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Protactinium(V) and uranium(V) tropolonates |
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Dalton Transactions,
Volume 1,
Issue 13,
1975,
Page 1249-1252
Kenneth W. Bagnall,
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摘要:
1975 1249 Protactinium(v) and Uranium(v) Tropolonates By Kenneth W. Bagnall and Akshya M. Bhandari Department of Chemistry Manchester University Man-Chester M13 9PL David Brown," Philip E. Lidster and Brian Whittaker Chemistry Division A.E.R.E. Harwell Penta(tropo1onato)-protactinium(v) and -uranium(v) [Pa(trop),] and [U(trop),] have been prepared by reac-tions involving tropolone and the appropriate pentaethoxide in anhydrous benzene. Reactions between uranium pentachloride and an excess of tropolone in non-aqueous-solvents have yielded chlorotetra(tropo1onato) uranium(v). [U (trop),CI]. Some physical and chemical properties of these complexes are reported and the UCI,-tropolone reaction is discussed. PROTACTINIUM (v) tropolonato-complexes of the type [Pa(trop),X] (X = C1 Br ClO, and OEt; Htrop = 2-hydroxycyclohepta-2,4,6-trien-l-one tropolone) and [Pa(trop),CI]*dmso (dmso = dimethyl sulphoxide) have been characterised previously but the only uranium(v) tropolonate reported to date is [UC14(trop)]*4Htrop.In view of the unusual composition of this uranium(v) complex and the paucity of data on uranium(v) tropolon-ates the U(OEt),- and UC1,-tropolone reactions have been investigated in an attempt to characterise [U(frop),] and new chlorouranium (v) tropolonates. During the course of these studies it became apparent that the previously reported [Pa(trop),(OEt)] had been in-correctly characterised and further work on the pro-tactinium (v)-tropolone system was undertaken to clarify the situation. RESULTS AND DISCUSSION Pentakis(tropolonato)-protactinium(v) and -uranizcnt(v) .-The reaction between tropolone (Htrop) and U(OEt), in anhydrous oxygen-free benzene (>5 1 mol ratio of reactants) at room temperature yielded an immediate black precipitate of pen takis (tropolonato)uranium(v) , [U(trop),] which is completely insoluble in this solvent. Attempts to convert [U(trop),] to [u(trop),] or [U(trop),Br] by bromine oxidation in chloroform contain-ing Htrop were unsuccessful. The complex [U(trop),] is stable in contact with refluxing benzene (5 h) provided the solvent is perfectly anhydrous and oxygen free. Traces of water result in decomposition to a reddish brown unidentified product and Htrop. In wet acetone the decomposition occurs much faster. Pentakis-(tropolonato)uranium(v) does not dissolve in or react with carbon disulphide ; the addition of chloroform, however results in formation of a brown solution the spectrum of which is identical with that of [U(trop),] in the same solvent.Similar decomposition appears to occur on addition of niethylene dichloride nitromethane, methyl cyanide and NN-dimethylformamide. The X-ray powder pattern of [U(trop)J was found to be identical with that previously recorded 1 for [Pa(trop),(OEt)] and since the analytical results for the former complex were reproducibly close to theoretical, it was necessary to reinvestigate the protactinium(v) complex which had been obtained during attempts to prepare [Pa(trop),] from relatively small-scale reactions 1 D. Brown and C. E. F. Rickard J .Chem. SOC. ( A ) 1970, 3373. involving [Pa(trop),Cl] and Li(trop) in ethanol. With larger-scale preparations using an improved micro-analytical technique for the determination of carbon in radioactive compounds together with a gravimetric method to determine protactinium rather than com-pound dissolution followed by CL spectrometry we have now shown that the complex previously believed to be [Pa(trop),(OEt)] is in fact [Pa(trop),]. It was obtained when Pa(OEt) was treated with Htrop in anhydrous benzene and when [Pa(trop),] and an alcoholic solution of Htrop were exposed to the atmosphere to induce oxidation of the protactinium(1v) complex. It now appears that the extra bands in the i.r. spectra of both [Pa(trop),] and [U(trop),] relative to the spectra of actinoid(1v) tropolonates (vix.1 100 1055 915 905, and 860 cm-l; see Table 1) are not as previously TABLE 1 1.r. spectral results (4 000-700 cm-l) [Wtrop) 51 1593s 1518s 1466m 1435s 1410s } 1 340s 1 249w 1232(sh) 1222m 1 lOOm 1055m 970w 924w 915w 905w 875m 860w 7 66 (sh) 75O(sh) 736m } 729m 706m Tentative assignment * C=O stretch C=C stretch C-C stretch C-H in-plane def. C-C-C def. comb. mode C-C-C ring def. overtone C-H out-of-plane def., C-C stretch [U (trap) 01 1 696s 1518s 1472m 1 432s 1 355s 1262w 1236(sh) 1 230m 1221(sh) 1 078vw 1 020vw 974m 9 2 6 ~ 878m 776(sh) 765(sh) 734m 7 10m * Based on previous i.r. and Raman results; s = strong sh = shoulder m = medium w = weak and vw = very weak.believed,l associated with an ethoxo-group but are probably due to the presence of one uniquely bonded Htrop molecule. This inference is substantiated to some extent by the chemical behaviour of [Pa(trop),]. Thus reactions previously attributed to [Pa (trop) ,( OE t )] Chem. 1970 32 3249. J. Selbin N. Ahmad and M. J. Pribble J . Inovg. Nuclear Y . Ikegami Bull. Chew SOC. Japale 1961 34 94 1250 J.C.S. Dalton include those with aqueous HCl- and aqueous HCl0,-acetone mixtures which yield [Pa(trop),Cl] and [Pa(trop),-(CIOJ] respectively. The i.r. spectra of these products do not contain the extra bands mentioned above. The complex [Pa(trop)J is appreciably more stable than its uranium analogue being unaffected by cold water and IM-HCl.It is insoluble in benzene carbon tetra-chloride diethyl ether and 2-methylbutane and has only a very limited solubility in methyl cyanide and nitromethane. ChZorouraniunz(v) Tro$oZonates.-Uranium penta-chloride reacted exothermically with Htrop in oxygen-free anhydrous benzene or carbon tetrachloride to yield insoluble dark brown to black products. Our first set of investigations were quite irreproducible yielding apparently different products under identical conditions; in addition many of these products had non-integral C1 U ratios. Furthermore with a large excess of Htrop over UCl (10 or 12 1 niol ratios) it appeared that fewer chlorine atoms were replaced than in reactions involving 4 or 6 1 mol ratios of reactants and in one instance (10 1 inol ratio) the product had a com-position close to [UC14(trop)]*4Htrop i.e.the same as the compound reported by Selbiii et nL2 Such observ-ations are at variance with results obtained1 for the PaC1,-Htrop reaction which with an excess of Htrop, resulted in formation of [Pa(trop),Cl] initially contamin-ated by unidentified impurities. The latter could be removed by washing the product with acetone ethanol, or water a procedure which could not be employed in the case of the uranium(v) products because of their ready decomposition. The apparent differences between the UCl,- and PaC1,-Htrop reactions and the irreproducibility in the former system have been traced to the formation of tropolone hydrochloride from the reaction between the liberated hydrogen chloride and some of the added Htrop.Reactions between Htrop and HC1 gas in benzene or carbon tetrachloride gave an immediate precipitate of white tropolone hydrochloride which is almost totally insoluble in these solvents. Thus the irreproducible analytical results obtained in our initial experiments were due in part to this insolubility and to the time for which the products had been vacuum dried, since the hydrochloride has a sufficiently high vapour pressure for it to be removed at ca. 17 n ~ g h-l on con-tinuous pumping at Torr partly as unchanged hydrochloride and as Htrop and HC1 gas.* Following these observations it was shown that the reaction between Htrop and UCl (10 1 mol ratio) in oxygen-free anhydrous benzene or carbon tetrachloride followed by vacuum drying of the product to constant weight (ca.50 h) yields pure [U(trop),Cl] which is iso-structural with the protactinium(v) analogue. It was also shown in control reactions that the ' molecular-weight ' changes (based on uranium assays) and the D. Brown B. Whittaker and J . Tacon J.C.S. Daltoiz 1975, It is decomposed by hot 8~-HNO,. 1 Torr = (101 325/760) Pa 1 nimHg z 13-6 x 9.8 Pa. 34. changes in C1 U ratios during this vacuum treatment were consistent with the removal of between 2-3 and 2.6 molecules of tropolone hydrochloride from the initial product i.e. [U (trop),C1]*2.3-2-6( Htrop-HC1) . The amount of tropolone hydrochloride formed in a given reaction will obviously vary with factors such as volume of solvent rate of addition temperature stirring, etc.and the observation that one of our earlier products not vacuum ' dried' to constant weight had a com-position close to [U(trop)C1,]*4( Htrop) was probably fortuitous. However using UCI in place of [UC15j*tcac (tcac = trichloroacryl chloride) we repeated the experi-ment of Selbin et aL2 (5 1 ratio Htrop UCI in benzene) and obtained initial products (vacuum dried for only 2 11) of ' composition ' ;U(trop)C14]*4(Htrop) (e.g. Found U 23.7; C1 13.7. Calc. U 24.05; C1, 14.35%). These products however lost weight on prolonged vacuum ' drying ' ; the composition of the final material at constant weight was variable suggesting that the initial products were mixtures of chloro-uranium(v) tropolonates and tropolone hydrochloride rather than [U(trop)CI4]*4(Htrop).This was confirmed by X-ray powder-diff raction analysis of the initial products the films containing lines due to tropolone hydrochloride which were not present after drying to constant weight. Physical Pro$erties.-The complexes [U(trop),] and [U(trop),Cl] are isostructural with [Pa(trop),] and [Pa(tr~p)~Cl] respectively for which X-ray powder-diffraction data were published previously.1 The i.r. spectra of [Pa(trop),] and [U(trop),] were virtually identical; details for the former (4000-700 cm-l) are given in Table 1 together with tentative assignments. Comparison with the i.r. results for [U(trop),] (Table 1) identifies those bands previously believed to be due to the presence of an ethoxide group in the supposed [Pa(trop),(OEt)J.The C=O (1 588-1 593 cm-l) and C=C (1 518-1 523 cm-l) vibrations for the actinoid(v) tropolonates occur close to those recorded previously for tctra- and penta-(tropolonates) of the types [M(tr~p)~] and Li[M(trop),j respectively (M = actinoid element) the positions being appreciably different from those observed for Htrop itself (1 613 and 1548 re-spectively) but at only slightly lower frequencies than observed for Li(trop) and Na(trop). The i.r. spectra of the penta(tropo1onato) complexes and the tetra(tropo1onato) chlorides were quite different from that of Htrop in the region 525-100 cm-1 as illustrated in the Figure where the spectra of [U(trop),] and Htrop are compared. The features at ca. 200 cm-1 are very similar to those observed* in the spectra of actinoid(1v) tetra(pentane-2,4-dionates) and are tenta-tively assigned to M-0 vibrations.In the absence of a full co-ordinate analysis it is not possible to decide whether there is any hi-0 vibration contribution to the apparently new band at 500 cm-l in the spectra of the metal(v) tropolonates. -4 similar band appears in the spectra of actinoid(1v) tetra- and penta-(tropolonato) complexes (490-498 cm-l) and in the spectrum o 1975 1251 [Nd(trop),] (481 cm-l) but not in that of Na(trop).l The positions of bands in the spectra of [ U ( t r ~ p ) ~ ] and [U(trop),Cl] are shown in Table 2 together with the results for [U(trop),] and Htrop. Due to ready decomposition of [U(trop),] in most common organic solvents we were unable to obtain visible-near-i.r.solution spectra. The solid-state trans-mission and reflectance spectra of [U(trop),Cl] and [U(trop)J both contained only three bands in the region 4 760-13000 cm-l with no features attributable to i )\\ 1 . r \ 1 I 1 I 500 400 300 200 100 Wavenumber 1cm-I 1.r. spectrum of (a) tropolone and (b) [U(trop),] TABLE 2 r u (trap) 51 ru (trap) *ClI r u (trap) PI H t rop 498s 502s 500s 434s 406w,b 405w,b 404m 375w 367w,b 390 (sh) 345m 228w 200s 212s 212s 182(sh) 190(sh) ,b 1 8 5 (sh) b c 166w 135w 145w,b 135w a b = Broad. 1.r. spectral results a in the region 525-50 cm-1 1 1 2w b -4 medium broad feature was also observed at 300 cm-l. Tcntatively assigned to M-0 vibrations. TABLE 3 Electronic spectra (C/cm-l) [U W P ) 51 [U(troP),C11 6 451s,b 6 518s,(sh) 6 622s,(sh) 7 812m,b 7 418m,b 9 389m,b 8 474m,b sh = Sharp.uranium(1v) species. The strongest band in each instance occurred at ca. 6 500 cm-1 (Table 3) a position close to those reported for bands characteristic of a 5 J. Selbin and J. D. Ortego Ckem. Rev. 1969 69 657. 6 R. G. Jones E. Bindschadler G. Karmas F. A. Yoeman, a n d H. Gilman J . Amev. Cheni. SOC. 1956 78 4287. wide range of uraniuni(v) complexes of varying stereo-chemistries and assigned in the case of octahedral species to the r,-I',' transition. No bands could be observed above ca. 11 000 cm-l for the uranium(v) tropolonates due to very strong absorption which started at approximately this wavelength and it is not possible to make any deduction regarding the stereo-chemistry of the complex from our spectral results.EXPERIMENTAL All preparative n.ork was done in inert-atmosphere glove-boxes (oxygen and water content each < 20 p.p.m.) because of the radioactive hazards associated with weighable amounts of protactinium-231 and the sensitivity of the uranium(v) complexes to moisture and oxygen. Samples were dispensed for analysis and for the various chemical and physical studies in such boxes. iWateriaZs.-Uranium pentaethoxide,6 uranium penta-~liloride,~ and protactinium pentachloride * were prepared by the published methods. I n addition U(OEt) was prepared by reactions between Cs[UCl,] and Na(0Et) in refluxing benzene the product being isolated by distillation (140 "C) under reduced pressure (0.06 mmHg) [Found: C 23-4; H 5.3; U 50.0.Calc. for U(OEt), C 25.9; H 5.4; U 51.40/,] yield 63%. Commercially available tropolone (Aldrich Chemicals) was recrystallised several times from 2-methylbutane (m.p. 48-50 "C). Ethanol was purified and dried by heating under reflux over freshly ignited quicklime followed by distillation a further dis-tillation froni sodium ethoxide and finally azeotropic distillation from benzene. Benzene was contacted with sodium wire for 2 d heated under reflus over sodium metal distilled and dried azeotropically with ethanol, Methyl cyanide was purified as described previou~ly.~ All solvents were dcoxygenated by flushing with high-purity nitrogen and stored in contact with degassed molecular sieves (type 5A) in inert-atmosphere glove-boxes.A naZysis.-Complexes were hydrolysed by treatment with aqueous ammonia-acetone mixtures chloride being precipitated as the silver(1) salt after acidification of the supernatant with dilute HKO,. It was shown in separate experiments that tropolone (Htrop) did not interfere under these conditions. However if the uranium(v) complex was first dissolved in 8ni-HX0 an orange precipitate formed together with AgCl on the addition of AgNO,. Uranium and protactinium were determined by ignition t o U,O and Pa,O, respectively after the destruction of weighed samples by repeated treatment with hot concen-trated HN03. Carbon and hydrogen were determined by TABLE 4 Analytical results (76) Found Calc. 7-v f [U(trop),] 27.8 49.6 3-5 28.2 49.8 3.0 [Pa(trop),j 27.5 50.1 27.6 50.2 A Comples RI c H CI M c H ci [U(trop),Clj 30.9 43.2 4-6 31.4 44.3 4.7 microanalytical techniques; in the case of [Pa(trop),], 10 mg samples were used.The analytical results are surumarised in Tablc 4. ' D. Brown P. I-idster S. P. Stocks and B. Whittaker un-published work. D. Brown and P. J. Jones J . Chem. SOC. ( A ) 1966 874. D. Brown and P. J. Joiies J . Chew. SOC. (.4) 1967 247 1252 Penta(tropoZonato)uranium(v) .-The complex U(OEt) in anhydrous oxygen-free benzene (0.63 g; 5 cm3) was added dropwise to a benzene solution ( 5 cm3) of Htrop (0.82 g) and the mixture was stirred and allowed to stand for ca. 1 h. The fine black product was isolated by filtration, washed with anhydrous oxygen-free benzene ( 5 x 1 cm3), and vacuum dried (10-4 Torr) at room temperature yield Penta(tropoZonato)protactinium(v) .-Sodium ethoxide (0.022 g) in ethanol (1.3 cm3) was added to PaC1 (0.07 g) and the mixture allowed to stand for ca.1 h. The ethanol was removed by vacuum evaporation and the penta-ethoxoprotactinium (v) lo extracted from sodium chloride into benzene (1 ~111~). Addition of an excess of Htrop (0.125 g) caused an immediate red colouration in the benzene following which the yellow Product precipitated rapidly. The mixture was allowed to stand overnight and the product was then isolated by centrifugation washed with benzene and vacuum dried at room temperature, yield > 95%. ClzZorotetra(tro~oZoizato)ura~zium(v) .-An excess of Htrop (10 1 mol ratio; 1-8 g) dissolved in either oxygen-free, anhydrous benzene or carbon tetrachloride (5 cm3) was lo A.G. Maddock and A. Pires de Matos Badiochirn. Acta, 1972 18 71. >95%. J.C.S. Dalton added to UCI (0.620 g) in the sanie solvent (5 cm3). The mixture was stirred well and allowed to stand overnight, following which the dark brown product was isolated by centrifugation and washed with benzene to remove excess of Htrop. Tropolone hydrochloride in the product was removed by prolonged pumping at Torr (ca. 50 h), yield 00%. The loss of weight on pumping and t h e analytical results before and after pumping indicated that between two and three molecules of tropolone hydrochloride were present in the initial product. Physical Measurements.-1.r. spectra electronic spectra, and X-ray powder-diffraction photographs were recorded as described previously.ll We thank the U.K.A.E.A. A.E.R.E. Harwell for a research grant (to K. W. B. and A. M. B.) Mr. A. M. Deanc (Chemistry Division A.E.R.E. Harwell) for the provision of i.r. facilities Mr. C. McInnes (Applied Chemistry Division, A.E.R.E. Harwell) for carbon analyses on the protactinium complex and Mr. M. A. Hart (hlanchester University) for carbon and hydrogen analyses on the uranium complexes. [4/2271 Received 4th November 19743 l1 P. J. Alvey K. W. Bagnall D. Brown and J. Edwards, J.C.S. Dalton 1973 2308
ISSN:1477-9226
DOI:10.1039/DT9750001249
出版商:RSC
年代:1975
数据来源: RSC
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