Anionic Ligand Exchange on ZrPO4Cl(dmso): Alkoxide and Carboxylate Derivatives

Article abstract of DOI:10.1021/ic034695r

This paper reports the preparation and characterization of a series of organic derivatives of ZrPO₄Cl(CH₃)₂SO obtained by topotactic anion exchange of chloride ligands with several n-alkoxide (RO) and carboxylate groups (RCOO). Exchange with alkoxides, with an alkyl chain length from 2 to 8 carbon atoms, gave products of general formula ZrPO₄RO(CH₃)₂SO. In these derivatives alkoxide groups, covalently bonded to zirconium atoms via Zr-O bonds, point toward the interlayer region. Carboxylate derivatives, of general formula ZrPO ₄[(RCOO)(CH₃)₂SO]_1-x(OH H ₂O)_x, were obtained using benzoate (x = 0), nitrobenzoate (x = 0.3), and phenylacetate (x = 0.2) groups. The thermal behavior of these organic derivatives is discussed. Due to this reactivity, ZrPO ₄Cl(CH₃)₂SO is an attractive precursor for materials chemistry.

Full text of DOI:10.1021/ic034695r

Inorg. Chem. 2004, 43, 368−374
Anionic Ligand Exchange on ZrPO Cl(dmso): Alkoxide and Carboxylate
4
Derivatives
Riccardo Vivani,* Silvia Masci, and Giulio Alberti
Department of Chemistry, UniVersity of Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy
Received June 18, 2003
This paper reports the preparation and characterization of a series of organic derivatives of ZrPO Cl(CH ) SO
4
3 2
obtained by topotactic anion exchange of chloride ligands with several n-alkoxide (RO) and carboxylate groups
(RCOO). Exchange with alkoxides, with an alkyl chain length from 2 to 8 carbon atoms, gave products of general
formula ZrPO RO(CH ) SO. In these derivatives alkoxide groups, covalently bonded to zirconium atoms via Zr−O
4
3 2
bonds, point toward the interlayer region. Carboxylate derivatives, of general formula ZrPO [(RCOO)(CH ) SO]1-x(OH
4
3 2
H O)x, were obtained using benzoate (x ) 0), nitrobenzoate (x ) 0.3), and phenylacetate (x ) 0.2) groups. The
2
thermal behavior of these organic derivatives is discussed. Due to this reactivity, ZrPO Cl(CH ) SO is an attractive
4
3 2
precursor for materials chemistry.
Introduction
these ligand exchange reactions are of topotactic type, and
the approximate disposition of organic moieties that occupy
the interlayer region can be easily predicted on the basis of
general stereochemistry rules.
Many layered solids are able to host several neutral or
ionic species in the interlayer region, by means of intercala-
tion or ion exchange reactions. In the resulting compounds,
host-guest interactions are generally weak, being of van der
Waals or polar type.
Following the work of Clearfield and co-workers,4 we
recently prepared a new layered zirconium phosphate, of
formula ZrPO4Cl(CH3)2SO (hereafter λ-ZrP), in which
zirconium atoms are coordinated by four phosphate groups
in four equatorial positions lying on the layer plane and by
a couple of anionic and neutral monodentate ligands, Cl-
and dimethyl sulfoxide (hereafter dmso), in trans-axial
positions.5 Due to the relative weakness of Zr-Cl bonds,
we found that it is possible to replace chloride ligands with
other inorganic anionic ligands, such as OH-, sulfate,
chromate, or molybdate, by simple topotactic exchange
reactions of type
Layered zirconium phosphates (hereafter ZrP) are known
to be good ion exchangers and intercalating hosts for cationic
or polar species, since they usually bear acidic P-OH groups
directed toward the interlayer region.1 A special behavior is
shown by ZrPO4[O2P(OH)2]‚2H2O (γ-ZrP). In this com-
pound, the O2P(OH)2 groups, covalently bonded to zirconium
on the external part of layers, can be replaced by other O2-
PRR′ groups by means of ligand exchange reactions. A large
variety of zirconium phosphate phosphonates, of general
formula ZrPO4O2PRR′, in which the organic groups are
covalently bonded to the inorganic layers, has been prepared
using soft conditions.1,2 We demonstrated that the structure
of inorganic layers does not change appreciably during these
reactions occurring on the surface of γ-layers.3 Therefore,
ZrPO4Cl(dmso) + L- f ZrPO4L(dmso) + Cl-
in which the parent compound is dispersed in a solution of
the corresponding anions to be exchanged.6
* To whom correspondence should be addressed. E-mail: ric@unipg.it.
(1) (a) Clearfield, A.; Costantino, U. In ComprehensiVe Supramolecular
Chemistry; Alberti, G., Bein, T., Eds.; Pergamon Elsevier Science
Ltd.: Oxford, U.K., 1996; Vol. 7, p 107. (b) Alberti, G. In
ComprehensiVe Supramolecular Chemistry; Alberti, G., Bein, T., Eds.;
Pergamon Elsevier Science Ltd.: Oxford, U.K., 1996; Vol. 7, p 151.
(c) Clearfield A. In Progress in Inorganic Chemistry; Karlin, K. D.,
Ed.; John Wiley & Sons: New York, 1998; Vol 47, p 374.
(2) (a) Alberti, G.; Casciola, M.; Costantino U.; Vivani, R. AdV. Mater.
1996, 8, 291. (b) Alberti, G.; Murcia-Mascaro´s, S.; Vivani, R. J. Am.
Chem. Soc. 1998, 120, 9291.
We found of interest to investigate the possibility to
introduce organic groups covalently bonded to λ-ZrP layers,
(3) Alberti, G.; Vivani, R.; Murcia Mascaro´s, S. J. Mol. Struct. 1998,
469, 81.
(4) Poojary, D. M.; Zhang, B.; Clearfield, A. J. Chem. Soc., Dalton Trans.
1994, 2453.
(5) Alberti, G.; Bartocci, M.; Santarelli, M.; Vivani, R. Inorg. Chem. 1997,
36, 3574.
(6) Alberti, G.; Masci, S.; Vivani, R. Inorg. Chem. 2002, 41, 1913.
368 Inorganic Chemistry, Vol. 43, No. 1, 2004
10.1021/ic034695r CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/09/2003

Anionic Ligand Exchange on ZrPO4Cl(dmso)
and this work describes the preparation and characterization
of alkoxide and carboxylate derivatives of λ-ZrP.
Experimental Section
Reagents. All reagents were C. Erba RPE grade. They were used
without further purification.
Preparation of ZrPO4Cl(dmso). It was prepared as previously
described.6
Preparation of Short-Chain Alkoxide Derivatives (Number
of Carbon Atoms in the Alkyl Chain ) 2-4). A 1 g amount of
ZrPO4Cl(dmso) was contacted, under nitrogen, with 68 mL of 0.1
M n-tributylamine solution using the corresponding anhydrous
n-alkanol as solvent. The reaction mixture was maintained in a
closed glass container at a temperature of 20 °C lower than the
alkanol boiling point, for 4 days. The solid was then separated by
centrifugation, washed twice with 100 mL of alkanol, dried at 70
°C for 2 h, and finally stored under nitrogen atmosphere.
Preparation of Long-Chain Alkoxide Derivatives (Number
of Carbon Atoms in the Alkyl Chain ) 5-8). For these
derivatives, the λ-butoxide derivative, ZrPO4C4H9O(dmso), prepared
as described above, was used as precursor. A 1 g amount of
ZrPO4C4H9O(dmso) was contacted, under nitrogen, with 68 mL of
0.1 M n-tributylamine solution using the corresponding anhydrous
n-alkanol as solvent. The reaction mixture was maintained in a
closed vessel at 80 °C, for 4 days. The solid was then treated as
described above.
Figure 1. Structure of ZrPO4Cldmso. Asterisk indicates methyl groups
of dmso having occupancy 0.5.
with a 0.03° 2θ step size and 1 s counting time in the 2-40° 2θ
range at room temperature. Unit cell parameters have been first
determined on the basis of 200 and 00l reflections, and then they
were refined using the CELREF program.7 Finally a whole profile
fit, using the Le Bail method, has been performed with the GSAS
program.8
Anal. Calcd (found) for ZrPO4C4H9O(CH3)2SO: Zr, 26.97 (27.2);
P, 9.17 (9.20); C, 21.29 (20.95); H, 4.73 (4.52). Similar results
were obtained for all other alkoxide derivatives.
Results and Discussion
Alkoxide Derivatives of λ-ZrP. Figure 1 shows the
structure of a λ-ZrP layer. The unit cell is tetragonal, space
group P4/n, with parameters a ) 6.5955(1) Å and c )
10.2422(4) Å.6
Preparation of Carboxylate Derivatives. A 1 g amount of
ZrPO4Cl(dmso) was contacted with 68 mL of a 0.05 M RCOOH
(R ) C6H5, C6H4NO2, CH2C6H5) and 0.05 M RCOONa solution
using a 1:1 v/v dmso-water mixture as solvent. The solid was
maintained in this solution for 3 days at 75 °C, and then it was
separated by centrifugation and washed twice with 100 mL of a
1:1 v/v dmso-water mixture. Finally it was dried at 80 °C.
Anal. Calcd (found) for ZrPO4C6H5CO2(CH3)2SO: Zr, 23.68
(23.54); P, 8.05 (7.95); C, 28.04 (27.84); H, 2.86 (3.22).
Characterization of the Products. The zirconium content of
samples was determined gravimetrically by dissolving a weighed
amount (0.150 g) in a few drops of concentrated HF, followed by
precipitation with Cupferron and subsequent calcination to ZrO2.
Phosphates and chlorides were determined by ion chromatog-
raphy. About 0.100 g of sample was refluxed for 3 h with 10 mL
of 1 M NaOH; after filtration and suitable dilution, the solution
was injected into a Dionex series 2000 i/sp instrument, using an
IonPack AS4A column and a buffer solution, with composition 1.7
× 10-3 M NaHCO3 and 1.8 × 10-3 M Na2CO3, as eluent.
Thermogravimetric analysis (TG) was carried out in air on a
Stanton Redcroft STA 780 apparatus from room temperature to
1100 °C at 5 °C/min heating rate.
Carbon and hydrogen elemental analysis was performed by a
Carlo Erba 1106 analyzer.
FT-IR spectra were recorded using a Bruker JFS V FT-IR
spectrometer, in the 400-4000 cm-1 spectral range. The samples
were prepared as pressed pellets in anhydrous KBr.
J-modulated 13C liquid NMR spectra of the samples were
obtained by a Bruker DPX 200 spectrometer. About 50 mg of
sample was dissolved in a few drops of concentrated HF and 0.5
mL of D2O.
X-ray powder diffraction (XRD) patterns were measured using
a Philips APD X′PERT diffractometer using the Cu KR radiation,
Chlorine atoms occupy an external position with respect
to the layer surface and are more exposed than the contiguous
dmso sites. Different from other zirconium phosphates, the
layers of λ-ZrP do not bear acidic or strongly polar groups.
Therefore, it is expected that this compound cannot inter-
calate guest species very easily. In agreement to this, any
intercalation compound of λ-ZrP is today known, and when
the solid was suspended in pure alkanols, no intercalation
reaction occurred, even under heating. On the other hand,
we showed that this compound is able to exchange chlorine
atoms with other anionic species, and alkoxide ions could
be exchanged with reactions of type
ZrPO4Cl(dmso) + RO- f ZrPO4RO(dmso) + Cl-
However, alkoxide ions are very strong Bro¨nsted bases,
and the concentration of the free anion in pure alkanol is,
generally, extremely low. We found that this reaction can
be promoted provided that the RO- concentration in the
contact solution is increased. Preliminary experiments have
been performed using the n-butoxide/n-butanol system. The
preparation of a butoxide derivative has been achieved by
three independent routes, which consisted in dispersing
ZrPO4Cl(dmso) in an anhydrous butanol solution of (a) KOH,
(7) Laugier, J.; Bochu, B. LMGP-Suite; ENSP/Laboratoire des Mate´riaux
et du Ge´nie Physique: BP 46, 38042 Saint Martin d’He`res, France.
(8) Larson, A. C.; von Dreele, R. B. Generalized Crystal Structure Analysis
System; Los Alamos National Laboratory: Los Alamos, NM, 2001.
Inorganic Chemistry, Vol. 43, No. 1, 2004 369

Vivani et al.
(b) sodium butoxide, or (c) an alkylamine. However, among
them, the use of a n-tributylamine solution was preferred.
In fact, the use of KOH hydroxyl ions, other than to favor
the deprotonation of the alkanol, was found to activate the
direct OH/Cl exchange on λ-ZrP, with the partial conversion
into the undesired ZrPO4OHdmso product; furthermore,
tributylammonium chloride, which is formed during the RO/
Cl exchange reaction using tributylamine, is more soluble
in the alcoholic medium than sodium or potassium chloride
formed when using RONa or KOH solutions, respectively.
These inorganic salts were collected as solid phases, mixed
with the λ-alkoxide derivative. Finally, among other alkyl-
amines, tributylamine was selected because of its high
basicity and large dimensions that prevented a direct reaction
with the host compound. During this investigation we have
found that small amines are able to replace dmso, bonded
to zirconium atoms in λ-ZrP, by a topotactic neutral ligand
exchange reaction. This process is faster in λ-alkoxide
derivatives, where the interlayer region is expanded due to
the presence of RO residues. Therefore, when these amines
are used as bases to favor alkanol deprotonation for RO/Cl
anion exchange reactions, an appreciable amount of amine/
dmso exchange was also observed. A deeper investigation
on this interesting behavior will be reported elsewhere.
However we found that this reaction can be avoided when
using a large amine, such as tributylamine, very likely
because it does not meet the steric requirements of λ-ZrP
sites.
Figure 2. XRD patterns of eptanoxide (a) and butoxide (b) derivatives of
λ-ZrP compared to that of the parent compound ZrPO4Cl(dmso) (c).
Figure 3. Interlayer distance of alkoxide derivatives of λ-ZrP as a function
of the number of carbon atoms in the alkyl chain.
J-modulated 13C liquid NMR of a sample dissolved in HF
confirmed the absence of amines after the reaction and, in
the same time, the presence of both alkoxide and dmso in
the exchanged solid, while ion chromatography revealed the
total absence of chlorides.
layers, some useful information on the arrangement of alkyl
groups can be derived. Each carbon atom added to the alkyl
chains causes a constant increment (∆) of the interlayer
distance equal to 2.0 Å. Therefore, the alkyl chains in the
different samples should be all in the same conformation
that can be reasonably assumed to be their all-trans confor-
mation. Under this model, the interlayer distances of different
samples should follow the equation
The RO/Cl exchange reaction in the presence of 0.1 M
tributylamine occurred in one step, as assessed by XRD
patterns, which showed that the ZrPO4Cl(dmso) phase
gradually disappeared while the amount of ZrPO4RO(dmso)
phase gradually increased. This reaction needed about 4 days
for the full conversion in ethoxide, propoxide, and butoxide
derivatives, while for the higher alkoxides (from pentoxide
to octanoxide) times increased considerably. Therefore, we
decided to prepare the long-chain alkoxide derivatives start-
ing from the preenlarged butoxide derivative, ZrPO4C4H9O-
(dmso), as precursor. Reaction times were thus limited to 4
days in all the syntheses. All the alkoxide derivatives from
2 to 8 carbon atoms in the alkyl chain were obtained as pure
phases, with composition ZrPO4RO(dmso). Their XRD
patterns are typical of layered materials (Figure 2).
d (Å) ) mnC1.27 sin R + B
(2)
where m is the number of monomolecular films in which
the chains are arranged between the layers and 1.27 Å is the
increment in length for an all-trans alkyl chain per each
additional carbon atom.9 By the combination of eqs 1 and
2, ∆ ) 2.0 ) m1.27 sin R. From composition data m must
be equal to 2, and R can be estimated to be about 52°. This
value is close to that calculated (55°) for an alkyl chain in
trans conformation with the first Zr-O bond perpendicular
to the plane of layers and a tetrahedral Zr-O-C angle. From
these data it is possible to build a structural model in which
alkoxide groups are coordinated to zirconium atoms belong-
ing to a λ-type layer and are directed toward the interlayer
region from both sides of layers. Figure 4 shows a schematic
model of the hexanoxide derivative of λ-ZrP.
The d values of the strong peak at low 2θ values can be
therefore associated with the interlayer distance. These d
values, when plotted as a function of the number of carbon
atoms, nC, in the alkyl chain of alkoxide groups, show a good
linear correlation that follows the equation
d (Å) ) 2.0nC + 7.7
(1)
This plot is reported in Figure 3.
If we reasonably assume that the process cannot ap-
preciably change the structure of the inorganic backbone of
(9) (a) Lagaly, G. Angew. Chem., Int. Ed. Engl. 1976, 15, 575. (b)
Costantino, U.; Vivani, R.; Zima, V.; Benes, L.; Mela´nova´, K.
Langmuir 2002, 18, 1211.
370 Inorganic Chemistry, Vol. 43, No. 1, 2004

Anionic Ligand Exchange on ZrPO4Cl(dmso)
Figure 5. Whole profile fit, with the Le Bail method, for the butoxide
derivative (under the P4/n space group, Rp ) 0.104) (a) and for the benzoate
derivative of λ-ZrP (under the P42/n space group, Rp ) 0.108) (b).
Figure 4. Schematic model of the structure of the hexanoxide derivative
of λ-ZrP.
The B parameter of eq 2 is a constant and represents the
interlayer distance of the structural residue when nC ) 0,
which roughly corresponds to the presence of one hydroxyl
group in the alkoxide site.
Alkoxide derivatives are obtained as poorly crystalline
compounds, as assessed by their XRD patterns (Figure 2).
Although these patterns are broadened and not suitable for
structural analysis, we found that they are consistent with
tetragonal unit cells of λ-type, that is with the a value of
about 6.6 Å and the c parameter corresponding to the
interlayer distance. For example, XRD pattern of the butoxide
derivative can be indexed with the tetragonal unit cell a )
6.601(1) Å and c ) 15.016(3) Å, and for the eptanoxide
derivative a ) 6.607(1) Å and c ) 22.115(3) Å. Figure 5a
shows the whole profile fit for the butoxide derivative pattern.
Figure 6. TG curve for the butoxide derivative of λ-ZrP.
of λ-ZrP as a precursor for the introduction of a large
magnetic moiety (a nitronyl nitroxide radical) inside this
structure.10
Thermal Behavior. Figure 6 shows the TG curve of the
butoxide derivative of λ-ZrP. Weight loss starts at about 200
°C, with the unresolved loss of both butoxide and dmso
moieties. At the end of the analysis, at 1100 °C, the formation
of an equimolar mixture of zirconium oxide and zirconium
pyrophosphate was assumed, according to the following
reaction of decomposition:
Therefore, in agreement with the hypothesis of a topotactic
process, the replacement of chlorides with alkoxide ions, and
even the successive replacement of short-chain with long-
chain alkoxides, did not change appreciably the inorganic
framework of layers.
Due to the high reactivity of the basic alkoxide groups,
these derivatives are not stable in air. A slow conversion
into the hydroxyl derivative, ZrPO4OH(dmso), was observed,
due to the reaction with water coming from air humidity.
On the other hand, alkoxide derivatives can be used as
preenlarged substrates in which large anionic species can
be introduced more easily than in the parent compound. In
a recent paper we successfully used the butoxide derivative
ZrPO4C4H9O(dmso) + nO2 f 1/2ZrO2 + 1/2ZrP2O7 +
gaseous products
The calculated % weight loss is 43.8%, in good agreement
with that experimentally found (42.3%). TG curves for all
other alkoxide derivatives are in agreement with this model.
(10) Caneschi, A.; Gatteschi, D.; Vaz, M. G. F.; Costantino, U.; Nocchetti,
M.; Vivani, R. Inorg. Chim. Acta 2002, 338, 127.
Inorganic Chemistry, Vol. 43, No. 1, 2004 371

Vivani et al.
Figure 7. Evolution, as a function of reaction time, of XRD patterns for
the product of benzoate/chloride exchange reaction on λ-ZrP.
Carboxylate Derivatives of λ-ZrP. (a) Benzoate Deriva-
tive. Carboxylate/Cl exchange reaction on λ-ZrP was first
tested with benzoate groups, by contacting the parent
compound with the free acid or one of its salt solutions, using
several solvents. While the reaction was extremely slow in
pure organic solvents, we found that the use of aqueous
solvents and the increase of the free benzoate fraction
(obtained by the addition of its salt forms) improved the
exchange rate. On the other hand, a certain degree of
hydrolysis on the sample was often found, because of the
concomitant OH/Cl exchange reaction. Best conditions were
the use of an equimolar mixture of benzoic acid and sodium
benzoate in 1:1 v/v water-dmso mixture as solvent, at 75
°C, in which the reaction
Figure 8. Schematic model of the structure of the benzoate derivative of
λ-ZrP.
ZrPO4Cl(dmso) + C6H5COO- f
ZrPO4C6H5COO(dmso) + Cl-
was completed in about 3 days. The reaction occurred in
one step, with the gradual conversion of the parent compound
(d ) 10.2 Å) into the benzoate phase (d ) 14.9 Å), as shown
by XRD pattern of the product, taken at different times,
reported in Figure 7.
Figure 9. TG curve for the benzoate derivative of λ-ZrP.
corresponds to a weight loss of 20.50% and is ascribed to
the loss of 1 mol of dmso/mol of zirconium. The compound
obtained after heating for 2 h at 220 °C had the composition
ZrPO4C6H5COO (hereafter II) and, once formed, is stable
from room temperature up to about 300 °C. The loss of dmso
causes a change of the interlayer distance from 14.9 to 13.2
Å, at room temperature, as shown by the XRD pattern
(Figure 10). The second step of weight loss starts at about
400 °C and can be ascribed to the decomposition of organics.
At the end of the analysis, at 1100 °C, an equimolar mixture
of ZrO2 and ZrP2O7 was formed according to the following
process:
The final product was pure, with the composition
ZrPO4C6H5COO(dmso) (compound I). Figure 8 shows a
hypothetical model of the benzoate derivative, built up under
the hypothesis that the structure of λ-layers does not
appreciably change due to the exchange reaction. As for
alkoxide derivatives, the crystallinity degree of this product
is not sufficient for a complete structural analysis. However,
we found that the XRD pattern of this compound is
compatible with the tetragonal cell of λ-type with a ) 6.585-
(1) Å and c ) 29.702(7) Å (see Figure 5b), that is with the
a parameter similar to that of ZrPO4Cldmso, while the c
parameter is the double of the interlayer distance. The
interlayer distance of this derivative, 14.9 Å, is now changed
according to the increased dimensions of the anionic ligands
bonded to zirconium.
ZrPO4C6H5COO(dmso) f ZrPO4C6H5COO +
gaseous products f 1/2ZrO2 + 1/2ZrP2O7 +
gaseous products
Different from alkoxide derivatives, carboxylate deriva-
tives are stable in air at room temperature, very probably
because of the low basic strength of carboxylate groups.
Thermal Behavior. Figure 9 shows the TG curve for I.
Weight loss is composed of two well-defined steps. The first
step occurs between 200 and 250 °C, temperature at which
the sample reaches a constant weight. This first step
The calculated weight loss is 49.58%, in good agreement
with that found experimentally (47.50%).
FT-IR Study. FT-IR analysis confirms composition data.
Figure 11a,b shows IR spectra of I and II, respectively. The
spectrum of the parent compound is also reported for
comparison. Spectra of parent compound and I show the
372 Inorganic Chemistry, Vol. 43, No. 1, 2004

Anionic Ligand Exchange on ZrPO4Cl(dmso)
Figure 12. Hypothetical change in the benzoate-metal atom bonding
before and after dmso loss, at 220 °C, for the benzoate derivative of λ-ZrP.
Figure 10. XRD patterns of the benzoate derivative of λ-ZrP before (a)
and after heating at 220 °C for 2 h (b).
Figure 13. XRD patterns of phenylacetate (a) and 2-nitrobenzoate (b)
derivatives of λ-ZrP.
The low-frequency regions of IR spectra of benzoate
derivatives are dominated by phosphate vibration bands,
while the sharp bands around 700 cm-1 may be assigned to
aromatic C-H out-of-plane bending vibrations.
Figure 11. FT-IR spectra of the benzoate derivative of λ-ZrP before (a)
and after heating at 200 °C for 2 h (b). The spectrum of ZrPO4Cl(dmso) is
also reported for comparison (c).
typical bands around 3000 cm-1, ascribed to C-H stretching
vibration of dmso. These bands are absent in II, confirming
the loss of dmso.
(b) Other Carboxylate Derivatives. On the basis of
benzoate exchange, two other carboxylate groups were
successfully exchanged of λ-ZrP, namely 2-nitrobenzoate and
phenylacetate groups, giving rise to the following deriva-
tives: ZrPO4[C6H4(NO2)COO(dmso)]0.7[OH H2O]0.3 and
ZrPO4[C6H5CH2COO(dmso)]0.8[OH H2O]0.2. In both deriva-
tives a small amount of hydrolysis, that is the exchange of
chlorine atoms and dmso groups by hydroxyl and water,
respectively, was found by chemical analysis. However, XRD
patterns of these two derivatives clearly show the presence
of only one phase (Figure 13). Very likely, these hydrolyzed
groups are desordered in the structure and/or they form a
small amount of amorphous phase not detected by XRD
analysis.
The amount of hydrolysis is higher for nitrobenzoate
derivative, probably due to the lateral steric hindrance of
nitrobenzoate groups that prevents a full exchange. The
interlayer distance of this derivative was 14.8 Å. As expected,
this value is close to that of the benzoate derivative, because
the nitro group, in the ortho position, does not evidently
contribute to the steric hindrance along the c axis. On the
contrary, the interlayer distance of phenylacetate derivative
is higher, 16.4 Å, due to the increased dimensions of this
group along the c axis.
The sharp band at 1657 cm-1 in I is due to CdO stretching
vibration of carboxylate group. This band is shifted at lower
frequency in II (1488 cm-1). In this sample, a further band
is present, at 1454 cm-1. These data might be interpreted on
the basis of the changes in the coordination of carboxylate
groups by metal atoms, due to thermal loss of dmso. Before
dmso loss, zirconium atoms are trans coordinated by dmso
and benzoate groups, these latter acting as monodentate (η1)
ligands, as shown in the model of Figure 8. The presence of
a sharp band at 1334 cm-1, which is probably due to the
C-OZr stretching vibration, may support this model. After
the loss of dmso, zirconium atoms remain unsaturated, and
there is sufficient room to coordinate benzoate groups as
bidentate (η2) ligands, as schematically shown in Figure 12.
This bonding condition implies that the two carboxylate C-O
bonds are almost equivalent, with a bond order less than two.
Therefore, the two bands at 1488 and 1454 cm-1 may be
ascribed to antisymmetric and symmetric stretching vibra-
tions, respectively, of bidentate carboxylate groups.11 This
change in coordination of carboxylate groups, from η1 to
η2, tends to saturate zirconium coordination sphere and may
justify the stability of II. However, in the absence of accurate
structural data, we cannot exclude any other hypothesis.
Thermal behaviors of these two derivatives are close to
that already described for the benzoate derivative: dmso is
lost in a well-defined step, in the 200-250 °C temperature
range, with the formation of a stable compound. FT-IR
(11) Nakamoto, K. Infrared spectra of inorganic and coordination
compounds; John Wiley & Sons: New York, 1963.
Inorganic Chemistry, Vol. 43, No. 1, 2004 373

Vivani et al.
spectra, before and after dmso loss, show similar features
that can be analogously discussed.
derivatives can be also formed using different anionic
ligands. This reactivity can be useful for the preparation of
solids containing in the interlayer region a vast variety of
functionalized organic groups.
Conclusion
This work shows that alkoxide and carboxylate groups can
be successfully introduced in λ-ZrP by topotactic ligand
exchange, with the formation of two distinct classes of
organic derivatives. It is likely that other classes of organic
Acknowledgment. This work was supported by MIUR,
Project No. 2002038793_001.
IC034695R
374 Inorganic Chemistry, Vol. 43, No. 1, 2004