Thermal decomposition of [Mg(NH3)6](NO 3)2, [Ni(NH3)6](NO3) 2 and [Ni(ND3)6](NO3)2

Article abstract of DOI:10.1016/j.tca.2004.01.035

The thermal decompositions of [Mg(NH₃)₆](NO ₃)₂, [Ni(NH₃)₆](NO₃) ₂ and [Ni(ND₃)₆](NO₃)₂ were studied by thermal gravimetry analysis (TGA) and simultaneous differential thermal analysis (SDTA) at a constant heating rate. The gaseous products of the decomposition were on-line identified by a quadruple mass spectrometer (QMS).The solid products were identified on the basis of Fourier transform mid infrared spectra (FT-MIR) and X-ray powder diffraction (XRPD) patterns. Deamination of hexaaminemagnesium nitrate(V) to diaminemagnesium nitrate(V) undergoes in two steps and two-third of the all NH₃ molecules are liberated. Deamination of both hexaaminenickel(II) nitrates(V) (non-deuterated and deuterated) to the diamines undergoes in three steps, and at two first steps one half of the NH₃ molecules are liberated. The thermal decomposition of [Ni(NH₃)₂](NO₃)₂ and [Ni(ND ₃)₂](NO₃)₂ is also different than that of [Mg(NH₃)₂](NO₃)₂. In both cases the decomposition is connected with the redox processes, but in the case of magnesium compound, contrary to the nickel compounds, in the second stage, besides of liberation of nitrogen, nitrogen oxides and H₂O, undergoes the liberation of NH₃ and the formation of Mg(NO₃) ₂, which in turn decomposes next, in the third stage, to the oxygen, nitrogen oxides and MgO. This third stage is not present in the case of both nickel compounds, and the decomposition of diaminenickel(II) nitrates(V) undergoes directly to the final products (NiO_1+x, nitrogen, nitrogen oxides and H₂O) without the formation of Ni(NO₃) ₂, because of the autocatalytic effect of the formed NiO.

Full text of DOI:10.1016/j.tca.2004.01.035

Thermochimica Acta 419 (2004) 223–229
Thermal decomposition of [Mg(NH3)6](NO3)2,
[Ni(NH3)6](NO3)2 and [Ni(ND3)6](NO3)2
a
b
c
a
A. Migdał-Mikulia,∗, E. Mikuli , R. Dziembaj , D. Majda , Ł. Hetmanczyk
´
a
Department of Chemical Physics, Faculty of Chemistry of the Jagiellonian University, ulica Ingardena 3, 30-060 Cracow, Poland
Department of Chemical Technology, Faculty of Chemistry of the Jagiellonian University, ulica Ingardena 3, 30-060 Cracow, Poland
Regional Laboratory of Physicochemical Analysis and Structural Research, Jagiellonian University, ulica Ingardena 3, 30-060 Cracow, Poland
Received 21 May 2003; received in revised form 8 January 2004; accepted 30 January 2004
Available online 21 April 2004
b
c
Abstract
The thermal decompositions of [Mg(NH3)6](NO3)2, [Ni(NH3)6](NO3)2 and [Ni(ND3)6](NO3)2 were studied by thermal gravimetry analysis
(TGA) and simultaneous differential thermal analysis (SDTA) at a constant heating rate. The gaseous products of the decomposition were
on-line identified by a quadruple mass spectrometer (QMS).The solid products were identified on the basis of Fourier transform mid infrared
spectra (FT-MIR) and X-ray powder diffraction (XRPD) patterns. Deamination of hexaaminemagnesium nitrate(V) to diaminemagnesium
nitrate(V) undergoes in two steps and two-third of the all NH3 molecules are liberated. Deamination of both hexaaminenickel(II) nitrates(V)
(non-deuterated and deuterated) to the diamines undergoes in three steps, and at two first steps one half of the NH3 molecules are liberated.
The thermal decomposition of [Ni(NH3)2](NO3)2 and [Ni(ND3)2](NO3)2 is also different than that of [Mg(NH3)2](NO3)2. In both cases the
decomposition is connected with the redox processes, but in the case of magnesium compound, contrary to the nickel compounds, in the
second stage, besides of liberation of nitrogen, nitrogen oxides and H2O, undergoes the liberation of NH3 and the formation of Mg(NO3)2,
which in turn decomposes next, in the third stage, to the oxygen, nitrogen oxides and MgO. This third stage is not present in the case of
both nickel compounds, and the decomposition of diaminenickel(II) nitrates(V) undergoes directly to the final products (NiO1+x, nitrogen,
nitrogen oxides and H2O) without the formation of Ni(NO3)2, because of the autocatalytic effect of the formed NiO.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Hexaaminemagnesium and hexaaminenickel(II) nitrates(V); Thermal decomposition; TGA; DTA; QMS; FT-MIR; XRPD
1. Introduction
of the NH3 groups freeze its fast reorientation. However,
while these compounds are heated up, the reorientation of
the above mentioned parts of the NH3 groups, which was
“frozen”, resumes gradually just before the phase transition:
phase III → phase II. After the transition to the phase II
all of the NH3 groups already reorientate fast. The phase
III → phase II transition on heating the compounds stud-
ied takes place at a much higher temperature (TCh2) than
the phase transition phase II → phase III on cooling them
(TCc2). The difference between these two phase transition
temperatures (TCh2 − TCc2) defines the width of the thermal
hysteresis loop of the phase II ↔ phase III transition. For
[Ni(NH3)6](NO3)2 the width of the thermal hysteresis loop
is ca. 90 K, for [Ni(ND3)6](NO3)2 it is ca.106 K, and for
[Mg(NH3)6](NO3)2 it is ca. 35 K [1–5].
It is a well-known fact that the title compounds exhibit in-
teresting phase polymorphism and large thermal hysteresis
of phase II ↔ phase III transition, which is connected with
the freezing (→) or set in motion (←) the fast reorientation
(i.e. reorientational correlation time amounts to several pi-
coseconds) of a characteristic part of the NH3 groups (see
Ref. [1,2] and the papers quoted there). In phase I and phase
II of these compounds all NH3 groups reorientate fast. On
cooling these compounds down, after the phase transition:
phase II → phase III, in the case of [Ni(NH3)6](NO3)2 (and
of [Ni(ND3)6](NO3)2 too) only one half of the so far fast
reorientating NH3 (ND3) groups stop this fast reorientation,
whereas, in the case of [Mg(NH3)6](NO3)2 only two-third
The aim of this study is to determine whether the above
described picture of the molecular reorientational motions
of the title compounds has some correlations with the
mechanism of their thermal deamination and what are the
∗
Corresponding author. Tel.: +48-12-633-63-77x2256;
fax: +48-12-634-05-15.
E-mail address: migdalmi@chemia.uj.edu.pl (A. Migdał-Mikuli).
0040-6031/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2004.01.035

224
A. Migdał-Mikuli et al. / Thermochimica Acta 419 (2004) 223–229
differences in the thermal decomposition of their deamina-
tion products.
measurements were made in the frequency range of
400–4000 cm−1 with the resolution of 2 cm−1
.
2. Experimental
3. Results and discussion
The chemical synthesis of the title compounds was de-
scribed elsewhere [3–5].
3.1. Decomposition of [Mg(NH3)6](NO3)2
A characterization of the decomposition process of the
title compounds was performed using a Mettler Toledo
TGA/SDTA 851e apparatus. Samples of masses given in
Tables 1–4 were placed in 150 ␮l corundum crucibles. The
thermo gravimetric analysis (TGA) measurements were
made in a flow of Argon from 300 up to 1000 K. The TGA
measurements were performed at a constant heating rate
of 10 K min−1. At a constant heating rate besides TG and
DTG curves, the simultaneous differential thermal analysis
(SDTA) curve and the simultaneous evolved gas analysis
(SEGA), with on-line quadruple mass spectrometer (QMS)
using a Balzer GSD 300T apparatus, were also registered.
The temperature was measured by a Pt–Pt/Rh thermocouple
with the accuracy of 0.5 K.
The X-ray powder diffraction (XRPD) analysis of the
solid decomposition products was made with a Philips
X’Pert PRO apparatus using filtrated Cu K␣1 radiation.
The spectroscopic identification of the deamination
products was performed using a Bruker EQUINOX-55
spectrometer. The Fourier transform mid infrared (FT-MIR)
Fig. 1 shows TG, DTG, QMS and DTA curves recorded
for [Mg(NH3)6](NO3)2 at a constant heating rate of
10 K min−1 in the temperature range of 300–1000 K. Dur-
ing the TG experiment, the QMS spectrum of masses were
followed from m/e = 1 to 100, however, for reasons of
graphic readability, only the masses of m/e = 17, 18, 28,
30, 32 and 44—representing NH3, H2O, N2, NO, O2 and
N2O are shown. The QMS spectrum of mass m/e = 17
represents also the OH fragment of H2O fragmentation,
which was taken into account in the determination of NH3
concentration. The temperatures, percentage mass losses
and the products of the decomposition at particular stages
are presented in Table 1.
The TG, DTG and QMS curves show that the decom-
position of the sample proceeds in three main stages. It
can be observed that the first stage involves the step-wise
freeing of four NH3 molecules. The composition of the
[Mg(NH3)2](NO3)2, the final product of the deamination
processes, was confirmed by the chemical analysis and the
FT-MIR spectrum. The second stage is connected with the
Table 1
Parameters of [Mg(NH3)6](NO3)2 thermal analysis
Sample
mass (mg)
Stage
number
Temperature
range (K)
Mass loss at
the stage (%)
Mass after
decomposition (%)
Calculated
values (%)
Products of the
decomposition
24.2809
Ia
Ib
300–391
392–496
497–607
608–850
11.6
15.4
19.8
35.1
13.6
13.6
56.7
2NH3
2NH3
IIa, IIb, IIc
III
2H2O + 113 NO + 2 N2O + 2 H3 + 1 N2 + 1 O2
3
3
3
2
18.1
16.1
MgO
Table 2
Parameters of [Mg(H2O)6](NO3)2 thermal analysis
Sample
mass (mg)
Stage
number
Temperature
range (K)
Mass loss at
the stage (%)
Mass after
decomposition (%)
Calculated
values (%)
Products of the
decomposition
163.924
Ia
Ib
II
300–550
551–620
621–770
35.02
6.93
41.85
35.13
7.03
42.13
15.71
5H2O
1H2O
2NO + 1 12 O2
16.20
MgO
Table 3
Parameters of [Ni(NH3)6](NO3)2 thermal analysis
Sample
mass (mg)
Stage
number
Temperature
range (K)
Mass loss at
the stage (%)
Mass after
decomposition (%)
Calculated
values (%)
Products of the
decomposition
30.4147
Ia
Ib
Ic
II
300–475
476–507
508–545
546–850
12.0
6.3
6.0
11.9
6.0
6.0
49.9
26.2
2NH3
1NH3
1NH3
49.5
3H2O + NO + N2O + 1 N2
2
26.2
NiO

A. Migdał-Mikuli et al. / Thermochimica Acta 419 (2004) 223–229
225
Table 4
Parameters of [Ni(ND3)6](NO3)2 thermal analysis
Sample
mass (mg)
Stage
number
Temperature
range (K)
Mass loss at
the stage (%)
Mass after
decomposition (%)
Calculated
values (%)
Products of the
decomposition
22.9349
Ia
Ib
Ic
II
300–462
463–489
490–570
570–850
12.9
13.2
6.6
6.6
48.9
24.7
2ND3
1ND3
1ND3
13.5
48.8
3D2O + NO + N2O + 1 N2
2
24.8
NiO
simultaneous liberation of ammonia, water and magnesium
oxide and the third stage with decomposition of resulting
Mg(NO3)2 to nitrogen oxides species, oxygen and solid
MgO. 18.1% of the initial mass of the sample remained after
the second stage of the decomposition and this figure corre-
sponds to the amount of magnesium oxide (see Table 1).
The profile of the SDTA curve of [Mg(NH3)6](NO3)2
shows three endothermic peaks and one exothermic peak.
The first two small endothermic peaks can be explained by
the two steps of the deamination resulting in the formation of
the tetra- and diamine, according to the following reactions:
The composition of the [Mg(NH3)2](NO3)2 was confirmed
by the chemical analysis and the FT-MIR spectrum.
The exothermic peak can be explained on the basis of
redox processes during the decomposition of the diamine
complex, according to the reactions:
IIa : [Mg(NH3)2](NO3)2 → MgO+N2+2NO+3H2O,
IIb : [Mg(NH3)2](NO3)2 → MgO + 2N2O + 3H2O,
IIc : [Mg(NH3)2](NO3)2 → Mg(NO3)2 + 2NH3.
(2)
The first two reactions (IIa and IIb) are not going completely,
because Mg(NO3)2 in the last stage decomposes to oxygen,
nitrogen oxides and solid MgO, according to the following
reactions:
Ia : [Mg(NH3)6](NO3)2 → [Mg(NH3)4](NO3)2+2NH3,
Ib : [Mg(NH3)4](NO3)2 → [Mg(NH3)2](NO3)2+2NH3.
(1)
[Mg(NH3)6](NO3)2
III : Mg(NO3)2
1
→ MgO + (N2O5) → MgO + O2 + N2O4
100
2
stage 3
stage 2
stage 1
80
60
40
20
1
→ MgO + O2 + 2NO2 ↔ MgO + 2NO + 112 O2. (3)
2
TG
The third broad and split endothermic peak in SDTA
curve, which is registered just after the exothermic peak,
is connected with presented above decomposition of the
Mg(NO3)2.
DTG
0.00
-0.02
-0.04
-0.06
In order to better recognition of the thermal decomposi-
tion process of Mg(NO3)2 in a flow of Argon, we performed
the thermal analysis of polycrystalline [Mg(H2O)6](NO3)2.
TG, DTG and SDTA curves are presented in Fig. 2. Thermal
decomposition process has two main parts: one connected
with the dehydration and the second with decomposition of
anhydrous magnesium nitrate to magnesium oxide, nitrogen
oxide and oxygen. The dehydration undergo in two steps:
at first step five H2O molecules per formula unit and at
the second step the last one H2O are freeing. Two thermal
dehydration processes of [Mg(H2O)6](NO3)2 presented by
Odochian [6], one in a flow of ambient atmosphere and
the second in a flow of nitrogen at 30 ml min−1, are very
similar to that presented by us in a flow of Argon. The
fragment of the SDTA curve, which was connected with
the decomposition of anhydrous Mg(NO3)2 we added as
an insertion in Fig. 1 in order to compare the obtained
results. The decomposition of Mg(NO3)2 undergo in a
way presented in Eq. (3). The temperatures, percentage
mass losses and the products of the decomposition of
[Mg(H2O)6](NO3)2 at particular stages are presented in
Table 2.
QMSa
0
20
b
c
d
e
40
60
f
80
a) signal of m/e = 44
b) signal of m/e = 28
c) signal of m/e = 32
d) signal of m/e = 30
e) signal of m/e = 17
f) signal of m/e = 18
100
120
140
160
180
2
SDTA
Mg(NO
)
3 2
0
-2
-4
-6
-8
2
0
SDTA
650 675 700 725 750 775 800 825
T/ K
-2
-4
∆
-6
300
400
500
600
700
800
900
1000
T / K
Fig. 1. TG, DTG, QMS and SDTA curves for [Mg(NH3)6](NO3)2 in the
range of 300–1000 K, heated at a constant heating rate of 10 K min−1
.

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A. Migdał-Mikuli et al. / Thermochimica Acta 419 (2004) 223–229
[Mg(H2O)6](NO3)2
[Ni(NH3)6](NO3)2
100
80
100
80
60
40
20
60
stage 2
stage 1
40
TG
TG
20
DTG
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
0.2
0.0
DTG
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
350
400
450
T/K
500
550
QMS
a
b
c
0
100
200
300
400
500
600
d
e
a) signal of m/e = 32
b) signal of m/e = 44
c) signal of m/e = 30
d) signal of m/e = 28
e) signal of m/e = 17
2
0
-2
-4
-6
SDTA
-8
15
10
5
-10
-12
-14
SDTA
0
300
400
500
600
700
800
900
-5
T / K
300
400
500
600
700
800
900
1000
Fig. 2. TG, DTG and SDTA curves for [Mg(H2O)6](NO3)2.
T / K
Fig. 3. TG, DTG, QMS and SDTA curves for [Ni(NH3)6](NO3)2 in the
3.2. Decomposition of [Ni(NH3)6](NO3)2 and
[Ni(ND3)6](NO3)2
range of 300–1000 K, heated at a constant heating rate of 10 K min−1
.
tion of the tetra-, tri- and diamine, in succession, according
to the following reactions:
Fig. 3 shows TG, DTG, QMS and SDTA curves
recorded for [Ni(NH3)6](NO3)2 at a constant heating rate
of 10 K min−1 in the temperature range of 300–1000 K.
During the TG experiment, the QMS spectra of masses
were followed from m/e = 1 to 100, however, for reasons
of graphic readability, only the masses of m/e = 17, 18,
28, 30, 32 and 44—representing NH3, H2O, N2, NO, O2
and N2O are shown. The QMS spectrum of mass m/e = 17
represents also the OH fragment of H2O fragmentation. The
temperatures, percentage mass losses and the products of the
decomposition at particular stages are presented in Table 3.
The TG, DTG and QMS curves show that the decom-
position of the sample proceeds in two main stages. It
can be observed that the first stage involve mainly the
step-wise freeing of four NH3 molecules (partial deamina-
tion), whereas the second stage—with the decomposition of
[Ni(NH3)2](NO3)2 to nitrogen, nitrogen oxides, water and
solid NiO.
Ia : [Ni(NH3)6](NO3)2 → [Ni(NH3)4](NO3)2 + 2NH3,
Ib : [Ni(NH3)4](NO3)2 → [Ni(NH3)3](NO3)2 + NH3,
Ic : [Ni(NH3)3](NO3)2 → [Ni(NH3)2](NO3)2 + NH3.
(4)
The composition of the [Ni(NH3)2](NO3)2, the final product
of the deamination process Ic (4), was confirmed by the
chemical analysis and the FT-MIR spectrum. Fig. 4 shows
the comparison of the FT-MIR spectra of the hexaamine-
and diamine-nickel(II) nitrates(V), the substrate and the final
product of the deamination process Ic (4), respectively.
The third endothermic peak is immediately followed by
a broad and big exothermic peak, contrary to the expected
enthalpy changes accompanying the decomposition of a sta-
ble [Ni(NH3)2](NO3)2 complex. The exothermic peak for
[Ni(NH3)2](NO3)2 can be explained by reduction and oxi-
dation (redox) processes taking place between the reductants
(NH3 ligands) and the oxidants (NO3−). The beginning of
the exothermic effect (at 550 K) is correlated with beginning
The profile of the SDTA curve of [Ni(NH3)6](NO3)2
shows three small endothermic peaks and one broad, big
exothermic peak. The endothermic peaks can be explained
by the three steps of the deamination resulting in the forma-

A. Migdał-Mikuli et al. / Thermochimica Acta 419 (2004) 223–229
227
between reductive NH3 molecules and oxidative nitrate
ions or nitrogen oxides. The rate acceleration in the case
of the second stage of the thermal decomposition, namely
during [Ni(NH3)2](NO3)2 final decomposition, may be
caused by an autocatalytic effect of the decomposition
product NiO1+x. Ettarh and Galway [9,10] showed that
transition metal oxides, among them NiO, catalyse ther-
mal decomposition of Co(NO3)2. A very similar complex
compound, [Co(NH3)6](NO3)2, decomposes according to
Wendlandt and Smith [11] in two steps. During the first
step [Co(NH3)4](NO3)2 is formed (at about 410 K). Above
480 K the tetraaminecobalt(II) nitrate(V) is decomposed
very rapidly with formation of H2O, N2 and Co3O4, besides
NH3 [11].
[Ni(NH3)6](NO3)2
[Ni(NH3)2](NO3)2
Fig. 5 shows TG, DTG and DTA curves recorded for
[Ni(ND3)6](NO3)2 at a constant heating rate of 10 K min−1
in the temperature range 300–1000 K. The temperatures, per-
centage mass losses and the products of the decomposition
at particular stages are presented in Table 4. The thermo-
gravimetric measurements for both isotope specimens show
that the decomposition of the deuterated compound pro-
ceeds, very similar like in the case of nondeuterated one, in
two main stages. First stage involves mainly the step-wise
1000
2000
3000
4000
Wavenumber [cm-1]
[Ni(ND3)6](NO3)2
Fig. 4. Comparison of the FT-MIR spectra of [Ni(NH3)6](NO3)2 (sub-
strate) and [Ni(NH3)2](NO3)2 (final product of the deamination processes
Ia, Ib and Ic).
100
80
of N2 molecules evolution observed in the simultaneous
evolved gas analysis (SEGA) with on-line QMS. The accel-
eration of exothermic effect is bounded with acceleration of
N2 production and additional evolution of N2O. Therefore,
the redox process is composed of two overall reactions:
stage 2
stage 1
60
40
20
TG
DTG
IIa : [Ni(NH3)2](NO3)2 → NiO + N2 + 2NO + 3H2O,
IIb : [Ni(NH3)2](NO3)2 → NiO + 2N2O + 3H2O. (5)
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
26.2% of the initial mass of the sample remained after the
second stage of the decomposition and this figure corre-
sponds to the amount of nickel oxide (see Table 3). The
XRPD analysis of the solid decomposition product con-
firmed that it was NiO, which has the cubic structure (Fm3m,
a = 4.1761 Å), as identified using ICDD No. 47-1049 data.
The role of transition metal cation in processes IIa and
IIb should not be ignored. Thermal decomposition of nickel
350
400
450
T/K
500
550
15
10
5
nitrate results in formation of non-stoichiometric NiO1−x
.
Małecki et al. [7,8] showed that the concentration of Ni3+
in the decomposition product achieve 1 at.% of Ni3+. The
non-stoichiometric nickel oxide can catalyse many redox
reactions. Perhaps, the delay in appearance of NO in the
gaseous products arose from a secondary reaction:
SDTA
0
-5
300
400
500
600
700
800
900
1000
NiO + xNO = NiO1+x + xN2.
(6)
T / K
The system of Ni3+/Ni2+ with anionic vacancies in the
oxide lattice can work as electron and oxygen transmitters
Fig. 5. TG, DTG and SDTA curves for [Ni(ND3)6](NO3)2 in the range
of 300–1000 K, heated at a constant heating rate of 10 K min−1
.

228
A. Migdał-Mikuli et al. / Thermochimica Acta 419 (2004) 223–229
freeing of four ND3 molecules, whereas the second stage
mainly the decomposition of [Ni(ND3)2](NO3)2 to nitrogen,
nitrogen oxides, heavy water and NiO. The composition of
the [Ni(ND3)2](NO3)2, the final product of the deamination
processes, was confirmed by the chemical analysis and the
FT-MIR spectrum.
24.8% of the initial mass of the sample remained after
the second stage of the decomposition and this figure cor-
responds to the amount of nickel oxide (see Table 4). The
XRPD analysis of the solid decomposition product con-
firmed that it was NiO, which has the cubic structure (Fm3m,
a = 4.176 Å), as identified using ICDD No. 47-1049 data.
Because of a great similarity of the mechanism of the ther-
mal decompositions of both isotope specimens we did not
recorded the QMS spectrum during the TG experiment for
[Ni(ND3)6](NO3)2. Moreover, it would demand exchange
of Ar into Ne as the current and eluent gas.
exothermic peak can be explained on the basis of redox pro-
cesses during the decomposition of the diamine complex,
according to the reactions very similar to reactions (5).
Comparing the thermal decomposition processes of
[Ni(NH3)6](NO3)2 and [Ni(ND3)6](NO3)2, registered at a
constant heating rate in a flow of Argon, we noticed that
they proceed in an almost identical way. The main differ-
ence is in a kinetic isotope effect. Fig. 6 shows comparison
of the DTG curves for the deuterated and non-deuterated
compound. It can be seen that the particular NH3 ligands
are liberated in a slightly lower temperature than the ND3
ones.
4. Conclusions
1. The thermal decomposition processes of [Ni(NH3)6]
(NO3)2 and [Ni(ND3)6](NO3)2 to respective diamines
are very similar. Whereas, the thermal decomposition
of [Mg(NH3)6](NO3)2 to diaminemagnesium nitrate(V)
is slightly different. In the case of hexaaminenickel(II)
nitrate(V) compounds the liberation of NH3 (ND3) un-
dergoing in the three steps and only one half of the
NH3 (ND3) molecules (2/6 + 1/6 = 1/2) are initially
liberated, and in the case of hexaaminemagnesium ni-
trate(V) compound the liberation undergoes in two steps
and two-third of the NH3 molecules (2/6 + 2/6 = 2/3)
are liberated. A possible reason of that difference is that
in the case of nickel compounds one half, and in the
case of magnesium compound two thirds, of all NH3
molecules are bonded weaker to the central metal atom
than the rest molecules, probably because of they take
a part in a−stronger hydrogen bonds with oxygen atoms
from NO3 anions. Thus, the reorientational motions of
this part of NH3 molecules may be frozen earlier than
that of the rest. If this is true, there is a great similarity
between the different manner of the liberation of the
NH3 ligands and the different character of the orien-
tational order-disorder process of these ligands in hex-
aaminenickel(II) nitrate(V) and in hexaaminemagnesium
nitrate(V).
2. The thermal decomposition of [Mg(NH3)2](NO3)2
is also different than that of [Ni(NH3)2](NO3)2 and
[Ni(ND3)2](NO3)2. In both cases the decomposition
is connected with the redox processes, but in the case
of magnesium compound, contrary to the nickel com-
pounds, in the second stage, besides of liberation of
nitrogen, nitrogen oxides and H2O, undergoes the liber-
ation of NH3 and the formation of Mg(NO3)2, which in
turn decomposes next, in the third stage, to the oxygen,
nitrogen oxides and MgO. This third stage is not present
in the case of both nickel compounds, and the decompo-
sition of diaminenickel(II) nitrates(V) undergoes directly
to the final products (NiO1+x, nitrogen, nitrogen oxides
and H2O) without the formation of Ni(NO3)2, because
of the autocatalytic effect of the formed NiO.
The profile of the SDTA curve of [Ni(ND3)6](NO3)2
shows three endothermic peaks and one single exothermic
peak. The endothermic peaks can be explained by the three
stages of the deamination resulting in the formation of
the tetra-, tri- and diamine, according to reactions that are
very similar to reactions (4). The third endothermic peak
is immediately followed by a sharp exothermic peak The
[Ni(NH ) ](NO )
3 6
3 2
[Ni(ND ) ](NO )
3 6 3 2
100
90
80
70
60
50
40
30
20
550
575
600
T /
625
650
K
300
400
500
600
700
800
900
1000
T / K
Fig. 6. Comparison of TG and DTG curves for [Ni(NH3)6](NO3)2 and
[Ni(ND3)6](NO3)2.

A. Migdał-Mikuli et al. / Thermochimica Acta 419 (2004) 223–229
229
´
Acknowledgements
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Janik, A. Migdał-Mikuli, E. Mikuli, M. Rachwalska, T. Stanek,
Physica B 138 (1986) 295.
Appreciations are due to Dr. M. Buæko, who made the
X-ray measurements and to I. Szpyt M.Sc., who registered
for us the FT-MIR spectra.
[5] J.A. Janik, J.M. Janik, A. Migdał-Mikuli, E. Mikuli, M. Rachwalska,
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[7] A. Małecki, R. Gajewski, S. Łabus´, B. Prochowska-Klisch, K. Wo-
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