Cerium(IV) phenylphosphonates and para-substituted phenylphosphonates: preparation and characterization

Article abstract of DOI:10.1007/s10847-017-0701-0

Cerium(IV) phenylphosphonates and 4-substituted phenylphosphonates were prepared by reaction of a cerium(IV) salt with corresponding acids (phenylphosphonic, 4-carboxyphenylphosphonic, 4-sulfamoylphenylphosphonic, 1,4-benzenediphosphonic, 1,4-biphenyldiphosphonic and 4-sulfophenylphosphonic acid) and characterized by elemental analysis, energy-dispersive X-ray analysis, TGA, powder X-ray diffraction and infrared spectroscopy. Three different cerium phenylphosphonates can be prepared in dependence on the reaction conditions. On the other hand, only one compound is formed in each 4-substituted phosphonate system regardless the variation of the reaction conditions. All three phenylphosphonates, 4-carboxyphenylphosphonate and 4-sulfamoylphenylphosphonate are layered with the organic parts pointed below and above the plane of the metal phosphonate layers, with the functional groups placed at the end of the organic part. 4-Sulfophenylphosphonate, 1,4-benzenediphosphonate and 4,4′-biphenyldiphosphonate form pillared structures. Cerium 4-carboxyphenylphosphonate is able to intercalate aliphatic amines due to the presence of the free carboxylic groups in its interlayer space.

Full text of DOI:10.1007/s10847-017-0701-0

J Incl Phenom Macrocycl Chem
DOI 10.1007/s10847-017-0701-0
ORIGINAL ARTICLE
Cerium(IV) phenylphosphonates and para-substituted
phenylphosphonates: preparation and characterization
K. Melánová1 · L. Beneš2 · J. Svoboda1 · V. Zima1 · M. Trchová1 · M. Vlček1 ·
N. Almonasy2
Received: 24 October 2016 / Accepted: 13 February 2017
© Springer Science+Business Media Dordrecht 2017
Abstract Cerium(IV) phenylphosphonates and 4-substi-
tuted phenylphosphonates were prepared by reaction of a
cerium(IV) salt with corresponding acids (phenylphospho-
nic, 4-carboxyphenylphosphonic, 4-sulfamoylphenylphos-
phonic, 1,4-benzenediphosphonic, 1,4-biphenyldiphospho-
nic and 4-sulfophenylphosphonic acid) and characterized
by elemental analysis, energy-dispersive X-ray analysis,
TGA, powder X-ray diffraction and infrared spectroscopy.
Three different cerium phenylphosphonates can be pre-
pared in dependence on the reaction conditions. On the
other hand, only one compound is formed in each 4-sub-
stituted phosphonate system regardless the variation of the
reaction conditions. All three phenylphosphonates, 4-car-
boxyphenylphosphonate and 4-sulfamoylphenylphospho-
nate are layered with the organic parts pointed below and
above the plane of the metal phosphonate layers, with the
functional groups placed at the end of the organic part.
Keywords Cerium(IV) phenylphosphonate · Layered
phosphonates · IR spectra · Intercalation
Introduction
Layered metal phosphonates are continually in the focus
of scientific interest because they represent a large class of
compounds, which can be considered as well-defined inor-
ganic–organic materials. A great advantage of these materi-
als, besides the versatility of organic skeleton, is the pos-
sibility to attach various functional groups to this skeleton.
Most stable organophosphonates are those of tetravalent
metals especially zirconium phosphonates, which were the
most thoroughly studied [1]. Less attention has been paid
to titanium(IV) [2–9] and tin(IV) phenylphosphonates [10],
and also to cerium(IV) phosphonates.
4-Sulfophenylphosphonate,
1,4-benzenediphosphonate
First information about cerium phenylphosphonate was
given in the papers of DiGiacomo [2, 3], but only a basal
spacing of 15.5 Å is mentioned without any further char-
acterization. A preparation of layered cerium phenylphos-
phonate is also mentioned in the paper by Jang et al. [11]
but the authors report a basal spacing of 14.0 Å for this
compound. Cerium 3-sulfophenylphosphonate with the
formula Ce(HO3SC6H4PO3)2·3.86H2O was prepared by a
reaction of cerium phenylphosphonate with fuming sulfuric
acid. This compound is also layered with a basal spacing
of 15.1 Å and exhibits relatively high protonic conductivity
in the range 25–200°C, which increases with the increase
of relative humidity [11]. A different synthesis of cerium
3-sulfophenylphosphonate is described in the paper by
Dong [12]. He prepared a layered solid with a basal spac-
ing of 14.83 Å by a reaction of ammonium cerium nitrate
with 3-sulfophenylphosphonic acid. Its conductivity of
0.13 S cm1 at 100°C under 100% relative humidity is very
and 4,4′-biphenyldiphosphonate form pillared structures.
Cerium 4-carboxyphenylphosphonate is able to intercalate
aliphatic amines due to the presence of the free carboxylic
groups in its interlayer space.
Electronic supplementary material The online version of this
article (doi:10.1007/s10847-017-0701-0) contains supplementary
material, which is available to authorized users.
* L. Beneš
ludvik.benes@upce.cz
1
Institute of Macromolecular Chemistry of Academy
of Sciences of the Czech Republic, Heyrovský Sq. 2,
162 06 Prague 6, Czech Republic
2
Faculty of Chemical Technology, University of Pardubice,
Studentská 95, 532 10 Pardubice, Czech Republic
Vol.:(0123456789)
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J Incl Phenom Macrocycl Chem
similar to the values given by Jang et al. [11]. Prepara-
tion and structure of cerium 1,2-phenylenediphosphonate
microanalyser IXRF Systems (detector GRESHAM Sirius
10). The accelerating voltage of the primary electron beam
was 20 kV. The measurements were done on three different
samples of each cerium phosphonate prepared.
Ce[C6H4(PO3H)(PO3H2)][C6H4(PO3H)(PO3)]·2H2O
is
described in the paper by Diwu [13] but this compound is
not layered; it consists of edge sharing dimers of CeO8 pol-
yhedra, which are bridged by diphosphonate ligands creat-
ing one-dimensional chains. A pillared cerium(IV) sulfate-
phosphonate was hydrothermally synthesized by a reaction
of cerium sulfate with N,N′-bisphosphonomethyl bipiperi-
dine acid. Its structure was solved from powder diffraction
data and its luminescent properties were described [14].
Despite all these reports, no systematic study on
cerium(IV) phenylphosphonates has been done yet. The
aim of this work is therefore to enlarge the knowledge on
cerium(IV) phenylphosphonates, with the focus on the
preparation and characterization of new 4-functionalized
cerium(IV) phenylphosphonates.
The thermogravimetric measurements were carried
out in air between 30 and 960°C at a heating rate of 5°C
min−1
.
Powder X-ray diffraction data were obtained with a D8
Advance diffractometer (Bruker AXS, Germany) with
Bragg–Brentano θ–θ geometry (40 kV, 30 mA) using
CuKα radiation with secondary graphite monochromator.
The diffraction angles were measured at room temperature
from 2 to 50° (2θ) in 0.025° steps with a counting time of
4 s per step.
Infrared spectra in the range of 400–4000 cm−1 were
recorded at 64 scans per spectrum at 2 cm−1 resolution
using a fully computerized Thermo Nicolet NEXUS 870
FTIR Spectrometer equipped with a DTGS TEC detector.
Measurements of the powdered samples were performed
ex situ in the transmission mode in KBr pellets. All spec-
tra were corrected for the presence of moisture and carbon
dioxide in the optical path.
Experimental
All starting chemicals were obtained from commercial
sources and were used without further purification. 4-Sub-
stituted phenylphosphonic acids were prepared as has been
described previously [15–17]. Three different procedures
were used for the preparation of cerium phenylphosphonate.
Method A A 0.25 M Ce(SO4)2 solution (5 mL) was
added to a 0.25 M phenylphosphonic acid solution (10 mL)
and the mixture was stirred at room temperature overnight.
Method B A 0.25 M Ce(SO4)2 solution (5 mL) was
added to a 0.25 M phenylphosphonic acid solution (10 mL)
and the mixture was refluxed overnight.
The reactions of cerium 4-carboxy- and 4-sulfophe-
nylphosphonates with sodium hydroxide were carried out
at room temperature with a computer-controlled Schott
Titronic 97 piston burette by the method described previ-
ously [18]. Using the burette, 0.096 M aqueous NaOH was
added to a host suspended in a water–ethanol mixture (1/1
v/v). The pH of the solution during the reaction was meas-
ured with a glass pH electrode.
Method C A 0.25 M Ce(SO4)2 solution (3 mL) was
added to a 0.25 M phenylphosphonic acid solution (6 mL);
the mixture was placed in a Teflon-lined 23-mL Parr acid
digestion bomb and heated under autogenous pressure at
180°C for 60 h.
Results and discussion
The denotation of the products and their formulas cal-
culated from the results of elemental analysis and basal
spacings are shown in Table 1. The P/Ce ratio is equal to
2 (except for the last compound listed, CeSPhP). It means
that cerium is tetravalent in all these compounds, taking
into account that all phosphonic groups in the ligands are
fully deprotonated (which follows from their IR spectra,
see below). In the case of CeSPhP the P/Ce ratio is 1.33.
Again, provided that both phosphonic and sulfonic groups
in CeSPhP are fully deprotonated (see the text on the IR
spectra below), cerium in this compound is also tetravalent.
Substituted cerium phenylphosphonates were prepared
in the same way using corresponding 4-substituted phe-
nylphosphonic acids. In the case of 1,4-benzenediphos-
phonic acid and 4,4′-biphenyldiphosphonic acid, only half
volume of 0.25 M solution were used to maintain the P/Ce
molar ratio of 2.
In all cases, a finely crystalline product precipitated in
almost quantitative yield. The reaction conditions were
chosen so that no side products were formed, as was proved
by powder XRD. Solid products were separated by centrif-
ugation, washed with water and dried in air at room tem-
perature and at relative humidity (RH) of 33%.
Cerium phenylphosphonates
Depending on the reaction temperature, three different
layered cerium phenylphosphonates were obtained by the
reaction of cerium salt with phenylphosphonic acid.
The phosphorus/cerium and phosphorus/sulfur ratios
were determined by an energy-dispersive X-ray analy-
sis (EDX) using an electron scanning microscope JEOL
JSM-5500LV equipped with an energy-dispersive X-ray
Yellow cerium phenylphosphonate monohydrate with
a basal spacing of 15.54 Å (CePhP·H2O) can be prepared
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J Incl Phenom Macrocycl Chem
Table 1 Denotation, formulas
and basal spacings of
cerium phenylphosphonates
and 4-substituted
Compound Formula
Molar
ratio P/
Ce
Elemental analysis found/calc Basal spacing [Å]
C %
H % N%
S%
phenylphosphonates together
with the results of elemental
analyses
CePhP·H2O Ce(C6H5PO3)2·H2O
1.9
2.0
2.0
2.1
2.1
2.15
2.0
31.07 2.54
30.65 2.57
–
–
–
–
–
–
–
15.54
14.82
15.63
9.98
CePhP-I
CePhP-II
CePPhP
Ce(C6H5PO3)2
Ce(C6H5PO3)2
Ce(O3PC6H4PO3)
32.06 2.11
–
31.87 2.23
31.72 2.31
31.87 2.23
–
19.39 1.54
–
19.26 1.08
CePPh-PhP Ce(O3PC12H8PO3)
30.71 2.38
32.01 1.79
–
14.25
18.56
CeCPhP
CeNSPhP
CeSPhP
Ce(HO2CC6H4PO3)2·
0.5 H2O
Ce(H2NO2SC6H4PO3)2
30.42 1.78
–
30.61 2.02
23.49 1.95 4.50 10.34 19.60
23.61 1.98 4.59 10.51
Ce3(O3SC6H4PO3)4·2.4H2O 1.3
19.48 1.42
–
8.36
10.18
20.51 1.49
9.13
Fig. 1 Powder diffraction patterns of cerium phenylphosphonates
prepared: a CePhP·H2O, b CePhP-I, c CePhP-II
Fig. 2 Thermogravimetric curves of cerium phenylphosphonates pre-
pared: a CePhP·H2O, b CePhP-I, c CePhP-II
only at room temperature (method A). Its diffraction pat-
tern contains only three relatively broad basal lines indi-
cating a low crystallinity of the sample (see Fig. 1a).
This compound decomposes in three steps (see Fig. 2a).
The first step with a weight loss of 3.5% corresponds to
a release of water (the theoretical weight loss calculated
for the release of one water molecule per formula unit
is 3.83%). The dehydration of CePhP⋅H2O is irrevers-
ible and anhydrous cerium phenylphosphonate with a
basal spacing of 14.82 Å (CePhP-I) is formed by heat-
ing at 200 °C. The second step corresponds to a phe-
nylphosphonate decomposition and the third step is a
release of oxygen given by condensation of the phosphate
groups to triphosphate, in which cerium(IV) is reduced to
cerium(III) [19, 20]. End product of the thermal decom-
position is a mixture of monazite CeIIIPO4 (JCPDS No
04-007-2786) and cerium triphosphate CeIIIP3O9 (JCPDS
No 04-009-0934) [21]. Quantitative phase analysis of this
decomposition product by means of the Rietveld method
shows that the molar ratio of monazite and cerium
triphosphate is equal to one, indicating that the P/Ce
molar ratio in the decomposition product is two, which
is in an agreement with the value found by EDX in the
starting phenylphosphonate. A diffraction pattern of the
decomposition product is given in Fig. S1 in the Support-
ing data. The total weight loss of 34.4% is in an agree-
ment with the calculated value of 34.92%.
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J Incl Phenom Macrocycl Chem
White anhydrous phase with a basal spacing of 14.82 Å
(CePhP-I) is formed by method B. This compound can
be also prepared by grinding cerium sulfate or ammo-
nium cerium nitrate with phenylphosphonic acid or by a
prolonged stirring of a cerium salt and phenylphosphonic
acid solution (for more than 24 h). The powder diffrac-
tion pattern of CePhP-I contains several non-basal reflec-
tions (see Fig. 1b). The pattern was indexed from 26 lines
in a monoclinic system with the following cell param-
eters: a=14.912(6) Å, b=5.642(2) Å, c=9.388(4) Å
and β=96.64(1)° using a DICVOL91 program from the
CRYSFIRE software package [22] with figures of merit
M20 =18.0 [23] and F20 =23.1(0.0087, 100) [24]. The most
probable space group is P21/c, as determined by CHEK-
CELL [25] (see Table S1 in supporting data). CePhP-I
decomposes in two steps (see Fig. 2b), the first one cor-
responds to the decomposition of phenylphosphonate and
the second one to the reduction of cerium and formation of
a mixture of CePO4 and CeP3O9 in a 1:1 molar ratio. The
total weight loss of 32.8% is in an agreement with the cal-
culated value of 32.33%. The powder pattern of CePhP-I is
very similar to that of cerium phenylphosphonate described
by Jang [11] though the basal spacing of our compound is
higher.
PO
b
PO ss
CH
oop
3
3
PO as
P-OH
3
CC
s
ar
P=O s
H2PhP
CePhP- II
CePhP- I
CePhP.H2O
SrPhP·2H2O
SrPhP
ZrPhP
2000 1800 1600 1400 1200 1000
800
600
400
-1
Wavenumbers [cm ]
Fig. 3 FTIR spectra of CePhP·H2O, CePhP-I and CePhPII. Spectra
of zirconium phenylphosphonate (ZrPhP), strontium phenylphospho-
nates (SrPhP·2H2O, SrPhP) and phenylphosphonic acid (H2PhP) are
shown for comparison
group is present in its fully deprotonated form, PO32−. The
spectra exhibit peaks of stretching ring vibrations at 1595,
1486, and 1438 cm−1, and peaks of corresponding out-of-
plane aromatic C–H vibrations at 756, 716 and 696 cm−1
.
Another white anhydrous phase with the basal spac-
ing of 15.63 Å (CePhP-II) was prepared by method C.
CePhP-II is usually accompanied by CePhP-I; the pres-
ence of CePhP-I can be suppressed when a longer reac-
tion time is used. If ammonium cerium nitrate is used as a
cerium source, the product is often accompanied by mona-
zite. The powder diffraction pattern of CePhP-II contains
only a series of sharp basal diffraction lines (see Fig. 1c).
As CePhP-I, also CePhP-II decomposes in two steps (see
Fig. 2c). The total weight loss of 32.7% is in an agreement
with the calculated value of 32.33%. CePhP-II is probably
analogous to the compound mentioned by Dines [3].
A peak of asymmetric PO3 stretching vibrations is slightly
shifted to lower wavenumbers (1145 cm−1) in the spec-
tra of cerium phenylphosphonates in comparison with the
spectrum of Zr(C6H5PO3)2. A second maximum at about
1115 cm−1 is observed in the spectra of the both anhydrous
samples. The spectrum of CePhP-I differs from the spec-
trum of CePhP·H2O by the presence of an additional peak
at 957 cm−1 belonging to P–O stretching vibrations, a new
peak at 608, and peaks at 569, 550, and 516 cm−1 of the
PO3 bending vibrations. The spectrum of CePhP-II differs
more from the spectra of both CePhP-I and CePhP·H2O.
The spectrum of CePhP-II is similar to the spectra of anhy-
drous strontium phenylphosphonate Sr(C6H5PO3) (SrPhP)
and its dihydrate (SrPhP·2H2O) [26]. These spectra exhibit
also two bands at about 1055 and 978 cm−1, and a peak
at 608 cm−1. Peaks of PO3 bending vibrations were also
detected at about 569 and 516 cm−1 in the spectrum of
Sr(C6H5PO3)·2H2O. The spectrum of CePhP-II is specific
by the presence of a broad absorption with maxima at about
Both anhydrous cerium phenylphosphonates are stable
in an acid environment, but they decompose in the pres-
ence of sodium hydroxide. After addition of stoichiometric
amount of sodium hydroxide, CePhP-I completely trans-
forms to hydrated amorphous cerium oxide. In the case
of CePhP-II, the diffractogram after the titration shows a
series of basal reflections corresponding to CePhP-II, but
the P/Ce ratio determined by EDX decreases to 1 indicating
a partial decomposition of CePhP-II.
1315 and 818 cm−1
.
We can conclude that cerium phenylphosphonate mono-
hydrate as well as both anhydrous phenylphosphonates
All three compounds, CePhP·H2O, CePhP-I and CePhP-
II, were further characterized by infrared spectroscopy
(Fig. 3). The spectra of CePhP⋅H2O and CePhP-I are similar
to the spectrum of Zr(C6H5PO3)2, which has been reported
previously [15]. It should be stressed that the spectra of all
cerium phosphonates do not contain a peak of P=O stretch-
ing vibrations situated at about 1220 cm−1 in the spectrum
of phenylphosphonic acid, indicating that the phosphonate
2−
contain the C6H5PO3 group; the presence of a hydrogen
phenylphosphonate group (C6H5PO3H−) can be excluded.
The spectra of CePhP·H2O and CePhP-I are similar to the
spectrum of Zr(C6H5PO3)2 (ZrPhP), and the spectrum of
CePhP-II is more similar to the spectrum of SrPhP. In the
structure of zirconium phenylphosphonate, three oxygen
2−
atoms of the PO3 group are bonded to three different
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J Incl Phenom Macrocycl Chem
zirconium atoms, which leads to a regular octahedral
geometry of the ZrO6 polyhedron [27]. On the other hand,
the coordination of the oxygen atoms to strontium is dif-
ferent [28]. Analogously, we can suppose that anhydrous
cerium phenylphosphonates CePhP-I and CePhP-II differ in
the way of the coordination of the phenylphosphonate ani-
ons to the cerium atoms.
the values calculated for the decomposition of the corre-
sponding phosphonate to a mixture of CePO4 and CeP3O9
in a 1:1 molar ratio.
In contrast to the above mentioned cerium 4-substituted
phenylphosphonates and zirconium and titanium 4-sulfo-
phenylphosphonates, which phosphorus/metal ratio is close
to 2, the P/Ce ratio in cerium 4-sulfophenylphosphonate
is equal 1.3, indicating that also the sulfonic groups are
bonded to cerium. The basal spacing of CeSPhP (10.18 Å)
is very close to the value of the basal spacing of CePPhP
(9.98 Å) and titanium 4-benzenediphosphonate (9.50 Å)
but it is halved compared to the basal spacing of titanium
and zirconium 4-sulfophenylphosphonates (20.15 and
19.94 Å, respectively) [9, 15]. The sulfophenylphospho-
nate anions probably form bridges connecting the adjacent
layers as in the case of 1,4-benzenediphosphonate. This
is different from the findings by Jang [11] and Dong [12]
on cerium 3-sulfophenylphosphonate, where the sulfonic
groups are not bonded to cerium atoms. CeSPhP decom-
poses in two steps (see Fig. 4c). Water is released very
slowly up to about 300°C, the weight loss of 3% is in an
agreement with the calculated value of 3.08%. The total
weight loss of 42% agrees well with the value of 44.66%
calculated for the decomposition of CeSPhP to a mixture
of 79 wt.% CePO4 and 21 wt.% CeP3O9, as was determined
by Rietveld analysis of the diffraction pattern of the decom-
position product (see Fig. S4 in Supporting information).
The P/Ce molar ratio in the decomposition product is 1.28,
which is in a good agreement with the P/Ce value of 1.3
found in CeSPhP using the EDX analysis. The basal spac-
ing of CeSPhP after dehydration at 400°C is the same as
that of the original hydrate, which confirms the assump-
tion that the water molecules are placed among the pil-
lars formed by the ligand skeletons. Also in this case, as in
CeCPhP, the dehydration is reversible when the sample of
CeSPhP is kept at very high relative humidity (90–100%).
In the infrared spectra of CePPhP and CePPh-PhP
(Fig. 5) we can distinguish peaks at about 1384, 1153,
1010, 947, 834, 713, 608, 550 and 456 cm−1 belonging to
various aromatic and phosphonic group vibrations detected
in the spectra of corresponding 1,4-benzenediphospho-
nic and 4,4′-biphenyldiphosphonic acids. Peaks of P=O
stretching vibrations at 1196 cm−1, P–O stretching vibra-
tions observed at 947 cm−1 and of PO3 bending vibra-
tions at about 550 cm−1 are suppressed in the spectra of
cerium(IV) 4-substituted phenylphosphonates. It indicates
that all phosphonate groups are deprotonated and bonded
to the cerium atoms, which is in an agreement with the
compositions of both phosphonates found by elemental
analysis.
Cerium 4-substituted phenylphosphonates
Cerium(IV) 4-substituted phenylphosphonates were pre-
pared by the reaction of the cerium salt with the corre-
sponding phosphonic acid according to methods A to C.
Their powder diffraction patterns (see Fig. S2 in Support-
ing data) contain series of basal reflections from which the
basal spacings were calculated. In contrast to cerium phe-
nylphosphonate, the basal spacings of the compounds pre-
pared are not affected by the reaction conditions, but the
crystallinity of the samples improves with increasing reac-
tion temperature (see Fig. S3 in Supporting data).
Cerium(IV) 4-sulfamoylphenylphosphonate, 1,4-ben-
zenediphosphonate and 4,4′-biphenyldiphosphonate are
anhydrous and decompose in several badly resolved steps
(See Fig. 4). 4-Carboxyphenylphosphonate contains 0.5
water molecule per formula unit, which is released on
heating to 100°C and the weight loss of 1.7% is in a good
agreement with the calculated value of 1.64%. The basal
spacing of CeCPhP after dehydration remains the same
(18.50 Å), which indicates that the water molecules are
placed among the phenyl rings of the phosphonate. The
dehydration is reversible when the sample is kept at relative
humidity of 90–100% for 1 week. Total weight losses for
all these substituted phenylphosphonates agreed well with
100
95
90
85
e
d
80
75
70
65
60
55
50
c
b
a
0
200
400
600
800
T [°C]
In the spectrum of cerium(IV) 4-carboxyphenylphos-
phonate, CeCPhP, peaks of the carboxyphenylphos-
phonate anion are well distinguished including a peak
Fig. 4 Thermogravimetric curves of the cerium 4-substituted phe-
nylphosphonates: a CeNSPhP, b CeCPhP, c CeSPhP, d CePPh-PhP,
e CePPhP
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J Incl Phenom Macrocycl Chem
at about 1400 cm−1, found in the spectra of Sr2 and Sr3
[29], are missing in the spectrum of CeCPhP. The bonding
of the phosphonic group of CeCPhP is analogous to that
in Sr2 and Sr3; it means that the phosphonate groups are
completely deprotonated and bonded to the cerium atoms.
The spectrum of CeSPhP contains peaks at 1154 and
1012 cm−1 of asymmetric and symmetric PO3 stretching
vibrations and peaks at 554 and 437 cm−1 of PO3 bend-
ing vibrations of the phosphonic group, as follows from
the comparison of their spectra with the spectrum of
Zr(C6H5PO3)2, which contains only phenylphosphonate
anion (Fig. 3). The peak of the PO3 symmetric vibrations
is shifted from 1044 to 1017 cm−1 due to the replace-
ment of Zr with Ce. The comparison of the infrared spec-
trum of cerium(IV) 4-sulfophenylphosphonate CeSPhP
with the spectra of Zr(HO3SC6H4PO3)2·2H2O (ZrSPhP),
sodium intercalated zirconium sulfophenylphosphonate
Zr(NaO3SC6H4PO3)2·2H2O (ZrSPhPNa) and pure sulfo-
phenylphosphonic acid is shown in Fig. 7. The peaks of
the phenylsulfonic group are situated at 1390 cm−1 (C–C
aromatic stretching vibration), 1048 cm−1 (symmetric
Fig. 5 FTIR spectra of the cerium(IV) 1,4-benzenediphosphonate
(CePPhP) and 4,4′-biphenyldiphosphonate (CePPh-PhP). Spectra of
1,4-benzenediphosphonic (H4PPhP) and 4,4′-biphenyldiphosphonic
(H4PPh-PhP) acids are shown for comparison
of C=O stretching vibrations observed at 1685 cm−1
(Fig. 6). The spectrum is similar to the spectrum
of Sr(HOOCC6H4PO3H)2 (Sr1) in the region of
1650–1750 cm−1, but it does not contain the peak at
1220 cm−1 of the stretching vibrations of the P=O bond
as the spectra of SrH(OOCC6H4PO3)·H2O (Sr2) and
Sr3(OOCC6H4PO3)2·4H2O (Sr3) [29]. We can deduce that
the interaction of the carboxyl group in CeCPhP is anal-
ogous to that in Sr1; that means that the C=O bond is a
part of a free COOH group in the interlayer space. Typi-
cal bands of the carboxylate anion at 1587, 1541 cm−1 and
−
SO3 stretching vibration), 830 cm−1 (1,4-disubstituted
benzene ring vibration), and 662 cm−1 (C–SO3− vibration).
In contrast to the spectrum of ZrSPhP [15], the spectrum of
CeSPhP contains an additional peak at about 1208 cm−1
.
This peak was observed in the spectrum of sodium inter-
calate, ZrSPhPNa, and can be assigned to an asymmetric
stretching vibration of the deprotonated SO3− group [30]. It
indicates that the SO3 groups in CeSPhP are bonded to the
cerium atoms, resulting in the proposed ligand/Ce ratio of
1.3, which is in accordance with the composition found by
elemental analysis and EDX. Thus, the infrared spectrum
PO ss
PO ss
PO as
3
CH
PO as
3
P=O s
3
PO
b
P=O s
oop
3
3
CC
s
P-OH
P-OH
ar
CH
CC
s
C-SO
oop
ar
C=O
3
PO
b
3
H2PhP
H3CPhP
Sr1
H3SPhP
ZrSPhP
CeSPhP
Sr2
Sr3
ZrSPhP-Na
CeCPhP
SO
SO
3 s
3
as
2000
1800
1600
1400
1200
1000
800
600
400
2000
1800
1600
1400
1200
1000
800
600
400
Wavenumbers [cm-1]
Wavenumbers [cm-1]
Fig. 6 FTIR spectra of the cerium 4-carboxyphenylphospho-
nate CeCPhP together with spectra of phenylphosphonic acid
(H2PhP), 4-carboxyphenylphosphonic acid (H3CPhP) and stron-
tium 4-carboxyphenylphosphonates: Sr(HOOCC6H4PO3H)2 (Sr1),
SrH(OOCC6H4PO3)·H2O (Sr2) and Sr3(OOCC6H4PO3)2·4H2O (Sr3)
Fig. 7 FTIR spectra of the cerium 4-sulfophenylphosphonate
(CeSPhP). The spectra of 4-sulfophenylphosphonic acid (H3SPhP),
zirconium sulfophenylphosphonate (ZrSPhP) and its sodium interca-
late Zr(NaO3SC6H4PO3)2·2H2O (ZrSPhP-Na) are shown for compari-
son
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J Incl Phenom Macrocycl Chem
H2NSPhP
CeNSPhP
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers [cm-1]
Fig. 8 FTIR spectra of the cerium 4-sulfamoylphenylphosphonate
(CeNSPhP) together with the spectrum of 4-sulfamoylphenylphos-
phonic acid (H2NSPhP)
Fig. 9 Titration of CeCPhP (a) and CeSPhP (b) with sodium hydrox-
ide solution
of CeSPhP supports our assumption that both phosphonic
and sulfonic groups are bonded to the cerium atoms and the
sulfophenylphosphonate anions form bridges connecting
adjacent layers.
for CeCPhP to 19.0 Å for the titration product. Similar
phenomenon, that is the lower amount of the intercalated
species than that corresponding to the theoretical amount,
was also observed on titration of titanium 4-carboxyphe-
nylphosphonate with NaOH and on titration of titanium
4-sulfophenylphosphonate with NaOH and hexylamine
solutions [9]. If CeSPhP is titrated with a NaOH solution,
a slow increase of pH is observed indicating a decomposi-
tion of the solid phase (see Fig. 9). This was confirmed by
the EDX and powder X-ray diffraction. The product after
the titration was amorphous and contained only cerium and
oxygen. These facts support our suggestion that the sulfonic
groups in CeSPhP are not free (i.e., are not present as pro-
tonated SO3H groups) but are bonded to the cerium atoms.
Therefore, in contrast to what was observed for zirconium
4-sulfophenylphosphonate [31], CeSPhP cannot serve as a
host for intercalation of basic species.
The infrared spectrum of cerium 4-sulfamoylphe-
nylphosphonate CeNSPhP (Fig. 8) differs from the spec-
trum of cerium(IV) 4-sulfophenylphosphonate CeSPhP.
Two strong peaks at 3379 and 3254 cm−1 in the spectrum
of 4-sulfamoylphenylphosphonic acid (H2NSPhP), which
are slightly shifted in the spectrum of CeNSPhP, are typi-
cal for N–H stretching vibrations of primary sulfonamides
[30]. A set of absorption bands with the strongest one at
about 1319 cm−1 and a strong band at 1161 cm−1 is due to
asymmetric and symmetric stretching vibrations of the SO2
group. The peak of NH deformation vibrations at about
1630 cm−1 and of NH out-of-plane deformations or para-
substituted ring deformations at 824 cm−1 detected in the
spectrum of H2NSPhP were also found at slightly shifted
positions in the spectrum of CeNSPhP. The peaks of para-
substituted aromatic rings at 3106, 1565 cm−1 and small
peaks below 2000 cm−1 can be seen in the spectra. Two
broad bands with maxima at 2853 and 2282 cm−1 can be
observed in the spectrum of pure H2NSPhP but not in the
spectrum of CeNSPhP.
Intercalation of aliphatic amines into CeCPhP was done
by shaking solid CeCPhP with an excess of liquid amines
at room temperature. Diffraction patterns of the intercalates
prepared are shown in Fig. 10. Propylamine and butyl-
amine intercalate very easily, forming intercalates contain-
ing about 1.3 amine molecule per formula unit. Intercalates
of pentylamine and hexylamine with the basal spacings of
31.09 and 33.71 Å, respectively, contain a small amount
of an unintercalated host. In the case of octylamine, only
a mixture of an intercalate with basal spacing of 25.90 Å
together with the parent host was obtained (see Fig. 10).
The basal spacing of this intercalate is significantly lower
than the basal spacings of the intercalates with the shorter
amines indicating a different arrangement and probably
also a lower amount of the intercalated guest. In contrast
to the other amine intercalates, the octylamine intercalate
The ability of cerium phosphonates containing acidic
groups (CeCPhP, CeSPhP) to interact with basic com-
pounds was tested by their titration with sodium hydroxide
solutions. The titration curves are shown in Fig. 9. In the
case of CeCPhP, only a part of the carboxyl groups was
neutralized by sodium hydroxide giving a product with for-
mula Ce(O2CC6H4PO3)2H0.7Na1.3·xH2O (confirmed by the
Na/P ratio of 0.65, found by EDX). During this titration
the basal spacing slightly increases from 18.56 Å found
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J Incl Phenom Macrocycl Chem
is fully released from CeCPhP at about 120°C while the
CeSPhP sample must be heated to almost 350°C to be fully
dehydrated. Amount of water in CeSPhP is also higher
(CeSPhP·2.4H2O) than in other hydrated cerium com-
pounds, which is most probably given by a stronger hydro-
philic nature of the sulfonic group.
Acknowledgements The authors thank the Czech Science Founda-
tion (Grant No 14-13368S) for financial support.
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