DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 7–13 7 Organophosphoryl derivatives of trivacant tungstophosphates of general formula ·-A-[PW9O34(RPO)2]52: synthesis and structure determination by multinuclear magnetic resonance spectroscopy (31P, 183W)‡ Cédric R. Mayer and René Thouvenot *,† Laboratoire de chimie des métaux de transition, URA CNRS 419, case 42, Université Pierre et Marie Curie, 4 place Jussieu, F75252 Paris cedex 05, France In the presence of NBun 4Br acting as phase-transfer reagent, organophosphonic acids RPO(OH)2 reacted in acetonitrile with the trivacant tungstophosphate sodium salt b-A-Na8[HPW9O34]?24H2O to give hybrid organophosphoryl polyoxotungstate derivatives a-A-[NBun 4]3Na2[PW9O34(RPO)2] (R = Et 1, Bun 2, But 3, allyl 4 or Ph 5) in satisfactory yield (>65%).The structure of the hybrid anions has been inferred from spectroscopic data, especially from multinuclear (31P, 183W) NMR studies. In particular, the five-line (1:2:2:2:2) 183W spectrum indicates a lowering of the symmetry of the tungstophosphate framework from C3v to Cs.According to spectroscopic observations and chemical analyses, the hybrid anion consists of an a-A-[PW9O34] framework on which are grafted two RPO groups through P]O]W bridges. This structure displays two nucleophilic oxygen atoms at the polyoxotungstate surface and thus remains unsaturated. Derivatized polyoxometalates (POMs) have received increasing attention for the last twenty years owing to their potential in bifunctional catalysis.2 It has been recognized for a long time that the versatility of the polyoxometalates and their catalytic applications can be significantly increased by grafting organic and organometallic groups onto the polyoxometalate surface.Our group is currently engaged in the systematic investigation of the reactivity of organohalogenosilanes SiRX3 towards plurivacant polyoxotungstates.1,3 For example the trivacant Keggin tungstate anions [XW9O34]n2 (X = SiIV or GeIV, n = 10; X = PV or AsV, n = 9) yield organosilyl derivatives such as [XW9O34(ButSiOH)3](n 2 6)2 and [XW9O34(RSiO)3- (RSi)](n 2 6)2.Similarly, [AsW9O33(ButSiOH)3]32 is obtained from the trivacant species B-[HAsIIIW9O33]82. All these hybrid anions are built up on the polyoxometalate surface which becomes saturated by formation of six Si]O]W bridges connecting three organosilyl groups RSi (Fig. 1). By an appropriate choice of the organic part, e.g.with the help of polymerizable groups or by setting up coupling reactions, one can conceive the easy synthesis of polyoxometalate-based interconnected networks which could give rise to polymeric hybrid organic– inorganic materials. The reactivity of polyvacant polytungstates with organochlorostannanes was systematically investigated by Pope and co-workers:4 because of the preference of tin for six-coordination, the structures of organotin derivatives are different from those of organosilyl hybrids, for example in [{b- A-(PW9O34)}2(PhSnOH)3]1224a and [{a-A-(SiW9O34)}2- (BuSnOH)3]1424b three organostannyl groups are embedded in between two 9-tungsto anions.To the best of our knowledge, the reaction of polyvacant polytungstates with organophosphonic acids has not yet been investigated. Except for a unique study of Kim and Hill5 on PhPO derivatives of monovacant tungsto-phosphate and -silicate, the other reported RPO derivatives of POMs were obtained by self-assembly processes and present some new structural arrangements.6 The present paper reports the synthesis and spectroscopic study of RPO derivatives of the trivacant tungstophosphate [PW9O34]92.The structural charac- † E-Mail: rth@ccr.jussieu.fr ‡ Organic–inorganic hybrids based on polyoxometalates. Part 3.1 terization of these new species is achieved through a detailed multinuclear NMR investigation (31P, 183W) in solution. Results A suspension of powdered b-A-Na8H[PW9O34]?24H2O7 in an acetonitrile solution of organophosphonic acid RPO(OH)2 (R = Et, Bun, But, allyl or Ph) and tetra-n-butylammonium bromide NBun 4Br was acidified with hydrochloric acid.After filtration and subsequent evaporation to dryness a white solid was obtained which was recrystallized from dimethylformamide (dmf). The compounds were characterized in the solid state by infrared spectroscopy and in solution by multinuclear magnetic resonance.Elemental analyses are consistent with the formula [NBun 4]3Na2[PW9O34(RPO)2]?xdmf (R = Et 1, Bun 2, But 3, allyl 4 or Ph 5; x = 0, 0.5 or 1). Infrared characterization The infrared spectra of all the compounds are very similar. A representative spectrum of 5 is shown in Fig. 2 and all data are given in Table 1. The low-wavenumber part (n& < 1000 cm21) is characteristic of the polyoxometalate framework.8 The stretching vibrational bands [nasym(W]Ob]W) and nasym(W]] Oter)] are shifted to higher frequency, compared to those of the starting trivacant [PW9O34]92 anion (Table 1).This effect, previously observed for organosilyl derivatives of trivacant polyoxotungstates,1,3 is attributed to a partial saturation of the polyoxometallic moiety through the fixation of RPO units. Moreover, the pattern of the 400–300 cm21 region is Fig. 1 Polyhedral representations of [PW9O34]92 and [PW9O34- (ButSiOH)3]328 J. Chem. Soc., Dalton Trans., 1998, Pages 7–13 Table 1 Infrared data (cm21) for [NBun 4]3Na2[PW9O34(RPO)2] and b-A-Na8H[PW9O34]?24H2O R Assignmenta n(P]C) nasym(P]O)b nasym(P]O)c nasym(W]] Oter) nasym(W]Ob]W) dasym(O]P]O) dasym(W]Ob]W) Et 1153w 1091s 1026m 1005m 958vs 877vs 859vs 750vs 600vw 523m 377m 367m 330w Bun 1153w 1091s 1023m 1002m 959vs 877vs 858vs 751vs 596vw 527m 378m 369m 326w But 1175w 1090s 1034m 1012m 955vs 878vs 858vs 747vs 601vw 527m 379m 367m 333w Allyl 1155w 1090s 1024m 1002m 959vs 877vs 857vs 601vw 522w 376m 367m 333w Ph 1134w 1089s 1029w 1004w 957vs 877vs 850vs 750vs 601w 527w 377m 369m 334w b-PW9 1056s 1014w 931vs 821vs 737vs 511w 363w 330m a Ref. 8. b PO4. c RPO. characteristic of the a isomer of the PW9O34 unit.9 The stretching vibration bands of the PO4 and RPO3 groups are observed between 1000 and 1100 cm21. As for the W]O modes, the high-frequency shift of the nasym(PO4) modes is indicative of the partial saturation of the polyoxometalate. 31P NMR characterization Each 31P NMR spectrum presents two lines with a relative intensity of 2 : 1 (Fig. 3). Integration was carried out on protoncoupled spectra, with interpulse delays allowing full relaxation of the nuclei. The high-frequency resonance, with the expected multiplicity according to R (see Fig. 3), is attributed to the RPO group. This line displays satellites due to heteronuclear coupling [2J(WP) ª 8 Hz, Table 2], which are most visible under protondecoupling conditions. Integration of these satellites with respect to the central line 10 shows that the P atom is connected to two tungsten atoms of the polyoxotungstate framework.The low-frequency singlet (d 211.46 ± 0.2 for all R) of relative intensity 1 is assigned to the central PO4 unit of the polyoxotungstate. 7 This chemical shift, which is intermediate between Fig. 2 Part of the IR spectrum (n& < 1750 cm21) of [NBun 4]3Na2- [PW9O34(PhPO)2] Table 2 The 31P NMR data a for [PW9O34(RPO)2]52 anions R Relative PW9O34 RPO Et 211.36 34.23 (7.9) Bun 211.26 33.37 (7.9) But 211.23 36 (7.6) Allyl 211.51 27.33 (7.9) Ph 211.66 17.82 (8.5) intensity b 1 2 a Chemical shifts in ppm relative to 85% H3PO4, 2J(WP) in Hz in parentheses.b Measured on fully relaxed undecoupled spectra. that of the starting anion [PW9O34]92 (d 25, in the solid state) 11 and that of [PW9O34(ButSiOH)3]32 (d 215.9),1 is in accordance with a partially saturated tungstophosphate structure. 183W NMR characterization The 183W NMR spectra of all species exhibit the same 1:2:2:2:2 pattern, consistent with Cs symmetry of the PW9O34 framework (Fig. 4). All the signals present several satellites due to homonuclear tungsten–tungsten couplings. However, because of overlapping of these satellites, the determination of the 2J(WW) coupling constants required broad-band 31P decoupling in order to suppress the multiplicity (see below). The three high-frequency lines appear as doublets due to the small coupling [2J(WP) < 2 Hz] with the central phosphorus atom of the PW9O34 unit (Table 3).The two remaining (lowfrequency) signals appear as doublets of doublets (Fig. 5); the smaller coupling [2J(WP) ª 1.5 Hz] is similar to the previous one and the stronger coupling (6–9 Hz) corresponds to the m-oxo junction W]O]P with the phosphorus atom of the RPO groups. For all species, the most shielded signal presents a significantly larger coupling (8–9 Hz) than the other one (6–8.5 Hz) (Table 3).These values are consistent with those observed by 31P NMR spectroscopy (see above). Assignment of heteronuclear couplings was confirmed by selective 31P decoupling experiments: by irradiating at the resonance frequency of the phosphonate group both low-frequency signals become doublets [keeping the small coupling 2J(WP) ª 1.5 Hz] while the other signals are unchanged. Discussion Syntheses The trivacant polyoxotungstate b-A-[PW9O34]92 reacts readily Fig. 3 Proton-coupled 31P NMR spectrum of a mother solution of [NBun 4]3Na2[PW9O34(EtPO)2] (pulse angle 258, acquisition time 0.8 s, relaxation delay 5 s) with expansion of the high-frequency line showing the tungsten satellitesJ.Chem. Soc., Dalton Trans., 1998, Pages 7–13 9 Table 3 The 183W NMR data a for [PW9O34(RPO)2]52 anions R Assignmentb W(1) W(6),W(7) W(2),W(3) W(4),W(9) W(5),W(8) Et 242.8 294.6 2140.0 2189.0 (6.1) 2193.8 (7.9) Bun 241.5 294.1 2138.5 2190.8 (6.6) 2193.3 (8.0) But 244.2 296.8 2141.6 2180.0 (6.4) 2190.4 (7.9) Allyl 239.9 293.9 2137.6 2191.3 (7.1) 2192.3 (7.9) Ph 240.4 292.5 2138.6 2191.1 (8.5) 2192.9 (9.0) Relative intensity 1 2 2 2 2 a Chemical shifts in ppm, 2J(WP) in Hz in parentheses (only coupling with RPO).b Numbering of the atoms, corresponding to structure I of Scheme 1. with electrophilic organophosphonic acids to yield hybrid organic–inorganic species [PW9O34(RPO)2]52. As for organochlorosilanes, 1,3 the reaction with organophosphonates proceeds under phase-transfer conditions with NBun 4 1 acting as phase-transfer agent, equation (1).After filtration of a white b-A-[PW9O34]92 1 2RPO(OH)2 1 4H1 MeCN NBun 4Br [PW9O34(RPO)2]52 1 4H2O (1) 1–5 solid consisting of NaCl, NaBr and a small amount of unchanged sodium polyoxotungstate, the acetonitrile solution contains a single hybrid anionic species, as shown by 31P NMR spectroscopy (see above), which has been isolated in high yield (ca. 70%) as its tetrabutylammonium salt.It can be recrystallized from a saturated dimethylformamide solution giving small well shaped plaquettes. Unfortunately all crystals (whatever R) appeared to be twinned and all our attempts to obtain suitable crystals for X-ray analyses (from other solvents and with other cations) were unsuccessful. The molecular structure of the hybrid anion is therefore derived from the spectroscopic results. Infrared spectroscopy The IR spectra of compounds 1–5 are nearly superimposable in the low-wavenumber (n& < 1000 cm21) region which is characteristic of the W]O stretching and bending vibrations.8 By comparison with b-A-Na8H[PW9O34]?24H2O, the vibrational bands of [NBun 4]3Na2[PW9O34(RPO)2] appear relatively narrow, as is Fig. 4 A 12.5 MHz 183W-{31P} NMR spectrum of [NBun 4]3Na2- [PW9O34(ButPO)2] in dmf–(CD3)2CO (0.3 M, pulse angle 908; acquisition time 1.64 s; number of scans 24 000; total acquisition time 11 h). The abscissa expansion of the d 244.2 and 296.8 lines shows the tungsten satellites (digital resolution 0.15 Hz per point after 24 K points zero filling).The asterisk indicates [PW12O40]32 impurity usually observed for tetrabutylammonium salts of polyoxometalates (Fig. 2).12 Moreover the bands are shifted to higher wavenumbers which is indicative of saturation of the polyoxotungstate framework. In addition, it appears that the fixation of the phosphonate groups induces a b æÆ a isomerization of the PW9O34 structure; this effect, deduced from the characteristic pattern in the 400–300 cm21 region,9 was also observed for organosilyl derivatives.1,3 31P NMR spectroscopy The attachment of phosphonate groups onto the polyoxotungstate surface is demonstrated by the presence of tungsten Fig. 5 Expansion of the d 2189 line of the 12.5 MHz 183W NMR spectrum of [NBun 4]3Na2[PW9O34(EtPO)2] in dmf–(CD3)2CO: (a) undecoupled, (b) selectively 31P decoupled (irradiation at the PW9O34 resonance) and (c) selectively 31P decoupled (irradiation at the EtPO resonance)10 J.Chem. Soc., Dalton Trans., 1998, Pages 7–13 Scheme 1 Representation of the four possible structures for the [PW9O34(RPO)2]52 anion, based on a-A-PW9O34 (I,II) and b-A-PW9O34 (III, IV) units. For the polyoxotungstate framework in the plane representation, heavy and thin lines represent edge and corner junctions between adjacent octahedra respectively. The dashed lines correspond to peculiar corner junctions with expected low 2J(WW) coupling constants (trans influence) satellites [2J(WP) ª 8 Hz] around the high-frequency [d 118 (5)–36 (3)] organophosphonate resonance.The relative intensity of these satellites with respect to the central line indicates that each RPO group is linked to two W atoms through two W]O]P bridges (Itheor = 24.6, Iexp ª 25%).10 Moreover the 31P NMR spectra of compounds 1–5 are consistent with the grafting of only two phosphonate groups. Indeed, for all R, the integration of the phosphonate resonance with respect to the phosphate resonance indicates a ratio of two RPO groups per polyoxometalate, which is consistent with the chemical analysis.This result is rather surprising, as in the case of the organosilyl derivatives of PW9O34 three RSi groups are simultaneously linked to the tungstophosphate framework. Partial ‘saturation’ of the polyoxotungstate surface in RPO derivatives is also revealed by the chemical shift of the PO4 unit (d 211.5) which is less shielded than in the ‘saturated’ organosilyl species [PW9O34(ButSiOH)3]32 (d 215.9).1 183W NMR spectroscopy The 183W NMR spectra of compounds 1–5 are also consistent with the loss of the ternary symmetry of the PW9O34 framework.Actually, five lines (1:2:2:2:2) are observed for all organophosphonate derivatives which is in agreement with Cs symmetry for the PW9O34 unit. Four different Cs structures can be considered (Scheme 1); two are based on a b-A-PW9O34 moiety (III, IV) and two on a a-A-PW9O34 moiety (I, II) with each RPO fragment linked either to a ditungsten group (I, III) or to two W atoms belonging to adjacent diads (II, IV).All resonances have been assigned for the But derivative 3, with the following guideline: homonuclear tungsten–tungsten couplings 2J(WW) are less than 10 Hz for nuclei belonging to the same di- or tri-metallic group, and of the order of 20 Hz in Scheme 2 The trans influence and its consequences on homonuclear 2J(WW) coupling constants (Oter = terminal oxygen, Ob = m-bridging oxygen) Oter Ob Oter Ob 150° 190pm 190pm Oter W O Ob Oter W Oter 150° 210pm 190pm Saturated anion 2 J(W-W) » 20Hz Lacunary anion 2 J(W-W) <10Hz the other cases,13 except for W]O]W bridges trans to a W]] Oter group [2J(WW) < 10 Hz]. The trans influence in polyoxotungstates.The first unambiguous assignment of 183W NMR spectra of polyoxotungstates relied on the differences in homonuclear tungsten–tungsten coupling constants: indeed Brévard and co-workers 13a observed rather small 2J(WW) coupling constants (10 Hz or less) for edge junctions, with W]O]W angle of about 1208, with respect to corner junctions, with W]O]W about 145–1508 [2J(WW) ª 20 Hz].It was shown later that more open m-oxo bridges such as those in Dawson-type polyoxotungstates (W]O]W about 1608) display even larger coupling constants (ª30 Hz).14 This correlation between 2J(WW) and the W]O]W angle holds only for saturated polyoxotungstates, with nearly symmetrical W]O]W bridges (both W]O bonds ª190 pm).In lacunary derivatives the W]O]W bridge trans to a W]] Oter group is dissymmetrical, displaying a long W]O bond, in the range of 210–220 ppm (trans influence). Consequently, the coupling constant through the corresponding bridge is significantly reduced (Scheme 2).10,15 For example a corner-junction coupling as small as 4.9 Hz has been observed in the 183W NMR spectrum of the divacant lacunary anion g-[SiW10O36]82.15 The normal coupling constant is recovered by filling the lacuna.15b,16 Assignments. The less-shielded resonance, with relative intensity one (d 241.3 ± 1.3), is unambiguously assigned to the tungsten atom W(1) lying in the plane of symmetry.Under 31P decoupling (Fig. 4), two pairs of satellites, with two different homonuclear coupling constant values [2J(WW) ª 7.3 and 24.4 Hz], are observed around this line.When considering the four different proposed structures (Scheme 1), in two of them (II, III) the W(1) atom is connected to W(4) [º W(9)] which carries two terminal oxygen atoms. According to the trans influence, the corresponding coupling constant would be relatively low and W(1) should contract two small couplings. Thus, the exceptionally large value (24.4 Hz) is inconsistent with structures II and III. Only the two remaining structures I and IV may account for the large 2J(WW) constant, owing to the presence of a heteronuclear P]O]W bridge between the phosphonate group and the W(4) atom.Consistently the small coupling constant (7.3 Hz) corresponds to the W(1)]O]W(2) [º W(1)]O]W(3)] bridge (a ª 1208) in the trimetallic group.13aJ. Chem. Soc., Dalton Trans., 1998, Pages 7–13 11 Table 4 The 183W chemical shifts/coupling constants connectivity matrix for [PW9O34(ButPO)2]52 * W(1) W(6),W(7) W(2),W(3) W(4),W(9) W(5),W(8) W(1) 244.2 7.3 24.4 W(6),W(7) 296.8 11.3 27.6 W(2),W(3) 7.5 11.3 2141.6 24.4 W(4),W(9) 24.4 2180.0 6.7 W(5),W(8) 27 24.1 6.3 2190.4 *Diagonal terms: chemical shifts, d.Off-diagonal terms: 2J(WW) in Hz. Numbering of the atoms as in structure I of Scheme 1. Unfortunately the other 183W resonance lines appear relatively broad even under 31P decoupling (Dn2� 1 ª 3–5 Hz). This prevents an accurate determination of the small tungsten– tungsten couplings, as the corresponding satellites appear generally as shoulders at the foot of the central resonance.The large couplings are more easily observed: indeed, all four remaining lines present satellites with 2J(WW) > 20 Hz. However, a coupling constant of nearly the same value (24–25 Hz) is observed for three resonances. Thus, the assignment of W(4) [º W(9)] is not possible on the basis of 2J(W1W4) [º 2J- (W1W9)] = 24.4 Hz. To proceed further with the assignment, we should consider the two most shielded resonances; they appear as doublets of doublets due to heteronuclear 2J(WP) couplings with the phosphorus atom of the PW9O34 moiety (J ª 2 Hz) and that of one RPO group (J ª 6–9 Hz, depending on R).These lines should be assigned to the two pairs W(4) [º W(9)] and W(5) [º W(8)] of the structures I and IV. Under broad-band 31P decoupling, the outermost line presents two pairs of tungsten satellites with large couplings [2J(WW) ª 24 (1W) and 27 Hz (1W)], whereas the second line exhibits only one pair of such satellites [2J(WW) ª 24 Hz (1W)] (Table 4, Fig. 4). Considering structure IV one would expect two strong couplings for both W(4) [º W(9)] and W(5) [º W(8)] pairs; therefore this structure can be ruled out and I remains as the only one consistent with the observed spectra. Consequently, the outermost line corresponds to W(5) and the second to W(4) with an observed homonuclear coupling constant [2J(W1W4) º 2J(W1W9) ª 25 Hz] consistent with the value (24.4 Hz) observed for the W(1) atom (see above).Among the two remaining lines, the one at about d 2140 clearly presents three pairs of satellites [2J(WW) ª 7.5, ª 11 and 24.5 Hz] while that around d 295 exhibits only two pairs (even with resolution enhancement) (Fig. 4). The latter therefore corresponds to W(6) [º W(7)], which is connected to W(5) through a strong coupling (ª27 Hz) and to W(2) [º W(3)] through a medium coupling (ª11 Hz). For two tungsten nuclei belonging to corner-sharing octahedra (W]O]W ª 1508), this relatively small coupling constant is consistent with the already mentioned trans influence (see above).Finally, assignment of the last line (d 2140) to W(2) is consistent with the observed coupling constants 2J(W1W2) [º 2J(W1W3)] = 7.3, 2J(W2W6) [º 2J(W3W7)] = 11.3 and 2J(W2W5) [º 2J(W3W8)] = 24.4 Hz respectively. Heteronuclear 2J(WP) couplings. The heteronuclear 2J(WP) coupling constants follow a pattern similar to that of the homonuclear 2J(WW): the coupling constant through the m-oxo bridge depends on the bridge angle and on both P]O and W]O distances. Mainly as a result of the long W]O bonds (ª230–240 pm) involving oxygen atoms of the central PO4 tetrahedron, the corresponding coupling constants are generally small (less than 2 Hz).One should notice that the two resonances of the tungsten atoms belonging to the trimetallic group W(1)–W(3) display a particularly small coupling constant with the central phosphorus nucleus (<1 Hz) whereas this constant is signifi- cantly larger (ª2 Hz) for the three other resonances. Such a decrease of 2J(WP) through mn]O bonds with increasing n is generally observed for phosphorus-centered Keggin and Dawson polyoxometalates.14,17 The phosphonate groups are connected to the polyoxotungstate framework through m-O oxygen atoms.Therefore the 2J(WP) coupling constants along these bridges are relatively large, of the order of 6–9 Hz. However they remain signifi- cantly smaller than those observed by Kim and Hill 5 for the phenylphosphonate derivatives of monovacant lacunary anions [PW11O39]72 and [SiW11O39]82 [2J(WP) ranging from 15 to 30 Hz].In the absence of any metrical parameter for our species, one can only speculate about the origin of these differences: although the anionic charge of the trivacant anion [PW9O34]92 is higher than that of the monovacant anion [PW11O39]72, the charge density is expected to be lower at each of the six oxygen atoms of the former species compared to the four oxygen atoms of the latter.Consequently the less nucleophilic O atoms of the trivacant anion should form weaker bonds with the phosphonate group. It should be noticed that a similar trend in heteronuclear coupling constants has been observed for organosilyl derivatives of lacunary polyoxotungstates: 2J(W]Si) is 6–7 Hz for the compounds derived from the trivacant anions a-A-[PW9O34]92 and a-A-[SiW9O34]102,1,3 whereas a coupling constant of 16.7 Hz has been reported for the vinylsilyl derivative of the monovacant tungstosilicate [SiW11O39]82.18 For [Xn1W11O39(PhPO)2](8 2 n)2 (Xn1 = P51 or Si41) two coupling constants 2J(WP) of 14–15 and 26–27 Hz were reported, corresponding to two different P]O]W bridges, with tungsten atoms belonging either to a diad or to a triad.5 Two different coupling constants 2J(WP) are also observed for [PW9O34- (RPO)2]52 (Table 3).However the differences are relatively small [2J(W4P) = 6–8.5, 2J(W5P) = 8–9 Hz] and arise only in the 183W NMR spectra.Indeed, according to the proposed structure, the bridge between the phosphonate group and the tungsten nuclei W(4) is not symmetrically related to that between the phosphonate group and the tungsten nuclei W(5). The different coupling constants 2J(WP) might reflect a slightly larger P]O]W angle or a shorter P]O bond in the (R)P]O]W(5) bridge than in the (R)P]O]W(4) bridge. Homonuclear 2J(WW) couplings.As a result of the low symmetry of the [PW9O34(RPO)2]52 anions, different tungsten– tungsten coupling constants are observed in the 183W NMR spectra. Compared to those of the organosilyl derivatives, the coupling constants involving the W atoms of the triad W(1)– W(3) and the tungsten atoms connected to the phosphonate are relatively large (25 compared to 22 Hz). The large coupling constants 2J(W5W6) [º 2J(W7W8)] should be considered together with the smalr one 2J(W2W6) [º 2J(W3W7)].Actually a redistribution of the homonuclear tungsten–tungsten coupling constants in the vicinity of a cis-WO2 unit has been observed in any case of a small corner coupling induced by trans influence. For example, in the monovacant polyoxotungstate [SiW11O39]82 and polyoxomolybdotungstate [SiMo2W9O39]82, the cis-WO2 units display two peculiar corner-coupling constants: a small one (ª10 Hz) which involves the oxygen atom trans to Oter and a large one (>25 Hz) (Scheme 3).15b,19 The same effect has also been observed in monovacant lacunary anions of the Dawson structure.2012 J.Chem. Soc., Dalton Trans., 1998, Pages 7–13 Scheme 3 Comparison of 2J(WW) corner-coupling constants for saturated and monovacant lacunary Keggin polyoxotungstates 15b,19 In the present case, as for monovacant species, the redistribution of the homonuclear coupling constants might be interpreted by a geometrical rearrangement in the vicinity of the cis-WO2 groups.As a consequence of the trans influence, the tungsten atom is markedly displaced from the centre of the WO6 octahedron. Molecular models show that this might result in a relatively large W]O]W angle (>1508) for the second corner junction. Conclusion Despite all our efforts to grow suitable crystals of the RPO derivatives of [PW9O34]92, no X-ray diffraction study was possible. Nevertheless the molecular structure of the hybrid anion can be confidently deduced from the spectroscopic data (Fig. 6). This anion consists of an a-A-PW9O34 unit on which are grafted two RPO groups through two P]O]W bridges. As for the analogous organosilyl derivatives, each RPO group is connected to two W atoms belonging to the same dimetallic unit (diad). However, contrary to organosilyl derivatives where the six nucleophilic oxygen atoms of the trivacant anion are saturated, the grafting of organophosphonates retains intact two oxygen atoms. Together with the two free oxygen atoms of the phosphonate groups, they define a new lacuna, for the binding of the two sodium cations revealed by chemical analysis.However the electrostatic interaction between Na1 and these oxygen atoms should be relatively weak so that the polyoxotungstate surface remains available to further electrophilic attack. Indeed the hybrid [PW9O34(RPO)2]52 anions react with trichloroorgano-silanes, -germanes and -stannanes to afford saturated derivatives. Work on this subject is in progress.Experimental General The compound b-A-Na8H[PW9O34]?24H2O was prepared according to the literature.7 Other reagents, [RPO(OH)2 and NBun 4Br] and solvents were from Aldrich and used as received. Elemental analyses were performed by the Service central de microanalyses du CNRS, Vernaison, France. The IR spectra (4000–250 cm21) were recorded on a Bio-Rad FTS 165 IR FT spectrometer with compounds sampled in KBr pellets, 13C (75.46) and 31P (121.5 MHz) NMR spectra at room temperature in 5 mm outside diameter tubes on a Bruker AC 300 spectrometer equipped with a QNP probehead.The chemical shifts are given according to the IUPAC convention, with respect to SiMe4 and 85% H3PO4 respectively. The 12.5 MHz 183W NMR spectra were recorded at 300 K on nearly saturated dmf–(CD3)2CO (90: 10, v/v) solutions in 10 mm outside diameter tubes on the same spectrometer equipped with a lowfrequency special VSP probehead. The chemical shifts are given with respect to 2 M Na2WO4 aqueous solution and were determined by the substitution method using a saturated D2O solution of tungstosilicic acid H4SiW12O40 as secondary standard Fig. 6 Polyhedral representation of the proposed structure for [PW9- O34(RPO)2]52 (R = Et)J. Chem. Soc., Dalton Trans., 1998, Pages 7–13 13 (d 2103.8). The 31P decoupling experiments were performed with a B-SV3 unit operating at 121.5 MHz and equipped with a B-BM1 broad-band modulator. Selective or broad-band decoupling was determined by appropriate choice of the synthesizer frequency and of the output power (4–40 W) before entering the decoupling coil of the low-frequency probehead.Preparations ·-A-[NBun 4]3Na2[PW9O34(EtPO)2] 1. The compounds b-ANa8H[ PW9O34]?24H2O (11.5 g, 4 mmol) and NBun 4Br (4.62 g, 14 mmol) were suspended in MeCN (50 cm3); EtPO(OH)2 (0.88 g, 8 mmol) was added under vigorous stirring, then HCl (1.36 cm3, 16 mmol) was added dropwise and the mixture stirred overnight at reflux.After separation of a white solid (NaCl, NaBr 1 traces of Na8H[PW9O34]), the white compound [NBun 4]3Na2[PW9O34(EtPO)2] was formed by evaporation of the resulting solution in a rotary evaporator. The crude compound was recrystallized from dmf. Yield: 8.5 g (67.5%) (Found: C, 20.22; H, 3.87; N, 1.30; Na, 1.34; P, 2.88, W, 51.10. Calc. for C52H118N3Na2O36P3W9: C, 19.80; H, 3.77; N, 1.33; Na, 1.46; P, 2.95; W, 52.44%). dC(75.46 MHz, solvent acetone, standard SiMe4) 22.73 [1C, d, J(PC) 147] and 7.25 [1C, d, J(PC) 6.49 Hz].·-A-[NBun 4]3Na2[PW9O34(BunPO)2]?dmf 2. This compound was similarly synthesized from b-A-Na8H[PW9O34]?24H2O (11.5 g, 4 mmol). NBun 4Br (4.62 g, 14 mmol), BunPO(OH)2 (1.1 g, 8 mmol) and HCl (1.36 cm3, 16 mmol). Yield: 8.9 g (67.4%) (Found: C, 21.12; H, 4.09; N, 1.74; Na, 1.36; P, 2.78; W, 49.75. Calc. for C59H133N4Na2O37P3W9: C, 21.58; H, 4.08; N, 1.71; Na, 1.40; P, 2.83; W, 50.38%). dC(75.46 MHz, solvent acetone, standard SiMe4) 27.90 [1C, d, J(PC) 146.5], 24.75 [1C, d, J(PC) 4], 23.0 [1C, d, J(PC) 7.1 Hz] and 12.65 (1C, s).·-A-[NBun 4]3Na2[PW9O34(ButPO)2]?0.5dmf 3. This compound was similarly synthesized from b-A-Na8H[PW9O34]? 24H2O (11.5 g, 4 mmol), NBun 4Br (4.62 g, 14 mmol), But- PO(OH)2 (1.1 g, 8 mmol) and HCl (1.36 cm3, 16 mmol). Yield: 9.0 g (68.1%) (Found: C, 21.14; H, 3.97; N, 1.43; Na, 1.41; P, 2.87; W, 51.16. Calc. for C57.5H129.5N3.5Na2O36.5P3W9: C, 21.27; H, 4.02; N, 1.51; Na, 1.42, P, 2.86; W, 50.95%).dC(75.46 MHz, solvent acetone, standard SiMe4) 33.04 [1C, d, J(PC) 148.3 Hz] and 26.29 (3C, s). ·-A-[NBun 4]3Na2[PW9O34(C3H5PO)2]?0.5dmf 4. This compound was similarly synthesized from b-A-Na8H[PW9O34]? 24H2O (11.5 g, 4 mmol), NBun 4Br (4.62 g, 14 mmol). C3H5PO(OH)2 (0.98 g, 8 mmol) and HCl (1.36 cm3, 16 mmol). Yield: 8.3 g (65.4%) (Found: C, 20.81; H, 3.81; N, 1.49; Na, 1.41; P, 2.82; W, 50.16. Calc. for C55.5H121.5N3.5Na2O36.5P3W9: C, 20.73; H, 3.81; N, 1.52; Na, 1.43; P, 2.89; W, 51.46%). dC(75.46 MHz, solvent acetone, standard SiMe4) 131.1 [1C, d, J(PC) 10.6], 115.8 [1C, d, J(PC) 15] and 34.42 [1C, d, J(PC) 146.0 Hz].·-A-[NBun 4]3Na2[PW9O34(PhPO)2] 5. This compound was similarly synthesized from b-A-Na8H[PW9O34]?24H2O (11.5 g, 4 mmol), NBun 4Br (4.62 g, 14 mmol), PhPO(OH)2 (1.26 g, 8 mmol) and HCl (1.36 cm3, 16 mmol). Yield: 9.2 g (71%) (Found: C, 21.79; H, 3.76; N, 1.27; Na, 1.39; P, 2.82; W, 49.96.Calc. for C60H118N3Na2O36P3W9: C, 22.17; H, 3.66; N, 1.29; Na, 1.41; P, 2.86; W, 50.89%). dC(75.46 MHz, solvent acetone, standard SiMe4) 136.5 [1C, d, J(PC) 147.5], 130.8 [2C, d, J(PC) 6], 129 (1C, s) and 127.72 [2C, d, J(PC) 9 Hz]. References 1 Part 2, A. Mazeaud, N. Ammari, F. Robert and R. Thouvenot, Angew. Chem., Int. Ed. Engl., 1996, 35, 1961; Angew Chem., 1996, 108, 2089. 2 See, for example, M. T. Pope and A. Müller, Angew. Chem., Int. Ed. Engl., 1991, 30, 34; Angew.Chem., 1991, 103, 56; Polyoxometalates: From Platonic Solids to Anti-Retroviral Activity, eds. M. T. Pope and A. Müller, Kluwer, Dordrecht, 1994. 3 N. Ammari, G. Hervé and R. Thouvenot, New. J. Chem., 1991, 15, 607; N. Ammari, Ph.D. Thesis, Université Pierre et Marie Curie, Paris, 1993. 4 (a) F. Xin and M. T. Pope, Organometallics, 1994, 13, 4881; (b) F. Xin, M. T. Pope, G. J. Long and U. Russo, Inorg. Chem., 1996, 35, 1207. 5 G. S. Kim and C. L. Hill, Inorg. Chem., 1992, 31, 5316. 6 P. R. Sethuraman, M. A. Leparulo, M. T. Pope, F. Zonnevijlle, C. Brévard and J. Lemerle, J. Am. Chem. Soc., 1981, 103, 7665; U. Kotz, B. Jameson and M. T. Pope, J. Am. Chem. Soc., 1994, 116, 2659. 7 R. Massart, R. Contant, J.-M. Fruchart, J.-P. Ciabrini and M. Fournier, Inorg. Chem., 1977, 16, 2916. 8 C. Rocchiccioli-Deltcheff, R. Thouvenot and R. Franck, Spectrochim. Acta, Part A, 1975, 32, 587. 9 R. Thouvenot, M. Fournier, R. Franck and C. Rocchiccioli- Deltcheff, Inorg. Chem., 1984, 23, 598. 10 R. Thouvenot, A. Tézé, R. Contant and G. Hervé, Inorg. Chem., 1988, 27, 524. 11 W. H. Knoth, P. J. Domaille and R. D. Farlee, Organometallics, 1985, 4, 62. 12 C. Rocchiccioli-Deltcheff, M. Fournier, R. Franck and R. Thouvenot, Inorg. Chem., 1983, 22, 207. 13 (a) J. Lefebvre, F. Chauveau, P. Doppelt and C. Brévard, J. Am. Chem. Soc., 1981, 103, 4589; (b) P. J. Domaille, J. Am. Chem. Soc., 1984, 106, 7677. 14 R. Contant and R. Thouvenot, Inorg. Chim. Acta, 1993, 212, 41. 15 (a) J. Canny, A. Tézé, R. Thouvenot and G. Hervé, Inorg. Chem., 1986, 25, 2114; (b) E. Cadot, R. Thouvenot, A. Tézé and G. Hervé, Inorg. Chem., 1992, 31, 4128. 16 A. Tézé, J. Canny, L. Gurban, R. Thouvenot and G. Hervé, Inorg. Chem., 1996, 35, 1001. 17 R. Acerete, C. F. Hammer and L. C. W. Baker, J. Am. Chem. Soc., 1979, 101, 267; R. Acerete, S. Harmalker, C. F. Hammer, M. T. Pope and L. C. W. Baker, J. Chem. Soc., Chem. Commun., 1979, 777; R. Acerete, C. F. Hammer and L. C. W. Baker, J. Am. Chem. Soc., 1982, 104, 5384; Inorg. Chem., 1984, 23, 1478; M. Abbessi, R. Contant, R. Thouvenot and G. Hervé, Inorg. Chem., 1991, 30, 1695. 18 P. Judeinstein, C. Deprun and L. Nadjo, J. Chem. Soc., Dalton Trans., 1991, 1991. 19 R. Contant, G. Hervé and R. Thouvenot, presented at the CNRSNSF polyoxometalate workshop, St-Lambert des Bois, 1983. 20 R. Thouvenot and R. Contant, unpublished work. Received 21st July 1997; Paper 7/05216B