Thermal analysis of new dimethyltin compounds with glycine and DL-valine

Article abstract of DOI:10.1007/s10973-005-0044-8

The new compounds [(CH₃)₂SnAACl]₂ (AA=glycinate, CH₂(NH₂)COO^-; DL-valinate, (CH₃)₂CHCH(NH₂)COO^-) were prepared and characterized by elemental ana

Full text of DOI:10.1007/s10973-005-0044-8

Journal of Thermal Analysis and Calorimetry, Vol. 79 (2005) 255–258
THERMAL ANALYSIS OF NEW DIMETHYLTIN COMPOUNDS WITH
GLYCINE AND DL-VALINE
R. S. Barbiéri1,2*, A. K. C. Dias2, S. F. da Silva1,2, V. R. Terra3 and E. P. de Lima2
1Faculdade de Minas - FAMINAS, 36880-000 Muriaé, MG, Brazil
2Universidade Vale do Rio Verde - UNINCOR, 37410-000 Três Corações, MG, Brazil
3Centro Federal de Formação Tecnológica - CEFET, 38045-000 Uberaba, MG, Brazil
The new compounds [(CH3)2SnAACl]2 (AA=glycinate, CH2(NH2)COO–; DL-valinate, (CH3)2CHCH(NH2)COO–) were prepared
and characterized by elemental analysis of carbon, hydrogen, nitrogen, chlorine and tin, through their infrared spectra, and by
Mössbauer and 119mSn-NMR spectroscopic studies, and they were examined using TG (DTG) method. The thermal decomposition
mechanisms were similar for both compounds and occurred in one step. TG curves suggested the formation of tin metal, in agree-
ment with the stoichiometry of the related compounds.
Keywords: organotin compounds, thermal decomposition, tin DL-valinate, tin glycinate
Introduction
Shimadzu DSC-50 equipment was used to record
the DSC curves. The experimental conditions were:
25–200°C temperature range, b=10 K min–1 heating
rate, helium purging with a flow rate of 50 mL min–1.
The initial sample masses were 6–8 mg.
Amino acids are potentially polydentate ligands, which
can link to metals, enabling the synthesis of com-
pounds with various structures, for which geometry
and the coordination numbers are governed by the size
of the replacing group and by the degree of branches of
the ligand [1]. It is verified from the literature that a rel-
atively high number of diorganotin compounds with
N-protected amino acids are known. However, the
studies on compounds having the same nature derived
from essential and simpler a-amino acids are scant,
containing only an amino group and a carboxyl group,
except by diglycinatotin(II) [2], trimethyltin(II)
glycinate and alaninate [1] and dimethyltin(IV)
glycinate and b-alaninate compounds [2]. The present
investigation relates to the preparation and character-
ization of two new complexes [(CH3)2SnAACl]2,
The melting points were determined on a FP-2
Mettler system.
The infrared spectra of complexes were recorded
between 5000–275 cm–1, using a Perkin Elmer Para-
gon 1000 spectrophotometer, in CsI pellets.
The X-ray fluorescence characterization of the
residues of the TG analyses was performed by means
of a Rigaku-Geigerflex spectrophotometer.
The elemental analysis for carbon, hydrogen and
nitrogen were carried out using Perkin Elmer 2400CHN
Elemental Analyzer.
Chlorine determination was done by neutron ac-
tivation analysis. The samples were irradiated in the
central tube of a Triga-3 reactor and the measurement
was performed applying a Low Lewel a/b Counting
System Model 2200 Canberra proportional detector,
on the Nuclear Development Technology Center, of
Nuclebrás, in Belo Horizonte-MG, Brazil.
The tin determination has been performed by
atomic absorption by means of a Hitachi Z-8200 spec-
trometer.
where
AA=glycinate,
CH2(NH2)COO–
and
DL-valinate, (CH3)2CHCH(NH2)COO– and the appli-
cation of TG and DSC techniques in dynamic helium
atmosphere.
Experiment
The 119mSn Mössbauer spectra were provided by
a constant acceleration spectrometer equipped at
BaSnO3 source, at 85 K.
The TG curves were recorded using Shimadzu TGA-50
model in the range of 25–700°C at a heating rate
of 20 K min–1 and in a dynamic helium atmosphere with
flow rate of 20 mL min–1. The initial sample masses
were 7–9 mg.
The 119mSn-NMR spectrum was obtained with a
Bruker DRX 400 MHz Avance spectrophotometer,
using D2O.
*
Author for correspondence: barbieri@faminas.edu.br
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2005 Akadémiai Kiadó, Budapest

BARBIÉRI et al.
The complex [(CH3)2SnGlyCl]2 (compound I)
The most representative stretching vibrations
taken from the infrared spectra of I and II are pre-
sented in Table 2. The evaluation of the infrared spec-
tra of glycine and DL-valine allowed to assign the
was synthesized reacting glycine, CH2(NH2)COOH,
and dimethyltin dichloride with 1:1 molar ratio. The
a-amino acid was added to stirred acetonitrile solu-
tions for 2 h. After adding the tin compound, the sys-
tem was further stirred and refluxed over night. The
mixture was then filtered at room temperature and the
obtained solid was washed with dichloromethane and
dried under vacuum.
nCOO values which were in a good agreement with
ass
the literature data [1]. In the infrared spectra of I
and II relatively small shifts for the nCOO values
ass
were verified for the highest region in the spectrum of
the complexes, in relation to the free a-amino acids.
The observed alterations are from 1600 to 1610 cm–1
for glycine in I and from 1595 to 1640 cm–1 for
DL-valine in II, indicating the participation of the
carboxyl of the a-amino acids in the coordination to
the tin [1]. Similar results were obtained for the other
compounds [(CH3)2Sn(AA)2] (AA=glycine, alanine).
The complex [(CH3)2SnValCl]2 (compound II)
was
synthesized
from
DL-valine,
(CH3)2CHCH(NH2)COOH, using similar procedures
which were written for compound I. The obtained
solid was washed with n-heptane and with dichloro-
methane and dried under vacuum.
Complexes I and II were characterized by their
IR spectra, by elementary analysis of carbon, hydro-
gen and tin and by Mössbauer and 119mSn-NMR spec-
troscopic studies.
In the infrared spectra of both complexes the nCOO
ass
values were shifted to 1605 cm–1 for free amino acids
and to 1629 cm–1 for the derivatives [2, 3].
The stretching of N–H may also help to explain the
coordination form of amino acid. Free NH2 groups were
found in the amino acid salts, like in sodium glycinate,
where nNH appeared at 3380 cm–1. Compared to the free
glycine, where the band of the zwitterion form
H3N+–CH2–COO–; appears at nNH=3170 cm–1 [4].
Glycine, in the H2N–CH2–COOH isolated form of
glycine, the experimental value of the N–H stretching
is 3411 cm–1 [4]. Thus, for the complexes with amino
acids which present nNH appear at about 3400 cm–1, the
amino group must be free. If the band is located be-
tween 3100–3300 cm–1, the amino group must be coor-
dinated to the metal [2–8]. For the studied complexes an
Results and discussion
The new complexes [(CH3)2SnGlyCl]2 (compound I)
and [(CH3)2SnValCl]2 (compound II), were both ob-
served using optical microscope. They exhibited
microcrystalline constitution. However, it was not
possible to obtain suitable single crystals to determine
their structures by X-ray crystallography. During sev-
eral attempts to recrystallize them, the complexes un-
derwent decomposition, even under inert atmosphere,
producing crystals of dimethyltin oxide, (CH3)2SnO.
The melting points and the results of elementary
analysis of carbon, hydrogen, nitrogen, chlorine and
tin for I and II are shown in Table 1.
alteration in nCOO from 3170 to 3250 cm–1 for glycine
ass
in I was verified. In case of DL-valine in II a shift
from 3140 to 3120 cm–1 was observed suggesting also
the participation of the NH2 group in the coordination of
the amino acids to the tin [2–8].
Table 1 Melting points and elementary analysis data of the dimethyltin complexes
C/%
H/%
N/%
Cl/%
Sn/%
found3
(calc.)
m.p.1/
°C
Tons
°C
/
2
Molecular mass/
g mol–1
found4
(calc.)
Compound
found
(calc.)
found
(calc.)
found
(calc.)
found
(calc.)
19.17
(18.60)
3.40
(3.90)
5.77
(5.42)
12±2
(13.72)
46.10
(45.95)
45.58
(45.95)
I
516.58
598.73
100–103
138–141
96.4
28.05
(28.08)
5.87
(5.05)
4.72
(4.68)
11±3
(11.84)
40.99
(39.65)
39.54
(39.65)
135.8
II
1Determined on a FP-2 Mettler system; 2Data taken from DSC curves; 3by atom absorption; 4by TG analysis
Table 2 Representative IR stretching data (cm–1) for the dimethyltin complexes
Free ligand
nNH
nCOO
Complexes
Compound
nCOO
nNH
nCH
nSnO
nSnC
nSnN
nSnCl
ass
ass
2930
2970
540
560
I
3170
3140
1600
1595
1610
1640
3250
520
450
485
300
2935
2955
535
550
II
3120
425
295
256
J. Therm. Anal. Cal., 79, 2005

THERMAL ANALYSIS OF NEW DIMETHYLTIN COMPOUNDS
In the 119Sn Mössbauer spectroscopy, a single
quadrupole splitting doublets was indicated, for the
studied compounds, making evidently that I and II pres-
ent only one site around the tin atoms, where the D and
of d isomer shift values, in mm s–1 (I: D=3.87, d=1.55;
II: D=3.79, d=1.49), are consistent with the slightly dis-
torted trans-octahedral tin species [9–11]. The
Mössbauer spectra of compound I is shown in Fig. 1.
Fig. 3 119mSn NMR spectrum of the dimethyltin glycinate
compound I – [(CH3)2SnGlyCl]2 (400 MHz, D2O)
Fig. 1 Mössbauer spectra of compound I – [(CH3)2SnGlyCl]2
(obtained at T=85 K, using a CaSnO3 source at room
temperature)
The presented data allowed the settlement of the
proposed formulations and the structures as they are
shown in Fig. 2.
Fig. 4 TG curves of dimethyltin complexes.
I – [(CH3)2SnGlyCl]2, II – [(CH3)2SnValCl]2
Fig. 2 Proposed structures for dimethyltin
complexes I – [(CH3)2SnGlyCl]2, II – [(CH3)2SnValCl]2
tive, this effect does not cause a decrease in its ther-
mal stability, as it can be observed for diorganotin
DL-mandelate complexes containing methyl and
butyl groups [12]. In both cases, the thermal decom-
position processes occur in one step, with final de-
composition temperatures at 155 and 217°C for com-
pounds I and II, respectively, producing tin metal as
final product proved by X-ray fluorescence.
The higher slope of the TG curve of II suggests
that its decomposition rate is higher than I has indi-
cating that the thermal stability of the compound II is
higher compared to compound I.
For compound I it was possible to obtain the
119mSn-NMR spectrum, in D2O is shown in Fig. 3. The
absorption signal d(119mSn) at –121.5 ppm indicates that
in solution the compound is present in dissociated form,
assuming pentacoordinated geometry [5, 7, 12, 13].
Due to its insolubility for compound II, it was
not possible to record the NMR spectra. The insolu-
bility of II, may be attributed to certain polymeriza-
tion, as observed for diorganotin compounds with
a-hydroxycarboxylic acid [12, 14].
TG curves of the compounds obtained in dy-
namic helium atmosphere, are presented in Fig. 4.
One can notice that the relative thermal stability of
the compounds is significantly different. While the
thermal degradation of the glycinate derivative starts
at 110°C, the DL-valinate starts to decompose
at 158°C. These results indicate that even the higher
hindrance effect in the case of the DL-valinate deriva-
The DSC curves of the compounds are presented
in Fig. 5.
Considering the heat of fusion values (DHfusion
=
–8.45 kJ mol–1 for I and (DHfusion= –22.23 kJ mol–1
for II) it can be concluded that the compounds exist in
dimer forms in solid-state.
J. Therm. Anal. Cal., 79, 2005
257

BARBIÉRI et al.
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Conclusions
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bridging in solid-state. These results are distinct from
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methyltin(II) glycinate and alaninate [1] and di-
methyltin(IV) glycinate and b-alaninate compounds [2]
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Acknowledgements
The authors are grateful to CNPq (Conselho Nacional do
Desenvolvimento Científico e Tecnológico, Brazil) and
FAPEMIG (Fundação de Amparo à Pesquisa do Estado de
Minas Gerais, Brazil) for financial support, and to Prof.
Alessandra Soares for our valuable discussions.
258
J. Therm. Anal. Cal., 79, 2005