THECRYSTAL STRUCTURE OF L I ~ P B ~
Sept., 1956
1275
Cm. -1. 1600
1650 I
I
I
1550 l
I
1350 I
1300 I
I
1250 I
I
1000 -
1
950 I
650 l
f
600
'
-
550500
450
u
Fig. 2.-Infrared absorption spectra of bissalicylaldehyde, inactive sample; -, ethylenediimineCo(I1): active sample; , active oxygenated sample; a, 1700900 cm.-l, and b, 700-400 cm.-l region. ~
vibration of Co-0-0-Co linkages in the oxygenated crystals. When the oxygenated sample was dissolved in chloroform, the evolution of oxygen was observed, and the resulting solution gave exactly the same. spectra as those of inactive or active samples. The dissolution of an oxygenated sample results in the breakdown of the crystal lattice and preferential coordination of the chloroform molecule to the
cobalt(I1) atom. As a result, the chloroform solution of the oxygenated form would be expected to have spectra identical to those of inactive or active samples. The fact that the spectrum of the deoxygenated sample, which was prepared by heating the oxygenated sample in vacuum, was identical to that of the active sample, indicates the reversibility of the oxygenation process.
INTERMETALLIC COMPOUNDS BETWEEN LITHIUM AND LEAD. 11. THE CRYSTAL STRUCTURE OF Li8Pb3* BY A. ZALKINA N D W. J. RAMSEY AND University of California Radiation Laboratory, Livermore Site, Livermore, Cal.
D. H. TEMPLETON Department of Chemistry and Radiation Laboratory, University of California, Berkeley, California Received February d l , 1966
The compound LisPba has been characterized by single crystal and powder X-ray diffraction data. It is monoclinic, space group C2/m, with a = 8.240, b = 4.757, c = 11.03 A., @ = 104' 25', and 2 = 2. There is a body centered cubic pseudocell with a = 3.364 A. and containing two atoms. The structure consists of ordered substitution in these sites in such a way that one-third of the P b atoms have 8 Li neighbors each.and two-thirds have one Pb and 7 Li neighbors each.
Introduction During a study of the compounds in the lithiumlead system, we investigated by X-ray diffraction techniques a phase with composition between LiPb and Li3Pb. Some preliminary diffraction data for this phase along with a determination of the structures of Li3Pb and Li7Pbz have already been publisheda2 Grube and Klaiber3 studied the phase (1) The work described in thia paper was sponsored by the U. S. Atomic Energy Commission. (2) A. Zalkin and W. J. Rrtmsey, THIBJOURNAL, 60, 234 (1956). (3) G. Grube and H. Klaiber, 2. Elsetrochem., 40, 754 (1934).
diagram for this system by means of thermal analysis and measurement.s of electrical resistivity as a function of temperature. The compound they referred to as Li,Pbz (Li/Pb = 2.50), we have found to be Li,Pb3 (Li/Pb = 2.67) on the basis of the crystallographic investigations and also by chemical analysis (Li/Ph = 2.68 + 0.01). It will be noted that the difference in compositions between the stoichiometry we have determined and that given by Grube and Klaiber3 amounts to only 0.013 mole fraction unit.
A. ZALKIN, W. J. RAMSEY AND D. H. TEMPLETON
1276
Vol. 60
which were not corrected for. The deviations between the observed and the calculated sin20 values are greater and more random than would be expected for absorption effects alone, showing that there is probably a slight deviation from this ideal shape. I n general, the lines of the powder pattern appear fairly sharp; however, toward the back reflection region some of the lines show multiplicity effects. Two sets of doublets (Ni2 = 363 and 484) are clearly discernible but not well enough defined t o Determination of Structure.-The single crystal separate out individual reflection planes. A check of the deviations between observed and photographs indicated a monoclinic cell with calculated sin20 indicates better agreement when dimensions a = 8.25 A., b = 4.75 c = 11.1 A., /3 = 106". Because of the poor quality of these the values of 1 in hkl run larger. This indicates that photographs, it is believed that the following the a and b axes are probably shorter than indicated results derived from the powder photograph as above by a few parts per thousand. The atomic positions of the body-centered cubic described below are more accurate: a = 8.24 A., structure can be described in space group C2/m as b = 4.76 A., c = 11.03 A., /3 = 104.5'. The systematic absences and Laue symmetry correspond a twofold set and 5 fourfold sets of special positions: to space groups C2, Cm or C2/m. A satisfactory 2W: (000) (C) structure was found in the higher symmetry, C2/m. 4(i): f (z0 z) (C) with x, z = 5/11, 4/11; 4/11, 1/11; The cell volume corresponds to about 22 atoms, 3/11, 9/11; 2/11, 6/11; and 1/11, 3/11 judging from the atomic volumes in the other lithium lead alloys.2 With the composition Li6Pb2, Six lead atoms can be accommodated in the set 2(a) the primitive unit would contain 3.15 lead atoms. and one of the sets 4(i). The 001 data listed in TaWith three lead atoms a structure was found which ble I1 show that only the parameter z = 4/11 is acis in good agreement with the intensity data; there- ceptable among the above choices. Inspection of fore, the composition is LisPb3 with two formula other rows of constant hk showed repetition a t inunits per unit cell. The density calculated from tervals of 11 in I of the same sequence of intensithe cell dimensions is 5.37 g. cm.-2; that measured ties, as would be expected for parameters which are integral multiples of 1/11. Calculations showed by argon displacement is 5.33 f 0.04 g. ern.+. The atomic positions were first deduced in the that these sequences occurred as expected for x, z = following way. I n L i 9 b 2 and LiPb4 the atoms 5/11, 4/11. Intensities were also calculated for have the body-centered cubic structure of metallic the powder data, as listed in Table I, and again lithium,6but with appropriate substitution of Li by agreement was obtained. No deviation from the Pb. Therefore a search was made for an arrange- ideal parameters has been detected with the dat,a. ment by which eleven cubic cells could be fitted The value of z can be in error by no more than into the observed monoclinic cell. One such 0.002. The value of x is not determined precisely arrangement was easily found, with the monoclinic because of the lack of single crystal data for high dimensions related to the cubic cell dimension a0 values of h. The lithium atomic positions are not determined and the cubic axes, all a2and a3as by the intensity data, but since the cell dimensions a = a1 a2 - 2 a ~ a = &ao and lead positions are in such good agreement with the hypothesis of the cubic arrangement, it is b = a1 - a2 b = 1/za0 likely that lithium fills the remaining positions with c = (3al 3az 5&)/2 e = dz/2a0 the parameters listed above. Thus we give the structure ¶ , = 104" 25' = sin-' ( l l / D ) If the monoclinic cell fits this cubic net exactly, 2Pb1 in 2(a): (000) (C) then the diffraction angles are given by the rela- 4PbII in 4(i): f (z0 z) (C) with = 5/11, z = 4/11 tion 4Li1 in 4(i) with x = 4/11, z = 1/11 sin2 e = (21.57~~ + 60.5k2 + 12P + Shl)X*/4(1laa)* 4Li11 in 4(i) with z = 3/11, z = 9/11 = NXa/4(llao)* 4Li111in 4(i) with x = 2/11, z = 6/11 4Li1v in 4(i) with z = 1/11, z = 3/11 It can be shown that N is always even if h k is even. The powder pattern was indexed according The structure is illustrated in Fig. 1. This arranget o this scheme, which is equivalent to taking a body ment disperses the lead atoms as much as is possible centered cubic cell with dimension llao and with in this unit cell and symmetry. Each PbI has 8 many absences. The value obtained for a0 was Li nearest neighbors. Each Pbrr has 7 Li and one 3.364 A., and from this the monoclinic dimensions P b nearest neighbors. For the parameters listed were deduced by the equations given above. The above, the nearest neighbor distance is 2.91 A. fit of the powder pattern (Table I) is good but not Each Li has 8 nearest neighbors and 6 next nearest perfect. These data suffer from absorption effects neighbors. The number of these which are P b atoms are 4 and 0,O and 6 , 3 and 3, and 4 and 0 for (4) H. Nowotny, 2.Mctollkunda, SS, 388 (1941). LiI, Lirl, LiuI and Lizv, respectively. (6) H.Perlit8 and E. Aruja, Phil. Moo., 80, 66 (1940). Experimental
The material was prepared b y fusing the two metals together in an argon atmosphere in a manner described in a previous paper.* All samples were re ared iq an argonfilled dry box to avoid reaction wit[ t f e atmosphere. A small metallic chunk, which turned out to be a poor single crystal, waa isolated in a thin-walled capillary of 0.3 mm. diameter. Single crystal patterns about the a-axis were photographed with the W eissenberg camera using CuKa radiation; a rotation pattern and layers zero, one and two were obtained. Powder dsraction patterns were photographed in a camera of 11.46 cm. diameter with samples mounted in capillaries.
w.,
+
+
+
+
+
+
+
+
THECRYSTAL STRUCTURE OF LIJ?B~
Sept., 1956
1277
TABLEI POWDER DIFFRACTION DATAFOR L&Pbs hkl
N/2 6
24 41 43 51 54 57 73
83 96 107 121 127 145 150 153 162 164 171 172 175 178 194 204
211 216 217 228 233 242 271 274 281 283 285 292 293 294 299 307 315 325 332 337 349 354 363
zoi
{$!
2
111 31i
5 14 300 2
313
18 19 120 14 41 2 56 240 9 56
314
9 19 27 14
315
150 111 120
316
130 i3i
23 240
131
93 5 15 120 111 3
132 132 133
vw
2794
2779
M
2939
2932
M+
3164
3143
W 8
3313 3366
3296 3354
M-
3730
3718
W W+ W
4044 4139 4173 4372
4044 4139 4159 4369
M+ M M
4641 5223 5290
4637 5193 5251
S-
5502
5462
M-
5658
5615
vw-
5767 5904 6081
5730 5883 6037
W+
MM-
9
317 133 M;
117
111 27 9 600
331 333
18
6 z i 628 208 11s 028 317 620 62a 607 603 409 227
2065 2333
vvw
2
604 118 516 227 513 318 605 226 517 20$ 118 606 333 427 514 22s 406
009
vs
5-
0796 0833 0988 1051 1100 1406 1599
2
3 40
486 490 491 505 508 513 514
M-
0786 0824 0977 1035 log2 1399 1591 1840 2051 2319
S M M W
9
330 332
603 008 500 207 423 405 426 316 601 408 424
vw
sin2 8' Obsd. Calcd.
2
6oi
369 384 387 393 395 402 413 415 417 428 453 457 459 475 484
0
b
