1. No category

526
Acta Cryst. (1959). 12, 526
Crystal Chemical Studies of the 5/-Series of Elements. XXV.
The Crystal Structure of S o d i u m Uranyl Acetate*
BY W. H. ZACHARIASE~ AND H. A. PLETT1-NGER
Argonne National Laboratory and Department of Physics, University of Chicago, Chicago, Illinois, U.S.A.
(Received 16 January 1959)
Sodium Uranyl acetate, NaUO~.(O~CCI-Ia)3, is cubic with space group P2t3 and a = 10.688±0-002/~.
The positions of all atoms were deduced from precisely measured X-ray diffraction intensities. In
the collinear uranyl group U-O = 1"71=t=0"04 A. Normal to the uranyl axis are six secondary bonds
from uranium to acetate oxygens with U - O = 2.49=f=0.02 A. Sodium is bonded to six acetate oxygens
with N a - O -----2.374-0.04 I . The bond lengths within the acetate group are C-C ---- 1.52±0.05 A,
C-O ---- 1"26=[=0"05 A and 1.28+0"04 A, and 121 ° is found for the carboxyl bond angle. A revised
bond length versus bond strength curve for UVZ-O bonds is presented.
Introduction
Experimental procedure
:Earher crystal s t r u c t u r e studies of u r a n y l salts h a v e
given some information a b o u t the crystal chemistry
of these compounds. I t has been shown t h a t the uranium atom, in addition to the two strong u r a n y l bonds,
forms four, five or six secondary bonds to oxygen or
fluorine atoms. The positions of the light atoms have
been determined with precision only for a small
n u m b e r of structures; but it was found t h a t the
lengths of the p r i m a r y as well as of the secondary
bonds varied considerably from compound to compound. This variation has been correlated with corresponding variation in the bond strengths (Zachariasen,
1954a). However, the published empirical bond length
versus bond strength curve was based upon a small
n u m b e r of observations, a n d the present investigation
was u n d e r t a k e n in the hope of obtaining f u r t h e r
reliable experimental results.
The crystal structure of sodium u r a n y l acetate,
NaUO2(OOCCH3)a, was first studied b y I. F a n k u c h e n
(1935). H e reported the space group P213 a n d four
molecules in a unit cube with a = 10-670+0.001 k X .
F a n k u c h e n described a complete s t r u c t u r e ; b u t only
the u r a n i u m sodium a n d u r a n y l oxygen positions
were deduced from the observed intensities. However,
this early work gave the i m p o r t a n t result t h a t the
The structure analysis of MgUO~02 (Zachariasen,
1954b) and of K3UO2F 5 (Zachariasen, 1954c) demons t r a t e d t h a t it is possible b y X - r a y diffraction m e t h o d s
to locate the positions of light a t o m s in the presence
of u r a n i u m to an accuracy of 0.03 •. I n order to reach
this precision it is necessary to measure intensities
with an accuracy a t t a i n a b l e only with counters a n d
to correct accurately for absorption and extinction
effects.
Crystals were prepared b y slow evaporation from
a solution of u r a n y l n i t r a t e a n d sodium a c e t a t e in
molar proportions. Most of the crystals so obtained
were found unsuitable for intensity measurements, as
the X - r a y showed a seemingly single crystal to consist
of two or more individuals in slight misalignment.
However, two excellent specimens were e v e n t u a l l y
found, and these were m a d e into n e a r l y perfect
spheres in the Bond Sphere Grinder. The radii of t h e
two spheres were 0.0116±0.0002 cm. a n d 0.0122±
0.0003 cm., where the limits of error denote the ext r e m e variation.
The intensity m e a s u r e m e n t s were carried out with
a General Electric X R D Spectrometer rebuilt for
single crystal work, using filtered Cu K radiation and
a proportional counter. The intensities of all possible
uranyl radical, by space group ~ymme~ry, had to be
HKO reflections were measured. Because of the very
collinear.
The isostructural n e p t u n i u m and p l u t o n i u m compounds were identified during the w a r (Zachariasen,
1949). A unit cube of a = 10.659±0.002 k X . was
reported for the n e p t u n i u m a n d of a -- 10.643+0.002
k X . for the p l u t o n i u m compound. The analogous
americium compound has since been added to the isos t r u c t u r a l series (Ellinger, 1956).
high absorption (,u = 470 cm. -1) v e r y small d e p a r t u r e s
from perfect spherical shape give rise to large intensity
differences for equivalent reflections. I n extreme cases
it was found t h a t the intensity could v a r y b y as much
as t h i r t y per cent from one equivalent plane to another, while intensity m e a s u r e m e n t s for a given plane
were reproducible to two per cent. I n order to minimize
this source of error m e a s u r e m e n t s were m a d e for all
planes of the same crystallographic form a n d the
average taken. As a means of f u r t h e r reducing t h e
experimental errors complete HKO d a t a were ob-
* Work done under the auspices of the Atomic Energy
Commission.
W . I-I. Z A C H A R I A S E : N
AND
t a i n e d for b o t h c r y s t a l spheres described above. W h e n
t h e i n t e n s i t i e s were reduced to s t r u c t u r e factors, t h e r e
was n e a r l y perfect a g r e e m e n t b e t w e e n t h e t w o sets of
complete d a t a .
Determination
H . A. P L E T T I N G E R
t w o of t h e difference s y n t h e s e s are s h o w n in Fig.
1 (a) a n d (b).
nimmm
;
iummmmmm:
-mmmmmmmmmu
ammmmmmmmm
amm"
mmmmmmmmmmmmmmm
mm
. , mmmmmmmmmmmmmmm
_a m m m m m m m m m m m m m m m m m m m m
nmmummmmmmmmmmmmmmn
Immmmmmmmmmmmmmr,
. Imm
of t h e s t r u c t u r e
I n a g r e e m e n t w i t h F a n k u c h e n ' s e a r l y w o r k i t was
f o u n d t h a t a - - 10.688+0.002 /~ w i t h four molecules
per u n i t cell a n d space g r o u p P213. T h e p o s i t i o n s of
t h i s space g r o u p a r e :
4a
12b
(z,x,x);
527
0-50
(½+x,½-x,~) ©;
(x,y,z) ©; (½+x, ½-y,~.) ~.~;
(½+y, ½ - z , 5) © ;
(~+z, ½ - x , 9) ~ .
o~
T h e u r a n i u m a t o m s m u s t be in p o s i t i o n s 4a. T h e
single p a r a m e t e r for u r a n i u m is r e a d i l y d e t e r m i n e d
from chance absences a n d f r o m m e a s u r e d s t r u c t u r e
f a c t o r ratios IFnxo]/]FxHo[ for H+K o d d a n d large.
As a p r e l i m i n a r y v a l u e s u b j e c t to f u r t h e r r e f i n e m e n t
one finds e a s i l y x -- 0"429+0.001.
Since t h e u r a n i u m s c a t t e r i n g p r e d o m i n a t e s , a n d
since t h e r e are i n v e r s i o n centers in t h e X Y p r o j e c t i o n ,
t h e positions of t h e l i g h t a t o m s were f o u n d d i r e c t l y
0-25
0~0
0.75
(a)
IloQdz. Difficulties
from F o u r i e r s y n t h e s e s of t h e t y p e
d u e to p a r t i a l s u p e r p o s i t i o n of n o n - e q u i v a l e n t a t o m s
were e l i m i n a t e d b y t h e use of difference s y n t h e s e s ,
o.75
1
T h e first s y n t h e s i s to be carried
out, f~ ( ~ - e . )
dz,
g a v e a p p r o x i m a t e c o o r d i n a t e s for s o d i u m a n d o x y g e n
a t o m s . These a t o m s were t h e n r e m o v e d in t h e second
difference s y n t h e s i s , a n d p r e l i m i n a r y positions for t h e
c a r b o n a t o m s were o b t a i n e d . F u r t h e r r e f i n e m e n t s were
carried o u t w i t h t h e aid of difference s y n t h e s e s in
which t h e effect of all b u t one set of a t o m s a t a t i m e
was removed. F o u r such successive r e f i n e m e n t s were
made. T h e final set of p a r a m e t e r s so o b t a i n e d is
s h o w n in T a b l e 1. T h e a t o m s U, N a , Oi a n d Ou are
in t h e special positions 4b a n d all o t h e r a t o m s in
g e n e r a l positions 12b. A c t u a l X - R A C p h o t o g r a p h s for
T a b l e 1.
U
Na
Oi
Oii
Oiii
x
x
x
x
x
y
z
OIv x
Y
z
CI
x
y
z
CH x
y
z
oa5
I
0.25
o-~o
y---~
o.~5
Atomic coordinates
Fankuchen (1935)
This study
0.428 ± 0.002
0.81 +0.03
0.31 +0.02
0"55 +0"02
-----------~
0.4292 ± 0.0003
0"8289:t: 0.0006
0.336 -/-0.002
0"521 +0"002
0.382 -b0.002
0.291 + 0"001
0.608 + 0.001
0"551 +0"001
0.241 +0"001
0"500 +0"002
0.482 +0-001
0.229 + 0.002
0.598 J= 0-001
0.509 +0-002
0-118 d=0.002
0.683 =t=0.001
Fig. 1. (a) shows the X-RAC photograph of a Fourier difference
synthesis in which a]! but the uranyl oxygens have been
removed. The two lowest contour lines have been deleted.
(b) is an X-RAC photograph of a Fourier difference synthesis
with all but acetate oxygen atoms removed. The large peak
at x = {, y - ~ ½ is due to the superposition of two Oiv
atoms.
I n t h e r e f i n e m e n t process it was a s s u m e d t h a t t h e
h e a t m o t i o n could be r e p r e s e n t e d a d e q u a t e l y b y t w o
i s o t r o p i c t e m p e r a t u r e factors, one for u r a n i u m a n d
t h e o t h e r c o m m o n to all l i g h t a t o m s . T h e effective
s c a t t e r i n g power of u r a n i u m was t a k e n to be f - 5 . 0 +
i14.0, w h e r e f is t h e n o r m a l f - c u r v e w i t h o u t a n o m a l o u s
dispersion ( D a u b e n & T e m p l e t o n , 1955). T h e imagin a r y t e r m in t h e a n o m a l o u s dispersion was t a k e n i n t o
528
CRYSTAL
CHEMICAL
STUDIES
OF THE
account by applying a correction to the experimental
s t r u c t u r e factors. This c o r r e c t i o n is
Foorr =
•
(]Fobs.l~-]Ful~) ½
(i)
r
,
w h e r e F v is t h e s t r u c t u r e f a c t o r for t h e u r a n i u m a t o m s
r e s u l t i n g f r o m t h e i m a g i n a r y d i s p e r s i o n t e r m alone.
This c o r r e c t i o n is small, b u t n o t c o n s t a n t , a n d h e n c e
it could n o t be i n c o r p o r a t e d i n t h e scale factor.
I n t h e course of t h e r e f i n e m e n t , it was f o u n d t h a t
e x t i n c t i o n effects w e r e small, b u t n o t negligible. F o r
s m a l l e x t i n c t i o n t h e i n t e n s i t y c o r r e c t i o n is
I¢orr. = Iobs./(1--2gIob~.)
w h e r e 2globs. < 1 for t h e s t r o n g e s t reflection. H e n c e ,
e x t i n c t i o n c o r r e c t i o n can b e a p p l i e d t o t h e e x p e r i m e n t a l s t r u c t u r e f a c t o r s as follows
Fcorr" ~ Fobs.(1 +/Clobs. )
(2)
w h e r e k is a c o n s t a n t .
W h e n t h e i n v e s t i g a t i o n was u n d e r t a k e n t h e r e was
neither hope nor expectation that the hydrogen atoms
w o u l d s h o w u p in t h e F o u r i e r p r o j e c t i o n s i n t h e
p r e s e n c e of t h e h e a v y u r a n i u m a t o m s . H o w e v e r , i n
s e v e r a l of t h e d i f f e r e n c e s y n t h e s e s small a n d diffuse
s e c o n d a r y m a x i m a a n d i r r e g u l a r i t i e s in t h e l o w e s t
c o n t o u r fines a b o u t o x y g e n a n d c a r b o n p e a k s w e r e
o b s e r v e d . A d i f f e r e n c e s y n t h e s i s w i t h all b u t h y d r o g e n
a t o m s was t h e r e f o r e c a r r i e d out. O n l y t e r m s for w h i c h
s i n 0 / ) . < 0.3 w e r e i n c l u d e d . T h e r e s u l t i n g X - R A C
s u m m a t i o n s h o w e d s m a l l p e a k s a t t h e u r a n i u m posit i o n s ( i n d i c a t i n g t h a t t h e scale f a c t o r was t o o s m a l l
b y a f r a c t i o n of one p e r cent) a n d p e a k s c o r r e s p o n d i n g
t o t h r e e sets of a t o m s i n g e n e r a l p o s i t i o n s 12b. T h e
c o o r d i n a t e s of t h e s e m a x i m a w e r e n o t c o n s i s t e n t t o
b e t t e r t h a n 0"03 b e c a u s e of diffuseness a n d superposition, a n d t h e r e was also c o n s i d e r a b l e v a r i a t i o n i n
t h e h e i g h t s of t h e p e a k s . T h e s e c o n c e n t r a t i o n s of
r e s i d u a l s c a t t e r i n g m a t t e r w e r e a t d i s t a n c e s of 0 . 8 1.5 ~_ f r o m t h e Cr~ a t o m s a n d are p r o b a b l y t o be
i d e n t i f i e d as t h e h y d r o g e n a t o m s . I n T a b l e 2 are
T a b l e 2. Hydrogen coordinates
Experimental values
tII
x
y
z
ttii x
y
z
HHI x
y
z
0-43
0.06
0.67
0.56
0.17
0-77
0-58
0.04
0.66
0.46
0.08
0.69
0.57
0.20
0.81
0.59
0.06
0-67
Idealized
0.43
0.06
0.67
0"52
0.15
0.77
0.58
0.07
0-65
s h o w n t h e c r u d e h y d r o g e n c o o r d i n a t e s as o b t a i n e d
d i r e c t l y f r o m t h e X - R A C p h o t o g r a p h s as well as a
s e t of i d e a l i z e d c o o r d i n a t e s . T h e l a t t e r set was deduced from the experimental values by adjustments
w i t h i n e x p e r i m e n t a l error so as to y i e l d m o r e r e a s o n able C - H b o n d l e n g t h s a n d b o n d angles.
5f-SERIES
OF ELEMENTS.
XXV
T a b l e 3. Observed and calculated structure factors*
HKO
_Fo
.Fc
ll0
200
210
120
220
310
130
320
230
4o0
410
140
330
420
240
430
340
510
150
520
250
440
53o
350
600
610
160
620
260
540
450
630
360
710
170
550
640
460
720
270
730
370
650
56o
8oo
810
180
740
470
820
280
45.0
--45.6
54.2
55.1
26.7
27.1
51.3
50.2
23.3
24.2
4 5 - 1 -46.1
13.3
14.1
2-1
0.9
40-5
43.4
7-8
-7.7
27.1
28.3
48-7
48.1
6"4
--4"2
8.4
7-2
2.8
1.6
60.9
59.9
9.1
9-4
42.5
-42.2
8.2
9.6
4 2 " 3 --44"0
34-9
35.8
9.3
10.1
18.9 -18.9
24.5
25-7
37.6
-38.0
3-7
3-2
16.0
16.5
31-2 -30.2
32.4
-35.9
26.4
29.2
32.0
34-2
26.3
26.2
0
-0-5
0
-0.4
17.3
19-1
25.6
26.6
5-3
3.9
3-2
1.5
35.1
-34.5
4.4
6.1
7.4
7.8
43.8
44.7
15.0
15.3
1 3 - 9 -14.3
33.2
-29.9
7.1
-7.4
15.5 -15.5
41.3
-40.2
4.4
4.6
17.5 -17.6
20.5
-20.7
HKO
660
830
380
750
570
840
480
910
190
920
290
760
670
850
580
930
390
940
490
770
10,0,0
860
680
10,1,0
1,10,0
10,2,0
2,10,0
950
590
10,3,0
3,10,0
870
780
10,4,0
4,10,0
960
690
11,1,0
1,11,0
11,2,0
2,11,0
10,5,0
5,10,0
880
11,3,0
3,11,0
970
790
10,6,0
6,10,0
Fo
30.3
10.8
1.8
3.3
25.6
8.0
9.5
22.2
9.4
14.2
21-1
15-6
0
7.7
5.4
4-2
23.0
22.6
22.4
0
6-1
21.2
18.6
7.5
25.2
2-8
8-2
13.4
9.7
25.1
8.2
0
8.2
0
0
7-5
7.1
23-5
4-3
1.7
16.2
16.3
9.6
18.0
5.2
1.4
16.2
3.2
4.3
2.1
.Fc
31.I
-]0.]
-2.1
5.1
25.9
6.9
9.8
20.4
10-4
-13.6
-19.4
-15-5
1.1
--8-8
7.3
3.6
20-5
-20-7
-22.2
--0"7
--3.5
20.6
18.1
-8-0
-24.6
-2-9
-7.4
-12.7
7.9
-24-1
-8.4
-0.4
8.6
0
0.7
-5.7
-6.3
21.4
-4-2
1-1
-15.7
-15-1
9.4
16.7
5-6
-1-9
-16.4
2-5
4.1
1-8
* Values are given per stoiehiometrie molecule. When H is
odd, the structure factor is purely imaginary.
T a b l e 3 shows t h e o b s e r v e d a n d c a l c u l a t e d s t r u c t u r e
factors. T h e o b s e r v e d v a l u e s h a v e b e e n c o r r e c t e d for
e x t i n c t i o n ( e q u a t i o n (2)) a n d for t h e i m a g i n a r y p a r t
of t h e a n o m a l o u s d i s p e r s i o n in u r a n i u m ( e q u a t i o n (1)).
T h e f - c u r v e of T h o m a s - F e r m i as g i v e n in ]nternationale
Tabellen was u s e d for u r a n i u m , of M c W e e n y (1951)
for h y d r o g e n , a n d of B e r g h u i s et el. (1955) for t h e
o t h e r a t o m s . T h e following t e m p e r a t u r e factors w e r e
o b t a i n e d : B = 2.9 ~2 for u r a n i u m , a n d B = 3.6 /~2
for t h e fight a t o m s . T h e a g r e e m e n t b e t w e e n exp e r i m e n t a l a n d c a l c u l a t e d s t r u c t u r e factors corres p o n d s to
R = ~ I I F o I - l ~ o l l + X i F c l = 0-055.
W. H . ZACHAI%IASElXI AlkYD I-I. A. P L E T T I ~ G E R
B o n d lengths
The lengths of the bonds formed by the various a t o m s
in the s t r u c t u r e are"
lY-10i
-1 Oii
-3 OIII
-3 OIv
A
A
A
A
Oii-1 lY ----- 1.704-0.04 A
Na-3 Oiii = 2.394-0.04 A
- 3 0 i v = 2.36+0.04 A
Oiii-1 U = 2.47±0.02 A
-1 Na = 2.394-0.03 A
-1 CI = 1.264-0.05 A
C I - 1 CII
-10IH
-10iv
OIII-Ci-OIv
=
=
=
=
1.724-0.04
1"704-0.04
2.47+0.02
2.514-0.02
Oi-1 U
= 1.74±0.04 A
Oiv-1 U = 2.51±0.02 A
-1 Na = 2.364-0.04 A
-1 Ci = 1.28±0.04 A
= 1-52±0.05 A
= 1.26±0.05 A
= 1.28±0.04 A
,m 121 °
cii-1 cl = 1.52±0.05 A
-1 I-I~ = 1.1 (o.8) A
-IH~I
=
1.0 (1.5) A
-1 Hill = 1.0 (1.1) A
The bond lengths given in parentheses for the Cll-H
bonds correspond to the crude experimental values
for t h e h y d r o g e n coordinates.
u
t
oo,- o,
529
oxygen separations. The same configuration of oxygen
a t o m s a b o u t the h e a v y a t o m as observed in this
structure has previously been found in RbUO2(N03) a
(Hoard & Stroupe, 1949), K P u 0 2 C O a (Ellinger &
Zachariasen, 1954) a n d UO~C03 (Christ, Clark &
E v a n s , 1955; Cromer & H a r p e r , 1955). I n other
structures with six secondary bonds where the hexagon
does not share edges with radicals such as nitrate,
carbonate or carboxyl, the hexagon becomes puckered
so as to yield larger 0 - 0 or F - F separations. Such
puckered hexagons h a v e been found in CaUO202
(Zachariasen, 1948a), UO2F 2 (Zachariasen, 1948b),
K A m O 2 F 2 (Asprey, Ellinger & Zachariasen, 1954).
W h e n u r a n i u m forms five or four secondary bonds to
fluorine or oxygen a t o m s as in K3UO2F 5 a n d MgU0202,
there is no steric problem a n d the polygons are found
to be planar. I n other words, whenever sterically
possible the secondary bonds lie in the plane n o r m a l
to the X O 2 axis.
Since t h e Oi a n d 0ii a t o m s are bonded only to
uranium, detailed valence balance requires t h a t a
bond strength of s = 2-00 be assigned to each u r a n y l
bond a n d of s = ½ to each secondary bond. The bond
length v e r s u s bond s t r e n g t h curve previously published
predicts U - O I = U - O n = 1.60 A a n d U - O n I = U - O I v
= 2.6 A, as against the observed values of 1.71±0.04
A and 2.49+0.02 A. There is a similar discrepancy
between predicted a n d observed values in the UO2CO.~
structure where the bond strengths are t h e same as
in the present case. I n t h a t s t r u c t u r e the values are
1.67±0.09 A a n d 2-49±0.05 A for the two bond
lengths.
These observations show t h a t t h e bond length
versus
bond s t r e n g t h curve needs revision. The revised
curve is shown in Fig. 3, a n d in analytical form in
Table 4.
j.29~.26 ~
2.50
It'521
e-
t~
H~I(+O.I)
H,r(-0"8)
H~(+I'O)
Fig. 2 shows the configuration about a uranium atom and
within the acetate group, as seen along a three fold axis.
The uranium atom lies in the projection plane. Numbers
in parentheses give the height in A above this plane.
o, z o o
1'50
0
I
0.50
I
1.00
I
1.50
2.00
Bond Strength,s
The configuration a b o u t a u r a n i u m a t o m is shown
in Fig. 2. As F a n k u c h e n first pointed out, the space
group requires the u r a n y l group to be collinear. I t is
seen t h a t the two u r a n y l bonds, U - O I a n d U-OII,
are equal within experimental error, a n d so are the
secondary bond lengths, U - O r e a n d U-Oiv. The seco n d a r y bonds are v e r y n e a r l y at right angles (89 ° )
to the u r a n y l axis. E v e r y other edge of the hexagon
f o r m e d b y the O m a n d 0 i v atoms is a n edge of a
carboxyl group. I n this m a n n e r the h e x a g o n can be
p l a n a r w i t h o u t causing u n r e a s o n a b l y small o x y g e n -
Fig. 3 shows the variation of bond length with bond strength.
The experimental points shown are the results obtained
from the structural studies of KsUO2Fs, MgUO202 and
NaUO2 (O2CCH3)3.
The six Oiiz a n d Ozv a t o m s a b o u t sodium form a
slightly distorted octahedron, a n d the observed bond
lengths are close to the usual value for six coordination.
I n the acetate group the carbon a n d oxygen a t o m s
are coplanar within experimental error, a n d this plane
530
CRYSTAL
CHEMICAL
STUDIES
OF
THE
5f-SERIES
OF
ELEMEIVTS.
XXV
Table 4. U - O bond lengths as function of bond strengths
Uranyl bond
8
2.00
1.75
1.50
1.25
1.00
Bond length
-1.70 A
1.74
1.83
1.95
2.08
Six secondary bonds
t,
s
0-33
0.42
0.50
0.58
0.67
is n e a r l y n o r m a l (86 °) to the associated u r a n y l axis.
The distances a n d bond angles within the group agree
well with those observed in other acetates.
The crude experimental determination of the hydrogen coordinates places the H m a t o m in the same
plane as the carbon a n d oxygen atoms, a n d this
feature was retained in modifying the experimental
coordinates for the h y d r o g e n atoms so as to give more
reasonable C - H distances a n d bond angles. H - 0 distances outside a given acetate group are all greater
t h a n 2-7 /~, showing t h a t there is no real bonding.
The 0m--0~v distances are 2.21+0.05 /~ within a n d
2-76±0-05/~ between acetate groups. These are altern a t i n g edges of the nearly plane hexagon of oxygen
atoms a b o u t the u r a n i u m a t o m shown in :Fig. 2.
The :Fourier syntheses were carried out on X - R A C ,
while all other calculations were m a d e by hand. The
authors are deeply grateful to Prof. R a y m o n d Pepins k y for the generous a n d hospitable m a n n e r in which
he m a d e X - R A C available to us, and to the X - R A C
personnel for their valuable help.
Bond length
2.49 /~.
2.43
2.38
2.33
2-28
_
Four secondary bonds
^
s
0.50
0.63
0.75
0.88
--
Bond length"
2.38 A
2.30
2.23
2.15
--
References
ASPREY, L. B., ELLINGER, F. H. (% ZACHA_RIASEN,W. H .
(1954). J. Amer. Chem. Soc. 76, 5235.
BERGHUIS, J., HAA~APPEL, I J . M., POTTERS, M., LooPSTRA, B. O., MAcGF_~T,Av~y,C. H. & VEENENDA_A_L,A.L.
(1955). Acta Cryst. 8, 478.
CHaIST, C. L., CLARK, J. R. & EVANS, H. T. (1955).
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CROMER, DON T. & HARPER, PAI~L E. (1955). Acta Gryst.
8, 847.
DAUBEN, C. H. & TEMPLETON, D. H. (1955). Acta Cryst.
8, 841.
ELLINGER, F. H. (1956). Private communication.
ET.T.INGEa, F. H. & ZACm~mIASEN,W. H. (1954). J. Phys.
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FANKUCEEN, I. (1935). Z. Kristallogr. 91, 473.
HOARD, J. L. & STROUPE,J. D. (1949). National Nuclear
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MCWEENY, R. (1951). Acta Cryst. 4, 513.
ZAeHARIASEN, W. H. (1948a). Acta Cryst. 1, 281.
ZACHARIASEN,W. H. (1948b). Acta Cryst. 1, 277.
ZACHA-~IASEN, W. H. (1949). Acta Cryst. 2, 388.
ZACtIARIASEN, W. H. (1954a). Acta Cryst. 7, 795.
ZACHARIASEN, W. H. (1954b). Aeta Cryst. 7, 788.
ZACHARIASEN, W. H. (1954c). Acta Cryst. 7, 783.
Acta Cryst. (1959). 12, 530
An Account of s o m e Computing Experiences
B Y MICHAEL G. R O S S M A ~ , R O B ~ T
A. JACOBSO~, F. L. HIRSHFELD AND WILLIAM N. LIPSCOMB
School of Chemistry, University of Minnesota, Minneapolis 14, Minnesota, U . S . A .
(Received 10 November 1958)
Experience is summarized in the use of fractional shifts of scale, temperature and distance parameters, values of r = 2:w(IFo]2--JFcl2)2/2:wl•or 4, the behavior of temperature factors and a threedimensional Patterson superposition program in the determination of a number of structures.
The increasing availability of high-speed digital computers in crystallography m a k e s it desirable t h a t
general accounts of procedures and experience be
available. Certain changes and developments in known
methods, especially greater emphasis on three-dimensional methods, as well as the development of new
methods, are t a k i n g place in a n u m b e r of different
laboratories. The v a r i e t y of computers now available
renders an account of programs for some particular
computer of only special interest, but we feel t h a t a
more general s t a t e m e n t of computer experience a n d
techniques is of interest to crystallographers.
The R e m i n g t o n R a n d 1103 U N I V A C S C I E N T I F I C
high-speed digital computer, in use for crystallographic
computations in this l a b o r a t o r y for over three years,
has a larger m e m o r y t h a n computers for which similar
computations have been described (Bennet & Kendrew, 1952; A h m e d & Cruickshank, 1953; M a y e r &
Trueblood, 1953; Thompson, Caminer, Fantl, W r i g h t
& King, 1954; Cochran & Douglas, 1955; Friedlander,