IR A B S O R P T I O N S P E C T R A OF W U R S T E R S A L T S

A . V. S a b i t s k i i a n d M. K u z n e t s o v UDC 541.515 : 535.33-15

The IR spectra of ten Wurster compounds were studied to c lar i fy the structure of the ion radicals and their interact ion in the crystal l ine phase. In the case of d iamagnet ic salts, effects of the c a t i o n - c a - tion interact ion type and formation of a hydrogen bond between the unsubstituted amino group of the cat ion and the anion were observed. The ionic interact ion is not significant in paramagnet ic salts.

A number of papers [1-3] have been devoted to an investigation of the IR spectra of the rad ica l salts of aro- mat ic amines . Major at tention was directed to c lar i f ica t ion of the in t ramolecular structure of the ion radicals, but the specif ic role of the interactions in the crystal were only sl ightly i l luminated . The fact that paramagnet ism of many rad ica l salts is manifested either sl ightly or not at al l indicates the interact ion of ion radicals in the crysta l -

line phase, In this connection, a comparat ive study of the structure of d iamagnet ic and paramagnet ic crystal l ine forms of rad ica l salts was of interest. In this paper, using the IR spectra, we have investigated Wurster compounds - products of one-e lec t ron oxidation of p -phenylened iamine (PPDA), N ,N-d ime thy l -p -pheny lened iamine (DMPD),

and N ,N ,N ' ,N ' - t e t r ame thy l -p -pheny lened iamine (TMPD). It is well known that the crystal l ine salts of PPDA + and DMPD + are diamagnet ic , while the crystal l ine salts of TMPD + are paramagnet ic at normal temperatures.

An assumption has been made that d iamagnet ic Wurster salts consist of products of disproportionation of the ion radicaIs with e lec t ron transfer [5]. The low-temperature modif icat ion of TMPD + CIO[, for example , has been

thus synthesized. However, the formation of complexes with covalent character can occur in definite cases. The data of x - r ay diffraction analysis of DMPD + Br- indicate that this salt is apparent ly related to structures of the l a t -

ter type [6]. There are DMPD + ions of only one form in the crystal, and they are si tuated in para l le l planes at close distances, as shown in Fig. 1.

E X P E R I M E N T A L

The bromides and chlorates of PPDA + and DMPD + and the perchlorate of TMPD + were obtained by the Piccard- Michaelis method [4, 7], while the iodides of DMPD + and TMPD + were prepared under modified conditions [6]. We started from the corresponding deutero derivatives of PPDA to prepare deuterated bromides of PPDA +. The synthesis of PPDA + bromides deuterated on the nitrogen was carried out in CHaCO2D and C2HsOD. Deuteration of PPDA onthe

nitrogen was achieved by recrysta l l iz ing it from D20. Comple te ly deuterated PPDA

i was obtained by heat ing a soiution of its hydrochloride in D20 at 100 ~ under anaer- obic conditions for two days with subsequent neutral izat ion of the solution with so- dium carbonate.

I.~ 1 I

Y I ! t

Fig. 1. Position of the in- teract ing ionradicals in a DMPD+Br" c rys ta l .

Ring-deuterated PPDA was obtained by recrysta l l iza t ion of com- p le te ly deuterated PPDA from water. All samples were purified by dis t i l la t ion at 130" (0.5 ram). The degree of deuterat ion in the bromides was ~ 80% on nitrogen and above 90~ on the ring.

The samples for the IR spectra were prepared by suspension in minera l oi l and in hexachlorobutadiene. The amine bases were also studied in solution. The sol- vent was carbon tetrachloride, except for the 700-900, 1200-1300, and 1500- 1600 cm -1 regions in which bromoform was used. The spectra were obtained with a UR-20 spectrometer .

Central Scientific-Research Laboratory of Chemical Packaging. Translated from Zhurnal Strukturnoi Khimii, Vol. 12, No. 3, pp. 423-429, May-June, 1971. Original article submitted April 2, 1969.

@1971 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New

York, N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever

without permission of the publisher. A copy of this article is available from the publisher for $15.00.

391

TABLE 1. IR Spectra of PPDA, DMPD, and TMPD

Types of vibrations

PPDA !DMPD TMPD

solution solid solution [ solid solution solid

%'r

vriln9~ bl~)

Vrin~ 24~b2u)

�9 v rin~ ~51"b2~)

X-sensit ive

20(blu) ,,5c11 26(b~u)

6cH 21 (b~) yc11 28(bau) X 'sens i t ive

22(b1~) ~' rin~

29~ba~)

"~;NH2 asym. %"N:H 2 syrrl.

.26~H~; v~11= ~H~ scissors

yN~ fan

%'qlt

CH deform

vcN asyrn ~CN syTn

3t10 w 3050m

3032 m 3018 s 1516 vs

1450 vs

1260 s

l130m 1064 w 1015 vw 829vs 720,m

508m

345s s 3382 s

3210 w 1612 s

640 m

Vibrations

3050 vw

3033 vw 3012 m 1518 vs

1448 m 1313 m

i265 s

1130 m 1,064 w

830 vs

518 s

of the benzene residue

3108 w 310~2 vw 3078 m 3072 W 3039 s 3033 w 3027 s 3022 w 3008 s

526 vs 1518vs

455 m 1453s

453 m 1452m

1334 m 1332w 276 s 1268 s

100 vs l107w 1094m 1011 w

820 vs 829s ' 744"m 721 w

533 s 541s

Vibrations of the amino group

3412 w 3457 m 3308m 3378 m 3380, m 3170m 3210 m ]3208 w 1630 m j1610 s 1633m 1612 m [ 1612m 722 s [ 638,s 688s

Vibrations of the d i m e t k d a m i n o groups

q

2983s 2952 vs 2880s 2833 s 12795 vs 1478m 1216m 1060m 950s

2981m 2'950 s 287s s 2838s 2793vs 1478m l190.m 1050m 940,m

3102 w 3048 m

1528 vs

1453 s

1446 s

1320, vs

1099 vs

820 vs 722 vw

547m

2985 s 2950 s 2879 s 2836 s 2798 vs 1479 s 1211 s 1060,,m 952 vs

3100 vw 3049 w

1523 vs

1450m

1445m

1322 vs

109~:VW

813 VS 7 2 4 m

543m

2982 m 2950 s 2876 s 2837 s 2791 vs 1478 m lgl 1 s 1060 s 953 vs

The spectral data are presented in Tables 1 and 2, where ~ are the valence vibrations, and 8 and g are the planar and nonplanar deformation vibrations (see [9] for their numbering and selection of coordinates).

IR S P E C T R A O F P P D A , D M P D , AND T M P D

The aggregate state has a different effect on the spectra of these amines. For TMPD, the observable differ-

ences between the spectra of the solid product and the solution are small. In the case of PPDA and, particularly, DMPD,the crystalline state causes the formation of a number of additional bands.

The spectra were interpreted by analogy with related compounds (p-dihalo derivatives of benzene [8] and anil ine [9, 10]) assuming l imited interaction between the vibrations of the benzene residue, the amino groups, and the dimethylamino groups (Table 1). It was noted that the spectrum of DMPD in solution corresponds to superposi-

tion of the spectra of PPDA and TMPD. Substituents in the para position of the benzene ring apparently do not have

a large effect on one another.

IR S P E C T R A OF R A D I C A L S A L T S

The spectra of the radical salts were assigned in analogy with the spectra of the starting amines and on the basis of isotope shifts of frequencies in the deuterated compounds (Table 2). The most noticeable changes in the

392

TA

BL

E 2

. IR

Sp

ectr

a o

f R

adic

al S

alts

Ty

pes

of

vib

rati

on

s

Vib

rati

on

s o

f th

e b

en

ze

ne

res

idu

e

VC

H(C

D)

vri

n~

X

- K

ensi

tiv

e ri

ng

6CH(CD)

ycm

cD)

28(b

a~)

X-s

ensi

tiv

e ri

ng

22

(bI~

) Y

ring

29

(b~

) V

ibra

tio

ns

ot

the

am

ino

gro

up

s 'V

N II

KN

D ~)

fi~

e

Vm

~(N

D~

bo

nd

ed

~NH

~(N

D~)

sci

sso

rs

tto

e Y

NI-I

~(N

D2)

fan

PP

DA

+C

10

4-

3070

w

t596

,vs

1539

vs

1507

s

1403

vs

1177

s

98

9m

84

7 s

83

9m

72

8 w

52

3m

34

30

,m

3340

s

32

'45

m

3390

w

3310

, s

3211

s

1644

vs

650

w

]PP

DA

+B

r-]P

PD

A~

Br-

+

Br

cu

ter

;-

PP

DA

~

a~ed

on

[,

deu

tera

ted

ln

itro

gen

l

in

the

rin

g

31

25

m

3040,

m

1590

vs

1539

s

15

09

m

1395

vs

11

68 s

984

m

841

m

831

m

723

w

521

w

3422

m

33

00

m

32

20

m

16

63

m

1627

w

65

0m

1589

vs

I5

50,

s

1400

s

843

m

/99

w

77

5 v

w

750

vw

72

8 w

22

87

w

22

64

m

15

56

vs

1501

s

1390

vs

11

43

m

988

m

823

vw

437

s

34

20

m

33

,00

m

32

40

m

16

60

m

1622

m

620

m

PP

DA

+B

r -

co

mp

lete

ly

de

ute

rate

d

2280

m

1556

vs

14

66

m

1392

vs

84

8m

792

m

740'

w

440

s

2450

w

23

27

s

)MP

D+

C1

0,q

3110

vw

30

90

vw

30

68

m

3046

v

w

300,

8 w

15

98 v

s 15

92 v

s

1397

vs

11

80

m

'988

s

838

s 81

,9 m

72

9 s

50 ~

S

3396

s

33,0

6 s

32ql

s

1630

s

650

s

DM

PD

+I -

2123

m

3004

vw

1597

vs

1550

s:

1398

vs

1173

vs

99

4m

8

20

vs

72

3m

509

s

3289

s

3221

m

3123

m

!6

26

s

594

s

DM

PD

+B

r-

31

5C

w

3138

w

30

92

m

3019

w

1594

vs

15

54

vs

1400

' vs

1171

S

1092

vs

820

s

722

w

509

m

3265

s

3191

m

30

92

m

1631

s

63

8m

TM

PD

*C

1O

ji T

MP

D +

i ~

31

70

m

3167

w

3136

w

31

28 w

3085

w

30

,75

w

3050

v

w

1547

vs

15

45s

1422

vs

14

19 v

s 13

80

s 1

38

0v

s 11

27 s

1@

92 w

9

79

,m

98

0m

83

0 vs

8

30

vs

727

w

728

w

521

m

520

m

r e,.O

r

TA

BL

E 2

(C

onti

nued

) t [

[PP

DA

+B

r' P

PD

A+

Br-

T

yp

e of

P

DA

+C

I04"

]P

PD

A+

Br-

jda~

g~r n

!d

eute

ratc

d vi

brat

ions

"

[ /n

itro

gen

'i

n t

ile

ring

Vib

rati

ons

of d

i-

m~

hy

lam

ino

gr

oups

CH

def

orm

atio

n

VCN

asy

m.

"r

syrfl.

Vib

rati

ons

in t

he

anio

n

vcl_

o (g

2)

1088

vs

1112

vs

[ 11

43

vs

0 --

C1

-- 0

def

or-

] 62

8 m

m

atio

n(F

~)

/

PP

DA

+B

r-

IDMP

D+Cl

O ]

completely

deu

tera

md

I

" 4 i

--

29

45

m

2880

w

2821

w

2758

w

2720

vw

26

60 w

--

14

40

m

1227

s

--

937

s

--

1088

vs

1112

vs

ld43

vs

--

6

30

m

DM

PD

+ I

-

2675

w

145,

1 w

12

26m

10

70 s

9

36

m

DM

PD

+ B

r-

2940

vw

2

89

7v

w

~8

80

vw

28

18 v

w

2770

w

27

25

vw

2

68

7m

14

60

m

12

29

m

1074

m

940

w

I TM

PD

+C

IO~

2995

w

2969

m

2946

m

2895

vw

28

52 w

28

20 w

2,

795

w

2721

w

1228

s

979

s

1098

vs

626

s

TMPD

+I -

2990

vw

29

95 v

w

2920

w

28

56

w

28

15

w

2790

vw

27

20

w

1450

w

12

31

m

944

s

spectra of the rad ica l salts in comparison with the spectra of the amines are observed in the range of skele ta l vibra- tion frequencies (1250-1600 cm-1). The tendency for increasing frequencies in the spectral range examined should

be noted. This tendency is apparent ly associated with an increase in the quinoid nature of the n i t rogen -ca rbon skel- eton in the ion radicals , also expected on the basis of the results of the ore t icaI calculat ions [11]. The 20(blu) and 24(bin) skele ta l vibrat ion frequencies, which ref lect the increase in the C - N and C - C bond orders [12], should in-

crease on passing from benzoid to quinoid systems.

A number of bands in the spectra of the rad ica l salts are observed with altered intensity in comparison with the spectra of the amines; this may be associated with a change in the effect ive atomic charges. The significant

decrease in the intensity of the C - H valence vibrations of the methyl groups and an increase in the intensity of planar deformation vibrations of the ring C - H should be noted.

Comparison of the IR spectra of d iamagnet ic PPDA + and DMPD + saks and paramagnet ic TMPD + salts makes it possible to establish definite differences between them which indicate a change in the planar vibrations of the

benzene residue. The observed changes in the spectra of the d iamagnet ic salts cannot be explained by formation of products of disproportionation of the ion radicals since, in this case, the IR spectrum should have been superposi-

t ion of the spectra of the corresponding amine and quinoidimmonium cation, which, in fact, is not observed. The compara t ive ly simple structure of the spectrum most l ike ly indicates the fact that the associate is constructed of equivalent links.

Two very intense bands with max ima at 1170 and 1590 cm "t, which are absent in the spectra of paramagnet ic

TMPD + salts, are observed in the spectra of the d iamagnet ic PPDA + and DMPD + salts. On the basis of the values of the isotopic shifts of frequencies in compounds with deuterated benzene rings one can conjecture that the frequency

at 1170 cm -1 corresponds to the deformation vibration of C - H , and the t590 cm -1 frequency corresponds pr imar i ly to skele ta l vibrat ion of the benzene ring (Table 2).

Similar bands were previously observed [1] in the IR spectra of para-substi tuted t r iphenylamine and the corre- sponding rad ica l salts, and a sharp increase in the intensities in the rad ica l salts was noted. These bands were as-

signed to the comple t e ly symmetr ica l C - H and benzene ring C - C vibrations, and the increase in their intensities in the spectra of the rad ica l salts was expla ined by a decrease in loca l symmetry of the para-subst imted benzene ring (Dab "-* C2v) as the result of development of positive charge on the central nitrogen atom. The bands observed in our case probably have a s imilar origin. From this point of view, the absence of 1170 and 1590 cm "1 frequencies in the spectra of TMPD + salts in which the benzene residue of the ion has high symmetry (D~h) [13] is understanda- ble. However, in the case of crystal l ine DMPD + salts, the benzene residue has lower symmetry (C2v), and positive charge of the ion is p r imar i ly concentrated on the nitrogen a tom of the unsubstituted amino group [6]. This creates

conditions for ac t iva t ion of the comple t e ly symmet r ica l vibrations of the benzene ring. Similar t rea tment of the spectra of PPDA + salts leads to the conclusion that the crystal l ine PPDA + ion should have unsymmetr ica l charge dis- tr ibution s imi lar to the crystal l ine PMPD + ion. The asymmetry of the ppDA+ ion may be only an intermolecu!ar effect, since the isolated ion should be symmet r i ca l ly constructed.

The anions have a definite effect on the spectra of the radical salts,as can be judged by comparing the spec- tra of salts obtained from the same base but with different anions. In the process, it should be remembered that the intense bands at 630 and 1080-1150 crn -1 are due to vibrations of the perchlorate ion. The anion effect is manifes t - ed pr imar i ly in the frequencies of the N - H valence vibrations in the spectra of PPDA + and DMPD + salts. Replace- ment of perch!orate ion by iodide or bromide ions in the DMPD + salts leads to a decrease in the frequencies by 110

or 130 cm -1, respect ively. The reason for the shift in frequencies is apparent ly the formation of a hydrogen bond between the anion and the amino group of the cat ion. Similar but stronger effects were previously observed [14] in the IR spectra of the ammonia complexes [Co(NH3)6]S+x3 - (X = C104- , NO3- , I ' , Br', C I ' ) . In the case o[ DMPD +

salts a smal l change in the frequencies of the valence and deformation vibrations of the C - H of the methyl groups under the influence of the anion is observed. The results obtained agree with the x - ray diffraction data [6] for DMPD+Br -. In the crystal , each bromide anion is surrounded by three DMPD + ions. Weak hydrogen bonds ( N . . . Br distance 3.46 .~) are formed from two of these which are presented to the anion by the amino groups. The third ca t - ion is presented to the anion by the d imethylamino group.

A portion of the spectrum of the PPDA + rad ica l salts due to N - H valence vibrations has a complex structure and occupies a broader spectral interval than is the case for DMPD + salts. The low-frequency boundary of this in- terval depends on the nature of the anion, while the h igh-frequency boundary is constant and is si tuated in the re- gion of valence vibrations Of free amino groups. On the basis of this, one can assume the presence of two types of amino groups in crystal l ine ppDA+ salts, those which par t ic ipate and those which do not par t ic ipate in the formation

395

of hydrogen bonds. In the case of the bromide, splitting of the band of the scissor vibration into two components is observed, which also may be due to the presence of free and associated amino groups. The anion probably forms a hydrogen bond, preferably with the amino group on which there is excess positive charge.

The anion has virtually no effect on the IR spectra of paramagnet ic TMPD + C10 4- and TMPD+I - salts. This can be compared with the x - ray diffraction data [13] for TMPD+! -, according to which not one of the molecular contacts is shorter than the sum of the van der Waals radii.

The data obtained make it possible to assume that association of the ion radicals in the PPDA + and DMPD + salts is due to interaction of delocalized electrons and is primari ly covalent in nature. The possibility of additional stabilization of the complexes by donor-acceptor forces arising during overlap of an occupied 4Ag orbital of one ion radical with the vacant TAg orbital of another cannot be excluded. The donor-acceptor interaction can be caused by unsymmetr ical charge distribution on the benzene skeleton. Anions neutralize the positive charge of the ion radi- cals and thereby lower the electrostat ic repulsion between them. It can be assumed that in the case of TMPD + salts dimethylamino groups sterically hinder effect ive approach of the ion radicals.

L I T E R A T U R E C I T E D

1. W. Otting and H. Kainer, Ber., 87__, 1205 (1954). 2. D.W. Sharp, J. Chem. Soc., 4804 (1957). 3. F. Ritschl, Spectrochim. Acta, 23A, 655 (1967); 23A, 997 (1967); Z. Chem., 7_, 165 (1967). 4. L. Miehaelis and S. Granick, J. Amer. Chem. Soe., 65__, No. 2, 1747 (t943). 5. M.J . Monkhorst, G. T. Pott, and J. Kommandeur, J. Chem. Phys., 47__., 40 (1967). 6. J. Tanake and N. Sakabe, Acta Crystallogr., B24, 1345 (1968). 7. J. Piccard, Ann., 381, 351 (1911). 8. A. Stojilkovic and D. H Whiffen, Spectrochim. Acta, 12__, 47 (1958). 9. J . C . Evans, Spectrochim. Acta, 1_~6, 428 (1960).

10. M. Tsuboi, Spectrochim. Acta, 1_~6, 505 (1960). 11. M.J . Monkhorst and J. Kommandeur, J. Chem. Phys., 47__, 391 (1967). I2. M. Davies and F. E. Pritchard, Trans. Faraday See., 59__, 1248 (1968). 13. J .L. de Boer and A. Vos, Acta Crystallogr., B24, 542 (1968). 14. K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds [Russian translation], Mir, Moscow

(1966), p. 199.

396