2076
NOTES
Vol. 63
A STRUCTURE PROPOSAL FOR Na.1ZreF31
In the course of this study, an accurate cell size for this compound was obtained. To refine the accuracy of the cell size measurement, two Chemistry Division. Oak Ridge National Laboratory,' Debye-Scherrer patterns were taken, using Cr-K, Oak Ridpe, Tennessee radiation. The samples were prepared by grinding Received June 18, 1960 several of the above mentioned single crystals. A structure for one of the binary phase compounds These patterns were measured with a steel scale occurring in the NaF-ZrF4 system2 is proposed. and vernier and corrections were made for film Powder diffractions data of samples crystallized shrinkage and sample absorption. All clearly from melts of the composition 50 mole % NaF-50 resolved and unambiguously indexed reflections in mole % ZrF4 have indicated that these crystals are the range 18" < 28 < 142' were used to obtain a isomorphous with crystals of NaUFs. The latter least squares fit of the cell size to the data by a were found by Zachariasen and reported by Kate method described elsewhere.6 The refined hexagand Rabinowitch4 to be rhombohedral with space onal cell size was found to be group R3-(C23i) and 6 molecules per unit cell. a = 13.802 0.002 R. The metal ions are in the sixfold general positions c = 9.420 f 0.001 A. (f): ( X Y Z ) ; (ZXY);( Y Z X ) with the parameters The corresponding rhombohedral unit cell is X Y z a = 8.565 R., a = 107'21' BY P. A. AGRON AND R. D. ELLISON
*
U Na
3/13 6/13
1/13 2/13
9/13 5/13
Density measurements made on the single solid phase produced from large melts of slightly different compositions, namely, 52 mole % NaF48 mole % ZrR and 53 mole % NaF-47 mole % ZrF4, indicate the existence of a stoichiometry different from NaZrFS. The densities observed are 52 mole % NaF: 4.14 =k 0.03 g./cc. 53 mole % NaF: 4.11 f 0.01 gJcc.6 while the calculated density for NaZrFb is 4.01 g./cc. The unit cell volumes of the solids crystallized from melts of compositions in the region 50 mole yo NaF to 53.8 mole yo NaF differ by less than 0.5%. In order to satisfy the requirements of a greater density with a greater amount of the lighter component in a substantially constant volume, it is necessary to assume the addition of an NaF molecule to the unit cell, rather than the substitution of a lighter sodium for a zirconium ion with the accompanying fluorine vacancies even further reducing the density. It is significant that the additional Na+ cation could fit into the vacant special position, (000), without changing the space group. This would yield a unit cell of the stoichiometric composition Na&eFal (7NaF.GZrF4) with a calculated density of 4.16 g./cc., in reasonable agreement with the above measured values. Single crystals obtained from melts of the 53 mole % NaF composition have become available. Diffraction patterns obtained by using film techniques on the Buerger precession and the Weissenberg cameras have confirmed that the space group R3 is still possible for this composition. It is hoped that further measurements of the diffracted intensities using counting techniques will yield the fluorine positions, as well as confirm the suggested position (000) for the added Na+. (1) Work performed for the U. 9. Atomic Energy Commission at the Oak Ridge National Laboratory, operated by the Union Carbide
Corporation, Oak Ridge, Tennessee. (2) C. J. Barton, W. R. Grimes, H. Insley, R. E. Moore and R. E. Thoma, Tam JOURNAL, 62, 665 (1958). (3) P. A. Agron and M. A. Bredig, ORNL-1729,47, 1954. (4) J. J. Kats and E. Rabinowitch, "The Chemistry of Uranium," McGraw-Hill Book Co., Inc., New York, N. Y.. 1951, p. 378. (5) 9. I. Cohen, Oak Ridge National L&boratory, personal communication.
(6) W. R. Busing and H. A. Levy, Acta Cryst., 11, 798
(1958).
THE TIN(I1) REDUCTION OF METHYL ORANGE' BY F. R. DUKEAND N. C. PETERSON
-
Institute for Atomic Research and Department of Chemistry, Iowa Stale Unzveraaty. Ames, Iowa Received June 88, 1068
The possibility that one particular Sn(I1) chloride complex might have high reactivity relative to others led to this kinetic study of the reduction of an azo compound to the amine 8C1
+ 4H + Ar-N=N-Ar +
+ 2Sn(11) +
2ArNHg
+ 2SnCla
The rates of reduction of a number of such compounds were measured by Goldschmidt and Braanaas,2 who reported a variable order in chloride ion, first order in azo compound and first order in Sn(I1). The recent equilibrium data for the Sn(11) chloride complexes3allow a more precise interpretation of the mechanism of the reaction relative to the role played by the chloride. The reduction of methyl orange was found to proceed at a convenient rate and, thus, was selected for study. Experimental Sn(I1) perchlorate was prepared by dissolving A.C .S. reagent grade Sn(I1) chloride in 2 N HCIOl and passing the solution through a column of Dowex 50 exchange resin in the acid form, followed by an elution with 2.0 m perchloric acid. Chloride ion was shown to be absent from the solution. Commercial methyl orange was recrystallized twice from water and dried in a desiccator over anhydrous calcium sulfate. Perchloric and hydrochloric acid solutions were prepared by diluting the concentrated reagents to 2.00 M with water distilled from alkaline permanganate. A model 6A Coleman Junior Spectrophotometer was used to follow absorbancy for all rate measurements, with Pyrex 1 om. cells. (1) Contribution No. 768. Work was performed in the Ames Laboratory of the U. 9. Atomic Energy Commission and Department of Chemistry at Iowa State University. (2) H. Goldachmidt and A. Braanaas, 2. physik. Chem., 96, 180 (1920).
(3) C. E. Vanderzee and D. E. Rhodea, J . A m . Chem. Soc., 1 4 , 3552 (1952),
*
I
I
