Synthesis and characterization of some Cr(III), Fe(III) and Zr(IV) compounds with substituted o-hydroxy benzophenone

Article abstract of DOI:10.1023/B:JTAN.0000042171.81071.e3

This work presents our data concerning the synthesis and characterization of some Cr(III), Fe(III) and Zr(IV) complexes with substituted (2-hydroxy-4-methoxy-phenyl)-phenyl-methanone - C₁₄H ₁₂O₃, denoted by (Ll). The synth

Full text of DOI:10.1023/B:JTAN.0000042171.81071.e3

Journal of Thermal Analysis and Calorimetry, Vol. 78 (2004) 239–249
SYNTHESIS AND CHARACTERIZATION OF SOME
Cr(III), Fe(III) AND Zr(IV) COMPOUNDS WITH
SUBSTITUTED o-HYDROXY BENZOPHENONE
N. Foca1, G. Lisa2* and I. Rusu1
1‘Gh. Asachi’ Technical University, Faculty of Industrial Chemistry, Department of Inorganic
Chemistry, 71 Mangeron Street, Iasi 700050, Romania
2‘Gh. Asachi’ Technical University, Faculty of Industrial Chemistry, Department of Physical
Chemistry, 71 Mangeron Street, Iasi 700050, Romania
(Received July 30, 2003; in revised form November 3, 2004)
Abstract
This work presents our data concerning the synthesis and characterization of some Cr(III), Fe(III) and
Zr(IV) complexes with substituted (2-hydroxy-4-methoxy-phenyl)-phenyl-methanone – C14H12O3,
denoted by (L1). The synthesis of these complex compounds was performed using melted urea as
reaction medium. The obtained complexes have been studied by chemical analysis, IR spectroscopy,
X-ray diffraction and thermogravimetric analysis. Based on the data resulting from the thermal
behaviour of the studied complex compounds, the kinetic parameters of the thermal decomposition
reactions have been determined.
Keywords: chrome, iron, melted urea, thermal behaviour, zirconium
Introduction
The ligand L1 (sample 4) used for the synthesis of the Cr(III), Fe(III) and Zr(IV)
complexes has the following structure:
The literature presents only a few data concerning the complex compounds of
different metallic cations with this ligand, fact due to its reduced reactivity under usual
*
Author for correspondence: E-mail: gapreot@ch.tuiasi.ro
1388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
© 2004 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

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FOCA et al.: Cr(III), Fe(III) AND Zr(IV) COMPLEXES
conditions. However, under certain reaction conditions concerning the nature of the
reaction medium, the pH, the temperature, etc., this ligand is able to form complexes
with a series of metallic cations, among which Cr(III), Fe(III) and Zr(IV).
Experimental
The reaction with the Cr(III), Fe(III) and Zr(IV) ions in organic solvents occurs quite
difficult under normal conditions. The M-L1 compounds can be formed in solution,
but they are difficult to separate in solid-state. The solid-state separation of the mixed
compounds of Cr(III), Fe(III) and Zr(IV) with urea and the ligand L1 occurs with
very good results if one uses melted urea as reaction medium [1–5].
The urea, which is used as both reaction medium and reagent, was introduced in
porcelain crucibles and heated on oil bath. The temperature was kept under control be-
tween 160–165°C, below the decomposition temperature of urea, which is of 182.5°C.
After the melting of urea, the corresponding chlorides (Merck reagents) of these cations:
CrCl3⋅6H2O, FeCl3⋅6H2O and ZrCl4⋅H2O were added. The heating continues at 165°C for
two more hours until no gases or steams are emitted.
After cooling, the samples were washed with DMF in order to remove the urea
excess, and subsequently the obtained compounds, [Cr(urea)6]Cl3, [Fe(urea)6]Cl3 and
[Zr(urea)6]Cl4, were separated [1–4]. After separation, the [M(urea)6]n+ complexes
were dried and used for the synthesis of the mixed complexes M-Urea-L1. For this,
the [M(urea)]n+ compounds were melted again, and small amounts of ligand L1 were
added step by step. The heating goes on for 1.5 h more until the reaction is com-
pleted, i.e. no gas (HCl) emission is noticed.
After cooling, the complexes were washed with small amounts of water and
ethanol and dried on CaCl2 until the mass remains constant. The dried compounds have
been chemically analysed in order to establish their molecular formulas. The Cr3+, Fe3+
and Zr4+ contents were determined by atomic absorption spectroscopy AAS, redox
potentiometry and gravimetric analyses [6–9]. The obtained data are listed in Table 1.
Based on the data obtained by the chemical analysis of the synthesized com-
pounds, the chemical formulas given in Table 2 were suggested. At the same time,
the melting points and their solubility in organic and inorganic solvents were deter-
mined, all the obtained data being given in the same table.
Results and discussion
Thermal analysis
The thermal stability of L1 and of its complex compounds with the Cr(III) (sample 1),
Fe(III) (sample 2) and Zr(IV) (sample 3) has been investigated by thermogravimetric
analysis under dynamic conditions of temperature. The experimental measurements were
performed with a thermal balance type Paulik–Paulik–Erdey (MOM, Hungary) under the
following conditions: mw=48 2 mg, reference material Al2O3, quartz crucible, heating
rate 8, 10 and 12°C min–1, in air, at temperatures ranging from 20 to 900°C.
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FOCA et al.: Cr(III), Fe(III) AND Zr(IV) COMPLEXES
Table 2 The proposed chemical formulas and some physical characteristics of the synthesized
complexes
The colour of
compounds
The solvent in which
they are soluble
No.
Chemical compound
Melting point/°C
1
[Cr(urea)6]Cl3
72–74
80–81
gray-greenish
olive-green
scarlet-brown
dark-brown
yellow-gray
light-brick
H2O, C2H5OH
DMF, CO(CH3)2
H2O, C2H5OH
DMF, C2H5OH
H2O, CH3OH
1‘
2
[Cr(L)2(urea)2]Cl
[Fe(urea)6]Cl3
95–97
2’
3
[Fe(L)2(urea)2]Cl
[Zr(urea)6]Cl4
110–112
80–82
3’
[Zr2(L)2(urea)4Cl2]Cl4
89–91
DMF, C2H5OH
The experimental results revealed that the degradation occurred in multiple
stages, following a complex mechanism. For each stage the kinetic parameters and
the thermogravimetric characteristics have been estimated.
The thermal decomposition is a complex process influenced by the nature of the
metallic cations, which determine the reaction development in multiple stages, with
different mass loss depending on their nature (Table 3).
From the data presented in Table 3 one can observe that the most important mass
loss has been registered during the last stage of the thermal decomposition process, at
temperatures ranging between 360 and 760°C. This last stage of the thermal degrada-
tion has a common characteristic, namely a constant conversion level and a strong
thermopositive effect, which increases depending on the nature of the metallic ion,
following the sequence:
Cr(III)>Fe(III)>Zr(IV)
The thermal degradation of the L1 occurs in only one stage, which starts at 160°C
and ends at 520°C. According to the data from Table 3, the thermal stability of the
analysed complexes, estimated by means of the starting temperature of the decomposi-
tion process, decreases as follows:
[Fe(L)2(urea)4]Cl>L1>[Zr2(L)2(urea)4Cl2]Cl4 >[Cr(L)2(urea)2]Cl
On the other hand, if one analyses the temperature domains of the thermal deg-
radation, it is obvious that the compound Cr(L)2(urea)2Cl has the lowest thermal deg-
radation rate (140–650°C). In all cases, after degradation remains an amount of solid
residue that ranges between 9 and 16%.
Taking into account the importance of the isoconversional methods in the ther-
mal analysis [10, 11], we have performed the kinetic calculations by means of the
method proposed by Vyazovkin et al. [12–14]. The dependence of the apparent acti-
vation energy, Ea, on the reacted fraction, α, is plotted in Figs 1–5. The models of the
decomposition processes for every step, f(α) and the pre-exponential factor, logA, are
listed in Table 4. The apparent activation energy depends on the reacted fraction, α,
revealing the complexity of thermal degradation [15, 16].
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FOCA et al.: Cr(III), Fe(III) AND Zr(IV) COMPLEXES
245
Fig. 1 The apparent activation energy as a function of the reacted fraction for the first
stage of the decomposition process
Fig. 2 The apparent activation energy as a function of the reacted fraction for the
second stage of the decomposition process
Fig. 3 The apparent activation energy as a function of the reacted fraction for the third
stage of the decomposition process
Fig. 4 The apparent activation energy as a function of the reacted fraction for the last
stage of the decomposition process (sample 2)
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FOCA et al.: Cr(III), Fe(III) AND Zr(IV) COMPLEXES
Fig. 5 The apparent activation energy as a function of the reacted fraction for the
decomposition process (sample 4)
The IR absorption spectra
The IR absorption spectra were recorded for the separated complexes, urea and the
ligand L1 by means of a UNICAM spectrometer within the frequency
range 400–4000 cm–1. The spectra were analysed and compared to those of L1 and
urea. One can notice important modifications in the vibration spectra of the –NH2
group from urea, as well as in those of the –OH and >c=O groups from the ligand’s
structure. The IR spectra of the obtained compounds present new absorption bands
within the 420–490 cm–1 range, which are characteristic to the M–O bonds resulted
from the complexing process [17–19].
X-ray diffraction spectra
The structure of the complex combinations of Cr(III), Fe(III) and Zr(IV) with this
ligand has been studied by means of the X-ray diffraction (powder method) at the room
temperature with a Siemens D. 500 diffractometer and nickel filter [20, 21]. The
diffractograms have been recorded using CuKα radiation, within the range 2–80° (2θ),
at a step of 0.1° s–1. Figure 6 presents the diffractograms of the complex compounds
with (2-hydroxy-4-methoxy-phenyl)-phenyl-methanone.
Fig. 6 The X-rays diffractograms of the complex compounds [Cr(L)2(urea)2]Cl,
[Fe(L)2(urea)2]Cl and [Zr2(L)2(urea)4Cl2]Cl4
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FOCA et al.: Cr(III), Fe(III) AND Zr(IV) COMPLEXES
The diffractograms were indexed by means of the TREOR software [22], the re-
sults being presented in Table 5. The data indicate that the reactions between the
above mentioned metallic ions and the ligand L1 occurred with the generation of the
complex compounds. One can notice that these complex combinations crystallize in
the orthorhombic and monoclinic systems.
Proposed structures for the obtained complexes
As it has already been shown, the newly synthesized compounds were analysed by a
series of methods, including the chemical and physico-chemical analyses. At the
same time, it was analysed the behaviour of these compounds in the reaction with sil-
ver nitrate. Based on the obtained data, we have proposed the following structures for
the hexacoordinated complexes of the Cr3+, Fe3+ and Zr4+ ions with L1 (Fig. 7).
Fig. 7 The hexacoordinated structures of the synthesized complexes
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