Intercalation of cyclic ketones into vanadyl phosphate

Article abstract of DOI:10.1016/j.jssc.2004.11.008

Intercalation compounds of vanadyl phosphate with cyclic ketones (cyclopentanone, cyclohexanone, 4-methylcyclohexanone, and 1,4-cyclohexanedione) were prepared from corresponding propanol or ethanol intercalates by a molecular exchange. The intercalates prepared were characterized using powder X-ray diffraction and thermogravimetric analysis. The intercalates are stable in dry environment and decompose slowly in humid air. Infrared and Raman spectra indicate that carbonyl oxygens of the guest molecules are coordinated to the vanadium atoms of the host layers. The local structure and interactions in the cyclopentanone intercalate have been suggested on the basis of quantum chemical calculations.

Full text of DOI:10.1016/j.jssc.2004.11.008

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Journal of Solid State Chemistry 178 (2005) 314–320
www.elsevier.com/locate/jssc
Intercalation of cyclic ketones into vanadyl phosphate
Ã
a
Vıtezslav Zimaa, , Klara Melanovaa, LudvıkBenes , Miroslava Trchovab, Jirı Dybalb
aJoint Laboratory of Solid State Chemistry, Institute of Macromolecular Chemistry of Academy of Sciences, University of Pardubice,
´
Studentska 84, CZ-532-10 Pardubice, Czech Republic
b
´
Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic
Received 24 September 2004; received in revised form 5 November 2004; accepted 11 November 2004
Abstract
Intercalation compounds of vanadyl phosphate with cyclic ketones (cyclopentanone, cyclohexanone, 4-methylcyclohexanone, and
1,4-cyclohexanedione) were prepared from corresponding propanol or ethanol intercalates by a molecular exchange. The
intercalates prepared were characterized using powder X-ray diffraction and thermogravimetric analysis. The intercalates are stable
in dry environment and decompose slowly in humid air. Infrared and Raman spectra indicate that carbonyl oxygens of the guest
molecules are coordinated to the vanadium atoms of the host layers. The local structure and interactions in the cyclopentanone
intercalate have been suggested on the basis of quantum chemical calculations.
r 2004 Elsevier Inc. All rights reserved.
Keywords: Intercalation; Vanadyl phosphate; Powder X-ray diffraction; Vibrational spectroscopy; Ab initio calculation
1. Introduction
decomposes at about 160 1C [19]). It indicates that the
host–guest interaction is very strong. Some of these
intercalates are well crystalline solids and their diffrac-
tograms show, besides a series of sharp (00l) reflections,
a number of (hkl) diffraction lines giving evidence of a
regular structure.
The present paper reports the results of the intercala-
tion of cyclopentanone, cyclohexanone, 4-methylcyclo-
hexanone, and 1,4-cyclohexanedione into vanadyl
phosphate.
Vanadyl phosphate dihydrate VOPO4 ꢀ 2H2O and
other isostructural layered compounds are able to
accommodate some types of organic molecules in the
interlayer space [1]. Aliphatic alcohols and diols [2–4],
amines [5], carboxylic acids [6], carboxamides [7],
aliphatic nitriles [8] belong to the compounds, which
can be intercalated in such a way. Great attention was
devoted to the intercalation of heterocyclic N- and S-
donors [9–13]. Recently, intercalation of ketones [14,15],
aldehydes [16], poly(ethylene glycol)s [17,18], hetero-
cycles with O-donor [18–20], and g-butyrolactone [21]
into vanadyl phosphate has been described. These guests
are anchored to the host layers by donor–acceptor
bonds of their carbonyl or etheric oxygen to the
vanadium atoms. These intercalates, except aliphatic
aldehyde intercalates, are generally very stable in air and
the guest molecules are released at relatively high
temperatures (for example tetrahydrofuran intercalate
2. Experimental
The propanol or ethanol intercalates were prepared
by suspending microcrystalline VOPO4 ꢀ 2H2O in dry
propanol or ethanol and subsequent short exposure to a
microwave field. The intercalation compounds were
obtained by displacing propanol or ethanol in VOPO4 ꢀ
2ROH with the corresponding guest. The cyclopenta-
none intercalate was prepared by stirring the propanol
intercalate (0.5 g) with cyclopentanone (20 mL) at
room temperature overnight. The cyclohexanone and
Ã
Corresponding author. Fax: +420 46 603 6151.
E-mail address: vitezslav.zima@upce.cz (V. Zima).
0022-4596/$ - see front matter r 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2004.11.008

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315
4-methylcyclohexanone intercalates were prepared by
stirring the ethanol intercalate (0.5 g) with 20 mL of the
guest at room temperature overnight. The intercalates
prepared were filtered off, washed with diisopropylether,
and dried in vacuo. The 1,4-cyclohexanedione inter-
calate was prepared by refluxing the ethanol intercalate
in an acetonitrile solution of the guest for 15 min. The
intercalate was filtered off, washed with acetonitrile and
dried in nitrogen.
Powder data were obtained with a D8-Advance
diffractometer (Bruker AXE, Germany) using CuKa
radiation with secondary graphite monochromator.
Diffraction angles were measured from 51 to 371 (2y).
The samples were covered with protection foil during
the measurement.
vanadyl phosphate layers were performed at a semi-
empirical level using the PM5 and AM1 methods.
3. Results and discussions
None of the cyclic ketones used can be intercalated
directly in anhydrous vanadyl phosphate or VO-
PO4 ꢀ 2H2O. All the intercalates can be prepared by
replacing either propanol or ethanol in the correspond-
ing VOPO4 intercalate with the desired guest. The
intercalates prepared were yellow crystalline solids, only
the 4-methylcyclohexanone intercalate was greenish-
yellow. This indicates that only a small part (less than
1 at % as follow from the vis spectra) of vanadium (V)
was reduced during the intercalation of 4-methylcyclo-
hexanone probably due to impurities present in the
guest. The composition of the intercalates was deter-
mined by thermogravimetric analysis. During heating,
the guest molecules are released in two steps. The
product of the thermal decomposition is anhydrous
vanadyl phosphate. Total weight losses correspond to
the stoichiometric ratio x given in Table 1 together with
the results of elemental analysis. The cyclopentanone,
cyclohexanone, and 4-methylcyclohexanone intercalates
contain one molecule of the guest per formula unit, the
cyclohexanedione intercalate contains half of the guest
molecule per formula unit.
TG analyses were performed using a Netzsch STA
449C. The measurements were carried out in air between
30 and 700 1C at a heating rate of 5 1C minꢁ1
Infrared measurements in the range from 400 to
.
4000 cmꢁ1 were made with a fully computerized Bruker
IFS 55 EQUINOX FTIR Spectrometer with
a
DLATGS detector (256 scans per spectrum at 4 cmꢁ1
resolution). Measurements of the intercalates were
performed ex situ by an ATR technique using a Golden
GateTM Heated Diamond ATR Top-Plate (Specac Ltd.)
at ambient temperature. The spectrum of the corre-
sponding liquid cyclopentanone was measured by an
ATR technique on a ZnSe crystal. The spectra were
corrected for the content of H2O and CO2 in the optical
path.
The diffractograms (see Fig. 1) of the intercalates
show a series of sharp (00l) reflections. Only weak(200)
and/or (201) and (110) reflections can be seen in the
diffractograms of the cyclopentanone, 4-methylcyclo-
hexanone, and 1,4-cyclohexanedione intercalates. The
absence of (hkl) lines in the intercalates is a character-
istic of a turbostratic structure where the original
tetragonal layers of the host are retained but mutually
shifted in the directions of the x and/or y axes. The
diffractogram of the cyclohexanone intercalate contain a
number of the (hkl) diffraction lines (see Fig. 1b) giving
evidence of a regular structure. These lines can be
indexed using the c parameter as a double of the basal
spacing. This is most likely caused by a mutual shift of
the host layers by a/2. The lattice parameters of all the
intercalates prepared are given in Table 1.
FT Raman spectra were collected using a Bruker IFS
55 EQUINOX FTIR Spectrometer equipped with an
FT Raman module FRA 106/S with a diode-pumped,
temperature-stabilized Nd YAG laser, and InGaAs
detector (128 interferograms were co-added per spec-
trum in the range from 4000 to (ꢁ1000) cmꢁ1 at 4 cmꢁ1
resolution).
Quantum chemical calculations were carried out at
the ab initio and semiempirical levels of the theory
employing Gaussian 98 [22] and MOPAC 2002 [23]
program packages, respectively. Local interactions and
structures in the intercalates of vanadyl phosphate with
cyclopentanone were studied at a DFT level using a
functional B3LYP with a basis set 6-31G(d). Geome-
trical optimizations of larger structures including two
Table 1
Tetragonal lattice parameters and the guest content x in the intercalates prepared
Guest
x
a (A)
c (A)
C%
H%
Found
Calculated
Found
Calculated
Cyclopentanone
Cyclohexanone
1.05
0.93
1.00
0.55
6.221(2)
6.212(1)
6.234(3)
6.218
13.53(2)
27.258(7)
14.71(1)
9.24(1)
24.50
27.15
30.10
16.61
24.21
27.50
30.45
16.53
4.30
4.45
5.22
1.90
4.06
4.62
5.11
1.85
4-Methylcyclohexanone
1,4-Cyclohexanedione

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Fig. 2. Changes of the diffractograms of the cyclopentanone
intercalate exposed to air (43% RH).
Fig. 1. The diffractograms of vanadyl phosphate intercalated with
cyclopentanone (a), cyclohexanone (b), 4-methylcyclohexanone (c),
and cyclohexanedione (d).
The intercalates are not stable in air (at relative
humidity (RH) higher than 40%). The guest molecules
are gradually replaced by water molecules. At 30% RH,
the intercalates are stable for several hours. The
cyclohexanedione intercalate is the most stable one,
the 4-methylcyclohexanone intercalate is the least stable
one. The stability of the cyclopentanone intercalate was
studied in detail. It is stable for several days at 33% RH
and lower. The diffractograms measured during its
hydration at 43% RH are given in Fig. 2. The (001) and
(002) reflections of a new phase with basal spacing of
11.9 A (marked II) appear very quickly together with a
small amount of vanadyl phosphate dihydrate. Dihy-
drate become the prevailing phase after 600 min.
For the infrared measurements, the sample of vanadyl
phosphate intercalated with cyclopentanone was placed
in a purged sample compartment of the spectrometer
(5% RH) for 5 min and for 22 h without removing the
sample from the crystal between the subsequent spectral
measurements. Another sample was exposed to ambient
conditions (60% RH) for 22 h and for 4 and 11 days.
Such conditions allow a progressive replacement of the
cyclopentanone molecules in the vanadyl phosphate
intercalate with atmospheric water. The infrared spectra
of the intercalate in various stages of the deintercalation
Fig. 3. FTIR spectra of vanadyl phosphate dihydrate, of pure
cyclopentanone and of vanadyl phosphate intercalated with cyclopen-
tanone after 5 min and 22 h in the purged spectrometer (5% RH), and
after 22 h, 4 and 11 days at ambient conditions (60% RH) in the region
from 2000 to 700 cmꢁ1
.
process at ambient conditions were compared with the
spectrum of vanadyl phosphate dihydrate and with the
spectrum of pure cyclopentanone as seen in Fig. 3 (for
the region from 2000 to 700 cmꢁ1) and in Fig. 4 (for the
region from 4000 to 2500 cmꢁ1).
The Raman spectra of vanadyl phosphate dihydrate,
vanadyl phosphate intercalated with cyclopentanone

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phosphate intercalated with cyclopentanone. The sharp
band at 995 cmꢁ1 in the spectrum of vanadyl phosphate
dihydrate came from a vanadyl V ¼ O stretching
vibration. The vanadyl stretching band appears to be
especially sensitive to the atoms coordinated to vana-
dium within an octahedral arrangement in the host
lattice structure. During the intercalation of water
molecules into VOPO4, its position at 1035 cmꢁ1 in the
anhydrous form changes to 995 cmꢁ1 typical for mono-
and dihydrate [24]. This indicates a coordination of the
oxygen atom of the water molecules to vanadium. In the
Raman spectrum of the intercalate with cyclopentanone
the band observed at 998 cmꢁ1 corresponds most
probably to the coordination of the oxygen atom of
cyclopentanone to vanadium and the band observed at
1036 cmꢁ1 to the anhydrous form of the host com-
pound. With the help of the Raman spectrum, we can
assign the band with the maximum at 942 cmꢁ1 in the
infrared spectrum (see Fig. 3) of vanadyl phosphate
dihydrate to the symmetric n(PO4) stretching vibration
which is infrared active due to the distortion of the
phosphate tetrahedron in the intercalate. The shoulder
at 1015 cmꢁ1 in the infrared spectrum is most probably
the V ¼ O stretching band of the vanadyl group. The
band at 1142 cmꢁ1 in the infrared spectrum of the host is
the asymmetric n(PO4) stretching vibration of phosphate
tetrahedron. In agreement with the authors [25] the
sharp bands near 3600 and 1620 cmꢁ1 in the spectrum of
VOPO4 ꢀ 2H2O are due to strongly bonded water
molecules within the crystalline lattice associated with
the water molecule bound to vanadium. The additional
water molecules, which are bonded to the host layers by
H-bonds, are indicated by a broadband near 3300 and
1620 cmꢁ1 in the spectrum of the dihydrate. In the
bending vibration at 1620 cmꢁ1, sharp and broadbands
are superimposed. The positions of the main spectral
bands of the host structure only slightly differ from
those of anhydrous vanadyl phosphate or its hydrated
form [24]. It confirms that the structure of the original
VOPO4 layers remains unchanged after the intercalation
reaction.
Fig. 4. FTIR spectra of vanadyl phosphate dihydrate, of pure
cyclopentanone and of vanadyl phosphate intercalated with cyclopen-
tanone after 5 min and 22 h in the purged spectrometer (5% RH), and
after 22 h, 4 and 11 days at ambient conditions (60% RH) in the region
from 4000 to 2500 cmꢁ1
.
Fig. 5. Raman spectra of vanadyl phosphate dihydrate, of vanadyl
phosphate intercalated with cyclopentanone and of pure cyclopenta-
none.
and pure cyclopentanone in the region from 2000 to
700 cmꢁ1 are shown in Fig. 5. Unfortunately, it was not
possible to measure the kinetics of the replacement of
cyclopentanone by Raman spectroscopy, because a
partial escape of the cyclopentanone molecules due to
the laser beam occurs during the measurements. Besides,
the Raman spectrum is influenced by a thermal emission
of the sample, which is due to the excitation in the NIR
range (1064 nm).
The bands of vibrations of the PO4 tetrahedron, of the
vanadyl group V ¼ O, and the P–O–V group can be
identified in all spectra. The intense band at 945 cmꢁ1 in
the Raman spectrum of vanadyl phosphate dihydrate
(see Fig. 5) corresponds to the symmetric n(PO4)
stretching vibration of the phosphate tetrahedron in
(VOPO4)N. This band is shifted to 940 cmꢁ1 in vanadyl
Some of the bands observed in the spectrum of pure
cyclopentanone are shifted in the spectrum of the
intercalate (see Figs. 3 and 4). Especially, the band of
the carbonyl stretching vibration observed at about
1739 cmꢁ1 is shifted to 1714 cmꢁ1 in the spectrum of the
intercalate. The bands of the C–H stretching vibrations
observed at 2965 and 2884 cmꢁ1 are shifted to 2962 and
2876 cmꢁ1, the bands of the C–H deformation vibra-
tions observed at 1407 and 1150 cmꢁ1 are shifted to 1397
and 1166 cmꢁ1 in the spectrum of the intercalate. Similar
shifts of position of the C ¼ O stretching vibration in
infrared spectra were observed in the intercalates of
vanadyl phosphate with other guests. Positions of this
band for individual intercalates together with those of
pure cyclic ketones are given in Table 2. On the basis of

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Table 2
Wavenumbers of the n(C ¼ O) vibration in the IR spectra of the pure
cyclic ketones and their intercalates
Guest
n(C ¼ O) (cmꢁ1
)
Pure guest
Intercalate
Cyclopentanone
Cyclohexanone
1739
1713
1716
1705
1714
1678
1676
1681
4-Methylcyclohexanone
1,4-Cyclohexanedione
the vibrational spectra, we suppose that the molecules of
cyclic ketones are coordinated to the vanadium atoms of
the host by their carbonyl oxygen atoms.
In the spectrum measured 5 min after taking out the
sample from the ampoule and putting it in the purged
sample compartment of the spectrometer (ꢁ51% RH) we
observe some sharp maximum at 3625 cm , a broad-
band at 3350 cmꢁ1 and a band at 1629 cmꢁ1. These
bands correspond to unbound water adsorbed on the
surface during manipulation of the sample after its
removal from the ampoule. These bands are more
pronounced in the spectrum of the sample measured at
ambient conditions (60% RH) after 22 h. The intensity
of the bands of cyclopentanone is reduced during the
exposition to ambient conditions for 4 and 8 days. At
the same time, the sharp maximum at 3625 cmꢁ1 shifts
to 3579 cmꢁ1 and the band observed at 1629 cmꢁ1 shifts
to 1616 cmꢁ1. These new positions correspond to the
spectrum of vanadyl phosphate dihydrate. The new
maximum observed at 1080 cmꢁ1 in the spectrum of the
intercalate after 4 and 8 days corresponds most
probably to the asymmetric n(PO4) stretching vibration
of the phosphate tetrahedron.
The character of the bonding between the guest
molecules and the host layers in the cyclopentanone
intercalate was investigated by the methods of quantum
mechanical calculations and modeling. Fig. 6 shows a
DFT optimized structure of the molecular segment
representing local interactions of vanadyl phosphate
with cyclopentanone, using a B3LYP functional and 6-
31G(d) basis set. In order to keep the overall planar
structure of the segment during full geometry optimiza-
tions and to make the electronic structure in the segment
close to the conditions appearing in the intercalates, an
oxygen atom was inserted between two neighboring PO4
groups and terminal oxygen atoms were substituted by
OH groups [21]. The total charge of the model
compound was set to +3. It was found that all geometry
optimizations with various starting orientations of
cyclopentanone with respect to the vanadyl group lead
to the structure displayed in Fig. 6 which indicates
formation of the C ¼ O-V bond in the intercalates.
The simulations of larger local intercalate structures
including two VOPO4 layers were performed using
Fig. 6. Optimized B3LYP/6-31G (d) structure of the molecular
segment modeling the vanadyl phosphate–cyclopentanone interaction
with indicated bond lengths (in A); the values in parentheses show the
C ¼ O and C–C bond lengths in free cyclopentanone.
semiempirical PM5 and AM1 quantum-chemical meth-
ods. Adequacy of the semiempirical methods for the
vanadyl phosphate intercalates was illustrated in pre-
vious studies of the intercalates in which the results of
the modeling were in a very good agreement with
experimental data obtained by X-ray, IR and Raman
spectroscopy [21,26,27]. The model structure shown in
Fig. 6 was also reoptimized with the PM5 and AM1
methods and only slight changes of parameters were
found in comparison with the DFT method. The
optimized geometries of the molecular segment repre-
senting two layers of VOPO4 and five molecules of
cyclopentanone intercalated between the two layers are
shown in Fig. 7. Terminal oxygen atoms were sub-
stituted by OH groups and the total charge of the model
compounds was set to -2. The coordinations of
cyclopentanone molecules to the vanadium atoms in
adjacent guest interlayer spaces were simulated by
coordinations with 2-propanone molecules not shown
in Fig. 7. The initial values of the bond lengths and
angles for the VOPO4 layers were taken from the
previous study of the vanadyl phosphate intercalates
with diethyl ether [27], the initial basal spacing was set to
the above given value of the lattice parameter c ¼
(
13:53 A determined by the X-ray diffraction and the
structure and bonding of cyclopentanone were taken
from the results of DFT calculations shown in Fig. 6.
All the variables defining the positions of the atoms both
in the host and guest layers were fully optimized with the
exception of the constraints exposed by the symmetry

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319
Fig. 7. Side views of the PM5 optimized geometry of the molecular segment modeling the arrangement of the cyclopentanone molecules between the
VOPO4 layers.
Fig. 8. Proposed arrangement of the guest molecules in the interlayer space of the cyclohexanone (a), 4-methylcyclohexanone (b), and 1,4-
cyclohexanedione intercalates.
conditions defining polyhedra in the VOPO4 layers and
relative orientations of the guest molecules in the
interlayer with respect to the VOPO4 layer. The basal
spacings calculated with the PM5 and AM1 methods are
13.28 and 13.21 A, respectively, which is in a good
agreement with the experimental value of 13.53 A. The
mutual positions of the successive tetragonal layers
exhibit a shift characterized by a vector with calculated
components of 0.02 and 2.44 A obtained with the PM5
method and 0.08 and 2.35 A with the AM1 method. This
result complies with the absence of the (hkl) lines in the
X-ray diffractograms of the intercalates, which is
characteristic of a turbostratic structure.
Analogously to the arrangement of cyclopentanone,
also arrangements of other cyclic ketones in the
interlayer space of the host layers can be deduced.
Taking into account the interlayer distance and assum-
ing that the distance between the ketonic oxygen and the
vanadium atom is the same as in the cyclopentanone
intercalate, we proposed the structure of other inter-
calates as depicted in Fig. 8. For the cyclohexanone
intercalate a slight interdigitation of the guest rings in
the interlayer space can be presumed. This interdigita-
tion is more pronounced in the case of the 4-
methylcyclohexanone intercalate. For 1,4-cyclohexane-
dione the determined interlayer distance allows only a
monomolecular arrangement of the host molecules,
which due to the presence of two ketonic oxygens in
the guest molecule, form pillars between the host layers.
Similarly as aliphatic ketones studied previously
[14,15], the cyclic ketones studied are anchored to
vanadium with their carbonyl oxygen. In contrast to
the acetone and methylethylketone intercalates, no
formation of an enol form was observed.
Acknowledgments
The help of the Ministry of Education, Youth and
Sports of the Czech Republic (MSM 253100001 and

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320
MSMT 113-2000-01) and the Academy of Sciences of
the Czech Republic (KSK4050111 and AVOZ4050913)
is appreciated.
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Mater. 11 (1999) 2173.
[18] K. Goubitz, P. Capkova, K. Melanova, W. Molleman,
H. Schenk, Acta Crystallogr. B 57 (2001) 178.
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