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Crystal structures of some group V compound Zobel, Tessa 1965

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CRYSTAL STRUCTURES OF SOME GROUP V COMPOUNDS by TESSA ZOBEL B.Sc.(Hons.), U n i v e r s i t y of B r i s t o l , 1963  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of CHEMISTRY  We accept t h i s standard  t h e s i s as conforming to the r e q u i r e d  THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1965  In the  requirements  British  mission  f o r an  Columbia, I  available  for extensive be  cation without  of my  Department  this  and  by  2*^  degree at  the  study,  the  of  permission.  CAg-A^iYT  /M^t  I  this  Head  Columbia,  AST  the  fulfilment  of  U n i v e r s i t y of  Library shall  make i t  f u r t h e r agree  that  freely per-  thesis for scholarly  o f my  I t i s understood  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  Date  thesis i n partial  thesis for financial  written  of  that  copying  granted  representatives.  this  advanced  agree  for reference  p u r p o s e s may his  presenting  Department  that.copying  gain  shall  not  or or  be  by publi-  allowed  ABSTRACT The  c r y s t a l and molecular s t r u c t u r e of c a c o d y l i c  acid,  (CH^^AsO.OH, has been determined by X-ray d i f f r a c t i o n of a single c r y s t a l .  The c r y s t a l s belong to the- t r i c l i n i c  system  w i t h a = 6.53, b = 6.82, c = 6.61 A, a = 77°30», P = 78°45», if = 5 5 ° 9 , z = 2, space group Pl". 1  The s t r u c t u r e was determined  from v i s u a l i n t e n s i t y data by P a t t e r s o n and  and F o u r i e r methods,  the p o s i t i o n a l and a n i s o t r o p i c thermal parameters were  r e f i n e d by l e a s t - s q u a r e s . 0,149  The f i n a l discrepancy f a c t o r i s  f o r 806 observed r e f l e c t i o n s . The  s t r u c t u r e c o n s i s t s of centrosymmetrical, hydrogeno  bonded dimers, w i t h 0-H...0 d i s t a n c e s  of 2.57A, the a r s e n i c  atoms having a t e t r a h e d r a l c o n f i g u r a t i o n w i t h bond angles i n the range 106°  - 115°.  C r y s t a l s of antimony t r i i o d i d e , S b l ^ , are rhombohedral o o _ w i t h ay = 7.48 A, Cjj = 20.90 A, z = 6, space group R3. The s t r u c t u r e was determined from h0.£ P a t t e r s o n ,  F o u r i e r and  d i f f e r e n c e p r o j e c t i o n s , the f i n a l discrepancy f a c t o r being 0,1314.  The antimony atoms are s i g n i f i c a n t l y d i s p l a c e d from the  centres  of i q d i n e octahedra, and have three near- neighbour o i o d i n e atoms a t 2.868 + 0.010 A, w i t h I-Sb-I = 95.8 + 0.3 , o 0  and three  f u r t h e r o f f at 3.316 + 0,010 A,  thus intermediate Asl^,  The s t r u c t u r e i s  between that of a molecular c r y s t a l , as i n  and an i o n i c arrangement. o C r y s t a l s of B i l  3  have a  R  = 7.52 A, c  o H  = 20.72 A«  Com-  p a r i s o n of measured and c a l c u l a t e d povder i n t e n s i t i e s suggests t h a t the bismuth atom i s s i t u a t e d a t the centre  of an i o d i n e  octahedron, so that the s t r u c t u r e i s probably l a r g e l y i o n i c .  Lone-pair s t e r i c e f f e c t s , as w e l l as changes are thought r e s p o n s i b l e  i n bonding  character,  f o r the d i f f e r e n c e s i n the c r y s t a l  s t r u c t u r e s of A s l - , S b l - and B i l - .  iii  ACKNOWLEDGEMENT S I t i s my Dr«  pleasant duty to express my  James T r o t t e r f o r h i s guidance and  thanks to  constant  encouragement  throughout the course of t h i s work. I would a l s o l i k e to thank Dr» W.R,  G u l l e n , who  suppli  the c r y s t a l sample of c a c o d y l i c a c i d , and made h i s l a b o r a t o r y f a c i l i t i e s a v a i l a b l e to me  f o r p r e p a r a t i v e work*  iv  TABLE OP CONTENTS Page TITLE PAGE  ....••»•••••*«••••»•.•••  ABSTRACT  .,  ACKNOWLEDGEMENTS  •  v  LIST OF FIGURES  ••  LIST OF TABLES  II.  i i iv  TABLE OF' CONTENTS  I»  i  vi v i i  THE STRUCTURE OF CACODYLIC ACID A.  Introduction  ............................  B.  Experimental  C.  Structure A n a l y s i s ......................  2  D.  Discussion  8  » . . . . » • • • » a . . . . . . . . . .  ..............................  1 1  THE STRUCTURES OF ANTIMONY AND BISMUTH TRIIODIDES A.  Introduction  B.  Experimental  C.  Structure Analysis  D.  Discussion  APPENDIX.  I ...........  11 12  ..............  13 19  CALCULATION OP THE LATTICE CONSTANTS OF BISMUTH TRIIODIDE .........  REFERENCES ....•••••••«».««»».«»«*».»... »•»«•«»<»«>»  v  24 26  LIST OF FIGURES Figure  Page CACODYLIC ACID  1  2  Superimposed s e c t i o n s of the three dimensional e l e c t r o n - d e n s i t y d i s t r i b u t i o n through the atomic centres p a r a l l e l to (OOl), and a p e r s p e c t i v e view of the molecule.  4  Packing of the molecules, p r o j e c t e d along the b - a x i s .  10  ANTIMONY TRIIODIDE 3  E l e c t r o n d e n s i t y p r o j e c t i o n along the b-axis.  vi  14  LIST OP TABLES  CACODYLIC ACID F i n a l measured and c a l c u l a t e d s t r u c t u r e factors P o s i t i o n a l parameters, with standard d e v i a t i o n s , and temperature f a c t o r s Bond lengths and valency angles, with standard d e v i a t i o n s Shorter i n t e r m o l e c u l a r d i s t a n c e s ANTIMONY AND BISMUTH TBIIODES C r y s t a l data F i n a l measured 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 . (Antimony t r i i o d i d e ) F r a c t i o n a l p o s i t i o n a l parametersj atomic d i s t a n c e s and bond angles  inter-  2 F i n a l measured and c a l c u l a t e d F (Bismuth t r i i o d i d e )  vii  values.  1 I.  CACODYLIC ACID  A. The  Introduction  s t r u c t u r e of c a c o d y l i c a c i d , d i m e t h y l a r s i n i c  (CH^) As0.0H was  determined i n order to i n v e s t i g a t e  2  stereochemistry  of the a r s e n i c atom, and  p o s s i b i l i t i e s i n the c r y s t a l .  I t was  the  acid,  the  hydrogen-bonding  expected that  the  s t r u c t u r e would involve e i t h e r hydrogen—bonded dimers as i n c a r b o x y l i c a c i d s , or endless s p i r a l s of molecules, and  that  the a r s e n i c atom would have a t e t r a h e d r a l c o n f i g u r a t i o n i n other As  compounds. B.  Experimental  C r y s t a l s of c a c o d y l i c a c i d are  c o l o u r l e s s prisms elongated  along the a-axis, w i t h (100), (010), and d e n s i t y was  (001)  developed.  the u n i t c e l l dimensions and  space group were  determined from r o t a t i o n f i l m s about the a — a x i s , 0k£ h0£  and  hkO  precession  Veissen-  photographs.  C r y s t a l Data (X, Cu - Ka = 1.5418A; X, Mo  - Ka = 0.7107A)  Cacodylic  138,0; m.p.  a c i d , C H 0 A s ; M, 2  T r i c l i n i c , a = 6.53 c = 6.61 •  7  2  + 0.01, +  b = 6.82  200°C  +0.01,  0.01A  a =. 77°30' + 5 ' , P = 78°45' ± 5 \  V=  55°9 * +  03  Volume of the u n i t c e l l = 234.9A -3 m g* * » z = 2, D = 1.95 D  =  The  measured by f l o t a t i o n i n a chloroform-bromoform  mixture, and  berg, and  as  1 , 9 5  c m  x  g.cm.  -3  5  1  A b s o r p t i o n c o e f f i c i e n t f o r X-rays, A = 1.5418A, -1 u = 95 cm. ot  P(000) = 136 No absent r e f l e c t i o n s ; space group P l or P l ; P l from s t r u c t u r e The  analysis  i n t e n s i t i e s of the r e f l e c t i o n s were measured v i s u a l l y  from Cu-Koc e q u i - i n c l i n a t i o n Veissenberg f i l m s of the 0k£ .. . 5k£ layers.  Two sets of f i l m s were taken f o r each l a y e r to record  the whole of r e c i p r o c a l space, and the v a r i o u s c o r r e l a t e d by c a r e f u l l y timed exposures. s e c t i o n was 0.2 x 0.2 mm.,  as usual  Patterson  e r r o r s are s m a l l ,  The s t r u c t u r e amplitudes were  f o r the 806 observed r e f l e c t i o n s . C.  The  The c r y s t a l c r o s s -  so that absorption  and. no c o r r e c t i o n s were a p p l i e d . derived  l a y e r s were  Structure  Analysis  a r s e n i c p o s i t i o n was determined from the three  axial  p r o j e c t i o n s , and the carbon and oxygen atoms were  l o c a t e d on a three-dimensional e l e c t r o n - d e n s i t y d i s t r i b u t i o n computed with signs based on the a r s e n i c The  contributions  alone.  map could be i n t e r p r e t e d i n terms of space group P l .  Structure factors  1  atoms.  f a c t o r s were c a l c u l a t e d using  standard s c a t t e r i n g  °2 , and an i s o t r o p i c temperature f a c t o r , B = 4.OA for a l l The discrepancy  factor,  R =  ^-l  F 0  ~  F c  l/ 2 F  Q  was 0.270  f o r the observed r e f l e c t i o n s . The  p o s i t i o n a l and thermal parameters, and an o v e r a l l  scale f a c t o r , were r e f i n e d by (block—diagonal) the f u n c t i o n minimized was  2w(F  when | F | < 1 8 , and V"w = 1 8 / | F J q  - P ) , with o c  when | F | ^ 1 8 . Q  least-squares; s/w = I F | / l 8 'o Three c y c l e s  w i t h i s o t r o p i c thermal parameters and three c y c l e s w i t h a n i s o t r o p i c thermal parameters completed 806  observed r e f l e c t i o n s , was A F  was  the refinement.  R, f o r the  reduced from 0.270 to 0.149, and  reduced from 6.9  x 10  to 2.9  x 10 .  measured 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 are l i s t e d  Final i n Table  1, and a f i n a l e l e c t r o n d e n s i t y d i s t r i b u t i o n i s shown i n F i g . 1 Co-ordinates and Molecular Dimensions The  f i n a l p o s i t i o n a l and a n i s o t r o p i c thermal parameters  are given i n Table 2.  x, y and z are f r a c t i o n a l co-ordinates  r e f e r r e d to the t r i c l i n i c  c r y s t a l axes; o  <f (x),  ^ ( y ) , and  are t h e i r standard d e v i a t i o n s ( i n A) computed from the squares r e s i d u a l s  (see Appendix);  X', J\  C^(z)  least-  and Z' are c o - o r d i n a t  i n A r e f e r r e d to orthogonal axes a' (= a . s i n c f ) , b, and  c*  (normal to a' and b ) ; b.. are the thermal parameters i n the expression: exp - ^b-j^-j^h + b h k + b 2  1 2  and  1 3  h£ + b  2 2  k  2  + b  k ^ + b^C  "j.  2  2 3  are the components of the mean—square v i b r a t i o n tensors The bond lengths and valency angles i n the molecule  g i v e n , w i t h t h e i r standard d e v i a t i o n s , i n Table 3. i n t e r m o l e c u l a r contacts are l i s t e d of  the molecules  are  The s h o r t e r  i n Table 4, and the packing  i s shown i n F i g . 2.  P i g . 1»  o  i  zK  Superimposed s e c t i o n s of the three-dimensional electron—densityd i s t r i b u t i o n through the atomic centres p a r a l l e l to. (OOl), contours at a r b i t r a r y i n t e r v a l s , a r s e n i c omitted f o r c l a r i t y . A p e r s p e c t i v e drawing of the molecule i s also shown.  5 Table 1 P i n a l measured and c a l c u l a t e d s t r u c t u r e > » * > obs. c a l c . respectively. h  k  F  0 0 0 0 0 0 0 0 0 a 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o ' 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 "0" 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 V 1 1 1 1 1 1 1 1 1 1  a  0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2" 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 5 5 5 S 5 5 5 5 5 5 5 5 6 6 6 6 6 6 6 6 7 7 1 I 1 1 1 I 3 0 0 0 0 0 b 0 0 0 0 0  l 2  1  4 5 6 7  n  b  -8 -7 1 2 3 4 5 6 7 8 -8 -7 -6  factors,  Columns are  F  2 7.3 34.2 -49.2 45.2 2 3.7 - 3 0 . 7" 1.6 -0.8 11.9 9.8 9.3 11.3 0. -0.3 6.6 -8.1 2.9 "3.0 9.6 11.5 5.6 7.6 13.2 -16.6 55.4 -44.5 18.0 -23.1 52.7 48.2 74.1 74.3 13.3 8.0 -5.9 8. 3 8.4 -9.1 3.2 4.6 '9. ; " 1 1 . 0 5.0 5.1 27.5 -?5.4 37.7 -41.7 2.5 3.4 45.4 50.0 22.9 17.5 20.6 -18.1 37.6 -29. 1 17. 3 - 1 2 . 4 22.0 19.0 31.9 26.2 9.3 7.1 10.1 -8.3 9.0 -8.4 8.4 8.6 2.0 -2.1 19.2 -20.4 2 3.8 -21.2 8.7 9.3 42. 3 34. 1 10.2 12.8 40.3 -34.0 44.9 -35.9 1.7 1 .;9r 24 29.4 20.1 18.8 3.4 2.5 8.1 -7.8 3.5 5.3 5. 3 -6.6 13. 1 - 1 3 . 9 4.5 -3.5 16.1 14.8 19.3 20.5 0. -1.8 37.3 -32.8 30.4 -26.6 6.2 6.2 25.5 20.2 16.2 12. 1 2.5 -1.7 10.2 -9.2 4.6 -5.7 15.4 -9.4 2.6 2.7 18.0 19.3 16.5 13.1 14.4 -12.5 31.3 -23. 7 11.7 -10.8 6.4 6.2 16.7 13.9 8.8 7.3" 6.8 -6.9 3.4 4.7 14.6 13.3 7.9 6. 7 14.8 -11.8 16:7 -15.0 3.1 -3.0 8.7 8.7 8.6 11.0 5.8 -7.4 7.7 -8.4 27.4 -36.6" 15.6 -22.4 6.4 9.5 18.2 23.0 9.3 10.6 2.6 -4.6 4.3 6.6 19.9 -26.4 21.6 -37.1 1.7 -3.9 28.8 26.5 24.8 25.9 0. 1.9 10.4 -12.7 6.5 -7.8 0. 0.1 9.6 9.8 10.7 9.1  8  -7 -6 -5 -4 -3 -2 -1 0 1 7 8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 -3 -2 -1 0 1 2 3 4 0 1 2 3 4 5  d  1 0 -5 6.1 -7.7 1 0 -4 27. 1 -27. 1 1 0 -3 27.4 -31.3 1 0 -2 0. 3.0 1 0 -1 56.9 58.4 1 0 0 35.7 40.4 1 1 -7 9.2 10.4 1 1 -6 5.6 5.0 1 1 -5 9.0 -10.3 1 1 -4 25.2 -24.4 1 1 -3 22.9 -24.7 1 1 10.4 -2 5.6 1 1 -1 42.9 52.3 1 1 0 10.2 13.5 1 1 1 -56.1 50.8 1 1 2 -45.6 44.5 1 1 10.4 3 12.2 1 1 41.5 4 35.6 1 1 5 21.4 23.7 1 1 6 8. 1 -5.8 1 1 7 12.0 -12.8 1 1 8 3.7 -4.0 9.1 1 2 -7 8.7 1 2 "-6 4.2 4. 1 -12.9 1 2 -5 11.4 1 2 -4 16.4 -21.7 1 2 -3 0. -0.9 1 2 -2 19.1 25.5 1 2 -1 15.4 20.9 1 2 0 6.7 -11.6 1 1 2 -55.9 46.6 1 2 2 54.7 -49.4 1 2 3 16.4 20.6 1 2 4 35. 1 46.0 1 2 5 13.8 12.1 1 2 6 17.9 -13.1" 7 1 2 10.4 -9.5 1 2 8 0. -0.1 1 3 -7 5.0 6.0 1 3 -6 0.6 2.2 1 3 -5 10.7 -11.3 1 3 -4 12.0 -12.8" 1 3 -3 9.7 9.8 1 3 -2 32.5 29.0 1 3 -1 15.3 17.3 1 3 0 31.4 -31.5 1 3 64.9 -58.7 1 1 3 " 2" 25T4 -21.3 1 3 3 30.7 45.2 1 3 4 36.4 , 27.6 1 3 5 0. -2.3 1 3 6 14.6 -13.7 1 3 7 8.6 -7.6 1 3 8 0. 2.0 1 4 -6 2.8 -4.2 1 4 -5 8.8 -8.4 -2.4 1 4 -4 3.6 1 4 -3 11.3 12. 1 1 4 -2 29. 7 27.5 14.0 1 4 -1 13.8 -34. 1 1 4 0 35.4 1 1 4 51.8 -43.8 1 4 2 8.3 5.2 1 4 3 37.1 30.0 1 4 4 11.0 9.7 1 4 " 5 " "10.8 - 10'. 1 1 4 6 -14.1 12.3 1 4 7 6.2 -6.9 1 4 8 4.7 0.5 1 5 -5 5.5 -7.4 1 5 -4 0. 1.7 1 5 -3 17.4 15.4 1 5 -2 17.9 19.5 1 5 -1 0. -2.0 I 5 0 31.0 -25.3 19.9 1 5 1 -16.3 13.7 i 5 2 14.2 1 5 3 22.9 21.5 1 5 4 ' 4.6 5.7 12.4 1 5 5 -13.1 1 5 6 14.7 -15.8 1 5 7 2.0 -3.5 15.9 13.7 I 6 -3 9.4 1 6 -2 10.2 12.4 1 6 -1 -11.1 0 21.6 -17. 1 1 6 0. 1 6 1 -0.0 15.9 1 6 2 16. 1 1 6 1 4 . 0 """ 1 5 . 7 V 4 1 6 2. 3 0.8 1 6 5 12.6 -14.4 6 -11.9 1 6 9.0 I 7 -2 2.0 1.1 1 7 -1 9.9 -9.7 " 1 7 " 0 "" "9.2 -10.9 1 7 3.4 1 3.4 1 7 13.7 2 16.0 1 10.4 11.4 1 7 I 7 4 4.3 -4.5 8 1 -1 0. -7.8 1 -1 9.2 -8.5" 1 b 3.5 3.9 1 -1 5 20.4 I -1 21.2  11.5 27.9 37.0 2~2"."2 48.6 19.6 1.6 16.3 21. 1 3.5 12.8 6.0 3.2 3.6 5.1 14.6 0. 29.9 24.9 18.4 39.1 " 15.8 1.9 18.3 12.2 5.7 Tl.7" 0. 8.1 9.1 9.2 21.5 9.1 9.9 23.0 19.6 8. 1  -5 -5 -5 -5 -5 -5 -5  J.8-3_ 2.5 12.1 7.0 3.5 10.1 12.0 2.6 11.3 14.4 3.5 11.9 11.4 3.5 10. 1 5.6 5.6 8.8 __0. 1173 9.5 6.0 11.6 4.6 5. I 8. 7 2.1 7.7 3.1 6.5 8.8 1.5 26.9 25.5 10.3 14.8 32.8 12.6 15.3 14.8 2. 7 10.9 0. 18.3 18.1 9.1 24.6 2.6 7.2 3.4 17.4 10.6 22.8 30.2 10.1 41.4 34.9 7.6 21.7 33.9 18.4 8.2 7. 3 2.8 8.6  15.2 -25.4 -39.2 ~f73~ 55.8 30.6 2.9 -21.1 -26.9 -2.5 14.8 6.7 -4.6 -3.5 6.2 1.0 -30.2 -28.2 21.2 44.6 23.7 -2.8 -22.4 -15.7 9.0 14.9 2.0 9.2 7.6 -11.0 -23.2 -10.7 11.6 26.6 18.8 -12.5 -24.3 -1.4 17.0 11.5 3.7 -11.4 ^16.8 -37 0 12.8 16.2 1.9 -17.9 -15.6 " 5.5" 16.1 8.8 -6.9 -9.8 0.1 13.9 9.8 -9.2 -17.1 -7.1 7.5 7 12 1 9.6 3.7 -9.3 -13.0 -3.2 -30.5 -37. I -14.3 18.7 32.2 11.0 -11.8 -10.3 1.7 9.3 -0.9 -18.2 -18.4 8.5 28.9 7. 1 5.8 -3.7 -14.9 -10.5 19.6 36.5 -7.9 -54.3 -40.0 -9.8 22.5 30.7 1.2 -18. 1 -6.7 6.5 2.7  2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 "2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 "2" 2 2 2 2 "2 2 2 2 2 2 2 2 2 2 2 2 2" 2 2 2 2 2  "i" 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2  2 -5 15.0 -12.3 2 -4 5.2 4.8 26.7 2 -3 27.2 22.9 2 -2 19.6 2 -1 6.0 -6.4 34.6 2 0 -40.1 56.3 -50.7 2 1 2 5.1 -4.7 2 2 3 38.3 39.0 17.9 17.7 2 4 -19.2 2 5 23.1 2 6 21.2 -19.5 2 0. -0.9 1 10.2 2 8 3 -6 10.8 -9.6 3 -5 11.5 -9.3 14.7 3 -4 12.2 3 -3 28.2 28.3 3 " - 2 "'" 12."8 13.3 3 -1 8.0 -9.5 3 0 25. 1 -29.5 3 1 37.2 -30.5 3 18.6 15.6 2 3 50.3 38.4 3 3 4 0. -0.3 32.0 3 5 -28.4 3 6 21.2 -18.0 7 4.5 3 2.0 13.1 10.2 3 8 4 -6 9.0 -7.8 4 -5 5.1 " - 4 . 0 13.7 4 -4 9.6 4 21.9 -3 20.7 13.4 4 -2 12.0 4 -1 17.2 -17.6 4 34.1 -29. 7 0 4 0. 1 2.8 4 2 46.2 35. 3 4 3 32. 1 22.6 4 4 14.2 -11.6 4 5 29. 7 -26.2 4 "6 "15.1 -14.9 4 7 7.2 4.7 4 8 13.1 10.5 5 -5 0. 0.2 5 -4 8.5 8.2 14.9 5 -3 11.1 5 -2 5.0 1.8 5 -1 22.6 -18.7 5 0 22.8 -18.8 16.6 15. 7 5 1 47.8 5 2 35.6 5 16.0 14.5 3 5 4 -15.1 18.2 5 27.8 -23.1 5 6.4 -6.9 5 6 10.4 5 7 9.4 8.7 6 -4 10.0 6 5.6 5. 1 -3 8.9 6 -9.5 -2 21.1 6 -1 -16.5 6 0 5.6 -4.8 21.2 15.9 6 1 30.0 24.9 6 2 6 3 9.3 8.2 22.9 4 -16.4 6 6 5 21.0 -16.4 2.9 3.1 6 6 7 -2 11.6 -10.5 7 -1 15.0 -13.3 7 0 0. 0.5 7 19. 1 15.6 1 7 1 7. 7 15. 1 2 7 3.7 -2.5 3 7 4 17.3 -15.3 7 5 6.2 -6.3 7.8 8 3 -8.8 6.7 2 7.1 6 8 13.8 12.8 1 -1 -7 9.3 9.9 -1 3.0 -6 3.3 -1 16.8 -16.9 -5 -1 -21.9 -4 20.7 -1 -3 2.1 -2.7 -1 22.3 19.9 -2 -1 25.6 -1 21.1 5.4 -I 0 -1.5 -1 28.4 -33.4 1 -1 14.5 -18. 1 2 -1 16.7 3 '15.0 -1 4 28.2 25.2 -1 11.7 10.9 5 - 1 8.8 -5. 1 6 -1 7 12.6 -9.7 -2 -7 6. 1 7.1 "-2" - 6 8 . 1" "7.6 -2 6.0 -8.6 -5 -2 -4 21.0 -24.5 11.5 -11.1 -2 -3 20.7 20.9 -2 -2  8.8  6 Table 1 - Continued 2 -2 2 -2 2 -2 2 -2 2 -2 2 -2 2 -2 2 -2 2 -2 2 -3 2 -3 2 -3 2 -3 2 -3 2 -3 2 -3 2 -3 2 -3 2 " -3 2 -3 2 -3 2 -3 2 -4 2 -4 2 "-tt 2 -4 2 -4 2 -tt 2 -tt 2 -tt 2 -tt'" 2 -tt 2 -5 2 -5 2 -5 2 -5 2 -5 ' 2 -5 0 3 0 3 J 0 0 3 3 0 0 3 3 0 0 3 3 1 3 1 3 i 3 1 3 1 3 I 3 1 3 I 3 1 3 1 1 3 3 1 3 1 1 3 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 2 3 3 3 3 3 3 3 "'3 3 3 3 3 3 4  <t  -1 0 1 2 3 tt  5 6 7 -6 -5 -4 -3 -2 -1 0 I 2 3 tt  5 6 -5 -tt  ~ i ' -2 -1 0 1 2 "3"  *  -3 -2 -1 0 1 2 0 1 2 3 tt  5 6 7 -5 -4 -3 -2 -1 0 1 2 3 tt  5 6 7 e -6 -5 -tt  -3 -2 -I 0 1 2 3 5 6 7 8 -6 -5 -tt  -3 -2 -1 0 1 2 3 5 6 7 B  -6 -5 -tt  4 4  tt tt  I  5 5 5 5 5 5 5 5 5  -3 -2 -1 0 1 2 3 tt  5 6 7 a -5 -tt  -3 -2 -1 0 1 2 3  27.5 3.5 23.2 16.2 tt. 1 17.5 9.6 0. 7.4 7.7 0. 15. 1 15.0 .12. B 30.7 11.2 8.0 16.7 6. 1 9. 1 13.9 0. 3.3 7.2 12.7 0. 18.1 17. 3 3.5 15.8 8.3 3.5 10.7 6.5 9. 1 14.5 0. 10. 1 46.0 11.5 15.5 16.8 1.7 11.0 9.8 2.0 8.3 12.2 32.5 B. 6 33.7 25.7 4.5 12.9 12.3 4.2 22.4 12. 1 5.3 a.2 9.5 4.5 16.a 29.4 0. 32. 1 13.6 21.a 19.9 a.o 18.5 26.5 7.2 7.5 7.9 9.0 1.8 16.0 11.1 9.1 22. 1 5.8 21.a 38.2 3.9 23.4 22.6 1.9 11.7 7.8 5.3 4.3 12.9 i.a 20.2 22. 1 6.2 36.6 30.5 0. 25. 3 20. 7 2.6 17.5 4.3 5.1 8.7 0. 21.6 18.9 13.3 33. 1 16.9 7.3  29.6 6. 7 -17.1 -16.2 2.4 15.3 10.9 -1.7 -7.9 B.7 -0. 1 -18.5 -14.9 13.3 25.3 11.3 -5.9 -15.2 -8. 3 7. 7 10.1 0.2 4.2 -8.0 -14. 1 0.1 18.7 15.7 -3. 1 -14.0 -a.6 2.3 -lo.a -6.3 9.6 13. 3 " -0.0 -9.1 -43.2 - 18.2 16.9 20.2 3.3 -10.9 -10.3 0.8 -7.1 12.8 •" 32.1 8.2 -34. 1 -29.3 -0.5 14.6 16.6 -3. 1 -21.3 -12.5 5. 3 9.4 -8.5 -2.4 1 7.0 26. 7 0.3 -31.5 -19.3 15.5 29.2 11. 1 -17.7 -25.7 -9.2 7.3 9.1 -7.9 3.6 16.9 10.9 -B.6  -20. 1 -10.3 25.8 42.0 6.4 -26.5 -23. 1 -3.8 9.3 7. 7 -4.8 5.0 13.7 2.8 -19.0 -20.5 6.1 33.1 29.7 0.7 -21.8 -17.8 2.7 13.5 4.5 5.0 7.8 -1.5 -20.5 -18.9 12.8 31.0 16.0 -6.3  4 22. > 5 11.0 5 5 5 6 12.7 3 7 15.8 5 3 6 -4 3.9 3 6 -3 6.6 3 6 -2 16.2 3 6 -1 3 6 0 '9.8 3 6 1 22.5 3 6 2 10. 7 3 6 3 15.0 3 6 4 20.9 3 6 5 0. 3 6 6 1 7.6 3 6 7 7.2 3 7 -3 9.4 3 7 -2 10.6 3 7 -1 0. 3 7 0 10.2 3 7 1 11.7 3 7 2 3 7 3 16.0 3 7 4 12.9 3 7 5 6.9 3 7 6 12.5 3 8 0 11.4 3 1 7.2 a 3 9.0 a '2" 3 15.3 a 3 3 -l 7 1.7 3 -i 6 7.3 3 -l 5 4.8 3 - l 4 5.2 3 -i 3 "" 18.3 3 - l 2 11.2 3 -i 1 20.9 3 -l 0 32.4 3 -2 0 15.7 3 -2 1 19.3 3 " -2 0. 2 3 -2 3 15.0 3 -2 4 10.0 3 -2 5 0. 3 -2 6 6. 1 3 -3 4 11.9 "3" -3" "3' "8.6 3 -3 2 5.7 3 -3 1 14.0 3 -3 0 4. 7 3 -3 - I 8.0 3 -3 -2 10.5 3 -3 -3 0". " 3 -3 -4 8.0 3 -3 -5 .6.5 3 -4 -4 5.1 3 -4 -3 2.6 3 -4 -2 7. 3 3 -4 -1 12.3 3 -4 0 2.3 3 -4 1 10.0 3 -4 2 5.2 3 -tt 3 3.2 3 -1 -1 2.2 3 -1 20.0 -2 3 -1 -3 10.7 -4 2.7 3 -1 3 -1 -5 a.i 2.9 -6 3 -1 3 -2 -6 0. 3 -2 -5 -4 5.2 3 -2 3 -2 -3 5.4 3 -2 -2 13.3 3 -2 -1 2.6 3 2 - 7 3.6 3 0 -7 0. 3 0 -6 7.5 0 -5 3 .a.o 3 0 -4 20.7 3 0 -3 ... ^ _ - j ~"18.4 3 0 -1 15.2 1 -6 7.7 3 4 -3 -3 6.7 4 -3 -2 4.0 4 -3 -1 2.5 4" -3 " 0 9.9 4 —3 1 6.1 4 -3 2 4.6 4 -3 3 8.6 4 0 11.6 0 1 13.0 4 0 4 0 — j - '" 19. 1 2.3 4 0 3 4 0 4 12.a 5 10.9 4 0 0. 4 0 6 7 4 0 1' 7 7.7 4 1 4 6 5.2 1 5 12.0 4 1 4 22.6 4 4 1 3 2.5 1 19.0 4 2 16.7 4 ~"i ...... 0 0. 4 i 4 -1 19.1 i 4 8.2 i -2 4 -3 7.4 i -4 12.4 4 l "4 ""7 ~"7".7 4 2 6 8.2 3 3 3  18.7  1.8  ]  7.8  3.8  5.8  -18.7 -9.1 12. 1 14.5 3.5 -7.1 -15.0 -8.6 9.7  20.0 8.4 -14. 1 -18.7 2.1 17.9 . 9.9 -a.4 -10.5 -0.2 9.9 11.2 -1.3  -17.7 -12.4 15.0 8.7 11.0 6.2 -9. 1 -15. 3 -2.8 -/.6 -3. 1 8.2 20.2 12.7 -22. 7 -36.1 -16.a -18.8 0.2 16. 7 12.9 -0. 3 -6.5 11.4 10.3 -5.6 -14.8 -5.0 10.3 13. 7 1.6 -10.4 -8.5 -8.6 -3.2 10.0 12.9 -0.3 -10.3 -5.8 3.4 -4.4 20. 7 13.1 -3. 7 -10. 7 -5.3 -2.2 -11.9 -8.9 8.3 17.0 3.3 -4.1 0.5 -7.5 -8.4 4.7 22. 1 17.9 -18.2 -8.2 7.0 5.5 -4.0 -11.3 -6.2 5.7 9.3 -14.0 15. 1 "19:5 -0.1 -14.6 -12.9 -1.6 6.5 7.7 3.0 -14.5 -23. 1 -3.6 23.3 " 23.0 -0.9 -18.5 -10.9 8.2 13.8 7.6 7.0  4 4 4 4 4  2 5 4 2 2 3 2 2 2 1 tt 0 2 4 2 -1 4 2 -2 4 2 -3 4 2" - 4 4 2 -5 7 4 3 4 3 6 4 3 5 4 3 4 '4' 3 ...... 4 3 2 4 3 1 4 3 0 4 3 -I 3 4 -2 4 3 -3 4 3 -4 4 3 -5 4 4 8 4 4 7 4 4 6 ' 4" 4 5 " 4 4 4 4 4 3 4 4 2 4 4 1 4 4 0 "4 4 -1 4 4 -2 4 4 -3 4 4 -4 4 4 -5 4 5 7 4 5 6 4 5 5 4 5 4 4 5 3 4 5 2 4 5 1 "4 '"" 5" "0 4 5 -1 4 5 -2 4 5 -3 4 5 -4 4 5 -5 "4 '6 7 4 6 6 4 6 5 4 6 4 4 6 3 4 6 2 '4 6 "1 4 6 0 4 6 -1 4 -z 4 6 -3 4 -4 4 7 6 4 7 5 4 7 4 4 7 3 4 7 2 7 4 1 7 4 0 4 7 -1 4 7 -2 4 7 -3 4 8 5 4 8 4 4 8 3 4 8 2 4 8 1 4 8 0 4 8 -1 4 -1 0 4 -1 1 4 -I 2 4 -1 3 4 -1 4 4 -1 5 4 ' - i "6 4 -2 1 4 -2 2 4 -2 3 4 -2 4 4 -2 5 4 0 -6 4 0 -5 4 0 -4 4 0 -3 4 0 -2 4 0 -1 4 1 -5 4 1 -6 4 -I -5 4 -1 -4 4 -1 -3 4 -1 -2 "4" -1 -1 4 -2 0 4 -2 -5 4 -2 -4 4 -2 -3 4 -2 -2 "4~" - 2 " -1 5 0 1 5 0 2  6.2 24.0 12. 1 16.5 33.6 11.7 17.3 21.3 0. 14. 3 5.6 8.0 9.4 2.4 14.2 15.2" 6.0 32. 1 14.5 13.1 20. 1 5.0 6.5 6.3 5.3 8.2 16. 1 7. 7 9.9 22.9 4.3 20.8 17.B 6.5 20.4 11.1 1.7 7.9 4.3 18.7 11.1 8.3 18.5 11.1 7.7 21.0 4.0 17.5 14.2 0. 6.9 0." 13.4 15. 1 1.7 19.4 18.3 0. " 18.0 9.2 9.3 12.7 0. 6.1 15.0 4.7 16.9 17.8 2.4 9.7 10.1 0. 6.8 7.0 5.9 5.4 14.5 5. 7 6. 1 9. 7 14.4 2.4 13.6 5.2 6.6 9.4 2.9 6.0 9.9 10.2 0. 7.8 3.1 2.6 7.9  -8.8 -24.0 -10.2 20.8 32.5 14. 1 -14.8 -20.3 0.4 13~.0 6. 1 8.0 10.3 1.5  -15.9 -20. 1 11.1 40. 1 20.5 -15.0 -21.3 -6.0 6.4 7.0 -5.1 8.3 15.9 8.2 -10.1 -20.8 -1.2 27.a 21.5 -6.5 -19. 1 -12.3 1.4 7.7 4.9 19. 1 13.0 -7.2 -18. 1 -12.1 8. 1 11.3 5.2 -16.6 -14.2 0.5 6.5 -0.6 14.2 16.5 -1.7 -19.5 -18.3 0.9 16.3 a.6 -a.5 -10.2 -1.7 6.4  14.7 4.4 -16.1 -18.4 -1.7 10.4 9. 1 0.5 -6.2 9. 7 6.8 -6.9 -14.3 -6.3 6.2 10.3 -17.3 2. 1 14.6 6.9 -6.3 -10. 1 -3.2 -6.2 10.3 1 1.4 -1.2 -7.0 -4.2 2. 1 10.8 13.5 10.a 0. -1.5 16.4 -22.6 3.9 4.6 4. 1 -4.0 0. -0.7 6.8 a.7 9.0 12.4 1.4 0. "12.7 "-16.6 12.4 -15.4 1.4 -3.3 7.3 5.2 9.0 9.3 4.1 3.0 6;t -8.4 15.0 15.2 4.4 4.9  5 0' 5 0 5 0 5 0 5 1 5 1 5 1 5 1 5 1 5 1 5 1 5 2 5 2 5 2 5 2 5 2 5 2 5 2 5 2 5 2 5 2 5 2 5 3 5 3 5 3 5 3 5 3 5 3 5 3 5 3 5 3 5 3 3 5 5 3 5 4 5 4 4 5 5 4 5 4 5 4 4 5 5 4 5 4 5 4 5 '' 4 5 4 5 4 5 5 5 5 5 5 5" 5 5 5 5 5 5 5 5 5 5 5 5 " 5" 5 5 5 5 5 6 5 6 5 6 5 "6 " 6 5 5 6 5 6 5 6 5 6 5 6 5 6 5 6 5 7 7 S 5 7 5 7 5 7 5 7 5 7 7 5 5" " 7 5 a 5 8 5 8 5 8 5 a 5 8 5 -1 5 -1 5 -1 5 -1 5 -1 5"' -1 5 -1 5 -1 5 -1 5 -I 5 -2 5 -2 5 -2 5 -2 5 -2 5 -2 5 0 5 0 5 0 5 0 5 0 0 5 5 1 5 "1 5 1 5 1 1 5 5 2 5 2  3 4 5 6  6  5 4 3 2 I 0 7 6 5 4 3 2  6.6 2.6 11.4 11.1  6.0  4.3 11.9 12.4 3.a  -1 -2 -3  15.0 a.2 2. 1 14.4 12.3 7.9 18.4 1.5 10.5 1.8 10.6 17.2  -4  4.2  1  7 0. 6 13.4 5 16.2 4 0. 3 18.0 2 '9.2 0 17.2 -1 4.5 -2 12.2 -3 15.4 -4 ' "" 5.1 -5 6.0 7 4. 7 6 10.3 20.9 5 4 7.7 3 12.0 2 25.2 0. 1 0 17.0 -1 7.9 -2 7.0 -3 10.3 -4 5. 3 -5 2.1 7 9.a 6 4.5 21.3 5 "4 '" 1 2 . 4 3 13. 1 2 24.0 1 8.9 0 9.9 13.4 -1 -2 0. -3 a.8 -4 7 6.9 3 ..9 6 6 8 5 12.8 4 14.1 3 4.4 2 18.0 1 15.8 0 4.9 -I 17.6 -2 7. 7 -3 6.2 -4 6.4 6 7.4 5 4.4 4 15.2 3 4.8 2 16.8 1 16.4 0 3.0 -1 14.0 -2 '9. 7" 4 10.a 3 a.6 2 6.2 1 12.2 0 2.8 -1 7.4 5 4.8 4 10.8 3 4.0 2 6.4 1 10.9 0" " i.e -1 6.4 -2 9.4 -3 3.2 -4 8. 3 3 0. 2 9.5" 1 7.6 0 0. 8.5 -1 -2 4. 7 0 10.5 -5 6. 1 -4 5.5 -3 3.7 -2 12.1 -1 3.H -1 0. -2 12.3 -3 8.5 -4 0. -5 7.2 0 -5 10. 1  12.8  -7.8 -11.6 -3.7 5. 1 a.3 2.7 -11.2  -13.5 3.4 19.4 15. 1 1.0 10.9 10.9  -6.6  -17.6 -1.4 17.9 2.3 -10.9 -12.2 -1.3 0.3 11.7 15.4 2.0 -16.5 -14.4 19.4 6.6  -10.8  -13.3 -3.2 4.4 -2.4 10.3 1 7.2 7.8 -14.3 -24.8 -3.3 17.9 9.5 -6.8 -9.8 -4.6 1.9 -7.0 5.1  17. 1 9.4 -12.5 -23.0 -10.3 8.9 13.2 2.5 -7.3 -6.2 -9.3 -2.4 12.0 11.7 -5.8 -18.6 -14.2 3.2 14.9 7.5 -4.9 -5.5 -7.1 4.7 13.3 3.5 -13.5 -13.7 1.7 11.4 7.1 11.2 a.3 -5.6 -10.4 -2.0 5.8 -4.8 -10.1 -4.3 7.3 10.2 ""1.4" -7.2 -6.6 0.9 6.4 -1.2 7.0 5.9 -3.3 -7.7 -3.7 10.2 4.9 5.9 -1.7 -10.9 -5.8 -2.8 -12.2 -6.4 2.8 5. 3 16.1 5.8  7 Table 2 P i n a l p o s i t i o n a l parameters ( f r a c t i o n a l ) w i t h standard and temperature Atom  deviations,  factors.  X  <T ( x )  z  y  <^(z  *(y)  As(l)  0.1667  0.0602  0.1785  0.007A  0.006A  0.006A  C(2)  0.4072  -0.2732  0.2794  0.066  0.056  0.068  C(3)  0.1953  0.2660  0.3049  0.069  0.057  0.054  0(4)  0.1879  0.1290  -0.0726  0.033  0.030  0.030  0(5)  -0.1089  0.1157  0.2543  0.060  0.047  0.043  Atom  T'  X'  Z' 0  As(l)  0.997A  1.288A  1.147A  C(2)  2.345  0.059  1.795  C(3)  1.223  2.978  1.959  Q(4)  0.966  1.477  -0.466  0(5)  -0.437  0.746  1.634  Atom  b  As(l)  325  C(2)  452 --426  0(3)  629  l l  b  12  13  b  22  b  23  b  32  i  10  x  - 82  183  -110  250  •-414  -114  320  -273  251  0(4)  398 --3 57  -140  272  - 71  200  0(5)  700 •-420  -232  304  -263  222  Atom  U  l l  •-268  b  u  1 2  u  1  3  -118  u  192  160  2  2  4  381  U  23  U  3 3  x  As(l)  5.09  -2.00  -0.71  2.85  C(2)  6.53  -3.20  -0.95  3.89  C(3)  9.10  -3.10  -0.99  4.98  -2.46  5.24  0(4)  5.75  -2.68  -1. 21  4.23  -0.64  4.18  0(5)  10.12  -3.15  -2.02  4.73  -2.37  4.63  -1.06 1.45  10  4.00A^ 7.97  2  D. The  a n a l y s i s has  Discussion e s t a b l i s h e d t h a t the a r s e n i c atom i n  c a c o d y l i c a c i d has the expected t e t r a h e d r a l c o n f i g u r a t i o n .  The  As-C  bond lengths do not d i f f e r s i g n i f i c a n t l y , and the mean o value of 1.91 + 0.04A i s not s i g n i f i c a n t l y d i f f e r e n t from the v usual A s - C distance (1.955 + 0.018A i n ( M e A s S ) f o r 2 0  2  example ).  The As-0  2  bond lengths are a l s o , s u r p r i s i n g l y ,  equal w i t h i n experimental  e r r o r , the mean value being  1.62  + 0.03A. Although i n f o r m a t i o n about As—0 bond lengths i s sparse, p a r t i c u l a r l y f o r As  , t h i s value i s comparable to that  r e p o r t e d f o r the A s - 0 a n d f o r the A s V  4  1 1 1  — 0 single bonds . 3  Table 3 o Bond d i s t a n c e s (A) and  valency angles, and  standard  deviations  As(l)-C(2)  1.937  ±  0.06  C(2)-As(l)-C(3)  109.9° +  As(l)-C(3)  1.890  +  0.06  C(2)-As(l)-0(4)  114.8  +  2.0  As(l)-0(4)  1.625  ±  0.03  C(2)-As(l.)-0(5)  107.8  +  2.3  As(l)-0(5)  1.609  +  0.05  C(3)-As(l)-0(4)  109.0  +  2.0  0(4)...(5')  2.567 +  0.06  C(3)-As(l)-0(5)  106.1  +  2.3  0(4)-As(l)-0(5)  108.9-  2.5°  +1.8  The  c r y s t a l isi b u i l t up from centrosymmetrical hydrogeno bonded dimers ( P i g . 2), with 0-H...0 = 2.57A, so t h a t the s t r u c t u r e i s s i m i l a r to that of c a r b o x y l i c a c i d s , r a t h e r than to a r s o n i c a c i d s , R A s O ^ H ^ , where the two  replaceable  hydrogen atoms give r i s e to more complex hydrogen bonding schemes 4 i n v o l v i n g endless chains of molecules • The f a c t that the  9 As—0 bond lengths i n c a c o d y l i c a c i d are found to be e q u i v a l e n t could imply a more completely carboxylic acids.  r e s o n a t i n g s t r u c t u r e than i n  However, another p o s s i b i l i t y  i s that the  d i f f e r e n c e between the As=0 and As-0 bond lengths i s too small to be detected  in this analysis.  e x p l a n a t i o n i n the l i g h t  This seems the more l i k e l y  of covalent r a d i i  measurements^.  A l l the other i n t e r m o l e c u l a r contacts correspond to  5  van der Yaals i n t e r a c t i o n s , the s h o r t e s t i n v o l v i n g oxygen atoms (Table 4 ) ; the shortest As...As and C»*.C contacts are o o 3.98A and 3.88A. Table 4 Shorter i n t e r m o l e c u l a r d i s t a n c e s ( A l l distances  ^  4A between molecule 1 and  molecules were c a l c u l a t e d ; Atom  ( i n molecule l )  only contacts  to Atom  neighbouring 0  < 3.5A are l i s t e d ) .  i n Molecule  d(2)  As(l)  0(4)  2  3.46  As(l)  0(5)  2  3.49  C(2)  0(4)  3  3.29  0(2)  0(5)  4  3.34  0(4)  0(5)  2  2.57  0(5)  0(4)  2  2.57  0(5)  0(5)  4  3.48  Molecule  1  at  x  y  z  2  at  -x  -y  -z  3  at  1-x  -y  -z  4  at  -x  -y  1-z  10  P i g . 2.  P r o j e c t i o n of the s t r u c t u r e along the b - a x i s j i l l u s t r a t i n g the molecular packing. The hydrogen bonds are shown as broken l i n e s .  II.  ANTIMONY AND BISMUTH TRIIODIDES A.  The  trihalides  a l l been reported  Introduction  of a r s e n i c , antimony and bismuth have  as having the "bismuth triiodide s t r u c t u r e " .  This has the a r s e n i c , antimony and bismuth atoms s i t u a t e d at the a  centres  of iodine octahedra, the i o d i n e atoms being i n  hexagonal close-packed a r r a y .  i n d i c a t e that a l l three  Such a s t r u c t u r e would  compounds form i o n i c c r y s t a l s , and  while t h i s i s probable f o r B i l ^ ,  i t seems u n l i k e l y f o r the  other compounds. 7  A reinvestigation triiodide reported^.  of the c r y s t a l s t r u c t u r e of a r s e n i c  i n d i c a t e d that the s t r u c t u r e was not as p r e v i o u s l y Preliminary  examination of the h0.-£ s t r u c t u r e  f a c t o r s i n d i c a t e d that the iodine atoms were s i t u a t e d close to (y, j , Y2") i n space group R3, as p r e v i o u s l y found*', but that b e t t e r agreement between observed and c a l c u l a t e d  structure  f a c t o r s was obtained f o r z about — r a t h e r than the As 5 previous value of ^, r e f e r r e d to a hexagonal u n i t c e l l . k  These  7  changes were confirmed by refinement of the a n a l y s i s .  Although  the i o d i n e atoms are i n an approximate hexagonal close-packed a r r a y , the a r s e n i c atoms are d i s p l a c e d from the centres of i o d i n e octahedra and the s t r u c t u r e may t h e r e f o r e  be  considered  as b u i l t up from d i s c r e t e A s l ^ molecules. Knowing t h i s , a s i m i l a r r e i n v e s t i g a t i o n of the c r y s t a l s t r u c t u r e s of antimony and bismuth t r i i o d i d e s was made.  B.  Experimental  C r y s t a l s of antimony t r i i o d i d e were prepared f l u x i n g i o d i n e and powdered antimony  by r e -  i n benzene, according  8 to  the method of B a i l a r and Cundy .  hexagonal p l a t e s with  They are orange-red  (OO.l) developed, and have a strong  tendency to twin on t h i s f a c e . determined from an h0.£  The  u n i t c e l l parameters were o  precession f i l m  S i n g l e c r y s t a l s of bismuth t r i i o d i d e  (A, MoKoc = 0.7107A).  could not be  obtained;  s u b l i m a t i o n i n vacuo, and v a r i o u s c r y s t a l l i z a t i o n  techniques  y i e l d e d only conglomerates of very small c r y s t a l s . c e l l dimensions were t h e r e f o r e determined by  The u n i t  least-squares g  treatment, with the i n c l u s i o n of a Nelson—Riley term, of the s i n 0 values from a powder f i l m — see Appendix.  The  extrapolation  (A, CuKa = 1.5418 A)  powder l i n e s were indexed  by  comparing  t h e i r measured 0 values with ones c a l c u l a t e d using p r e v i o u s l y r e p o r t e d c e l l dimensions .  The  c r y s t a l data f o r Asl-j  ( i n c l u d e d f o r comparison), S b l ^ and B i l ^ are summarized i n Table  5. For S b l ^ the i n t e n s i t i e s of the h0«-£ r e f l e c t i o n s were  recorded  on p r e c e s s i o n f i l m s with MoKoc r a d i a t i o n , estimated  v i s u a l l y , c o r r e c t e d f o r Lorentz and p o l a r i z a t i o n f a c t o r s , and the s t r u c t u r e amplitudes were d e r i v e d .  The  a very small hexagonal p l a t e with edge 0.1 0.02  mm.,  mm.  and a b s o r p t i o n c o r r e c t i o n s were not  necessary. two  c r y s t a l used  The  c r y s t a l was  and  was  thickness  considered  twinned w i t h the volumes of the  p a r t s i n the r a t i o 1.2:1, and the i n t e n s i t i e s of r e f l e c t i o n s  such as 303 Asl-,  and 303 were d e r i v e d by assuming t h a t , as found i n  they had  equal F v a l u e s .  (Such r e f l e c t i o n s were super-  imposed on the f i l m s ) . could not be  For B i l ^ ,  f o r which s i n g l e c r y s t a l s  obtained, the i n t e n s i t i e s were recorded, w i t h  CuKoc r a d i a t i o n , on a powder f i l m which was  photometered,  and  the  i n t e g r a t e d i n t e n s i t i e s were then measured with a p l a n i m e t e r .  The  sample was  mounted i n a t h i n - w a l l e d Lindemann glass  c a p i l l a r y , of diameter 0.3 p o l a r i z a t i o n f a c t o r s , and  mm.  The  appropriate  Lorentz  c y l i n d r i c a l absorption 2  (uR = 24) were a p p l i e d , and were d e r i v e d .  The  the F  and  corrections  v a l u e s f o r each powder l i n e  photograph showed evidence of some p r e f e r r e d  o r i e n t a t i o n , which was  p a r t i c u l a r l y marked f o r the  00.£  reflections. C.  Structure  For. S b l ^ , the h0.£ structure  Analysis  Patterson  projection indicated a  s i m i l a r to that of A s l ^ , but w i t h Z g ^ = 0.18.  e l e c t r o n d e n s i t y map  showed the antimony and  iodine atoms  w e l l r e s o l v e d with s i g n i f i c a n t changes i n i o d i n e also indicated firmed by 0*18,  (Fig. 3).  The value of Z g ^ = 0.18  positions was  con-  computing s t r u c t u r e f a c t o r s f o r Z g ^ = 0.16,  0.19,  0.20,  the F ' s c  b e t t e r agreement (R = 0.2l) of the  An  other s e t s .  Tables, ,  w i t h z = 0.18  giving  significantly  with the measured values than  S c a t t e r i n g f a c t o r s from the  c o r r e c t e d f o r anomalous d i s p e r s i o n and  1  0.17,  any  International with  °2 B = 4.5  A  f o r a l l atoms, were used i n the c a l c u l a t i o n s .  Refinement of the p o s i t i o n a l and meters was Difference  achieved by computing four F o u r i e r (P ) and (F - F ) syntheses s u c c e s s i v e l y ; the discrepancy o c  f a c t o r R, was as \  a n t  d  i s o t r o p i c temperature para-  thus f i n a l l y reduced to 0.131.  With z,  a l l other parameters as t h e i r f i n a l v a l u e s ,  taken R  14  F i g . 3.  E l e c t r o n - d e n s i t y p r o j e c t i o n along the b - a x i s , with contours at i n t e r v a l s of 10 e l e c t r o n s about Sb and I .  15  Table 5 C r y s t a l data f o r Asl-j, S b l ^ and B i l ^ Formula  Asl^  Sbl.  Bil  Mol. wt.  455.7  502.5  589.8  146  170.5  439 °C  m.p. C r y s t a l system a  H H  U, H  3  L  3  Rhombohedral  Rhombohedral  Rhombohedral  7.208 + 0.001  7.48 + 0.02  7.516 + 0 .003 A  21.436 + 0.001  20.90 + 0.05  964.5  1012.7  X  20.718 + 0.02 A °3 1013.5 A  J  6  6  8.156 A  aR  8.269  8,20  aR  51°41'  54°18»  54°52'  321.5  337.6  o337.8 A'  2  2  2  4.75  4.85  5.7 g.cm  4.71  4.94  -3 5.80 g.cm.  1220  1423  1600  200  178  386  1152  1260  R3  R3  R 2R  D m x u(CuKa) u(MoKa) F(OOO) (hexagonal cell) Space group  cm  -3  -1  cm"  1  1452 e l e c t r o n s  R3  Table 6 Measured and c a l c u l a t e d  f a c t o r s f o r S b l ^ , h0,4> r e f l e c  structure  tions.  i  Kl  3  227  c -223  6  528  9  I  Kl  13  -551  247  12  h  F  h  i  l ol  46  c -59  T  23  52  c 6  16  49  65  5  2  51  -34  -224  19  54  -66  5  74  47  517  519  22  56  42  8  117  -99  15  75  78  25  54  -19  11  76  80  18  233  -241  0  761  754  14  35  -29  21  65  -37  3  139  -139  17  24  22  24  54  74  6  343  -358  20  55  -26  1  98  99  9  171  -151  23  53  10  4  28  -22  12  306  361  1  73  72  7  33  -18  15  53  55  4  64  -37  10  63  65  18  148  -176  7  37  -41  13  84  -95  21  38  -27  10  84  44  16  86  84  24  26  54  13  54  -15  19  50  -58  3  139  -139  16  55  27  22  55  42  6  343  -3 58  19  55  -40  9  171  -151  22  52  23  0  256  263  F  2  3  *3  7  F  F  2  236 . -196  5  194  218  12  306  361  8  135  -178  15  53  55  3  59  -49  11  92  149  18  148  -176  6  142  -127  14  104  -120  21  38  -27  9  52  -56  17  81  73  24  26  54  12  140  137  20  55  -32  1  48  26  15  37  22  23  50  13  4  48  10  18  83  -70  2  103  -124  7  49  10  21  48  -11  5  153  153  10  26  23  24  44  22  8  180  -190  13  82  -69  3  59  -50  11  120  150  16  56  56  6  142  -127  14  69  -85  19  55  -26  9  52  -56  17  52  56  22  55  23  12  140  137  20  55  -41  2  158  -119  15  37  21  23  56  16  5  109  129  18  83  -70  26  55  1  8  75  -75  21  48  -11  4  T  6  *6  Table 6 - Continued F  I  l ol P  F  126  11  84  71  114  -53  14  60  -83  7  30  -54  17  68  48  10  93  78  20  56  -12  /  l ol  1  116  4  P  c  h  c  h  I 24  i n c r e a s e s to 0.270.  Measured 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  are l i s t e d i n Table 6.  The f i n a l p o s i t i o n a l parameters are  given i n Table 7, and t h e i r standard d e v i a t i o n s , c a l c u l a t e d from Cruickshank' s f o r m u l a e ^ ,  are :  1  <f(x),  d'(y), ( f ( z ) =  0,  0, 0.014A  0.007, 0.007, 0.009A  f o r Sb, for  Ii  °2 The f i n a l thermal parameters are B = 4.5A  f o r a l l atoms.  Interatomic d i s t a n c e s and angles are a l s o given i n Table  7,  together with the corresponding parameters f o r A s l ^ which are i n c l u d e d f o r  comparison.  E x t r a p o l a t i o n of the atomic p o s i t i o n a l parameters f o r A s l ^ and S b l ^ to bismuth t r i i o d i d e , based on v a r i a t i o n of a parameter such as covalent r a d i u s , suggests t h a t i n B i l ^ , z_. must be about \. S t r u c t u r e f a c t o r s were c a l c u l a t e d f o r Bi 6 a l l the three—dimensional r e f l e c t i o n s of B i l ^ , using the same p o s i t i o n a l parameters as f o r S b l ^ , but with z^^ =  The  2 F v a l u e s f o r each powder l i n e were then d e r i v e d by summing ,c the values f o r the r e f l e c t i o n s c o n t r i b u t i n g to the l i n e , with allowance f o r m u l t i p l i c i t y p. An o v e r a l l thermal parameter 2 and the F scale f a c t o r were determined from a p l o t of o ' 2 2\ 2 F / F Jagainst s i n 0. The slope of the l i n e i n d i c a t e d  (  r  fi  °2 B = 0 A •  Q  The values of F  o  2  and F  c  2  are compared i n Table  8;  the agreement i s q u i t e good, the only poor agreement being f o r 2 the 00.<£ r e f l e c t i o n s , f o r which the F v a l u e s are too high as o a r e s u l t of p r e f e r r e d o r i e n t a t i o n .  U n f o r t u n a t e l y , the powder  data do not allow a more p r e c i s e determination of the parameters, since the accuracy of i n t e n s i t y measurement i s not s u f f i c i e n t l y high to d e t e c t the small d i f f e r e n c e s i n  SpF  c  produced by small changes i n , f o r example, Z g ^ . The p o s i t i o n a l parameters  used to c a l c u l a t e F 's i n Table 8 are i n c l u d e d w i t h c  the Asl-j and S b l ^ values i n Table 7. D.  Discussion  The present analyses of S b l ^ and B i l ^ , and the 7 corresponding r e d e t e r m i n a t i o n of the Asl-j s t r u c t u r e  , show  that i n a l l three compounds the i o d i n e s are i n an approximately hexagonal  close-packed a r r a y .  In B i l ^ , Z i g ^ does not d i f f e r  s i g n i f i c a n t l y from ^, so that each bismuth atom i s a t the centre of an octahedron of i o d i n e atoms.  This arrangement  i s t y p i c a l of a compound which i s l a r g e l y i o n i c i n c h a r a c t e r . In Asl-j, A s z  =  and, the s t r u c t u r e i s b u i l t up from  d i s c r e t e A s l ^ molecules, which have dimensions those of the molecules i n the vapour phase.  i d e n t i c a l with  In S b l ^ ,  Zgk = 0.1820, so t h a t , as with the a r s e n i c atoms i n A s l ^ , the antimony atoms are d i s p l a c e d from the centres of i o d i n e octahedra, and have only three near neighbour  i o d i n e atoms,  at 2.868 + 0.010 A, w i t h I - Sb - I = 95.8° + 0.3°. o three i o d i n e neighbours  are a t 3.316 + 0.010A.  atom has s i x iodine neighbours two  The next  Each i o d i n e  i n a plane p a r a l l e l to ( 0 0 . l ) ;  of these are i n the same Sbl-j molecule  and are at 4.25. A,  and the other four are at 4.29A (two), and 4.41 A (two).  In  a d d i t i o n there are s i x other near neighbours, three above o the plane at 4.40, 4.37, 4,37 A and three below at 4.12, 4.22, o 4.22 A. The i n t e r m o l e c u l a r I...I contacts i n S b l ^ and B i l ^ (Table 7) are q u i t e s i m i l a r to those i n Asl-j, and a l l correspond 5 to normal van der Vaals i n t e r a c t i o n s . The dimensions of the S b l ^ molecule i n the vapour p h a s e 1 1  20 are  o Sb — I = 2.67 ± 0.03 A, I - Sb - I = 99  + 1 , indicating  that the s t r u c t u r e i n the c r y s t a l i s intermediate between a p u r e l y molecular c r y s t a l and an i o n i c one. The  s t r u c t u r e s of A s l ^ , S b l ^ and B i l ^ , as summarized i n  Table 7, exemplify the change from molecular, through  inter-  mediate, to i o n i c arrangement as would be expected from compounds of elements  i n the same group.  similar  In a l l these  compounds there i s a l o n e - e l e c t r o n p a i r on the c e n t r a l atom. 3 In A s l ^ , t h i s l o n e - p a i r , having almost sp  character, i s  s t e r i c a l l y a c t i v e and could e x p l a i n the displacement of the a r s e n i c atom from the centre of the i o d i n e octahedron.  The  e f f e c t l e s s e n s i n proceeding down the group and i n B i l ^ , the l o n e — p a i r would be expected to have almost s—character and consequently, a n e g l i g i b l e s t e r i c e f f e c t .  The bismuth atom  could then be s i t u a t e d at the centre of the i o d i n e  octahedron.  A theory based on l o n e - p a i r p a r t i c i p a t i o n alone r e q u i r e s no change i n the c h a r a c t e r of the "metal" — i o d i n e bond, but some change towards i o n i c c h a r a c t e r i n B i l ^ i s expected.  A  combination of the two e f f e c t s , changes i n l o n e - p a i r bond and "metal" — i o d i n e bond c h a r a c t e r , r a t h e r than e i t h e r one considered alone i s p r e f e r r e d as an e x p l a n a t i o n of the observed differences i n crystal  structures.  21 Table 7 o F r a c t i o n a l p o s i t i o n a l parameters, i n t e r a t o m i c d i s t a n c e s (A) and angles i n A s l ^ , S b l ^ and B i l ^ . M = As  Bi  Sb  P o s i t i o n a l parameters 6M i n 6 c  z = 0.1985  0.1820  0.1667  181 i n 18 f  x = 0.3485  0.3415  (0.3415)  y = 0.3333  0.3395  (0.3395)  z •'*= 0.0822  0.0805  (0.0805)  Interatomic d i s t a n c e s Intramolecular M - I I - M - I  2.556 + 0.004 102.0° + 0.1°  2.868 + 0.010  3.1  95.8° + 0.3°  3.97  4.25  3.50  3.32  Intermolecular M ... I I ... I  4.26(2x),4.26(2x) 4,29(2x),4.41(2x) 4.21,4.30(2x),  4.12,4i22(2x)  4.29,4.38(2x)  4.37,4.40(2x)  Dimensions of gaseous molecules M - I  2.55 +0.03  2.67 + 0.03  I  101° + 1.5°  99° + 1°  —  M - I  3.1  Table 8 Measured and c a l c u l a t e d F h  k  £  2 P  c  2  P c P  x 10  2  values f o r B i l ^ F  2 0  x IO"  6  0 meas  (CuKoc)  0  0  3  -431  0.37  1.0  6*57  0 0  1 0  5 6  237 -378  0.62  1.1  13.06  1 1 2  1 1 0  3 3 1  244 -1171 251  8.96  8.3  13.66  2 1 1  0 1 1  5 6  7.95  7.6  17.78  %  182 872 729  0  0  9  -527  0.55  1.6  19*70  0 3  2 0  7 0  7.74  8.0  20,95  3 3  0 3 0 T  -355 -355  1.52  1.2  22.00  1  1 1  9 9  -933 269  5.65  6.6  23.27  3 3 2 2 0  6 6 3  -300 -300 -984 191 178 187  7.50  6.8  25.30  1  0 0 2 2 1 3  0  0  12  1029  2.12  5.1  26,65  3 2 2  1 2 2  5 6  6.02  5.5  27.97  r  244 625 744  2 3 3  1 0 0  10 -138 9 -460 -460  2.65  4.4  29.31  2 2 0  2 2 1  9  4.56  3.8  32.09  1  T n l  167 1123  277 -821 14 -186  23 Table h  k  €  4 1 3 1 4 3 4 1 5 1 4 3 1 3 3 2  3 0 0 0  F  c  £pP  2  c  x  IO"  9.41  10 -226 12 915 12 915 14 - 1 4 0  10.46  11 1 15  -  F  x  Continued 10  0  160 160 -871 -871  4 1 6 1 4 6 4 1 Z 1 4 3"  6  8  673 673 566 566  9.28  5.52  e meas (CuKoc)  9.5  33.75  10.4  34*89  5.7  36.02  8.2  36.59  3 0 1 1 2  1 5 1 1 3  8  109 227 81 -893 -227  3  3  0  887  4.72  2.4  38.11  3 2 10 - 1 5 7 4 1 9 -741 1 4 9 _ 7 4 i  7.20  6.0  39.74  13  A  \  1  4  \ 9  2 2 4  2 2 2  15 15 8  -813 68 -92  4.05  3.9  44.02  0 3 3 1 1 4 1 4 1  5 3 3 1 1 1 4 1 4  10 -113 9 -385 9 —383 18 696 IS 407 12 -50 12 -50 12 142 12 142  6.01  7.2  44,58  197 197  24 APPENDIX C a l c u l a t i o n of the l a t t i c e constants  12  of bismuth t r i i o d i d e  An accurate redetermination of the l a t t i c e constants of bismuth t r i i o d i d e u s i n g i n f o r m a t i o n from a povder f i l m o (A, CuKoc = 1.5418A) i s d e s c r i b e d below. The  systematic e r r o r s i n d, the i n t e r p l a n a r spacing,  were taken as p r o p o r t i o n a l to ^£cos ©/sin © + cos2©/©J - the o N e l s o n — R i l e y f u n c t i o n - and the best v a l u e s of the u n i t - c e l l 2  13 parameters, a and c, were obtained by the l e a s t - s q u a r e s method u s i n g the measured 0 values of a l l the d i f f r a c t i o n l i n e s which could be unambiguously  indexed.  2 For the hexagonal and t r i g o n a l system the s i n © equation  is  sin^O^  = A(h  2  + hk + k ) 2  + Ct  2  where A = A /3a , 2  2  C = A /4c 2  .  2  With systematic e r r o r s i n d values p r o p o r t i o n a l to ^[cos ©/sin © + cos©/©3 , i t can be shown that the e r r o r s i n .2 2 s i n © are p r o p o r t i o n a l to t h i s expression m u l t i p l i e d by s i n ©. 2  2  P u t t i n g 5 equal to 10 times t h i s l a t t e r expression (the f a c t o r 10 being introduced to make the S values more n e a r l y equal to the other terms i n v o l v e d , thus f a c i l i t a t i n g computation),  and  a l l o w i n g f o r random o b s e r v a t i o n a l e r r o r s , then f o r each d i f f r action  line,  k(h  2  ±  + h ^  + k ) 2  i  +  Cl  i  2  + D6  i  - sinV =  £ i  *  25 where D i s the p r o p o r t i o n a l i t y constant. The best r e s u l t s of A, C and D are those which minimize 2 J £ ^ , the sum of the squares of the d i f f e r e n c e s between the  2 c a l c u l a t e d and observed v a l u e s of s i n 0 . of  the l e a s t - s q u a r e s method.  This i s the p r i n c i p l e  The f i r s t d e r i v a t i v e s of  with r e s p e c t to A, C and D are equated to zero, and the r e s u l t i n g three simultaneous  equations  are solved f o r the three unknowns.  (the normal  equations)  The u n i t c e l l parameters  may then be c a l c u l a t e d by means of the r e l a t i o n s h i p s already given. Standard  d e v i a t i o n s of these parameters may be obtained  from the l e a s t - s q u a r e s r e s i d u a l s :  E_ ire . -x -a 2  cT^x) where a ^ of  -  1  =  1  (number of planes - number of parameters)  i s the appropriate diagonal element i n the i n v e r s e  the matrix used i n the c a l c u l a t i o n of the u n i t c e l l  para-  meters. The method of l e a s t - s q u a r e s i s e x t e n s i v e l y used f o r the refinement  of atomic p o s i t i o n a l and thermal parameters.  There  are, of course, u s u a l l y many more parameters, and the c a l c u l a t i o n i n v o l v e d can only be handled  e f f e c t i v e l y by a computer.  How-  ever, the c a l c u l a t i o n i s e s s e n t i a l l y the same as t h a t d e s c r i b e d here.  26 REFERENCES  1.  " I n t e r n a t i o n a l Tables f o r X-ray C r y s t a l l o g r a p h y " , V o l . I l l , Kynoch Press, Birmingham, 1962.  2.  N. Camerman and J . T r o t t e r , J . Chem. Soc.,  3*  V.R. C u l l e n and J . T r o t t e r , Canad. J . Chem.. 1962, 40. 1113; 1963, 41, 2983.  4.  A.Shimada, B u l l , Chem. Soc. Japan, 1959, 32, 309; 1960, 33, 301; 1961, 34, 639; 1962, 35, 1600.  5m  L . P a u l i n g , "The Nature of the Chemical Bond", 3rd. Edii., Cornell U n i v e r s i t y Press, Ithaca, 1960.  6.  S t r u k t u r b e r i c h t . 2. 25, 294; S t r u c t u r e Reports.  7.  J . T r o t t e r , Z. K r i s t a l l o g r . , 1965 ( i n p r e s s ) .  8.  J.C. B a i l a r and P.F. Cundy i n "Inorganic Syntheses", McGraw-Hill Book Company, 1939, Ed. H. S. Booth,  9.  J.B. Nelson and D.P. R i l e y , Proc. Phys. S o c , 1945, 57,  1964, 219.  11. 272.  V o l . I, p. 104.  160. 10.  D»¥.J. Cruickshank,  11.  "Tables of Interatomic Distances and C o n f i g u r a t i o n i n Molecules  A c t a . C r y s t . , 1949, 2, 65.  and Ions", Chem. Soc. Spec. P u b l . No. 11, 1958.  12.  J . T r o t t e r , A c t a . C r y s t . . 1960, 13. 86.  13.  M.U. Cohen, Rev. S c i . I n s t r . . 1935, 6, 68; 1936, 7, 155.  14.  L.V. Az&roff and M.J. Buerger, "The Powder Method i n X-ray C r y s t a l l o g r a p h y " , McGraw-Hill, New York, 1958.  

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