Iron, nickel and zinc malates coordination compounds synthesis, characterization and thermal behaviour

Article abstract of DOI:10.1023/A:1023948526145

The coordinations compounds (NH₄)[Fe(C₄H₄O₅)(OH)₂] ·0.5H₂O,[Ni(C₄H₄ O₅)]·3H₂O and [Zn(C₄H₄ O₅)]·5H₂O were synthesized by a precipitation method and characterized by chemical analysis, spectral (IR, UV-VIS) and magnetical investigations. In the range 50-600°C stepped thermal decompositions occur with formation of anhydrous malates, malonates, oxoacetates (iron and nickel compounds) and hydroxocarbonate (Zn compound) as intermediates observed by FT-IR spectroscopy. α-Fe₂ O₃, NiO and ZnO constitute the final decomposition products.

Full text of DOI:10.1023/A:1023948526145

Journal of Thermal Analysis and Calorimetry, Vol. 72 (2003) 281–288
IRON, NICKEL AND ZINC MALATES COORDINATION
COMPOUNDS
Synthesis, characterization and thermal behaviour
1
L. Patron , O. Carp , I. Mindru , G. Marinescu and E. Segal
1*
1
1
2
1
Institute of Physical Chemistry ‘I. G. Murgulescu’, Splaiul Independentei no. 202, sector 6,
Bucharest, Romania
Department of Physical Chemistry, Faculty of Chemistry, University of Bucharest,
2
B-dul Elisabeta no. 4–12, sector 4, Bucharest, Romania
Abstract
The coordinations compounds (NH )[Fe(C
4
4
H
4
O
5
)(OH)
2
]⋅0.5H
2
O, [Ni(C
4
H
4
O
5
)]⋅3H
2
O and
[
Zn(C )]⋅5H O were synthesized by a precipitation method and characterized by chemical anal-
4
H
4
O
5
2
ysis, spectral (IR, UV-VIS) and magnetical investigations. In the range 50–600°C stepped thermal
decompositions occur with formation of anhydrous malates, malonates, oxoacetates (iron and nickel
compounds) and hydroxocarbonate (Zn compound) as intermediates observed by FT-IR spectros-
2 3
copy. α-Fe O , NiO and ZnO constitute the final decomposition products.
Keywords: iron-, nickel-, zinc-malate coordination compound, non-isothermal analysis
Introduction
Due to their capacity in chelating metallic ions and low decomposition temperatures
with evolving nontoxic compounds (CO, CO , H O), ligands belonging to carboxylic
2
2
acids class are suited for obtaining precursor systems of transition metal oxides [1–8].
Although detailed investigations has been made concerning the obtaining of the sim-
ple/mixed oxides through thermal decomposition of formates, acetates, tartrates pre-
cursors, a similar interest for complex malates is relative lacking [9–12].
The paper reports the synthesis, characterization and thermal behaviour of Fe,
Ni and Zn malates coordination compounds. From practical point of view the under-
taken investigations permit to determine a new route of simple oxide synthesis. From
the theoretical one, it represents a first but necessary step in elucidation the solid state
pathway of mixed oxides formation.
*
Author for correspondence: E-mail: carp@apia.ro
1
388–6150/2003/ $ 20.00
Akadémiai Kiadó, Budapest
©
2003 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

2
82
PATRON et al.: IRON, NICKEL AND ZINC MALATES
Experimental
Precursors preparation
As starting materials, Fe(NO ) ⋅9H O, Ni(NO ) ⋅6H O, Zn(CH COO) and malic
3
3
2
3 2
2
3
2
acid of reagent grade quality were used. The compounds and some of their thermal
decomposition intermediates were characterized by elemental chemical analysis: the
metal content was determined by atomic absorption technique; the carbon, nitrogen
and hydrogen content were obtained by microcombustion technique.
(
NH )[Fe(C H O )(OH) ]⋅0.5H O and [Ni(C H O )]⋅3H O – metallic salts
4
4
4
5
2
2
4
4
5
2
(
malic acid (6 mmol (0.804 g), 4 mmol (0.536 g)) in molar ratios Fe : malic acid=1:3
2 mmol (0.808 g) of Fe(NO ) ⋅9H O and 2 mmol (0.58 g) of Ni(NO ) ⋅6H O) and
3
3
2
3 2
2
3+
2
+
and Ni : malic acid=1:2, were dissolved in a minimum amount of distilled water
50 mL) and mixed. Subsequently, ethanol was added under stirring till the reaction
medium is 1:1=aqueous/ethanolic. For a complete precipitation, the pH was adjusted
(
to 4.5–5 with a NH OH 25% : ethanol 1:1 solution. Yellow brown iron containing
4
compound and pale green containing zinc one were obtained. Afterward, the precipi-
tates were aged for 24 h at 4°C. Next, they were filtered, washed with ethanol and
vacuum dried. FeC H NO calcd./found Fe%: 22.4/21.78; C%: 19.28/19.43; H%:
4
11
7.5
4
1
3
.42/4.50; N%: 5.62/5.74. NiC H O calcd./found Ni%: 20.89/21.40; C%:
4 14 10
7.10/17.00; H%: 4.98/5.08. NiC H O (reaction intermediate) calcd./found Ni%:
3
2
4
6.50/37.40; C%: 22.41/20.90; H%: 1.24/0.85.
Zn(C H O )]⋅5H O – to the reaction mixture prepared by mixing stoichiometric
[
quantities of aqueous solutions of 2 mmol Zn(CH COO) (0.438 g) and 4 mmol malic
4
4
5
2
3
2
2+
acid (0.536 g), molar ratio Zn : malic acid=1:2, ethanol was added under stirring till the
reaction medium is 1:1 aqueous/ethanolic. A white compound was formed. After 24 h at
4°C aging, the compound was filtered, washed with ethanol and dried in vacuum.
ZnC H O calcd./found Zn%: 24.27/23.89; C%: 17.81/18.04; H%: 4.45/4.55.
4
12
9
ZnC H O (reaction intermediate) calcd./found Zn%: 39.06/40.19; C%: 21.50/19.47;
3
2
4
H%: 1.19/0.82.
Characterization
–
1
The UV-VIS reflectance spectra (11 000–54 000 cm ) were recorded with a
JASCO V550 spectrophotometer using MgO as standard. IR spectra
–
400–4000 cm ) were recorded with a BIO-RAD FTIR 125 type device, in KBr pel-
1
(
lets. The thermal measurements were performed using a Q–1500 D derivatograph in a
static air atmosphere, with α-Al O as the reference compound, at a heating rate of
2
3
–
K min . The magnetic susceptibility at room temperature were determined using a
1
5
Faraday balance with Ni as calibrant.
J. Therm. Anal. Cal., 72, 2003

PATRON et al.: IRON, NICKEL AND ZINC MALATES
283
Results and discussion
Synthesis and physico-chemical characterization of precursors
2+
3+
From the system M /or M -malic acid the following coordination compounds were iso-
lated: (NH )[Fe(C H O )(OH) ]⋅0.5H O; [Ni(C H O )]⋅5H O; [Zn(C H O )]⋅4H O.
4
4
4
5
2
2
4
4
5
2
4
4
5
2
Analyzing the three IR spectra (Figs 1–3 (a)) the following features may be
pointed out:
–
1
•
the broad bands in the region 3600–2700 cm are due to the symmetric and
asymmetric stretching frequencies of the weakly bonded crystallization water
molecules and hydroxyl groups;
–
1
•
•
the water presence is confirmed also by the shoulder at ∼ 1650 cm character-
istic for its bending mode;
–
the free vibration of C=O from 1730 cm is split into two very strong bands
1
characteristic for coordinated carboxylic group, respective ν vibration
as(OCO)
–
1
–1
one at 1401–1382 cm ;
at 1590–1550 cm and ν
s(OCO)
–1
•
•
in the range 1092–1083 cm a medium absorption band assigned to the stretch-
ing vibration of alcoholic hydroxyl is also present [13]. The shift of ν(C–OH) to-
ward lower frequencies indicates a possible coordination of this group to the me-
tallic ions;
the bands which appear in the range 563–500 cm are assigned to M–O
stretching vibrations.
–
1
Fig. 1 IR spectra of the (NH
its solid reaction
4
)[Fe(C
4
H
4
O
5
)(OH)
2
2
]⋅0.5H O coordination compound and
On the basis of spectroscopic criteria, the magnitude of separation ∆ν=νasym–νsym
may represent an indication of the different coordination modes of the carboxylate ions.
–1
So, ∆ν values included in the range 140–160 cm , lower than those observed for ionic
–1
compounds (∆Na (C H O )=180 cm ), suggest a bridging bidentate bonding. On the
2
4
4
5
J. Therm. Anal. Cal., 72, 2003

2
84
PATRON et al.: IRON, NICKEL AND ZINC MALATES
Fig. 2 IR spectra of the [Ni(C
tion decomposition intermediates
4
H
4
O
5 2
)]⋅5H O coordination compound and its solid reac-
Fig. 3 IR spectra of the [Zn(C
tion decomposition intermediates
4
H
4
O
5
2
)]⋅4H O coordination compound and its solid reac-
–1
other hand, values of ∆ν>180 cm are characteristic for unidentate coordination com-
pounds.
Concerning our three compounds the following conclusions may be marked:
–
1
–
the ∆ν value of 190 cm observed for zinc coordination compound suggests a
monodentate bonding of the carboxylate group. Such a linkage conduct to a polymer
structure of the compound similar with other transitional metal carboxylate compounds;
J. Therm. Anal. Cal., 72, 2003

PATRON et al.: IRON, NICKEL AND ZINC MALATES
285
–
the splitting into two components of the νsymm vibration detected for nickel co-
–1
ordination compound, leading to ∆ν =163 and ∆ν =189 cm values, suggest two dif-
ferent bonding of COO group: a bidentate one (corresponding to ∆ν value) and a
1
2
–
1
monodentate one (corresponding to ∆ν value);
2
–
for iron coordination compound the splitting of the band localized in
1
–
–1
1
440–1380 cm range is due to the bridging bidentate bond (∆ν=168 cm ) and the
presence of NH ion (∼ 1430 cm ).
+
–1
4
At room temperature, the effective magnetic moments of nickel and iron com-
pound was found to be µ=3.39 and µ=6.12 BM in agreement with an octahedral con-
2
+
3+
figuration of Ni and Fe high spin [14]. The value obtained for nickel compound
which is higher than that corresponding to the spin value (µ=2.83 BM) could be ex-
plained through the coupling spin–orbit, which is also found in the slight splitting in
the electron spectrum of band ν .
2
The octahedral environments of the two metallic ions are evidenced also by
UV-VIS reflectance investigations.
Thermal decompositions of the three coordination compounds
A stepped thermal decompositions of the coordination compounds occur in the range
5
0–600°C. In order to determine the stages involved in the thermal processes, the de-
composition intermediates were identified by means of elemental chemical analysis
and IR spectroscopy.
(NH
4
)[Fe(C
4
H O
4 5
)(OH)
]⋅0.5H O coordination compound
2 2
The results of thermal analysis revealed five distinct steps of mass loss (Fig. 4). The
experimental total mass loss recorded by TG measurements is 67.82% in comparison
with the theoretical value of 67.91% assuming the solid residue to be α-Fe O .
2
3
Fig. 4 Thermoanalytical curves of (NH
4
)[Fe(C
4
H
4
O
5
)(OH)
pound (initial mass 51.09 mg, heating rate 5°C min , static air)
2
2
]⋅0.5H O coordination com-
–
1
J. Therm. Anal. Cal., 72, 2003

2
86
PATRON et al.: IRON, NICKEL AND ZINC MALATES
The first step (42–138°C) represents the endothermic evolving of 0.5 water and one
NH OH molecules (calcd./found 17.99/17.68%). The anhydrous malate compound is
converted into a malonic one (138–178°C) due to the anion degradation (calcd./found
4
12.76/12.05%). The next decomposition step (178–225°C) assigned to the formation of
an iron oxoacetate FeO(CH COO) (calcd./found 17.89/18.08%) which decomposes fur-
3
ther (225–331°C), leading to a mixture of iron oxide and oxohydroxides. Subsequently, a
well-defined decomposition step (401–448°C), assigned to water releasing from oxo-
hydroxides generated in the reaction medium occurs.
In the IR spectra of the decomposition intermediates, the presence of malonates
–
Fig. 1 b) is identified by the disappearance of the band assigned to HO group
(
(
–
1040 cm ), the formation of an acetate compound by the bands characteristic to
1
–
1
–1
–
CH group at 1100–1000 cm and shoulder at ∼ 1360 cm (Fig. 1 c) [15]. At 350°C
3
the IR spectrum (Fig. 1 d) shows a mixture of lepidocrite (γ-FeOOH, band at
–
1
–1
–1
1
(
022 cm , shoulder at 750 cm ), maghemite (shoulder at ∼ 600 cm ) and α-Fe O
2
3
–1 –1
bands at 543 and 470 cm ). The band evidenced at 2362 cm for the intermediates
–
1
obtained at 200 and 350 cm is due to the ν(CO ), suggesting its presence in a
2
trapped state within the solid matrix.
[
Ni(C H O )]⋅5H O coordination compound
4
4
5
2
For this compound five decomposition mass losses followed by a mass gain are evi-
denced (Fig. 5). The experimental and theoretical mass losses assuming NiO forma-
tion are close (calcd./found 73.40/74.20%).
Fig. 5 Thermoanalytical curves of [Ni(C
4
H
4
O
5
2
)]⋅5H O coordination compound (initial
–
1
mass 49.56 mg, heating rate 5°C min , static air)
The decomposition starts with two endothermic processes (70–298°C) which
can be attributed to water evolving. The first one (70–190°C) represents the elimina-
tion of three crystallization water molecules (calcd./found 19.23/20.23%), while the
J. Therm. Anal. Cal., 72, 2003

PATRON et al.: IRON, NICKEL AND ZINC MALATES
287
second which occur at higher temperatures (190–298°C), of two water molecules co-
ordinated bonded to the metallic ion (calcd./found 12.83/13.40%). The next step
(
298–338°C) is assigned to the oxidative fragmentation of the malate ion with forma-
tion of a malonate intermediate (calcd./found 10.69/10.02%). The malonate interme-
diate is identified by chemical analysis and by IR investigations through the disap-
–
pearance of the bands assigned to OH group (1032 cm , Fig. 2 b).
1
On further heating (338–425°C) the malonate intermediate decomposition occurs
via an oxoacetate intermediate (338–360°C, calcd./found 17.89/18.08%, Fig. 2 c). The
–1
–1
shoulder at ∼ 1300 cm and the weak band at ∼ 1050 cm are characteristic for CH
group.
A mass gain (1.26%) may be detected at the end of thermal decomposition
425–445°C). It is known that NiO promotes oxidation of carbon containing materi-
3
(
als. Thus, it is reasonable to suppose that the carbonaceous moieties are oxidized on
the NiO surface, with a concomitant reduction NiO→Ni. Since the process is con-
ducted in air, the metal undergoes a rapid reoxidation. NiO is identified by the ab-
–
1
sorption at 495 and 435 cm (Fig. 2 d).
[
ZnC H O ]⋅4H O coordination compound
4
4
5
2
The coordination compound undergoes a stepwise decomposition in four distinct
stages of mass loss (Fig. 6). The observed mass loss (67.12%) is in good agreement
with the calculated one (67.27%) considering as residue ZnO.
Fig. 6 Thermoanalytical curves of [Zn(C
4
H
4
O
5
2
)]⋅4H O coordination compound (initial
–
1
mass 49.13 mg, heating rate 5°C min , static air)
The decomposition starts with two endothermic steps (55–275°C) correspond-
ing to release of two (calcd./found 13.00/13.98%) and respectively one (calcd./found
7.16./7.88%) water molecules. The next decomposition step (275–350°C) represent
the oxidative fragmentation of malate anion with formation of the malonic intermedi-
J. Therm. Anal. Cal., 72, 2003

2
88
PATRON et al.: IRON, NICKEL AND ZINC MALATES
ate (calcd./found 11.93/11.42%), identified by chemical analysis and IR spectros-
copy (Fig. 3 curve b). On further heating, this compound decompose with formation
of hydrozincite [Zn (CO ) ⋅6(OH)]. At this stage the absorptions at 1380, 877 and
5
3 2
–
1
2–
–1
675 cm indicates de formation of CO , while the weak band from 3710 cm and
–
the shoulder from 1737 cm evidence the presence of HO group (Fig. 3 c).
3
–
1
Solid state mechanism
By means of thermoanalytical, chemical analysis and IR measurements the following
thermal decomposition steps of the coordination compounds compound may be as-
sumed:
4
2–138°C
(
NH )[Fe(ma)(OH) ]⋅5H O   → [Fe(ma)(OH)]
4
2
2
1
38–178°C
178–225°C

 → [Fe(mal)(OH]   → FeO(CH COO)
3
2

25–331°C
401–448°C
 → mixture γ-FeOOH, γ-Fe
O
and α-Fe
O
  → 0.5α-Fe
O
(1)
2
3
2
3
2
3
7
0–190°C
190–298°C
298–338°C
[
Ni(ma)]⋅5H O   → [Ni(ma)]⋅2H O   → [Ni(ma)]   → [Ni(mal)]
2
2
3
38–360°C
360–425°C
425–445°C

 → NiO0.5(CH
3
COO)   → mixture NiO and Ni   → NiO
(2)
(3)
5
5–180°C
180–275°C
275–350°C
[
Zn(ma)]⋅4H O   → [Zn(ma)]⋅H O   → [Zn(ma)]   → [Zn(mal)]
2
2
3

50–374°C
374–471°C
 → 1/5Zn
(CO ) (OH)   → ZnO
3 2 6
5
where ma, mal represent the dianions of malic and malonic acids.
* *
*
The financial support by MATNANTECH program is gratefully acknowledged.
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1
2
3
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5
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