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35Cl and 37Cl quadrupole resonance in normal and deuterated KH(CCl3COO)2 and NH4(CCl3COO)2
Volume 25A, number 4
PHYSICS LETTERS
28 August 1967
35C1 AND 37C1 QUADRUPOLE RESONANCE IN NORMAL AND DEUTERATED KH(CC13COO) 2 AND NH4(CC13COO) 2 R. BLINC, M. MALI and Z. T R O N T E L J The University of Ljubljana and Nuclear Institute "J.Stefan", Ljubl~ana, Yugoslavia Received 24 July 1967
The existence of only 3 35C1 and 37C1 quadrupole resonance lines, respectively, in undeuterated and deuterated KH(CC13COO)2 and NH4H(CC13COO)2 demonstrates that the proton as well as the deuteron are centrally located in the O-H--O bonds on the quadrupole resonance time scale and that the H-bond potential does not change on deuteration.
In view of the l a r g e isotope effects on d e u t e r ation in h y d r o g e n - b o n d e d f e r r o e l e c t r i c s a s well as b e c a u s e of the biological i m p l i c a t i o n s of Hbonding [1-3], quite an effort has r e c e n t l y been made to e s t a b l i s h whether the s t r e n g t h and s y m m e t r y of the d e u t e r i u m bond d i f f e r s f r o m that of the hydrogen bond in s t r o n g l y H-bonded s u b s t a n ces [4]. To throw additional light on this p r o b l e m we decided to i n v e s t i g a t e the 35C1 and 37C1 p u r e quadrupole r e s o n a n c e s p e c t r a of p o l y c r y s t a l l i n e KH(CC13COO)2 and KD(CC13COO)2 a s well a s of i s o m o r p h o u s NH4H(CC13COO)2 and ND4D(CC13COO)2. T h e s e acid s a l t s a r e known to f o r m d i m e r s containing a v e r y s h o r t ( R o - - o = = 2.47~,) and p o s s i b l y s y m m e t r i c O - H - - O bond [5], and a r e in addition v e r y well suited for q u a drupole i n v e s t i g a t i o n s of H-bonding. If the H or D n u c l e u s is c e n t r a l l y located in the O - H - - O bond, all CC13 groups a r e c r y s t a l l o g r a p h i c a l l y e q u i -
v a l e n t , and one finds only 3 35C1 or 37C1 q u a d r u pole r e s o n a n c e l i n e s , r e s p e c t i v e l y . H, on the other hand, the H - b o n d potential is not s y m m e t r i c and the d i m e r can be d e s c r i b e d as c o n s i s t i n g of CC13COOH and CC13COO- u n i t s , the l i f e t i m e of which i s l o n g e r than 10-8s, one expects to find 6 35C1 or 37C1 r e s o n a n c e s f r e q u e n c i e s , r e s p e c tively, as t h e r e a r e now six n o n - e q u i v a l e n t c h l o r i n e s i t e s in the unit cell on the quadrupole r e s o n a n c e t i m e s c a l e . The v i b r a t i o n a l s p e c t r a as well as i n e l a s t i c n e u t r o n s c a t t e r i n g data in the u n d e u t e r a t e d compounds a r e in favour of the f i r s t p o s s i b i l i t y and W e i s s [6] r e a l l y found only 3 35C1 r e s o n a n c e l i n e s at 77OK. We i n v e s t i g a t e d the 35C1 and to extend the t i m e s c a l e of our m e a s u r e m e n t s a l s o the 37C1 r e s o n a n c e region. In the t e m p e r a t u r e r a n g e f r o m 90° to 63°K only 3 35C1 and 3 37C1 l i n e s w e r e found in KH(CCI3COO) 2 (v315 = 39 745 MHz, v3ii5 : 39 143 IOta --{4)
31~ . ,7oo
393001 ~ 6O
I
~
1.2.3: C|35 , ,.,o-'
i.m.m:c
060
' 79
/ / J J
3
70
60
T ('°K]
90 3090060
~O
~
TC'l]
90
60t TC'l ] 90,
Fig. 1. Temperature dependence (a) and relative change (b) of the 35C1 and 37C1 quadrupole resonance frequencies in NH4H(CC13COO)2 as a function of temperature. 289
Volume 25A, number 4 MHz
PHYSICS LETTERS
v 35 i i i = 39 110 MHz at 77°K) and
NH4H(CC13CO0)2 (v 35 = 39 765 MHz, v 35 = = 39 395 MHz, v ~ i =~39 285 MHz at 77°~) thus c o n f i r m i n g the c~iiclusion that on the t i m e s c a l e of the q u a d r u p o l e r e s o n a n c e m e a s u r e m e n t s the proton o c c u p i e s a" ¢en£ral position in the O - H - - O bond in t h e s e compounds. On the b a s i s of the quadrupole r e s o n a n c e data alone one is not able to say wh et h er this is a t r u l y s y m m e t r i c a l single m i n i m u m type of H-bond o r w h e th e r the a p p e a r ance of only 3 q u a d r u p o l e l in e s is the r e s u l t of r a p i d flipping of the proton between two e q u i v a l e n t e q u i l i b r i u m s i t e s . In combination with i n f o r m a tion f r o m the m e t h o d s [7], h o w e v e r , the e x i s tance of a single m i n i m u m H-bond p o t e n ti a l s e e m s to be m o r e p r o b a b l e . In KD(CC13COO) 2 and in ND4D(CC13COO)2 both the n u m b e r and f r e quency of the 35C1 and 37C1 r e s o n a n c e l i n e s c o i n c i d e with the ones found in the u n d e u t e r a t e d a n a l o g u e s , within the l i m i t s of e x p e r i m e n t a l e r r o r (KD(CC13COO)2 : v 35 = 39 744 MHz, v ~ ~= 39 1 4 5 M H z , v 35 =39111 MHz; III ND4D(CC13COO)2 : v 35 = 39 765 MHz, v ~
=
= 3 9 3 9 8 M H z , v 3 ~ = 3 9 2 8 7 M H z ) . Thus one may say that in t h e s e compounds the d e u t e r o n as well as the proton a r e c e n t r a l l y l o c a t e d in the O - H - - O bonds on the quadrupole r e s o n a n c e t i m e s c a l e , and that the s y m m e t r y of the H-bond p o t e n t i a l does not change on d e u t e r a t i o n . As a b y - p r o d u c t of this i n v e s t i g a t i o n , we have a l s o studied the r e l a t i v e change (w m -co)/¢om of the 35Cl and 37C1 quadrupole r e s o n a n c e f r e q u e n -
28 August 1967
c i e s as a function of t e m p e r a t u r e . If the t e m p e r a t u r e f a c t o r s due to t o r s i o n a l and v i b r a t i o n a l m o tion [8] would be equal for all 3 c h l o r i n e s i t e s and f o r both i s o t o p e s , all e x p e r i m e n t a l points should fit the s a m e (w m -w)/w m v e r s u s T c u r v e . This is not the c a s e (fig. 1). W h e r e a s f o r the two low f r e q u e n c y l i n e s (II and HI) the 35C1 c u r v e s depend m o r e s t r o n g l y on t e m p e r a t u r e than the 37C1 ones, the opposite is t r u e for the high f r e q u e n c y line (I). The usual, s i m p l i f i e d p i c t u r e of the t o r s i o n a l motion as the only f a c t o r which d e t e r m i n e s the t e m p e r a t u r e dependence of the e l e c t r i c field g r a d i e n t s in c r y s t a l s [8] is thus c l e a r l y not a d e quate and o t h er v i b r a t i o n a l m o d e s as well as v i b r o n i c i n t e r a c t i o n s have to be taken into a c count.
References 1. G. Shirane and F. Jona, Ferroe]ectric crystals, (Oxford 1962). 2. G. C. Pimentel, The hydrogen bond (San Francisco and London 1960). 3. D. Had~i, H-bonding, (Pergamon Press, London, 1957). 4. J.A. Ibers, J. Chem. Phys. 36 (1962) 1356. 5. J.C. Speakman et al., J. Chem. Soc. (London) (1949) 3357; (1951) 185; (1954) 180, 787; (1961) 1151,1164; (1963) 4350, 4355. 6. D. Biedenkapp and A.Weiss, Ber. Bunsenges. Phys. Chem. 70 (1966) 788. 7. B. Bline, D. Had~i and A. Novak, Z. Elektrochem., Bet. Bunsenges. Phys. Chem. 64 (1960) 567. 8. H. Bayer, Z. Physik 130 (1951) 227.
PHYSICS LETTERS
28 August 1967
35C1 AND 37C1 QUADRUPOLE RESONANCE IN NORMAL AND DEUTERATED KH(CC13COO) 2 AND NH4(CC13COO) 2 R. BLINC, M. MALI and Z. T R O N T E L J The University of Ljubljana and Nuclear Institute "J.Stefan", Ljubl~ana, Yugoslavia Received 24 July 1967
The existence of only 3 35C1 and 37C1 quadrupole resonance lines, respectively, in undeuterated and deuterated KH(CC13COO)2 and NH4H(CC13COO)2 demonstrates that the proton as well as the deuteron are centrally located in the O-H--O bonds on the quadrupole resonance time scale and that the H-bond potential does not change on deuteration.
In view of the l a r g e isotope effects on d e u t e r ation in h y d r o g e n - b o n d e d f e r r o e l e c t r i c s a s well as b e c a u s e of the biological i m p l i c a t i o n s of Hbonding [1-3], quite an effort has r e c e n t l y been made to e s t a b l i s h whether the s t r e n g t h and s y m m e t r y of the d e u t e r i u m bond d i f f e r s f r o m that of the hydrogen bond in s t r o n g l y H-bonded s u b s t a n ces [4]. To throw additional light on this p r o b l e m we decided to i n v e s t i g a t e the 35C1 and 37C1 p u r e quadrupole r e s o n a n c e s p e c t r a of p o l y c r y s t a l l i n e KH(CC13COO)2 and KD(CC13COO)2 a s well a s of i s o m o r p h o u s NH4H(CC13COO)2 and ND4D(CC13COO)2. T h e s e acid s a l t s a r e known to f o r m d i m e r s containing a v e r y s h o r t ( R o - - o = = 2.47~,) and p o s s i b l y s y m m e t r i c O - H - - O bond [5], and a r e in addition v e r y well suited for q u a drupole i n v e s t i g a t i o n s of H-bonding. If the H or D n u c l e u s is c e n t r a l l y located in the O - H - - O bond, all CC13 groups a r e c r y s t a l l o g r a p h i c a l l y e q u i -
v a l e n t , and one finds only 3 35C1 or 37C1 q u a d r u pole r e s o n a n c e l i n e s , r e s p e c t i v e l y . H, on the other hand, the H - b o n d potential is not s y m m e t r i c and the d i m e r can be d e s c r i b e d as c o n s i s t i n g of CC13COOH and CC13COO- u n i t s , the l i f e t i m e of which i s l o n g e r than 10-8s, one expects to find 6 35C1 or 37C1 r e s o n a n c e s f r e q u e n c i e s , r e s p e c tively, as t h e r e a r e now six n o n - e q u i v a l e n t c h l o r i n e s i t e s in the unit cell on the quadrupole r e s o n a n c e t i m e s c a l e . The v i b r a t i o n a l s p e c t r a as well as i n e l a s t i c n e u t r o n s c a t t e r i n g data in the u n d e u t e r a t e d compounds a r e in favour of the f i r s t p o s s i b i l i t y and W e i s s [6] r e a l l y found only 3 35C1 r e s o n a n c e l i n e s at 77OK. We i n v e s t i g a t e d the 35C1 and to extend the t i m e s c a l e of our m e a s u r e m e n t s a l s o the 37C1 r e s o n a n c e region. In the t e m p e r a t u r e r a n g e f r o m 90° to 63°K only 3 35C1 and 3 37C1 l i n e s w e r e found in KH(CCI3COO) 2 (v315 = 39 745 MHz, v3ii5 : 39 143 IOta --{4)
31~ . ,7oo
393001 ~ 6O
I
~
1.2.3: C|35 , ,.,o-'
i.m.m:c
060
' 79
/ / J J
3
70
60
T ('°K]
90 3090060
~O
~
TC'l]
90
60t TC'l ] 90,
Fig. 1. Temperature dependence (a) and relative change (b) of the 35C1 and 37C1 quadrupole resonance frequencies in NH4H(CC13COO)2 as a function of temperature. 289
Volume 25A, number 4 MHz
PHYSICS LETTERS
v 35 i i i = 39 110 MHz at 77°K) and
NH4H(CC13CO0)2 (v 35 = 39 765 MHz, v 35 = = 39 395 MHz, v ~ i =~39 285 MHz at 77°~) thus c o n f i r m i n g the c~iiclusion that on the t i m e s c a l e of the q u a d r u p o l e r e s o n a n c e m e a s u r e m e n t s the proton o c c u p i e s a" ¢en£ral position in the O - H - - O bond in t h e s e compounds. On the b a s i s of the quadrupole r e s o n a n c e data alone one is not able to say wh et h er this is a t r u l y s y m m e t r i c a l single m i n i m u m type of H-bond o r w h e th e r the a p p e a r ance of only 3 q u a d r u p o l e l in e s is the r e s u l t of r a p i d flipping of the proton between two e q u i v a l e n t e q u i l i b r i u m s i t e s . In combination with i n f o r m a tion f r o m the m e t h o d s [7], h o w e v e r , the e x i s tance of a single m i n i m u m H-bond p o t e n ti a l s e e m s to be m o r e p r o b a b l e . In KD(CC13COO) 2 and in ND4D(CC13COO)2 both the n u m b e r and f r e quency of the 35C1 and 37C1 r e s o n a n c e l i n e s c o i n c i d e with the ones found in the u n d e u t e r a t e d a n a l o g u e s , within the l i m i t s of e x p e r i m e n t a l e r r o r (KD(CC13COO)2 : v 35 = 39 744 MHz, v ~ ~= 39 1 4 5 M H z , v 35 =39111 MHz; III ND4D(CC13COO)2 : v 35 = 39 765 MHz, v ~
=
= 3 9 3 9 8 M H z , v 3 ~ = 3 9 2 8 7 M H z ) . Thus one may say that in t h e s e compounds the d e u t e r o n as well as the proton a r e c e n t r a l l y l o c a t e d in the O - H - - O bonds on the quadrupole r e s o n a n c e t i m e s c a l e , and that the s y m m e t r y of the H-bond p o t e n t i a l does not change on d e u t e r a t i o n . As a b y - p r o d u c t of this i n v e s t i g a t i o n , we have a l s o studied the r e l a t i v e change (w m -co)/¢om of the 35Cl and 37C1 quadrupole r e s o n a n c e f r e q u e n -
28 August 1967
c i e s as a function of t e m p e r a t u r e . If the t e m p e r a t u r e f a c t o r s due to t o r s i o n a l and v i b r a t i o n a l m o tion [8] would be equal for all 3 c h l o r i n e s i t e s and f o r both i s o t o p e s , all e x p e r i m e n t a l points should fit the s a m e (w m -w)/w m v e r s u s T c u r v e . This is not the c a s e (fig. 1). W h e r e a s f o r the two low f r e q u e n c y l i n e s (II and HI) the 35C1 c u r v e s depend m o r e s t r o n g l y on t e m p e r a t u r e than the 37C1 ones, the opposite is t r u e for the high f r e q u e n c y line (I). The usual, s i m p l i f i e d p i c t u r e of the t o r s i o n a l motion as the only f a c t o r which d e t e r m i n e s the t e m p e r a t u r e dependence of the e l e c t r i c field g r a d i e n t s in c r y s t a l s [8] is thus c l e a r l y not a d e quate and o t h er v i b r a t i o n a l m o d e s as well as v i b r o n i c i n t e r a c t i o n s have to be taken into a c count.
References 1. G. Shirane and F. Jona, Ferroe]ectric crystals, (Oxford 1962). 2. G. C. Pimentel, The hydrogen bond (San Francisco and London 1960). 3. D. Had~i, H-bonding, (Pergamon Press, London, 1957). 4. J.A. Ibers, J. Chem. Phys. 36 (1962) 1356. 5. J.C. Speakman et al., J. Chem. Soc. (London) (1949) 3357; (1951) 185; (1954) 180, 787; (1961) 1151,1164; (1963) 4350, 4355. 6. D. Biedenkapp and A.Weiss, Ber. Bunsenges. Phys. Chem. 70 (1966) 788. 7. B. Bline, D. Had~i and A. Novak, Z. Elektrochem., Bet. Bunsenges. Phys. Chem. 64 (1960) 567. 8. H. Bayer, Z. Physik 130 (1951) 227.