Thermochemical parameters and calculations ab-initio of the bisdimethyldithiocarbamate zinc(ii) complex

Article abstract of DOI:10.1007/s10973-005-0055-5

The standard molar enthalpy of formation of crystalline bisdimethyldithiocarbamate zinc(II) complex, Zn[S₂CN(CH ₃)₂]₂ was determined through reaction-solution calorimetry in acetone, at 298 K. Using the standard

Full text of DOI:10.1007/s10973-005-0055-5

Journal of Thermal Analysis and Calorimetry, Vol. 79 (2005) 309–312
THERMOCHEMICAL PARAMETERS AND CALCULATIONS AB-INITIO
OF THE BISDIMETHYLDITHIOCARBAMATE ZINC(II) COMPLEX
1
J. R. Botelho , A. G. Souza , A. D. Gondim , P. F. Athayde-Filho , P. O. Dunstan ,
*
1
1
1
2
3
C. D. Pinheiro , E. Longo and L. H. Carvalho
4
5
1
DQ, CCEN, Universidade Federal da Paraíba, 58059-900 Jo±o Pessoa, Paraíba, Brazil
IQ, Universidades Estaduais de Campinas, 13083-970 Campinas, S±o Paulo, Brazil
DCEN, CFP, Universidade Federal de Campina Grande, 58900-000 Cajazeiras, Paraíba, Brazil
DQ, CMDMC, UFSCar, S±o Carlos, 13565-905 S±o Paulo, Brazil
2
3
4
5
DEMA, CCT, Universidade Federal de Campina Grande, 58000-000, Campina Grande, Paraíba, Brazil
The standard molar enthalpy of formation of crystalline bisdimethyldithiocarbamate zinc(II) complex, Zn[S
determined through reaction–solution calorimetry in acetone, at 298 K. Using the standard molar enthalpy of formation of the
2 3 2 2
CN(CH ) ] was
–1
–1
gaseous chelate, the homolytic (–619.78±8.95 kJ mol ) and heterolytic (–2747.71±8.95 kJ mol ) mean enthalpies of zinc–sulphur
bond dissociation were calculated. The investigation on the electronic structure involved the use of molecule orbital calculations.
Keywords: ab-initio, dimethyldithiocarbamate zinc, thermochemistry
Introduction
methyldithiocarbamate
) ]
3 2 2
zinc(II)
complex
Zn[S CN(CH was synthetized from the direct re-
2
Thermochemical data in the literature, concerning
dithiocarbamates, are essentialy originated from tech-
niques such as: thermogravimetry, differential thermal
analysis, differential scanning calorimetry, chromatog-
raphy in gaseous phase, mass spectrometry and in
smaller extend from solution calorimetry and thermo-
metric titration [1–8].
The thermal properties of some metal dithio-
carbamate complex [3–5, 8] together with the deter-
mination of the standard molar enthalpies of forma-
tion of zinc, cadmium and palladium chelates through
reaction–solution calorimetry were used to estimate
the homolytic and heterolytic metal–sulphur bond
enthalpies. Recently, the kinetic parameters of the
thermal decomposition of zinc(II) dialkyldithio-
carbamate complex was studied [9].
action of ZnCl with dimethylamine and carbon
2
disulphide in acetone.
The microanalyses (C, H, N) were carried out
with a PerkinElmer elemental analyser. Infrared spec-
tra were recorded in KBr pellets using a Bomem model
MB – 102 spectrometer. TG curves were obtained us-
ing Shimadzu model TGA-50 thermobalance, at a
–1
heating rate of 10 K min in a dynamic nitrogen atmo-
–1
sphere with a flow rate of 0.83 mL s . Mass spectra of
the ligand and chelates were obtained using a
Hewlett-Packard model 5988A mass spectrometer,
with an ionization energy of 70 eV at 523 K.
All solution calorimetric determination were
carried out in an LKB 8700-1 isoperibolic precision
calorimeter system as described before [10].
Decomposition of the chelates were determined in a
Shimadzu model DSC-50, Differential Scanning
Molecule orbital calculation was done to simulate
the variation of the electronic structure. Gaussian98
package was used for these calculations.
–
1
Calorimeter; at a heating rate of 10 K m , purged
with dry nitrogen [10, 11].
In this work, we obtained the structural properties
of the bisdimethyldithiocarbamate zinc(II) complex
using calculations ab-initio in level Hartree–Fock–
Roothaan. We have performed all the calculations by
using the Gaussian98 software [12], with effective core
potential and double-x basis set, LanL2DZ [13] on Zn
and 6-31G(*) [14] on H, N, S and C.
Experimental
The ammonium chloride salt, (CH ) NH Cl and
2
3
2
dimethylammonium
(
dimethyldithiocarbamate,
CH ) NH S CN(CH ) were synthesized. Their ele-
3
2
2
2
3 2
mental analyses were in agreement with the data cal-
culated from their chemical formulas. The bisdi-
*
Author for correspondence: rbotelho@openline.com.br
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2005 Akadémiai Kiadó, Budapest

BOTELHO et al.
Results and discussion
The CHN elemental analysis of the complex,
Zn[S CN(CH ) ] are in a good agreement with the cal-
culated results. The main absorptions in the infrared
2
3 2 2
–1
spectra (cm ) are: n(C–S)=973.30, n(C=N)=1522.99
and n(Zn–S)=163.30.
The melting point of the complex is 253.1°C, ob-
tained by DSC. By the comparison of TG and DSC
curves is well visible that the mass loss process starts be-
fore the melting of the chelate, i.e. in its solid-state. The
TG curve indicates that the ligand is released in one
step. For zinc complex, Zn[S CN(CH ) ] , complete
2 3 2 2
mass loss took place in one step between 244–340°C, as
it is shown in the TG/DSC curves (Fig. 1).
2 3 2 2
Fig. 2 Infrared spectra of the Zn[S CN(CH ) ] complex
2 3 2 2
Fig. 1 TG/DSC curves of the Zn[S CN(CH ) ] complex
Results of infrared spectroscopy experiments are
enthalpies. This value for each reagent and product
dissolved in acetone are given in Table 1. A strict
stoichiometric control was maintained, following the
general reaction [5–8]:
–1
presented in Fig. 2. The nCN (1522.99 cm ) band as-
sumes a double-band character, which is reflected in
the appearance of a stretching band shifted to a higher
frequency. The frequency of this band is higher than
the respective ligand’s band has. On the other hand, a
ZnCl
2
(s)+2(CH
) NH S CN(CH ) (s)®
3 2 2 2 3 2
–1
decrease in the frequency of the nCS (973.30 cm )
stretching band is observed and an isolated band
®
Zn(S CN(CH ) ) (s)+
2 3 2 2
0
–1
+
2NH (CH ) Cl(s); D H
(1)
near 1000 cm indicates that the ligand is bonded to
metal in a bidentated manner [15]. The mass spectra of
the complex, Zn[S CN(CH ) ] indicated the presence
2
3 2
r
m
The standard molar enthalpy for each reaction
was calculated from these values, applying a conve-
nient thermochemical cycle. Individual enthalpy val-
ues used for the calculation are listed in Table 2.
2
3 2 2
of the molecular ion, which relative intensity is 100%
(parent peak), suggesting a high stability.
0
D H , the standard molar enthalpy of reaction
was obtained at 298 K, from the reaction–solution
r
m
Table 1 Standard molar enthalpies of solution–reaction, at 298 K
0
–1
Reactant
(CH NH
ZnCl (s)
Zn(S CN(CH
(CH NH Cl(s)
Solvent
acetone
Solution
D H /kJ mol
i
m
2
3
)
2
2
S
2
CN(CH
3
)
2
(s)
A
1
A
2
A
3
A
4
10.68±0.35
2
A
1
–37.48±0.56
26.86±2.12
15.58±1.11
2
3
)
2
)
2
(s)
acetone
2
3
)
2
2
A
3
310
J. Therm. Anal. Cal., 79, 2005

BISDIMETHYLDITHIOCARBAMATE ZINC(II) COMPLEX
The standard molar enthalpy of formation of the
0
enthalpies of chelate formation in gaseous phase and
the dissociation energy of the Zn–S binding was neces-
crystalline chelate were determined from D H and
r
m
0
×·
the respective standard molar enthalpies of formation
of zinc chloride [16], ligand [17, 18] and ammonium
chloride [19, 20], using expression (1) are given in
Table 2, while the auxiliary data are listed in Table 3.
sary to use the D H [ S CN(CH ) , g] and
f
m
2
3 2
0 –
D H [ S CN(CH ) , g] values, which were calcu-
lated from the experimental data of standard molar
f
m
2
3 2
0
enthalpies of formation D H [HS CN(CH ) , g].
According to the standard molar enthalpies of
dissociation of the S–H binding of different com-
f
m
2
3 2
Table 2 Standard molar enthalpies for the chelate
–
1
Parameters
kJ mol
pounds, Benson [24] determined that D (S–H)=
385.0±5.0 kJ mol . Using the equation
m
–
1
0
D H
–69.24±2.49
–216.25±7.72
189.80±0.91
–26.45±7.77
–619.78±8.95
–2747.71±8.95
154.95±8.95
686.93±8.95
r
m
0
×·
0
D H (s)
D H [ S CN(CH ) , g] =
f
m
f
m
2
3 2
g
0
0
D H
s
m
= D (S – H) + D H [HS CN(CH ) , g] –
m
f
m
2
3 2
0
D H (g)
0
·
f
m
–
D H (H , g),
0
f
m
D H
ho
m
0
·
–1
0
where D H (H , g) =218.00±0.01 kJ mol [17, 18],
standard molar enthalpy of radical formation in gaseous
D H
f
m
he
m
<
<
D>(Zn–S)
·
phase were calculated [ S CN(CH ) , g]. To calculate
3 2
2
D¢>(Zn–S)
the standard molar enthalpies of formation in gaseous
–
phase [ S CN(CH ) , g], the equation
2
3 2
Table 3 Auxiliary data
0
–
D H [ S CN(CH ) , g] =
f
m
2
3 2
0
–1
Species
D H /kJ mol
Reference
0
–
0
–
f
m
=
E + D H [ S CN(CH ) , g] +–D H (e )
L
f
m
2
3
2
f
m
ZnCl
2
(s)
–415.05±0.02
–144.00±6.40
–278.00±7.04
130.73±0.01
2782.78±0.03
231.30±4.45
–30.76±4.45
[16]
[17]
[19]
[16]
[16]
[17]
[22]
–1
was used, where E = –200.42±0.05 kJ mol and
L
(
CH
3
)
2
2
NH
2
2
2 3 2
S CN(CH ) (s)
0
–
D H (e ) = 0.The values of standard molar enthalpies
f
m
(
CH
3
)
NH
Cl(s)
of formation and dissociation energies of the complex,
using homolytic and heterolytic parameters, are pre-
sented in Table 2.
Auxiliary data, listed in Table 3, enable the cal-
culation of the mean enthalpy of zinc–sulphur bond
5–8, 10, 11] for homolytic,< D > (Zn – S) =
D H / 4,
·
Zn (g)
2
Zn (g)
+
·
2
(
CH
3
3
)
)
2
2
NCS (g)
–
(CH
NCS (g)
2
[
0
and
heterolytic
parameters,
ho
m
0
The standard molar enthalpy of sublimation, < D¢ > (Zn – S) =D H /4, whose values are listed in
he
m
g
0
D H were determined using DSC and estimation
methods [5–8, 17, 18, 21].
Table 2.
s
m
Several calculations have been performed to
obtain a structure belonging to lower energy. The
XCrysDen program was used to develop the structure
(Fig. 3) with lower energy [25]. The sulfur atoms
complexed with the zinc atom and formed a diagonal
angle of 90° according to Fig. 3. Figure 4 illustrates
the plot of energy vs. DOS. The data originated from
the optimized structure by the Gaussian98 software.
On the top of the valence band to the HOMO and the
The complex Zn[S CN(CH ) ] (s) decomposes in
2
3 2 2
solid phase. Consequently it was not possible to calcu-
late the sublimation enthalpy, according to Eq. (2).
Tfus
g
0
l
0
D H
=
C (s)dT + D H
98.15 K
+
s
m
ò
p
s
m
2
(
2)
Tvap
T298.15 K
g
0
+
C (l)dT + D H
+
C (g)dT
p
p
l
m
ò
ò
Tfus
Tvap
Botelho et al. reported that the standard molar
enthalpy of ligand decomposition is equal to its appar-
ent enthalpy of sublimation [22]. Literature
data [17, 18] for standard molar enthalpies of ligand
–1
decomposition are 189.80±0.91 kJ mol . Standard
molar enthalpy of sublimation of the complex
Zn[S CN(CH ) ] (s) can be considered as being equal
2
3 2 2
to the standard molar enthalpy of sublimation of its
ligand [23]. According to homolytic and heterolytic
parameters for the calculation of the standard molar
Fig. 3 Schematic representation of the cluster of
2 3 2 2
Zn[S CN(CH ) ] optimized. Spheres indicate the
atomic positions
J. Therm. Anal. Cal., 79, 2005
311

BOTELHO et al.
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