Nuclear quadrupole and magnetic resonance studies of structure and the molecular motion in SYMC6Cl3F3

Nuclear quadrupole and magnetic resonance studies of structure and the molecular motion in SYMC6Cl3F3

195 JoumalofMotecularStnrctu~,1l1(1983)195-199 ELsevierSciencePublishersB.V.,Amsterdam-F?intedinTheNetherlsnds NUCLEAR QUADRUPOLE MOLECULAR Y. A...

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195

JoumalofMotecularStnrctu~,1l1(1983)195-199 ELsevierSciencePublishersB.V.,Amsterdam-F?intedinTheNetherlsnds

NUCLEAR

QUADRUPOLE

MOLECULAR

Y.

AND

MOTION

N.

YOSHIOKA,

Department

MAGNETIC

NAKAMJRA

and

of Chemistry,

Toyonaka,

560,

RESONANCE

STUDIES

OF

STRUCTURE

AND

THE

IN SYH-C6C13F3

H. CHIHARA

Faculty

of Science,

Osaka

University,

Japan

ABSTRACT

35C1 and lgF relaxation time measurements were carried out on sym-C6C13F3. NMR spectra and the 35C1 spin-lattice The analyses of the lgF high-resolution relaxation time showed that the crystal belongs to a trigonal or a hexagonal crystal system in vhich the molecules undergo three-fold reorientation about the molecular figure axis with the correlation time rr/s=3.42-lo-'exp(18.2 kJ mol-l JRP). Temperature dependences of the 35C1 NQR ffequency and 19~ spinlattice relaxation times are such that only a minor structural change is associated with the phase transition at 296 K.

INTRODUCTION SyrPC6Cl3F3 D3d

(1,3,5-trichloro-2,4.6-trifluorobenzene)

symmetry.

77 K

(ref.11,

equivalent.

35C1

early

showing

and NQR

the

and

NQR

that

In order

lar motion out

An

all

XMR

of

found

in

the

the bonding

the phase

measurements

is a molecule

a single

chlorines

to examine

nature

"F

study

resonance crystal

are

this

at

296.7

at

having

39.312

the

MHz

at

crystallographically

characteristics

transition on

line

K

as well

as molecu-

(ref.2)

we

carried

substance.

EXPERIMENTAL The

material

of commercial

recrystallization A single by

the

tained

crystal

by

The 10

minicomputer

pulse 35C1

a newly time

methods NQR

time

times.

domain

The

fr'equency,

00!z2-2a60/s3/.$03.00

was

fed

converted linevidth

to within recovery

T2 were

0 1983Ehevier

was

Co.

of

grown

with

the

8 ppm

(ref.

a MATEC

SciencePubEshersB.V.

accumu-

spectrum

(320

Hz)

by a

was

ob-

lyF spin-lattice

saturation-go0

the magnetization with

3).

ob-

pulsed

recorder,

frequency

of about

by

solution were

a home-built

a transient

the

purified

N'NX spectra

into

system

was

sublimation.

in n-heptane

into

20 I by

measured

Ltd.)

by vacuum

at 40 XHz

field-locking

The

T 1, and

and

opr.imum

measured

at 10 MHz.

shape

method

signal

developed

Chemicals followed

lgF high-resolution

sequence

averaged,

TI was

prism

30 “C.

at

pulse

(Alfa

solution,

a hexagonal

(NOVA-01).

with

relaxation

source

n-heptane

method

the XfZV-8

about

tained

with

evaporation

spectrometer. lated

from

was pulsed

and

90'~90°

exponential. NQR

system.

lg_s-..

: .. : .: .\.

RESULTS The

AND

.:-

.... :

DISCUSSION

spectrum from a single crystal of sym-CgC1gF3 gave

IqF high-resolution

only on& line vith a linevidth of about 30 ppm (1.2 kHz),. indicating

not

only

that all fluorines sl-e,+ystallographically

equivalent but also that all C-F

bond

some

directions

al pattern ternal

are

for

field

chemical

the

(+85

shielding

that

figure

From

above

of

the

The

gross can

15.7

or

feature

The

an almost along

molecular

is shown

constant

this

axis

it

motion.

The

rotation-

in Fig.

1.

When

axis

of

the

crystal,

value

(-43

ppm

from

takes

a maximum

hexagonal

apparent

results

T1

k.J mol-l

which

Tl agrees

the

activation

T2 of

relation energy

was

of

reported

of

time 35Cl. vith

the

exthe

liquid

value

of

the

unique

axes

crystal

the molecular

The the

+ 0.5

in ref.4.

crystalline figure

at

axis

room

belongs

tem-

to

system.

results

previous

T1 -'=3.27-10-4T2 18.2

the

their that

crystal

correlation and

that about

it is obvious

the hexagonal

concerning by

with

a reorientation

deter;;llne, the ve ?neasured

be reproduced

x%01-l/RT). than

the

trigonal

In order-to

the

axis coincides

undergo

reor.ientation

TI

assumes

is applied

solecules

perature. either

Ro

about

specinen

characteristic rotational patterns indicate that the direction

themolecular

and

tensor

when

'Such

ppd-

by

single-crystalline

-ilois rotated

CSH;F),whereas

of

effectively'averaged

three-fold given

result

in Fig.

(ref.4).

is slightly

decrease

in Tp

Fig. 1. The,rotation-pattern for the lqF.high-resolution spectrum Ihe chemical shifr is measured .from lyF in liquid CG'H~F.

at

2.

The

f 3.90-10-6exp(-18.2

kJ mol-' The

are

W

larger above

200

20 "C.

K

197

I

I

10

5

15 @K/T

Fig. 2. The spin-lattice and spin-spin relaxation times of 35C1.

is-an evidence

of

marked

line

broadening

above

this

temperature.

The correlation time for the three-fold reorientation is calculated by using the relation r,=(3/4)Tl (ref.5) and is plotted in Fig. 3.

This figure shows

that =c at 300 K is about 51-10~" s, which is just the order of magnitude to average out the parallel components of the "F Beat capacity measurements

shielding tensor.

(ref.2 and ref.6) found

2

higher order phase

transition in this substance at T,=296.7 K with an enthalpy change of only 18 J mol-l_

We measured

result in

Fig.

4 shows

35C1 NQR frequency up to the m.p. (334.9 K, ref.6): The only

sma!.l

deflection in the NQR frequency vs. tempera-

ture plot at T,, suggesting the absence of any large structural change at the 'phase transition. around T, (Fig. 5).

On the other hand T1 of 13F UIR showed a shallow minimum Therefore, there is

2

possibility that the phase transition

affects the molecular motion to some extent.

3-o

50

L-0

60

7.0

8.0

IO’KIT

Fig.

3. The

Fig.

correlation

time

-4. Temperature

for

the

dependence

three-fold

of

35C1

reorientation

NQR

frequency.

of molecules.

199

Fig.

5. The

spin-lattice

relaxation

time

of

lgF at

10 MHz.

REFERENCES 1

2 3 4 5

6

G.K. Semin, L.S. Kobrina and G.G. Yakobson, Izv. Sib. Otdel. AN SSSR, Ser. Chem. Sci., 9 (196s) 84. I.E. Paukov and L.K. Glukhikh, Russ. J. Phys. Chem., 43 (1969) 120. Y. Yoshioka, N. Nakamura and H. Chihara, to be published. 1-M. Alymov, V.M. Burbelo, V.A. Egorov and R.Sh. Lotfullin, First Specialized "COLLOQUE AHPERE", (1973) 186. S. Alexander and A. Tzalmona, Phys. Rev., Al38 (1965) 845. R.J.L. Andon and J.F. &!zrtin. JCS Faraday Trans., 169 (1973) 871.