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.