176
SERGIENKO et al.
Synthesis of HLn. A solution of 1.94 g (0.01 mol) of
VII) with R-salicylidene-2-furfurylamines are sum-
marized in Table 1.
2-furfurylamine in 20 mL of ethanol was added to a
hot solution of 0.01 mol of the corresponding alde-
hyde in 20 mL of ethanol; the resulting solution was
heated under reflux for 30 min, evaporated to one-
half, and left for 24 h for crystallization. HL1 was a vis-
cous liquid; therefore, it was purified by vacuum distil-
lation. The other o-hydroxyazomethines were purified
by crystallization from ethanol. The purity of the com-
pounds was monitored by TLC. HL2: lemon crystals,
mp 70–71°C; HL3: lemon crystals, mp 76–77°C.
The IR spectra were recorded as Nujol mulls on an
IKS-29 spectrophotometer.
X-ray crystallography. Experimental material for
crystals of I and HL2 was collected on an automated
Enraf-Nonius CAD-4 diffractometer. In both cases,
the structure was solved by direct methods (SHELXL-97)
[13] and refined by least-squares calculation in the
full-matrix anisotropic approximation for all non-
hydrogen atoms (SHELXL-97) [14]. The hydrogen
atoms were introduced into geometrically calculated
positions and refined as riding on their bonded atoms.
The H(1) atoms in the structures of I and HL2 were
located from difference Fourier syntheses and refined
isotropically. The unit cell parameters and key experi-
mental details are presented in Table 2. Complete crys-
tallographic data were deposited with the Cambridge
Crystallographic Data Centre (CCDC no. 1481909 (I),
1481910 (HL2); http://www.ccdc.cam.ac.uk/deposit/).
Synthesis of MCs. Molecular complexes were syn-
thesized by the reaction of MoO2Cl2 with HLn at the
ratio metal : ligand = 1 : 2 in dry ethyl acetate at room
temperature. A solution of 0.402 g (0.002 mol) of HL1
was added dropwise to a stirred solution of 0.199 g
(0.001 mol) of MoO2Cl2 in 10 mL of ethyl acetate. The
resulting precipitate was filtered off on a Schott filter
funnel equipped with calcium chloride tube, and dried
in a dry argon flow and then in a vacuum desiccator
over Р2O5. MCs with other azomethines were synthe-
sized analogously. The yield of the products was ~90%
of the theoretical one.
RESULTS AND DISCUSSION
It has been experimentally demonstrated that, at
any ratio of the reagents, the reaction of MoO2Cl2 with
salicylidene-2-furfurylamines in low-polarity solvents
(ethyl acetate, diethyl ether, tetrahydrofuran) gives
MCs II–IV of only one composition, MoO2Cl2 · 2HLn
(Table 1), which are lemon or yellow amorphous pow-
ders readily soluble in alcohols, dimethylformamide,
and dimethyl sulfoxide to form conducting solutions.
Synthesis of ICCs. ICCs were synthesized by boil-
ing methanol solutions of molybdenyl acetylacetonate
and azomethines for 30 min. A portion of 0.326 g
(0.001 mol) of MoO2(Асас)2 was dissolved in 20 mL of
methanol on heating under reflux, and then 20 mL of
a methanol solution containing 0.002 mol of HLn was
added. The reaction mixture was heated under reflux
for 30 min, evaporated to 30 mL, and left for crystalli-
zation at 0°C for 24 h. The resulting crystals were fil-
tered off on a filter, washed with cold methanol, and
dried in a dry air flow. The yield of the products was
80–90% of the theoretical one.
n
The ICCs have the composition
(Table 1).
МоО2L2
In addition, the reaction with 3-methoxysalicylidene-
2-furfurylamine leads to binuclear complex I. The
synthesized ICCs are high-melting lemon to brown
crystalline powders poorly soluble in cold methanol
and moderately soluble in dimethylformamide and
dimethyl sulfoxide to give non-conducting solutions.
In the course of the experiment, it was found that
the composition of the dioxomolybdenum(VI) ICC
with azomethine HL2 depended noticeably on synthe-
sis conditions. The reaction of MoO2(Асас)2 with HL2
on cooling or at room temperature led to the formation
of a fine orange powder of the MoO2(L2)2 composi-
tion. Boiling this reaction mixture in methanol led,
within a few minutes, to the formation of a brown
solution from which crystals of tentative composition
[{MoO2(L2)(CН3OН)}2(μ–O)] were precipitated on
cooling; this composition was supported by X-ray
crystallography data.
To determine the type of the complexes and loca-
tion of coordinate bond, we studied their spectra of
compounds II–VII. Changes in the spectra in the
range of azomethine bond absorption are of greatest
interest. Formation of ICCs leads to a low-frequency
shift of the ν(C=N) absorption band by 8–10 cm–1,
which indicates that the nitrogen atom of the C=N
group is involved in donor–acceptor interaction. In
the spectra of MCs, the same range displays a strong
band at ~1650 cm–1; by analogy with MCs of MoO2Cl2
with other salicylideneimines [1, 3, 10], this band
should be assigned to the red-shifted C=O absorption
of the quinoid tautomer of o-hydroxyazomethines.
This is supported by the appearance of the N–H
stretching vibration band at 3170–3190 cm–1 in the
spectra of MCs.
Molybdenum was quantified by calcining a
weighed portion of the complex at 450°C to MoO3 as
a gravimetric form [11]. Chlorine was determined by
the Volhard method after preliminary hydrolysis with
an alkali solution. Nitrogen was quantified using the
Dumas method [12].
A strong doublet in the range 900–950 cm–1 is due
to symmetric and antisymmetric stretching vibrations
of the cis-MoO2 group [3]. A broad and strong absorp-
Physicochemical and IR spectroscopy data for
dioxomolybdenum(VI) MCs (II–IV) and ICCs (V–
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 62
No. 2
2017
Sergienko
