Clays and Clay Minerals, 1968, Vol. 16, pp. 93-97.
Pergamon Press.
Printed in Great Britain
I N F R A R E D S T U D Y OF THE O R I E N T A T I O N OF
C H L O R O B E N Z E N E S O R B E D O N PYRIDINIUMMONTMORILLONITE
J. M. SERRATOSA
Environmental Health Engineering, The University of Texas, Austin, Texas
(Received 28 August 1967)
Abstract-The pyridinium-montmorillonite complex has the ability to sorb additional aromatic
molecules between the layers. The neutral molecules occupy the vacant space produced by the change
in orientation of the pyridinium ion from a parallel to a perpendicular position and with the N-H group
directed toward the negative unit layer surface.
In favorable cases the orientation of the additional neutral molecules can be ascertained by infrared
spectroscopy. Examples of this analysis are presented in the complexes of pyridinium-montmorillonite
with chlorobenzene. The molecules adopt a vertical orientation but with the halogen bond axes parallel
to the layers.
LAYER silicates in which the exchangeable inorganic
rated from the support and converted to the pyridinium form-by treatment with pyridinium hydrochloride solution and successively washed with
distilled water. The films were immersed in
chiorobenzene for several hours. After this
period the films that had become completely transparent were removed from the liquid and put in a
desiccator to allow evaporation of the excess of
chlorobenzene. Infrared spectra were recorded in
the region 600-4000 cm -~, for two incidence angles,
0 ~ and 40 ~ using a Beckman IR7 infrared spectrophotometer. Concurrently an X-ray record was
obtained for the 001 diffraction sequence.
In smectites with relatively low surface charge
( C E C - 8 0 m - e q u i v . / 1 0 0 g ) the pyridinium ion
adopts a disposition with the plane of the molecule
parallel to the silicate layers and probably hydrogen
bonded to water. This orientation has been substantiated by X-ray and i.r. analysis. The measured
001 spacing is 12.5,~, and when an oriented aggregate of the complex is analyzed by i.r., only the
absorption bands corresponding to the out-of-plane
vibrations (dipole moment change perpendicular
to the molecular plane) increase significantly in
intensity with increasing incidence angle (Fig. 1).
The pyridinium complex can sorb neutral aromatic molecules, such as benzene, with an increase
of the 001 spacing to 14-6 ,~ (Green-Kelly, 1956).
This increase and infrared evidence suggests that
the benzene molecule occupies the vacant space
produced by the change of orientation of the pyridinium ion from a fiat to a perpendicular orientation
with the N - H group directed to the negative unit
layer surface (van Olphen, 1963; F a r m e r and
Mortland, 1966).
Other neutral molecules can also be sorbed by
the same mechanism. In certain cases the symmetry
ions have been substituted by organic cations have
the ability to sorb selectively additional neutral
organic molecules. The process is accompanied by
a separation of the silicate layers and generally with
a reorientation of the organic ion. The sorption can
be restricted to a single monolayer of the additional
molecules or can sometimes proceed to a complete
separation of the mineral layers (Jordan, 1950;
Weiss, 1963).
The process can be followed by X-ray diffraction
through measurement of the interlayer spacings.
However, due to the nature of the material, sufficient data can seldom be collected to permit the
location of the individual atoms. In many analyses
the molecules are only fitted in the available space
according with their dimensions. Such fit is especially uncertain in the case of heterogeneous complexes in which different kinds of molecules are
present and may therefore have more than one
orientation.
Infrared spectroscopy has been found highly
useful in establishing the orientation of the molecules on clay-organic complexes (Serratosa, 1965
and 1966; F a r m e r and Mortland, 1966). This is
accomplished by determining the changes in intensity of specific absorption bands as the direction of
the incident infrared radiation is varied relative to
strongly preferred orientated aggregates.
This paper is concerned with the analysis of the
molecular orientation in complexes of pyridiniummontmorillonite with monochlorobenzene and
other halogen derivatives of benzene.
Oriented films of Na-montmorillonite (Wyoming)
of appropriate thickness (2-3 mg]cm 2) were prepared by filtering the clay suspension through a
micropore filter. After drying the films were sepa93
94
J. M. SERRATOSA
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1
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,
,
T%
T %
4 0 0 0 3600 3200 2 8 0 0 2 4 0 0 2 0 0 0 1900 1800 1700 1600 1500 1400 1300 1200 I100 I000 9 0 0
800
700
v (r
Fig. l. Infrared spectra of pyridinium-montmorillonite-chlorobenzene complex (upper curve)
and pyridinium-montmorillonite complex (lower curve). In the last case, the spectrum
(dashed lines) for 40~incidence in the 1000-650 cm i region, has also been included to show
the directional dependence of the features at 677 and 748 cm 1 (out-of-plane vibrations,
symmetry class B2).
I00
of the molecule presents a favorable case for the
T
I
analysis of the orientation by infrared spectroscopy.
The monohalogen derivatives of benzene, like
the pyridinium ion itself, belong to the point group
C2v. The molecule posesses a two-fold axis, (C2)
defined by the two mutually perpendicular planes
(try), one of which is the molecular plane (Fig. 2).
The molecules possess 30 normal vibrations that
are classified in four symmetry classes AI, A2, B~,
and B2. The A2 vibrations are i.r. inactive. The
T%
changes of dipole moment associated with the other
II
II
three classes are along three mutually perpendicular
50
I
axes. Their i.r. spectra have been extensively
studied, and Whiffen (1956) made a complete
assignment of the observed frequencies to the
different vibrational modes.
The i.r. spectrum of chlorobenzene sorbed on
pyridinium-montmorillonite is similar to that of
liquid chlorobenzene, Fig. 1. The main absorptions
CIB
6 8 7 , 7 0 2 , 7 4 5 , 1446, 1477, and 1583 cm -1 are easity
recognized. The identification of other bands is
40*
more doubtful, either because they are weak or fall
close to an absorption of the pyridinium ion or of
z (Ad
0
1
the silicate substrate.
1600
1500
1400
1300
After the sorption of chlorobenzene, several
changes are observed in the spectrum of the pyri~" (cm-')
dinium ion. The pattern of bands between 2800Fig.
2.
Infrared
spectrum
of pyridinium-montmorillonite
3200cm -1 disappears, and the 3 2 7 0 c m -a band
complex in the region 1650-1300 cm-1, for two angles of
shifts to a higher frequency (3285 cm-a). These
incidence, showing the directional dependence of the A1
absorptions have been assigned to N - - H stretching adsorption bands of pyridinium and the B~ absorption
vibrations in pyridinium salts. The two bands
bands of chlorobenzene. The diagram in the lower right
between 1600-1700 cm -1 become sharper and well corner illustrates the symmetry elements of both molecules
resolved. I n the region between 1200-1700 there is (point group C2v) and the directions of the dipole moment
a general shift to lower wave numbers of about
change for each vibration class.
F
-1511l
U
!I
"iI
o
-
-
-
-
-
INFRARED STUDY OF CHLOROBENZENE
10 cm -a (Table 1). The new positions are similar to
the positions shown by pyridinium ions when
adsorbed in highly charged smectites in which it is
known that the ions adopt an almost vertical
position.
The orientation studies indicate that,, after the
sorption of chlorobenzene, the pyridinium ion
adopt also a nearly vertical orientation with the
N - - H group directed to the surface oxygens. The
disappearance of the adsorptions between 28003200 cm -~ and the shift of the 3270 cm -1 band to
higher frequency, 3285 cm -~, indicates that the
hydrogen bond is weaker in the perpendicular position. This fact can also explain some of the other
shifts observed; for example, the 1553 cm -~ band
which corresponds to a vibration in which N - - H
bending is involved, moves to lower frequency,
1545 cm -1, as expected, when the hydrogen bond is
weaker. The observed displacements, therefore,
may not be necessarily related to the interaction of
the pyridinium and chlorobenzene molecules.
Figure 2 shows the infrared spectra of the pyridinium-montmorillonite-chlorobenzene complex
for two angles of incidence 0~ and 40 ~ in the region
between 1300 and 1700 cm -~. This region is completely free of silicate absorptions and the bands
arising from the organic species are well-defined, of
strong intensity and unequivocally assigned.
Significant increases in intensity, of the order of
two times, are observed for the bands at 1302, 1446,
1487 and 1635 cm -1, when the incidence angle is
95
varied from 0~ to 40 ~ The intensities of the rest of
the bands remain practically unchanged.
The bands at 1487 and 1635 cm -~ correspond to
vibrations of symmetry class A1 of the pyridinium
ion (dipole moment change along the C2 axis).
The increase in intensity with the inclination indicates that the pyridinium ions have a nearly vertical
disposition with the C2 axis at a large angle to the
silicate layers and with the N - - H groups directed
to these layers. A less marked intensity increase
with the inclination is also observed for the 3285
cm -~ band ( N - - H stretching).
The bands at 1302, observed only for inclined
incidence, and 1446 cm -1 have been assigned to
vibrations of symmetry class B~ (oscillating dipole
moment in the plane of the molecule but perpendicular to the C2 axis) of the chlorobenzene molecules. The changes in intensity with the inclination
indicate that these molecules are also disposed with
their planes nearly normal to the silicate layers but
with the C2 axis parallel to them, i.e. with the
chlorine atoms situated midway between the negative oxygen surfaces of the silicate sheets.
The bands that do not change with the inclination
correspond to vibrations of symmetry class B1 of
the pyridinium ion or symmetry class A~ of the
chlorobenzene molecule, and are indicated in
Fig. 2.
The measured 001 spacing for the chlorobenzenepyridinium complexes is 15.0A (8 orders observed),
Fig. 4. The interlayer clearance is only about 5.8A,
Table 1. Observed frequencies (cm ~) for pyridinium and chlorobenzene in
the complexes
Pyridiniummontmorillonite
Pryidinium-montmorillonitechlorobenzene
Symmetry class
Pyridinium
Chlorobenzene
677
675
748
--
687
702
745
1302
1342
1395
1330
1386
1492
1553
1487
1540
1625
1640
28003270
1610
1635
B2
A~
B2
B~
B1
A~
B1
A~
B~
A1
B1
A1
3285
(N--H)
30203200
3020t3200
1446
1477
1583
302013200
(c-n)
96
J . M . SERRATOSA
not sufficient to accommodate the molecules in
either of the completely vertical positions unless a
keying mechanism takes place. This is more unlikely
for the observed orientation of the chlorobenzene,
and probably indicates that the molecules are slightly tilted from the vertical.
The chlorobenzene-pyridinium complex is
relatively stable and decomposes only very slowly
when left in the atmosphere. The shifts in frequency
of the absorption bands of pyridinium depending on
its orientation permit one to follow the desorption
process. Figure 3 shows the i.r. spectrum of the
complex after 4 8 h r in the atmosphere. Bands
I00
1
i
[
I
'
Py(f) py(v)
T%
5O
I
montmorillonite and the molecules adopt a similar
orientation although the complexes are not as
stable as in the case of chlorobenzene.
'
CtB
Pytvl
Pytfl
oi
-
m
0*
---
40*
I
1700
~
-I
---J
I
J I
40
t
i
~ I
I
~
I
I
50
I
20
I
I
I J I
I0
t
]
~
2
20
I
1600
I
I
t500
I
I
1400
I
1300
!7 (cm-')
Fig. 3. Infrared spectrum of the partially decomposed
pyridinium-montmorillonite-chlorobenzene complex in
the 1750-1300 cm ] region, for two incidence angles. The
absorption bands corresponding to the fiat and vertical
position of the pyridinium ion have been indicated.
corresponding to the flat and vertical position of the
pyridinium ion are observed in the doublets at
1553-1540 cm -1 and at 1492-1487 cm -1. The 1487
band corresponding to the ions disposed vertically
shows intense dichroism; the 1492cm -1 is not
sensitive to the inclination as it corresponds to a
flat orientation. The X-ray pattern (Fig. 4c) indicates a mixed-layer structure of 12.5A and 15.0,~
species. At the illustrated stage the diffraction
effects of some remaining 15 A complex are superimposed on those of the mixed-layer system.
Other halogen derivatives of benzene, the fluoro-,
bromo-, and iodo-, and p-dichloro-benzene (point
g r o u p - D 2 h ) are also adsorbed by the pyridinium-
Fig. 4. X-ray diffraction patterns of, (a) pyridiniummontmorillonite, (b) pyridinium-montmorillonite-chlorobenzene and (c) pyridinium-montmorillonite-chlorobenzene partially decomposed. The small peak at 20 =
22~is attributed to an impurity of opal.
A c k n o w l e d g m e n t s - T h i s research was supported in part
by The University of Texas (Environmental Health
Engineering Research Laboratories) and a U.S. Public
Health Service Training Grant from the Industrial and
Urban Health Ceqter.
REFERENCES
Farmer, V. C., and Mortland, M. M. (1966) An infrared
study of the coordination of pyridine and water to
exchangeable cations in montmorillonite and saponite:
J. Chem. Soc. (A), 344-351.
Greene-Kelly, R. (1956) Swelling of organophilic montmorillonite in liquids: J. Colloid. Sci. 11, 77-79.
Jordan, J. V. (1949) Organophilic bentonites. I. Swelling
m organic liquids: J. Phys. Colloid Chem. 53, 294-306.
Serratosa, J. M. (1965) Use of infrared spectroscopy to
determine the orientation of pyridine sorbed on montmorillonite: Nature, 208, 679-681.
I N F R A R E D S T U D Y OF C H L O R O B E N Z E N E
Serratosa, J. M. (1966) Infrared analysis of the orientation
of pyridine molecules in clay complexes: Clays and
Clay Minerals, Pergamon Press. Oxford, 14, 385-391.
Van Olphen, H. (1963) Clay-organic complexes and the
retention of hydrocarbons by source rocks: Proc. Intern.
Clay Conf., Stockholm, Pergamon Press. Oxford, Vol.
1,307-317.
Weiss, A. (1963) Organic derivatives of mica-type layersilicates: Angew. Chem., Intern. Ed. Engl. 2, 134-144.
Whiffen, D. H. ( 1956) Vibrational frequencies and thermodynamic properties of fluoro-, chloro-, bromo- and iodobenzene: J. Chem. Soc., 1350-1356.
R6sum6- Le complexe pyridinium-montmorillonite peut absorber des mol6cules aromatiques suppl6mentaires entre les feuillets. Les molecules neutres occupent l'espace vide produit par le changement
d'orientation de l'ion pyridinium 5. partir d'une position parall~le 5. une position perpendiculaire et
avec le groupe N-H dirig6 vers la surface de le feuillet de 1-61~ment n6gatif.
Dans des cas favorables, l'orientation des molecules neutre suppl6mentaires peut &re d~finies par
spectroscopie. Des exemples de cette analuse sont pr6sent~s dans les complexes de pyridiniummontmorillonite avec du chlorobenz~ne. Les molecules adoptent une orientation verticale mais avec
les axes du lien halog6n6 parall~le aux feuillets.
K u r z r e f e r a t - D e r Pyridinium-Montmorillonit-Komplex hat die F~ihigkeit zus~itzliche aromatische
Molekiile zwischen den Schichten aufzunehmen. Die neutralen Molekiile besetzen die durch die
Ver~inderung der Orientierung des Pyridinium-Ions aus einer parallelen in eine senkrechte Lage
leergebliebenen R~iume, wobei die N-H Gruppe der negativen Schichtoberfl~iche zugewandt ist.
In giinstigen Fallen kann die Orientierung der zus~itzlichen Neutralmolekiile durch Ultrarotspektroskopie festgestellt werden. Beispiele dieser Analyse stellen die Komplexe von PyridiniumMontmorillonit mit Chlorbenzol dar. Die Molekiile nehmen eine vertikale Orientierung ein, jedoch
mit den Achsen der Halogenbindung parallel zu den Schichten.
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97