Gas-phase on-line production of vanadium oxytrihalides, VOX3 and their identification by infrared spectroscopy

Article abstract of DOI:10.1016/S1386-1425(00)00305-X

A new route has been devised, leading to the production of VOX₃ molecules where X = F, Br and I by an on-line process using vanadium oxytrichloride, VOCl₃ as a starting compound passed over the following heated salts NaF, KBr and KI at 375, 700 and 550 °C, respectively. The products have been characterized by the IR spectra of their vapors. The low resolution gas phase on-line Fourier transform infrared spectra reported for the first time show strong bands with PQR type structure, centered at 1058, 1035, 1030 and 1025 cm^-1 assigned to the ν₁(a₁), the O = V stretching fundamental mode of VOF₃, VOCl₃, VOBr₃ and VOI₃, respectively.

Full text of DOI:10.1016/S1386-1425(00)00305-X

Spectrochimica Acta Part A 56 (2000) 2693–2698
www.elsevier.nl/locate/saa
The gas-phase on-line production of vanadium oxytrihalides,
VOX3 and their identification by infrared spectroscopy
Mohammed D. Zidan, Abdul W. Allaf *
Department of Chemistry, Atomic Energy Commission of Syria, P.O. Box 6091, Damascus, Syria
Received 28 January 2000; received in revised form 9 May 2000; accepted 9 May 2000
Abstract
A new route has been devised, leading to the production of VOX3 molecules where XꢀF, Br and I by an on-line
process using vanadium oxytrichloride, VOCl3 as a starting compound passed over the following heated salts NaF,
KBr and KI at 375, 700 and 550°C, respectively. The products have been characterized by the IR spectra of their
vapors. The low resolution gas phase on-line Fourier transform infrared spectra reported for the first time show
strong bands with PQR type structure, centered at 1058, 1035, 1030 and 1025 cm−1 assigned to the w1(a1), the OꢀV
stretching fundamental mode of VOF3, VOCl3, VOBr3 and VOI3, respectively. © 2000 Elsevier Science B.V. All rights
reserved.
Keywords: Gas-phase; Infrared spectra; On-line Production; Vanadium oxytrihalides
1. Introduction
and VOX2 have been reported by Greenwood and
Earnshaw [1].
The oxohalides of vanadium compounds are
generally prepared from the oxides but are not
particularly well known. They are limited almost
entirely to the oxidation states of +4 and +5. The
oxidation state +5, such as VOX3 and VO2X
where X is a halogen, is relatively stable. The +4
oxidation state vanadium oxohalides compounds
such as VOX2 are notably hydroscopic and hy-
drolyze vigorously to the hydrous pentoxide. The
chemical and physical properties of VOX3, VO2X
The vanadium oxytrihalides, VOX3 are expected
to have C3w symmetry by comparison with the
phosphoryl halides, POX3 [2]. Therefore, there
must be six fundamentals modes, all infrared and
Raman active. Three of these are totally symmetric
vibrations, of species a1, and three are doubly
degenerate vibrations of species e. In the infrared
spectrum, the former show up as parallel type
bands and the latter as perpendicular bands.
Selig and Claassen recorded the infrared spec-
trum of VOF3 vapour and interpreted the molecule
in terms of C3w symmetry and all six fundamentals
were observed [3]. The infrared spectra of the
liquid and the gaseous Raman spectra of VOCl3
have been reported by Miller and Ozin [4,5].
* Corresponding author. Tel.: +963-11-6111926; fax: +
963-11-6112289.
E-mail address: atomic@net.sy (A.W. Allaf).
1386-1425/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S1386-1425(00)00305-X

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The infrared spectrum of liquid VOBr3 has been
recorded from 75 to 3000 cm−1 [6].
The products from these reactions were passed
directly into an IR cell (15 cm path length) fitted
with two KBr windows. A similar experimental
set-up was used in the previous work [2]. The
distance between the heated furnace and the IR cell
was about 3 cm. The cell was pumped out via a
liquid nitrogen trap with a rotary pump (RV8,
Edwards) displacing 8.5 m3 h−1. The IR spectra
were recorded on a JASCO 300E FTIR spectrom-
eter at a resolution of 2 cm−1. Regarding the VOI3,
the experiment was performed at 1 cm−1 in order
to resolve its OꢀV stretching band.
The gas phase on-line production of the
analogous species, POX3 where XꢀF, Cl, Br and I
and their identification by infrared spectroscopy
have been reported [2]. Continuing our previous
observations and the recent work regarding the
antimony oxide trihalides, SbOX3 [7], this paper
investigates the on-line production of vanadium
oxytrihalides, VOX3 where XꢀF, Br and I and their
gas phase IR spectra, which have not been reported
previously, using VOCl3 as a starting material
passed over heated NaF, KBr and KI for VOF3,
VOBr3 and VOI3 production, respectively. It
should be mentioned that no previous experimental
and spectroscopic data for VOI3 are available and
the reported results can be considered as the first
attempt to investigate such a molecule.
3. Results and discussion
Fig. 1 shows the infrared spectra of VOCl3 (top)
and POCl3 (bottom). The top spectrum is the result
of heating the VOCl3 only with heating tape to
2. Experimental
The first step was to optimize the production
conditions of vanadium oxytrichloride, VOCl3, in
order to carry on observing the VOF3, VOBr3 and
VOI3 infrared spectra by on-line process using
VOCl3 as starting material. VOCl3 (Fluka, 99.9%)
was first degassed in the vacuum line using liquid
nitrogen. The on-line process involved heating the
VOCl3 with heating tape to about 40°C to obtain
enough vapor pressure and the vapor was passed
via a vacuum line into an IR cell fitted with two
KBr windows. The remaining conditions were fast
flow, 2 cm−1 resolution and under 0.5 torr pres-
sure. The yellow color of VOCl3 material was seen
in the IR cell.
The synthesis routes for VOF3, VOBr3 and VOI3
can be written as follows:
375°C
VOCl3(g)+3NaF(s) “ 3NaCl(g)+VOF3(g)
700°C
VOCl3(g)+3KBr(s) “ 3KCl(g)+VOBr3(g)
550°C
VOCl3(g)+3KI(s) “ 3KCl(g)+VOI3(g)
The salts containing halogens used in these
experiments were obtained from Aldrich with a
purity of 99.9%. The final reaction colors from the
above three syntheses were yellow, deep red and
pink, respectively.
Fig. 1. The gas phase infrared spectra of VOCl3 (top) and
POCl3 (bottom) in the range (400–1500) cm−1
.

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2695
cm−1 is assigned to the w4(e), mode of VOCl3. The
last band centered at 408 cm−1 is assigned to the
w2(a1), the VCl3 umbrella mode of VOCl3. These
results are identical to those observed by gas phase
Raman spectroscopy at 1035, 504 and 408 cm−1
,
respectively [5]. The bottom spectrum is presented
here for comparison only. An identical type of
structure was observed for the OꢀP stretching mode
of POCl3 [2] w1(a1). The band is centered at 1312.9
cm−1 where the second band at 590 cm−1 is
assigned to the w4(e), fundamental of POCl3.
Fig. 2 shows three new spectra A, C and D
(400–1200 cm−1) where spectrum B is the precur-
sor (VOCl3). Spectrum A is the result of passing
VOCl3 gas over heated NaF at 375°C. The three
characteristic bands of VOF3 were observed within
the spectrometer range used at 1058, 806 and 722
cm−1. This spectrum fits very well with that ex-
pected. The two bands centered at 1058 and 722
cm−1 each have the sharp Q branch characteristic
of parallel bands. Similarly, the band at 806 cm−1
can clearly be assigned as a perpendicular, or
species (e), band because it does not have a strong
Q branch. Therefore, the first band at 1058 cm−1
can be assigned to w1(a1), the OꢀV stretching mode
of VOF3.
This result is consistent with expectations and the
band is shifted to higher frequency when fluorine
replaces the chlorine in VOCl3 to form VOF3 which
is similar to the POX3 study [2]. The second band
at 806 cm−1 is assigned to the w4(e), the VꢁF
stretching mode of VOF3. The third band at 722
cm−1 is assigned to the w2(a1), the VF3 umbrella
mode of VOF3 and this band has a PQR-type
structure as expected. The last band shown in the
spectrum at 673 cm−1 is assigned as a combination
band 2w6(e)+w3(a1) of VOF3. Our infrared spec-
trum results for VOF3 are in excellent agreement
with the previous gas phase infrared results [3] after
VOF3 was prepared by the method of Trevorrow
using V2O5/HF [8]. Their observed frequencies were
at 1057.8, 806 and 721.5 cm−1, respectively [3].
Note that the observed frequencies are identical to
those observed before using two different methods
of preparation.
Fig. 2. Full gas phase infrared spectra of VOX3 where XꢀF,
Cl, Br and I in the range (400–1200) cm−1
.
about 40°C to obtain enough vapor pressure. Three
strong bands were observed in the spectrometer
range (400–4000 cm−1) at 1035, 505 and 408
cm−1. The first band centered at 1035 cm−1, is
assigned to the w1(a1), the OꢀV stretching mode of
VOCl3 and shows typical PQR-type structure and
with a strong Q-head. The second band at 505
Having confirmed the existence of VOF3 by the
new route, the next step was to generate and

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M.D. Zidan, A.W. Allaf / Spectrochimica Acta Part A 56 (2000) 2693–2698
observe the infrared spectrum of VOBr3. Spec-
trum C in Fig. 2 is the result of passing VOCl3 gas
over heated KBr at 700°C. Two new bands were
observed within the spectrometer range used at
1030, and 400 cm−1. The first band at 1030 cm−1
is assigned to w1(a1), the OꢀV stretching mode of
VOBr3. This result is consistent with expectation
and the band is shifted to lower frequency when
the bromine replaces the chlorine in VOCl3 to
form VOBr3. Once again, the band shows typical
PQR-type structure with a strong Q-head. The
second band at 400 cm−1 is assigned to the w4(e)
mode of VOBr3. The third band in the spectrum is
due to the precursor, VOCl3. Miller and Baer
have recorded the infrared spectrum of liquid
VOBr3 [6]. Therefore, the obtained gas phase IR
results for VOBr3 can be compared with the in-
frared spectrum of liquid VOBr3 after the follow-
ing synthesis:
The PR profile can be seen in spectrum D (Fig. 2),
the Q-head was not observed and a high resolu-
tion spectrum would reveal the structure of the
band. It seems to be that in some stages of the
reaction VOCl2I or VOClI2 may be formed before
VOI3 formation and this could explain the other
bands shown in spectrum D. Therefore, it can be
said that the other peaks shown in the VOI3
spectrum are due to the impurities, which were
500°C
V2O5+2H2 “ V2O3+2H2O
V2O3+3Br2+C20“0°C2VOBr3+CO
The OꢀV stretching mode of VOBr3, which was
generated by our on-line method in comparison
with those of liquid production is shifted 5 cm−1
.
This may be due to the fact that the two spectra
were generated from different phases.
The final step is shown in Fig. 2 (spectrum D)
which is the result of passing VOCl3 gas over
heated KI at 550°C. The gas phase infrared spec-
trum of VOI3 is recorded here for the first time
and no other spectroscopic data are available.
Because there are no previous experimental spec-
troscopic data for VOI3, the assignment of the
new spectrum can be analyzed considering the
previous analogous molecules. It should be men-
tioned here that the production of pure VOI3 is
also difficult due to easy sublimation of iodine at
the high temperature of heated KI. Nevertheless,
the most characteristic band of VOI3 is observed.
This band is positioned to the right side of the
VOCl3 band and centered at 1025 cm−1 and
assigned to the w1(a1), the OꢀV stretching mode of
VOI3. The observed band has a PR-type structure
and this experiment has been performed under 1
cm−1 as the lowest available resolution in our
spectrometer in order to resolve this structure.
Fig. 3. The w1(a1), the OꢀV stretching mode of VOX3 where
XꢀF, Cl, Br and I in the range (900–1200) cm−1
.

M.D. Zidan, A.W. Allaf / Spectrochimica Acta Part A 56 (2000) 2693–2698
2697
Table 1
Observed gas phase IR frequencies of VOX3, in comparison with other results including the P–R separation (cm−1
)
Molecule
Mode Assignment
Observed
P–R separation
Related results This work (IR) gas-phase on-line production
Obs.
19.0
Calc.
VOF3
w1
w4
w2
w3
w5
w6
a1(OꢀV str.)
e(VꢁF str.)
a1 VF3 umbrella
a1 FVO def.
e(OꢀVF3 rock)
e(VF3 def.)
1057.8a
806
721.5
257.8
308
1058
806
722
–
18.3
15.7
12.0
5.3
–
204.3
–
VOCl3
VOBr3
VOI3
w1
w4
w2
w3
w5
w6
a1(OꢀV str.)
e(VꢁCl str.)
1035b
504
1035
505
408
–
16.0
12.1
6.0
a1 VCl3 umbrella 408
a1 ClVO def.
e(OꢀVCl3 rock)
e(VCl3 def.)
165
249
129
–
–
w1
w4
w2
w3
w5
w6
a1(OꢀV str.)
e(VꢁBr str.)
1025c
400
1030
400
–
a1 VBr3 umbrella 271
a1 BrVO def.
e(OꢀVBr3 rock)
e(VBr3 def.)
120
212
83
–
–
–
w1
w4
w2
w3
w5
w6
a1(OꢀV str.)
e(VꢁI str.)
a1 VI3 umbrella
a1 IVO def.
e(OꢀVI3 rock)
e(VI3 def.)
–
–
–
–
–
–
1025
–
–
–
–
–
a Gas phase infrared spectrum of VOF3 applying another route of production.
b Raman spectrum of gaseous VOCl3.
c Infrared spectrum of liquid VOBr3 applying another method of production.
detection of VOX3 using the FTIR technique. Our
experimental data agree with the expectation and
a satisfactory trend was observed. Our results are
compared with previous study regarding the gas
phase infrared spectrum of VOF3 and VOCl3 and
also with the infrared spectrum of liquid VOBr3.
The observed results are in excellent agreement
with previous reported work.
originated from VOCl3. Fig. 3 shows w1(a1), the
OꢀV stretching mode of VOX3 where XꢀF, Cl, Br
and I in the range (900–1200) cm−1. It should be
pointed out here that the left-hand side of w1(a1)
in VOI3 spectrum (Fig. 3) is due to the w1(a1) of
VOCl3.
All the observed frequencies (cm−1) of VOF3
determined by this gas phase infrared spec-
troscopy work in comparison with the data ob-
tained by gas and liquid phase of VOF3 and
VOBr3, respectively are listed in Table 1 including
the observed and calculated values of PR separa-
tion using the method of Paul and Dijkstra [9] for
the w1(a1) VOX3 where XꢀF, Cl, Br and I. It is
concluded that the present work reports for the
first time, the gas phase on-line production and
Acknowledgements
We would like to thank Professor I. Othman,
the Director General, and Professors G. Zazafoon
and B. Masrani, heads of Chemistry and Physics
Departments, respectively for their encourage-

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[2] A.W. Allaf, Spectrochim. Acta Part A 54 (1998) 921.
[3] H. Selig, H.H. Claassen, J. Chem. Phys. 44 (1966) 1404.
[4] F.A. Miller, L.R. Cousins, J. Chem. Phys. 26 (1957) 329.
[5] G.A. Ozin, D.J. Reynolds, J. R. Soc. Chem. Chem. Com-
mun., 884 (1969).
ment and support. We are very grateful to Profes-
sors H. Kellawi, Ahmad Haj Said, D.R.M. Wal-
ton and R. Suffolk for reviewing the work as well
as to D. Naima and N. Odeh for setting up the
experiments.
[6] F.A. Miller, W.K. Baer, Spectrochim. Acta Part A 17
(1961) 112.
[7] A.W. Allaf, Z. Ajji, Spectrochim. Acta, Part A, 2000, in
press.
[8] L.E. Trevorrow, J. Phys. Chem. 62 (1958) 362.
[9] W.A. Seth Paul, G. Dijkstra, Spectrochim. Acta Part A 23
(1967) 2861.
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