Far-infrared spectra of some β-hydroquinone clathrates

277 Journal of Molecular @

Structure,

Elsevier Scientific Publishing

FAR-INFRARED CLATHRATES

18 (19?3)

Company,

277-284.

Amsterdam

- Printed in The Netherlands

SPECTRA OF SOME /.%H~ROQUINONE

KUNIO FUKUSHIhfA Department

(Received

of Chemistry,

Faculty

of Science,

Shizuoka

Unicersity,

836, Oya,

Shizuoka

(Japarr)

2 April 1973)

ABSTRACT

Far-infrared spectra (400-30 cm-‘) of Nujol mulls of the p-hydroquinone clathrates containing the following grrestmolecules were investigated: formic acid, formic acid-d,, methanol, methanol-d,, acetonitrile, acetonitrile-d,, sulphur dioxide and also both of methanol and sulphur dioxide. The observed infrared bands of the mulls in the region of 4000-30 cmLi were classified into those due to the host lattice and those due to the guest molecules. On the basis of the comparison of the spectra, some bands were assigned to the translational or the rotational vibrations of guest molecules. Appearance of those bands suggested that some guest molecules are considerably bound in the cavities of the host lattice. Effect of temperature change on the bands was also measured. INTRODUCTION

The interaction between the host lattice and the guest molecules in /?-hydroquinone clathrates has been investigated by infrared spectroscopy in the spectral region 4000-600 cm- ’ (refs. l-4), and also by Raman spectroscopyss6. In these researches, intramolecular vibrations of guest molecules were used for analyses of the interaction. Measurements of the low frequency infrared bands (100-10 cm-1)7-11 or Raman linesI o f guest molecules have been made for some guest molecules, and rotational motion was found for hydrogen chloride and hydrogen bromide guest molecules8~l2 and also for hydrogen sulphide guest _maleculeslo. In the present work, the infrared bands -due to the translational or the rotational vibrations of some /?-hydroquinone clathrates whose guest molecules are expected to have somewhat restricted rotational and-translational motion are studied. EXPERIMEl$TAL

The /&hydroquinone clathrates :of formic acid, methanol, acetonitrile an+ acetonitrile-df were prepaied by cooling saturated solutions of r_hy_droquinone

278 in each compound according to Palin and Powell’3, the fi-hydroquinone-d, clathrates of formic acid-d, and methanol-d4 were prepared in a similar manner. The /I-hydroquinone clathrate of sulphur dioxide and that containing both sulphur dioxide and methanol were prepared by passing sulphur dioxide gas into a saturated aqueous solution of a-hydroquinone or a saturated solution of a-hydroquinone in methanol. The infrared spectra of the Nujol mulls of the samples were recorded with a Hitachi EPI-G3 spectrometer and a Hitachi FIS-3 far-infrared spectrometer. The spectra of the samples at low temperature were measured using a low temperature cell and liquid nitrogen_ The results are shown in Figs. l-4 and Tables l-3. RESULTS AND DISCUSSION

As infrared spectra in the region 4000-600 cm-’ have already been reported for many fl-hydroquinone cIathratesrW6, in this paper the infrared bands of those of formic acid-d, and methanol-d,, which have not been reported so far in the literature, are shown in Table 1. Table 2 shows an assignment of infrared bands to the host lattice of the /?-hydroquinone clathrates and also to the guest molecules on the basis of comparison of the spectra of the clathrates and gas spectra of the guest molecules. The spectra between 400 and 30 cm-l : The host spectra

Four bands common to all the /Lhydroquinone clathrates appear at -380 cm-‘, -200 cm-i and in the regions, 120-110 cm-l, 80-70 cm-’ as shown in Figs. la, Ic, 2, 3 and 4. These bands, which have frequency values different from those of a-hydroquinone, are assigned to the host lattice of /?-hydroquinone clathrates. Among the bands one at 380 cm- ’ shifts to 375 cm-’ on deuteration of hydroxyl groups (see Figs. lb, 2 and 3). The guest spectra (i) The /3-hydroquinone clathrate of acetonitrile. As shown in Fig. la, two bands appear at 375 cm-’ and at 98 cm-‘, which cannot be assigned to the host lattice. Corresponding bands of the clathrate of acetonitrile-d, are found at 345 cm-’ and at 93 cm-l as shown in Fig. lc. The band at 375 cm-’ (acetonitrile) and one at 345 cm-’ (acetonitrile-d,) are due to the C-C-N skeletal deformation vibrations of the guest molecules on the basis of the assignment-for gaseous acetonitrile and acetonitrile-d,14. On the other hand, the bands at 98 cm-’ (acetonitrile) and at 93 cm-’ (acetonitrile-d,) cannot be assigned to any intramolecular vibrations of the guest molecules but they are due to the translational or the rotational vibrations of the guest molecules. It has already been found that the intramolecular vibrations of the guest molecules have frequencies close to

279 TABLE 1 INFRARED BANDS OF &HYDROQtJINONE-d2 Guest nxdecule

CLATHRATES=

Intensity

CHjCN

DCOOD

CDoOD

2723 2682

2706

2727

VW

2672

sh W

2563 2401 2351 2256

2380 2350

1644 1508 1500 I365 1355 1340 1299 1287 1242 1224 1199

1871 1705 1629 1507 1500 1426 1366 1354 1340 1286 1243 1225 1205 1179

1161 1149 1101

1104

2450 2376 2356

980 972

OD str.,

sh sh

g. g

CD str.,

g g h

: h

sh W VW

CD

1645 1510 1502 1428 1367

W

1344 1297 1288 1244 1226 1203 1163 1155 1121 1107 1099

VW

: h h h

sh

h

sh sh

h

S

h h h

sh W

h h

m m

h

sh W VW sh VW

CD

bend.,

973

sh m sh W sh VW VW

bend.,

CD3

bend.,

g h z h h h

C-O C-O

str., str.,

g E h

OD

bend., f

CD3

rock.,

CD bend.,

g : h

m Sh sh

6 h h

CD3

W sh sh VW VW sh sh

833 815 80.5

E h

str.,

sh

1008 984

885

str.,

VW C=O

946

834’

sh sh m

sh

895 873 832 817

h h

2245 2180 2060 1995 1874

1076 1034

969 926

h

CN str., CD str., CD str.,

1096

1006

h

VW

2230

1871

Assignment

OD bend.,

g (continued

overleaf)

TABLE

1 (continued) Intensity

Guest molecule cN,cIv 747

DCOOD

cs,OD

747

748

624 550 523

701

m sh

625

VW W

544 524 497

520

Assignment

h

h h OCO bend.,

W W

w

490

W

sh

485

C-O tars., c-o tars.,

: h h g ZT

J The bands masked by Nujol bands are not included. g = guest molecule, h = host lattice, s = strong, m = medium, w = weak, VW = very weak, sh = shoulder.

1 400

I 300

200 cm-’

loo

200 cm-’ (b)

Fig. 1. Far-infrared sped,“, of &hydroquinone clathrate of CH,CN in Nujol mu11 (solid line) and those of (a) a-hydroquinone in Nujol mull, (b) &hydroquinone-dz clathrate of CHSCN in Nujoi mull, and {c) #?-hydroquinone clathrate of CD&N in Nujol mull (do&ted fine).

those of the molecules in gaseous state’-‘. In addition to this fact, the host lattice spectra are similar among the /_Ghydroquinone clathrates. These facts suggest that the interactions of the host lattice with the guest molecules are very weak. Therefore,. in the case that the guest molecules oscillate, almost- independently of the host lattice, around their equilibrium positions, the frequency ratios of these vibrations of the fi-hydroquinone clathrat& of acetopitrile-d, to those of the flhydroquinone- clathr$e of acetonitrile are 0.97 for the translational vibration, -0-94 .for thi rc&tional_vibration. aTGun the gxis perpendicular to C-C-N .and

281 TAl3LE 2 INFRARED

BANDS

OF j%HYDROQWINONE

CLATHRATESa

Abbreviations as in Table 1. Guest molecde CH~CN

CD&V

ZnZensity HCOOH

CH@H

SOz

3624 3147 2721 2696 2595 2455 2360 2295

3140 2725 2594 2453 2360

3473 3147 2727 2693 2600 2457

3140 2720 2690 2458

so=, 3624

3140 2720 2690 2592 2450

3147 2716 2686 2606 2455

2263 2254 1873

1872

1646 1513 1365 1356 1341 I326 1246

1645 1510 1363 1353 1341 1326 1245

1205 1191

1206 1190

1155 1121

1155 1121

1096 1034

1094 1030

1006 926 835 829 757 721 700 624 522

1007

1872 1747 1650 1512 1367 1354 1344 1322 1248 1220 1210 1196

I875

1160 1110 1094

1007

1871

ix&G W

sh s

I872 1647 1509 I363 1354 1342 1325 1247 1220 1209 1192

1155 1125

1645 1513 1364 1357 1341 1325 1248 1220 1210 1190 l165 11.50 1120

1095

1096

1093

1343 1330 1248 1210 1192

1152 1120

ioos

1021 1006

W

834 823

833

833 828

833 820

760 722

760 721

760 722 700

759 720

624 526

680 624 524

613 525 519

a The bands masked by Nujol bands are not induded.

h h CN str., CN str., c-o

SW-, h” h h h h h h h h h

W s

m sh W W

m sh sh s sh sh

SO str., : h

W

m VW W

co

SW., hg

CHs rock., C& rock., cc

SW., h” h

CDs rock.,

VW

675 624 540

W

m m sh

g h”

W

m sh VW s m

g 6 h”

W

VW

835 829 810 758 722 702 687 619 523

h h

W

W

1022 1007

g f

sh

W

1650 1.511 1364

OH str., OH str..

W

sh VW VW vw

2370

Assignment

SOL def.,

h” h h h h h g

:I/ . , , , * , 400

3cKl

200 cm-’

)

loo

Fig. 2 (left). Far-infrared spectra of /%hydroquinone cfathrate of HCOOH in Nujol mull (upper ciathrate of DCOOD in Nujol mull (lower figure).

figure) and those of &hydroquinone-d,

Fig. 3 (right). Far-infrared spectra of &hydroquinone clathrate of CHJOH in Nujol mull (upper figure) and those of &hydroquinone-d, clathrate of CDsOD in Nujol mull (lower figure).

Fig- I Far-infrared spectra of fl-hydroquinone clatbrate of SOz in Nujol mull (upper figure) and those of ~-hydroquinone clathrate containing both SO2 and C&OH in Nujol mull (Iower figure).

0.71 for the rofatioqal vibration around C-C-N axis. The expected frequency values of the /3-hydroquinone clatbrate of acetonitrile-d 3, which were calculated using the above ra?ios from the observed frequency, 98 km-‘, of the &hydroquinone clathrkte of acetonitrile are as follows: 95 cm-l (the transiationai vibra-

283

tion), 92 cm-’ ( the rotational vibration around the axis perpendicular to C-C-N axis), 70 cm-’ ( the rotational vibration around C-C-N axis). The observed frequency, 93 cm-l, of the hydroquinone clathrate of acetonitriie-d, is most close to the frequency, 92 cm-l. This favors the assignment of the band at 98 cm-’ to the rotational vibration around the axis perpendicular to C-C-N axis, and suggests that the guest molecules are not in the state of free rotation around the axis. The interpretation is consistent with the conclusion by Dryden and Meakins15. At low temperature the &hydroquinone clathrate of acetonitrile has two bands at 115 cm-l and at 106 cm-’ beside the band at 98 cm-’ as shown in Table 3. These might be due to translational vibrations. TABLE INFRARED

3 BANDS

(I

50-30

Cm-‘)

OF /?-HYDROQUINONE

CLATHRATES

AT LOW

TEMPERATURE

Guest molecule CH3CN

-

HCOOH

so2

-

136 w 126 m

129 m

129

106 w 9s sh

-

I15 w

-

-

m

-

62 w 54 sh

(ii) The jGhydroquinone clathrate of formic acid. Both this clathrate and that containing formic acid-d, have no bands of the guest molecules in the region of 400-30 cm- ’ as shown in Fig. 2. Even at Iow temperature no bands of the guest molecules were found. This fact does not seem to be in accord with the conclusion by Davies and Williams I7 that the formic acid guest molecule has a large activation energy AH: of 3.34 kcsl/mol. Probably the bands of the translational and rotational vibrations may lie below 30 cm-’ because of the very much weaker bound state of the guest molecules and their larger moment of inertia. (iii) The /3-hydroquinone clathrate of methanol. Beside the bands of the host lattice a weak broad band appears at 280 cm-‘, which shifts to lower frequency in the case of the /I-hydroquinone clathrate of methanol-d, and corresponds to the band at 270 cm-’ for gaseous methanol. The corresponding band of the methanol-d, guest molecule is at 160 cm-‘. No bands of translational and rotational vibrations are found in the region of 400-30 cm- ‘, indicating that these may have frequencies lower than 30 cm- ‘. (iv) The /3-hydroquinone clathrate of sulphur dioxide. As shown in Fig. 4, two bands, which are not in the host lattice, appear at 70 cm- ’ and at 53 cm- ‘. It is true that a broad band of the host lattice exists at 70 cm-‘, however, this band is sharp and decreases its intensity in the case of the /I-hydroquinone clathrate

284 containing both sulphur dioxide and methanol as shown in Fig. 4. Therefore, it is clearly the band due to the sulphur dioxide guest molecule. As the lowest frequency of the intramolecular vibrations of sulphur dioxide has been concluded tobe519cm-’ (ref. 16), the two bands at 70 cm-’ and at 53 cm-’ are considered to be due to the translational or rotational vibrations of sulphur dioxide guest molecules. At low temperature the bands persist at 62 cm-’ and at 54 cm-‘. These facts indicate that the translational or the rotational vibrations of the sulphur dioxide guest molecules are considerably restricted even at room temperature. As Davies and Williams concluded by dielectric relaxation measurement that sulphur dioxide guest molecules rotate almost freely in the host latticer7, the bands may be due to the translational vibrations_

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