The Crystal Structures of the Acid Salts of Some Aromatic Acids

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THE CRYSTAL STRUCTURES OP THE ACID SAITS OP SOME AROMATIC ACIDS*

^

THESIS P r e s e n te d f o r tn e D egree o f D o c to r o f P h ilo s o p h y i n th e U n i v e r s i t y o f Glasgow by Jo h n M aeP h ail S k in n e r, B. Sc.

University or Glasgow. Jtagttst, 1950.

ProQuest N um ber: 13850818

All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is d e p e n d e n t upon the quality of the copy subm itted. In the unlikely e v e n t that the a u thor did not send a c o m p le te m anuscript and there are missing pages, these will be noted. Also, if m aterial had to be rem oved, a n o te will ind ica te the deletion.

uest ProQuest 13850818 Published by ProQuest LLC(2019). C opyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C o d e M icroform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346

PREFACE

The r e s u l t s o f t h e i n v e s t i g a t i o n o f t h e s t r u c t u r e o f p o ta s s iu m h y d ro g en b is - p - h y d r o x y b e n z o a t e , d e s c r ib e d i n P a r t I o f t h i s t h e s i s , a re b e in g p u b lis h e d c o n j o i n t l y w it h Dr. J . C. Speakman. I w is h t o e x p r e s s my s in c e r e th a n k s t o my s u p e r v is o r s , P r o f e s s o r J . M. R o b ertso n and Dr. J . C. Speakman, f o r s u g g e s t in g t h e problem f o r r e s e a r c h , and f o r c o n s ta n t encouragem ent and a d v ic e d u r in g th e c o u r s e o f t h e w ork. I am in d e b te d t o Dr. Speakman f o r sam p les o f v a r io u s a c id s a l t s .

I a l s o w is h t o th a n k t h e D epartm ent o f

S c i e n t i f i c and I n d u s t r i a l R e se a r c h f o r a M ain ten an ce A llo w a n c e .

J . M. S.

U n i v e r s it y o f G lasgow . A u g u st, 1 9 5 0 .

SUMMARY The c r y s t a l s t r u c t u r e s o f th e a c id p o ta s s iu m s a l t s o f p -h y d r o x y b e n z o ic , b e n z o ic and a n i s i c a c id h a v e b een exam ined by t h e X -ra y d i f f r a c t i o n m ethod. I t h a s b een shown t h a t p o ta ssiu m h yd rogen b is - p - h y d r o x y b e n z o a te i s a m onohydrate and t h a t i t s c r y s t a l s t r u c t u r e i s c l o s e l y s im i l a r t o t h a t o f p o ta ss iu m h yd rogen b i s p h e n y la c e t a t e . The p r i n c i p a l common f e a t u r e i s i n t h e li n k i n g o f th e c a r b o x y l g ro u p s by a s h o r t , and a p p a r e n tly s y m m e tr ic a l, h yd rogen bon d. I t i s th o u g h t t h a t t h e c r y s t a l s t r u c t u r e s o f th e a c id s a l t s o f m ost m o n o ca r b o x y lic a c id s may g e n e r a lly conform t o t h i s p la n . F u r th e r e v id e n c e f o r t h i s s u g g e s t io n h a s a l s o b een o b ta in e d from a p r e lim in a r y a n a l y s i s o f t h e s t r u c t u r e of p o ta ss iu m h y d ro g en b is b e n z o a t e w h ich a p p ea rs t o be b u i l t on t h e same p la n .

The c r y s t a l s t r u c t u r e o f p o ta ss iu m

h yd ro g en b i s a n i s a t e h a s a l s o b ee n exam ined b u t, a s y e t , l i t t l e p r o g r e s s h a s b een made w it h th e a n a l y s i s .

iii. CONTENTS. P age. P r e fa c e

........................................................................................

i

S u m m a r y ................................................................................................ i i I n t r o d u c t i o n ..........................................................

.

.

1

Part I P o ta ssiu m h y d ro g en b is - p - h y d r o x y b en zo a te C r y s t a l D a t a ................................................................

6

E x p e r i m e n t a l ...........................................................

6

A n a ly s is o f t h e S t r u c t u r e ..............................

9

D is c u s s io n

...........................................................

27

Appendix

45 Part I I

P o ta ssiu m h y d ro g en b is b e n z o a t e C r y s t a l D a ta .

.

.

.

.

.

.

.

.

53

E x p e r i m e n t a l .......................................................

53

A n a ly s is o f t h e S t r u c t u r e ...................................... 56 P o ta ssiu m h y d ro g en b i s a n i s a t e C r y s t a l D a t a ............................................ E x p e r im e n ta l A n a ly s is o f t h e S tr u c tu r e

.

68

....................................... 68 •

69

R e f e r e n c e s .........................................................................................74

1 I n t r o d u c t io n A cid s a l t s o f m onobasic a c id s , i n w h ic h a m o le c u le o f n orm a l s a l t i s com bined w it h one or more m o le c u le s of th e p a r e n t a c id , a r e form ed by m ost a c id s and m ost m e t a ls , d e t a i l e d su r v e y s e e Sm ith, 1 9 4 9 )

(F o r a

Many o f t h e a c id sodium and

p o ta ss iu m s a l t s o f m cn o c a r b o x y lic a c id s a re m en tion ed i n th e lite r a tu r e o

Of p a r t i c u l a r l y f r e q u e n t o c c u r r e n c e h e r e i s tn e

1 : 1 compound i . e . w here one m o le c u le o f a c id (HX) i s com bined w it h one m o le c u le o f norm al s a l t (KX) t o g i v e th e a c id s a l t (KHX2 )o

W h ile t h e sodium s a l t s a re o f t e n h y d r a te d , th e

p o ta s s iu m s a l t s a r e , i n g e n e r a l, an h yd rou s.

T h is much h a s

b e e n known f o r some c o n s id e r a b le t im e , b u t l i t t l e t h e p h y s i c a l p r o p e r t i e s o f t h e s e com pounds. m easu rem en ts (d e F ocran d, 1883;

i s known o f

T herm ochem ical

R i v a l s , 1897) c l e a r l y in d i c a t e d

how ever t h a t t h e r e was a d e f i n i t e lin k a g e b etw een a c id and s a l t . O c c a s io n a lly sa n e a u th o r s h a v e s u g g e s te d p o s s i b l e s t r u c t u r a l fo r m u la e f o r t h e s e com pounds.

Farmer ( 1 9 0 3 ) , f o r

ex a m p le, r e l a t e d them t o oxonium s a l t s and p ro p o se d s t r u c t u r e s su ch a s: R.CO

K 0S E.COg H

On t h e o th e r hand P f e i f f e r (1 9 1 4 ) s u g g e s te d tw o p o s s i b l e str u c tu r e s, a ) R .C = 0 I 0M

H-O-C-B II 0

b ) R .C -0 I OH

M-O-C-E I 0

S tr u c tu r e ( b ) , i n w h ich t h e r e i s c o - o r d in a t io n t o a c e n t r a l

2 m e ta l atom , w as p r e f e r r e d s i n c e compounds more com plex th a n t h e 1 : 1 ty p e ca n a l s o he fo r m u la te d i n t h i s m anner.

More

r e c e n t l y (R o ss and M o rriso n , 1933) a s im i la r s t r u c t u r e h a s b een p r o p o se d , v i z . R-C=0 -----M---1 OH

-© -1 0-C-R I 0

V i t a l e ( 1 9 3 6 ) , h o w ev er, p r e f e r s a c y c l i c s t r u c t u r e OH NaO 0 —C-R y p R 'O-C-OH R b e c a u s e a s tu d y o f th e Raman s p e c t r a o f such compounds h a s shown th e a b se n c e o f a c a r b o n y l f r e q u e n c y .

T here i s l i t t l e

p o s i t i v e e v id e n c e a v a i l a b l e t o e n a b le a d e c i s i o n t o be made b etw een t h e s e p o s s i b l e fo r m u la e . R e c e n tly (Speakm an, 1949) an X -ra y i n v e s t i g a t i o n o f t h e s t r u c t u r e o f p o ta s s iu m h yd rogen b i s - p h e n y la c e t a t e KH( c 8h o2 ) 2 h a s b een c a r r ie d o u t.

I t h a s b een shown t o b e b u i l t up of

i n f i n i t e l a y e r s o f p o ta ssiu m and h yd rogen atom s ( o r io n s ) b etw een p a i r s o f l a y e r s o f p h e n y la c e t a t e r e s i d u e s .

A d ja cen t

c a r b o x y l g ro u p s a r e lin k e d by a v e r y s h o r t h yd rogen bond r e m in is c e n t o f t h e s tr o n g h yd rogen bonds fou n d i n in o r g a n ic a c id s a lts .

Of p a r t i c u l a r i n t e r e s t i s th e f a c t t h a t t h i s bond

a p p e a r s t o be sy m m e tr ic a l s in c e t h e oxygen atom s i n q u e s t io n are s i t u a t e d ab ou t a c e n t r e o f sym m etry.

5. The p o s i t i o n o f tn e p r o to n ta k in g p a r t i n h yd rogen bond fo r m a tio n h a s b een t h e s u b j e c t o f c o n s id e r a b le s p e c u la t i o n . D ir e c t e v id e n c e on t n i s p o in t i s d i f f i c u l t t o o b ta in s in c e i t i s r a r e l y p o s s i b l e t o e s t a b l i s h t h e p o s i t i o n s o f h yd rogen atom s by t h e X -ra y m eth od .

B e r n a l and Megaw (1 9 3 5 ) h a v e s u g g e s te d

t h a t i n th e s h o r t h yd rogen b o n d s, such a s o c c u r i n in o r g a n ic a c id s a l t s , th e h y d ro g en atom may b e s y m m e tr ic a lly lo c a t e d . The lo n g e r bonds ( 2 .7 0 A . or m o r e ), found i n h y d ro x y com pounds, a re c o n s id e r e d t o be u n sy m m e tr ic a l and c a l l e d "hydroxyl" b o n d s. H owever, s p e c t r o s c o p ic i n v e s t i g a t i o n o f a la r g e number o f compounds c o n t a in in g h y d ro g en b on d s h a s a lw a y s r e v e a le d t h e p r e s e n c e o f an CH a b s o r p tio n band w n ich w ould be e x p e c te d t o be a b se n t i n a sy m m e tr ic a l 0-H . . 0 a rran gem en t.

T h is d i s ­

symmetry i n t h e h y d ro g en bond a l s o e x p la in s s u c c e s s f u l l y t h e o c c u r r e n c e o f th e " r e s id u a l en trop y" i n many compounds such a s i c e and in o r g a n ic a c id s a l t s .

A su r v e y o f t h e e v id e n c e on

t h i s q u e s t io n h a s b een g iv e n by D a v ie s ( 1 9 4 6 ) .

On tn e o th e r

h an d , U b b elch d e ( 1 9 4 9 ) m a in ta in s t h a t p r o t o n ic r e so n a n c e m akes a c e r t a i n c o n t r i b u t i o n t o th e a t t r a c t i v e f o r c e s w h ich a re o p e r a t iv e i n h y d ro g en bond f o r m a tio n , and h e h a s s u g g e s t e d t h a t i n c e r t a i n c ir c u m s ta n c e s th e p r o to n may be s it u a t e d midway b etw een t n e tw o oxygen a to m s. In v ie w o f th e i n t e r e s t i n g f e a t u r e s fou n d by Speakman i n t h e s t r u c t u r e o f p o ta ss iu m h y d ro g en b is - p h e n y la c e t a t e i t

seem ed

w o r th w h ile t o e x te n d th e e x a m in a tio n t o t h e p o ta s s iu m s a l t s o f

4. o th e r m on obasic a c i d s .

P art I .

o f t h i s T h e s is d e s c r ib e s an

i n v e s t i g a t i o n o f t n e s t r u c t u r e o f p o ta ss iu m h yd rogen p -h y d r o x y b e n z o a te .

T h is compound was p rep a red by a method

a n a lo g o u s t o t h a t o u t lin e d by Parmer ( l o c . c i t . ) who c la im e d t h a t i t w as anhydrous*

As th e a n a l y s i s p r o c e e d e d i t became

c l e a r t h a t t n e s a l t w as h y d r a te d .

C o n firm a to ry e v id e n c e on

t h i s p o in t i s g iv e n i n an A ppendix t o P a r t I 0

In p a r t I I .

d e t a i l s a re g iv e n o f a l e s s c o m p le te i n v e s t i g a t i o n o f t h e s t r u c ­ t u r e s o f p o ta s s iu m h yd rogen b e n z o a te and p o ta s s iu m h yd rogen a n is a te .

PART

6. P o ta ssiu m Hydrogen B is -p -H y d r o x y b e n z o a te . C r y s t a l .Data. '.The f o ll o w i n g d a ta w ere e s t a b l is h e d by s i n g l e - c r y s t a l r o t a t i o n and o s c i l l a t i o n p h o to g r a p h s , u s in g co p p er K -^ r a d i a t i o n (A « 1 .5 4 A ). P o ta ssiu m h yd rogen b is-p -h y d r o x y b e n z o a t© m onohydrate KH(G7 H5 C3 ) 2 *H2 0;

m o le c u la r w e ig h t 332*3;

ab ove POO C., m o n o c iin ic p r is m a t ic ; b « 3 .8 2 ( ± . 0 2 ) ,

c

a*

= 1 1 .3 0 ( ± . 0 2 ) A . f * ,

u n i t c e l l , 7 0 6 .6 a ;

in .p t . d ecom p oses

16 • 4 0 ( :f . 0 5 ) , 9 ? .5 ° ( + 0 .5 * ) ;

volu m e o f

d e n s i t y , c a l c u l a t e d , 1 .5 6 , fo u n d , 1 .5 4 ;

tw o m o le c u le s p e r u n i t c e l l ;

P(CCO), 3 4 4 ;

a b s o r p tio n c o e f f i c i e n t

f o r X -r a y s (Xa 1 .5 4 A. )ji = 3 6 .9 cm?1 A bsent s p e c t r a : h0£ when I i s or C pjj-P S/c.

odd.

o Space group C g -°c

The l a t t e r sp a c e group w as ad op ted and i s

j u s t i f i e d by t h e outcom e;

i t i m p li e s t h a t each m o le c u le

p o s s e s s e s e i t h e r a c e n t r e o f symmetry or a t w o - f o ld a x i s . E x p e r im e n ta l. The s a l t w as r e c r y s t a l l i s e d from a b s o lu t e a l c o h o l , t h e r e b e in g l i t t l e c h o ic e o f s o lv e n t s in c e t h e compound i s r e a d i l y b rok en down i n t o i t s c o n s t i t u e n t s (HX and KX) i n s o l u t i o n . The la th -s h a p e d c r y s t a l s t h u s o b ta in e d , i n w h ich (1 0 0 ) f a c e o n ly i s w e l l d e v e lo p e d , showed s t r a i g h t e x t i n c t i o n u n d er t h e p o l a r i s i n g m ic r o sc o p e and w ere r a t h e r b r i t t l e b u t c o u ld be c u t t o s u i t a b l e d im e n s io n s.

7. M easurement o f I n t e n s i t i e s . The h 0 £ , hkO and Ok^ r e f l e c t i o n s w ere o b ta in e d from W eisse n b e rg f i l m s o f t h e z e r o l a y e r l i n e s f o r c r y s t a l s r o t a t e d about t h e b , c and a a x e s .

In o rd er t o o b ta in

r e l a t i v e - i n t e n s i t y m easurem ents t h e m u lt ip le f i l m te c h n iq u e (R o b e r ts o n , 1 9 4 3 ) w as u s e d .

The ra n g e o f i n t e n s i t i e s

c o v e r e d w as a b o u t 1 0 0 0 :1 and e x p o s u r e s o f 8 h o u r s w e r e , i n g e n e r a l , s u f f i c i e n t f o r t h e hO I zo n e b u t t h e s e had t o be in c r e a s e d c o n s id e r a b ly (up t o ab ou t 16 h o u r s ) f o r t h e hkO and Okt z o n e s , on a c c o u n t o f t h e much w eak er r e f l e c t i o n s i n t h e s e zon es.

The o b se r v ed i n t e n s i t i e s w ere u l t i m a t e l y p la c e d on

an ap p roxim ate a b s o lu t e s c a l e by c o r r e l a t i o n w it h th e s t r u c t u r e f a c t o r s c a l c u l a t e d from t h e a to m ic p a r a m e te r s . C r y s t a l D im e n sio n s. F or t h e h O i zon e th e c r y s t a l u se d had a c r o s s - s e c t i o n n orm al t o t h e b - a x i s o f 0.30mmo by O.ICmm., f o r t h e hkO zo n e t h e c r o s s - s e c t i o n norm al t o t h e c - a x i s w as 0.25mnu by 0 .2 0mm. and f o r th e 0k£ zo n e t h e c r o s s - s e c t i o n n orm al t o t h e a - a x i s w as 0.50mm. by 05Ctam. A b so r p tio n c o r r e c t i o n s w ere th u s o n ly r e q u ir e d i n t h e h0£ zone.

The a v e r a g e p a th th ro u g h th e c e n t r e o f t h e c r y s t a l

w as fou n d f o r e a c h i n d i v i d u a l r e f l e c t i o n by m aking a c e l l u l o i d s c a l e m odel o f t h e c r o s s - s e c t i o n o f t h e c r y s t a l and p l a c i n g t h i s a t t h e c e n t r e o f a c e l l u l o i d s h e e t on w h ich th e r e f l e c t i n g c i r c l e had b een m arked.

By p l a c in g th e w h o le on a d raw in g

o f t h e r e c i p r o c a l l a t t i c e th e p a th f o r e a c h r e f l e x i o n c o a id be r e a d i l y m ea su red .

C o r r e c t io n s made i n t h i s manner

d id n o t a p p r e c ia b ly a l t e r t h e v a lu e s o f F m easured and w ere t h e r e f o r e n o t a d o p te d . 3Ehe i n t e n s i t i e s w ere a l s o c o r r e c t e d w it h th e u s u a l X oren tz and p o l a r i s a t i o n f a c t o r s .

9 A n a ly s is o f t h e S t r u c t u r e . An i n t e r e s t i n g f e a t u r e o f t h e c e l l d im e n s io n s i s t h e v e r y s h o r t le n g t h o f th e b - a x is * t h a t th e m o le c u le must l i e a x is *

T h is a t once s u g g e s te d

a lm o st a t r i g h t a n g le s t o t h i s

H ence a p r o j e c t i o n a lo n g th e b - a x i s sh o u ld g i v e good

r e s o l u t i o n and a t t e n t i o n w as th u s d ir e c t e d t o t h i s p r o j e c t io n * S in c e t h e r e a re o n ly two p o ta ss iu m atom s i n t h e u n i t c e l l , t h e s e atom s m ust l i e e i t h e r a t c e n t r e s o f symmetry or on t h e t w o - f o l d a x e s , s i n c e t h e s e are t h e o n ly t w o - f o ld p o s it io n s in th e u n it c e ll*

No such r e s t r i c t i o n a p p l i e s

t o th e o th e r atom s i n t n e u n i t c e l l b u t i t w a s hoped t h a t u s e f u l in fo r m a t io n w ould be o b ta in e d from a P a t t e r s o n p r o j e c t i o n o f t h e h O l zone* P a t t e r s o n (1 9 3 4 ) h a s shown t h a t t h e f u n c t i o n (,-+oo £=+cO

'P [jc -li z )

=

Z_. Z ]

^ =

Z_.

F h k i c o s 2 ^ (hx+' ky+lz. )

e x h i b i t s p e a k s a t v e c t o r d i s t a n c e s from th e o r ig in e q u a l t o v e c t o r d i s t a n c e s b etw een p a i r s o f maxima i n e l e c t r o n d e n s it y *

In m ost c a s e s th e i n t e r p r e t a t i o n o f a P a t t e r s o n

d iagram i s a m a tte r o f some c o m p le x it y .

In a tw o -d im e n s io n a l

p r o j e c t i o n , b e c a u s e o f o v e r la p p in g o f maxima, i t becom es e v e n more d i f f i c u l t . I f , h o w ev er, t h e s u b s ta n c e c o n t a in s a h ea v y atom th e n t h e p ea k s due t o v e c t o r d i s t a n c e s b etw een t h e h ea v y atom and any o th e r atom s w i l l sta n d out and i t i s p o s s i b l e t o o b t a in a to m ic c o o r d in a t e s f o r t h e s e atoms*

In c a s e s w here

1C. t h e h ea v y atom l i e s i n a s p e c i a l p o s i t i o n ( c e n t r e or a p p a ren t c e n t r e o f symmetry ) , t h e diagram th e n a p p r o x im a te s t o th e t y p i c a l F o u r ie r diagram and t h e a c t u a l c o - o r d i n a t e s o f th e l i g h t e r atom s a re o b ta in e d . The f u n c t i o n P(xO z) = E C

FhOl ^ c o s 2 /K h x + lz )

w as e v a lu a te d by t h e method o f B e e v e r s and l i p s o n (1 9 3 4 ) u s i n g 2 t h e F v a l u e s o b ta in e d from t h e o b served i n t e n s i t i e s o f th e hO^ r e f l e x i o n s .

The r e s u l t s o f t h i s s y n t h e s i s are shown i n

F i g . l and i t w i l l be s e e n t h a t th e s i t u a t i o n i s somewhat the

co n fu sed .

One o f th e p o s s i b l e c a u s e s i s t h a t "'potassium atom

h a s n o t s u f f i c i e n t d i f f r a c t i n g power t o swamp t h a t o f th e o th e r a to m s.

The o b v io u s s o l u t i o n t o t h i s d i f f i c u l t y was t o a tte m p t

isom o rp h o u s r e p la c e m e n t o f th e p o ta ss iu m by a h e a v ie r atom su ch a s t h a lliu m

or ru b id iu m .

No t h a l l o u s s a l t c o u ld be p rep a red b u t rub id iu m h y d ro g en p -h y d r o x y b e n z o a te p roved t o be isom orp h ou s w it h t h e p o ta s s iu m s a lt.

As m ig h t be e x p e c te d t h e r e w ere s m a ll b u t n o t i c e a b l e

d i f f e r e n c e s i n t h e l a t t i c e d im e n s io n s v i z . b — 3 . 9 1 ^ *02A . , c = 1 1 .5 0 +_ . 02A.

a = 1 6 .4 7 +. . 04A„,

From m oving f i l m

d a ta

o

B w as fou n d t o b e a p p r o x im a te ly 9 3 .6 • A s e t o f r e l a t i v e i n t e n s i t i e s f o r t h e h 0 £ zo n e w as o b ta in e d from a m u lt ip le f i l m b - a x is .

s e r i e s o f t h e z e r o la y e r of t h e

As i n t h e c a s e o f t h e p o ta ss iu m s a l t ,

p r o j e c t i o n w as made a lo n g t h e b - a x i s . is

a P a tte r so n

The r e s u l t a n t d iagram

shown i n F i g . 2 and i t w i l l be s e e n t h a t t h e r e s o l u t i o n i n

P ig . 1 . P a t t e r s o n s y n t h e s i s ( I ^ O l l ^ ) ^ or b en zo a te.

C o n t o u r - lin e s c a l e a r b it r a r y .

iiyd rogen p -h y d r o x y

12.

O

sca le

P ig .2 . P a tte r so n s y n th e s is ( b en zo a te *

* or ruki& iu® h y d ro g en p -h y d r o x y

C o n t o u r -lin e s c a l e a r b it r a r y .

13. T a b le 1 . C o o r d in a te s from P a t t e r s o n diagram i n P i g . 2 . Atom

x /a

2 n x /a

z /c

2 f iz /c

Rb

0 .0 0

0 .0

0 .0 0

0 .0

0 (1 )

0 .5 0

1 8 0 .0

0 .0 0

0 .0

0 (2 )

0 .0 6

2 1 .6

0 .2 1

7 5 .6

0 (3 )

0 .1 1

3 9 .6

0 .3 9

1 4 0 .4

0 (4 )

0 .4 4

1 5 8 .4

0 .1 7

6 1 .2

0 (1 )

0 .1 2

4 3 .2

0 .3 1

1 1 1 .6

0 (2 )

0 .2 1

7 5 .6

0 .2 7

9 7 .2

0 (3 )

0 .2 2

7 9 .2

0 .1 4

5 0 .4

0 (4 )

0 .3 1

1 1 1 .6

0 .1 2

4 3 .2

0 (5 )

0 .3 6

1 2 9 .6

0 .2 0

7 2 .0

0 (6 )

0 .3 4

1 2 2 .4

0 .3 2

1 1 5 .2

0 (7 )

0 .2 7

9 7 .2

0 .3 4

1 2 2 .4

14. t h i s c a s e w as e x c e l l e n t .

A s e t of x and z c o o r d in a t e s , g iv e n

in T able 1 w as o b ta in e d f o r t h e atom s w h ich g a v e a good agreem ent w it h th e ob serv ed s t r u c t u r e a m p litu d e s .

U sin g th e

same c o o r d in a t e s f o r t h e p o ta ss iu m s a l t and c a l c u l a t i n g t h e c o r r e s p o n d in g hO^ s t r u c t u r e f a c t o r s , th e agreem ent w as l e s s c lo s e .

No a llo w a n c e w as made a t t h i s s t a g e f o r t h e p r e s e n c e

o f th e w a te r m o le c u le .

It is

o b v io u s t h a t t h e a d v e r s e e f f e c t

on

o f t h i s " 'd iscrep an cy b etw een F c a l c u l a t e d and F m easured w i l l b e more pron ou n ced f o r th e p o ta ss iu m s a l t . At t h i s s t a g e t h e e x p e r im e n ts t o p r o v e th e t r u e c o m p o s itio n o f t h e s a l t w ere u n d e r ta k e n .

Once i t w as p ro v ed t o be a

h y d r a t e , t h e r e fin e m e n t o f t h e hO I zon e p a r a m e te r s o f th e ru b id iu m s a l t by s u c c e s s i v e F o u r ie r a n a l y s i s w as soon a c h ie v e d . When t h e d is c r e p a n c y b etw een F m easured and F c a l c u l a t e d w as 2 1 $ f o r th e o b se rv ed p l a n e s , t h e c o o r d in a t e s o b ta in e d w ere u s e d t o c a l c u l a t e s ig n s f o r t h e s t r u c t u r e a m p litu d e s o f th e p o ta s s iu m s a l t .

The f i n a l e l e c t r o n d e n s i t y map o b ta in e d by

t h e summation o f t h e s e r i e s

p{ is

x ,z

) =

£ Ffco£ c o s 2 f T ( h x /a + l z / c )

shewn i n F i g . 3 , w it h an e x p la n a to r y diagram i n F i g . 4 .

The e l e c t r o n d e n s i t y w as e v a lu a te d a t 6 ° i n t e r v a l s a lo n g each a x is .

The a and c a x e s w ere d iv id e d i n t o 6 0 p a r t s , c o r r e sp o n d ­

in g t o i n t e r v a l s o f .188A a lo n g c and .2 7 3 A a lo n g a .

For

t h e sum m ation, t h e t h r e e f i g u r e s t e n c i l m ethod (R o b e r tso n 1948) w as u se d and th e d e n s it y th u s com puted a t 900 p o i n t s i n t h e asym m etric p r o j e c t i o n .

Sca.le

F ig . 3 . F o u r ie r s y n t h e s i s (F ^ q-^) f o r p o ta ss iu m h y d ro g en p -h y d ro x y b e n z o a t e , p r o j e c t e d a lo n g t h e b - a x i s .

The c o n to u r s r e p r e s e n t

d e n s i t y in c r e m e n ts o f one e l e c t r o n p e r A oxygen atom s and tw o e l e c t r o n s p e r A The o n e - e le c t r o n c o n to u r i s d o t t e d .

i n t h e carb on and

i n t h e p o ta ssiu m atom .

16.

o

21

F ig . 4 . Arrangem ent o f atom s i n b - a x i s p r o j e c t i o n .

The c e n t r e s o f

symmetry shown on t h e l i n e x = 0 a r e a t y a 0 or l / 2 b ; on x « l / 2 a a r e a t y = 3 /2 b or 0*

th o se

17. The f i n a l x and z c o o r d in a t e s c h o se n from t h e F o u r ie r map a re marked by d o t s i n F i g . 3*

S tr u c tu r e f a c t o r s f o r th e h O l

zo n e w ere r e c a l c u l a t e d and, s i n c e t h e r e w ere n o f u r t h e r s ig n c h a n g e s , r e fin e m e n t w as c o n s id e r e d c o m p le te - a t l e a s t by t h e d o u b le F o u r ie r s y n t h e s is m ethod .

The d is c r e p a n c y ,

exp ressed as £ |F m eas. w as 17«9$ f o r t h e o b serv ed p l a n e s .

In t h i s zon e 138 out o f

a p o s s i b l e 232 p la n e s w ere o b se r v e d . In t h i s p r o j e c t i o n c e n t r e s and t w o - f o ld a x e s o f symmetry are in d is tin g u is h a b le .

I f t h e p o ta ssiu m a t an i s s i t u a t e d a t

a c e n t r e o f symmetry th e n th e m id -p o in t o f 0 ( 2 ) . . . is

on an a x i s .

0 (2 * )

However, t h e d i s t a n c e b etw een 0 (2 ) and 0 (2 * )

i s , i n p r o j e c t i o n , 2 .3 A . w h ich i s much t o o lo n g f o r a s im p le c o v a le n t bond and t o o s h o r t f o r a h yd rogen bond or no bond at a ll. lie

C o n se q u e n tly i t m ust be presum ed t h a t th e oxygen atcm s

a t d i f f e r e n t l e v e l s and are r e l a t e d by a c e n t r e o f symmetry

w h ich w as th u s c h o s e n a s o r i g i n . B eca u se ox t h e v e r y s h o r t b - a x i s i t i s u n l i k e l y m a t r e s o l u t i o n i n t h e hkO or 0k£ z o n e s w i l l be g o o d , b u t i n a r r iv in g a t a p r e lim in a r y s e t o f y -p a r a m e te r s some u s e f u l g u id a n c e may be o b ta in ed by d e t a i l e d c o n s id e r a t i o n o f th e h O t p r o je c tio n .

F or exam p le, th e d i s t a n c e C (3)-C (t>) i s ab ou t 2 .6 A .

and i f a r e g u la r h e x a g o n a l s t r u c t u r e be assum ed f o r t h e b en zen e r i n g th e n t h e d i f f e r e n c e i n t h e y - c o o r d in a t e s o f C (3) and C (6) m ust be 1A0

T here w ere o b v io u s i n d i c a t i o n s o f some i r r e g u l a r i t y

18. i n t h e a ro m a tic r i n g , f o r th e p r o j e c t e d d is t a n c e C (2 )-C (5 ) is

a lm o st 2 .8 A . h u t th e d i s t a n c e s b etw een C (3 )-C (4 ) and

C (o )-C (7 ) a r e o n ly 1 .3 A.

As a f i r s t a p p ro x im a tio n a d i f f e r e n c e

i n l e v e l o f .5A w as assumed b etw een C (2) and C ( 5 ).

In a

s im i l a r manner t h e c o o r d in a t e s o f atom s C (4) and C( 7 ) ap peared t o d i f f e r by ab ou t 1A« 0 ( 2 ) and 0 ( 3 ) m ust be a t a lm o st t h e same l e v e l f o r t h e d is t a n c e b etw een them m ea su res 2 .2 A .

T h is s u g g e s t io n i s

r e in f o r c e d by t h e f a c t t h a t t h e l i n e j o in i n g 0 (2 ) and 0 (3 ) i s a lm o st p e r p e n d ic u la r t o th e d i r e c t i o n C ( l ) - C ( 2 ) . The p o s i t i o n s o f th e p o ta ss iu m and oxygen 0 (1 ) atom s w ere fou n d a p p r o x im a te ly from a c o n s id e r a t io n o f t h e h l O r e fle x io n s .

T hese w ere o b se rv ed t o be s m a ll when A i s ev en

and r e l a t i v e l y la r g e when J l i s

odd.

An arrangem ent w as th u s

so u g h t i n w h ich t h e c o n t r i b u t i o n s of b o th atom s t o th e s t r u c t u r e f a c t o r r e in f o r c e d each o th e r when A I s odd and w ere opposed when 4i i s e v e n .

T h is i s t h e c a s e i f t h e p o ta ss iu m atom i s

s it u a t e d a t a p p r o x im a te ly y = l/3 b and t h e oxygen a t an a t z e r o d is t a n c e a lo n g t h e b - a x i s . On t h e s e l i n e s a s e t o f y - c o o r d in a t e s w as o b ta in e d w h ic h , bl«d w it h m inor a l t e r a t i o n s , ^ s i g n s t o be g iv e n t o t h e s t r u c t u r e ■enq

f a c t o r s o f t h e hkO z o n e .

A F o u r ie r s y n t h e s i s w as c a r r ie d

ou t b u t , a p a r t £rom c o n fir m in g t h e p o s i t i o n s o f atom s K ,0 ( 1 ) and 0 ( 4 ) , w as o f l i t t l e v a l u e .

The a n a l y s i s th u s p ro ce e d e d

m a in ly by t r i a l and e r r o r u n t i l a s t r u c t u r e w as o b ta in e d g i v i n g

19. a 30 $ d is c r e p a n c y betw een F m easured and F c a l c u l a t e d .

Even

a t t h i s s t a g e t h e F o u r ie r map p roved t o be u n in fo r m a tiv e and showed no s ig n o f r e f i n i n g .

I t w as c o n s id e r e d p o s s i b l e t h a t

t h i s m igh t b e d u e , i n p a r t , t o th e n o n - i n f i n i t e l i m i t s of sum m ation.

In t h i s zo n e o n ly 4 o r d e r s o f k a r e a c c e s s i b l e

t o Cu K >