Octafluoroprotactinates (V) 1 Grosse, A

No.4971 February 6, 1965 NATURE 589

Table 1. ATOHIO PARAMETERS OP TETRAGONAL STRONllUH OXALATE hydrolysed by ammoniacal solution. The sodium salt is Atom z y z B (A.') isostructural with• sodium octafluorouranate (VJ, possess Sr 0·301 0·196 0·0 0·8 ing tetragonal symmetry. Tho lithium complex, for 0(1) 0·469 0·231 0·179 3·5 0(2) 0·639 0·248 0·180 1·7 which there appears to be no quinquevalent niobium, 0(wl) 0·106 0·149 0·0 4·8 tantalum and uranium analogue, is also tetragonal; O(w2) 0·390 0·013 0·0 4·7 O(tc3) 0·0 O·O 0·282 4·3 owing to the presence of several weak reflexions, extra to 0 0·555 0·241 0·101 1·5 those observed on the powder pattern of Na3PaF 8 , the X-ray powder diffraction data are best interpreted on the (X,;;; 0·5). However, the unit cell of tetragonal strontium basis of a larger cell obtained by doubling a • The results is slightly larger, and the average distance of 0 oxalat.e of the diffraction investigations are shown in Table 1, the 8-co-ordinated strontium atom, is 2·59 Sr-0, for A lithium and sodium salts having the space groups (2·56- 2·61 A). the The C-C bond of the oxalat.e ion is bisected by a sym P42212-D~ and 1/mmm-DU respectively. metry plane. The bond-lengths are as follows : C-C, Table 1. UNIT CELL DATA 1·52 0·04 C-0(1), 1·25 0-02 A, C-0(2), 1·24 + A; ± ± Compound Symmetry a, (A) c, (A) n (g/cm') 0·02 A. The bond angles are C-C-0(1), 117·7 ± 1·0°; Ll3PaF, Tetragonal 10·386 10·89 8 4·568 C-C-0(2), 118·5 ± 1·0°; O(l)-C-0(2), 123·8 ± 1·7°. Na,PaF, Tetragonal 6·487 10·89 2 4·577 The oxalate ion therefore has the symmetry mmm, within a very small limit of error. We understand from Dr. A.G. Maddock6 that he and his This work was supported, in part, by the Computer associates, working at Cambridge, have also recently Cent.er of the University of California at Davis. prepared Na3PaF8 using conditions similar to those for CLARENCE STERLING the preparation of the tantalum (V) analogue. Our Department of Food Science and Technology, preliminary report of the preparation of the octafluoro University of California, protactinates (V) will be supplemented by a detailed Davis. account of their chemistry, to be published elsewhere, 1 Sterling, C., Science, 148, 518 (1964). including a full structure analysis of Na,PaF 8 and of • Kla8ens, H. A., Perdok, W. G., and Terpstra, P., z. Kristallogr,, A, 96,227 potassium heptafluoroprotactinate (V) and the isostruc (1037). tural sodium and rubidium complexes. D. BROWN J.E. EASEY CHEMISTRY Atomic Energy Research Establishment, Harwell, Didcot. Octafluoroprotactinates (V) 1 Grosse, A. V., J. Amer. Chem. Soc., 56, 2501 (1934); Proc. Roy. Soc., A, 50, ALTHOUGH potassium heptafluoroprotactinate (V), 363 (1935). 1 • Asprey, L.B., and Penneman, R. A., Science, 145, 1124 (1964). K PaF , has been known for several years and a number 2 7 3 Brown, D., and Easey, J. F. (unpublished Information). of hexafluoroprotactina.tes (VJ, Af1PaF6, (Mi = NH4 +, • Hoffman, J. I., and Lundell, D, E. J., J. Re,. Nat. Bur. Stand., 20, 607 K+ and Rb+) have boon recently reported•, octafluoro (1938). protactinates (V) have not been recorded. In an investiga • Rtidorff, W.,and Leutner, H., Annalen, 632, l (1960). tion of the preparation and properties of the fluoro • Maddock, A. G. (personal communication). oomplexes of quinquevalent protactinium, using bromine trifluoride and aqueous hydrofluoric acid as solvents, we have isolated lithium and sodium octafluoroprotactin Compounds containing Mercury - Iron Bonds 1 ates (VJ, Li,PaF 8 and Na3PaF 8 respectively, from reactions Hock and Stuhlman discovered that the reaction of iron in the latter solvent. pentacarbonyl with mercuric halides yielded solid pro Solutions approximately 0·5 M in protactinium (V) ducts, which they formulated as addition compounds

were obtained by dissolving protactinium pentoxide, Fe(C0)4Hg·(HgX2 ), containing the Fe(C0)4Hg moiety Pa20., previously ignited at 750°, in 48 per cent hydro which itself can be obtained by reaction of iron pents fluoric acid. Sufficient alkali metal fluoride, MF (M = carbonyl and mercuric sulphate. No structural informa Li+, Na+ and K+), to give a 3: 1 mole ratio of MF: Pa tion on these compounds is available, although W ells2 has was dissolved in hydrofluoric acid, added to the protactin suggested that Fe(COJ,Hg is polymeric and trans. ium (VJ solution in a platinum crucible and the mixture We find that although the compounds Fe(CO),Hg2X 1 con0entrated to approximately half-volume by heating are sufficiently soluble in polar solvents to permit recrystal under an infra-red lamp. Addition of acetone to the lization, they do not give sufficiently concentrated solu mixtures containing sodium and potassium fluoride tions for mol. wt. or dipole moment determination. Their 1 produced an immediate precipitate of octa- and hepta elemental analyses and infra-red spectra (2,200--175 cro- ) fluoroprotactinate (V) respectively, the latter identified can be consistently explained on the basis of a monomeric by its X-ray diffraction pattern•. Lithium octafluoro structure, cis-Fe(C0)4 (HgX)2, in which there are two protactinate (VJ, which was not formed under the afore mercury-iron bonds. Fe(C0)4Hg is insoluble in all said conditions, could only be obtained by evaporating organic solvents and is most probably polymeric; both it the hydrofluoric acid solution of the component fluorides and the corresponding cadmium compound we also to dryness and was identified from its X-ray powder believe to have the cis-configuration with mercury or pattern. The isolated products were vacuum dried at cadmium-iron bonds. about 100°. Protactinium analyses were performed by The pattern of carbonyl stretching frequencies is typical dissolving the complex in 10 per cent nitric acid solution, of that found for cis-M(C0)4L 2 molecules. For trans precipitating the hydroxide and igniting it to the pentoxide M(C0)4L2 only one band would be expected. The spectra at 750°. Fluoride in the supernatant was determined of all five compounds (Table l) are similar in the region gravimetrically4 as lead chloro-fluoride: found for the 620-400 cm-1, where 8(MCO) and v(M-CO) modes absorb•, sodium complex: Pa, 49·38 per cent; F, 33·54 per cent; and contain more bands than would be expected for a required for Na3PaF8 : Pa, 51·1 per cent: F, 33·63 per cent. trans- structure. A further, very weak, feature near 250 The octafluoroprotactinates (VJ are white, non cm-1 is common to all spectra and may be the first over hygroscopic solids, which are soluble in dilute hydro tone of a 8(CFeC) mode. The only other band in the fluoric acid, water and dilute nitric acid. It is interesting Fe(COJ,Hg spectrum, 195·9 cm-1 (s), we assign to a mer to note that no signs of hydrolysis are observed in the cury-iron stretching mode on the grounds that no vibra last two solutions, further evidonce of the strong fluoride tional mode of an M(CO),. grouping is likely to absorb in complexing of protactinium (VJ. Both are immediately that region3 • Consistent with this assignment is the