THE CRYSTAL STRUCTURE OF IiPuOaCOa, NH4PuO2CO3AND RbAmOzCOal BY F. H. ELLINGER AND W. H. ZACHARIASEN~ Los Alamos ScientiJic Laboratory, University of California, Los Alamos, New Mexico Universily of Chicago, Chicago, Illinois Received December l 4 * 1.965
X-Ray diffraction data and chemical information are used to identify the compounds KPuOlCOa, NHdPu02C03 and Rbcompounds are hexagonal with two stoichiometric molecules per unit cell. The unit cell Am02C03. These i~ost~ructural dimensions are listed. The space group is C 6/m m c (De:), and the atomic positions are: 2 R in (O,O,O) (0,0,1/2), 2 X in i (1/3, 2/3,.1/4), 2C in f: (213, 1/3, 1/4), 6 01in i (2,2x, 1/4)(2~,~11/4)(~,~11/4)1 4 011in i (1/3, 2/3,. 1/4 2 ) . Fqr the potassium compound, the parameter values are taken to be 2 = 0.812, z = 0.197. The structure contains collinear radicals 10-x-O] + which with the carbonate groups form endless layers of average composition ( x o & O ~ ) - . The layers are held together by the alkali ions which lie halfway between layers. Ezch X atom forms six secondary bonds to carbonate oxygens in addition to the two short oxygen bonds within the radical [XOJ +. Each alkali ion is bonded to twelve oxygen &oms. The struct,ure gives reasonable values for all interatomic distances.
+
The preceding article describes the preparation of a number of alkali carbonates of pentavalent neptunium, plutonium or americium. The results of X-ray diffraction studies of some of these carbonate precipitates are presented in the present paper. The preparations to be dealt with are the K-Pu(V) (at low pH), NHrPu(V) and Rb-Am(V) precipitates which form one isostructural series. I n the case of the other preparations discussed in
TABLE I1 X-RAY DIFFRACTION DATAFOR THE NH4-Pu COMPOUND. CU K a
TABLE I X-RAY DIFFRACTION DATA FOR THE K-Pu COMPOUND. CU KCY sin2 e sin2 e Intensity obsd.
obsd .
40 15 100 40 15 40 12 17 4
0.0244 .0303 ,0365 .0549 .OS59 .0915 .0983 .1157 .1222
45
.1288
20 18 8 22
.1467 .1781 .1853 .1901
35
.2205
10 6 14
,2396 ,2526 .2694
22
.2760
10
.3000
10
.a127
4 6
.3319 .3460
25
.3687
12
.3741
14
.3925
HIHZHI
002 100 101 102 103 110 004 112 200
{% 202 203 105 114 211
{ ::: 212 106 213
{ 302 z: { ?;: 107 206
{ 304 222
(1) This work was sponsored b y the AEC. (2) Consultant t o Loa Alamos Scientific Laboratory.
calcd.
0.0246 .0305 .0366 .0551 .0858 .0914 .0982 .1160 .1219 .1280 ,1287 .1465 .1772 .1840 .1896 ,2194 .2201 .2210 ,2379 ,2515 .2686 .2743 .2754 ,2989 .3115 . 3124 ,3314 .3429 .3657 .3668 .3725 .3903 .3928 .3962
Intensity obsd.
sins 9 obsd.
HiHiHa
50 30 100 40 25 15 50 30 5 5 50 20 15 25 30 6 6 4 40 8 10 17 20 17 15 18
0.0230 .0309 ,0369 .0532 .0810 .0890 ,0925 .1147 .1197 .1230 .1288 .14GO .1696 .1729 .1814 .1987 .2106 .2139 .2211 .2290 .2370 .2613 .2642 .2764 .2009 .2995
002 100 101 102 103 004 110 112 104 200 20 1 202 105 203 114 006 204 210 211 106 212 205 213 300 116 302
12
.3016
10 25 17 17
.3220 .3512 .3650 .3671
{ 206 8;: 215 304 220
sins e calcd.
0.0221 .0306 .0371 .0527 ,0803 .0883 .0917 .1138 .1189 .1223 .1278 ,1444 .1686 .1720 .1800
,1987 ,2106 .2140 .2195 .2293 ,2361 .2603 .2637 .2751 .2904 ,2972 .3023 .3011
.3210
.3520 .3634 .3669
the preceding article, the X-ray work did not Iead to reliable conclusions as to chemical formula and crystal structure. Interpretation of the X-Ray Diffraction Data.The X-ray work is based exclusively on the powder method, single crystals not being available. The diffraction data for the three compounds under consideration are given in Tables 1-111. The observed diffraction lines correspond to a hexagonaI unit cell, the dimensions for the three compounds being a],R . aa, A . K-PU NH4-Pu Rb-Am
5.09 f 0.01 5.09 f0.01 5.12 f0.01
9.83 f0.02 10.39 f 0 . 0 2 10.46 10.04
F. H. ELLINGER A N D w. H. ZACHARIASEN
406
VOl. 58
TABLEI11 easily seen in Table IV, where observed intensities X-RAY DIFFRACTION DATAFOR THE RB-AAI COMPOUND. for the ammonium and rubidium compounds are compared. Elementary structure factor consideracu I L Intensity obsd.
sin2 0 obsd.
HiHaHa
30 100 80 25 25 60 13 4 40 30 15 20 35 30 13 20 13 15 17 5
0.0216 .0358 .0520 ,0789 .0863 .0910 .I127 .1214 .1269 ,1430 .I651 .1703 .1776 .2175 .2248 .2336 .2561 .2615 .2727 .2852
002 101 102 103 004 110 112 200 20 1 202 105 203 114 21 1 106 212 205 213 300 116
9
,2948
10
.3157
20
.3473
\ 215
20 20 5
.3594 .3G41 .3771
304 220 108
1;:; f
214 206
008
sin2 B calcd.
0.0216 ,0356 ,0518 ,0788 ,0864 .0905 .1121 .1207 .1261 .1423 .1652 .I693 .1769 ,2166 .2246 .2328 ,2557 .2598 .2716 ,2849 .2932 .2948 ,2976 .3151 .3456 .3462 ,3580 .3621 ,3758
tions show that the observed intensity variation with the alkali constituent requires two alkali atoms per unit cell and in positions 2 R in (0, 0, 0) (0, 0, l / ~ ) . As described in the preceding article, chemical analysis showed that there is one carbonate group per heavy atom X. Accordingly, the unit cell contains two carbonate radicals.
TABLEIV OF ALKALI IONSON DIFFRACTION INTENSITIES THEEFFECT H I H ~ H ~ "4-Pu
100 101 102 103
30 100 40 25
Rb-Am
HiHzHa
NHd-Pu
Rb-Am
Trace 100 80 25
104 110 112 114
5 50 30 30
60 13 35
0
The unit cell content so far deduced, namely, R2X2(C03)2,does not account for the observed unit cell volume, nor are the valences balanced. Previous work on compounds of the heavy elem e n t ~has ~ shown that the unit cell volume, V , can be represented as the sum ZVi of the volume requirements of the individual constituents. Since the heavy ion is so small as to fit into the interstices between the anions, its volume requirement is negligible. The experimental values for the volume requirements of other ions which come into consideration are Ion Vi, A.'
K+ 21
NH4+ 20
Rbf 28
0-2,
OH-, HzO C01-2 18 54
The unit cell vglumes are 221 for the K-Pu It is of interest to point out that the K-Pu compound,, 233 A.3 for the NHd-Pu compound, and NH4-Pu compounds were observed during the and 237 A.3 for the Rb-Am compound. The ware3 At the time, they were believed to be double alkali and carbgnate ions require a volume of 150, hydroxides of alkali and Pu(V1). On this basis, 160 and 164 A.3 for the three compounds, rethe interpretation of the X-ray data led to the in- spectively, leaving 71-73 A.3 of the unit cell correct formula R P u O ~ ( O H ) ~G. . E. Moore and volume to be accounted for by oxygen and hyD. E. Koshland4 subsequently showed that the droxyl ions and water molecules. The residual compounds in all probability were alkali hydroxides volume shows that there are altogether four such of Pu(V). This suggestion as to composition was, constituents. Since the heavy atom is known to however, incompatible with the X-ray results. be present in the pentapositive state, balancing of The unit cell dimensions for the plutonium com- valences requires eight anion charges for the addipounds given above and the obser~iationsin Tables tional atoms. Hence, the possibility of some of I and I1 are those obtained during the war. these four additional constituents being hydroxyl In the ammonium compound, plutonium is by ions or water molecules must be ruled out, i.e., the far the predominant scatterer, so that the main chemical formula of the compounds is of the form features of the intensity distribution must be RX02C03 with two stoichiometric molecules per ascribed to the plutonium configuration. It is unit cell. seen from Table I1 that the structure factor is zero The chemical compositions having been eswhen HI - HZ = 3n and H3 odd, large when tablished, the densities can be calculated, and the H1 - Hz = 3n and H3 even, large when Hl - Hz + result is p = 5.57 for KPuOZC03, p = 4.99 for 3n and H, odd, small when HI - H2 # 311 and NH4Pu0zCO3, and p = 6.06 for RbAmOzC03. H3 even. Accordingly it is necessary to have two The incorrect formula suggested for the plutonium heavy atoms per unit cell and in positions 2 X compounds during the war, RX02(0H)3, corin *-( l / 3 , 2/3, ~ I / d responds to precisely the same volume as the corThe marked increase in the cz3 period with the rect formula, the volume requirement of three size of the alkali ion is proof that this ion is a hydroxyl groups equaling that of one carbonate constituent of the structure. Indeed, the effect of group. the alkali ions on the diffraction intensities is Determination of the Structure.-The positions (3) W . H. Zachariasen, Manhattan Project Reports CN-2010. Jan. of the heavy atoms and of the alkali atoms have 1945, and CN-2742, Feb. 1945. already been deduced from intensity considerations (4) G.E. Moore and D. E. Koshland, Clinton Laboratories Report e
CL-P-404, Apr. 1945.
(5) W. H. Zachariasen, J . Am. Chem. S o c , , 70, 2147 (1948).
May, 1954
CRYSTAL STRUCTURE OF I
