Solid State Ionics 35 (1989) 73-77
North-Holland, Amsterdam
INTERCALATION OF M O N O M E R S INTO ALPHA-TIN(IV) HYDROGEN PHOSPHATE
AND THE EFFECTS OF H I G H PRESSURES ON INTERCALATION
Michael J. H U D S O N , Paul SYLVESTER
Department of Chemistry, University of Reading, Box 224, Whiteknights, Reading RG6 2AD, UK
and
Enrique R O D R I G U E Z - C A S T E L L O N
Departamento de Quimica Inorganica, Cristalografiay Mineralogia, Universidadde Malaga, 29071 Malaga, Spain
Received 27 July 1988; accepted for publication 2 l October 1988
Monomers which contain unsaturated linkagesand amine groups have been rapidly intercalated into a-tin (IV) hydrogenphosphate to form either mono- or bilayers. The monomer trans-N,N'-diethyl-2-butene-1,4-diamine (NNBD) has been intercalated
to form a monolayer (doo2= 1.35 nm) in which the amine groups are paired to protons on the opposite faces of the phosphate
layers. The resultant compound has the formula Sn(C8H~8N2)o73(HPOa)2'H20 indicating the guest molecule NNBD covers a
large proportion of the available protons, which are unavailable for further reaction. Allylamine forms a bilayer in which the
formula of the resulting intercalation compound is Sn (C3HTN)2(HPO4)2'H20 which indicates that uniform bilayers are formed
(doo2= 1.67 nm) and there is little or no covering effect. There may be some overlap of the double bonds in the layer of the guest
molecule. Some intercalation reactions have been studied at high pressure (5 kbar). With acrylonitrile and hexamethylenetetramine (HMTA), there is little effect on intercalation but with HMTA, high pressures greatly enhance surface modification.
1. Introduction
There has been extensive interest in the preparation and properties of layered c o m p o u n d s but little
attention has been paid towards the possibility of intercalating monomers. This lack of attention is surprising because the intercalation of unsaturated molecules may lead to c o m p o u n d s which have a high
degree of ordering of the guest molecule and are capable of further modification to produce alternate
layers of ordered inorganic and organic polymers.
Such materials could have potential in the fields of
attenuators, proton exchangers a n d synthesis of
highly ordered polymers. There have been no previous studies on the affects of high pressures on intercalation and on surface modification of layered
compounds.
The conditions for surface modification or intercalation into ct-SnP have been studied [ 1-3 ] and it
has been shown that strong bases are involved in both
intercalation and surface modification but weak bases
such as 4-vinyl pyridine are only involved in surface
modification.
2. Experimental
ct-SnP was prepared as described elsewhere [1].
The intercalation c o m p o u n d s were obtained by
shaking the appropriate a m o u n t of the guest comp o u n d with ct-SnP in either toluene or in water.
Weighed a m o u n t s of ct-SnP were suspended, at room
temperature, in toluene solutions of allylamine for
one hour and of N N B D for two days, which represented 200% of the exchange capacity. The suspensions were filtered through a n u m b e r 4 glass filter,
and the solids were washed with acetone. Finally, the
products were air-dried and stored over concentrated sulphuric acid vapour to remove the loosely
b o u n d amine. Infra-red, thermal analyses and elemental analysis were all carried out after equilibration with the acid vapour. In all cases T G A and el-
0 167-2738/89/$ 03.50 © Elsevier Science Publishers B.V.
( North-Holland Physics Publishing Division )
74
M.J. Hudson et aL/Intercalation of monomers into o~-tin(IV) hydrogen phosphate
emental analysis are in good agreement. The uptake
o f allylamine as a function o f time was m o n i t o r e d by
the batch procedure. Structural changes o f the intercalates were e x a m i n e d by means o f X-ray powder
diffractometry. In all cases, the powder patterns can
be indexed on monoclinic unit cells, where a and b
lattice constants are very similar to those of ~-SnP.
The layered structures have been expanded. All the
starting product hk0 lines were present in the intercalates with systematic absences when h+ k=2n.
The reactions at high pressure were carried out using the following procedure. To a-SnP (0.5 g) in polythene high pressure tube was a d d e d hexamethylenetetramine (0.84 g) dissolved in laboratory grade
toluene (3 ml). After evaporating any t r a p p e d air
with butane gas, the tube was subjected to a pressure
of 5 kbar at r o o m t e m p e r a t u r e for 24 h. The product
was filtered off and stored as above. In the case o f
acrylonitrile, 0.6 ml o f acrylonitrile were dissolved
in 3 ml o f toluene and the procedure was the same
as that in the case o f H T M A . The same reactions were
carried out at atmospheric pressure.
Fig. 1. ldealised structure of the NNBD/et-tin(1V) hydrogen
phosphate intercalate.
31
o
2'
3. Results and discussion
Allylamine
3. I. Trans-N,N'-diethyl-2-butene- I, 4-diamine
This molecule has two a m i n e groups and each of
these is able to b i n d to the proton sites on the ct-SnP.
The X-ray diffraction data indicate that the spacing
between the layers (doo2) is 1.35 to 1.38 n m as measured on different samples. This corresponds to an
increase in the basal spacing of 0.56 to 0.59 nm,
which implies that a m o n o l a y e r is f o r m e d when the
terminal amine groups b i n d to protons on opposite
faces. The resulting c o m p o u n d has a formula which
a p p r o x i m a t e s to Sn ( C a l l ~8N2 ) 0.73 ( H P O 4 ) 2' H 2 0 indicating that a p p r o x i m a t e l y one quarter o f the protons are unavailable for b o n d i n g to the amine. An
idealised configuration o f N N B D into ct-SnP, where
N N B D forms a m o n o l a y e r of molecules inclined at
an angle of 60 ° with respect to the sheet is given in
fig. 1. A similar disposition was observed when 1,4b u t a n e d i a m i n e was intercalated into ct-ZrP [4].
<
3
5
10
15
25
35
65
ReactionTime(rains)
Fig. 2. Rate of extraction of allylamine (mol/mol ct-SNP).
3.2. AUylamine
Allylamine ( C H 2 = C H - C H 2 ' N H 2 ) was intercalated into the a-SnP. Whereas the intercalation o f
amines into ~-ZrP has been reported to be slow [ 5,6 ],
the intercalation into ct-SnP is rapid [ 7 ] as shown in
fig. 2. The time for half o f the amine to be extracted
is well under three minutes and the reaction is completed between five and ten minutes. The resulting
M.J. Hudson et aL /Intercalation of monomers into a-tin(Ill) hydrogen phosphate
compounds have the approximate
formula
Sn (HPO4) 2(C3H7 N ) 2' nH20 (after equilibration in
sulphuric acid vapour) in which the number of waters
determined by thermal analysis was variable over the
range of 1.5 to 2. The X-ray diffraction powder studies indicated that the basal spacing doo2 was 1.67 nm
from toluene and 1.56 nm from water. This difference may be due to the retention of a molecule of
water which does not diffuse into the hydrophobic
solvent. These values suggest that the allylamine intercalates as a bilayer as has been observed for other
monoamines [8]. One particular interest with allylamine is that the unsaturated linkages come close to
each other in the intercalate. Moreover, the formulation above indicates that all the available protons
are used for immobilising the amine and consequently these intercalation compounds are poor conductors of protons. In the infra-red spectrum of the
intercalation compound, there is clear evidence for
the protonation of the guest allylamine molecule. The
band at 2100 c m - l is assigned to the N - H stretching
vibration in the RNHJ- group and the band at 1540
cm i is the corresponding N - H bending vibration.
These bands are present in all of the intercalation
compounds of allylamine even when short contact
times are used. The infra-red spectrum of the intercalate which is formed after only three minutes is illustrated in table 1 and it can be seen that the bands
at 1640 cm -1 (C=C stretch); 1450 cm -I ( C - H deformation) and additional bands which can be associated with allylamine are all present. The bands
at 2100 and 1540 cm -l are quite clear and so it can
be inferred that the mechanism of intercalation involves the protonation of the amine groups by the
hydrogen phosphate groups on the host layer compound and this is consistent with earlier studies
[ 1,8 ]. The corresponding X-ray diffractogram is totally similar to those of the allylamine intercalation
compound after one hour contact time (fig. 3 ), where
the reflection line at 0.79 nm corresponding to a-SnP
disappears, and reflection lines corresponding to the
doo2 ( 1.67 nm) and higher harmonics (004, 006) of
the swelled phase were observed.
The molecular orientation of the guest molecules
in the bilayer may be one of two extreme types. That
is to say, the hydrophobic parts of the molecules may
be end-on or they may overlap to some degree. However, there does appear to be some grounds for be-
75
Table 1
Infrared spectrum of the allylamine intercalation compound after
only three minutes contact time.
Wavenumber
Assignment
(cm-')
3400
2800
2100
1640
1540
1450
1420
1360
ll00
62o}
540
420
free O-H stretch
broad band due to mixture
of allylamine and metal
phosphate vibrations
NH~- (N-H) stretch
>C=C< (C=C) stretch
NHf (N-H) bending
C-H deformation
allylamine fingerprint
peaks
broad band due to
phosphate vibration
metal phosphate
fingerprint peaks
lieving that there is significant overlap by comparison of the basal spacings in related systems. With
propylamine, the basal-spacings were 1.86 nm (toluene) and 1.72 nm (water) and the value using toluene was again greater than that from water. The increase of 0.19 nm compared with allylamine is due
to the difference in the Van der Waals radii of the
two hydrocarbon groups. A scale drawing of the orientation of the allylamine molecules is given in fig.
4. The circles refer to the Van der Waals radii and it
can be seen that there is significant overlap of the
hydrophobic regions but that the double bonds are
not adjacent.
3. 3. Acrylonitrile
Acrylonitrile (CHzCHCN), was studied as a guest
molecule by carrying out reactions at ambient pressures and also at 5 kbar. It was considered possible
that the molecule could, in effect, be squeezed between the layers of ct-SnP at elevated pressures. At
both pressures similar intercalation compounds were
prepared and the formula approximated to
Sn(HPO4)z'H20" (CH2CHCN)o o7. The increase in
pressure did not appear to enhance intercalation. Although acrytonitrile does not have free amine groups,
76
M.J. Hudson et al./Intercalation of monomers into a-tin(IV) hydrogen phosphate
E
c:
r,-.
E
,r-
¢,,)
c~
fi
c:
g
E
cO
E
c:
r.-.
¢O
o"
O
E
E
2.00
I
5.00
i
10.00
I
14.00
I
1800
I
22.00
I
26.00
I "
30.00
I
34.00
I
36.00
,I
20,"
Fig. 3. X-ray powder diffractogram of the allylamine intercalation compound after one hour contact time
? ~tlIR
Fig. 4. Scale drawing of the allylamine intercalation compound.
M.J. Hudson et al./Intercalation of monomers into c~-tin(IV) hydrogen phosphate
there was clearly some intercalation at both pressures because there were new peaks at 1.50 n m
(weak) and 1.17 nm ( w e a k ) . These peaks a p p e a r to
correspond to bilayers a n d monolayers respectively.
3.4. H e x a m e t h y l e n e t e t r a m i n e
Amines such as hexamethylenetetramine ( H M T A )
may be used in curing reactions o f epoxy-resins.
Consequently, it was o f interest to evaluate the effects o f pressure on the intercalation o f this a m i n e as
a p o l y m e r could be p r o d u c e d which is strongly adherent to the surface or layers o f the ct-SnP. At ambient pressures, a product which analysed for
Sn(HPOa)2'H2O'(C6HI2N4)o.59 was p r e p a r e d but
interestingly, at 5 kbar a product which analysed for
Sn(HPO4)2"H20" (C6H12N4)I.85 was produced.
Clearly, there is a significant increase in the a m o u n t
o f the hexamethylenetetramine which is b o u n d to the
phosphate. These samples are being further studied
but it appears at the m o m e n t , that the reaction involves a surface reaction rather than intercalation
because there is no a p p a r e n t increase in the basal
spacing for the samples which were p r e p a r e d either
at the low pressure or at high pressure. H M T A reacts
with the P O H groups present at the surface o f the
microcrystals, and with high pressure, d e l a m i n a t i o n
o f a-SnP must occur with a consequent increase in
the available external surface. H M T A m a y he regarded as an N - N diacetal and is readily hydrolysed
by acids to give a m m o n i a and formaldehyde. There
is no evidence, however, that any a m m o n i a is formed
during the surface reaction with H M T A because any
so formed would be rapidly intercalated. It appears
that high pressures have enhanced the a d s o r p t i o n o f
H M T A and to the best o f our knowledge this is the
77
first example in which such a surface modification
reaction has been observed at high pressure. It is interesting to note that there does not a p p e a r to be extensive hydrolysis o f H M T A even though the surface
phosphate groups are quite strongly acidic. The ct-SnP
which has been surface m o d i f i e d by the H M T A at
high pressure is appreciably soluble in water.
Acknowledgement
We thank Accion Itegrada H i s p a n o Britanica
(Ministerio de Educacion y Ciencia and British
Council) for financial support. This work has also
been supported by the U.K. D e p a r t m e n t o f the Env i r o n m e n t as part o f their R a d i o a c t i v e Waste Management Programme. The results m a y be used in the
formulation of g o v e r n m e n t policy but at this stage
do not necessarily represent government policy.
References
[ 1] E. Rodriguez-Castellon, A. Rodriguez-Garcia and S. Bruque,
Inorg. Chem. 24 ( 1985 ) 1187.
[ 2 ] C.O. Giwa, M.J. Hudson, L. Moreno-Real and E. RodriguezCastellon, J. Chem. Soc., Chem. Commun. (1987) 536.
[ 3 ] M.J. Hudson and E. Rodriguez-Castellon, J. Incl. Phen., to
be published.
[4] U. Costantino, in: Inorganic ion exchange materials, ed. A.
Clearfield (CRC Press, Boca Raton, F1., 1982) chapt. 3.
[5] A. Clearfield and R.M. Twinda, J. Inorg. Nucl. Chem. 41
(1979) 871.
[6] G. Alberti, M. Casciola and U. Costantino, J. Coll. Int. Sci.
107 (1985) 256.
[ 7 ] R. Martin, Undergraduate project (Reading, 1988).
[ 8 ] E. Rodriguez-Castellon, S. Bruque and A. Rodriguez-Garcia,
J. Chem. Soc., Dalton Trans. (1985) 213.