- Email: [email protected]
Synthesis and spectroscopic characterization of organophosphoryl polyoxotungstates [C6H11P(O)]2Xn+W11O39(8−n)− (Xn+=P5+, Si4+, B3+, Ga3+)
www.elsevier.nl/locate/poly Polyhedron 19 (2000) 125–128
Synthesis and spectroscopic characterization of organophosphoryl polyoxotungstates [C6H11P(O)]2XnqW11O39(8yn)y (XnqsP5q, Si4q, B3q, Ga3q) Zhen-Gang Sun, Qun Liu, Jing-Fu Liu * Department of Chemistry, Northeast Normal University, Changchun 130024, PR China Received 7 July 1999; accepted 14 October 1999
Abstract In the presence of NBu4Br acting as a phase-transfer reagent, the monovalent polyoxotungstates a-XnqW11O39(12yn)y (XsP, Si, B, Ga) react with electrophilic cyclohexane phosphonyl chloride to give hybrid organophosphoryl polyoxotungstates [(C6H11P(O)]2XW11O39(8yn)y, which have been characterized by elemental analysis and IR, 31P and 183W NMR spectroscopy. The six-line 183W spectra indicate that the hybrid anions possess Cs symmetry in solution. According to spectroscopic observations and chemical analyses, the hybrid anion consists of an a-[XW11O39] framework on which are grafted two equivalent C6H5P(O) groups through P–O–W bridges. q2000 Elsevier Science Ltd All rights reserved. Keywords: Organophosphoryl polyoxotungstate; Polyoxometalate; Synthesis; 183W NMR
1. Introduction Derivatized polyoxometalates have received increasing attention during the last 20 years owing to their potential use in catalysis, medicine and materials science [1]. It has been recognized for a long time that, by grafting appropriate organic and organometallic groups onto the polyoxometalate surface, the solubility and other physical properties of the complexes may be modified, which would increase their utility and versatility in catalysis and various medical applications, including antiviral and antitumoral chemotherapy [2– 4]. The reactivity of lacunary polyoxotungstates with organic and organometallic groups has been summarized [5]. To date, the reaction of lacunary polyoxotungstates with organophosphonic acid has been reported rarely, except for a unique study by Kim et al. [6] on PhPO derivatives of monovalent tungstophosphate and tungstosilicate, and that of Mayer and Thouvenot [7] on RPO derivatives of trivalent tungstophosphate. As a continuation of these studies, we report here the synthesis and spectroscopic characterization of the title compounds [C6H11P(O)]2XW11O39(8yn)y (XsP, Si, B, Ga). * Corresponding author. Tel.: q86-564-9825; e-mail: sdjingfu@ public.cc.jl.cn
2. Experimental 2.1. Reagents and apparatus All reagents were of analytical or guaranteed purity. CH3CN was distilled over P2O5 and used immediately. Sodium and potassium salts of XnqW11O39(12yn)y (XsP, Si, B, Ga) were prepared using procedures describd in the literature [8,9]. Cyclohexanephosphonyl chloride was prepared according to a published method [10]. IR spectra were recorded on an Alpha Centauri FTIR spectrometer (2000– 400 cmy1 range) with KBr pellets. 31P NMR spectra were recorded with a JNM-FX-100 NMR spectrometer, and chemical shifts were given with respect to external 85% H3PO4 for 31 P in CD3CN. 183W NMR spectra were recorded at 16.64 MHz on a Unity-400 spectrometer using a 10-mm diameter NMR tube at 208C; chemical shifts were referenced to 2 M Na2WO4 in D2O. 2.2. Preparation of the compounds 2.2.1. [NBu4]3[C6H11P(O)]2PW11O39 (1) a-Na7PW11O39P13H2O (1.42 g, 0.5 mmol) and NBu4Br (0.97 g, 3 mmol) were suspended in CH3CN (25 ml), and an acetonitrile solution of C6H11POCl2 (0.201 g, 1 mmol in 15 ml of acetonitrile) was added dropwise under vigorous
0277-5387/00/$ - see front matter q2000 Elsevier Science Ltd All rights reserved. PII S 0 2 7 7 - 5 3 8 7 ( 9 9 ) 0 0 3 2 6 - 5
Tuesday Feb 01 09:29 AM
StyleTag -- Journal: POLY (Polyhedron)
Article: 3283
126
Z.-G. Sun et al. / Polyhedron 19 (2000) 125–128
stirring. The flask was sealed with a septum stopper, and the mixture was stirred for 48 h at room temperature. After separation of a white solid (NaCl, NaBr and traces of Na7PW11O39), the resulting solution was concentrated on a rotary evaporator, and was then diluted with 100 ml of absolute ethanol to produce a white precipitate. The white precipitate was isolated by filtration, and the solid isolated was reprecipitated again from 5 ml of acetonitrile solution by adding 100 ml of ethanol to give 1.1 g (49.12%) of a white powder. Found: C, 19.31; H, 3.58; N, 1.19; P, 2.82; W, 55.82. Calc. for C60H130N3O41P3W11: C, 19.65; H, 3.50; N, 1.15; P, 2.54; W, 55.23%. 2.2.2. [NBu4]4[C6H11P(O)]2SiW11O39 (2) This compound was similarly synthesized from aK6Na2SiW11O39P13H2O (2.54 g, 0.8 mmol), NBu4Br (1.29 g, 4 mmol) and C6H11POCl2 (0.32 g, 1.6 mmol). Yield: 1.4 g (44.87%). Found: C, 23.48; H, 4.30; N, 1.47; Si, 0.74; P, 1.62; W, 51.62. Calc. for C76H166N4O41P2SiW11: C, 23.36; H, 4.25; N, 1.43; Si, 0.72; P, 1.59; W, 51.84%. 2.2.3. [NBu4]4H[C6H11P(O)]2BW11O39 (3) This compound was similarly synthesized from aK7NaHBW11O39P13H2O (2.54 g, 0.8 mmol), NBu4Br (1.29 g, 4 mmol) and C6H11POCl2 (0.32 g, 1.6 mmol). Yield: 1.35 g (43.41%). Found: C, 26.72; H, 4.33; N, 1.48; B, 0.26; P, 1.61; W, 52.14. Calc. for C76H167N4O41P2BW11: C, 26.54; H, 4.29; N, 1.44; B, 0.28; P, 1.59; W, 52.06%.
Ga3q), using NBu4Br acting as a phase-transfer reagent. The overall reaction is: MeCN
X nqW11 O(12yn)y qC 6 H11 P(O)Cl 2 ™ 39 NBu 4 Br
[C 6 H11 P(O)]2 X nqW11 O(8yn)y 39 After filtration of a white solid consisting of NaCl, NaBr or KCl, KBr and a small amount of unchanged sodium or potassium polyoxotungstate, the acetonitrile solution contains a single hybrid anionic species, which has been isolated as its tetrabutylammonium salt. Elemental analysis results are consistent with the formulation of the title compounds. In contrast, the reaction between the sodium salt of a[PW11O39]7y with C6H11P(O)Cl2 in water did not show any evidence for the attachment of the organic group. This indicates that the anhydrous condition is needed for the reaction of C6H11P(O)Cl2 with the lacunary polyoxotungstate. In addition, direct reaction of the lacunary precursor with C2H5OP(O)Cl2 in acetonitrile does not give any isolable product, showing that a highly electrophilic organophosphonoyl moiety is needed for the above reaction. 3.2. Infrared spectra
3. Results and discussion
The infrared spectra of all the compounds are very similar; all data and IR assignments are given in Table 1. The P–O stretching vibration bands of the organic group and central PO4 moiety are observed between 1000 and 1060 cmy1 and the highest wavenumber (1120–1150 cmy1) is assigned to the stretching vibration of the P–C bond of the C6H11P(O) unit. The low wavenumber region (n-1000 cmy1) is characteristic of the W–O stretching and bending vibration in the polyoxotungstate. It is of interest to compare the n3 stretching modes of the PO4 unit (F2) [11] for compound 1 with the IR spectra of the other structurally related anions. It is well known that a decrease in symmetry from Td (XW12) to Cs (XW11) leads to splitting of the n3 vibration (F2) of the PO4 group into two components. The value of the splitting, Dn, is decreased when the triply bridging oxygen of the PO4 unit interacts with a transition metal ion [11,12]. It can be seen from Table 1 that the value of Dn is decreased when two organophosphoryl groups are bound in the cavity, and the stretching vibrational bands, nas (WsOter) and nas (W–Ob–W), are shifted to a higher frequency than those of the starting lacunary polyanions. This effect is attributed to a partial saturation of the polyoxometallic moiety through attachment of RPO units.
3.1. Synthesis
3.3. 31P NMR spectra
The monovalent polyoxotungstates a-XnqW11O39(12yn)y react with electrophilic cyclohexane phosphonyl chloride in acetonitrile to yield organic/inorganic species [C6H11P(O)]2 XnqW11O39(8yn)y (XnqsP5q, Si4q, B3q,
The attachment of phosphoryl groups onto the polyoxotungstate surface is demonstrated by the resonances in the 31 P NMR spectra, which are all distinct from that of C6H11P(O)Cl2 (Table 2).
2.2.4. [NBu4]4K[C6H11P(O)]2GaW11O39 (4) This compound was similarly synthesized from aK9GaW11O39P13H2O (2.64 g, 0.8 mmol), NBu4Br (1.29 g, 4 mmol) and C6H11POCl2 (0.32 g, 1.6 mmol). Yield: 1.28 g (40.15%). Found: C, 22.62; H, 4.24; N, 1.45; Ga, 1.72; K, 0.96; P, 1.59; W, 50.68. Calc. for C76H166N4KO41P2GaW11: C, 22.89; H, 4.17; N, 1.41; Ga, 1.76; K, 0.98; P, 1.56; W, 50.79%. 2.3. Chemical analyses Tungsten, phosphorus, silica, boron and gallium were determined by means of inductively coupled plasma–Auger electron spectroscopy (ICP–AES). K was determined by atomic absorption spectroscopy. C, H, N were determined using a PE-2400 elemental analyzer.
Tuesday Feb 01 09:29 AM
StyleTag -- Journal: POLY (Polyhedron)
Article: 3283
Z.-G. Sun et al. / Polyhedron 19 (2000) 125–128
127
Table 1 Comparison of infrared stretching frequencies (cmy1) Q3PW12 a
Q4H2NaPW11 a
1080 977
Assignment
1
2
3
4
1148 1042
1144 1039
1119 1026
1107 1051 958
1120 1043 1060 1027 976
n (P–C) nas (P–O) b nas (P–O) c
884 828 807 752 517
880 827 795 740 525
974 916 889 811 738
970 913 832 788 741
nas (W–Od) nas (X–Oa) d nas (W–Ob) nas (W–Oc)
534
532
954 566 881 790 763 701 566
896 830 808 513 a
Compound
d (W–O–W)
q
Qs(n-C4H9)4N . C6H11PO. c PO4. d XsSi, B, Ga. b
Table 2 P NMR data for [C6H11P(O)]2XnqW11O39(8yn)y
31
Compound
Chemical shift (d, ppm)
C6H11P(O)Cl2 [Bu4N]3[C6H11P(O)]2PW11O39 [Bu4N]4[C6H11P(O)]2SiW11O39 [Bu4N]4H[C6H11P(O)]2BW11O39 [Bu4N]4K[C6H11P(O)]2GaW11O39
58.5 34.2, y13.7 31.4 35.2 29.9
The 31P NMR spectrum of compound 1 exhibits two lines at 34.2 and y13.7 ppm with a relative intensity of 2:1 (see Fig. 1). The high-frequency resonance is attributed to the phosphoryl group, and the low-frequency singlet is assigned to the central PO4 unit of the polyoxotungstate. This chemical shift, which is intermediate between that of the starting lacunary anion a-[PW11O39]7y (dsy10.4 ppm) and that of a[PW12O40]3y (dsy14.9 ppm), is in accord with a partially saturated tungstophosphate structure. The relative intensity is consistent with the grafting of only two phosphoryl groups. A heteropolyanion with a Keggin structure becomes the Cs lacunary polyanion XnqM11O39(12yn)y after losing one
heavy atom and its terminal oxygen, which contains three W3O13 triads and one W2O10 diad. These anions have a hole surrounded by five oxygen atoms, one Oa, two Ob and two Oc (see Fig. 2). When two double-bonded phosphoryl groups each bridges two of the five oxygen atoms that define the hole in the lacunary polyanion, there are two possibilities, i.e. the groups can bridge the oxygens such that they are either unequivalent or equivalent. The single resonance in the 31P NMR spectra indicates that the mode of attachment of the organic groups to the lacunary anion is equivalent, i.e. each organic group is connected to two W atoms belonging to a triad and a diad, respectively (see Fig. 3).
Fig. 2. Idealized structures of a-XM12 (Keggin structure) (a) and a-XM11 (defective Keggin structure) (b). Oa, oxygen shared by three MO6 octahedra and the XO4 tetrahedron; Ob and Oc, oxygen linked to two different M atoms; Od, terminal unshared oxygen.
Fig. 1. The 31P NMR spectrum of compound 1 in CD3CN (0.075 M).
Tuesday Feb 01 09:29 AM
Fig. 3. Schematic representation of a-[C6H11P(O)2]XnqW11O39(8yn)y.
StyleTag -- Journal: POLY (Polyhedron)
Article: 3283
128
Z.-G. Sun et al. / Polyhedron 19 (2000) 125–128
Table 3 183 W NMR data for [C6H11P(O)]2XnqW11O39(8yn)y Compound
Chemical shift (yd, ppm)
[Bu4N]3[C6H11P(O)]2PW11O39 [Bu4N]4[C6H11P(O)]2SiW11O39 [Bu4N]4H[C6H11P(O)]2BW11O39 [Bu4N]4K[C6H11P(O)]2GaW11O39
80.9(2), 82.9(2), 96.6(1), 103.1(2), 113.5(2), 121.5(2) 82.5(2), 98.3(2), 111.2(1), 123.5(2), 140.1(2), 180.9(2) 91.9(2), 110.3(2), 115.7(1), 122.2(2), 190.3(3), 196.8(2) 62.5(2), 70.9(1), 93.1(2), 96.3(2), 126.3(2), 147.9(2)
Fig. 4. The 183W NMR spectrum of compound 3 in CD3CN (0.08 M).
be characterized in solid state by IR spectroscopy and in the CD3CN solution by 31P and 183W NMR. This hybrid anion consists of an a-[XW11O39] framework on which are grafted two equivalent C6H5P(O) groups through P–O–W bridges; each organic group is connected to two W atoms belonging to a triad and diad, respectively.
3.4. 183W NMR spectra The 183W NMR spectrum of compound 3 and chemical shifts of all compounds are shown in Fig. 4 and Table 3, respectively. The 183W NMR spectra of all species consist of six peaks, establishing that all species have Cs symmetry in solution. This feature was observed for other derivatives of Keggintype heteropolytungstates that bear organometallic ligands [13].
4. Conclusions The sodium or potassium of XnqW11O39(12yn)y (XsP, Si, B, Ga) and tetra-n-butylammonium bromide (NBu4Br) were suspended in acetonitrile, and an acetonitrile solution of C6H11POCl2 was added dropwise under vigorous stirring. After filtration, the resulting solution was concentrated and was then diluted with absolute ethanol to produce a white precipitate; the solid isolated was reprecipitated again from acetonitrile solution by adding absolute ethanol. Despite all our efforts to grow suitable crystals of the C6H11(O) derivatives of XnqW11O39(12yn)y (XsP, Si, B, Ga), no X-ray diffraction study was possible. Thus the compounds have to
Tuesday Feb 01 09:29 AM
Acknowledgements The support of the National Natural Science Foundation of China (No. 29571008) is gratefully acknowledged.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
M.T. Pope, A. Muller, Angew. Chem., Int. Ed. Engl. 30 (1991) 34. N. Mizuno, M. Misono, Chem. Rev. 98 (1998) 199. M. Weeks, C.L. Hill, R.F. Schinazi, J. Med. Chem. 35 (1992) 1216. Y. Chen, J. Liu, Q. Liu, Y. Xing, Y. Lin, H. Jia, Polyhedron 18 (1998) 481. P. Gouzerh, A. Proust, Chem. Rev. 98 (1998) 77. G.S. Kim, K.S. Hagen, C.L. Hill, Inorg. Chem. 31 (1992) 5316. C.R. Mayer, R. Thouvenot, J. Chem. Soc., Dalton Trans. (1998) 7. C. Brevard, R. Schimpf, G. Tourne, C.M. Tourne, J. Am. Chem. Soc. 105 (1983) 7059. N. Haraguchi, Y. Okaue, T. Isobe, Y. Matsuda, Inorg. Chem. 33 (1994) 1015. J.O. Clayton, W.L. Jensen, J. Am. Chem. Soc. 70 (1948) 3880. C. Rocchiccioli-Deltcheff, R. Thouvenot, J. Chem. Res. Synop. (1977) 46. ´ G.F. Tourne, ´ Inorg. Chem. 21 (1982) F. Zonnevijlle, C.M. Tourne, 2742. O.A. Gansow, R.K.C. Ho, W.G. Klemperer, J. Organomet. Chem. 187 (1980) C27.
StyleTag -- Journal: POLY (Polyhedron)
Article: 3283
Synthesis and spectroscopic characterization of organophosphoryl polyoxotungstates [C6H11P(O)]2XnqW11O39(8yn)y (XnqsP5q, Si4q, B3q, Ga3q) Zhen-Gang Sun, Qun Liu, Jing-Fu Liu * Department of Chemistry, Northeast Normal University, Changchun 130024, PR China Received 7 July 1999; accepted 14 October 1999
Abstract In the presence of NBu4Br acting as a phase-transfer reagent, the monovalent polyoxotungstates a-XnqW11O39(12yn)y (XsP, Si, B, Ga) react with electrophilic cyclohexane phosphonyl chloride to give hybrid organophosphoryl polyoxotungstates [(C6H11P(O)]2XW11O39(8yn)y, which have been characterized by elemental analysis and IR, 31P and 183W NMR spectroscopy. The six-line 183W spectra indicate that the hybrid anions possess Cs symmetry in solution. According to spectroscopic observations and chemical analyses, the hybrid anion consists of an a-[XW11O39] framework on which are grafted two equivalent C6H5P(O) groups through P–O–W bridges. q2000 Elsevier Science Ltd All rights reserved. Keywords: Organophosphoryl polyoxotungstate; Polyoxometalate; Synthesis; 183W NMR
1. Introduction Derivatized polyoxometalates have received increasing attention during the last 20 years owing to their potential use in catalysis, medicine and materials science [1]. It has been recognized for a long time that, by grafting appropriate organic and organometallic groups onto the polyoxometalate surface, the solubility and other physical properties of the complexes may be modified, which would increase their utility and versatility in catalysis and various medical applications, including antiviral and antitumoral chemotherapy [2– 4]. The reactivity of lacunary polyoxotungstates with organic and organometallic groups has been summarized [5]. To date, the reaction of lacunary polyoxotungstates with organophosphonic acid has been reported rarely, except for a unique study by Kim et al. [6] on PhPO derivatives of monovalent tungstophosphate and tungstosilicate, and that of Mayer and Thouvenot [7] on RPO derivatives of trivalent tungstophosphate. As a continuation of these studies, we report here the synthesis and spectroscopic characterization of the title compounds [C6H11P(O)]2XW11O39(8yn)y (XsP, Si, B, Ga). * Corresponding author. Tel.: q86-564-9825; e-mail: sdjingfu@ public.cc.jl.cn
2. Experimental 2.1. Reagents and apparatus All reagents were of analytical or guaranteed purity. CH3CN was distilled over P2O5 and used immediately. Sodium and potassium salts of XnqW11O39(12yn)y (XsP, Si, B, Ga) were prepared using procedures describd in the literature [8,9]. Cyclohexanephosphonyl chloride was prepared according to a published method [10]. IR spectra were recorded on an Alpha Centauri FTIR spectrometer (2000– 400 cmy1 range) with KBr pellets. 31P NMR spectra were recorded with a JNM-FX-100 NMR spectrometer, and chemical shifts were given with respect to external 85% H3PO4 for 31 P in CD3CN. 183W NMR spectra were recorded at 16.64 MHz on a Unity-400 spectrometer using a 10-mm diameter NMR tube at 208C; chemical shifts were referenced to 2 M Na2WO4 in D2O. 2.2. Preparation of the compounds 2.2.1. [NBu4]3[C6H11P(O)]2PW11O39 (1) a-Na7PW11O39P13H2O (1.42 g, 0.5 mmol) and NBu4Br (0.97 g, 3 mmol) were suspended in CH3CN (25 ml), and an acetonitrile solution of C6H11POCl2 (0.201 g, 1 mmol in 15 ml of acetonitrile) was added dropwise under vigorous
0277-5387/00/$ - see front matter q2000 Elsevier Science Ltd All rights reserved. PII S 0 2 7 7 - 5 3 8 7 ( 9 9 ) 0 0 3 2 6 - 5
Tuesday Feb 01 09:29 AM
StyleTag -- Journal: POLY (Polyhedron)
Article: 3283
126
Z.-G. Sun et al. / Polyhedron 19 (2000) 125–128
stirring. The flask was sealed with a septum stopper, and the mixture was stirred for 48 h at room temperature. After separation of a white solid (NaCl, NaBr and traces of Na7PW11O39), the resulting solution was concentrated on a rotary evaporator, and was then diluted with 100 ml of absolute ethanol to produce a white precipitate. The white precipitate was isolated by filtration, and the solid isolated was reprecipitated again from 5 ml of acetonitrile solution by adding 100 ml of ethanol to give 1.1 g (49.12%) of a white powder. Found: C, 19.31; H, 3.58; N, 1.19; P, 2.82; W, 55.82. Calc. for C60H130N3O41P3W11: C, 19.65; H, 3.50; N, 1.15; P, 2.54; W, 55.23%. 2.2.2. [NBu4]4[C6H11P(O)]2SiW11O39 (2) This compound was similarly synthesized from aK6Na2SiW11O39P13H2O (2.54 g, 0.8 mmol), NBu4Br (1.29 g, 4 mmol) and C6H11POCl2 (0.32 g, 1.6 mmol). Yield: 1.4 g (44.87%). Found: C, 23.48; H, 4.30; N, 1.47; Si, 0.74; P, 1.62; W, 51.62. Calc. for C76H166N4O41P2SiW11: C, 23.36; H, 4.25; N, 1.43; Si, 0.72; P, 1.59; W, 51.84%. 2.2.3. [NBu4]4H[C6H11P(O)]2BW11O39 (3) This compound was similarly synthesized from aK7NaHBW11O39P13H2O (2.54 g, 0.8 mmol), NBu4Br (1.29 g, 4 mmol) and C6H11POCl2 (0.32 g, 1.6 mmol). Yield: 1.35 g (43.41%). Found: C, 26.72; H, 4.33; N, 1.48; B, 0.26; P, 1.61; W, 52.14. Calc. for C76H167N4O41P2BW11: C, 26.54; H, 4.29; N, 1.44; B, 0.28; P, 1.59; W, 52.06%.
Ga3q), using NBu4Br acting as a phase-transfer reagent. The overall reaction is: MeCN
X nqW11 O(12yn)y qC 6 H11 P(O)Cl 2 ™ 39 NBu 4 Br
[C 6 H11 P(O)]2 X nqW11 O(8yn)y 39 After filtration of a white solid consisting of NaCl, NaBr or KCl, KBr and a small amount of unchanged sodium or potassium polyoxotungstate, the acetonitrile solution contains a single hybrid anionic species, which has been isolated as its tetrabutylammonium salt. Elemental analysis results are consistent with the formulation of the title compounds. In contrast, the reaction between the sodium salt of a[PW11O39]7y with C6H11P(O)Cl2 in water did not show any evidence for the attachment of the organic group. This indicates that the anhydrous condition is needed for the reaction of C6H11P(O)Cl2 with the lacunary polyoxotungstate. In addition, direct reaction of the lacunary precursor with C2H5OP(O)Cl2 in acetonitrile does not give any isolable product, showing that a highly electrophilic organophosphonoyl moiety is needed for the above reaction. 3.2. Infrared spectra
3. Results and discussion
The infrared spectra of all the compounds are very similar; all data and IR assignments are given in Table 1. The P–O stretching vibration bands of the organic group and central PO4 moiety are observed between 1000 and 1060 cmy1 and the highest wavenumber (1120–1150 cmy1) is assigned to the stretching vibration of the P–C bond of the C6H11P(O) unit. The low wavenumber region (n-1000 cmy1) is characteristic of the W–O stretching and bending vibration in the polyoxotungstate. It is of interest to compare the n3 stretching modes of the PO4 unit (F2) [11] for compound 1 with the IR spectra of the other structurally related anions. It is well known that a decrease in symmetry from Td (XW12) to Cs (XW11) leads to splitting of the n3 vibration (F2) of the PO4 group into two components. The value of the splitting, Dn, is decreased when the triply bridging oxygen of the PO4 unit interacts with a transition metal ion [11,12]. It can be seen from Table 1 that the value of Dn is decreased when two organophosphoryl groups are bound in the cavity, and the stretching vibrational bands, nas (WsOter) and nas (W–Ob–W), are shifted to a higher frequency than those of the starting lacunary polyanions. This effect is attributed to a partial saturation of the polyoxometallic moiety through attachment of RPO units.
3.1. Synthesis
3.3. 31P NMR spectra
The monovalent polyoxotungstates a-XnqW11O39(12yn)y react with electrophilic cyclohexane phosphonyl chloride in acetonitrile to yield organic/inorganic species [C6H11P(O)]2 XnqW11O39(8yn)y (XnqsP5q, Si4q, B3q,
The attachment of phosphoryl groups onto the polyoxotungstate surface is demonstrated by the resonances in the 31 P NMR spectra, which are all distinct from that of C6H11P(O)Cl2 (Table 2).
2.2.4. [NBu4]4K[C6H11P(O)]2GaW11O39 (4) This compound was similarly synthesized from aK9GaW11O39P13H2O (2.64 g, 0.8 mmol), NBu4Br (1.29 g, 4 mmol) and C6H11POCl2 (0.32 g, 1.6 mmol). Yield: 1.28 g (40.15%). Found: C, 22.62; H, 4.24; N, 1.45; Ga, 1.72; K, 0.96; P, 1.59; W, 50.68. Calc. for C76H166N4KO41P2GaW11: C, 22.89; H, 4.17; N, 1.41; Ga, 1.76; K, 0.98; P, 1.56; W, 50.79%. 2.3. Chemical analyses Tungsten, phosphorus, silica, boron and gallium were determined by means of inductively coupled plasma–Auger electron spectroscopy (ICP–AES). K was determined by atomic absorption spectroscopy. C, H, N were determined using a PE-2400 elemental analyzer.
Tuesday Feb 01 09:29 AM
StyleTag -- Journal: POLY (Polyhedron)
Article: 3283
Z.-G. Sun et al. / Polyhedron 19 (2000) 125–128
127
Table 1 Comparison of infrared stretching frequencies (cmy1) Q3PW12 a
Q4H2NaPW11 a
1080 977
Assignment
1
2
3
4
1148 1042
1144 1039
1119 1026
1107 1051 958
1120 1043 1060 1027 976
n (P–C) nas (P–O) b nas (P–O) c
884 828 807 752 517
880 827 795 740 525
974 916 889 811 738
970 913 832 788 741
nas (W–Od) nas (X–Oa) d nas (W–Ob) nas (W–Oc)
534
532
954 566 881 790 763 701 566
896 830 808 513 a
Compound
d (W–O–W)
q
Qs(n-C4H9)4N . C6H11PO. c PO4. d XsSi, B, Ga. b
Table 2 P NMR data for [C6H11P(O)]2XnqW11O39(8yn)y
31
Compound
Chemical shift (d, ppm)
C6H11P(O)Cl2 [Bu4N]3[C6H11P(O)]2PW11O39 [Bu4N]4[C6H11P(O)]2SiW11O39 [Bu4N]4H[C6H11P(O)]2BW11O39 [Bu4N]4K[C6H11P(O)]2GaW11O39
58.5 34.2, y13.7 31.4 35.2 29.9
The 31P NMR spectrum of compound 1 exhibits two lines at 34.2 and y13.7 ppm with a relative intensity of 2:1 (see Fig. 1). The high-frequency resonance is attributed to the phosphoryl group, and the low-frequency singlet is assigned to the central PO4 unit of the polyoxotungstate. This chemical shift, which is intermediate between that of the starting lacunary anion a-[PW11O39]7y (dsy10.4 ppm) and that of a[PW12O40]3y (dsy14.9 ppm), is in accord with a partially saturated tungstophosphate structure. The relative intensity is consistent with the grafting of only two phosphoryl groups. A heteropolyanion with a Keggin structure becomes the Cs lacunary polyanion XnqM11O39(12yn)y after losing one
heavy atom and its terminal oxygen, which contains three W3O13 triads and one W2O10 diad. These anions have a hole surrounded by five oxygen atoms, one Oa, two Ob and two Oc (see Fig. 2). When two double-bonded phosphoryl groups each bridges two of the five oxygen atoms that define the hole in the lacunary polyanion, there are two possibilities, i.e. the groups can bridge the oxygens such that they are either unequivalent or equivalent. The single resonance in the 31P NMR spectra indicates that the mode of attachment of the organic groups to the lacunary anion is equivalent, i.e. each organic group is connected to two W atoms belonging to a triad and a diad, respectively (see Fig. 3).
Fig. 2. Idealized structures of a-XM12 (Keggin structure) (a) and a-XM11 (defective Keggin structure) (b). Oa, oxygen shared by three MO6 octahedra and the XO4 tetrahedron; Ob and Oc, oxygen linked to two different M atoms; Od, terminal unshared oxygen.
Fig. 1. The 31P NMR spectrum of compound 1 in CD3CN (0.075 M).
Tuesday Feb 01 09:29 AM
Fig. 3. Schematic representation of a-[C6H11P(O)2]XnqW11O39(8yn)y.
StyleTag -- Journal: POLY (Polyhedron)
Article: 3283
128
Z.-G. Sun et al. / Polyhedron 19 (2000) 125–128
Table 3 183 W NMR data for [C6H11P(O)]2XnqW11O39(8yn)y Compound
Chemical shift (yd, ppm)
[Bu4N]3[C6H11P(O)]2PW11O39 [Bu4N]4[C6H11P(O)]2SiW11O39 [Bu4N]4H[C6H11P(O)]2BW11O39 [Bu4N]4K[C6H11P(O)]2GaW11O39
80.9(2), 82.9(2), 96.6(1), 103.1(2), 113.5(2), 121.5(2) 82.5(2), 98.3(2), 111.2(1), 123.5(2), 140.1(2), 180.9(2) 91.9(2), 110.3(2), 115.7(1), 122.2(2), 190.3(3), 196.8(2) 62.5(2), 70.9(1), 93.1(2), 96.3(2), 126.3(2), 147.9(2)
Fig. 4. The 183W NMR spectrum of compound 3 in CD3CN (0.08 M).
be characterized in solid state by IR spectroscopy and in the CD3CN solution by 31P and 183W NMR. This hybrid anion consists of an a-[XW11O39] framework on which are grafted two equivalent C6H5P(O) groups through P–O–W bridges; each organic group is connected to two W atoms belonging to a triad and diad, respectively.
3.4. 183W NMR spectra The 183W NMR spectrum of compound 3 and chemical shifts of all compounds are shown in Fig. 4 and Table 3, respectively. The 183W NMR spectra of all species consist of six peaks, establishing that all species have Cs symmetry in solution. This feature was observed for other derivatives of Keggintype heteropolytungstates that bear organometallic ligands [13].
4. Conclusions The sodium or potassium of XnqW11O39(12yn)y (XsP, Si, B, Ga) and tetra-n-butylammonium bromide (NBu4Br) were suspended in acetonitrile, and an acetonitrile solution of C6H11POCl2 was added dropwise under vigorous stirring. After filtration, the resulting solution was concentrated and was then diluted with absolute ethanol to produce a white precipitate; the solid isolated was reprecipitated again from acetonitrile solution by adding absolute ethanol. Despite all our efforts to grow suitable crystals of the C6H11(O) derivatives of XnqW11O39(12yn)y (XsP, Si, B, Ga), no X-ray diffraction study was possible. Thus the compounds have to
Tuesday Feb 01 09:29 AM
Acknowledgements The support of the National Natural Science Foundation of China (No. 29571008) is gratefully acknowledged.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
M.T. Pope, A. Muller, Angew. Chem., Int. Ed. Engl. 30 (1991) 34. N. Mizuno, M. Misono, Chem. Rev. 98 (1998) 199. M. Weeks, C.L. Hill, R.F. Schinazi, J. Med. Chem. 35 (1992) 1216. Y. Chen, J. Liu, Q. Liu, Y. Xing, Y. Lin, H. Jia, Polyhedron 18 (1998) 481. P. Gouzerh, A. Proust, Chem. Rev. 98 (1998) 77. G.S. Kim, K.S. Hagen, C.L. Hill, Inorg. Chem. 31 (1992) 5316. C.R. Mayer, R. Thouvenot, J. Chem. Soc., Dalton Trans. (1998) 7. C. Brevard, R. Schimpf, G. Tourne, C.M. Tourne, J. Am. Chem. Soc. 105 (1983) 7059. N. Haraguchi, Y. Okaue, T. Isobe, Y. Matsuda, Inorg. Chem. 33 (1994) 1015. J.O. Clayton, W.L. Jensen, J. Am. Chem. Soc. 70 (1948) 3880. C. Rocchiccioli-Deltcheff, R. Thouvenot, J. Chem. Res. Synop. (1977) 46. ´ G.F. Tourne, ´ Inorg. Chem. 21 (1982) F. Zonnevijlle, C.M. Tourne, 2742. O.A. Gansow, R.K.C. Ho, W.G. Klemperer, J. Organomet. Chem. 187 (1980) C27.
StyleTag -- Journal: POLY (Polyhedron)
Article: 3283