Synthesis and IR spectroscopic study of molecular complexes of molybdenum oxotetrachloride with azomethines

Article abstract of DOI:10.1023/a:1012575224360

Molecular complexes of MoOCl₄ with benzal- and salicylalanilines were synthesized, and their IR spectra were investigated. The complexes have octahedral structure. Salicylalaniline and its derivatives were suggested to be coordinated by the cen

Full text of DOI:10.1023/a:1012575224360

Russian Journal of Coordination Chemistry, Vol. 27, No. 11, 2001, pp. 819–822. Translated from Koordinatsionnaya Khimiya, Vol. 27, No. 11, 2001, pp. 869–872.
Original Russian Text Copyright © 2001 by Abramenko.
Synthesis and IR Spectroscopic Study of Molecular Complexes
of Molybdenum Oxotetrachloride with Azomethines
V. L. Abramenko
East Ukrainian National University, Lugansk, Ukraine
Received January 22, 2001
Abstract—Molecular complexes of MoOCl with benzal- and salicylalanilines were synthesized, and their IR
4
spectra were investigated. The complexes have octahedral structure. Salicylalaniline and its derivatives were
suggested to be coordinated by the central atom through the carbonyl oxygen atom of quinoid tautomeric form.
The synthesis of molecular complexes (adducts) of similar reactions with papaverine and papaverine hydro-
MoOCl with organic ligands involves some experi- chloride yield Mo(V) and W(V) oxochloride complexes.
4
mental difficulties, first of all, because molybdenum
X-ray structural analysis [6] unambiguously indi-
oxotetrachloride is prone to enter the reactions of sub-
6
+
cated that MoOF forms adducts with krypton and
4
stitution of the chlorine ions; moreover, Mo reveals
high oxidation activity and the Mo–Cl bond can be
hydrolyzed in the presence of even a small amount of
water, which is present in solvents and cannot be
removed [1]. According to the data from [2], MoOCl4
reacts with some chlorinated aromatic hydrocarbons
xenon difluorides only in the case of molybdenum
oxotetrafluoride. The authors of [7], who studied solu-
1
9
tions of MoOF in acetonitrile using F NMR spectros-
4
copy, also suggested the formation of MoOF · CH CN.
4
3
Spectroscopic and conductometric studies of dissolu-
tion of MoOCl in dimethyl formamide showed that
4
and is reduced to MoOCl with elimination of hydro-
3
interaction of the components both in solution and in
solid phase yields solvato complexes [8].
chloride. The reactions with acetylacetone, benzophe-
none, and pyridine [2, 3] also lead to reduction of
Mo(VI) to lower oxidation states.
In this work, the synthesis of molecular complexes
The reaction of MoOCl with a tenfold amount of of MoOCl with azomethines was investigated. Chloral-
4
4
6+
triethylamine results in the reduction of Mo and the for- kanes (CCl , CHCl , and C H Cl ), in which molybde-
4
3
2
4
2
mation of [MoOCl · N(CH ) ] of polymer structure (as num oxotetrachloride is readily soluble [1], were used
3
3 n
follows from IR spectroscopy data) [4]. However, the as inert media. A series of azomethines—derivatives of
products obtained in [5] by reacting molybdenum and benzaldehyde (A) and salicylaldehyde (B) and aro-
tungsten oxotetrachlorides with Atophan (L) in sealed matic amines with different substitutes in the aromatic
ampoules at a high temperature were identified by the ring—was selected for elucidating the influence of
authors as MOCl ·L adducts (M = Mo, W). These data call electronic and steric factors on the composition and
4
for verification, because the authors of [5] also found that properties of the compounds under investigation:
OH
N
R2
N
R1
R
(
Ä)
(B)
2
1
R = H: R = N(CH ) (I), OCH (II), CH (III), R = H (XII), 5-Br (XIII), 5-NO2 (XIV),
3
2
3
3
3
-OCH (XV)
3
H (IV), Br (V), NO (VI);
R = H: R = N(CH ) (VII), OCH (VIII), CH (IX),
2
1
2
3
2
3
3
Br (X), NO (XI)
2
EXPERIMENTAL
sion of MoO in thionyl chloride was boiled for 5 h in a
3
flask equipped with a reflux condenser and a hood with
Molybdenum oxotetrachloride was synthesized calcium chloride. Unreacted MoO was filtered off, and
3
by reacting MoO with thionyl chloride [9]. A suspen- the red solution formed was evaporated in vacuum.
3
1
070-3284/01/2711-0819$25.00 © 2001 åÄIä “Nauka /Interperiodica”

8
20
ABRAMENKO
After the product was purified by sublimation at 80°C a concentration of 10–3 mol/l). Methanolysis of the
in a flow of dry argon, virtually pure green crystals of complexes can be presented by the following scheme
molybdenum oxotetrachloride were obtained; their (with no account of dissociation):
m.p. 100–102°C agrees with the literature data.
MoOCl ⋅ HL + 4CH OH
4
3
Azomethines were synthesized through the conden-
sation of aldehydes and amines in boiled ethanol [10];
they were further recrystallized from alcohol and kept
in a vacuum desiccator over freshly calcined calcium
chloride.
Complex compounds were obtained through the
direct reaction of molybdenum oxotetrachlorides with
azomethines in a chloralkane medium at room temper-
MoO(OCH ) + 4HCl + HL,
3
4
this was confirmed by the rapid precipitation of chlo-
ride ions exhibited when a methanol solution of silver
nitrate was added to a solution of the complex com-
pound.
Benzalanilines are monodentate ligands whose
2
ature or upon slight heating (30–35°C). Since MoOCl4 nitrogen atom has close to sp hybridization of its atom
is highly hygroscopic, all solvents were purified and orbitals and acts as a donor center [13], the unshared
thoroughly dried using known procedures. The proce- electron pair of the N atom being involved in nπ-conju-
dure of synthesis of complex MoOCl with salicylal- gation. The formation of molecular complexes of Lewis
4
aniline is described as an example. A solution of 0.197 g acids with benzalanilines coordinated through the
(
0.001 mole) of salicylalaniline in 20 ml of chloroform nitrogen atom of the azomethine group can be judged
was slowly added in drops to a solution of 0.254 g from the high-frequency shift of the ν(C=N) band in the
0.001 mole) of MoOCl in 20 ml of chloroform with IR spectra [14], because this shift depends on both the
(
4
stirring. Argon dried over P O was bubbled continu- nature of the central metal and the saturation of the π-
2
5
ously through the reaction mixture. The precipitate electron density of the C=N group [15]. This criterion
formed was placed on a glass filter equipped with a dry- is rather reliable and has been repeatedly verified. In the
ing system, filtered off, and dried in an argon flow with IR spectra of complexes of MoOCl with benzal-
4
slight heating. The complex yield was almost quantita- anilines, the band of stretching vibrations of the azome-
tive.
thine group is shifted toward high frequencies by 30–
–
1
3
5 cm (table), which is close to the ∆ν(C=N) values
Analysis for molybdenum was carried out by cal-
for analogous complexes with other metals [13–15].
cining a sample of the complex at 450°C until MoO3
formed and by weighing the product [11]. Chlorine
It is obvious that the Mo N bond strength and,
content was determined using the Folgard method after consequently, the spectral properties of the complexes
the complex was preliminarily hydrolyzed in an alka- should be markedly affected by electronic and steric
line medium [12].
effects produced by donor–acceptor interaction of
MoOCl with benzalanilines and by substituents in aro-
IR spectra were recorded on a IKS-29 spectrometer
suspension in mineral oil held over metallic sodium).
4
(
matic rings of the ligand molecules. As is seen from the
table, the correlation between the electron-donor prop-
erties of substituents and the spectra of molybdenum
oxotetrachloride complexes becomes most evident
when the substituents in the aniline fragment of benzal-
aniline molecules are varied: the magnitude of
Conductometric measurements were carried out on
a bridge system operating at 1000 Hz.
RESULTS AND DISCUSSION
∆
ν(C=N) and the complex stability increase with
Preliminary experiments showed that low-polar or
inert solvents, in particular, chlorinated hydrocarbons,
are optimal media for the synthesis of adducts of
increasing electron-donor properties of the substitu-
ents. However, it is hardly possible to elucidate a dis-
tinct correlation between ∆ν(C=N) and the Gammet
MoOCl with azomethines. However, these compounds
4
1
σ-constant of the substituents because the effect of R
and R substituents is moderate. The fact that the
ν(C=N) values for all studied complexes of MoOCl4
with benzalanilines I–XI are comparable allows one to
suggest that the nitrogen atom of the azomethine group
is the only coordination center.
can also be precipitated in other anhydrous solvents,
such as diethyl ether, tetrahydrofurane, acetonitrile, and
aromatic hydrocarbons.
2
∆
The elemental analysis data (table) indicated that
only equimolar complexes were formed under these
conditions, independent of the ratio of reacting com-
pounds. The products obtained are mainly green pow-
Salicylalanilines XII–XV are ambidentate ligands.
ders stable in dry air which melt with decomposition at Since their solutions in organic solvents are character-
temperatures above 140°C. In the presence of moisture ized by benzoid–quinoid (ketoamine–enolimine) tauto-
and, especially, in open air, the complexes change their meric equilibria, they can form both molecular and che-
color to yellow or yellow-brown due to hydrolysis. When late metal complexes [16]. The structure of chelate
the complexes are dissolved in methanol, colorless compounds can be easily determined using different
(
ligands A) or yellow (ligands B) solutions are formed, physicochemical methods, including X-ray structural
their conductivity reaching the values typical of solutions analysis [16]; however, X-ray diffraction data for sali-
–1
2
–1
of free MoOCl in methanol (450 Ohm cm mol for cylalanilines are scarce; therefore, the questions of how
4
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 11 2001

SYNTHESIS AND IR SPECTROSCOPIC STUDY OF MOLECULAR COMPLEXES
821
Results of physicochemical and IR spectral studies of molecular complexes of MoOCl with azomethines
4
Complex MoOCl · L
Content (found/calcd), %
ν, cm–1
4
ligand
L)
complex MoOCl · L
4
(
Ligand
L)
(
empirical formula color of complex m.p., °C
Mo
Cl
I
II
III
IV
V
C H Cl MoN O
C H Cl MoNO
14 13 4 2
C H Cl MoNO
14 13 4
Greenish brown
Yellow green
Green
170–172 20.24/20.07 29.58/29.66 1622
157–159 20.47/20.63 30.45/30.50 1625
135–137 21.26/21.37 31.68/31.58 1629
>140(@) 22.13/22.06 32.75/32.60 1631
168–170 18.48/18.67 27.80/27.60 1628
175–177 19.80/19.99 29.37/29.55 1632
164–166 20.04/20.07 29.52/29.66 1610
148–150 20.80/20.63 30.56/30.50 1625
>140(@) 21.25/21.37 31.44/31.58 1626
166–168 18.77/18.67 27.75/27.60 1630
174–176 20.04/19.99 29.40/29.55 1632
125–127 21.15/21.27 31.57/31.44 1623
140–142 18.06/18.11 26.69/26.76 1615
155–157 19.22/19.34 28.70/28.59 1621
145–147 20.05/19.95 29.42/29.48 1623
1660
1658
1658
1660
1662
1660
1647
1655
1657
1660
1657
965
972
974
968
975
978
972
974
975
978
980
970
978
975
973
1
5
16
4
2
C H Cl MoNO
Green
1
3
11
4
C H BrCl MoNO Green
1
3
10
4
VI
C H Cl MoN O
3
Yellow green
Greenish brown
Light green
1
3
10
4
2
VII
VIII
IX
X
XI
XII
XIII
XIV
XV
C H Cl MoN O
15 16 4 2
C H Cl MoNO
2
1
4
13
4
C H Cl MoNO
Light green
1
4
13
4
C H BrCl MoNO Light green
13 10 4
C H Cl MoN O
3
Light green
Green
1
3
10
4
2
C H Cl MoNO
2
1648
1643
1650
1647
1
3
11
4
C H BrCl MoNO Yellow green
1
3
10
4
2
C H Cl MoN O
4
Green
Green
1
3
10
4
2
C H Cl MoNO
3
1
4
13
4
these compounds are coordinated and which tautomeric stretching vibration of the C=N bond of the azomethine
form is involved in the molecular complex are debatable. group, whose frequency, by analogy with benzalanilines,
Until recently, the band detected in the IR spectrum of was shifted toward the high-frequency region due to the
–1
the complexes at about 1650 cm was attributed to the formation of a metal–nitrogen coordination bond (a):
MXn
O
MXn
O–
MXn
O
H
N
H
N
H
N+
CH
R m
CH
R m
CH
R m
(
a)
(b)
(c)
However, X-ray diffraction analysis of the molecu- [22] by X-ray structural analysis, seems to be more reli-
lar complexes of some metals with Ó-oxyazomethines able.
[
17–19] demonstrated that the quinoid form of the
Structure (b) in complexes XII–XV is confirmed by
ligand is fixed in the complex and coordinated by the
central atom through an unshared electron pair of the
carbonyl oxygen atom (structure b). In the IR spectra of
the fact that an intense band of stretching vibrations of
–1
the NH group at 3170–3200 cm occurs in their IR
spectra, while the absorption bond of the immonium
complexes of MoOCl with Ó-oxyazomethines XII–
XV (see table), an intense band was also observed at
+
4
–1
group =NH– (~2600 cm ) typical of zwitter-ionic
forms of oxyazomethines in molecular complexes of
calcium (structure c) [19] is not observed. The intense
–1
~
1650 cm ; it can be produced by both the vibrations
ν(C=N) of benzoid tautomer (a) and the stretching
vibrations ν(C=O) of quinoid tautomer (b), whose fre-
quency is decreased due to complexation. Accounting
for the data reported in [17, 18], structure (b), which
–
1
singlet in the 960–980 cm range is due to the stretch-
ing vibrations of the Mo=O bond [22].
Thus, the data obtained are evidence that in inert and
includes not the quinoid tautomeric form typical of low-polar solvents, where solvolysis of the Mo–Cl
crystalline salicylalalkyl- and arylamines [20, 21] but a bond is impossible, molybdenum oxotetrachloride and
form recently determined for salicylaltetrarylimines azomethines form molecular complexes in which the
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 11 2001

8
22
ABRAMENKO
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Organic Reagents for Inorganic Analysis), Moscow:
Mosk. Gos. Univ., 1972.
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[23]. Four equivalent chlorine atoms are located in the
equatorial plane. As in the structure of complexes of
1
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Nauk SSSR, 1962.
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4
consistency rule [24], the oxygen atoms of the Mo=O
bond and the donor atom of the ligand (the benzal-
aniline nitrogen atom or carbonyl oxygen atom of the
quinoid tautomer of salicylalimines) are arranged in the
apical plane in the trans-position with respect to each
other.
1
2. Kreshkov, A.P., Osnovy analiticheskoi khimii (Founda-
tions of Analytical Chemistry), Moscow: Khimiya,
1
970, vol. 2, p. 324.
1
1
3. Kogan, V.A., Doctoral (Chem.) Dissertation, Rostov-on-
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Khim., 1974, vol. 19, no. 7, p. 1800.
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RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 11 2001