2920m, 2457w, 1583m, 1485w, 1458w, 1283m, 1189w, 1110m, 1038m, 950w, 780s, 728s, 703s, 581s, 522s, 482s, 416m. In a typical synthesis for 2, a mixture of GeO2 (0.15 g), H2O (0.5 ml), ethylene glycol (1.33 ml) and N,N 0 bis(3-aminopropyl)ethylene diamine (2.2 ml) in a molar ratio of 1:25:15:8 was stirred under ambient conditions. The resulting gel, with a pH of 9, was sealed in a Teflon-lined steel autoclave and heated in 170 C for 7 days and then cooled to room temperature. The resulting product, which contained colorless prism-like crystals,
2.2. Crystal structure determination A suitable single crystal of as-synthesized compounds with the dimensions of 0.29 · 0.11 · 0.06 mm for 1 and 0.33 · 0.20 · 0.16 mm for 2 was carefully selected under an optical microscope and glued to a thin glass fiber with epoxy resin, respectively. Crystal structure determination by X-ray diffraction was performed on a Siemens SMART CCD diffractometer with graphite-monochro˚ ) radiation in the x and mated MoKa (k = 0.71073 A u scanning mode at room temperature. Both structures were solved by direct methods and refined on F2 by fullmatrix least-squares methods using the SHELX97 program package [22,23]. The crystal structure of 1 was solved in the orthorhombic space group Pbca (No. 61). The cadmium and germanium atoms were first located, and the carbon, nitrogen, and oxygen atoms were found in the final difference Fourier map. The cadmium atom is disorder over two positions, with the occupancies of 90% and 10%, respectively. The H atom were positioned at idealized geometry and refined using a riding model, except the hydrogen attached to O(10) and N(1) atoms. All non-hydrogen atoms were refined anisotropically. Experimental details for the structure determination are presented in Table 1. The coordinates of all non-H atoms are given in Table 2. Selected bond distances are listed in Table 3. The determination of the crystal structure of 2 followed the same procedure as outlined for 1 with location of the Ge atoms from direct methods (space
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207
Table 1 Crystal data and structure refinement for 1 and 2
Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
Volume Z Density (calcd) Absorption coefficient F(0 0 0) Crystal size h range for data collection Limiting indices Reflections collected Independent reflections Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)]a R indices (all data)a Largest diff. peak and hole a
1
2
C6H28Cd2Ge9N6O22 1414.45 293(2) K ˚ 0.71073 A
C8H30Ge9N4O22 1187.67 293(2) K ˚ 0.71073 A
Orthorhombic Pbca ˚ a = 14.318(3) A ˚ b = 13.106(3) A ˚ c = 14.580(3) A ˚3 2736.0(9) A
Orthorhombic Pbca ˚ a = 14.158(3) A ˚ b = 13.213(3) A ˚ c = 14.553(3) A ˚3 2722.5(9) A
4 3.434 g cm3 11.359 mm1 2664 0.29 · 0.11 · 0.06 mm 2.53–27.48 18 6 h 6 18, 16 6 k 6 17, 18 6 l 6 18 5783 3082 [R(int) = 0.0426] Full-matrix least-squares on F2 3082/0/214 1.090 R1 = 0.0591, wR2 = 0.1230 R1 = 0.0794, wR2 = 0.1291 ˚ 3 1.238 and 1.535 eA
4 2.898 g cm3 9.892 mm1 2280 0.33 · 0.20 · 0.16 mm 2.53–27.48 18 6 h 6 18, 17 6 k 6 17, 18 6 l 6 18 5782 3070 [R(int) = 0.0274] Full-matrix least-squares on F2 3070/0/166 0.947 R1 = 0.0407, wR2 = 0.0885 R1 = 0.0585, wR2 = 0.0927 ˚ 3 1.567 and 0.964 eA
R1 = RkFojjFck/R jFoj, wR2 ¼ ½R½wðF 2o F 2c Þ2 =R½wðF 2o Þ2 1=2 .
Table 2 Atomic coordinates (·104) and equivalent isotropic displacement ˚ 2 · 103) for 1 parameters (A
Cd(1) Cd(1 0 ) Ge(1) Ge(2) Ge(3) Ge(4) Ge(5) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) O(10) O(11) N(1) N(2) N(3) C(1) C(2) C(3)
x
y
z
U(eq)a
3542(1) 3266(9) 5138(1) 6564(1) 4949(1) 3609(1) 5000 6256(4) 6183(5) 6100(4) 5218(5) 5001(4) 3982(5) 2763(5) 4621(4) 4198(5) 4699(5) 2758(5) 2460(9) 2831(13) 4066(16) 1965(14) 2418(17) 4582(14)
9048(1) 8593(11) 6779(1) 6668(1) 7851(1) 7241(1) 5000 5401(5) 7210(6) 7305(5) 6925(6) 5486(5) 7856(6) 8284(5) 6302(5) 7532(6) 8888(6) 6288(6) 8419(11) 10,546(11) 10,279(15) 9299(17) 10,260(20) 10,219(18)
3404(1) 3162(9) 3565(1) 5121(1) 1504(1) 5035(1) 5000 5140(5) 4089(5) 6078(5) 2399(5) 3784(5) 6050(5) 4765(5) 5395(4) 3977(5) 2265(5) 4986(7) 2469(9) 2773(15) 4249(19) 2094(15) 1979(15) 5100(19)
27(1) 49(3) 13(1) 13(1) 14(1) 14(1) 12(1) 16(2) 19(2) 17(2) 23(2) 17(2) 20(2) 18(2) 14(1) 21(2) 22(2) 32(2) 52(3) 99(7) 144(11) 87(7) 27(5) 96(8)
a U(eq) is defined as one-third of the trace of the orthogonalized Uij tensor.
group Pbca; No. 61), and subsequent difference Fourier analysis in order to locate the carbon, nitrogen, and
Table 3 ˚ ) for 1a Selected bond lengths (A Cd(1)–N(3) Cd(1)–N(1) Cd(1)–O(9) Cd(1)–O(10) Cd(1)–N(2) Cd(1)–O(7) Ge(1)–O(4) Ge(1)–O(5) Ge(1)–O(2) Ge(1)–O(9) Ge(2)–O(1) Ge(2)–O(7)#1 Ge(2)–O(2) Ge(2)–O(3) Ge(3)–O(3)#2
2.163(19) 2.223(12) 2.352(7) 2.356(7) 2.395(16) 2.486(7) 1.715(7) 1.736(7) 1.772(7) 1.773(7) 1.719(7) 1.725(7) 1.751(7) 1.757(7) 1.772(6)
Ge(3)–O(10) Ge(3)–O(6)#2 Ge(3)–O(4) Ge(3)–O(8)#2 Ge(4)–O(11) Ge(4)–O(6) Ge(4)–O(9) Ge(4)–O(7) Ge(4)–O(8) Ge(5)–O(8) Ge(5)–O(8)#3 Ge(5)–O(5) Ge(5)–O(5)#3 Ge(5)–O(1)#3 Ge(5)–O(1)
1.791(7) 1.793(7) 1.823(7) 2.018(7) 1.747(8) 1.768(7) 1.798(7) 1.869(7) 1.972(6) 1.880(7) 1.880(7) 1.884(7) 1.884(7) 1.885(6) 1.885(6)
a
Symmetry transformations used to generate equivalent atoms: #1 x + 1/2, y + 3/2, z + 1; #2 x, y + 3/2, z1/2; #3 x + 1, y + 1, z + 1.
oxygen atoms. There is one protonated N,N 0 -bis(3aminopropyl)ethylene diamine per formula, which is disordered within the cavities of the structure. The hydrogen atoms were positioned at idealized geometry and all the framework atoms were refined anisotropically. Experimental details for the structure determination are presented in Table 1. The coordinates of all non-H atoms are given in Table 4. Selected bond distances are listed in Table 5.
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Table 4 Atomic coordinates (·104) and equivalent isotropic displacement ˚ 2 · 103) for 2 parameters (A
Ge(1) Ge(2) Ge(3) Ge(4) Ge(5) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) O(10) O(11) N(1) N(2) C(1) C(2) C(3) C(4)
x
y
z
U(eq)a
5133(1) 6596(1) 5026(1) 3639(1) 5000 6284(3) 6192(3) 6193(3) 5276(4) 4989(3) 4068(4) 2819(3) 4658(3) 4172(3) 4846(4) 2753(3) 1580(30) 3890(20) 2431(19) 2860(30) 3607(16) 4930(20)
6766(1) 6651(1) 7836(1) 7263(1) 5000 5372(3) 7219(3) 7313(3) 6882(3) 5475(3) 7880(4) 8335(3) 6325(3) 7484(3) 8859(3) 6326(4) 5010(30) 4860(20) 4756(19) 5410(30) 4855(17) 4909(19)
3559(1) 5095(1) 1507(1) 5038(1) 5000 5127(3) 4076(3) 6059(3) 2389(3) 3778(3) 6057(3) 4860(3) 5402(3) 3944(3) 2262(3) 5052(4) 3330(30) 580(20) 2650(20) 2230(30) 1619(17) 468(16)
13(1) 12(1) 16(1) 15(1) 10(1) 15(1) 21(1) 22(1) 27(1) 17(1) 29(1) 21(1) 12(1) 25(1) 35(1) 35(1) 410(20) 268(13) 211(12) 310(20) 166(9) 196(11)
a
U(eq) is defined as one-third of the trace of the orthogonalized Uij tensor.
Table 5 ˚ ) and angles (degree) for 2a Selected bond lengths (A Ge(1)–O(4) Ge(1)–O(5) Ge(1)–O(9) Ge(1)–O(2) Ge(2)–O(7)#1 Ge(2)–O(1) Ge(2)–O(3) Ge(2)–O(2) Ge(3)–O(10) Ge(3)–O(6)#2 Ge(3)–O(3)#2 Ge(3)–O(4)
1.721(4) 1.747(4) 1.750(4) 1.781(4) 1.733(5) 1.747(4) 1.749(4) 1.758(4) 1.761(4) 1.779(5) 1.787(4) 1.834(4)
Ge(3)–O(8)#2 Ge(4)–O(11) Ge(4)–O(9) Ge(4)–O(6) Ge(4)–O(7) Ge(4)–O(8) Ge(5)–O(5) Ge(5)–O(5)#3 Ge(5)–O(1) Ge(5)–O(1)#3 Ge(5)–O(8)#3 Ge(5)–O(8)
2.022(4) 1.762(5) 1.786(4) 1.799(4) 1.850(4) 1.975(4) 1.886(4) 1.886(4) 1.893(4) 1.893(4) 1.909(4) 1.909(4)
a
Symmetry transformations used to generate equivalent atoms: #1 x + 1/2, y + 3/2, z + 1; #2 x, y + 3/2, z1/2; #3 x + 1, y + 1, z + 1.
3. Results 3.1. Crystal structure of [Cd2(C2N2H8)3][Ge9O18(OH)4] 1 The asymmetric unit of 1 consists of 23 non-hydrogen atoms, as shown in Fig. 1. There are one crystallographically distinct cadmium atom and five unique germanium atoms. The cadmium atom is octahedrally coordinated, bonded to three oxygen atoms [Cd–O ˚ ] and three nitrogen atoms [Cd–N (ave.) (ave.) 2.399 A ˚ 2.260 A] from ethylenediamine ligands. Of the five independent Ge atoms, Ge(1) and Ge(2) atoms are tetrahed-
Fig. 1. ORTEP view of the asymmetric unit of 1, with 30% thermal ellipsoids and the atom-labeling scheme.
rally coordinated, with the Ge–O distances in the range ˚ (ave. 1.743 A ˚ ) and the O–Ge–O 1.715(7)–1.773(7) A angles in the range of 106.4(3)–113.2(3). Ge(3) and Ge(4) atoms are coordinated to five oxygen atoms, with the Ge–O bond distances varying from 1.747(8) to ˚ (ave. 1.836 A ˚ ). Ge(5) is located at the inver2.018(7) A sion center and is octahedrally coordinated, with Ge–O ˚ (ave. 1.883 distances between 1.880(7) and 1.885(6) A ˚ ). These geometric parameters are in accord with those A observed for open-framework germanates containing Ge9O18(OH)4 clusters [24–27]. Assuming the usual valence of Cd, Ge, and O atoms to be +2, +4, and 2, respectively, the framework stoichiometry of [CdGe4.5O11] creates a net charge of 2, which is needed to be balanced. Bond valence sum values indicate that O(10) and O(11) are hydroxyl groups. The structure of 1 is constructed from two distinct motifs, a body-centered [Ge9O18(OH)4] cluster and a cadmium complex [Cd2(C2N2H8)3O6], which integrate to generate a 3D architecture with neutral framework (Fig. 2a and b). As shown in Fig. 3a, the Ge9 building block is condensed from four GeO4 tetrahedra, four GeO4(OH) trigonal bipyramids, and one GeO6 octahedron. The GeO6 occupies the center of the cluster and links the four GeO4 and four GeO4(OH) through doubly bridging oxygen atoms and tri-bridging oxygen atoms. Each of such building units is connected to eight adjacent Ge9 units in a body-centered manner to form a three-dimensional framework. The second structural building block is a cadmium complex [Cd2(C2N2H8)3O6] containing two types of ethylenediamine molecules, one acts as chelating ligand and protrudes into the 8-ring channel and the other serves as a bridge to connect two symmetry-related cadmium atoms (Fig. 3b). In addition to the three nitrogen donors from the ethylenediamine ligands, each cadmium atom is connected to the germanate framework through O(7), O(9) and O(10) atoms.
Z.-E. Lin et al. / Microporous and Mesoporous Materials 74 (2004) 205–211
209
Fig. 2. View of the structure of 1 along the (a) [0 1 0] and (b) [1 1 0] direction, respectively.
Fig. 3. The 3D framework of 1 is constructed from the building blocks of (a) Ge9O18(OH)4 clusters and (b) Cd2(C2N2H8)3O3 complexes.
Fig. 4. ORTEP view of the coordination environments of the germanium atoms in 2, with 30% thermal ellipsoids and the atomlabeling scheme.
3.2. Crystal structure of (C8N4H26)[Ge9O18(OH)4] 2 As seen in Fig. 4, the asymmetric unit of 2 contains five crystallographically distinct germanium atoms, which have three different coordination numbers. Ge(1) and Ge(2) each has typical tetrahedral coordination, with the Ge–O distances in the range 1.721(4)– ˚ (ave. 1.748 A ˚ ) and the O–Ge–O angles in 1.781(4) A the range of 105.38(19)–112.6(2). Ge(3) and Ge(4) each is coordinated to five oxygen atoms, one of them being a terminal –OH group. Ge(5) is located at the inversion center and adopts an octahedral coordination. The Ge–O distances within the trigonal bipyramidal and octahedral germanium centers are between 1.761(4) ˚ , which are markedly longer than those and 2.022(4) A found in the GeO4 tetrahedra. The connectivity of GeO4 tetrahedra, GeO5 trigonal bipyramids and GeO6 octahedra gives rise to the 3D
framework. In the structure, there are three types of channels. The smaller one has an eight-membered ring and runs along the [0 1 0] direction, as shown in Fig. 5. The diameter of the channel is approximately 5.9 · 6.1 ˚ (corresponding to the interatomic O–O distances). A Intersecting this channel are the two elliptical 10-membered windows, which have the same aperture and run along the [1 0 1] and [1 0 1] directions, respectively. The diameter of the channels is approximately 7.1 · ˚ (Fig. 6). 7.6 A The quadruply protonated N,N 0 -bis(3-aminopropyl)ethylene diamine molecules are located in the 10ring channels and interact with the inorganic framework through hydrogen bonds as N(1)–H(4) O(10) [d = ˚ ], N(1)–H(5) O(4) [d = 2.39 A ˚ ], N(2)–H(6) 2.27 A ˚ ˚ ]. O(11) [d = 2.20 A], and N(2)–H(7) O(7) [d = 2.12 A The extensive interactions between the organic moieties
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Fig. 5. Polyhedral view of the 3D framework of 2 along the [0 1 0] direction, showing the 8-ring channels. Guest molecules are omitted for clarity.
Fig. 6. Polyhedral view of the 3D framework of 2 along the [1 0 1] direction, showing the 10-ring channels. Guest molecules are omitted for clarity.
and the inorganic framework may play an important role to stabilize the structure, because attempts to remove of the organic moieties by calcination make the structure collapse.
4. Discussion Two new 3D open-framework germanates, [Cd2(C2N2H8)3][Ge9O18(OH)4] (1) and (C8N4H26)[Ge9O18(OH)4] (2), have been obtained as good-quality single crystals under similar hydrothermal conditions. The two compounds possess similar germanate framework that is assembled from Ge9O18(OH)4 clusters. Interestingly, the molecular Ge9 cluster has been successfully
isolated under hydrothermal conditions by Tripathi et al. [28]. According to the aufbau principle of building higher-dimensional structures from that of the lowerdimensional ones [29], it is conceivable that the use of this Ge9 clusters as the precursor to produce novel open frameworks may be realized either in the solid state or via a solution mediated process. The role of the metal complex in the structure of 1 is subtle and merits some attention. In previous literatures, metal complexes are usually used as structure-directing agents to direct the formation of specific inorganic frameworks [30–38]. These complexes are accommodated in the free voids of the structures and interact with the macroanionic ‘‘host’’ frameworks through H-bonding interactions. In the present compound 1 the Cd atom is bound to the host via covalent bonds. The framework ˚3 density defined as the number of polyhedra per 1000 A is 16.1 for 1, compared with the value of 16.7 for the structurally related zinc germanates ZnGe-1A(B) [39], and 16.4 for the cobalt germanate [Co2(C2N2H8)3][Ge9O18(OH)4] [40]. Compound 2 possesses a similar germanate framework constructed from Ge9O18(OH)4 clusters, however, the framework density of 13.2 for 2 makes it more of an open framework structure than 1. Another way to quantify the openness of these types of compounds is to calculate the fraction of the unit cell volume not occupied by the framework atoms, assuming typical van der Waals radii for these species. A void space analysis with PLATON indicates that the inorganic framework of 2 occupies 58.0% of the unit cell volume, leaving 42.0% ˚ 3 out of the unit cell volume of 2722.5 A ˚ 3) as (1142.2 A ‘‘solvent accessible’’ space [41]. However, only 427.9 ˚ 3 (15.6% of the unit cell volume) for compound 1 reA mains unoccupied, when the C, N, and H atoms of the ethylenediamine molecules are ignored. The decreased free space of compound 1 is due to that the cadmium complexes block the 10-ring channels along the [1 0 1] and [1 0 1] directions.
5. Conclusion Two new open-framework germanates, [Cd2(C2N2H8)3][Ge9O18(OH)4] (1) and (C8N4H26)[Ge9O18(OH)4] (2), were obtained as good quality single crystals under hydrothermal conditions. The structural analyses demonstrate that they have 3D structures assembled from the building unit of [Ge9O18(OH)4] clusters. For 1, the connectivity between the [Ge9O18(OH)4] clusters and the cadmium complexes results in a neutral inorganicorganic hybrid framework; while the structures of 2 has a macroanionic inorganic framework with 8-, 10-, and 10-ring channels along the [0 1 0], [1 0 1] and [1 0 1] directions.
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Acknowledgments This work was supported by the NSF of China (Grant nos. 20271050 and 20171045), the SRF for ROCS of State Education Ministry, the Ministry of Finance of China and the Talents Program of Chinese Academy of Sciences, and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry of Jilin University. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.micromeso.2004.06.020. References [1] M.E. Davis, Nature 417 (2002) 813. [2] J. Cheng, R. Xu, J. Chem. Soc., Chem. Commun. (1991) 483. [3] J. Cheng, R. Xu, G. Yang, J. Chem. Soc., Dalton Trans. (1991) 1537. [4] R.H. Jones, J. Chen, J.M. Thomas, A. George, M.B. Hursthouse, R. Xu, S. Li, Y. Lu, G. Yang, Chem. Mater. 4 (1992) 808. [5] H. Li, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998) 10569. [6] C. Cascales, E. Gutie´rrez-Puebla, M. Iglesias, M.A. Monge, C. Ruız-Valero, Angew. Chem. Int. Ed. 38 (1999) 2436. [7] X. Bu, P. Feng, G.D. Stucky, Chem. Mater. 11 (1999) 3025. [8] X. Bu, P. Feng, G.D. Stucky, Chem. Mater. 11 (1999) 3423. [9] H. Li, M. Eddaoudi, J. Ple´vert, M. OKeeffe, O.M. Yaghi, J. Am. Chem. Soc. 122 (2000) 12409. [10] M.S. Dadachov, K. Sun, T. Conradsson, X. Zou, Angew. Chem., Int. Ed. 39 (2000) 3674. [11] T. Conradsson, M.S. Dadachov, X. Zou, Micropor. Mesopor. Mater. 41 (2000) 183. [12] C. Cascales, E. Gutie´rrez-Puebla, M. Iglesias, M.A. Monge, C. Ruız-Valero, N. Snejko, Chem. Commun. (2000) 2145. [13] L. Beitone, T. Loiseau, G. Fe´rey, Inorg. Chem. 41 (2002) 3962. [14] D. Pitzschke, W. Bensch, Angew. Chem. Int. Ed. 42 (2003) 4389. [15] X. Bu, P. Feng, G.D. Stucky, J. Am. Chem. Soc. 120 (1998) 11204.
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