The study of new zinc(II) aliphatic carboxylate complex compounds by methods of thermal analysis

Article abstract of DOI:10.1023/A:1019910412072

Four new complex compounds were prepared by the reaction of zinc bromobutyrate and organic ligands. The general formula of the synthetized complex compounds are (2-Brbut)₂Zn·L and (4-Brbut)₂Zn·L₂·nH₂O (but=butyr

Full text of DOI:10.1023/A:1019910412072

Journal of Thermal Analysis and Calorimetry, Vol. 69 (2002) 245–253
THE STUDY OF NEW ZINC(II) ALIPHATIC
CARBOXYLATE COMPLEX COMPOUNDS BY
METHODS OF THERMAL ANALYSIS
1
1*
2
E. Andogová , K. Györyová and F. A. Nour El-Dien
1
Department of Inorganic Chemistry, P. J. Šafárik University, Moyzesova 11, 041 54 Košice,
Slovak Republic
Chemistry Department, Faculty of Science, Cairo University Giza, A. R. Egypt
2
Abstract
Four new complex compounds were prepared by the reaction of zinc bromobutyrate and organic lig-
ands. The general formula of the synthetized complex compounds are (2-Brbut)
2
Zn·L and
(
4-Brbut) Zn·L ·nH O (but=butyrate, L=theobromine (tbr), theophylline (tph), methyl-3-pyridyl
2
2
2
carbamate (mpc), n=0–1). The compounds were characterized by chemical analysis and IR spectros-
copy. The thermal behaviour of the zinc(II) complexes was studied by thermal analysis. Thermal de-
composition in the case of hydrated compounds starts with the release of water molecules. Then
molecules of organic ligands and the bromobutyrate anion are released and decomposed.
3 2 2 2 2
CH CH CH=O, CO, CH =CHCH=O, CH O and ZnBr were found as gaseous products of thermal
decomposition during heating up to 700°C. IR, mass spectroscopy, X-ray powder diffraction and
chemical analysis were used for the determination of solid and gaseous intermediates and products
of the thermal decomposition.
Keywords: methyl-3-pyridyl carbamate, theobromine, theophylline, thermal analysis, zinc(II)
carboxylates
Introduction
Zinc is one of the most important trace elements. It is essential for all the living sys-
tems, even for microorganisms. There are about 300 metalloenzymes, where zinc ion
is presented in their active site or it plays a structural role [1, 2]. While zinc is a struc-
tural and catalytic co-factor of many metalloproteins, its deficit causes metabolism
defects and growth inhibition in microorganisms [3]. On the other hand, zinc also has
antimicrobial properties. This microelement inhibits the growth of Escherichea coli,
Streptococcus faecalis, Klebsiella pneumoniae, Staphylococcus aureus and some soil
bacteria [4, 5]. That is the reason why zinc(II) compounds are considered to have
pharmaceutical effects. For example: zinc(II) picolinate Zn(pic) and zinc(II)
2
asparate Zn(asp) are effective for the treatment of the diseases caused by the Herpes
2
*
Author for correspondence: E-mail: gyoryova@kosice.upjs.sk
1
418–2874/2002/ $ 5.00
Akadémiai Kiadó, Budapest
©
2002 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

2
46
ANDOGOVA et al.: NEW ZINC(II) COMPLEX COMPOUNDS
simplex virus. The zinc(II) complexes with 8-hydroxyquinoline and salicylic acid as
well as cobalt(II) and zinc(II) complexes with indane-1, 3-dione-2-imine-N-
CH COOH have antimicrobial activities against Escherichea coli, Proteus mirabilis,
2
Staphylococcus aureus and Streptococcus faecalis. Zinc(II) complexes with
porphyrine, 2-(3-benzoylphenyl)propionate and pyrithione have biological properties
used in the treatment of skin disseases. Some of zinc(II) chelate macrocyclic com-
pounds are very important as lipophilic carriers for anti-HIV substances [6].
Until now, we have developed synthesis of some zinc(II) aliphatic carboxylates
with N- and O-donor ligands. We have studied spectral, thermal properties and also
the crystal structures of some zinc(II) formates, acetates, propionates and their
halogenoderivatives [7–16]. A few of our complex compunds with papaverine and
phenazone were tested against two bacterial species Staphylococcus aureus and
Escherichia coli and a specie of fungi Candida albicans. It was shown that these
compounds had bactericidal activity [17] .
The present paper is dealing with the synthesis and the spectral and thermal be-
haviour of new zinc(II) halogenobutyrates with theobromine, theophylline and
methyl-3-pyridylcarbamate which are potentially biologically active substances.
Experimental
Materials
The following A.R. grade chemicals were used: Zn(OH) (freshly prepared from
2
ZnCl and NaOH – Lachema Neratovice), 2-BrbutCOOH 97, 4-BrbutCOOH 98%
2
(
Aldrich), theobromine, theophylline, methyl-3-pyridyl carbamate (Merck).
Synthesis of the compounds
The synthesis can be expressed by the following equation:
2
RCOOH+Zn(OH) ®(RCOO) Zn+2H O
2 2 2
(
RCOO) Zn+nL®(RCOO) Zn·nL
2 2
where R=(2-Brbut)-, (4-Brbut)-, n=1–2
Preparation of (2-Brbut) Zn·tbr (I)
2
3
Zinc(II) 2-bromobutyrate was prepared by neutralization of 0.77 cm 97% 2-bromo-
butyric acid (0.00719 mol) and 0.35 g Zn(OH) (0.00352 mol). The water solution of
2
0
2
.62 g theobromine (0.00344 mol) was added to the water solution of zinc(II)
-bromobutyrate, stirring continously. After 30 min, the compound was filtered,
evaporated and left to stand. Yellow products (molecular mass: 578.67) precipitated
within several days. The compound is soluble in water, methanol, ethanol and insolu-
ble in diethylether and benzene. The yield of the reaction is 42%.
J. Therm. Anal. Cal., 69, 2002

ANDOGOVA et al.: NEW ZINC(II) COMPLEX COMPOUNDS
247
Preparation of (2-Brbut) Zn·tph (II)
2
3
0
.77 cm 97% 2-bromobutyric acid (0.00719 mol) was dissolved in water and added
to a water suspension of 0.35 g Zn(OH) (0.00352 mol) with continual stirring. The
2
water solution of 0.62 g theophylline (0.00344 mol) was added to the reaction mix-
ture of zinc(II) 2-bromobutyrate. The solution was filtered, evaporated and left to
stand at room temperature. A yellow product (molecular mass: 578.67) crystallized
after several days. The compound is soluble in water, methanol and insoluble in
diethylether. The reaction yield is 38%.
Preparation of (4-Brbut) Zn·tbr ·H O (III)
2
2
2
0
.89 g 98% 4-bromobutyric acid (0.00533 mol) was neutralized with 0.26 g Zn(OH)2
0.00262 mol) under continual stirring and zinc(II) 4-bromobutyrate was formed. The
water solution of 0.93 g theobromine (0.00936 mol) was added to the solution of zinc(II)
-bromobutyrate. After 30 min the reaction mixture was filtered, evaporated and left to
(
4
stand. Within a few days a yellow product precipitated (molecular mass: 776.86).
The compound is soluble in water and methanol and insoluble in diethylether.
The reaction yield is 45%.
Preparation of (4-Brbut)
2
Zn·mpc
(IV)
2
0
0
.49 g 98% 4-bromobutyric acid (0.00293 mol) was added to methanolic suspension of
.14 g Zn(OH) (0.00141 mol). After forming zinc organic salt, 0.87 g methyl-3-pyridyl
2
carbamate (0.00572 mol) dissolved in hot methanol, was added to the reaction mixture
and refluxed for 4 h. The solution was filtered and left to stand at room temperature. After
a few days white crystalls (molecular mass: 701.70) precipitated. The compound is solu-
ble in hot methanol. The reaction yield is 55%.
Characterization
The content of zinc was determined complexometrically by using Complexone III as
a reagent and Eriochrome black T as an indicator.
Infrared spectra were recorded with Specord IR M–80 spectrophotometer in the
–
1
region 4000–400 cm using KBr pellets (5 mg/500 mg KBr) and gaseous cuvette
technique.
The thermal decomposition (TG/DTG, DTA) was studied in air atmosphere in
–
1
Pt crucibles (heating rate 9°C min , 100 mg sample) under dynamic conditions on
Derivatograph MOM OD 102 (Budapest, Hungary) and Netzsch STA 409 thermo-
–
1
analyser (heating rate 9°C min , 3 mg sample).
Gaseous products were determined by IR spectra, methods of qualitative and
quantitative chemical analysis and by Mass spectrometer MS 5988 and QMG 420
(
Balzers GmbH). Solid intermediate products of the thermal decomposition were an-
alyzed by X-ray powder diffraction analysis with Micrometa (Chirana CSFR).
J. Therm. Anal. Cal., 69, 2002

2
48
ANDOGOVA et al.: NEW ZINC(II) COMPLEX COMPOUNDS
Results and discussion
The prepared complexes (2-Brbut) Zn·tbr (I), (2-Brbut) Zn·tph (II),
2
2
(
4-Brbut) Zn·tbr ·H O (III) are yellow and the complex (4-Brbut) Zn·mpc (IV) is
2
2
2
2
2
white. They are all stable in air. The experimental results of chemical analysis are in
good accordance with theoretical ones.
IR spectroscopy study
The characteristic absorption bands of IR spectra used for the identification of
synthetized compounds are presented in Table 1. The observed absorption bands are
adjusted in accordance with literature data [18].
–
1
Table 1 Characteristic absorption bands (n/cm ) in infrared spectra
Assignment
(I)
–
(II)
–
(III)
3400m
2960m
1650s
(IV)
–
n(O–H)H O
2
n(C–H)met
n(C=O)
2970w
1680s
1640m
–
2970w
1680s
1640m
–
2975m
1726s
–
n(C=N)pyrimidine
1610m
1600m
1610s
d(O–H)H O
–
2
–
n
n
as(COO )
1600s
1410s
190
1600s
1400s
200
1557s
1300s
257
–
–
a
(COO )
1420s
DnCOO
190
n(C=C)pyrimidine
n(C–C)pyrimidine
1550m
940m, 850w
680s
1560m
910m, 810w
650s
1560m
920m, 860w
680s
–
–
d(COO )
710s
697m
n(C–Br)
650m
610m
650m
s – strong, m – medium, w – weak; (I): (2-Brbut)
2 2
Zn×tbr, (II): (2-Brbut) Zn×tph,
(
III): (4-Brbut) Zn×tbr ×H O, (IV): (4-Br but) Zn×mpc
2
2
2
2
2
The symmetric stretching vibration of C=O group of purine ring in methyl deriva-
-
1
tives of xantines (theobromine, theophylline) (I, II, III) (Table 1) appears at 1680 cm in
–
1
spectra of compounds (I) and (II), and at 1650 cm in compound (III). The stretching vi-
–
1
bration (C=O) of C=O group of methyl-3-pyridyl carbamate occurs at 1726 cm for com-
pound (IV). The experimental values agree with data in literature [18].
–
The symmetric stretching vibration of the COO group for compounds (I)
–
1
and (II) occurs at 1600, compound (III) at 1610 and compound (IV) at 1557 cm .
–
Symmetric stretching vibration n (COO ) is observed at 1410 for (I), at 1400 for (II),
s
–
1
–
at 1420 for (III) and at 1300 cm for (IV). The analysis of COO group band frequen-
cies allowed the determination of DnCOO=n (COO )–n (COO ) whose magnitude has
–
–
as
s
been used as a criterion of the carboxylate binding with metal ions [19]. Calculated
J. Therm. Anal. Cal., 69, 2002

ANDOGOVA et al.: NEW ZINC(II) COMPLEX COMPOUNDS
249
–
1
from the IR spectra, values of DnCOO are in the range 257–190 cm for the com-
plexes (I)–(IV) and they are in good accordance with literature data for unidentately
bonded carboxylate structures [19].
The presence of the crystal water in the compound (III) is demonstrated by a
–
1
–1
stretching vibration at 3400 cm and by a bending vibration d(O–H) at 1600 cm .
Other characteristic absorption bands of the prepared complex compounds are un-
changed in comparison with basic zinc compounds and free organic ligands which
agrees with literature data [18].
Thermal behaviour
(
2-Brbut) Zn·tbr (I)
2
This complex is stable up to 60°C (Fig. 1). Above this temperature the sample loses
one molecule of theobromine, two molecules of propylaldehyde and two molecules
–
1
of carbon monooxide (exp. 351.7, theor. 353.27 mg mmol ) by an endothermic effect
on the DTA curve at 80 and 290°C. The formation and release of zinc bromide (exp.
–
1
2
26.8, theor. 225.4 mg mmol ) occurs above 500°C. The following reaction is pro-
posed for the thermal decomposition:
(
CH CH CHBrCOO) Zn·tbr ® tbr+2CH CH CHO+2CO+ZnBr
3 2 2 3 2 2
2
Fig. 1 TG, DTG and DTA curves of (2-Brbut) Zn×tbr
J. Therm. Anal. Cal., 69, 2002

2
50
ANDOGOVA et al.: NEW ZINC(II) COMPLEX COMPOUNDS
(
2-Brbut) Zn×tph (II)
2
This complex is stable up to 60°C (Fig. 2). The release of theophylline (exp.
–
1
1
81.8, theor. 180.17 mg mmol ) occurs above this temperature with an endothermic
2
Fig. 2 TG, DTG and DTA curves of (2-Brbut) Zn×tph
2 2 2
Fig. 3 TG, DTG and DTA curves of (4-Brbut) Zn×tbr ×H O
J. Therm. Anal. Cal., 69, 2002

ANDOGOVA et al.: NEW ZINC(II) COMPLEX COMPOUNDS
251
effect in the DTA curve at 220°C. The next step of the thermal decomposition is the
release of two molecules of propylaldehyde and two molecules of carbon monooxide
–
1
(
3
exp. 172.5, theor. 173.1 mg mmol ) with an exothermic effect at temperature range
50–400 with a maximum at 390°C. At higher temperatures zinc bromide is formed
–
1
and released (exp. 222.5, theor. 225.4 mg mmol ). The following reaction is pro-
posed for the thermal decomposition:
(
CH CH CHBrCOO) Zn×tph®tph+2CH CH CHO+2CO+ZnBr
3 2 2 3 2 2
(
4-Brbut) Zn×tbr ×H O (III)
2 2 2
This compound is stable up to 70°C (Fig. 3). Above this temperature one molecule of
–
1
water is released (exp. 18.6, theor. 18.02 mg mmol ) with an endothermic effect in
the DTA curve at 80°C. It is followed by the release of two molecules of
theobromine, two molecules of acrylaldehyde and two molecules of formaldehyde
–
1
(
exp. 531.5, theor. 533.44 mg mmol ). It is demonstrated on the DTA curve at 230°C
by an endothermic effect and in temperature range 410–440 by an exothermic effect
with a maximum at 420°C. The last product of thermal decomposition zinc bromide
–
1
(
exp. 226.7, theor. 225.4 mg mmol ) is formed and released above this temperature.
The following reaction is proposed for the decomposition process:
(
BrCH CH CH COO) Zn×tbr ×H O®H O+2tbr+2CH =CHCHO+2CH O+ZnBr
2 2 2 2 2 2 2 2 2 2
2 2
Fig. 4 TG, DTG and DTA curves of (4-Brbut) Zn×mpc
J. Therm. Anal. Cal., 69, 2002

2
52
ANDOGOVA et al.: NEW ZINC(II) COMPLEX COMPOUNDS
(
4-Brbut) Zn×mpc (IV)
2 2
This complex is stable up to 140°C (Fig. 4). Methyl-3-pyridyl carbamate is released
above this temperature with an endothermic peak at 220°C (exp.
–
1
3
07.7, theor. 304.3 mg mmol ). Methyl-3-pyridyl carbamate was detected by mass
spectrometry (m/z=152) as is demonstrated in Fig. 5. Above this temperature two
–
1
molecules of formaldehyde are obtained (exp. 61.5, theor. 60.0 mg mmol ). The final
step is the release of two molecules of acrylaldehyde and ZnBr (exp. 335.7, theor.
2
–
1
3
tion:
37.4 mg mmol ). The following reaction is proposed for the thermal decomposi-
(
BrCH CH CH COO) Zn×mpc ® 2mpc+2CH O+2CH =CHCHO+ZnBr
2
2
2
2
2
2
2
2
Fig. 5 Mass spectrum of (4-Brbut)
2
Zn×mpc
2
heated to 220°C
Conclusions
The thermal behaviour of the synthetized compounds depends on the character of or-
ganic ligand and on the position of the bromine atom. Thermal decomposition of the
hydrated compound begins with the release of a water molecule above 70°C. After
dehydration the organic ligands are released. This is followed by pyrolysis of the
carboxylate anion. In the case of 2-bromobutyrates the volatile products are
CH CH CH=O, CO, ZnBr and in the case of 4-bromobutyrates they are
3
2
2
J. Therm. Anal. Cal., 69, 2002

ANDOGOVA et al.: NEW ZINC(II) COMPLEX COMPOUNDS
253
CH =CHCH=O, CH O, ZnBr . The most stable of our new synthetized compounds
2
2
2
are those with theophylline and methyl-3-pyridyl carbamate:
(
2-Brbut) Zn×tph=(4-Brbut) Zn×mpc >(4-Brbut) Zn×tbr ×H O=(2-Brbut) Zn×tbr
2
2
2
2
2
2
2
(
II)
(IV)
220 endo
(III)
80 endo
(I)
DTA: 220 endo
=
>
=
80 endo/°C
The mechanism and products of thermal decomposition of the newly
synthetized zinc(II) bromobutyrates (I, II, III, IV) correspond with the thermal de-
composition of previously studied zinc(II) complexes [12, 15]. The only differences
were in the initial temperature of the thermal decomposition depending on the type of
organic ligand in complex compound.
*
* *
This work was supported by the Slovak Ministry of Education Grant No. 1/9247/02. This financial
support is gratefully acknowledged.
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