3060
The Structure of Ammonium
Table 111: X-Ray Powder Data for BeS04
Hexanitratocerate(1V) in Solutionla d , obsd.,
I/Il% obsd.
A.
3 77 3 48 3 18 2 34
100 3 3 18
1
2 03 1 926 1 876
6 3
1 585
1
1 509
5
1 441 1 412 1 369
1 1 2
1 308
2 1
1 250 1 220 1 164
2 1
1 132
1
1 093
1
1 073 1 063
1 1
d , calcd.,
A.
3 3 3 2
760 450 171 335 2 243 2 047 1 926 1 880 1 725 1 586 1 515 1 512 1 461 1 441 1 418 1 367 1 319 1 312 1 253 1 224 1 167 1 150 1 137 1 121 11 096 I 1 094 1 081 1 075 1 066
hkl
101 002 110 112 103 21 1 202 004 220 114 213 301 222 310 204 105 312 303 321 224 006 215
400 314 323 116 411 402
Acknowledgment. Thanks are due to Drs. H. G. Langer and R. S. Gohlke of the Eastern Research Laboratory of The Dow Chemical Co. for executing the hZTA experiment; this method, coupled with DTA and XRD, is seen to provide a useful and convenient tool for the study of phase relationships. ~
~
~~
~~~
(13) P. Kokkoros, Tschermalcs mineral. petrog. mttt.. 6 , 116 (1956); Chem. Abstr., 5 0 , 14,307 (1956).
(14) See ref. 9, card 4-0843
T h e Journal of Physical Chemistry
Departmont of Chemistry, K e n t State University, K e n t . Ohio (Received A p r i l SO, 1.964)
200
and by Kokkoros.13 The anhydrate was found by them to be related structurally t o cristobalite and to conforn? to the tetragonal space group 14, with a = 4.485 A., c = 6.90 A. The powder datal4 and structure of Be0 are ell known and need no comment. We may conclude that the thermal dehydration and decomposition sequence of BeS04.4Hz0 leads through the stages : tetrahydrate to dihydrate to monohydrate to anhydrate to oxide. The rejection2 of BeS04.HzO as a true phase thus is shown to be unfounded.
~~
by Russell D. LarsenIb and Glenn H. Brown
A question of interest is posed in the chemical literature concerning the structure of ammonium hexanitratocerate(1V) (conmon name : ceric aninionium nitrate) both in the solid state and in solution. Xo direct structural evidence exists on this compound in either state. The question of interest to chemists is whether the Ce(N03)6-2 ion exists either in the salt or in solution. For yeajrs2it was felt that no appreciable complex ion formation occurred between cerium(1V) and nitrate ion in solution. Other evidence3 suggests the existence of a nitrate complex; however, this question was not answered by definitive structural studies. Smith, Sullivan, and Frank13in proposing this salt as a primary standard for oxidimetry, indicated that, on the basis of its chemical behavior in solution, the salt is a complex salt in contrast to a [‘double” salt such as cerium(1V) ammonium sulfate. This chemical evidence consists of: the lack of hydrolysis of the nitrate to give insoluble cerium(1V) salts; solutions of the complex in nitric acid are salted out with ammonium nitrate but not with nitric acid; the nitrate salt is cleanly separated froin solutions of cerium group metals (except thorium) without double salt formation in contrast to the more conirnon double salt behavior. -4nitrate complex of this type is somewhat unique, however, in that bidentate nitrate complexes are known for only a few atoms. Thorium, uranium, and silver ions are also thought to form such c o m p l e x e ~ . ~ ~ ~ ~ ~ ~ I n this note results of an X-ray diffraction study of an aqueous solution of ammonium hexanitratocerate(1) (a) Abstracted in part from the Ph.D. dissertation of R. D. Larsen, Kent State University, Kent, Ohio, 1964; (b) Frick Chemical Laboratory, Princeton University, Princeton, N. J. (2) D. M. Yost, H. Russell, and C. S. Garner, “The Rare-Earth Elements and Their Compounds,” John Wiley and Sons, Inc., New York, N. Y . , 1947, p. 61. (3) G. F. Smith, V. R. Sullivan, and G. Frank, Ind. Eng. Chem., A n a l . Ed., 8 , 449 (1936). (4) Discussion of G. E. Walrafen indicates that Raman spectral evidence on molten silver nitrate by G. E. Walrafen and D. E. Irish, J . Chem. P h y s . , 40, 911 (1964), allows for a structural configuration in which Ag ions are probably nearest neighbors t o two oxygens of a single nitrate ion; however, the 0-Ag-0 linkage is probably not covalent. !4n) NOTEADDEDI N PRooF.-Recently results have been reported for the existence of nn eight-coordinate complex of the tetranitrntocobaltate(I1) ion in which each nitrate is bidentnte; c f . F. A. Cotton and J. G. Bergmann, J . Am. Chem. SOC.,8 6 , 2941 (1964). +
NOTES
3061
(IV) are reported in which evidence is presented for the existence of hexanitratocerate(1V) ion in solution.
Experimental Xethod. The radial distribution method of analysis of X-ray diffraction data as applied to polyatoinic liquids was used in this s t ~ d y . Radial ~ distribution functions were calculated using the formalism of Waser and Schomakero as extensively applied by Levy7 and Kruh*to other systems. Materzals. The samples (53.7% by weight in water) were prepared by direct weight of reagent grade ammonium hexanitratocerate(1V) purchased from the G. Fredrick Smith Chemical Co. Apparatus. X-Ray diffraction data were collected using a Picker X-ray unit with a horizontal-axis diffractonieter and a flat sample holder; the radiation was 35 kv. and 20 ma. 1\30 K a which was monochroniatized by filters and a pulse height analyzer. The timecount-diffraction anglle data were recorded from a digital print-out for 4//160 28 increments up to 30’) 28, and for 2 ” 28 increments up to goo, 28. Proceduye. The time-count-diff ra ction angle data were converted to a cclmmon basis of counts per minute. Replicate samples were averaged and corrected for the sample-container contribution and for polarization. The coherent scattering factors for cerium were corrected for dispersion. The incoherent scattering factors for cerium were calculated by the method of Be.wi10gua.~ The corrected experimental intensity data were normalized to the total theoretical intensities using the methods of Krogh-l\30e10andl Norman.ll The Waser-Schomaker formalism involves the convolution of a modification function with the intensity function. The particular modification function that was used in this study was of the general form employed by Levy7
M(s)
= [fx(O)/fx(s)
l2
(1)
where fx is the coherent scattering factor of an atom x ( i e . , cerium ion) chosen as the unit of composition to which the other atonis in the polyatoniic liquid are stoichiometrically related. A convergence factor was not eniployed in calculating the areas under the radial distribution maxima. Of the various distribution functions that were calculated the following function was used in evaluating the areas under the maxima
D(r)
= 4ar2g1
+2
Sm
r i ~ ls i ( s ) M ( s )sinrsds
(2)
where g1 is, the average electron density in units of e l e c t r o n ~ ~ / A .sm ~ ; is the upper limit of integration. The intensity function (si(s)is
si(s) = s [ l , u - 2 f m 2 ] (3) where Ie,“ is the corrected and normalized experimental coherent intensity in electron units. The Zfm2 term is the theoretical coherent data suninied over a stoichiometric unit consisting of 1 niole of water to 0.03813 niole of solute. D(1‘) is a superposition of modified pair distribution functions,’ the transforms of each being the so-called “shape functions” T m n ( r ) = 1’ T
lm
f n , f n M ( ~ ) COS rs ds
(4)
where fin and fn are the coherent scattering factors of atoms m and n, respectively. M ( s ) is the modification function defined by eq. 1.
Results and Discussion Radial distribution curves for 53.7% aninionium hexanitratocerate(1V) solution show that interactions occur at 1.35, 2.15, 2.85, 3.60, 4.30, and 5.10 8. and at other higher radial distances that cannot be interpreted as siniple pair interactions. Above 5.0 8. there is little deviation from the bulk scattering indicating that the short-range order is restricted to a rather sinall range of interaction. The 1.35- and 2.15-8. distances are readily attributable to X-0 and 0-0 interactions, respectively, within a nitrate ion. The 2.85-8. peak can be attributed to Ce-0 interactions. There is good agreement of 106.6% for 12 Ce-0 interactions in comparing the area for this number of “pure” interactions to the experinlentally determined area. Figure 1 shows the shape function for 12 Ce-0 interactions compared with the experimental radial distribution peak at 2.85 8. This agreement presents strong evidence for 12coordination of oxygen around cerium. This can be interpreted as corresponding to six bidentate nitrate ions coordinated to a central cerium(1V) ion. It is postulated on the basis of the evidence afforded by this work that the nitrate configuration about cerium is in the approximate geometrical shape of an icosahedron. An icosahedral configuration econoniically allows for a 12-coordination of bidentate ligands. (5) A summary of the pertinent theory and general procedure is given in the Ph.D. dissertation of R. D. Larsen. (6) J. Waser and V. Schomaker, Rev. Mod. P h y s . , 2 5 , 671 (1953). (7) H. A. Levy, P. A. Agron, YI.A. Bredig, and M. D. Danford, Ann. N . Y.Acad. Sci., 7 9 , 762 (1960); H. A. Levy and M .D. Danford in “Molten Salt Chemistry,” 31. Blander, Ed., Interscience Publishers, New York, N. Y., 1964, p. 109. (8) R. F. Kruh, Chem. Rel;., 62, 319 (1962). (9) L. Bewilogua, Physik. Z., 3 2 , 740 (1931). (10) J. Krogh-Moe, Acta Cryst., 9 , 951 (1956). (11) N. Norman, ibid., 10, 370 (1957).
V o l u m e 68, N u m b e r 10
October, 1964
3062
KOTES
for hydrolysis and polyinerizatiori of Ce(1V) and Th(IV) found in other studies at lower c o n c e n t r a t i ~ n s ~ ~ ~ ~ ~ cannot be supported at these higher concentrations. If the hydrolytic and polymeric species are present, their concentrations are probably so low that they are not able to be detected in these concentrated solutions These results are, however, consistent with those found in dilute, strongly acidic solutions. It would be of considerable interest to know at what point anion penetration predominates over solvation in the first coordination sphere surrounding a tetrapositive heavy metal ion.
.A Experimentalo RDF with maximum a t 2.85 A 0 Shape function for 12 C e - 0 interactions
4
/ I
3
2
Radial distance,
4 T
(A.1
Figure 1. T h e shape function for 12 Ce-0 interactions compare$ with the experimental radial distribution peak a t 2.85 A.
Favorable support for an icosahedral arrangement is afforded by consideration of the critical radius ratios of cerium(1V) with surrounding ions. A similar geometric arrangement has been reported for another rare earth salt. Martin, Rundle, and Golden12 found a 1%coordinate arrangement around one of the lanthanum ions in La2(S04)3.9He0for which they proposed a? icosahedral configuration as the most favorable. Their argument is based upon considerations of critical radius ratios and upon the geometry of the atoms established by X-ray analysis of the solid. I t might be expected that thorium(1T‘) or cerium(1V) ions, which are of comparable size, will be surrounded by equal numbers of coniplexing species. The striking difference between cerium(1V) and thorium(FV) nitrate complexes, however, is the coordination number of 1I .2 (experiment~al)~~ found for cerium(1V) contrasted to the coordination number of 8.5 (average experimental value for four different solutions) found for thorium(117) in aqueous and acidic media in a similar diffraction study.’* In this study as well as the thorium nitrate study, no evidence is indicated for metal ion-metal ion interactions in solution. The absence of a marked distribution function maximum and the internal consistency of radial distances, “peak shapes,” and coordination numbers all preclude the existence of Ce-Ce or Th-Th interactions. Consequently, wit>h the apparent absence of metal ion-metal ion interactions, the evidence The Journal of Physical Chemisbru
Acknowledgnzent. The authors wish to thank Dr. Richard J. DeSando of Monsanto Research Corp., AIiamisburg, Ohio, for his helpful discussions and interest in this mork. Acknowledgnient is also extended to the B. F. Goodrich Computer Center for kind use of the IBM 7074. (12) D , S. Martin, R. E. Rundle, and S. A. Golden, J . Chem. Phys., 24, 1114 (1956).
(13) Figure 1 shows the agreement betw-een the experiniental coordination number of 11.2 and the assumed 12-coordinate shape function for six Ce-0 interactions, These areas agree within 106.670. An 11.2-coordinate shape function gives even better agreement with the experimental curve but does not, of course, correspond to a simple integral geometrical configuration. (14) R . D. Larsen and G. H. Brown, to be published. (15) K. A. Kraus and R. W. Holmberg, J . P h y s . Chem., 5 8 , 326 (1954). (16) S. Hietanen and L. G. SillBn, Acta Chem. Scund., 13, 533 (1959).
Recalculated Values for the Diffusion Coefficients of Several Aqueous Ternary Systems a t 25”’
by Peter J. Dunlop2 Institute f o r Enzume Research, Unlnizersity of Wisconsin, Madison, Wisconsin 63706 (Receiced M u y 7, 1964)
There exist in the literature some accurate ternary diffusion data3-6 which were obtained several years ( I ) This work was.supported. in part, by research grants from the U. S. National Science Foundation (GP-179) and from the National Institute of Arthritis and Metabolic Diseases (U.S.P.H.S.) (Akl05177). (2) Department of Physical and Inorganic Chemistry, Adelaide Cniversity, South Australia. (3) P. J. Dunlop and L. J. Gosting, J . Am. Chem. Soc., 77, 5238 (1955). (4) P. J. Dunlop, J . P h y s . Chem., 61, 994 (1957). (5) P. J. Dunlop, ibid., 61, 1619 (1957).
