ANALYTICAL CHEMISTRY
1056 OPTICALPROPERTIES Uniaxial positive. Refractive Indices (5893 A.). no = 1.965 =k 0.005; no 2.08; geometric mean 2.00. Molecular refraction 31.2 cc. Color, 0 = olive green; E = brownish green.
=
Axial Elements. u : c = 1:0.902 (derived from unit cell dimensions). Habit. Dipyramidal { 101), often with subordinate { O O l 1. DATA X-RAY DIFFRACTION The structure of uranium tetrachloride has been determined by Mooney ( 1 ) . The space group is I 4 / u m d (D::). Cell Dimensions. uo = 8.298 =k 0.001 A , ; co = i.486 =t0.001 A. Cell volume 515.5 A? Mooney reported an = 8.296 =t 0.009 A.; co = 7.487 =t0.009 ,4. Formula Weights per Cell. 4. Formula Weight. 379.90. Density. 4.894 grams per cc. (x-ray).
Absorption Spectrum (Band maxima, mp, and relative intensities a s viewed with a Zeiss prism microspectrometric eyepiece) 0 E 680 medium .. 668 weak 668 weak 660 weak 660 weak 649 very strong 634 very strong 628 medium 618 strong }GO3 medium strong !OO weak 597 weak 5'92 strong 592 medium strong 590 weak .. ,582 weak 573 strong wide 573 medium strong, wide ,565 medium weak 565 mecjiuin weak 552 medium weak 553 medium weak 548 strong, wide 543 strong, wide 541 strong, wide 531 strong, \vide 5ii strong, wide 521 strong, wide 521 medium 514 weak ;OS medium strong 508 medium v e a k 505 weak 505 medium
OPTICALPROPERTIES Uniaxial, negative. Refractive Indices (5893 ii.). no = 2.03; n E = 1.92; geometric mean 1.993. Molecular refraction 38.6 cc. Color. 0 = greenish yellow; E = green. Absorption Spectrum (Absorption maxima and relative intensity of bands as viewed in a Zeiss prism microspectrometer eyepiece) E 0 685 strong 6i0 strong 1 665 very strong 655 medium strong/ 645 medium strong 640 medium weak 608 very strong 608 medium 577 medium 558 medium strong 563 medium 518 strong (very wide) 518 medium weak 495 medium weak 495 medium strong (wide) 483 medium weak 483 medium (wide)
L I T E R 4 T U R E CITED
(1) Zschsriasen, R . €I., Acta Cryst. 1, 265-9 (1948). WORKdone under the auspices of the Atomic Energy Commission.
LITERATURE CITED
(1) Mooney, R. C . L., Acta Cryst. 2, 189-91 (1949).
127. Uranium Tetrachloride, UCI,
WORKdone under the auspices of the Atomic Energy Commission,
EUGENE STARITZKY, The University of California, Loo Alarnos Scientific Laboratory, Los Alarnos, N. M.
128. Uranium Trifluoride, UF,
may be prepared by halogenation U uraniumtetrachloride trichloride with chlorine at 2.50" C. RAKIUM
of
The University of California, Los Alarnos Scientific Laboratory, Los Alarnos, N. M.
CRYSTAL MORPHOLOQY System and Class.
EUGENE STARITZKY and R. M. DOUGLASS
Tetragonal, ditetragonal-dipyramidnl.
~ H E D R A Lcrystals
of uranium trifluoride were prepared by
-4.W. Savage of this laboratory by heating a mixture of uranium tetrafluoride and uranium metal a t 1050" C. in a hydro1.
Partial Powder X-Ray Diffraction Pattern of Uranium Tetrachloride hkl 101
200 211 112 220 202
301
103 321 312 400 213 411 004 420 303 402 332 204 323 422 501, 431 224 413
d, A., C alcd. .5,558
4.149 3.32.:3 , 15.3, 2,9338 2.7792 2,5946 2,3896 2,1998 2.148G 2.0745' 2.0707? 1.9436 1.8715 1.8555 1,8528) 1.8144 1.733.5 1,7060 1,6918 1.6624
d. A., Obsd." R ,53 4.12 3 30 3.14
2.92 2.77 2.38
2.38.5 2.191 2.137 2,064 1.039 1.862 1.847
:
1 730 1.703 1.090
1/1 h IO0 4 r, 35 J0 10 20 70 65 45 85 50
25 50
35
..
30 29
..
1 ' 620 30 1.8778 1 570 25 1,5665 1.662 20 314 1,523 1,5237 ? .I21 1,6092 1.504 512 25 1.4924 1.489 105 1,4734 1.467 10 1 ,4669} 440 a Philips 114.6-mm.-diameter powder camera, Straumanis mounting.: h(CuKrr) = 1.5418 A . b Relative peak intensities (above background) from densitometer measurements.
I , 13203
gen atmosphere for 2 hours. A crystal structure for rare earth trifluorides, belonging to the noncentrosymmetrical space group P6322 (D:), was proposed by Oftedal ( 2 ) from Laue and powder x-ray diffraction data for the mineral tysonite, (Ce, La,. . .)Fa. From oscillation photographs and piezoelectric tests (results negative) made later, Oftedal (3) proposed a revised structure belonging to centrosymmetrical space group P63/mon (I)&). Both of these structures are based on a unit cell with ao = 7.138, co = 7.295 A. (for tysonite), containing six formular units. As pointed out by Oftedal (2, 3 ) for rare earth trifluorides, and confirmed and extended t o isomorphous actinide trifluorides by Zachariasen (5),powder data from these phases are explicable in terms of a smaller cell containing two formular units, with a0 equal to 1/43 times that of Oftedal's structures, the a axes of the two cells lying at 30 degrees to one another in the plane normal to the c axis. Thus for uranium trifluoride Zachariasen gave, from poivder data only, ao = 4.146 i= 0.003 A., co = 7.348 f 0.004 A, space group P6s/minc (D&), and cell content 2UF3. As discussed by Wyckoff ( 4 ) , Oftedal's revised structure has atoms in special positions of P6a/mcm with only t x o parameters in the equatorial zone unfixed by symmetry: for tysonite, z (metal atom in position g) = ca. 0.34 and z (fluorine atom in position k ) = ca. 2/3. If these two parameters were exactly 1/3 and 2/3, respectively, this arrangement would reduce to a simpler
