Crystal structure of dipotassium tetranitroethide determined by single crystal X-ray diffraction technique

Dyke, M.

Sass, R. L.

English

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W N Maurice Dyke’ and Ronald L .  Sass  
,Department of Chemistry, W i l l i a m  Marsh Rice U n i v e r s i t y  
7 Houston, Texas 
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ABSTRACT 
The s t r u c t u r e  of dipotassium t e t r a n i t r o e t h i d e  K ( N 0  ) CC(N0 ) K has 
2 2  2 2  
been determined by s i n g l e  c r y s t a l  X-ray d i f f r a c t i o n  t echn iques .  
compound c r y s t a l l i z e s  i n  t h e  centro-symmetric space group C2/c wi th  c e l l  
c o n s t a n t s  of a = 13.03 A ,  b = 7.56 A ,  c = 13.55 A ,  and 4 = 140.87O. 
u n i t  c e l l  con ta ins  fou r  molecules ,  w i th  t h e  anions cen te red  on two-fold 
r o t a t i o n  a x e s .  Atomic and thermal v i b r a t i o n  parameters were r e f i n e d  by 
i s o t r o p i c  l e a s t  squa res  method t o  g ive  a f i n a l  s t r u c t u r e  with an R value 
of 12.3%. The c o n f i g u r a t i o n  of each carbon atom and i t s  t h r e e  s u b s t i t u e n t s  
is  p l a n a r  w i t h i n  experimental  e r r o r .  There i s  a t w i s t i n g  of t he  n i t r o g e n  
atoms about t h e  C-C molecular  ax i s  t o  produce an ang le  of 63.1 between 
t h e  N-C-N planes i s  t h e  t e t r a n i t r o e t h i d e  anion.  The C-C bond d i s t a n c e  i s  
1.43 A .  
The 
Each 
0 
INTRODUCTION 
I n  previous i n v e s t i g a t i o n s ,  t h e  c r y s t a l  s t r u c t u r e s  of t he  s t a b l e  
2 3 
ca rban ion  s a l t s  ammonium tr icyanomethide , pyridinum dicyanomethylide , 
and potassium pa ran i t ropheny ld icyanmeth ide  were determined. It *as thought 
t h a t  t h e  s t r u c t u r e  de t e rmina t ion  of dipotassium t e t r a n i t r o e t h i d e  
K ( N 0  ) CC(N0 ) K would be an i n t e r e s t i n g  e x t e n s i o n  of the  previous work 
because t h i s  s a l t  c o n t a i n s  a p o l y n i t r o - s u b s t i t u t e d  d i ca rban ion .  
4 
# 
2 2  2 2  
https://ntrs.nasa.gov/search.jsp?R=19670022949 2020-03-12T11:16:33+00:00Z
EXPERIMENTAL 
Dipotassium t e t r a n i t r o e t h i d e  was prepared from t h e  r e a c t i o n  of 
t r i b r m o n i t r o m e t h a n e  wi th  a n  anhydrous e t h a n o l  s o l u t i o n  of potassium 
iod ide  .by t h e  method of H ~ n t e r . ~  Well formed rhombohedral s i n g l e  c r y s t a l s  
of dipotassium t e t r a n i t r o e t h i d e  were ob ta ined  by l e a v i n g  l o o s e l y  covered 
beakers  of a s a t u r a t e d  s o l u t i o n  prepared from t h e  p u r i f i e d  s a l t  and water 
a t  room temperature  i n  a r e f r i g e r a t o r  u n t i l  t he  c r y s t a l s  formed. 
C r y s t a l s  w i th  a diameter  of about 0 . 2  mm were s e l e c t e d  a s  specimens 
f o r  X-ray d i f f r a c t i o n  a n a l y s i s  and mounted on g l a s s  f i b e r s .  Weissenberg 
and Ro ta t ion  photographs showed the dipotassium t e t r a n i t r o e t h i d e  u n i t  
c e l l  t o  be monocl inic  wi th  c e l l  cons t an t s  of a = 13.02 2 0.02 A ,  
b = 7.56 2 0.02 A ,  c = 13.55 5 0.02 A ,  and 8 = 140.87 5 0.50'. 
r o t a t i o n  a x i s  ilas found t o  be co inc iden t  w i t h  t h e  needle  a x i s  of t h e  
c r y s t a l  while t h e  b r o t a t i o n  a x i s  w a s  pe rpend icu la r  t o  t h e  needle  a x i s  and 
c o i n c i d e n t  w i th  t h e  s h o r t e r  edge d i agona l  of t h e  n e e d l e .  
The c 
A l l  r e f l e c t i o n s  with h + k = 2n + 1 were a b s e n t ,  i n d i c a t i n g  a C 
c e n t e r e d  u n i t  c e l l .  Sys t ema t i c  absences were a l s o  observed f o r  hOf 
r e f l e c t i o n s  wi th  9 = 2n + 1 which showed t h e  presence of a c g l i d e -  
p l ane  pe rpend icu la r  t o  t h e  b a x i s .  
The cen t ro - symet r i c  space group C2/c-C6 and t h e  noncentro-synrmetric 2h 
4 
space  group C c - C  are t h e  only monocl inic  space groups c o n t a i n i n g  symmetry 
elements  c o n s i s t e n t  with t h e  above absences.  These space groups can no t  
b e  d i s t i n g u i s h e d  from each o t h e r  on t h e  b a s i s  of s y s t e m a t i c  absences .  
However, ou r  refinement of a t r i a l  s t r u c t u r e  de r ived  by t h e  assumption of 
centrosymmetric.  symmetry i n d i c a t e s  t h a t  C2/c i s  t h e  c o r r e c t  space group 
for  dipotassium t e t r a n i t r o e t h i d e .  
S 
An expe r imen ta l  d e n s i t y  de t e rmina t ion  by t h e  f l o t a t i o n  method u s i n g  a 
m i x t u r e  of CH B r  and CC14 gave a v a l u e  of 2 . 2 4  g/cc.  Comparison of t h i s  2 2  
-2- 
va lue  wi th  t h e  t h e o r e t i c a l  d e n s i t y  of 0.58 g/cc f o r  each molecule of 
compound contained i n  t h e  u n i t  c e l l  showed t h e  m u l t i p l i c i t y  t o  be f o u r .  
I n t e g r a t e d  i n t e n s i t i e s  f o r  530 independent r e f l e c t i o n s  were recorded 
on m u l t i p l e  f i l m s  u s i n g  a Nonius i n t e g r a t i n g  Weissenberg camera and n i c k e l  
f i l t e r e d  CuK r a d i a t i o n .  Weissenberg d a t a  were obtained around t h e  b 
r o t a t i o n  a x i s  f o r  k = 0 through 4 and around t h e  c r o t a t i o n  a x i s  f o r  
1. = 0 through 6 .  The i n t e g r a t e d  i n t e n s i t y  va lues  were measured wi th  a 
Welch Densichron dens i tome te r .  Correct ions were app l i ed  f o r  t h e  Loren tz ,  
p o l a r i z a t i o n ,  and Tunnel1 e f f e c t s .  No c o r r e c t i o n s  were made f o r  abso rp t ion  
and e x t i n c t i o n .  
2 
Our i n i t i a l  assumption of C 2 / c  c e l l  symmetry w i l l  e i g h t f o l d  general  
p o s i t i o n s  and t h e  observed m u l t i p l i c i t y  of fou r  implied t h a t  t he  c e n t e r  of 
each t e t r a n i t r o e t h i d e  anion w a s  on a twofold a x i s  or  a c e n t e r  of symmetry 
i n  a u n i t  c e l l  c o n t a i n i n g  one potassium ion  a t  each of e i g h t  gene ra l  p o s i t i o n s .  
S y n t h e s i s  of t h e  [ 010 ] P a t t e r s o n  p r o j e c t i o n  y i e l d e d  a heavy peak a t  
u = 0.75 and w = 0.60  from which t h e  :: and z t r i a l  parameters  of t h e  
potassium ion were o b t a i n e d .  The [ 010 ] s u p e r p o s i t i o n  p r o j e c t i o n  was 
c a l c u l a t e d  v i a  t h e  CY 
r e l a t i v e  i n t e n s i t i e s  of t h e  observed hO!, r e f l e c t i o n s .  An image of a 
t e t r a n i t r 0 e t h j . d e  anion c e n t e r e d  on a twofold a x i s  was l o c a t e d  i n  t h e  
s u p e r p o s i t i o n  p r o j e c t i o n .  The p o s i t i o n s  of t h e  peaks i n  t h i s  image were 
used t o  c a l c u l a t e  t h e  x and z anion parameters f o r  a two-dimensional 
t r i a l  s t r u c t u r e .  A l e a s t - s q u a r e s  ref inement  of t h e s e  parameters reduced 
t h e  R from an i n i t i a l  v a l u e  of 39% t o  a f i n a l  v a l u e  of 16%. 
s y n t h e s i s 6  u s i n g  t h e s e  t r i a l  parameters and t h e  
gen 
Heavy atom peaks i n  t h e  three-dimensional  P a t t e r s o n  s y n t h e s i s  showed 
t h e  y parameter  of t h e  potassium i o n  t o  be 2 0.092 or 0.408 w i t h  t h e  
c h o i c e  of s i g n  s e r v i n g  t o  determine t h e  d i r e c t i o n  of t h e  p o s i t i v e  b a x i s  i n  
t h e  c o o r d i n a t e  system. The P a t t e r s o n  f u n c t i o n ' s  i n h e r e n t  twofold ambiguity 
i n  t h e  numerical  va lue  of t h e  heavy atom y parameter  was r e so lved  by 
-3-  
t e s t i n g  t h e  r e l a t e d  t r i a l  s t r u c t u r e s  f o r  agreement wi th  t h e  experimental  d a t a .  
The anion y parameters f o r  t h e  three-dimensional  t r i a l  s t r u c t u r e  were obtained 
from packing c o n s i d e r a t i o n s  and the knowledge t h a t  t h e  anion must possess  
a twofold r o t  a t  i on  a x i s  . 
RESULTS 
A three-dimensional  i s o t r o p i c  l e a s t - s q u a r e s  refinement was used t o  
reduce t h e  R of t h e  t r i a l  s t r u c t u r e  from 43% t o  12.3%. The c a l c u l a t i o n  
w a s  done w i t h  an  IBM 7094 computer u s i n g  t h e  l e a s t - s q u a r e s  a n a l y s i s  
program OWLS w r i t t e n  by Busing, Mar t in ,  and Levy. Unobserved r e f l e c t i o n s  
were omit ted from t h e  ref inement .  During t h e  l a t t e r  s t a g e s  of t h e  refinement 
t h e  o r i g i n a l  u n i t  weight ing scheme was abandoned i n  f avor  of a modified 
L Hughes we igh t ing  scheme. With t h i s  scheme w was s e t  equa l  t o  1/F f o r  a l l  
4 F ' s  l a r g e r  t h a n  4F . For a l l  o t h e r  F ' s ,  a w of 16 F:in/F w a s  used*. m i n  
Table  1 gives  t h e  f i n a l  atomic parameters ob ta ined  by t h e  refinement and 
t h e i r  e s t ima ted  s t a n d a r d  d e v i a t i o n s .  
DISCUSSION 
Figure  1 sho s t h e  [ 010 ] p r o j e c t i o n  of t h e  c r y s t a l  s t r u c t u r e  of 
dipotassium t e t r a n i t r o e t h i d e .  The i n t e r a t o m i c  d i s t a n c e s  and ang le s  i n  t h e  
t e t r a n i t r o e t h i d e  d i a n i o n  a r e  shown i n  Table  2 .  I n  nitromethane t h e  C - N  
and N-0 bond l e n g t h s  a r e  1 .46  and 1 . 2 1  r e s p e c t i v e l y . 8  
l eng then ing  of t h e  N - 0  bond and a s h o r t e n i n g  of t h e  C-N bond i n  t h e  
t e t r a n i t r o e t h i d e  i o n .  These changes may be a t t r i b u t e d  t o  resonance 
Thus t h e r e  i s  a 
2- 
w- i n t e r a c t i o n s  of t h e  type R -N+ 2 
Perhaps t h e  most s t r i k i n g  f e a t u r e  of t h e  t e t r a n i t r o e t h i d e  a n i o n ' s  
s t r u c t u r e  i s  t h e  t w i s t  of t h e  n i t r o g e n  atoms about t h e  C 1 - C 2  molecular  
axis t o  produce a n  ang le  of 63.1 0 between t h e  N l - C 2 - N 2  and N 3 - C l - N 4  
* A t a b l e  of observed and c a l c u l a t e d  s t r u c t u r e  f a c t o r s  can be ob ta ined  
by w r i t i n g  t h e  a u t h o r s .  
- 4- 
p l a n e s .  
w i th  t h e  N l - C 2 - N 2  plane r e s p e c t i v e l y .  
The 01-N1-02 and 03-N2-04 planes make ang le s  of 13.0' and 6.3' 
A t o m  N 1  i s  0.017 A above the 01-Ci-02 p l ane  while  N 2  i s  0.035 A 
below t h e  03-C2-04 p l a n e .  The carbon atom C 2  is  0.040 A below t h e  plane 
of i t s  s u b s t i t u t e n t s  N 1 ,  N2, and C 1  i n d i c a t i n g  a p l ana r  carbanion 
c o n f i g u r a t i o n  w i t h i n  t h e  l i m i t s  of t h e  experimental  e r r o r .  
The v i b r a t i o n s  i n  the conf igu ra t ions  of t h e  two n i t r o  groups may be 
due t o  f o r c e s  i n  the  c r y s t a l  l a t t i c e  s i n c e  each of t h e  n i t ro -g roup  oxygens 
is  i n  a d i f f e r e n t  chemical environment i n  t h e  l a t t i c e .  Each oxygen atom 
has two potassium ions as i t s  n e a r e s t  i n t e rmolecu la r  atomic neighbors 
wi th  corresponding 0 - K  d i s t a n c e  of 2.81 and 2.87 A f o r  01 ,  
2.79 and 3.00 A f o r  02 ,  2.68 and 2.85 A f o r  03 ,  and 2 .76  and 2.84 A f o r  
0 4 .  The s h o r t e s t  0-0 i n t e rmolecu la r  d i s t a n c e  i s  3.09 A a c r o s s  a c e n t e r  
of symmetry. The s h o r t e s t  K-C approach i s  4.00 A .  The minimum 0 - K  
d i s t a n c e  of 2 .68 A i s  c o n s i s t e n t  v i t h  t h e  v a l u e s  of 2.73 A i n  potassium 
paranitr~phenylidicyanomethide~, 2.70 A i n  dipotassium n i t r o a c e t a t e  9 , 
10 and 2.68 A i n  potassium b ica rbona te  . 
Acknowledgments. Th i s  work was supported by g r a n t s  from the  Na t iona l  
Aeronaut ics  and Space Adminis t ra t  i on  and the  Robert A .  Welch Foundat ion 
of Houston, Texas.  The 7094 computer c a l c u l a t i o n s  were done a t  the 
Common Research Computer F a c i l i t y  l o c a t e d  i n  the Texas Medical Center  and 
supported by USPE Grant ,FR-00254. 
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.. 
I -  
* 
REFERENCES 
1. Presen t  address :  Department of Chemistry,  Sam Houston S t a t e  Co l l ege ,  
H u n t s v i l l e ,  Texas 
2 .  R .  Des ide ra to  and R .  S a s s ,  Acta  C r y s t . ,  l8, 1 (1965).  
3 .  C .  Bugg and R .  Sass, Acta C r y s t .  , l.8, 591 (1965). 
4 .  C .  Bugg and R .  Sass,  Acta  Crys t .  , i n  press .  
5 .  C .  Hunter ,  2. Chem. Soc. , 543 (1923).  
6. G .  N .  Ramachandran and S .  Roman, Acta C r y s t .  , l2, 957 (1959). 
7. W. R .  Busing,, K .  0 .  Mar t in ,  and H .  A .  Levy, 'I OR FLS, A FORTRAN 
C r y s t a l l o g r a p h i c  Least-Squares Program", ORNL-TM-305 , Oak Ridge 
Na t iona l  Labora tory ,  Oak Ridge , Tenn. , 1962. 
8 .  L .  0 .  Brockway, J .  Y .  Beach, and L .  Pau l ing ,  J. &. Chem. %. , 
- 57,  2693 (1935).  
9 .  D .  S u t o r ,  F .  J .  Lelewellyn,  and H .  S .  Moslen, Acta  C r y s t . ,  L ,  
145 ( 1 9 5 4 ) .  
10. I .  N i t t a ,  Y .  Tomiie,  and C .  Hoe Koo, Acta C r y s t . ,  5,  292 (1952) .  
- 6- 
.. 
Atom 
c2 
01 
02 
03 
04 
N 1  
N2 
K 
TABLE 1 
Final A t o m i c  Parameters f o r  K C N 0 2 2 4 8  
X 
0 .5621 (14) 
0.4144 (13) 
0.6274 (14) 
0.7322 (11) 
0.8270 (12) 
0.5371 (13) 
0.7098 (13) 
0.3725 ( 3) 
Y 
0.5459 (16) 
0.7313 (14) 
0.6177 (18) 
0.4054 (15) 
0.4750 (15) 
0.6359 (15) 
0.4692 (15) 
0.0999 ( 5) 
Z 
0.3335 (13) 
0.3173 (12) 
0.5431 (14) 
0.3553 (11) 
0.3701 (12) 
0.4042 (13) 
0.4216 (12) 
0.3012 ( 4) 
B 
0 .45  (19) 
1.62 (19) 
2.67 (24) 
1.33 ( 1 7 )  
1.49 (18) 
0.82 (19) 
0 .51 ( 1 7 )  
0 .96  ( 7) 
.. 
Dis tance  
Cl-C2 
C2-Nl 
C 2 -N2 
N 1 - 0 1  
N1-02 
N2-03 
N2-04 
N 1  -N2 
N2 -N4 
N l - N 3  
01-02 
03-04 
01-06 
03-08 
01-03 
01 -04 
02-03 
02-04 
TABLE 2 
In t e ra tomic  Dimensions i n  K C N 0 
2 2 4 8  
1.43 (2) A 
1 .40 (2) 
1 .38  (2) 
1 .24  (2) 
1 .23  (2) 
1 .24  (2)  
1 .27  (2) 
2.43 (2) 
3 .06  (2) 
3 .06  (2) 
2.15 (2) 
2 .17 (2) 
2 .87 (2) 
2.87 (2) 
4.49 (2) 
3.98 (2) 
4 .04 (2) 
2 .57  (2) 
Angle 
0 1 - N 1 - 0  2 
03 -N2-04 
0 1 - N 1  -C2 
03-N2-C2 
0 2 - N 1  -C2 
04-N2-C2 
Nl-C2-N2 
N 1  -C2-C 1 
N2-C2-C 1 
121 (2)" 
119 (2) 
116 (2) 
119 (2) 
122 (2) 
120 (2) 
121 (2) 
120 (2) 
118 (2) 



The crystal structure of dipotassium tetranitroethide

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