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Synthesis, structure and characterization of a inorganic–organic hybrid Dawson polyoxotungstate (H2en)3[P2W18O62]·6.48H2O
Journal of Molecular Structure 783 (2006) 176–183 www.elsevier.com/locate/molstruc
Synthesis, structure and characterization of a inorganic–organic hybrid Dawson polyoxotungstate (H2en)3[P2W18O62]$6.48H2O Zhen Li, Bi-Zhou Lin *, Jin-Fei Zhang, Feng Geng, Guo-Hua Han, Pei-De Liu Institute of Materials Physical Chemistry, Huaqiao University, Quanzhou 362021, People’s Republic of China Received 14 August 2005; revised 1 September 2005; accepted 6 September 2005 Available online 19 October 2005
Abstract A Dawson polyoxotungstate (H2en)3[P2W18O62]$6.48H2O 1 was prepared from the hydrothermal reaction of Na2WO4, CdCl2, H3PO4, ethylenediamine and H2O at 150 8C, and characterized by single crystal X-ray diffraction and spectroscopic methods. The compound crystallizes ˚ , bZ95.116(3) 8, ZZ4, R1Z0.0568 for 12645 in the monoclinic system, space group P 2(1)/n with aZ14.647(2), bZ19.417(3), cZ23.729(3) A observed reflections. The crystal is made up of [P2W18O62]6K Dawson anions, [H2en]2C complex cations and H2O molecules of crystallization. The [H2en]2C complex cations and Dawson anions are held together into a three-dimensional supermolecular network through hydrogen-bonding interactions. A probe reaction of the oxidation of cyclohexene into adipic acid with H2O2 as oxidation reagent and compound 1 as the catalyst showed that the hybrid material has a high oxidative activity in the reaction. q 2005 Elsevier B.V. All rights reserved. Keywords: Hydrothermal synthesis; Crystal structure; Polyoxotungstate; Organic–inorganic hybrid materials; Catalytic property
1. Introduction There exists growing interest in metal oxide clusters, or polyoxometalates, reflecting their diverse properties, which endow them with applications in the fields such as catalysis, medicine, analytical chemistry and photochemistry [1–3]. Contemporarily, polyoxometalates are found to be extremely versatile inorganic building blocks for constructions of organic–inorganic hybrid materials with novel structures and unusual properties [4–6]. The design and synthesis of polyoxometalates-based hybrids are still at the forefront of the materials chemistry research, and the use of the welldefined metal oxide clusters for the construction of polyoxometalates-based hybrids materials with more or less predictable connectivity in the crystalline state is more and more attractive. The hydrothermal synthesis techniques, in combination with the organic templates, have been demonstrated to be a popular strategy in the isolation of such materials [5,7–10]. The polyoxotungstates based on Keggin or Dawson units have received considerable attention and * Corresponding author. Tel.: C86 595 22692548; fax: C86 595 22692508. E-mail address: [email protected] (B.-Z. Lin).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2005.09.003
have been synthesized and studied in aqueous solution for their catalytic properties in organic oxidation [11–13]. Compared with the Keggin polyoxotungstates associated with organic donors [9,10,14–16], the polyoxotungstates based on Dawson units to produce organic–inorganic hybrid materials remains largely unexplored [17–19]. Previously, we have hydrothermal synthesized a Keggin polyoxotungstates associated with organic ligand ethylenediamine [20]. Under the synthetic condition of this study, we also used ethylenediamine for the structure-directing agent and synthesized a new Dawson polyoxotungstate. Here, we report the hydrothermal synthesis and structural characterization of this new Dawson polyoxotungstate (H2en)3[P2W18O62]$6.48H2O 1 (enZethylenediamine), where Dawson anions and [H2en]2C complex cations are held together into a threedimensional supermolecular network through hydrogenbonding interactions. Its catalytic activity has been explored by means of a probe reaction of the oxidation of cyclohexene. 2. Experimental 2.1. General procedures All chemicals were commercially purchased and used without further purification. Elemental analyses were
Z. Li et al. / Journal of Molecular Structure 783 (2006) 176–183
performed on a Perkin–Elmer 2400 element analyzer and inductively coupled plasma analysis on a Perkin–Elmer Optima 3300DV ICP spectrometer. The infrared spectrum was recorded at room temperature on a Nicolet 470 FTIR spectrophotometer as KBr pellets in the 4000–400 cmK1 region. Thermogravimetric analysis was performed in flowing N2 at a heating rate of 10 8C minK1 on a Universal V2.4F TA instrument. 2.2. Hydrothermal synthesis Compound 1 was hydrothermally synthesized under autogenous pressure in a 17 mL Teflon-lined stainless steel autoclave with a fill factor of approximate 40%. A mixture of Na2WO4$2H2O, CdCl2$2.5H2O, H3PO4, ethylenediamine and water in the molar ratio of 1:1:7.64:2.32:232 was stirred, and then heated at 150 8C for 96 h. After cooling to room temperature, green block crystals of compound 1 were isolated. The crystals were filtered, washed with distilled water and dried in a desiccator at ambient temperature, yielding ca. 70% based on tungsten. The pH value of the reactive system increased from 1.46 before heating to 2.55 at the end of the reaction. Anal. Calc. (%) for C6H42.96N6O68.48P2W18: C, 1.55; H, 0.93; N, 1.80; P, 1.33; W, 71.05. Found (%): C, 1.59; H, 0.96; N, 1.76; P, 1.35; W, 70.73. 2.3. X-ray crystallography The data on a crystal with dimensions 0.26!0.12! 0.10 mm were collected on a Bruker P4 diffractometer equipped with a SMART CCD system at 293 K using ˚ ). graphite-monochromatized Mo Ka radiation (lZ0.71073 A A total of 38,864 reflections (2qmaxZ548) were collected, of which 14,643 unique reflections (RintZ0.0646) were used to structural elucidation. The data were integrated using the Siemens SAINT program [21], with the intensities corrected for Lorentz factor, polarization, air absorption and absorption due to variation in the path length through the detector faceplate. The program SADABS was used for the absorption correction [22]. The structure was solved by direct methods, successive Fourier difference synthesis, and refined by fullmatrix least-squares techniques on F2 using SHELXTL-97 [23]. Anisotropic thermal parameters are refined for all nonhydrogen atoms, except atoms O(69) and N(5), which are refined isotropically. The occupancy of a disordered water molecule was refined to be 0.48, which were further supported by element analyses and thermal analyses. The hydrogen atoms attached to oxygen atoms were located from the difference Fourier map and those attached to carbon and nitrogen atoms were placed geometrically. Crystallographic and refinement details are summarized in Table 1. The selected bond lengths and angles are given in Table 2. Atomic coordinates and equivalent isotropic displacement parameters are given in Table S1. Cystallographic data for compound 1 have been deposited with the Cambridge Crystallographic Data Center as
177
Table 1 Crystal data and structure refinement for compound 1 C6H42.96N6O68.48P2W18 4666.34 293(2) K Monoclinic P21/n ˚ aZ14.647(2) A ˚ bZ19.417(3) A ˚ cZ23.729(3) A bZ95.116(3)8 ˚3 6721.8(17) A 4, 4.611 g/cm3 30.828 mmK1 8123.2 1.36–27.008 K18% h%18, 0%k%24, 0%l%30 38,864 14,643 (RintZ0.0646) 12,645 902 1.010 0.0568, 0.1386 0.0660, 0.1460
Empirical formula Formula weight Temperature Crystal system Space group Unit cell dimensions
V Z, DCalc m F(000) q range Limiting indices Reflections collected Independent reflections Observed data (IO2s(I)) Parameters Goodness-of-fit on F2 R1, R2 (IO2s(I))a R1, R2 (all data) a
R1Z
P
jjF0 jKjFc jj=
P
jF0 j;wR2Z
P
w½ðF0 Þ2 KðFc Þ2 2 =
P
w½ðF0 Þ2 2
1=2
.
supplementary publications (CCDC no. 281054) Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: (44) 1223 336 033; e-mail: [email protected]) or at http:// www.ccdc.cam.ac.uk/conts/retrieving.html. 2.4. Catalytic test Catalytic reaction was carried out in a 100 ml three-necked quartz flask placed on a magnetic stirrer. The three-necked flask was charged with cyclohexene (50 mmol), H2O2 (269 mmol) and succinic acid. When the solution was heated to 82 8C, the powder of compound 1 (0.05 mmol) was added to the solution. After lasting for 1 h at the same temperature, the reaction was stopped and the catalyst was filtered out. The filtrate was put into a refrigerator at 0 8C for 24 h. The white power was separated out, filtered, dried and weighed. The product was analyzed by the infrared spectrum and was mensurated by the melting point. In a comparative experiment, H6P2W18O62$nH2O was used as the catalyst instead of compound 1, where H6P2W18O62$nH2O (nZ12.5) was prepared according to the literature method and was identified by TG analysis, IR and UV spectra [24].
3. Results and discussion 3.1. Synthesis Because the mechanism by which the assembly is organized remains elusive, the hydrothermal process is relatively complex affected by many factors such as initial materials,
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Z. Li et al. / Journal of Molecular Structure 783 (2006) 176–183
Table 2 ˚ ] and angles [8] for compound 1 Selected bond lengths [A W(1)–O(1) W(1)–O(23) W(2)–O(23) W(3)–O(3) W(3)–O(26) W(4)–O(41) W(5)–O(5) W(5)–O(35) W(6)–O(29) W(7)–O(7) W(7)–O(43) W(8)–O(32) W(9)–O(9) W(9)–O(24) W(10)–O(48) W(11)–O(11) W(11)–O(59) W(12)–O(50) W(13)–O(13) W(13)–O(42) W(14)–O(41) W(15)–O(15) W(15)–O(49) W(16)–O(62) W(17)–O(17) W(17)–O(57) W(18)–O(56) P(1)–O(20) P(2)–O(46) O(1)–W(1)–O(24) O(1)–W(1)–O(26) O(1)–W(1)–O(23) O(26)–W(1)–O(23) O(28)–W(1)–O(19) O(2)–W(2)–O(27) O(2)–W(2)–O(30) O(2)–W(2)–O(25) O(30)–W(2)–O(25) O(23)–W(2)–O(19) O(3)–W(3)–O(25) O(3)–W(3)–O(31) O(3)–W(3)–O(26) O(31)–W(3)–O(26) O(29)–W(3)–O(19) O(4)–W(4)–O(36) O(4)–W(4)–O(34) O(4)–W(4)–O(27) O(34)–W(4)–O(27) O(41)–W(4)–O(21) O(5)–W(5)–O(42) O(5)–W(5)–O(34) O(5)–W(5)–O(35) O(34)–W(5)–O(35) O(30)–W(5)–O(20) O(6)–W(6)–O(33) O(6)–W(6)–O(40) O(6)–W(6)–O(35) O(40)–W(6)–O(35) O(29)–W(6)–O(20) O(7)–W(7)–O(33) O(7)–W(7)–O(37) O(7)–W(7)–O(43) O(37)–W(7)–O(43)
1.742(12) 1.916(11) 1.919(10) 1.723(11) 1.931(10) 1.886(10) 1.717(12) 1.921(10) 1.912(10) 1.709(11) 1.939(10) 1.891(10) 1.735(11) 1.956(10) 1.900(10) 1.716(11) 1.991(10) 1.898(10) 1.700(11) 1.948(9) 1.900(10) 1.687(11) 1.944(10) 1.926(10) 1.732(11) 1.920(10) 1.870(10) 1.531(11) 1.553(11) 103.9(5) 98.7(5) 99.9(5) 86.5(5) 83.3(4) 102.6(5) 101.8(5) 103.2(5) 89.4(5) 72.3(4) 101.5(5) 101.2(5) 102.2(5) 87.6(4) 83.5(4) 99.1(5) 102.2(5) 97.7(5) 86.1(5) 82.5(4) 98.0(5) 101.2(5) 99.7(5) 159.0(4) 81.4(4) 103.6(5) 100.6(5) 98.8(5) 88.0(4) 81.0(4) 103.5(5) 100.3(5) 100.0(5) 87.1(4)
W(1)–O(24) W(1)–O(19) W(2)–O(30) W(3)–O(25) W(3)–O(19) W(4)–O(34) W(5)–O(42) W(5)–O(20) W(6)–O(40) W(7)–O(33) W(7)–O(22) W(8)–O(37) W(9)–O(38) W(9)–O(21) W(10)–O(39) W(11)–O(43) W(11)–O(44) W(12)–O(53) W(13)–O(52) W(13)–O(47) W(14)–O(52) W(15)–O(48) W(15)–O(46) W(16)–O(54) W(17)–O(55) W(17)–O(45) W(18)–O(61) P(1)–O(19) P(2)–O(47) O(1)–W(1)–O(28) O(24)–W(1)–O(26) O(24)–W(1)–O(23) O(1)–W(1)–O(19) O(26)–W(1)–O(19) O(2)–W(2)–O(23) O(27)–W(2)–O(30) O(27)–W(2)–O(25) O(2)–W(2)–O(19) O(30)–W(2)–O(19) O(3)–W(3)–O(29) O(25)–W(3)–O(31) O(25)–W(3)–O(26) O(3)–W(3)–O(19) O(31)–W(3)–O(19) O(4)–W(4)–O(41) O(36)–W(4)–O(34) O(36)–W(4)–O(27) O(4)–W(4)–O(21) O(34)–W(4)–O(21) O(5)–W(5)–O(30) O(42)–W(5)–O(34) O(42)–W(5)–O(35) O(5)–W(5)–O(20) O(34)–W(5)–O(20) O(6)–W(6)–O(29) O(33)–W(6)–O(40) O(33)–W(6)–O(35) O(6)–W(6)–O(20) O(40)–W(6)–O(20) O(7)–W(7)–O(31) O(33)–W(7)–O(37) O(33)–W(7)–O(43) O(7)–W(7)–O(22)
1.869(10) 2.372(11) 1.932(11) 1.868(10) 2.382(11) 1.903(10) 1.870(10) 2.326(10) 1.916(10) 1.873(10) 2.373(10) 1.896(10) 1.873(10) 2.306(10) 1.914(9) 1.845(10) 2.299(10) 1.910(10) 1.888(10) 2.362(10) 1.908(10) 1.893(10) 2.333(11) 1.928(11) 1.897(10) 2.405(11) 1.932(10) 1.545(12) 1.558(11) 103.7(5) 157.4(4) 89.0(4) 169.4(5) 73.2(4) 102.8(5) 85.2(5) 154.2(4) 173.3(5) 83.3(4) 102.0(5) 157.3(4) 88.0(5) 173.1(5) 83.3(4) 100.5(5) 158.6(5) 89.5(5) 171.0(5) 86.3(4) 97.2(5) 89.2(5) 88.6(5) 173.9(5) 84.6(4) 95.9(5) 89.3(4) 157.6(4) 170.4(5) 82.7(4) 97.0(5) 156.2(4) 88.7(4) 171.9(5)
W(1)–O(28) W(2)–O(2) W(2)–O(25) W(3)–O(29) W(4)–O(4) W(4)–O(27) W(5)–O(30) W(6)–O(6) W(6)–O(35) W(7)–O(31) W(8)–O(8) W(8)–O(28) W(9)–O(32) W(10)–O(10) W(10)–O(51) W(11)–O(50) W(12)–O(12) W(12)–O(56) W(13)–O(53) W(14)–O(14) W(14)–O(54) W(15)–O(38) W(16)–O(16) W(16)–O(60) W(17)–O(61) W(18)–O(18) W(18)–O(62) P(1)–O(22) P(2)–O(45) O(24)–W(1)–O(28) O(28)–W(1)–O(26) O(28)–W(1)–O(23) O(24)–W(1)–O(19) O(23)–W(1)–O(19) O(27)–W(2)–O(23) O(23)–W(2)–O(30) O(23)–W(2)–O(25) O(27)–W(2)–O(19) O(25)–W(2)–O(19) O(25)–W(3)–O(29) O(29)–W(3)–O(31) O(29)–W(3)–O(26) O(25)–W(3)–O(19) O(26)–W(3)–O(19) O(36)–W(4)–O(41) O(41)–W(4)–O(34) O(41)–W(4)–O(27) O(36)–W(4)–O(21) O(27)–W(4)–O(21) O(42)–W(5)–O(30) O(30)–W(5)–O(34) O(30)–W(5)–O(35) O(42)–W(5)–O(20) O(35)–W(5)–O(20) O(33)–W(6)–O(29) O(29)–W(6)–O(40) O(29)–W(6)–O(35) O(33)–W(6)–O(20) O(35)–W(6)–O(20) O(33)–W(7)–O(31) O(31)–W(7)–O(37) O(31)–W(7)–O(43) O(33)–W(7)–O(22)
1.873(10) 1.710(11) 1.949(9) 1.922(10) 1.689(12) 1.918(10) 1.893(11) 1.711(11) 1.929(10) 1.894(9) 1.700(11) 1.940(10) 1.906(10) 1.679(11) 1.918(10) 1.885(10) 1.711(11) 1.973(10) 1.935(10) 1.710(11) 1.908(11) 1.917(10) 1.681(12) 1.933(10) 1.901(10) 1.712(10) 1.934(10) 1.552(11) 1.568(11) 86.8(5) 88.6(5) 156.4(4) 84.3(4) 73.2(4) 89.1(5) 155.4(4) 85.5(5) 82.1(4) 72.3(4) 89.1(5) 85.8(4) 155.7(4) 74.2(4) 72.6(4) 90.1(5) 87.7(4) 161.7(5) 72.3(4) 79.9(4) 164.7(5) 86.6(5) 90.2(5) 83.6(4) 74.4(4) 86.9(4) 163.5(4) 89.5(4) 85.3(4) 72.2(4) 87.5(4) 89.7(4) 163.0(4) 84.5(4)
W(1)–O(26) W(2)–O(27) W(2)–O(19) W(3)–O(31) W(4)–O(36) W(4)–O(21) W(5)–O(34) W(6)–O(33) W(6)–O(20) W(7)–O(37) W(8)–O(39) W(8)–O(22) W(9)–O(36) W(10)–O(57) W(10)–O(44) W(11)–O(51) W(12)–O(40) W(12)–O(47) W(13)–O(58) W(14)–O(49) W(14)–O(46) W(15)–O(55) W(16)–O(58) W(16)–O(45) W(17)–O(60) W(18)–O(59) W(18)–O(45) P(1)–O(21) P(2)–O(44)
1.907(10) 1.909(10) 2.408(11) 1.923(9) 1.863(11) 2.368(10) 1.896(10) 1.903(10) 2.413(10) 1.911(10) 1.875(9) 2.344(10) 1.949(10) 1.897(11) 2.350(10) 1.906(10) 1.884(10) 2.354(10) 1.938(10) 1.846(11) 2.361(10) 1.922(10) 1.909(11) 2.403(10) 1.902(10) 1.863(10) 2.334(10) 1.571(10) 1.568(10)
Z. Li et al. / Journal of Molecular Structure 783 (2006) 176–183 Table 2 (continued) O(31)–W(7)–O(22) O(8)–W(8)–O(39) O(8)–W(8)–O(37) O(8)–W(8)–O(28) O(37)–W(8)–O(28) O(32)–W(8)–O(22) O(9)–W(9)–O(38) O(9)–W(9)–O(36) O(9)–W(9)–O(24) O(36)–W(9)–O(24) O(32)–W(9)–O(21) O(10)–W(10)–O(57) O(10)–W(10)–O(39) O(10)–W(10)–O(51) O(39)–W(10)–O(51) O(48)–W(10)–O(44) O(11)–W(11)–O(43) O(11)–W(11)–O(51) O(11)–W(11)–O(59) O(51)–W(11)–O(59) O(50)–W(11)–O(44) O(12)–W(12)–O(40) O(12)–W(12)–O(53) O(12)–W(12)–O(56) O(53)–W(12)–O(56) O(50)–W(12)–O(47) O(13)–W(13)–O(52) O(13)–W(13)–O(58) O(13)–W(13)–O(42) O(58)–W(13)–O(42) O(53)–W(13)–O(47) O(14)–W(14)–O(49) O(14)–W(14)–O(52) O(14)–W(14)–O(54) O(52)–W(14)–O(54) O(41)–W(14)–O(46) O(15)–W(15)–O(48) O(15)–W(15)–O(55) O(15)–W(15)–O(49) O(55)–W(15)–O(49) O(38)–W(15)–O(46) O(16)–W(16)–O(58) O(16)–W(16)–O(54) O(16)–W(16)–O(60) O(54)–W(16)–O(60) O(62)–W(16)–O(45) O(17)–W(17)–O(55) O(17)–W(17)–O(60) O(17)–W(17)–O(57) O(60)–W(17)–O(57) O(61)–W(17)–O(45) O(18)–W(18)–O(59) O(18)–W(18)–O(61) O(18)–W(18)–O(62) O(61)–W(18)–O(62) O(56)–W(18)–O(45) O(20)–P(1)–O(19) O(20)–P(1)–O(21) O(46)–P(2)–O(47) O(46)–P(2)–O(44)
82.0(4) 99.8(5) 103.5(5) 95.9(5) 89.9(4) 85.3(4) 97.8(5) 101.2(5) 98.0(5) 89.5(4) 85.1(4) 98.9(5) 98.3(5) 101.1(5) 88.5(4) 85.4(4) 101.1(5) 101.9(5) 93.3(5) 88.3(4) 84.4(4) 100.1(5) 97.5(5) 95.9(5) 87.0(5) 83.6(4) 101.9(5) 96.4(5) 98.8(5) 164.8(4) 72.9(4) 102.3(5) 99.5(5) 96.9(5) 85.2(5) 82.4(4) 100.3(5) 98.9(5) 103.3(5) 89.2(4) 81.7(4) 101.9(5) 103.2(5) 102.2(5) 87.6(5) 72.5(4) 102.6(5) 102.0(5) 101.3(5) 156.7(5) 71.7(4) 99.5(5) 101.1(5) 102.2(5) 86.0(5) 83.2(4) 107.8(6) 110.9(6) 112.5(6) 112.4(6)
O(37)–W(7)–O(22) O(8)–W(8)–O(32) O(39)–W(8)–O(37) O(39)–W(8)–O(28) O(8)–W(8)–O(22) O(37)–W(8)–O(22) O(9)–W(9)–O(32) O(38)–W(9)–O(36) O(38)–W(9)–O(24) O(9)–W(9)–O(21) O(36)–W(9)–O(21) O(10)–W(10)–O(48) O(57)–W(10)–O(39) O(57)–W(10)–O(51) O(10)–W(10)–O(44) O(39)–W(10)–O(44) O(11)–W(11)–O(50) O(43)–W(11)–O(51) O(43)–W(11)–O(59) O(11)–W(11)–O(44) O(51)–W(11)–O(44) O(12)–W(12)–O(50) O(40)–W(12)–O(53) O(40)–W(12)–O(56) O(12)–W(12)–O(47) O(53)–W(12)–O(47) O(13)–W(13)–O(53) O(52)–W(13)–O(58) O(52)–W(13)–O(42) O(13)–W(13)–O(47) O(58)–W(13)–O(47) O(14)–W(14)–O(41) O(49)–W(14)–O(52) O(49)–W(14)–O(54) O(14)–W(14)–O(46) O(52)–W(14)–O(46) O(15)–W(15)–O(38) O(48)–W(15)–O(55) O(48)–W(15)–O(49) O(15)–W(15)–O(46) O(55)–W(15)–O(46) O(16)–W(16)–O(62) O(58)–W(16)–O(54) O(58)–W(16)–O(60) O(16)–W(16)–O(45) O(54)–W(16)–O(45) O(17)–W(17)–O(61) O(55)–W(17)–O(60) O(55)–W(17)–O(57) O(17)–W(17)–O(45) O(60)–W(17)–O(45) O(18)–W(18)–O(56) O(59)–W(18)–O(61) O(59)–W(18)–O(62) O(18)–W(18)–O(45) O(61)–W(18)–O(45) O(20)–P(1)–O(22) O(19)–P(1)–O(21) O(46)–P(2)–O(45) O(47)–P(2)–O(44)
71.7(4) 98.5(5) 91.5(5) 163.4(4) 175.0(5) 72.6(4) 101.3(5) 88.5(5) 164.2(4) 173.6(5) 72.4(4) 101.2(5) 162.7(5) 90.7(4) 173.4(5) 81.7(4) 99.3(5) 92.5(4) 165.1(4) 172.2(5) 73.7(4) 105.0(5) 89.9(5) 164.0(4) 170.6(5) 73.5(4) 99.8(5) 86.5(5) 90.2(5) 172.6(5) 82.0(4) 100.0(5) 158.1(5) 89.3(5) 174.7(5) 85.3(4) 98.3(5) 85.7(5) 156.4(5) 175.3(5) 81.4(4) 100.6(5) 86.8(5) 155.9(4) 171.8(5) 83.7(4) 101.3(5) 88.7(5) 85.3(5) 171.8(4) 73.9(4) 102.9(5) 88.3(5) 158.3(4) 172.9(4) 72.9(4) 113.2(6) 106.5(6) 107.4(6) 111.3(6)
O(43)–W(7)–O(22) O(39)–W(8)–O(32) O(32)–W(8)–O(37) O(32)–W(8)–O(28) O(39)–W(8)–O(22) O(28)–W(8)–O(22) O(38)–W(9)–O(32) O(32)–W(9)–O(36) O(32)–W(9)–O(24) O(38)–W(9)–O(21) O(24)–W(9)–O(21) O(57)–W(10)–O(48) O(48)–W(10)–O(39) O(48)–W(10)–O(51) O(57)–W(10)–O(44) O(51)–W(10)–O(44) O(43)–W(11)–O(50) O(50)–W(11)–O(51) O(50)–W(11)–O(59) O(43)–W(11)–O(44) O(59)–W(11)–O(44) O(40)–W(12)–O(50) O(50)–W(12)–O(53) O(50)–W(12)–O(56) O(40)–W(12)–O(47) O(56)–W(12)–O(47) O(52)–W(13)–O(53) O(53)–W(13)–O(58) O(53)–W(13)–O(42) O(52)–W(13)–O(47) O(42)–W(13)–O(47) O(49)–W(14)–O(41) O(41)–W(14)–O(52) O(41)–W(14)–O(54) O(49)–W(14)–O(46) O(54)–W(14)–O(46) O(48)–W(15)–O(38) O(38)–W(15)–O(55) O(38)–W(15)–O(49) O(48)–W(15)–O(46) O(49)–W(15)–O(46) O(58)–W(16)–O(62) O(62)–W(16)–O(54) O(62)–W(16)–O(60) O(58)–W(16)–O(45) O(60)–W(16)–O(45) O(55)–W(17)–O(61) O(61)–W(17)–O(60) O(61)–W(17)–O(57) O(55)–W(17)–O(45) O(57)–W(17)–O(45) O(59)–W(18)–O(56) O(56)–W(18)–O(61) O(56)–W(18)–O(62) O(59)–W(18)–O(45) O(62)–W(18)–O(45) O(19)–P(1)–O(22) O(22)–P(1)–O(21) O(47)–P(2)–O(45) O(45)–P(2)–O(44)
81.2(4) 88.9(4) 157.7(4) 83.6(4) 83.5(4) 81.2(4) 90.5(5) 157.4(5) 85.4(4) 83.1(4) 81.3(4) 85.7(5) 88.5(5) 157.7(5) 81.5(4) 72.3(4) 90.4(4) 157.6(4) 83.4(4) 85.7(4) 80.2(4) 92.4(4) 156.6(4) 84.4(4) 83.2(4) 80.9(4) 157.9(5) 87.4(5) 90.1(5) 85.2(4) 82.9(4) 91.8(5) 87.3(5) 162.4(4) 72.9(4) 81.1(4) 88.6(5) 162.6(5) 89.5(4) 84.4(4) 72.0(4) 88.0(5) 156.2(4) 87.7(5) 82.6(4) 73.5(4) 156.0(5) 88.1(5) 88.3(5) 84.6(4) 83.1(4) 88.7(5) 156.1(4) 88.0(5) 84.2(4) 74.1(4) 107.4(6) 110.7(6) 107.9(6) 104.9(6)
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starting concentration, temperature, pH, and pressure [3,5]. Although Cd2C is not incorporated in the final structure, the species appears to be needed in the isolation of compound 1. Without CdCl2 or CdCl2 replaced by ZnCl2 or CuCl2, attempts to synthesize 1 proved fruitless and amorphous mixtures were obtained. It was observed that the pH value of the reaction mixture plays a very important role on the formation of 1. When the initial pH value reduced to 1.2, amorphous mixtures were found; and when the initial pH raised to 3.0, the yield of 1 reduced to only 10% (based on tungsten). Nevertheless, the reaction of a mixture of Na2WO4, CdCl2, H3PO4, en, and H2O in the molar ratio of 1:1:7.64:2.32:232 with the initial pH value of 1.46 at 150 8C for 96 h produced green block-like crystals of 1 in a good yield. 3.2. Crystal structure The asymmetric unit of 1 consists of one classical a-Dawson type [P2W18O62]6K polyoxoanion, three [H2en]2C cations and 6.48$H2O molecules of crystallization. Like usually observed in Dawson type anions [17–19,25], the [P2W18O62]6K anion is closed to the D3h point symmetry and contains two [a-A-PW9O34]9K units which are derived from the a-Keggin type [a-PW12O40]3K anion by removal of a set of three corner-sharing WO6 octahedrons and these two [a-APW9O34]9K units are linked through corner-sharing with the elimination of six oxygen atoms, as show in Fig. 1. In the Dawson type polyoxoanion, there are two structurally distinct types of W atoms: six ‘cap’ atoms on vertical mirror-planes and grouped in two sets of three, on the other hand, 12 ‘belt’ atoms are grouped in two sets of six, but not lie on mirrorplanes. In the [P2W18O62]6K cluster, the oxygen atoms can be divided into four groups according to the numbers of atoms that the oxygen atoms are coordinated to: (1) 18 terminal oxygen atoms (Ot) only bonding to one W atom with W–O
˚ ; (2) 36 oxygen bond distances of 1.679(11)–1.742(12) A atoms (m2-O) connecting with two W atoms with W–O bond ˚ ; (3) 6 oxygen atoms distances of 1.845(10)–1.991(10) A (m3-O) which are combined with one P atom and two W atoms and the W–O bond distances vary from 2.299(10) to 2.413(10) ˚ ; (4) 2 oxygen atoms (m4-O) which are coordinated to one P A atom and three W atoms and the W–O bond distances are ˚ . These bond distances between 2.372(11) and 2.408(11) A have a rule of W–Ot ! W–(m2-O)(W–(m3-O), W–(m4-O), and they are in accord with those in the well-known a-Dawson type anions [17–19,25–28]. The P–O distances range from ˚ . Bond valence sum calculation [29] 1.531(10) to 1.571(10) A demonstrates that W atoms in 1 have their valence sums ranging from 5.97 to 6.43, with a average value of 6.15, very close to the ideal value of six for W(VI). There is extensive hydrogen bonging in the crystal structure of 1. As listed in Table 3, the N–H/O hydrogen bonding between the complex cation [H2en]2C and the oxygen atoms from the Dawson units with N/O interatomic ˚ and N–H/O distances ranging from 2.76(2) to 3.18(3) A angles between 110.0 and 160.9 is observed. It is noteworthy that compound 1 has C–H/O hydrogen bonds between the C–H groups from the complex cation [H2en]2C and the oxygen atoms from the Dawson units have C/O interatomic ˚ . It is similar to the distances from 3.148(19) to 3.36(2) A compound (pbpy)8H3[PW12O40]$2H2O [30], in which C–H/ O hydrogen bonds with C/O distances between 3.101 and ˚ were observed. In the crystal structure of 1, one en 3.355 A molecule is connected with its four adjacent Dawson clusters through five N–H/O and four C–H/O hydrogen bonds, and a second en molecule connected with its four neighboring Dawson units through nine N–H/O hydrogen bonds, while the other en molecule connected with its three neighboring Dawson clusters through four N–H/O hydrogen bonds. These hydrogen bonds make the cation [H2en]2C and
Fig. 1. Structure of the Dawson unit [P2W18O62]6K in compound 1, where (a) for a polyhedral representation, and (b) for an ORTEP representation with the atom labeling scheme shown at 50% thermal probability.
Z. Li et al. / Journal of Molecular Structure 783 (2006) 176–183 Table 3 ˚ , 8) for compound 1 Hydrogen-bonding geometry (A D–H/A
d(D–H)
d(H/A)
d(D/A)
!(DHA)
N(1)–H(1C)/O(67a) N(1)–H(1D)/O(63a) N(1)–H(1E)/O(3b) N(1)–H(1E)/O(12) N(2)–H(2C)/O(66) N(2)–H(2D)/O(23a) N(2)–H(2D)/O(17c) N(2)–H(2E)/O(7b) N(3)–H(3C)/O(18d) N(3)–H(3C)/O(18e) N(3)–H(3D)/O(9) N(3)–H(3D)/O(11d) N(3)–H(3E)/O(63) N(4)–H(4C)/O(68) N(4)–H(4D)/O(11d) N(4)–H(4D)/O(9) N(4)–H(4E)/O(35f) N(5)–H(5E)/O(2) N(6)–H(6C)/O(4) N(6)–H(6C)/O(67) N(6)–H(6D)/O(64d) N(6)–H(6E)/O(17d) N(6)–H(6E)/O(26g) C(1)–H(1B)/O(23a) C(2)–H(2A)/O(7b) C(2)–H(2A)/O(12) C(2)–H(2B)/O(53) C(3)–H(3B)/O(3f) O(63)–H(63A)/O(65) O(63)–H(63B)/O(53e) O(64)–H(64A)/O(66f) O(64)–H(64B)/O(10) O(65)–H(65A)/O(16e) O(65)–H(65B)/O(8) O(66)–H(66A)/O(15c) O(66)–H(66B)/O(42) O(67)–H(67A)/O(36) O(67)–H(67B)/O(59d) O(67)–H(67B)/O(61d) O(68)–H(68A)/O(8) O(68)–H(68B)/O(48) O(69)–H(69A)/O(10d) O(69)–H(69B)/O(69h)
0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.97 0.97 0.97 0.97 0.97 0.85 0.86 0.88 0.94 0.85 0.85 0.85 0.85 0.85 0.85 0.85 0.83 0.89 0.85 0.85
1.88 1.92 2.22 2.24 2.12 2.12 2.49 2.56 2.26 2.50 2.20 2.22 2.10 1.84 2.18 2.37 2.24 2.45 2.52 2.07 2.35 2.42 2.12 2.51 2.53 2.54 2.56 2.50 1.85 2.47 2.26 2.14 2.04 2.27 1.95 2.40 2.00 2.56 2.02 2.59 2.34 2.39 2.30
2.74(3) 2.80(2) 2.76(2) 3.04(2) 2.92(3) 2.97(2) 2.918(19) 2.99(2) 3.046(17) 2.944(18) 2.837(18) 2.964(18) 2.92(2) 2.69(3) 2.901(18) 3.027(19) 2.955(19) 3.18(3) 3.10(2) 2.83(3) 3.21(4) 2.92(2) 2.95(2) 3.36(2) 3.15(2) 3.28(2) 3.148(19) 3.352(18) 2.69(3) 3.33(2) 3.14(4) 3.08(3) 2.89(3) 3.12(3) 2.80(2) 3.25(2) 2.85(2) 3.11(2) 2.81(2) 3.42(3) 3.18(3) 3.23(6) 3.15(12)
160.4 170.7 119.3 148.6 148.4 160.9 110.5 110.0 147.8 111.1 128.1 140.5 152.7 157.5 137.5 130.9 136.8 140.7 123.6 142.8 162.5 115.3 155.1 147.2 121.0 133.1 118.9 146.6 176.5 178.2 176.2 179.0 178.8 175.6 177.7 179.3 178.4 124.0 152.7 177.0 157.5 167.0 176.9
Symmetry transformations used to generate equivalent atoms: (a) xK1/2,K yC1/2,zC1/2; (b) KxC1,KyC1,KzC1; (c) xC1/2,KyC1/2,zC1/2; (d) K xC1/2,yK1/2,KzC1/2; (e) xC1/2,KyC1/2,zK1/2; (f) xK1/2,KyC1/2,zK 1/2; (g) KxC3/2,yK1/2,KzC1/2; (h) KxC1,Ky,KzC1.
the Dawson units form into an extended three-dimensional supermolecular network, where H2O molecules of crystallization are located in the interspace and interact with the network through O–H/O hydrogen bonding with O/O ˚ and N–H/O hydrogen distances from 2.69(3) to 3.42(3) A ˚ bonding with N/O distances between 2.69(3) and 2.92(3) A (Fig. 2). 3.3. IR spectrum and thermal analysis In the infrared spectrum of compound 1, as shown in Fig. S1, the strong bands at 1090 cmK1 could be ascribed to
181
n(P–(m-O)), that at 958 cmK1 to n(WaOt), and those at 910 and 770 cmK1 to n(W–(m-O)). There are some characteristic bands for the cations at 3140, 1510 and 1320 cmK1, where are assigned to n(CH2), t(CH2) and n(C–N), respectively. In addition, the bonds at 3500 and 1590 cmK1 are due to n(O–H) and d(HOH), respectively, and their wide shapes are resulted from the extensive O–H/O hydrogen bonds in the structure. A two-stage weight-loss scheme was observed on the thermogravimetric curve of compound 1, as shown in Fig. 3. The first decomposition stage, which occurs between 111 and 185 8C, is attributed to the release of some H2O molecules of crystallization with observed weight-loss of 1.65%. The weight-loss ranging from 328 to 659 8C is 4.75%, which is associated to the removal of the ethylenediamine and the residual H2O molecules of crystallization. The overall weightloss of 6.40% is accordant with the calculated value of ethylenediamine and H2O molecules of crystallization of 6.36%. 3.4. Catalytic reaction A probe reaction of the oxidation of cyclohexene into adipic acid with H2O2 as oxidation reagent and compound 1 as the catalyst was carried out to examine the oxidative catalytic activity. The infrared spectrum of the product is illustrated in Fig. 4, which is similar to adipic acid. The melting point of the product was measured to be 150–152 8C, very close to adipic acid, whose melting point is 152 8C. It was deduced that the product is adipic acid and the selectivity for adipic acid is nearly 100%. The influence of the amount of succinic acid on the amount of adipic acid is shown in Fig. 5. When the amount of succinic acid was 1.0 mmol, the curve reached its peak and 2.6156 g adipic acid was obtained from the oxidation of 50 mmol cyclohexene. The best proportion of compound 1, cyclohexene, succinic acid and H2O2 in the catalytic reaction was 1:1000:20:5380, and the hybrid material exhibited a catalytic activity of 52.312 g adipic acid/mmol catalyst per hour. In a comparative experiment, where 0.05 mmol H6P2W18O62$nH2O was used instead of compound 1 (Fig. 5), the best proportion was 1:1000:15:5380, and 1.0326 g adipic acid was obtained. H6P2W18O62$nH2O showed a catalytic activity of 20.652 g adipic acid/mmol catalyst per hour, which was 2.5 times less than that of the as-synthesized hybrid material. The comparison tests indicated that the as-synthesized hybrid material might become an effective catalyst in some organic oxidation.
4. Conclusions Utilizing the hydrothermal synthesis methodology, we have prepared successfully a new Dawson polyoxotungstate (H2en)3[P2W18O62]$6.48H2O. There are extensive hydrogenbonding interactions between the Dawson clusters and [H2en]2C complex cations These hydrogen bonds make
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Fig. 2. A packing view of (H2en)3[P2W18O62]$6.48H2O along the a-axis.
them hold together into a three-dimensional supermolecular network. A probe reaction of the oxidation of cyclohexene indicates that compound 1 is useful as an oxidative catalyst in the oxidation of cyclohexene into adipic acid with H2O2, and the best proportion of compound 1, cyclohexene, succinic acid and H2O2 in the reaction was 1:1000:20: 5380. The formation of 1 demonstrates that the hydrothermal synthesis techniques are well suited for exploratory investigations of the diverse structure chemistry of Dawson polyoxotungstates.
Fig. 3. TG curve of (H2en)3[P2W18O62]$6.48H2O in flowing N2 at 10 8C minK1.
Fig. 4. The IR spectrum of adipic acid and product.
Fig. 5. Influence of the amount of succinic acid on the amount of adipic acid.
Z. Li et al. / Journal of Molecular Structure 783 (2006) 176–183
Acknowledgements This work is supported by the Natural Science Foundation of Fujian Province of China (No. E0420001), NSF of China (No. 50172016) and the Science Foundation of Huaqiao University (No. 03HZR9). Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.molstruc.2005.09. 003
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Synthesis, structure and characterization of a inorganic–organic hybrid Dawson polyoxotungstate (H2en)3[P2W18O62]$6.48H2O Zhen Li, Bi-Zhou Lin *, Jin-Fei Zhang, Feng Geng, Guo-Hua Han, Pei-De Liu Institute of Materials Physical Chemistry, Huaqiao University, Quanzhou 362021, People’s Republic of China Received 14 August 2005; revised 1 September 2005; accepted 6 September 2005 Available online 19 October 2005
Abstract A Dawson polyoxotungstate (H2en)3[P2W18O62]$6.48H2O 1 was prepared from the hydrothermal reaction of Na2WO4, CdCl2, H3PO4, ethylenediamine and H2O at 150 8C, and characterized by single crystal X-ray diffraction and spectroscopic methods. The compound crystallizes ˚ , bZ95.116(3) 8, ZZ4, R1Z0.0568 for 12645 in the monoclinic system, space group P 2(1)/n with aZ14.647(2), bZ19.417(3), cZ23.729(3) A observed reflections. The crystal is made up of [P2W18O62]6K Dawson anions, [H2en]2C complex cations and H2O molecules of crystallization. The [H2en]2C complex cations and Dawson anions are held together into a three-dimensional supermolecular network through hydrogen-bonding interactions. A probe reaction of the oxidation of cyclohexene into adipic acid with H2O2 as oxidation reagent and compound 1 as the catalyst showed that the hybrid material has a high oxidative activity in the reaction. q 2005 Elsevier B.V. All rights reserved. Keywords: Hydrothermal synthesis; Crystal structure; Polyoxotungstate; Organic–inorganic hybrid materials; Catalytic property
1. Introduction There exists growing interest in metal oxide clusters, or polyoxometalates, reflecting their diverse properties, which endow them with applications in the fields such as catalysis, medicine, analytical chemistry and photochemistry [1–3]. Contemporarily, polyoxometalates are found to be extremely versatile inorganic building blocks for constructions of organic–inorganic hybrid materials with novel structures and unusual properties [4–6]. The design and synthesis of polyoxometalates-based hybrids are still at the forefront of the materials chemistry research, and the use of the welldefined metal oxide clusters for the construction of polyoxometalates-based hybrids materials with more or less predictable connectivity in the crystalline state is more and more attractive. The hydrothermal synthesis techniques, in combination with the organic templates, have been demonstrated to be a popular strategy in the isolation of such materials [5,7–10]. The polyoxotungstates based on Keggin or Dawson units have received considerable attention and * Corresponding author. Tel.: C86 595 22692548; fax: C86 595 22692508. E-mail address: [email protected] (B.-Z. Lin).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2005.09.003
have been synthesized and studied in aqueous solution for their catalytic properties in organic oxidation [11–13]. Compared with the Keggin polyoxotungstates associated with organic donors [9,10,14–16], the polyoxotungstates based on Dawson units to produce organic–inorganic hybrid materials remains largely unexplored [17–19]. Previously, we have hydrothermal synthesized a Keggin polyoxotungstates associated with organic ligand ethylenediamine [20]. Under the synthetic condition of this study, we also used ethylenediamine for the structure-directing agent and synthesized a new Dawson polyoxotungstate. Here, we report the hydrothermal synthesis and structural characterization of this new Dawson polyoxotungstate (H2en)3[P2W18O62]$6.48H2O 1 (enZethylenediamine), where Dawson anions and [H2en]2C complex cations are held together into a threedimensional supermolecular network through hydrogenbonding interactions. Its catalytic activity has been explored by means of a probe reaction of the oxidation of cyclohexene. 2. Experimental 2.1. General procedures All chemicals were commercially purchased and used without further purification. Elemental analyses were
Z. Li et al. / Journal of Molecular Structure 783 (2006) 176–183
performed on a Perkin–Elmer 2400 element analyzer and inductively coupled plasma analysis on a Perkin–Elmer Optima 3300DV ICP spectrometer. The infrared spectrum was recorded at room temperature on a Nicolet 470 FTIR spectrophotometer as KBr pellets in the 4000–400 cmK1 region. Thermogravimetric analysis was performed in flowing N2 at a heating rate of 10 8C minK1 on a Universal V2.4F TA instrument. 2.2. Hydrothermal synthesis Compound 1 was hydrothermally synthesized under autogenous pressure in a 17 mL Teflon-lined stainless steel autoclave with a fill factor of approximate 40%. A mixture of Na2WO4$2H2O, CdCl2$2.5H2O, H3PO4, ethylenediamine and water in the molar ratio of 1:1:7.64:2.32:232 was stirred, and then heated at 150 8C for 96 h. After cooling to room temperature, green block crystals of compound 1 were isolated. The crystals were filtered, washed with distilled water and dried in a desiccator at ambient temperature, yielding ca. 70% based on tungsten. The pH value of the reactive system increased from 1.46 before heating to 2.55 at the end of the reaction. Anal. Calc. (%) for C6H42.96N6O68.48P2W18: C, 1.55; H, 0.93; N, 1.80; P, 1.33; W, 71.05. Found (%): C, 1.59; H, 0.96; N, 1.76; P, 1.35; W, 70.73. 2.3. X-ray crystallography The data on a crystal with dimensions 0.26!0.12! 0.10 mm were collected on a Bruker P4 diffractometer equipped with a SMART CCD system at 293 K using ˚ ). graphite-monochromatized Mo Ka radiation (lZ0.71073 A A total of 38,864 reflections (2qmaxZ548) were collected, of which 14,643 unique reflections (RintZ0.0646) were used to structural elucidation. The data were integrated using the Siemens SAINT program [21], with the intensities corrected for Lorentz factor, polarization, air absorption and absorption due to variation in the path length through the detector faceplate. The program SADABS was used for the absorption correction [22]. The structure was solved by direct methods, successive Fourier difference synthesis, and refined by fullmatrix least-squares techniques on F2 using SHELXTL-97 [23]. Anisotropic thermal parameters are refined for all nonhydrogen atoms, except atoms O(69) and N(5), which are refined isotropically. The occupancy of a disordered water molecule was refined to be 0.48, which were further supported by element analyses and thermal analyses. The hydrogen atoms attached to oxygen atoms were located from the difference Fourier map and those attached to carbon and nitrogen atoms were placed geometrically. Crystallographic and refinement details are summarized in Table 1. The selected bond lengths and angles are given in Table 2. Atomic coordinates and equivalent isotropic displacement parameters are given in Table S1. Cystallographic data for compound 1 have been deposited with the Cambridge Crystallographic Data Center as
177
Table 1 Crystal data and structure refinement for compound 1 C6H42.96N6O68.48P2W18 4666.34 293(2) K Monoclinic P21/n ˚ aZ14.647(2) A ˚ bZ19.417(3) A ˚ cZ23.729(3) A bZ95.116(3)8 ˚3 6721.8(17) A 4, 4.611 g/cm3 30.828 mmK1 8123.2 1.36–27.008 K18% h%18, 0%k%24, 0%l%30 38,864 14,643 (RintZ0.0646) 12,645 902 1.010 0.0568, 0.1386 0.0660, 0.1460
Empirical formula Formula weight Temperature Crystal system Space group Unit cell dimensions
V Z, DCalc m F(000) q range Limiting indices Reflections collected Independent reflections Observed data (IO2s(I)) Parameters Goodness-of-fit on F2 R1, R2 (IO2s(I))a R1, R2 (all data) a
R1Z
P
jjF0 jKjFc jj=
P
jF0 j;wR2Z
P
w½ðF0 Þ2 KðFc Þ2 2 =
P
w½ðF0 Þ2 2
1=2
.
supplementary publications (CCDC no. 281054) Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: (44) 1223 336 033; e-mail: [email protected]) or at http:// www.ccdc.cam.ac.uk/conts/retrieving.html. 2.4. Catalytic test Catalytic reaction was carried out in a 100 ml three-necked quartz flask placed on a magnetic stirrer. The three-necked flask was charged with cyclohexene (50 mmol), H2O2 (269 mmol) and succinic acid. When the solution was heated to 82 8C, the powder of compound 1 (0.05 mmol) was added to the solution. After lasting for 1 h at the same temperature, the reaction was stopped and the catalyst was filtered out. The filtrate was put into a refrigerator at 0 8C for 24 h. The white power was separated out, filtered, dried and weighed. The product was analyzed by the infrared spectrum and was mensurated by the melting point. In a comparative experiment, H6P2W18O62$nH2O was used as the catalyst instead of compound 1, where H6P2W18O62$nH2O (nZ12.5) was prepared according to the literature method and was identified by TG analysis, IR and UV spectra [24].
3. Results and discussion 3.1. Synthesis Because the mechanism by which the assembly is organized remains elusive, the hydrothermal process is relatively complex affected by many factors such as initial materials,
178
Z. Li et al. / Journal of Molecular Structure 783 (2006) 176–183
Table 2 ˚ ] and angles [8] for compound 1 Selected bond lengths [A W(1)–O(1) W(1)–O(23) W(2)–O(23) W(3)–O(3) W(3)–O(26) W(4)–O(41) W(5)–O(5) W(5)–O(35) W(6)–O(29) W(7)–O(7) W(7)–O(43) W(8)–O(32) W(9)–O(9) W(9)–O(24) W(10)–O(48) W(11)–O(11) W(11)–O(59) W(12)–O(50) W(13)–O(13) W(13)–O(42) W(14)–O(41) W(15)–O(15) W(15)–O(49) W(16)–O(62) W(17)–O(17) W(17)–O(57) W(18)–O(56) P(1)–O(20) P(2)–O(46) O(1)–W(1)–O(24) O(1)–W(1)–O(26) O(1)–W(1)–O(23) O(26)–W(1)–O(23) O(28)–W(1)–O(19) O(2)–W(2)–O(27) O(2)–W(2)–O(30) O(2)–W(2)–O(25) O(30)–W(2)–O(25) O(23)–W(2)–O(19) O(3)–W(3)–O(25) O(3)–W(3)–O(31) O(3)–W(3)–O(26) O(31)–W(3)–O(26) O(29)–W(3)–O(19) O(4)–W(4)–O(36) O(4)–W(4)–O(34) O(4)–W(4)–O(27) O(34)–W(4)–O(27) O(41)–W(4)–O(21) O(5)–W(5)–O(42) O(5)–W(5)–O(34) O(5)–W(5)–O(35) O(34)–W(5)–O(35) O(30)–W(5)–O(20) O(6)–W(6)–O(33) O(6)–W(6)–O(40) O(6)–W(6)–O(35) O(40)–W(6)–O(35) O(29)–W(6)–O(20) O(7)–W(7)–O(33) O(7)–W(7)–O(37) O(7)–W(7)–O(43) O(37)–W(7)–O(43)
1.742(12) 1.916(11) 1.919(10) 1.723(11) 1.931(10) 1.886(10) 1.717(12) 1.921(10) 1.912(10) 1.709(11) 1.939(10) 1.891(10) 1.735(11) 1.956(10) 1.900(10) 1.716(11) 1.991(10) 1.898(10) 1.700(11) 1.948(9) 1.900(10) 1.687(11) 1.944(10) 1.926(10) 1.732(11) 1.920(10) 1.870(10) 1.531(11) 1.553(11) 103.9(5) 98.7(5) 99.9(5) 86.5(5) 83.3(4) 102.6(5) 101.8(5) 103.2(5) 89.4(5) 72.3(4) 101.5(5) 101.2(5) 102.2(5) 87.6(4) 83.5(4) 99.1(5) 102.2(5) 97.7(5) 86.1(5) 82.5(4) 98.0(5) 101.2(5) 99.7(5) 159.0(4) 81.4(4) 103.6(5) 100.6(5) 98.8(5) 88.0(4) 81.0(4) 103.5(5) 100.3(5) 100.0(5) 87.1(4)
W(1)–O(24) W(1)–O(19) W(2)–O(30) W(3)–O(25) W(3)–O(19) W(4)–O(34) W(5)–O(42) W(5)–O(20) W(6)–O(40) W(7)–O(33) W(7)–O(22) W(8)–O(37) W(9)–O(38) W(9)–O(21) W(10)–O(39) W(11)–O(43) W(11)–O(44) W(12)–O(53) W(13)–O(52) W(13)–O(47) W(14)–O(52) W(15)–O(48) W(15)–O(46) W(16)–O(54) W(17)–O(55) W(17)–O(45) W(18)–O(61) P(1)–O(19) P(2)–O(47) O(1)–W(1)–O(28) O(24)–W(1)–O(26) O(24)–W(1)–O(23) O(1)–W(1)–O(19) O(26)–W(1)–O(19) O(2)–W(2)–O(23) O(27)–W(2)–O(30) O(27)–W(2)–O(25) O(2)–W(2)–O(19) O(30)–W(2)–O(19) O(3)–W(3)–O(29) O(25)–W(3)–O(31) O(25)–W(3)–O(26) O(3)–W(3)–O(19) O(31)–W(3)–O(19) O(4)–W(4)–O(41) O(36)–W(4)–O(34) O(36)–W(4)–O(27) O(4)–W(4)–O(21) O(34)–W(4)–O(21) O(5)–W(5)–O(30) O(42)–W(5)–O(34) O(42)–W(5)–O(35) O(5)–W(5)–O(20) O(34)–W(5)–O(20) O(6)–W(6)–O(29) O(33)–W(6)–O(40) O(33)–W(6)–O(35) O(6)–W(6)–O(20) O(40)–W(6)–O(20) O(7)–W(7)–O(31) O(33)–W(7)–O(37) O(33)–W(7)–O(43) O(7)–W(7)–O(22)
1.869(10) 2.372(11) 1.932(11) 1.868(10) 2.382(11) 1.903(10) 1.870(10) 2.326(10) 1.916(10) 1.873(10) 2.373(10) 1.896(10) 1.873(10) 2.306(10) 1.914(9) 1.845(10) 2.299(10) 1.910(10) 1.888(10) 2.362(10) 1.908(10) 1.893(10) 2.333(11) 1.928(11) 1.897(10) 2.405(11) 1.932(10) 1.545(12) 1.558(11) 103.7(5) 157.4(4) 89.0(4) 169.4(5) 73.2(4) 102.8(5) 85.2(5) 154.2(4) 173.3(5) 83.3(4) 102.0(5) 157.3(4) 88.0(5) 173.1(5) 83.3(4) 100.5(5) 158.6(5) 89.5(5) 171.0(5) 86.3(4) 97.2(5) 89.2(5) 88.6(5) 173.9(5) 84.6(4) 95.9(5) 89.3(4) 157.6(4) 170.4(5) 82.7(4) 97.0(5) 156.2(4) 88.7(4) 171.9(5)
W(1)–O(28) W(2)–O(2) W(2)–O(25) W(3)–O(29) W(4)–O(4) W(4)–O(27) W(5)–O(30) W(6)–O(6) W(6)–O(35) W(7)–O(31) W(8)–O(8) W(8)–O(28) W(9)–O(32) W(10)–O(10) W(10)–O(51) W(11)–O(50) W(12)–O(12) W(12)–O(56) W(13)–O(53) W(14)–O(14) W(14)–O(54) W(15)–O(38) W(16)–O(16) W(16)–O(60) W(17)–O(61) W(18)–O(18) W(18)–O(62) P(1)–O(22) P(2)–O(45) O(24)–W(1)–O(28) O(28)–W(1)–O(26) O(28)–W(1)–O(23) O(24)–W(1)–O(19) O(23)–W(1)–O(19) O(27)–W(2)–O(23) O(23)–W(2)–O(30) O(23)–W(2)–O(25) O(27)–W(2)–O(19) O(25)–W(2)–O(19) O(25)–W(3)–O(29) O(29)–W(3)–O(31) O(29)–W(3)–O(26) O(25)–W(3)–O(19) O(26)–W(3)–O(19) O(36)–W(4)–O(41) O(41)–W(4)–O(34) O(41)–W(4)–O(27) O(36)–W(4)–O(21) O(27)–W(4)–O(21) O(42)–W(5)–O(30) O(30)–W(5)–O(34) O(30)–W(5)–O(35) O(42)–W(5)–O(20) O(35)–W(5)–O(20) O(33)–W(6)–O(29) O(29)–W(6)–O(40) O(29)–W(6)–O(35) O(33)–W(6)–O(20) O(35)–W(6)–O(20) O(33)–W(7)–O(31) O(31)–W(7)–O(37) O(31)–W(7)–O(43) O(33)–W(7)–O(22)
1.873(10) 1.710(11) 1.949(9) 1.922(10) 1.689(12) 1.918(10) 1.893(11) 1.711(11) 1.929(10) 1.894(9) 1.700(11) 1.940(10) 1.906(10) 1.679(11) 1.918(10) 1.885(10) 1.711(11) 1.973(10) 1.935(10) 1.710(11) 1.908(11) 1.917(10) 1.681(12) 1.933(10) 1.901(10) 1.712(10) 1.934(10) 1.552(11) 1.568(11) 86.8(5) 88.6(5) 156.4(4) 84.3(4) 73.2(4) 89.1(5) 155.4(4) 85.5(5) 82.1(4) 72.3(4) 89.1(5) 85.8(4) 155.7(4) 74.2(4) 72.6(4) 90.1(5) 87.7(4) 161.7(5) 72.3(4) 79.9(4) 164.7(5) 86.6(5) 90.2(5) 83.6(4) 74.4(4) 86.9(4) 163.5(4) 89.5(4) 85.3(4) 72.2(4) 87.5(4) 89.7(4) 163.0(4) 84.5(4)
W(1)–O(26) W(2)–O(27) W(2)–O(19) W(3)–O(31) W(4)–O(36) W(4)–O(21) W(5)–O(34) W(6)–O(33) W(6)–O(20) W(7)–O(37) W(8)–O(39) W(8)–O(22) W(9)–O(36) W(10)–O(57) W(10)–O(44) W(11)–O(51) W(12)–O(40) W(12)–O(47) W(13)–O(58) W(14)–O(49) W(14)–O(46) W(15)–O(55) W(16)–O(58) W(16)–O(45) W(17)–O(60) W(18)–O(59) W(18)–O(45) P(1)–O(21) P(2)–O(44)
1.907(10) 1.909(10) 2.408(11) 1.923(9) 1.863(11) 2.368(10) 1.896(10) 1.903(10) 2.413(10) 1.911(10) 1.875(9) 2.344(10) 1.949(10) 1.897(11) 2.350(10) 1.906(10) 1.884(10) 2.354(10) 1.938(10) 1.846(11) 2.361(10) 1.922(10) 1.909(11) 2.403(10) 1.902(10) 1.863(10) 2.334(10) 1.571(10) 1.568(10)
Z. Li et al. / Journal of Molecular Structure 783 (2006) 176–183 Table 2 (continued) O(31)–W(7)–O(22) O(8)–W(8)–O(39) O(8)–W(8)–O(37) O(8)–W(8)–O(28) O(37)–W(8)–O(28) O(32)–W(8)–O(22) O(9)–W(9)–O(38) O(9)–W(9)–O(36) O(9)–W(9)–O(24) O(36)–W(9)–O(24) O(32)–W(9)–O(21) O(10)–W(10)–O(57) O(10)–W(10)–O(39) O(10)–W(10)–O(51) O(39)–W(10)–O(51) O(48)–W(10)–O(44) O(11)–W(11)–O(43) O(11)–W(11)–O(51) O(11)–W(11)–O(59) O(51)–W(11)–O(59) O(50)–W(11)–O(44) O(12)–W(12)–O(40) O(12)–W(12)–O(53) O(12)–W(12)–O(56) O(53)–W(12)–O(56) O(50)–W(12)–O(47) O(13)–W(13)–O(52) O(13)–W(13)–O(58) O(13)–W(13)–O(42) O(58)–W(13)–O(42) O(53)–W(13)–O(47) O(14)–W(14)–O(49) O(14)–W(14)–O(52) O(14)–W(14)–O(54) O(52)–W(14)–O(54) O(41)–W(14)–O(46) O(15)–W(15)–O(48) O(15)–W(15)–O(55) O(15)–W(15)–O(49) O(55)–W(15)–O(49) O(38)–W(15)–O(46) O(16)–W(16)–O(58) O(16)–W(16)–O(54) O(16)–W(16)–O(60) O(54)–W(16)–O(60) O(62)–W(16)–O(45) O(17)–W(17)–O(55) O(17)–W(17)–O(60) O(17)–W(17)–O(57) O(60)–W(17)–O(57) O(61)–W(17)–O(45) O(18)–W(18)–O(59) O(18)–W(18)–O(61) O(18)–W(18)–O(62) O(61)–W(18)–O(62) O(56)–W(18)–O(45) O(20)–P(1)–O(19) O(20)–P(1)–O(21) O(46)–P(2)–O(47) O(46)–P(2)–O(44)
82.0(4) 99.8(5) 103.5(5) 95.9(5) 89.9(4) 85.3(4) 97.8(5) 101.2(5) 98.0(5) 89.5(4) 85.1(4) 98.9(5) 98.3(5) 101.1(5) 88.5(4) 85.4(4) 101.1(5) 101.9(5) 93.3(5) 88.3(4) 84.4(4) 100.1(5) 97.5(5) 95.9(5) 87.0(5) 83.6(4) 101.9(5) 96.4(5) 98.8(5) 164.8(4) 72.9(4) 102.3(5) 99.5(5) 96.9(5) 85.2(5) 82.4(4) 100.3(5) 98.9(5) 103.3(5) 89.2(4) 81.7(4) 101.9(5) 103.2(5) 102.2(5) 87.6(5) 72.5(4) 102.6(5) 102.0(5) 101.3(5) 156.7(5) 71.7(4) 99.5(5) 101.1(5) 102.2(5) 86.0(5) 83.2(4) 107.8(6) 110.9(6) 112.5(6) 112.4(6)
O(37)–W(7)–O(22) O(8)–W(8)–O(32) O(39)–W(8)–O(37) O(39)–W(8)–O(28) O(8)–W(8)–O(22) O(37)–W(8)–O(22) O(9)–W(9)–O(32) O(38)–W(9)–O(36) O(38)–W(9)–O(24) O(9)–W(9)–O(21) O(36)–W(9)–O(21) O(10)–W(10)–O(48) O(57)–W(10)–O(39) O(57)–W(10)–O(51) O(10)–W(10)–O(44) O(39)–W(10)–O(44) O(11)–W(11)–O(50) O(43)–W(11)–O(51) O(43)–W(11)–O(59) O(11)–W(11)–O(44) O(51)–W(11)–O(44) O(12)–W(12)–O(50) O(40)–W(12)–O(53) O(40)–W(12)–O(56) O(12)–W(12)–O(47) O(53)–W(12)–O(47) O(13)–W(13)–O(53) O(52)–W(13)–O(58) O(52)–W(13)–O(42) O(13)–W(13)–O(47) O(58)–W(13)–O(47) O(14)–W(14)–O(41) O(49)–W(14)–O(52) O(49)–W(14)–O(54) O(14)–W(14)–O(46) O(52)–W(14)–O(46) O(15)–W(15)–O(38) O(48)–W(15)–O(55) O(48)–W(15)–O(49) O(15)–W(15)–O(46) O(55)–W(15)–O(46) O(16)–W(16)–O(62) O(58)–W(16)–O(54) O(58)–W(16)–O(60) O(16)–W(16)–O(45) O(54)–W(16)–O(45) O(17)–W(17)–O(61) O(55)–W(17)–O(60) O(55)–W(17)–O(57) O(17)–W(17)–O(45) O(60)–W(17)–O(45) O(18)–W(18)–O(56) O(59)–W(18)–O(61) O(59)–W(18)–O(62) O(18)–W(18)–O(45) O(61)–W(18)–O(45) O(20)–P(1)–O(22) O(19)–P(1)–O(21) O(46)–P(2)–O(45) O(47)–P(2)–O(44)
71.7(4) 98.5(5) 91.5(5) 163.4(4) 175.0(5) 72.6(4) 101.3(5) 88.5(5) 164.2(4) 173.6(5) 72.4(4) 101.2(5) 162.7(5) 90.7(4) 173.4(5) 81.7(4) 99.3(5) 92.5(4) 165.1(4) 172.2(5) 73.7(4) 105.0(5) 89.9(5) 164.0(4) 170.6(5) 73.5(4) 99.8(5) 86.5(5) 90.2(5) 172.6(5) 82.0(4) 100.0(5) 158.1(5) 89.3(5) 174.7(5) 85.3(4) 98.3(5) 85.7(5) 156.4(5) 175.3(5) 81.4(4) 100.6(5) 86.8(5) 155.9(4) 171.8(5) 83.7(4) 101.3(5) 88.7(5) 85.3(5) 171.8(4) 73.9(4) 102.9(5) 88.3(5) 158.3(4) 172.9(4) 72.9(4) 113.2(6) 106.5(6) 107.4(6) 111.3(6)
O(43)–W(7)–O(22) O(39)–W(8)–O(32) O(32)–W(8)–O(37) O(32)–W(8)–O(28) O(39)–W(8)–O(22) O(28)–W(8)–O(22) O(38)–W(9)–O(32) O(32)–W(9)–O(36) O(32)–W(9)–O(24) O(38)–W(9)–O(21) O(24)–W(9)–O(21) O(57)–W(10)–O(48) O(48)–W(10)–O(39) O(48)–W(10)–O(51) O(57)–W(10)–O(44) O(51)–W(10)–O(44) O(43)–W(11)–O(50) O(50)–W(11)–O(51) O(50)–W(11)–O(59) O(43)–W(11)–O(44) O(59)–W(11)–O(44) O(40)–W(12)–O(50) O(50)–W(12)–O(53) O(50)–W(12)–O(56) O(40)–W(12)–O(47) O(56)–W(12)–O(47) O(52)–W(13)–O(53) O(53)–W(13)–O(58) O(53)–W(13)–O(42) O(52)–W(13)–O(47) O(42)–W(13)–O(47) O(49)–W(14)–O(41) O(41)–W(14)–O(52) O(41)–W(14)–O(54) O(49)–W(14)–O(46) O(54)–W(14)–O(46) O(48)–W(15)–O(38) O(38)–W(15)–O(55) O(38)–W(15)–O(49) O(48)–W(15)–O(46) O(49)–W(15)–O(46) O(58)–W(16)–O(62) O(62)–W(16)–O(54) O(62)–W(16)–O(60) O(58)–W(16)–O(45) O(60)–W(16)–O(45) O(55)–W(17)–O(61) O(61)–W(17)–O(60) O(61)–W(17)–O(57) O(55)–W(17)–O(45) O(57)–W(17)–O(45) O(59)–W(18)–O(56) O(56)–W(18)–O(61) O(56)–W(18)–O(62) O(59)–W(18)–O(45) O(62)–W(18)–O(45) O(19)–P(1)–O(22) O(22)–P(1)–O(21) O(47)–P(2)–O(45) O(45)–P(2)–O(44)
81.2(4) 88.9(4) 157.7(4) 83.6(4) 83.5(4) 81.2(4) 90.5(5) 157.4(5) 85.4(4) 83.1(4) 81.3(4) 85.7(5) 88.5(5) 157.7(5) 81.5(4) 72.3(4) 90.4(4) 157.6(4) 83.4(4) 85.7(4) 80.2(4) 92.4(4) 156.6(4) 84.4(4) 83.2(4) 80.9(4) 157.9(5) 87.4(5) 90.1(5) 85.2(4) 82.9(4) 91.8(5) 87.3(5) 162.4(4) 72.9(4) 81.1(4) 88.6(5) 162.6(5) 89.5(4) 84.4(4) 72.0(4) 88.0(5) 156.2(4) 87.7(5) 82.6(4) 73.5(4) 156.0(5) 88.1(5) 88.3(5) 84.6(4) 83.1(4) 88.7(5) 156.1(4) 88.0(5) 84.2(4) 74.1(4) 107.4(6) 110.7(6) 107.9(6) 104.9(6)
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starting concentration, temperature, pH, and pressure [3,5]. Although Cd2C is not incorporated in the final structure, the species appears to be needed in the isolation of compound 1. Without CdCl2 or CdCl2 replaced by ZnCl2 or CuCl2, attempts to synthesize 1 proved fruitless and amorphous mixtures were obtained. It was observed that the pH value of the reaction mixture plays a very important role on the formation of 1. When the initial pH value reduced to 1.2, amorphous mixtures were found; and when the initial pH raised to 3.0, the yield of 1 reduced to only 10% (based on tungsten). Nevertheless, the reaction of a mixture of Na2WO4, CdCl2, H3PO4, en, and H2O in the molar ratio of 1:1:7.64:2.32:232 with the initial pH value of 1.46 at 150 8C for 96 h produced green block-like crystals of 1 in a good yield. 3.2. Crystal structure The asymmetric unit of 1 consists of one classical a-Dawson type [P2W18O62]6K polyoxoanion, three [H2en]2C cations and 6.48$H2O molecules of crystallization. Like usually observed in Dawson type anions [17–19,25], the [P2W18O62]6K anion is closed to the D3h point symmetry and contains two [a-A-PW9O34]9K units which are derived from the a-Keggin type [a-PW12O40]3K anion by removal of a set of three corner-sharing WO6 octahedrons and these two [a-APW9O34]9K units are linked through corner-sharing with the elimination of six oxygen atoms, as show in Fig. 1. In the Dawson type polyoxoanion, there are two structurally distinct types of W atoms: six ‘cap’ atoms on vertical mirror-planes and grouped in two sets of three, on the other hand, 12 ‘belt’ atoms are grouped in two sets of six, but not lie on mirrorplanes. In the [P2W18O62]6K cluster, the oxygen atoms can be divided into four groups according to the numbers of atoms that the oxygen atoms are coordinated to: (1) 18 terminal oxygen atoms (Ot) only bonding to one W atom with W–O
˚ ; (2) 36 oxygen bond distances of 1.679(11)–1.742(12) A atoms (m2-O) connecting with two W atoms with W–O bond ˚ ; (3) 6 oxygen atoms distances of 1.845(10)–1.991(10) A (m3-O) which are combined with one P atom and two W atoms and the W–O bond distances vary from 2.299(10) to 2.413(10) ˚ ; (4) 2 oxygen atoms (m4-O) which are coordinated to one P A atom and three W atoms and the W–O bond distances are ˚ . These bond distances between 2.372(11) and 2.408(11) A have a rule of W–Ot ! W–(m2-O)(W–(m3-O), W–(m4-O), and they are in accord with those in the well-known a-Dawson type anions [17–19,25–28]. The P–O distances range from ˚ . Bond valence sum calculation [29] 1.531(10) to 1.571(10) A demonstrates that W atoms in 1 have their valence sums ranging from 5.97 to 6.43, with a average value of 6.15, very close to the ideal value of six for W(VI). There is extensive hydrogen bonging in the crystal structure of 1. As listed in Table 3, the N–H/O hydrogen bonding between the complex cation [H2en]2C and the oxygen atoms from the Dawson units with N/O interatomic ˚ and N–H/O distances ranging from 2.76(2) to 3.18(3) A angles between 110.0 and 160.9 is observed. It is noteworthy that compound 1 has C–H/O hydrogen bonds between the C–H groups from the complex cation [H2en]2C and the oxygen atoms from the Dawson units have C/O interatomic ˚ . It is similar to the distances from 3.148(19) to 3.36(2) A compound (pbpy)8H3[PW12O40]$2H2O [30], in which C–H/ O hydrogen bonds with C/O distances between 3.101 and ˚ were observed. In the crystal structure of 1, one en 3.355 A molecule is connected with its four adjacent Dawson clusters through five N–H/O and four C–H/O hydrogen bonds, and a second en molecule connected with its four neighboring Dawson units through nine N–H/O hydrogen bonds, while the other en molecule connected with its three neighboring Dawson clusters through four N–H/O hydrogen bonds. These hydrogen bonds make the cation [H2en]2C and
Fig. 1. Structure of the Dawson unit [P2W18O62]6K in compound 1, where (a) for a polyhedral representation, and (b) for an ORTEP representation with the atom labeling scheme shown at 50% thermal probability.
Z. Li et al. / Journal of Molecular Structure 783 (2006) 176–183 Table 3 ˚ , 8) for compound 1 Hydrogen-bonding geometry (A D–H/A
d(D–H)
d(H/A)
d(D/A)
!(DHA)
N(1)–H(1C)/O(67a) N(1)–H(1D)/O(63a) N(1)–H(1E)/O(3b) N(1)–H(1E)/O(12) N(2)–H(2C)/O(66) N(2)–H(2D)/O(23a) N(2)–H(2D)/O(17c) N(2)–H(2E)/O(7b) N(3)–H(3C)/O(18d) N(3)–H(3C)/O(18e) N(3)–H(3D)/O(9) N(3)–H(3D)/O(11d) N(3)–H(3E)/O(63) N(4)–H(4C)/O(68) N(4)–H(4D)/O(11d) N(4)–H(4D)/O(9) N(4)–H(4E)/O(35f) N(5)–H(5E)/O(2) N(6)–H(6C)/O(4) N(6)–H(6C)/O(67) N(6)–H(6D)/O(64d) N(6)–H(6E)/O(17d) N(6)–H(6E)/O(26g) C(1)–H(1B)/O(23a) C(2)–H(2A)/O(7b) C(2)–H(2A)/O(12) C(2)–H(2B)/O(53) C(3)–H(3B)/O(3f) O(63)–H(63A)/O(65) O(63)–H(63B)/O(53e) O(64)–H(64A)/O(66f) O(64)–H(64B)/O(10) O(65)–H(65A)/O(16e) O(65)–H(65B)/O(8) O(66)–H(66A)/O(15c) O(66)–H(66B)/O(42) O(67)–H(67A)/O(36) O(67)–H(67B)/O(59d) O(67)–H(67B)/O(61d) O(68)–H(68A)/O(8) O(68)–H(68B)/O(48) O(69)–H(69A)/O(10d) O(69)–H(69B)/O(69h)
0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.97 0.97 0.97 0.97 0.97 0.85 0.86 0.88 0.94 0.85 0.85 0.85 0.85 0.85 0.85 0.85 0.83 0.89 0.85 0.85
1.88 1.92 2.22 2.24 2.12 2.12 2.49 2.56 2.26 2.50 2.20 2.22 2.10 1.84 2.18 2.37 2.24 2.45 2.52 2.07 2.35 2.42 2.12 2.51 2.53 2.54 2.56 2.50 1.85 2.47 2.26 2.14 2.04 2.27 1.95 2.40 2.00 2.56 2.02 2.59 2.34 2.39 2.30
2.74(3) 2.80(2) 2.76(2) 3.04(2) 2.92(3) 2.97(2) 2.918(19) 2.99(2) 3.046(17) 2.944(18) 2.837(18) 2.964(18) 2.92(2) 2.69(3) 2.901(18) 3.027(19) 2.955(19) 3.18(3) 3.10(2) 2.83(3) 3.21(4) 2.92(2) 2.95(2) 3.36(2) 3.15(2) 3.28(2) 3.148(19) 3.352(18) 2.69(3) 3.33(2) 3.14(4) 3.08(3) 2.89(3) 3.12(3) 2.80(2) 3.25(2) 2.85(2) 3.11(2) 2.81(2) 3.42(3) 3.18(3) 3.23(6) 3.15(12)
160.4 170.7 119.3 148.6 148.4 160.9 110.5 110.0 147.8 111.1 128.1 140.5 152.7 157.5 137.5 130.9 136.8 140.7 123.6 142.8 162.5 115.3 155.1 147.2 121.0 133.1 118.9 146.6 176.5 178.2 176.2 179.0 178.8 175.6 177.7 179.3 178.4 124.0 152.7 177.0 157.5 167.0 176.9
Symmetry transformations used to generate equivalent atoms: (a) xK1/2,K yC1/2,zC1/2; (b) KxC1,KyC1,KzC1; (c) xC1/2,KyC1/2,zC1/2; (d) K xC1/2,yK1/2,KzC1/2; (e) xC1/2,KyC1/2,zK1/2; (f) xK1/2,KyC1/2,zK 1/2; (g) KxC3/2,yK1/2,KzC1/2; (h) KxC1,Ky,KzC1.
the Dawson units form into an extended three-dimensional supermolecular network, where H2O molecules of crystallization are located in the interspace and interact with the network through O–H/O hydrogen bonding with O/O ˚ and N–H/O hydrogen distances from 2.69(3) to 3.42(3) A ˚ bonding with N/O distances between 2.69(3) and 2.92(3) A (Fig. 2). 3.3. IR spectrum and thermal analysis In the infrared spectrum of compound 1, as shown in Fig. S1, the strong bands at 1090 cmK1 could be ascribed to
181
n(P–(m-O)), that at 958 cmK1 to n(WaOt), and those at 910 and 770 cmK1 to n(W–(m-O)). There are some characteristic bands for the cations at 3140, 1510 and 1320 cmK1, where are assigned to n(CH2), t(CH2) and n(C–N), respectively. In addition, the bonds at 3500 and 1590 cmK1 are due to n(O–H) and d(HOH), respectively, and their wide shapes are resulted from the extensive O–H/O hydrogen bonds in the structure. A two-stage weight-loss scheme was observed on the thermogravimetric curve of compound 1, as shown in Fig. 3. The first decomposition stage, which occurs between 111 and 185 8C, is attributed to the release of some H2O molecules of crystallization with observed weight-loss of 1.65%. The weight-loss ranging from 328 to 659 8C is 4.75%, which is associated to the removal of the ethylenediamine and the residual H2O molecules of crystallization. The overall weightloss of 6.40% is accordant with the calculated value of ethylenediamine and H2O molecules of crystallization of 6.36%. 3.4. Catalytic reaction A probe reaction of the oxidation of cyclohexene into adipic acid with H2O2 as oxidation reagent and compound 1 as the catalyst was carried out to examine the oxidative catalytic activity. The infrared spectrum of the product is illustrated in Fig. 4, which is similar to adipic acid. The melting point of the product was measured to be 150–152 8C, very close to adipic acid, whose melting point is 152 8C. It was deduced that the product is adipic acid and the selectivity for adipic acid is nearly 100%. The influence of the amount of succinic acid on the amount of adipic acid is shown in Fig. 5. When the amount of succinic acid was 1.0 mmol, the curve reached its peak and 2.6156 g adipic acid was obtained from the oxidation of 50 mmol cyclohexene. The best proportion of compound 1, cyclohexene, succinic acid and H2O2 in the catalytic reaction was 1:1000:20:5380, and the hybrid material exhibited a catalytic activity of 52.312 g adipic acid/mmol catalyst per hour. In a comparative experiment, where 0.05 mmol H6P2W18O62$nH2O was used instead of compound 1 (Fig. 5), the best proportion was 1:1000:15:5380, and 1.0326 g adipic acid was obtained. H6P2W18O62$nH2O showed a catalytic activity of 20.652 g adipic acid/mmol catalyst per hour, which was 2.5 times less than that of the as-synthesized hybrid material. The comparison tests indicated that the as-synthesized hybrid material might become an effective catalyst in some organic oxidation.
4. Conclusions Utilizing the hydrothermal synthesis methodology, we have prepared successfully a new Dawson polyoxotungstate (H2en)3[P2W18O62]$6.48H2O. There are extensive hydrogenbonding interactions between the Dawson clusters and [H2en]2C complex cations These hydrogen bonds make
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Fig. 2. A packing view of (H2en)3[P2W18O62]$6.48H2O along the a-axis.
them hold together into a three-dimensional supermolecular network. A probe reaction of the oxidation of cyclohexene indicates that compound 1 is useful as an oxidative catalyst in the oxidation of cyclohexene into adipic acid with H2O2, and the best proportion of compound 1, cyclohexene, succinic acid and H2O2 in the reaction was 1:1000:20: 5380. The formation of 1 demonstrates that the hydrothermal synthesis techniques are well suited for exploratory investigations of the diverse structure chemistry of Dawson polyoxotungstates.
Fig. 3. TG curve of (H2en)3[P2W18O62]$6.48H2O in flowing N2 at 10 8C minK1.
Fig. 4. The IR spectrum of adipic acid and product.
Fig. 5. Influence of the amount of succinic acid on the amount of adipic acid.
Z. Li et al. / Journal of Molecular Structure 783 (2006) 176–183
Acknowledgements This work is supported by the Natural Science Foundation of Fujian Province of China (No. E0420001), NSF of China (No. 50172016) and the Science Foundation of Huaqiao University (No. 03HZR9). Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.molstruc.2005.09. 003
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