Syntheses and Structures of One-and Two-Dimensional Organic

ACS Appl. Bio Mater. .... Compounds 1 and 2 reveal the one-dimensional chain infinitely extended ... Crystal Growth & Design 2013 13 (10), 4368-4377 ...
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CRYSTAL GROWTH & DESIGN

Syntheses and Structures of One- and Two-Dimensional Organic-Inorganic Hybrid Rare Earth Derivatives Based on Monovacant Keggin-Type Polyoxotungstates

2006 VOL. 6, NO. 2 507-513

Jing-Ping Wang,† Jun-Wei Zhao,‡ Xian-Ying Duan,§ and Jing-Yang Niu*,† Institute of Molecule and Crystal Engineering, School of Chemistry and Chemical Engineering, Henan UniVersity, Kaifeng 475001, P. R. China, State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, P. R. China, and State Key Laboratory of Coordination Chemistry, Nanjing UniVersity, Nanjing 210093, P. R. China ReceiVed August 22, 2005; ReVised Manuscript ReceiVed December 6, 2005

ABSTRACT: Three novel organic-inorganic hybrid monovacant Keggin-type silicotungstates and germanotungstates containing lanthanideIII cations with 1D and 2D infinitely extended structures, [Sm(H2O)6]0.25[Sm(H2O)5]0.25H0.5{Sm(H2O)7[Sm(H2O)2(DMSO)(R-SiW11O39)]}‚4.5H2O (DMSO ) dimethyl sulfoxide) (1), [Dy(H2O)4]0.25[Dy(H2O)6]0.25H0.5{Dy(H2O)7[Dy(H2O)2(DMSO)(RGeW11O39)]}‚5.25H2O (2), and H{[Sm(H2O)5.5(DMF)0.5]2[Sm(H2O)2(DMF)][Sm(H2O)3(R-SiW11O39)]2} (DMF ) N,N-dimethyl formamide) (3), have been synthesized in aqueous solution under moderate conditions and further characterized by elemental analyses, inductively coupled plasma (ICP) analyses, IR, UV spectra, and X-ray diffraction. Compounds 1 and 2 reveal the one-dimensional chain infinitely extended structure, while compound 3 represents the first example of a two-dimensional network structure formed by the monovacant Keggin-type [R-SiW11O39]8- chain through the linkage of rare earth metal-organic coordination cations. From thermogravimetric (TG/DTA) analyses, the polyanion frameworks of 1 and 2 retain a comparatively good thermal stability. Variable temperature magnetic susceptibility indicates that compounds 1 and 3 obey the Curie-Weiss law in the higher temperature region from 130 to 300 K, while in the lower temperature region from 2 to 130 K they show the occurrence of strong spin-orbital coupling interactions and very weak ferromagnetic responses. Introduction Much current research activity of polyoxometalate chemistry is driven by potential, perceived, and realized applications in many areas, especially catalysis, separations, ion exchange, imaging, sorption, medicine, functional materials, and molecular electronics in addition to optical, electrical, magnetic, and supraconductive fields.1-20 Polyoxometalates may be versatile inorganic building blocks for the construction of molecularbased materials. By means of their multiple coordination requirements and oxophilicity, transition metal and lanthanide cations are suitable to link polyoxometalate building blocks to form new classes of materials with potentially useful magnetic and luminescent properties.21-24 The behavior of plenary silicotungstates in solution has been widely studied and the monovacant, divacant, and trivacant derivatives of the [SiW12O40]4- Keggin-type anion have also been characterized.25,26 Among the four identified isomers of the [SiW11O39]8- monovacant complexes, only the [R-SiW11O39]8species has been found to be stable in solution. Peacock and Weakley studied the interactions between this isomer and lanthanide cations,27 and they reported that the [R-SiW11O39]8forms both 1:1 and 1:2 compounds with rare earth metals. In 2000, Pope et al. investigated the structural characterization of the one-dimensional 1:1 [Ln(R-SiW11O39)(H2O)3]5- (Ln ) LaIII, CeIII) compounds, showing that these anions are polymeric in the solid state.28 In 2003, Mialane et al. also reported the solidstate structures of the Ln/[R-SiW11O39]8- (Ln ) YbIII, NdIII, EuIII, GdIII).29 Interestingly, both Pope and Mialane noticed that some differences of molecular structures exist in the solid-state * To whom correspondence should be addressed. E-mail: jyniu@ henu.edu.cn. † Henan University. ‡ Chinese Academy of Sciences. § Nanjing University.

polymers. In 2004, Mialane et al. reported the dimeric K12[(SiW11O39Ln)2(µ-CH3COO)2] (Ln ) GdIII, YbIII) complexes.30 All above studies indicated the fascinating interest in the lanthanide cation and monovacant Keggin-type polyanion system. To date, 1D and 2D organic-inorganic hybrid chains and networks constructed by monovacant Keggin-type polyanions through transition metal coordination ions by means of hydrothermal synthesis were reported,9,20 However, the 1D and 2D organic-inorganic hybrid rare earth derivatives based on monovacant Keggin-type [R-SiW11O39]8- or [R-GeW11O39]8polyanions have not been studied. In the course of exploring the lanthanide cations and monovacant Keggin-type [R-SiW11O39]8- polyanion system, we also extended the investigation of the system based on lanthanide cations and the monovacant Keggin-type [R-GeW11O39]8- polyanion. Herein for the first time, we report the syntheses and crystal structures of three novel organic-inorganic hybrid monovacant Keggin-type silicotungstates and germanotungstates containing lanthanideIII cations with 1D and 2D infinitely extended structures, [Sm(H 2 O) 6 ] 0.25 [Sm(H 2 O) 5 ] 0.25 H 0.5 {Sm(H 2 O) 7 [Sm(H 2 O) 2 (DMSO)(R-SiW11O39)]}‚4.5H2O(1),[Dy(H2O)4]0.25[Dy(H2O)6]0.25H0.5{Dy(H2O)7[Dy(H2O)2(DMSO)(R-GeW11O39)]}‚5.25H2O (2), and H{[Sm(H2O)5.5(DMF)0.5]2[Sm(H2O)2(DMF)][Sm(H2O)3(RSiW11O39)]2} (3). Compounds 1 and 2 reveal the onedimensional chain infinitely extended structures, while compound 3 represents the first example of a two-dimensional network structure formed by the monovacant Keggin-type [R-SiW11O39]8- polyanions and rare earth metal organic coordination cations. Experimental Section General Methods and Materials. R-K8SiW11O39‚13H2O and R-K8GeW11O39‚nH2O were prepared according to procedures in the literature25 and confirmed by IR spectra. Other reagents were purchased

10.1021/cg050433j CCC: $33.50 © 2006 American Chemical Society Published on Web 01/07/2006

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Table 1. Crystal Data and Structure Refinement for 1, 2, and 3

empirical formula fw crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z Dc, g cm-3 abs coeff, mm-1 T, K no. of reflns collected no. of independent reflns data/restrains/params GOF on F2 final R indices [I > 2σ(I)] R indices (all data) largest diff peak and hole (e Å-3)

1

2

3

C2H39O56.25SSiSm2.50W11 3421.59 monoclinic P21/c 23.602(5) 11.601(2) 23.545(5) 90 109.05(3) 90 6094(2) 4 3.732 23.193 293(2) 15770 9742 9742/282/784 0.974 R1 ) 0.0609; wR2 ) 0.1238 R1 ) 0.0865; wR2 ) 0.1322 3.542 and -3.280

C2H41Dy2.50O56.75SGeW11 3506.48 monoclinic P21/c 23.537(5) 11.516(2) 23.418(5) 90 109.17(3) 90 5995(2) 4 3.851 24.712 293(2) 16676 9746 9746/108/766 1.045 R1 ) 0.0477; wR2 ) 0.0950 R1 ) 0.0717; wR2 ) 0.1017 2.375 and -2.543

C6H53N2O99Si2Sm5W22 6590.13 triclinic P1h 12.894(3) 13.193(3) 20.591(4) 108.09(3) 90.69(3) 107.79(3) 3148.1(11) 1 3.476 22.400 293(2) 7927 7927 7927/412/676 1.023 R1 ) 0.0798; wR2 ) 0.1640 R1 ) 0.1031; wR2 ) 0.1782 3.317 and -2.820

commercially and used without further purification. Elemental analyses (C, H, N, and S) were conducted on a Perkin-Elmer 240C analyzer. Inductively coupled plasma (ICP) analyses were carried out on JarrelAsh J-A1100 spectrometer. The infrared spectra were obtained from a sample powder palletized with KBr on Nicolet AVATAR 360 FTIR spectrophotometer over the range 4000-400 cm-1. UV spectra were obtained on a Unican UV-500 spectrometer (distilled water as solvent) in the range of 400-190 nm. The thermogravimetric (TG/DTA) analysis was on an Exstar 6000 analyzer in air atmosphere with a heating rate of 10 °C/min. The variable-temperature magnetic susceptibility data on polycrystalline samples of compounds 1 and 3 were measured with a quantum design MPMS7 SQUID magnetometer in the temperature region of 2-300 K. Synthesis of [Sm(H2O)6]0.25[Sm(H2O)5]0.25H0.5{Sm(H2O)7[Sm(H2O)2(DMSO)(r-SiW11O39)]}‚4.5H2O (1). The oxide Sm2O3 (0.52 g, 1.5 mmol) was first suspended in distilled water (5 mL), to which a solution of HClO4 (1.50 mL, 12.19 M) was added dropwise under stirring. The resulting mixture was refluxed until the solution became clear at the temperature of 70 °C under stirring, and then the pH value was adjusted to 5.15 by addition of a solution of NaOH (0.4 M). Then R-K8SiW11O39‚13H2O (1.65 g, 0.5 mmol) and dimethyl sulfoxide (1.5 mL) were added accompanying the formation of KClO4 (confirmed by IR spectra). The mixture was refluxed continuously for 1 h and then allowed to cool to the ambient temperature. After separation of the resulting KClO4, distilled water (20 mL) was added to the filtrate, and the obtained solution was left to evaporate slowly at room temperature; polyhedral crystals were obtained after several weeks. Yield: 0.74 g (43%). Anal. Calcd for C2H39O56.25SSiSm2.50W11: H, 1.15; C, 0.70; S, 0.94; Si, 0.82; Sm, 10.99; W, 59.10. Found: H, 1.04; C, 0.77; S, 0.98; Si, 0.79; Sm, 11.07; W, 59.19. Synthesis of [Dy(H2O)4]0.25[Dy(H2O)6]0.25H0.5{Dy(H2O)7[Dy(H2O)2(DMSO)(r-GeW11O39)]}‚5.25H2O (2). A solution of HClO4 (12.19 M) was added dropwise into the powder Dy2O3 (2.14 g, 5.74 mmol) under heating until Dy2O3 was completely dissolved. Under stirring, the above solution was added to a clear solution (100 mL) containing R-K8GeW11O39‚nH2O (6 g, ca. 2 mmol) at 70 °C, following the appearance of the white KClO4 precipitate. The mixture was concentrated for 1 h to 15 mL, cooled, and filtered, and 1 mL DMSO was added. Then the obtained solution was refluxed in a hot water bath (70 °C) for half an hour. The resulting clear solution was left to evaporate at room temperature. Several days later, polyhedral crystals were collected. Yield: 3.86 g (ca. 55%). Anal. Calcd for C2H41Dy2.50O56.75SGeW11: H, 1.18; C, 0.69; S, 0.91; Ge, 2.07; Dy, 11.59; W, 57.67. Found: H, 0.97; C, 0.72; S, 0.89; Ge, 2.20; Dy, 11.40; W, 57.60. Synthesis of H{[Sm(H2O)5.5(DMF)0.5]2[Sm(H2O)2(DMF)][Sm(H2O)3(r-SiW11O39)]2} (3). The preparation of the compound 3 is similar to that of 1. Replacing DMSO with DMF leads to the formation of 3. Yield: 0.77 g (47%). Anal. Calcd for C6H53N2O99Si2Sm5W22: H,

0.85; C, 1.09; N, 0.96; Si, 0.85; Sm, 11.41; W, 61.37. Found: H, 0.97; C, 0.96; N, 0.89; Si, 0.79; Sm, 11.29; W, 61.52. X-ray Crystallography. Crystals of compounds 1 (dimensions 0.18 × 0.11 × 0.10 mm3), 2 (dimensions 0.18 × 0.12 × 0.10 mm3), and 3 (dimensions 0.26 × 0.12 × 0.08 mm3) were carefully selected under an optical microscope and glued at the tip of a thin glass fiber with cyanoacrylate (super glue) adhesive. Intensity data were collected with a Rigaku RAXIS-IV image plate area detector using graphite monochromatized Mo KR radiation (λ ) 0.710 73 Å) at 293(2) K. The structures were solved by direct methods and refined by the full-matrix least-squares method on F2 using the SHELXTL-97 package.31 Intensity data were corrected for Lorentz and polarization effects, as well as for empirical absorption. All of the non-hydrogen atoms were refined anisotropically. Experimental details for the structural determination of compounds 1, 2, and 3 are listed in Table 1. Selected bond distances and angles for 1, 2, and 3 are represented in Tables 2, 3 and 4, respectively, of the Supporting Information.

Results and Discussion Synthesis. In comparison with the previous work,29 the synthetic conditions on the preparation of 1 and 3 were further explored in the synthetic strategy. The experimental results showed that compounds 1 and 3 could be formed in the pH range of 4.5-5.5. In addition, the study scope of organicinorganic hybrid rare earth (RE) derivatives with monovacant Keggin polyanions is extended to the [R-GeW11O39]8- polyanion. Moreover, to introduce more RE (SmIII, DyIII) cations into the one-dimensional and two-dimensional frameworks of compounds 1, 2, and 3 with monovacant Keggin-type [R-SiW11O39]8or [R-GeW11O39]8- precursors in the synthetic process, we employed much more HClO4 than the previous method29 to remove all the K+ countercations, mainly because the resulting KClO4 can be precipitated and filtered out. Therefore, according to our experimental results, we believe that using much more ClO4- ions to eliminate all the K+ ions may provide the necessary conditions for the introduction of by far more Sm3+ or Dy3+ cations into the frameworks of compounds 1, 2, and 3 in the one-dimensional and two-dimensional structural construction. In addition, the amount of DMSO was also investigated. When the amount of DMSO changes in the range of 1-4 mL under the given condition above, it was always found that there is only one DMSO in the asymmetric structural units of compounds 1 and 2. If the amount of DMSO is more than 4 mL under the given conditions, the reaction mixture cannot

Organic-Inorganic Hybrid Rare Earth Derivatives

produce crystals but only amorphous powders. However, the amount of DMF under the given conditions was not explored. So, further investigation about the extension and reproducibility of the preparation is under way. IR and UV Spectral Characterization. In the low-wavenumber region (ν < 1000 cm-1) of the IR spectra, compounds 1, 2, and 3 display characteristic vibration patterns of the Keggin-type structure. Four characteristic vibration sharp peaks resulting from the Keggin-type polyanions, namely, ν(W-Od), ν(Si/Ge-Oa), ν(W-Ob), and ν(W-Oc), appear at 949, 894, 831, and 703 cm-1 for 1, at 947, 523, 816, and 704 cm-1 for 2, and at 951, 889, 831, and 703 cm-1 for 3, respectively. In comparison with IR spectra of the precursor R-K8SiW11O39‚ 13H2O, the ν(W-Od) vibration frequency for 1 and 3 has a red shift of 5-7 cm-1; compared to R-K8GeW11O39‚nH2O, the ν(W-Od) vibration frequency for 2 has a red shift of 12 cm-1, the possible major reasons for which may be that the charge compensation cations have stronger interactions to the terminal oxygen atoms of the polyanions, impairing the W-Od bond, reducing the W-Od bond force constant and leading to decreasing of the W-Od vibration frequency. The ν(Si-Oa), ν(W-Ob-W), and ν(W-Oc-W) vibration frequencies for 1 and 3 have blue shifts of 7-15, 31, and 24 cm-1, respectively; the ν(Ge-Oa), ν(W-Ob-W), and ν(W-Oc-W) vibration frequencies for 2 have blue shifts of 4, 17, and 34 cm-1, respectively, the possible reasons for which are that the polyanion symmetry of compounds 1, 2, and 3 increases as compared to that of R-K8SiW11O39‚13H2O or R-K8GeW11O39‚ nH2O. In addition, the resonance at ca. 1006 cm-1 in compounds 1 and 2 is assigned to ν(SdO) asymmetric stretching vibration of DMSO molecules. Comparing with that of free DMSO,32 the ν(SdO) shift from 1055 to 1006 cm-1. In the compound 3, the vibration peak of the CdO in DMF molecules has a red shift from 1678 to 1652 cm-1 as compared to the free DMF.33 These results suggest that the DMSO and DMF ligands are coordinated to the metal ion by means of the oxygen atoms. It can explain the decreasing of the charge density over the oxygen and sulfur or carbon atoms owing to O atoms from the SdO or CdO bonds coordinated to metal ion. The IR spectral studies also indicate that there are strong interactions between the monovacant polyanions and rare earth metal-organic cations in the solid state. The UV spectra in aqueous solution for compounds 1, 2, and 3 in the range of 400-190 nm reveal an absorption band at ca. 250-270 nm, which is assigned to the pπ-dπ charge-transfer transitions of the Ob(c) f W bond.34 Structural Description. To the best of our knowledge, the crystal structures of the 1D and 2D organic-inorganic hybrid rare earth derivatives with monovacant [R-SiW11O39]8- or [R-GeW11O39]8- building blocks have not been reported. The investigation of the X-ray single-crystal structures of [Sm(H2O)6]0.25[Sm(H2O)5]0.25H0.5{Sm(H2O)7[Sm(H2O)2(DMSO)(RSiW11O39)]}‚4.5H2O (1), [Dy(H2O)4]0.25[Dy(H2O)6]0.25H0.5{Dy(H2O)7[Dy(H2O)2(DMSO)(R-GeW11O39)]}‚5.25H2O (2), and H{[Sm(H 2 O) 5.5 (DMF) 0.5 ] 2 [Sm(H 2 O) 2 (DMF)][Sm(H 2 O) 3 (R-SiW11O39)]2} (3) is the first case. The asymmetric structural unit of 1 consists of 0.5 H+, 0.25 discrete [Sm(3)(H2O)6]3+, 0.25 discrete [Sm(4)(H2O)5]3+, a {Sm(2)(H2O)7[Sm(1)(H2O)2(DMSO)(R-SiW11O39)]}2- polyanion unit, and 4.5 water of crystallization (Figure 1). The polyanion unit {Sm(2)(H2O)7[Sm(1)(H2O)2(DMSO)(R-SiW11O39)]}2- is composed of one [Sm(2)(H2O)7]3+, one [Sm(1)(H2O)2(DMSO)]3+, and one [R-SiW11O39]8- building blocks. The neighboring polyanion units {Sm(2)(H2O)7[Sm(1)(H2O)2(DMSO)(R-SiW11O39)]}2- are bridged together forming

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Figure 1. Representation of the molecular structure unit of 1. The hydrogen atoms, discrete Sm3+ coordination ions, and crystal water molecules are omitted for clarity.

a novel 1D chain structure by means of [Sm(1)(H2O)2(DMSO)]3+ (Figure 2). Sm3+(1) coordination cation, which is incorporated into the vacant site of the [R-SiW11O39]8- fragment, is eight-coordinate, adopting a distorted square antiprism geometry with the Sm(1)-O distances of 2.361(13)-2.518(14) Å, consistent with the results of previous study,35 in which two coordination oxygen atoms come from water molecules, one from the DMSO, and five from the [R-SiW11O39]8- fragment. In the coordination polyhedron around the Sm3+(1) cation, the O9, O1W, O2W, and O1A group and the O24, O29, O32, and O14 group constitute two bottom planes of the square antiprism, and their average deviations from their ideal planes are 0.0993 and 0.0067 Å, respectively. The distances between the Sm3+(1) cation and the two bottom planes are 1.3149 and 1.2088 Å, respectively. The Sm(1)-O(9) [2.421(13) Å] distance is much longer than those of other Sm-Od distances because the W-Od-Sm(1)-O(9)-W linkage acts as the bridge forming a novel 1D chain structure. The Sm3+(2) coordination cation is also eight-coordinate with a distorted square antiprism environment with Sm(2)-O distances of 2.372(14)-2.460(14) Å, defined by eight coordination oxygen atoms, seven from water molecules and one from the [R-SiW11O39]8- framework. In the coordination polyhedron around the Sm3+(2) cation, the O10, O3W, O6W, and O7W group and the O4W, O7W, O8W, and O9W group constitute the two bottom planes of the square antiprism, and their average deviations are 0.0637 and 0.0218 Å, respectively. The distances between the Sm3+(2) cation and the two bottom planes are 1.2920 and 1.3465 Å, respectively. The disordered Sm3+(3) and Sm3+(4) coordination cations with the occupation rate of 0.25 are six-coordinate and fivecoordinate, respectively. In the polyanion unit, {Sm(2)(H2O)7[Sm(1)(H2O)2(DMSO)(R-SiW11O39)]}2-, the Si atom resides in the center of a SiO4 tetrahedron, which has been somewhat deformed resulting from the removal of one [WdOd]4+ group and the complete incorporation of a SmIII atom into the monovacant polyoxometalate framework as compared to saturated Keggin structure. The Si-O bond distances in the SiO4 polyhedron vary between 1.606(12) and 1.642(13) Å, which are in approximate accordance with the previous work,32 and the O-Si-O bond angles are in the range of 101.7(6)°-112.6(6)°. Similarly, all the WO6 octahedra are distorted to some extent. The crystal structure of 2 is very similar to that of 1, the asymmetric structural unit of 2 consists of 0.5 H+, 0.25 discrete

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Figure 2. The 1D chain motif constructed from the molecular structure units in compound 1. The hydrogen atoms, discrete Sm3+ coordination ions, and crystal water molecules are omitted for clarity.

Figure 3. Representation of the molecular structure unit of 2. The hydrogen atoms, discrete Dy3+ coordination ions, and crystal water molecules are omitted for clarity.

[Dy(3)(H2O)4]3+, 0.25 discrete [Dy(4)(H2O)6]3+, a {Dy(2)(H2O)7[Dy(1)(H2O)2(DMSO)(R-GeW11O39)]}2- polyanion unit, and 5.25 water of crystallization (Figure 3). The neighboring polyanion units {Dy(2)(H2O)7[Dy(1)(H2O)2(DMSO)(RGeW11O39)]}2- are bridged together forming a novel 1D chain structure by means of [Dy(1)(H2O)2(DMSO)]3+. The occupancy rate of four-coordinate [Dy(3)(H2O)4]3+ and six-coordinate [Dy(4)(H2O)6]3+ ions is also 0.25 in the crystal lattice. Dy3+(1) coordination cation located in the defect site of the [R-GeW11O39]8- fragment resides in a distorted square antiprism with the Dy(1)-O distances of 2.316(12)-2.471(13) Å. In the coordination geometry of the Dy3+(1) cation, the O32, O33, O34, and O35 group and the O9, O1A, O1W, and O2W group constitute the two bottom planes of the square antiprism, and their average deviations are 0.0051 and 0.1215 Å, respectively. The distances between the Dy3+(1) cation and the two bottom planes are 1.1314 and 1.3965 Å, respectively. The eightcoordinate Dy3+(2) coordination polyhedron can be described as a distorted square antiprism with Dy(2)-O distances of 2.332(10)-2.389(13) Å, defined by seven water molecules and one terminal oxygen atom from the [R-GeW11O39]8- precursor. In the coordination polyhedron around the Dy3+(2) ion, the O10, O5W, O7W, and O8W group and the O3W, O4W, O6W, and O9W group constitute the two bottom planes of the square antiprism, and their average deviations are 0.0637 and 0.0016 Å, respectively. The distances between the Dy3+(2) cation and the two bottom planes are 1.2815 and 1.2948 Å, respectively. In addition, the sulfur atom of DMSO in the [Sm(1)(H2O)2(DMSO)]3+ for 1 and [Dy(1)(H2O)2(DMSO)]3+ cations for 2 is crystallographically disordered and occupies two positions. The S-O distances for 1 and 2 are in the ranges 1.36(4)1.494(18) Å and 1.44(3)-1.462(14) Å, respectively, which are

Figure 4. Representation of the molecular structure unit of 3. The hydrogen atoms are omitted for clarity.

nearly consistent with the bond length range of SdO.36 In the case of the bridging µ-O coordination of DMSO, the S-O distances are within 1.50-1.56 Å.37-39 The differences in the bond lengths may be partially caused by the disordered S atoms and other reasons, as pointed out in the literature:40 because of the large uncertainties, these distances do not differ in a statistically significant sense. The construction motifs of lanthanide cations and monovacant Keggin-type [R-SiW11O39]8- or [R-GeW11O39]8- polyanion systems in 1 and 2 are very similar with those of [Nd2(RSiW11O39)(H2O)11]2-,29 whose monovacant polyanion precursors are bridged via Ot-RE-Ot linkages generating the 1D chainlike structure. The asymmetric polyanion unit {[Sm(H2O)5.5(DMF)0.5]2[Sm(H2O)2(DMF)][Sm(H2O)3 (R-SiW11O39)]2}- of 3 consists of two [Sm(1)(H2O)3]3-, two [Sm(2)(H2O)5.5(DMF)0.5]3+, one [Sm(3)(H2O)2(DMF)]3+, and two [R-SiW11O39]8- building blocks (Figure 4). In the structural construction of the {[Sm(H2O)5.5(DMF)0.5]2[Sm(H2O)2(DMF)][Sm(H2O)3(R-SiW11O39)]2}- unit, the [Sm(1)(H2O)3]3- subunit is grafted into the defect site of [R-SiW11O39]8- building block, which makes the defect [R-SiW11O39]8- subunit become crystallographically partially saturated as compared to the [R-SiW12O40]4- polyanion. The IR spectra can also confirm this case. More interestingly, the adjacent {[Sm(H2O)5.5(DMF)0.5]2[Sm(H2O)2(DMF)][Sm(H2O)3(R-SiW11O39)]2}- asymmetric polyanionic units connect to each other through the participation of [Sm(1)(H2O)3]3-, [Sm(2)(H2O)5(H2O)0.5(DMF)0.5]3+, and [Sm(3)(H2O)2(DMF)]3+ subunits forming the two-dimensional infinitely extended network structure. To date, only one two-dimensional organic-inorganic hybrid network supported by monovacant Keggin-type

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Figure 5. Polyhedralview of the packing of layers in 3 along the b and c axis. All hydrogen atoms are omitted for clarity.

[HPCuMo11O39]4- polyanions and transition metal coordination ions [Cu(4,4′-bpy)]2+ was reported;20 however, it was synthesized by hydrothermal synthesis. Therefore, the two-dimensional infinitely extended network structure of {[Sm(H2O)5.5(DMF)0.5]2[Sm(H2O)2(DMF)] [Sm(H2O)3(R-SiW11O39)]2}- by conventional aqueous solution is very meaningful for further exploration in the structural construction based on monovacant Keggin-type polyanions and rare earth metal coordination ions. In compound 3, the eight-coordinate Sm3+(1) coordination cation adopts a distorted square antiprismatic geometry. The O3, O1W, O2W, and O3W group and the O15, O22, O27, and O28 group constitute the two bottom planes of the square antiprism with Sm(1)-O distances of 2.333(16)-2.52 (3) Å, and their average deviations from their ideal planes are 0.1000 and 0.0561 Å, respectively. The distances between the Sm3+(1) cation and the two bottom planes are 1.4412 and 1.2287 Å, respectively. However, the Sm3+(2) coordination cation is in a nine-coordinate monocapped square antiprismatic geometry with Sm(2)-O distances of 2.41(2)-2.54 (3) Å. The O4W, O5W, O6W, and O7W group and the O1A, O4, O8W, and O9W group constitute the two bottom planes of the square antiprism, and their average deviations are 0.0065 and 0.2699 Å, respectively. The distances between Sm3+(2) cation and the two bottom planes are 0.9323 and 1.4612 Å, respectively. O10 occupies the “cap” position over the plane defined by the O4W, O5W, O6W, and O7W group. The distance between the “cap” oxygen atom and the plane is 1.5737 Å. It is worth noting that the occupation rates of the DMF and H2O (denoted O9W) ligands are 0.5 in the [Sm(2)(H2O)5.5(DMF)0.5]3+ coordination sphere. In addition, the Sm3+(3) coordination ion is crystallographically disordered and occupies two positions. The two-dimensional networks in compound 3 are arranged in parallel along the b and c axes in Figure 5. The crystal structure of compound 3 shows that the {[Sm(H2O)5.5(DMF)0.5]2[Sm(H2O)2(DMF)][Sm(H2O)3(R-SiW11O39)]2}- building blocks lined up along the crystallographic b axis reveal one type of “rhomb” columns, which are arranged to construct straight channels with the sizes of 10.6 × 17.5 Å2. Interestingly, this architecture pattern may act as a useful model for the design and assembly of functional molecule-based compounds, especially in the field of molecular sieve materials. Thermal Analysis of Compounds 1 and 2. The TG curve of compound 1 shows a slow weight loss of 11.45% between 15 and 700 °C, which approximately agrees with the theoretical

value of 10.97%. In the corresponding DTA curve, there is a strong endothermal peak at 73 °C resulting from the removal of water of crystallization, coordination water, structural water, and DMSO in 1. In addition, the exothermal peak observed at 584 °C in the DTA curve indicates the polyanion backbone destruction according to the West theory on decomposition of polyanions.41 The TG curve of compound 2 also shows a slow weight loss of 11.87% between 34 and 750 °C, which approximately agrees with the theoretical value of 10.84%. In the corresponding DTA curve, there is a strong endothermal peak at 275 °C, resulting from the removal of water of crystallization, coordination water, structural water, and DMSO in 2. The exothermal peak observed at 671 °C in the DTA curve indicates the collapse of the polyanion framework. All the data above illustrate that compounds 1 and 2 retain a comparatively good thermal stability. Variable Temperature Magnetic Susceptibility of Compounds 1 and 3. Variable-temperature magnetic susceptibility studies were undertaken to determine whether both 1 and 3 reveal any interesting magnetic properties. The plots of the temperature dependence of χM, χMT, and 1/χM for compounds 1 and 3 are displayed in Figures 6 and 7, respectively, in the temperature range of 2-300 K. The χMT value decreases continuously with decreasing temperature, reaching the minimum value of 0.106 emu‚K‚mol-1 at 2 K for 1 and 0.307 emu‚K‚mol-1 at 2 K for 3. The relationship of 1/χM versus T in 130-300 K can be fitted to the Curie-Weiss law, χM ) C/(T - θ) and χM ) Ng2µβ2s(s + 1)/(3k(T - θ)) with Curie constant C ) 0.9265 emu‚K‚mol-1 and Weiss constant θ ) -283.3920 K for 1 and Curie constant C ) 8.5852 emu‚K‚mol-1 and Weiss constant θ ) -496.2618 K for 3. As the temperature decreases from 130 to 2 K, the relation of 1/χM versus T for both compounds does not follow the Curie-Weiss law, indicating the occurrence of strong spin-orbital coupling interactions and very weak ferromagnetic responses. The continuous decrease in χMT upon cooling should be in fact mainly attributed to the crystal field effects around the SmIII ion, similar to those reported previously.42-44 It is well-known that the depopulation of the SmIII Stark levels as the temperature decreases is a distinct magnetic phenomenon. The 6H5/2 free-ion ground state in the crystal field is split into three Kramers doublets.45 At room temperature, those doublets are equally populated; as the temperature decreases, the Kramers doublets of higher energy are successively depopulated, and the magnetic behavior devi-

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Wang et al.

to the superexchange interactions among Sm3+ ions through the WO6 octahedra,46 resulting from the their distinct structure architecture. Conclusions Three novel organic-inorganic hybrid monovacant Keggintype silicotungstates or germanotungstates containing lanthanideIII cations with 1D and 2D infinitely extended structures were successfully achieved, and their structures were elucidated by X-ray crystallography. Under similar conditions, some extended experiments can be done: if we employ other rare earth ions or transition metal ions taking the place of SmIII or DyIII ions, or we use other monovacant heteropolyanions ([SiMo11O39]8-, [TiW11O39]8-, [P2W17O61]6-, etc.) in place of [R-SiW11O39]8- or [R-GeW11O39]8- precursors, many possible novel structure species are very likely to be obtained, which paves the way for further development in the exploration of our synthetic work. Now, we are currently exploring this avenue. Acknowledgment. This work was supported by the Specialized Research Fund for the Doctoral Program of Higher Education, Henan Innovation Project for University Prominent Research Talents, the Foundation of Educational Department of Henan Province, and Natural Science Foundation of Henan Province. Figure 6. Plot of the temperature dependence of χM, χMT, and 1/χM for 1.

Supporting Information Available: Crystallographic information files and selected bond distances and angles of compounds 1-3. This material is available free of charge via the Internet at http://pubs.acs.org.

References

Figure 7. Plot of the temperature dependence of χM, χMT, and 1/χM for 3.

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