Kinetic analyis of TF data, XXXV. Spectroscopic and thermal studies of some cobalt(III) chelates with ethylenediamine

Article abstract of DOI:10.1023/A:1011577319016

A number of 30 [Co(en)₃]Y₃, [Co(en)₂X₂]Y and [Co(en)₂X(amine)]Y₂ type complexes (X=Cl, Br; Y=Cl, Br, I, NCO, NCS, NO₃, ClO₄, etc.; amine=aromatic and alkylamines) were obtained from trans-[Co(en)₂Cl₂]Cl by double decomposition and by substitution reactions, respectively. The structure of the complexes was proved by means of far and middle FTIR spectra. The thermal decomposition was studied by TG, DTA and DSC measurements. Mass spectra were also recorded. In the case of [Co(en)₃]Y₃ complexes the nitrate, perchlorate and dimesoperiodates decompose suddenly, frequently explosion like. The halides and thiocyanates seem to substitute an ethylenediamine ligand, yielding a rather unstable intermediate. The pyrolysis of [Co(en)₂X₂]Y type derivatives yields no relatively stable intermediates, but the decomposition temperatures may be correlated with the nature of Y and with the cis or trans configuration of the compound. With the [Co(en)₂X(amine)]Y₂ type complexes one observes the formation of [Co(en)₂XY]Y as intermediate product. From the TG curves kinetic parameters were derived for some dehydration and deamination processes, by using the nomogram method. The validity of a nonlinear kinetic compensation law was observed.

Full text of DOI:10.1023/A:1011577319016

Journal of Thermal Analysis and Calorimetry, Vol. 64 (2001) 843–856
KINETIC ANALYIS OF TG DATA
XXXV. Spectroscopic and thermal studies of some
cobalt(III) chelates with ethylenediamine
J. Zsakó1, G. Pokol2, Cs. Novák2, Cs. Várhelyi1, A. Dobó3
and G. Liptay2
1Department of Mathematics and Natural Sciences, Transsylvanian Museum Association,
RO-3400, Cluj, Romania
2Institute of General and Analytical Chemistry, University of Technology and Economics,
1521-Budapest, Hungary
3Central Chemical Research Institute, Budapest, Hungary
Abstract
A number of 30 [Co(en)3]Y3, [Co(en)2X2]Y and [Co(en)2X(amine)]Y2 type complexes (X=Cl, Br;
Y=Cl, Br, I, NCO, NCS, NO3, ClO4, etc.; amine=aromatic and alkylamines) were obtained from
trans-[Co(en)2Cl2]Cl by double decomposition and by substitution reactions, respectively. The struc-
ture of the complexes was proved by means of far and middle FTIR spectra. The thermal decomposi-
tion was studied by TG, DTA and DSC measurements. Mass spectra were also recorded. In the case of
[Co(en)3]Y3 complexes the nitrate, perchlorate and dimesoperiodates decompose suddenly, frequently
explosion like. The halides and thiocyanates seem to substitute an ethylenediamine ligand, yielding a
rather unstable intermediate. The pyrolysis of [Co(en)2X2]Y type derivatives yields no relatively stable
intermediates, but the decomposition temperatures may be correlated with the nature of Y and with the
cis or trans configuration of the compound. With the [Co(en)2X(amine)]Y2 type complexes one ob-
serves the formation of [Co(en)2XY]Y as intermediate product. From the TG curves kinetic parameters
were derived for some dehydration and deamination processes, by using the nomogram method. The
validity of a nonlinear kinetic compensation law was observed.
Keywords: cobalt(III) complexes, DSC, DTA, kinetics, FTIR and IR spectra of Co(III) com-
plexes, TG
Introduction
The aromatic, alicyclic, N-heterocyclic and especially the various aliphatic diamines
form homogeneous ([Co(diamine)n]2+,3+) and mixed chelates ([Co(diamine)2AB])
with Co(II) and Co(III). From coordination chemical point of view the most impor-
tant complexes are the ethylenediamine Co(III) derivatives, with very stable five
member Co-heterocyclic ring systems. The homologues of this aliphatic diamine:
1,2-, 1,3-, 1,4-, 1,5-diamines form also complex compounds with the above men-
tioned metal ion. The stability of these chelate ring systems decreases in the order:
1418–2874/2001/ $ 5.00
Akadémiai Kiadó, Budapest
© 2001 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

844
ZSAKÓ et al.: SOME COBALT(III) CHELATES WITH ETHYLENEDIAMINE
en>1,2-propane>1,3-propane>1,4-butane>1,5-diamines.
The formation of 7...10 atomic chelate rings is very difficult due to steric hin-
drances.
Some attempts were also made aiming the synthesis of N-substituted mono- and
di-ethylenediamine derivatives as ligands for coordination chemical purposes (mono-
and dialkyl, mono- and diphenyl ethylenediamines were also mentioned in the litera-
ture) [1–6].
The most significant cobalt(III) complex with ethylene diamine, the
trans-[Co(en)2Cl2]Cl, is the starting material in various substitution reactions, as seen
in Fig. 1.
Fig. 1 Substitution reactions of 1,6-[Co(en)2Cl2]+.
L – various amines (4<pK<11); LL′ – 1,2-diamines; Z– – CN–, NCO–, NCS–,
NCSe–, NO–2 , NH–3 ; C – catalyst
It is worth mentioning, that unlike the [Co(Diox.H)2I2]– and the
[Co(Diox.H)2I(amine)] derivatives (diox.H2 stands for an aliphatic or alicyclic
α-dioxime), the [Co(en)2I2]+ and [Co(en)2I(amine)]2+ derivatives cannot be obtained.
The substitution reactions of [Co(en)2Cl2]+ and [Co(en)2Br2] with aliphatic,
alicyclic and heterocyclic monoamines (basicity constant: 4<pKb<11) lead to the for-
mation of monoacido-pentamin-derivatives (excepting α-picoline, 2,6-lutidine,
2,4,6-symm.collidine, which exhibit steric hindrances). In the presence of the latter
pyridine derivatives and with very weak bases (12p<Kb<14) trans-cis geometric iso-
merisation can be observed. Nevertheless, the pKb value of the amine is not the only
factor determining the above mentioned substitution processes [7–11].
The substitution of the halogens (Cl–, Br–) may be performed also in the presence
of catalysts (e.g. charcoal, silicagel, etc.) and various mono- and di-amines (L –NH3,
LL′ -en, pn, dyp, o-phen, etc.) e.g.:
[Co(en)2X2]++LL′ → [Co(en)2(LL′)]3++2X–
(1)
J. Therm. Anal. Cal., 64, 2001

ZSAKÓ et al.: SOME COBALT(III) CHELATES WITH ETHYLENEDIAMINE
845
Results and discussions
In this paper a number of 30 [Co(en)3]Y3, [Co(en)2X2]Y and [Co(en)2X(amine)]Y2
type complexes (X – Cl, Br; Y – halides and pseudohalides, oxoanions, etc.) were
studied by spectral and thermal methods. The Co(III)-complexes studied are charac-
terized in Tables 1–3.
Table 1 [Co(en)3]Y3 type complexes
Mol.
mass
calc.
Analysis
calc.
Appearance
(microscopic)
No. Formula
found
1
2
3
4
[Co(en)3]Cl3·3H2O
399.3 brown great prisms Co
Cl
14.7
26.6
13.5
14.6
26.7
13.3
H2O
Co(en)3]Br3·3H2O
[Co(en)3]I3·H2O
[Co(en)3](NCS)3
532.7 orange prisms
637.7 brown crops
413.2 orange plates
Co
Br
H2O
11.1
45.0
10.1
11.2
44.7
10.8
Co
I
H2O
9.2
59.7
2.8
9.5
60.1
3.1
Co
14.2
42.1
13.8
43.0
NCS
5
6
7
[Co(en)3](ClO4)3
[Co(en)3](NO3)3
537.3 orange needles
Co
Co
10.9
13.9
11.1
13.5
425.0 orange irreg.cryst.
[Co(en)3]HI2O9·3H2O
691.8 sparkling yellow
needles
Co
I
8.5
36.7
8.4
37.0
8
9
[Co(en)3]4(I2O9)3
2149.2 voluminous
microcryst.
Co
I
11.0
35.4
10.8
35.0
[Co(en)3][Cr(NCS)6]
639.5 brown microcryst.
Co+Cr
NCS
17.3
54.5
17.7
55.0
10 [Co(en)3][Cr(NCS)4(NH3)2]3 1194.0 reddish brown
microcryst.
Co+Cr
HN3
18.0
8.5
18.3
8.2
Synthesis
The starting compounds, [Co(en)3]Cl3, and trans-[Co(en)2Cl2]Cl were obtained by air
oxidation of a mixture of CoCl2 and ethylene diamine in aqueous solution in the pres-
ence of catalyst (in the case of [Co(en)3]Cl3), and in its absence (with the
[Co(en)2Cl2]Cl derivative). For double decomposition reactions an excess of NaX so-
lutions was used (X – Br–, I–, NCS–, NCO–, NO–3 , ClO–4 , IO4– , 1/3[Cr(NCS)6]3–,
[Cr(NCS)4(NH3)2]–).
J. Therm. Anal. Cal., 64, 2001

846
ZSAKÓ et al.: SOME COBALT(III) CHELATES WITH ETHYLENEDIAMINE
Table 2 [Co(en)2X(amine)]Y2 type complexes
Analysis
calc.
Mol. mass
No. Formula
calc.
Appearance
found
11 cis-[Co(en)2Cl-
(trimethylamine)]Cl2·H2O
362.4
396.3
424.3
444.3
thick red prisms Co
Cl
16.2
29.3
5.0
16.4
28.9
5.3
H2O
12 cis-[Co(en)2Cl-
great red irreg.
prisms
Co
Cl
14.9
26.8
4.5
14.8
27.0
4.2
(aniline)]Cl2·H2O
H2O
13 cis-[Co(en)2Cl-
red needles
Co
13.9
25.0
4.2
14.1
25.2
4.5
(o-ethylaniline)]Cl2·H2O
Cl
H2O
14 cis-[Co(en)2Cl-
(o-anisidine)]Cl2·2H2O
sparkling red
stars
Co
Cl
13.2
23.9
8.1
13.5
23.6
8.0
H2O
15 cis-[Co(en)2Cl-
575.4
619.8
brown plates in
star form
Co
I
10.2
44.1
10.1
43.9
(benzylamine)]I2
16 cis-[Co(en)2Br-
square brown
plates
Co
I
9.5
40.9
9.4
41.2
(benzylamine)]I2
Table 3 [Co(en)2X2]Y type complexes
Analysis
Mol.
mass calc.
No. Formula
Appearance
calc. found
17 cis-[Co(en)2Cl2]Cl·H2O
18 trans-[Co(en)2Cl2]Cl
19 cis-[Co(en)2Cl2]Br·H2O
20 trans-[Co(en)2Cl2]Br
21 cis-[Co(en)2Cl2]I
303.8
285.3
347.8
329.8
376.8
376.8
307.9
307.9
291.9
291.9
436.7
violet prisms
green prisms
violet tables
green plates
brown needles
Co
19.4
20.6
16.9
17.9
15.6
15.6
19.1
19.1
20.2
20.2
19.4
20.6
16.7
17.9
15.5
15.7
19.0
19.3
20.3
20.1
Co
Co
Co
Co
22 trans-[Co(en)2Cl2]I
yellow-brown prisms Co
23 cis-[Co(en)2Cl2]NCS
24 trans-[Co(en)2Cl2]NCS
25 cis-[Co(en)2Cl2]NCO
26 trans-[Co(en)2Cl2]NCO
27 trans-[Co(en)2Br2]Br·H2O
violet plates
Co
Co
Co
Co
green plates
violet prisms
green prisms
green-yellow prisms
Co
H2O
13.5
4.1
13.4
4.3
28 trans-[Co(en)2Br2]I
465.7
380.8
396.8
green-brown needles
green prisms
Co
Co
Co
12.6
15.5
14.9
12.5
15.6
14.7
29 trans-[Co(en)2Br2]NCO
30 trans-[Co(en)2Br2]NCS
green needles
J. Therm. Anal. Cal., 64, 2001

ZSAKÓ et al.: SOME COBALT(III) CHELATES WITH ETHYLENEDIAMINE
847
Spectral studies
Some FTIR spectral data in the middle IR region for several complexes studied are
presented in Table 4. These data show the green [Co(en)2Cl2]Cl and the
[Co(en)2Br2]Br to have a trans geometric configuration (a single δrCH band in the
2
870–910 cm–1 region). The [Co(en)2Cl(amine)]Y2 and the [Co(en)2Br(amine)]Y2 de-
rivatives present a cis sterical arrangement (two deformation bands in the mentioned
spectral range) [12].
Table 4 Middle FTIR spectral data on some cobalt(III)-ethylene-diamine complexes
Assignment
1
2
3
4
5
νN–H
3245 s
3200 m
3160 m
3230 m
3240 s
3250 s
3180 s
3100 s
3155 s
3150 m
3160 m
νC–H
2955 vs
2860 m
2965 s
2860 m
2980 m
2885 m
2975 m
2885 m
2980 s
2870 s
δsNH
1610 vs
–
1610 vs
1590 vs
1475 m
1395 vs
1630 m
1575 m
1460 vs
1395 s
1625 m
1585 vs
1470 m
1380 s
1620 s
–
2
νC–C(arom)
δCH
1460 vs
1395 vs
1355 s
1470 vs
1380 vs
1350 s
2
δNH
2
δCH
1365 m
1340 s
1365 vs
1320 vs
1320 m
2
δrCH
890 m
890 m
870 s
900 m
880 m
905 m
875 m
900 m
2
γ
NH2
845 m
730 m
830 s
705 s
840 w
810 s
840 s
730 s
765 vs
710 vs
710 vs
γC–H
1 – trans-[Co(en)2Cl2]I; 2 – cis-[Co(en)2Cl(aniline)]Cl2; 3 – cis-[Co(en)2Cl(benzylamine)]I2;
4 – cis-[Co(en)2Br(benzylamine)]I2; 5 – [Co(en)3]Cl3
The νN–H (3250–3150 cm–1), δsNH , (1610–1630 cm–1) and δas (1380–1390 cm–1)
2
frequencies show strong covalent Co–N bonds. The νC–H and δCH bands are not af-
2
fected by coordination effects.
In the far IR region the νCo–N(en), νCo–N(L), νCo–Cl, νCo–Br stretching vibrations and the
Nen–Co–Nen, Nen–Co–NL, Nen–Co–Cl, Nen–Co–Br, NL–Co–Cl, etc., and various skele-
tal vibrations of the aromatic and heterocyclic L ligands and those of the five-
membered chelate rings (250–50 cm–1) appear. Generally, these bands are in some ex-
tent overlapped by each other.
Certain discrepancies appear at the assignement of the metal-nitrogen vibrations
in metal-ethylenediamine complexes. Large frequency ranges are assigned to the
M–N vibration (550–350 cm–1). The difficulty in making the assignment may arise
from the coupling of the vibration with the NH2 rocking mode and with a low fre-
quency skeletal mode. The Co–N bond in ethylenediamine complexes is stengthened
J. Therm. Anal. Cal., 64, 2001

Table 5 Far infrared spectral data of some Co(III)-ethylenediamine complexes
Skelet. co-octa-
hedral (lattice)
δ
νCo–N
δN–Co–N
νCo–X
Formula
NH2
Skeletal bending
[Co(en)3]I3
580 s
545 m
497 m
439 s
305 m
271 vs
153 w
144 m
136 w
119 s
40 m
30 m
–
cis-[Co(en)2Cl(aniline)]Cl2
583.5 s
572 m
553 s
515 w
503 s
425 s
354 s
332 w
271 vs
286 w
179 m
149 vs
135 s
119 m
31 m
30 s
cis-[Co(en)2Cl(o-anisidine)]Cl2
589 s
569 vs
528 m
496 s
465 s
341 w
323 w
277 vs
289 s
205 s
183 s
151 s
126 vs
cis-[Co(en)2Cl-
(o-ethylaniline)]Cl2
578.5 vs
510 vs
460 s
442 w
321 s
269 vs
285 s
185 vs
145 w
130 s
30 m
cis-[Co(en)2Cl(benzylamine)]I2
575 vs
565 s
515 m
459 ws
484 m
323 w
304 m
263 vs
207 s
190 m
52 m
143 m
35 m
31 m
cis-[Co(en)2Cl-
(trimethylamine)]Cl2
577.8 vs
510 s
347 m
321 m
267.8 vs
285 s
210 m
167 m
130 m
110 m
31 m

ZSAKÓ et al.: SOME COBALT(III) CHELATES WITH ETHYLENEDIAMINE
849
primarily by the chelation effect, as any π interaction would be slight. When ethyl-
enediamine coordinates to a metal as a chelating ligand, it may adopt eight different
conformations, especially with the [Me(en)3]n+ ions. Thus, it is rather difficult to ob-
tain sure conformational information from the vibrational spectra [13–14].
In Table 5 an attempt is made to assign several far IR bands to different molecu-
lar vibrations.
Thermal investigations
Thermal decomposition of ethylenediamine and substituted ethylenediamine contain-
ing transition metal (Ni, Cu, Pd) complexes has been studied in air atmosphere by
means of thermogravimetry in order to determine the decomposition temperatures
and to obtain information concerning the stoechiometry of the pyrolysis [15–20]. The
derivatographic study of [Co(en)3]Y3 type complexes in air atmosphere suggested the
idea that if Y=Cl, a partial deamination reaction may occur corresponding to [21–22]
[Co(en)3]Y3 → [Co(en)2Y2]Y+en
(2)
A similar reaction was observed to occur in almost stoechiometric extent in the
case of the analogous [Cr(en)3]Y3 complexes [23–24] and this reaction is valorified in
the thermal matrix method, allowing the preparation of [Cr(en)2Y2]Y type complexes
which cannot be synthesized in aqueous solutions [25–26].
Fig. 2 TG and DTA curves of [Co(en)3](ClO4)3
The present thermal study of the [Co(en)3]Y3 type complexes showed that if Y is
the anion of some oxyacids as nitric, perchloric, dimesoperiodic acids, the decompo-
sition is explosion like. The TG curves show only a decomposition temperature and
nothing else, the DTA one exhibits a sharp exothermic peak, as seen from Fig. 2. If
the anion is a complex one, the decomposition of the cation and of the anion occurs in
J. Therm. Anal. Cal., 64, 2001

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ZSAKÓ et al.: SOME COBALT(III) CHELATES WITH ETHYLENEDIAMINE
Fig. 3 TG and DTA curves of [Co(en)3]Cl3·3H2O
the same time and a continuous mass loss is observed without mass loss stops or
inflexions at stoechiometric ratios until the sample is transformed into a mixture of
oxides of the corresponding transition metals.
If the anion is a halogen, or NCS, the shape of the TG curve is consistent with
the presumption that after the loss of the crystallization water, reaction (3) occurs. No
mass loss stop is observed, only an inflexion point. Thus in this decomposition
[Co(en)2Y2]Y is not a sufficiently stable intermediate and the reaction is more com-
plicated than with the analogous [Cr(en)3]Y3 complexes. Presumably, the relative in-
stability of the intermediate is correlated with the possibility of Co(III) → Co(II) re-
dox reactions. Mass spectral data are in agreement with this hypothesis. As an exam-
ple we give in Fig. 3 the TG and DTA curve of [Co(en)3]Cl3·H2O. As seen, the first
step of the pyrolysis is an endothermic dehydration and at about 240°C begins reac-
tion (2). The elimination of an en ligand corresponds to 15% mass loss (marked in
Fig. 3) and the decomposition rate slows down at about this point but the decomposi-
tion continues, i.e. reaction (2) is partially overlapped by other processes.
It is interesting to compare the endothermic DTA peak temperatures of different
complexes, both in the case of dehydration and deamination reactions. As seen from
Table 6, the dehydration peak temperature of [Co(en)3]Y3 complexes increases in the
order Cl<Br<I. This means that the thermal stability of the hydrated anions increases
in the same order. With respect to the deamination peak temperatures, one observes
that it is much lower in the case of the NCS– as compared to the halogen ions. This
must be correlated with the high stability of the Co–NCS bond, due to the possibility
of π-bond formation.
J. Therm. Anal. Cal., 64, 2001

ZSAKÓ et al.: SOME COBALT(III) CHELATES WITH ETHYLENEDIAMINE
851
Table 6 Endothermic DTA peak temperatures (°C) of [Co(en)3]Y3 and [Co(en)2X(amine)]Y2
type complexes
Formula
Dehydration
Deamination
267
[Co(en)3]Cl3·3H2O
76
109
121
–
[Co(en)3]Br3·3H2O
279
[Co(en)3]I3·H2O
275
[Co(en)3](NCS)3
216
cis-[Co(en)2Cl-(trimethylamine)]Cl2·H2O
cis-[Co(en)2Cl(aniline)]Cl2·H2O
cis-[Co(en)2Cl-(o-ethylaniline)]Cl2·H2O
cis-[Co(en)2Cl-(o-anisidine)]Cl2·2H2O
cis-[Co(en)2Cl(benzylamine)]I2
cis-[Co(en)2Br(benzylamine)]I2
130
81
240
239
131
89
241
170
–
177
–
178
The thermal decomposition of [Co(en)2X(amine)]Y2 type complexes may also
imply a deamination reaction, namely the substitution of the amine ligand for the ex-
ternal sphere anion, i.e.
[Co(en)2X(amine)]Y2 → [Co(en)2XY]Y+amine
(3)
If Y is a halide or a pseudohalide, the TG curves show an inflexion at a mass loss
corresponding to an amine molecule, suggesting that reaction (3) occurs indeed, but it
is partially overlapped by other decomposition processes. The DTA endothermic
peak temperatures given also in Table 6, show that the nature of the external sphere
anion is the most important. This temperature is much lower for Y=I, than for Y=Cl.
Obviously, it is influenced also by the nature of the amine ligand, which is substi-
tuted. Thus, in the case of the o-anisidine derivative, the decomposition temperature
is lower due to the steric hindrance diminishing the strength of the Co–N bond.
Table 7 Endothermic DTA peak temperatures (°C) at the deamination of [Co(en)2X2]Y type
complexes
X=Cl
X=Br
trans
–
Y
cis
trans
192
181
176
162
168
Cl
Br
182
178
174
168
152
185
184
182
160
I
NCS
NCO
At the thermal decomposition of [Co(en)2X2]Y type complexes, up to about
150°C, neither the TG, nor the DTA curves show any changes. This means, that under
our working conditions, no ionization metameric transformation occurs. The begin-
J. Therm. Anal. Cal., 64, 2001

Table 8 Kinetic parameters derived from the TG curves of some [Co(en)3]Y3 and [Co(en)2X(amine)]Y2 type complexes
E/
T0.1/K
Formula
Reaction
n
logA
logA′
kJ mol–1
60.8
Co(en)3]Cl3·3H2O
dehydr.
deamin.
dehydr.
deamin.
dehydr.
dehydr.
dehydr.
deamin.
dehydr.
dehydr.
313.8
524.1
355.6
539.2
370.9
386.8
330.3
449.7
381.7
336.7
1.40
0.91
1.07
1.42
1.32
1.58
2.17
1.60
1.31
1.33
7.2
37.5
13.6
75.4
17.7
32.8
15.8
80.0
19.1
14.3
7.29
37.70
13.62
75.55
17.76
32.82
15.96
80.20
19.00
14.32
Co(en)3]Cl3·3H2O
402.8
110.9
802.1
144.6
260.6
117.3
708.2
157.7
109.3
Co(en)3]Br3·3H2O
Co(en)3]Br3·3H2O
Co(en)3]I3·H2O
cis-[Co(en)2Cl(trimethylamine)]Cl2·H2O
cis-[Co(en)2Cl(aniline)]Cl2·H2O
cis-[Co(en)2Cl(aniline)]Cl2·H2O
cis-[Co(en)2Cl(o-ethylaniline)]Cl2·H2O
cis-[Co(en)2Cl(o-anisidine)]Cl2·2H2O

ZSAKÓ et al.: SOME COBALT(III) CHELATES WITH ETHYLENEDIAMINE
853
ning of the decomposition is marked on the DTA curve by an endothermic peak. The
corresponding peak temperatures are presented in Table 7.
As seen from this table, the peak temperatures are shifted towards lower values
as function of the external sphere anion in the following order:
Cl>Br>I>NCS>NCO
This order might be correlated with the Co–Y bond strength, which increases in
the same order. One may observe further that the thermal stability of the trans iso-
mers is higher than that of the cis ones. The decomposition temperature is influenced
also by the nature of the X ligand, víz. the DTA peak temperatures are a little higher in
the case of the bromo derivatives, as compared to the chloro ones. On the TG curves
the formation of no relatively stable intermediate is observed, i.e. the pyrolysis is a
complex process consisting of several simultaneous reactions.
The shape of several TG curves allowed us to derive kinetic parameters for a few
decomposition steps, víz. for dehydration of crystallohydrates and deamination of
some [Co(en)2X(amine)]Y2 type complexes. For this purpose the nomogram method
[28, 29] was used. Results are presented in Table 8.
In this table T0.1 stands for the temperature at which the conversion in the consid-
ered decomposition stage attains α=0.1. The magnitudes n, E and A stand for the ap-
parent reaction order, activation energy and the pre-exponential factor in the Arr-
henius equation, respectively. As seen from this table, the apparent activation ener-
gies are higher in the case of the deamination reactions, as compared to the dehydra-
tion ones, but it is obvious, that the E values cannot be correlated with the molecular
structure. This is in agreement with our view, that the apparent activation parameters
derived from TG curves do not characterize the chemical process. They are parame-
ters characterizing the TG curve of the given sample and they depend on a consider-
able number of procedural variables.
One observes further that logA values increase with increasing E values. This is
the so-called kinetic compensation effect. As shown in our earlier paper [30], this ef-
fect obeys the following non-linear law:
E
qE
T02.1
logA′=
+ log
−1.85
(4)
RT0.1ln10
In this equation R and q stand for the gas constant and for the heating rate, re-
spectively, the latter one being expressed in K s–1. The logA′ values calculated by
means of Eq. (4) are presented in the last column of Table 8. These calculated values
are in good agreement with logA values derived directly from the TG curves.
Mass spectral data
The m/z values for six complexes are pesented in Table 9. The fragmentation of the
complex ion occurs in a complicated manner and between the products always appear
the peaks of the single and double ionized en (at 60 and 30, respectively), of the coor-
dinated X ligand (at 36 and 79, respectively), of the coordinated amine as aniline (93),
J. Therm. Anal. Cal., 64, 2001

854
ZSAKÓ et al.: SOME COBALT(III) CHELATES WITH ETHYLENEDIAMINE
o-anisidine (123), benzylamine (106). Other fragmentation products correspond to
Co(en)Cl, double ionized Co(en)2 and to Co(en)2Cl, the latter one being in agreement
with the above presumed reaction (3). One observes further the signal of the external
sphere anion at 36 and 127 respectively. In the case of the iodides there is a signal at
254, corresponding to I2, which means that also redox reactions may occur.
Table 9 Mass spectral data of some Co(III)-ethylenediamine complexes
Formula
m/z
60(5%)
65(30%)
66(6%)
93(100%)
128(10%)
28(30%)
30(50%)
36(20%)
39(25%)
54(8%)
182(15%)
224(18%)
246(15%)
373(4%)
cis-[Co(en)2Cl(aniline)]Cl2
571.5(6%)
28(58%)
30(100%)
35(27%)
43(13%)
60(5%)
106(4%)
128(23%)
186(3%)
215(3%)
246(25%)
313(3%)
373(4%)
445(12%)
572(18%)
cis-[Co(en)2Cl(o-ethylaniline)]Cl2
cis-[Co(en)2Cl(o-anisidine)]Cl2
28(43%)
30(100%)
36(37%)
53(30%)
60(7%)
80(70%)
92(15%)
108(78%)
123(77%)
127(10%)
154(20%)
186(8%)
246(30%)
373(5%)
445(6%)
572(10%)
65(24%)
28(34%)
30(100%)
36(10%)
51(10%)
77(15%)
79(20%)
91(15%)
106(55%)
118(10%)
127(15%)
154(5%)
186(5%)
254(20%)
313(5%)
373(5%)
cis-[Co(en)2Cl(benzylamine)]I2
cis-[Co(en)2Br(benzylamine)]I2
28(70%)
32(15%)
63(10%)
77(25%)
70(40%)
91(20%)
106(100%)
127(15%)
254(15%)
313(5%)
28(33%)
30(100%)
43(12%)
59(15%)
60(10%)
75(6%)
88(10%)
127(30%)
186(20%)
198(8%)
215(10%)
246(80%)
254(35%)
313(10%)
373(18%)
445(10%)
572(30%)
614(5%)
[Co(en)3]I3
In all spectra appears a quite strong signal at m/z=28. It could be assigned to N2
and/or to CH2–CH2. Besides the fragmentation processes also condensation ones
must occur since one observes a considerable number of peaks at m/z values de-
passing the molar mass of the complex ion. Presumably, the coordinated amine mole-
cules are at first eliminated, further the break up of the Co(en) chelate ring occurs, al-
lowing the free NH2 group of en to be linked to an other Co atom. Thus polynuclear
J. Therm. Anal. Cal., 64, 2001

ZSAKÓ et al.: SOME COBALT(III) CHELATES WITH ETHYLENEDIAMINE
855
formations appear, such as (en)2Co(en)Co(en)NH (313), (en)2Co(en)Co(en)2NH
(373), (en)2Co(en)Co(Cl)(en)Co(en)2 (572).
Experimental
[Co(en)3]Y3
0.1 mol CoCl2 and 0.3 mol en in 500 mL aqueous solution, in the presence of 0.5 g
charcoal were oxidized by air bubbling during 5–6 h. After filtration the brown solu-
tion was used for double decomposition reactions with 2–10% solutions of NaY salts.
The mesoperiodates were prepared with a mixture of KIO4+dil. H2SO4 and dil. KOH,
respectively.
[Co(en)2X(amine)]Y2
0.05 mol trans-[Co(en)2Cl2]Cl or trans-[Co(en)2Br2]Br were treated with 0.06 mol
amine and 5–10 mL water in a mortar. After 2–5 h stirring the red-violet mass is di-
luted with water, filtered and crystallized by standing 24–48 h. Some salts were ob-
tained by double decomposition.
Analysis
Co was determined complexometrically, Cl, Br, I potentiometrically by titration with
0.01 N AgNO3, NCS as BaSO4 (gravimetrically), the sum Co+Cr by calcination at
800°C (Co3O4+Cr2O3).
Thermal measurements
Thermal measurements were performed with 951-TG and 910-DSC calorimeter
(DuPont Instruments) in argon atmosphere at a heating rate of 10 K min–1. The
derivatographic ones with a MOM Derivatograph (Budapest) in air atmosphere.
Spectral measurements
Far IR spectra were recorded with Bio-Rad-Ninn spectrophotometer in polyethylene
pellets, while the middle FTIR ones with Perkin Elmer 2000 apparatus in KBr pellets.
* * *
Support of Domus Hungarica Scientiarium et Artium Foundation is gratefully acknowledged.
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