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Compounds of Fe(III) and Co(II) Coordinated with Oxygen Atoms
SIMONA TURCUMAN (ANTIGHIN)1, DOINA SIBIESCU1, IOAN ROSCA1, MARIUS SEBASTIAN SECULA1, IGOR CRETESCU2*,
1
”Gh. Asachi” Technical University, Faculty of Chemical Engineering and Environmental Protection, Chemical Engineering
Department, 73 D. Mangeron, 700050, Iasi, Romania
2
”Gh. Asachi” Technical University, Faculty of Chemical Engineering and Environmental Protection, Environmental Engineering
and Management Department, 73 D. Mangeron, 700050, Iasi, Romania
The authors present the synthesis and characterization of some novel coordinative compounds derived
from the interaction between Fe(III) and Co(II) respectively with morfolin-4-carboditioic acid-2-(3,5-dibrome,4methyl,2-hydroxy-phenyl)-2-oxo-ethyl-ester organic ligand. The synthesized compounds were characterized
by using the following methods: elemental chemical analysis, thermogravimetry, IR absorption spectroscopy,
Electron Spin Resonance (ESR) spectroscopy, Mössbauer spectroscopy and X-ray diffraction. From the
obtained results it can be noticed that the central atoms are hexacoordinated by oxygen atoms from 〉 C = O
and - O(H) groups of the organic ligand. The obtaining reactions of these novel compounds might be applied
in gravimetric determination of Fe(III) and Co(II) respectively.
Keywords: morfolin-4-carboditioic acid-2-(3,5-dibrome,4-methyl,2-hydroxy-phenyl)-2-oxo-ethyl-ester, Fe(III),
Co(II), Mössbauer spectra, precipitating reagent.
Organic ligands such as: morfolin-4-carboditioic acid-2(3,5-dibrome,4-methyl,2-hydroxy-phenyl)-2-oxo-ethyl-ester
are used in the synthesis of Fe(III) and Co(II) coordination
compounds. Some of these ligands can be applied in
gravimetric determinations of metal ions [1-10].
In this study is presented the synthesis and study of
coordinative compounds obtained from the reactions:
morfolin-4-carboditioic acid-2-(3,5-dibrome,4-methyl,2hydroxy-phenyl)-2-oxo-ethyl-ester ligand with Fe(III) and
Co(II) ions in the combination ratio of 3:1, in case of Fe(III),
and 2:1, in case of Co(II). The novel compounds were
investigated by the following methods: chemical analysis,
termogravimetry, IR absorption spectroscopy, ESR and
Mössbauer spectroscopy and X-ray diffraction.
Experimental part
As reactant were used FeCl3, CoCl2 x 6H2O (Merck A.R.)
and : morfolin-4-carboditioic acid-2-(3,5-dibrome,4-methyl,2hydroxy-phenyl)-2-oxo-ethyl-ester prepared according to the
directions in literature [11-13].
The syntheses of the coordination compounds
presented in this work were carried out according to the
method described in literature [11]. The reactant solutions
of 0.2 M concentration were prepared using as solvent a
mixture of ethylic alcohol (98%) and water in the ratio of
1:1 (in volumes) for the salts of Fe(III) and Co(II), and
dimethyleformamide (DMF) solvent: morfolin-4-carboditioic
acid-2-(3,5-dibrome,4-methyl,2-hydroxy-phenyl)-2-oxo-ethylester (noted HL herein further).
The obtaining reactions of the synthesized compounds
were performed by mixing and stirring at room temperature,
for 70 min, 200 mL of HL with 200 mL from each solutions
containing Fe(III) and Co(II) respectively.
1. FeCl3+3 (C14H15NO3S2Br2) →
→ Fe(C14H14 NO3S2Br2)3 + 3 HCl
2. CoCl2+ 2(C14H15NO3S2Br2)+2H2O →
→ Co(C14H14 NO3S2Br2)2 + 2 H2O + 2HCl
The resulted precipitates were separated by filtration,
washed on a funnel vacuum nozzle, and then dried at
100oC until a constant weight was reached. Under the
specified conditions, efficiencies of 100 % were achieved.
The contents of C, H, N, S, Fe(III) and Co(II) were
determined for each synthesized compound using
adequate conventional methods [11- 13].
Thermogravimetric parameters of thermal decomposing
reactions [14-16] were achieved by processing the
derivatograms recorded by means of a Q1500D (MOM
Budapesta) derivatograph, according to the procedure
described in the previously works [3,5].
The absorption spectra in the IR range 200 and 4000
cm-1, respectively were recorded and processed according
to the methodology presented in the previously papers [3,5].
Results and discussions
Analyzing the experimental data concerning the
combination ratio of Fe(III) and Co(II): morfolin-4carboditioic acid-2-(3,5-dibrome,4-methyl,2-hydroxy-phenyl)2-oxo-ethyl-ester ligand, it results that the chemical analysis
of the synthesized compounds (table 1) was performed
with an error of ±0.27% in relation to the content of
C,H,N,S,Br, Fe(III) and Co(II).
Table 1
ELEMENTAL COMPOSITION (%) OF THE SYNTHESIZED COMPOUNDS
* email: [email protected]; Tel.: + 40 0741914342
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Table 2
CHARACTERISTIC TEMPERATURES OF THERMAL DECOMPOSITION STAGES, REACTION ORDERS AND
ACTIVATION ENERGIES, OF THE SYNTHESIZED COMPOUNDS.
The novel compounds have the formula:
Fe(C 14 H 14 NO 3S 2Br 2) 3 and Co(C 14 H 14 NO 3S 2Br 2) 2 x 2H 2 O
respectively. Further, these compounds will be referred as
FeL3 and CoL2 x 2H2O respectively.
The characteristic temperature stages of thermal
decomposing of the synthesized compounds, reaction order
and activation energy values were calculated according
to Freeman-Carrol method [14] and are presented in table
2.
Thermal decomposition stages listed in table 2
corresponds to the thermal decomposition that follows the
elimination of coordination water. Water was eliminated
at 180°C from FeL3, and at 230°C from CoL2 x 2H2O. The
coordination water is eliminated at higher temperatures
than the crystallization and zeolitic water.
Processes taking place under the action of temperature
and oxygen from air are sometimes very complicated and
difficult to interpret. Usually, the temperatures at the start
and end of thermal decomposing stages are emphasized,
and the reaction parameters, such as reaction order and
activation energy, are calculated [14-18]. The thermal
stability of synthesized compounds is established.
After the coordination water is eliminated, two thermal
decomposing stages follow. The final solid products of
thermal decomposing reactions are oxides of the
respective metals: FeO and CoO. The molecular structure
of the gaseous products formed could not be identified.
The thermal stability decreases with the increase of
alkalinity of the central atom: FeL3> CoL2 [11-13, 17, 18].
In fact, the layer of substance thermally decomposed
can be of a few millimeters and its thickness decreases as
thermal decomposing advances step by step, and in the
same time the dispersion degree increases due to the
chemical reaction. Consequently, the gaseous products
encounter a lower resistance during “vaporization”, and
the reaction order tend to unity in accordance to the data
reported in literature [11, 15, 16].
IR absorption spectra of the ligand and synthesized
compounds bring important information on the chemical
Fig 1 Structure of morfolin-4-carboditioic acid-2-(3,5-dibrome, 4methyl,2-hydroxy-phenyl)-2-oxo-ethyl-ester ligand
bonds of the central atoms of Fe(III) and Co(II) respectively
with some of the ligand atoms (table 3).
By means of IR absorption spectra of the synthesized
compounds, it was established whether there are
absorptions corresponding to bonds such as O-M, >C =
O→ M and M ← OH2, originating from the interaction of
functional groups -O(H) and >C=O in ligand and
respectively due to the coordination water (fig. 1).
Based also on the IR adsorption spectra of the
synthesized compounds, it was outlined the existence of
some very important bonds between central atoms of
Fe(III) and Co(II) respectively and the donor atoms in
ligand, such as oxygen and nitrogen that correspond the
stretch vibrations:νM-O and νM-N (table 3).
In concordance with data reported by other authors
[6,11], in the low frequencies range (450-1500 cm-1) occur
bends corresponding both to the valence vibrations of
simple bonds: C-C, C-O, Fe-O, Co-O, and to the deformation
vibrations of other bonds.
The bands with frequencies of 467 cm-1 and 437 cm-1
correspond to the stretch frequencies: νCo-O and ν Fe-O
respectively. The bands of vibration frequency of C-O group
observed in the region 1267-1287 cm -1 in the ligand
spectrum are shifted towards higher wavelengths and
become less intense in the spectra of the investigated
compounds [19-23].
Fig. 2. Thermogram of FeL3
compound.
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Table 3
IR SPECTRAL BANDS CHARACTERISTIC FOR THE SYNTHESIZED COMPOUNDS
The stretch (valence) vibrations of carbonyl groups occur
at 1715 cm-1, in case of ligand, while in the synthesized
compounds occur at 1657 cm-1 and 1640 cm-1 for FeL3 and
CoL2·2H2O respectively. This supports the assumption that
the central atoms of Fe(III) and Co(II) coordinate with the
oxygen atom in carbonyl group: M ← O=C< where M =
Fe, Co.
The spectral bands characteristics of IR absorption
spectra of the synthesized compounds are presented in
table 3. Full IR absorption spectra is presented only for CoL2
x 2H2O compound (fig. 3). The absorption of OH phenol
group in orto position is located in the range 3277-3275
cm-1, and disappears in the investigated compounds.
In case of phenols, the most important band [19-23] is
located between 773-1426 cm-1 (νC-OH). By substituting the
hydrogen atom with a central atom of Fe(III) or Co(II), the
peaks corresponding to OH group in IR spectra of the
synthesized compounds disappear.
Hence, it can be stated that each central atom binds to
an oxygen atom from the phenol group where, in fact, a
hydrogen atom is substituted with Fe(III) and Co(II)
respectively.
According to ESR spectra, both synthesized compounds
contain central atoms with odd electrons: 5 in case of
Fe(III) and 3 in case of Co(II).
The spectroscopic splitting factor takes values between
2.0225 and 2.018, hence, much higher than that of the free
electron (2.0023) due to the contribution of the orbital
momentum and covalence degree of bonds where central
atoms such as Fe(III) and Co(II) are involved. These values
are in agreement with other works reported in literature
[5-9].
The conclusions based on the Mössbauer spectra
[24]supports that the central atom in FeL3 is in the IIIrd
oxidation state with high spin (S=5/2) which indicates a
relative ionic character of Fe-O bond.
The value of ΔEQ parameter (table 5) supports the
octahedral encompassment of Fe(III) with electrons
distributed on the last level: t32g, e2g
It is of very high importance that due to the symmetric
electron configuration 3 d5 of Fe(III) central atom, it was
not observed any splitting of quadrupole in case of
octahedral coordination only by oxygen atoms.
In case of FeL3, it was observed a dependence of the
isomer shift on the temperature of 0.05 mm/s 100 °C, which
is higher than that obtained in case of most coordinative
compounds.
This behavior is in agreement with the second-order
Doppler effect. It can be explained as the temperature
increases from 80 to 300 K, at the same time as the
oscillations of Fe(III) atoms in the crystalline network
increase, it takes also place a shift of the electronic density
of spin s within the ligand-central atom bond.
The X-ray diffractograms of the HL ligand and
synthesized compounds (FeL3, CoL2 x 2H2O) lead to the
conclusion that these compounds crystallize in monoclinic
Table 4
VALUES OF THE SPECTROSCOPIC SPLITTING FACTOR (g), INTENSITY OF THE MAGNETIC
FIELD CORRESPONDING TO THE SPECTRUM CENTER OF THE SAMPLE (Hx, GAUSS) AND
ODD ELECTRON NUMBER OF THE CENTRAL ATOM (n)
Fig. 3. IR absorption spectrum of CoL2·2H2O compound
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Fig. 4. Mossbauer spectrum of FeL3
recorded at 80 K
Table 6
VALUES OF ELEMENTAL CELL PARAMETERS FOR HL
LIGAND, FeL3 AND CoL2×2H2O COMPOUNDS
Table5
PARAMETER VALUES OF MÖSSBAUER SPECTRUM
OF FeL3
FeL3
CoL3 x 2H2O
Fig. 5. Structural formula of the synthesized compounds
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REV. CHIM. (Bucharest) ♦ 62♦ No. 2 ♦ 2011
Fig. 6. Diffractograms of HL(1)
ligand and CoL2·2H2O compound.
system due to the crystallographic characteristics of the
ligand that keeps its monoclinic crystalline structure. The
elemental cell parameters are shown in table 6.
Based on the elemental cell parameters of FeL3 and
CoL2 x 2H2O compounds, it results that in both cases the
values of a and c parameters are relatively close though
they are much lower than the b value. This shows that the
central atoms of Fe(III) and Co(II) coordinates with H2O
respectively in the ac plan of the elemental cell towards b
side accompanied by volume compression.
The coordination of ligand by central atoms Fe(III) and
Co(II) is achieved in the ac plane of the elemental cell
accompanied by its volume compression. In the same time
it can be noted a slight distortion of α angle that leads to
the conclusion that water molecules coordinate with the
central atoms of Fe(III) and Co(II) above and beneath the
ab plane accompanied by volume compression of
compound elemental cell due to coordination.
In both structures of these compounds can be noted a
slight distortion of β angle probably due to the distribution
of water molecules and OH groups above and beneath the
plane were are located the ligands derived from morfolin4-carboditioic acid-2-(3,5-dibrome,4-methyl,2-hydroxyphenyl)-2-oxoetil-ester .
Based on the data obtained by means of chemical
analysis, IR absorption spectroscopy, thermogravimetric
analysis, electron spin resonance and Mössbauer
spectroscopy and X-ray diffraction, it can be concluded
that the central atoms of Fe(III) and Co(II) are
hexacoordinated in octahedral structures[25-29].
Both central atoms, Fe(III) and Co(II) respectively, are
hexacoordinated by oxygen atoms from >C=O and –O(H)
groups of HL ligand (fig. 5).
Conclusions
Two novel compounds of Fe(III) and Co(II) with morfolin4-carboditioic acid-2-(3,5-dibrome,4-methyl,2-hydroxyphenyl)-2-oxo-ethyl-ester ligand in the molar ration central
atom:ligand of 1:2 in case of Co(II) and 1:3 in case of
Fe(III) were synthesized and characterized.
The synthesized compounds were characterized by
means of modern technical methods such as elemental
chemical analysis,thermogravimetric analysis, IR
absorption spectroscopy, ESR and Mössbauer spectroscopy
and X-ray diffraction. By means of these techniques, it was
shown that the synthesized compounds are of high spin
REV. CHIM. (Bucharest) ♦ 62♦ No. 2 ♦ 2011
having hexacoordinated central atoms and octahedral
crystalline structure.
The obtaining reaction of the new synthesized
compounds can be used in order to determine
gravimetrically the ions of Fe(III) and Co(II) with a
maximum error of ± 0.27%.
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