Thermal decomposition mechanism and thermodynamic properties of [Ni(H 2O)6](NTO)2·2H2O

Article abstract of DOI:10.1016/j.tca.2003.12.002

The single crystal of nickel complex of 3-nitro-1,2,4-triazol-5-one (NTO), [Ni(H₂O)₆](NTO)₂·2H₂O was prepared and the crystal structure was determined by a four-circle X-ray diffractometer. Based on the results of thermal analysis, the thermal decomposition mechanism of [Ni(H₂O)₆](NTO) ₂·2H₂O was derived. From measurements of the enthalpy of solution in water of [Ni(H₂O)₆](NTO) ₂·2H₂O at 298.15 K, the standard enthalpy of formation, lattice enthalpy and lattice energy have been determined as -(2585.6±4.5), -2832.59, and -2797.58 kJ mol^-1, respectively.

Full text of DOI:10.1016/j.tca.2003.12.002

Thermochimica Acta 416 (2004) 39–42
Thermal decomposition mechanism and thermodynamic properties
of [Ni(H O) ](NTO) ·2H O
Jirong Song , Jie Huang , Haixia Ma , Rongzu Hu
2
6
2
2
a,∗
a
a
b
a
College of Chemical Engineering, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, Northwest University, Xi’an 710069, PR China
b
Xi’an Modern Chemistry Research Institute, Xi’an 710065, PR China
Received 2 October 2002; received in revised form 10 November 2002; accepted 20 December 2002
Available online 3 February 2004
Abstract
The single crystal of nickel complex of 3-nitro-1,2,4-triazol-5-one (NTO), [Ni(H
was determined by a four-circle X-ray diffractometer. Based on the results of thermal analysis, the thermal decomposition mechanism of
Ni(H O) ](NTO) O was derived. From measurements of the enthalpy of solution in water of [Ni(H O) ](NTO) O at 298.15 K, the
2
O)
6
](NTO)
2
2
·2H O was prepared and the crystal structure
[
2
6
2
·2H
2
2
6
2
·2H
2
−
1
standardenthalpyofformation, latticeenthalpyandlatticeenergyhavebeendeterminedas −(2585.6± 4.5), −2832.59, and−2797.58 kJ mol
,
respectively.
©
2003 Elsevier B.V. All rights reserved.
Keywords: Crystal structure; Nickel complex; NTO; Thermal decomposition mechanism; Thermodynamic properties
1
. Introduction
was gradually dropped into an aqueous solution of nickel
sulfate at 60 C to get green precipitates. The precipitates
◦
Much attention has been paid to 3-nitro-1,2,4-triazol-5-one
NTO) as a high energy and low sensitivity energetic mate-
were recrystallized with distilled water at room temperature
to obtain the green single crystal for X-ray measurement.
Its purity was more than 99.6%. Dimensions of the single
crystal were 0.15 mm × 0.15 mm × 0.20 mm.
(
rial [1,2]. Its metal complexes also have some potential uses
in ammunition [3–7]. Therefore, the authors prepared the
single crystal of the nickel complex of NTO, determined
its structure, studied its thermal decomposition mechanism
and thermodynamic properties.
2.2. Experimental equipment and conditions
The elemental analysis was performed on a MOD1106
(
Carlo Erba, Italy) elemental analysis instrument. The
2
. Experimental
infrared spectra of the decomposition residues were
recorded in KBr discs on a 60 SXRFT-IR (Nicolet, USA)
spectrometer.
2
.1. Materials
In the determination of the structure of the single crystal,
X-ray intensities were recorded by a CAD4PDP 11/44 au-
tomatic diffractometer with graphite, monochromatized Mo
K␣ radiation, λ = 0.071073 nm. Cell parameters were de-
termined from 25 reflections. Data were collected by θ/2θ,
[
Ni(H2O) ](NTO)2·2H2O used in this research work
6
was prepared according to the following method: an ap-
propriate amount of NTO was put into the distilled water
(
M:V = 1:4), then stirred and titrated with an aqueous so-
◦
◦
lution of lithium hydroxide under 60 C until the pH value
of the mixture reached a value of 6. The resulting solution
scan mode in the range of θ = 2–25 , h = 0–11, k = 0–16,
l = −7 to 7, and the 1651 independent reflections were
obtained, among which 1337 with I > 3.0␴(I) were used
for the determination and refinement of the crystal struc-
ture. Lorentz-polarization correction was applied but not for
absorption correction. The coordinates of Ni atom were ob-
∗
Corresponding author. Tel.: +86-29-830-2899;
fax: +86-29-830-2899.
E-mail address: changma@sohu.com (J. Song).
0
040-6031/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2003.12.002

4
0
J. Song et al. / Thermochimica Acta 416 (2004) 39–42
tained by the Patterson method and those of non-hydrogen
and hydrogen atoms were obtained by difference Fourier
synthesis. Refinement was performed by the block-diagonal
least-squares method using anisotropic thermal parameters
for non-hydrogen atoms and isotropic thermal parameters
for hydrogen atoms.
Table 1
Bond distances (nm)
Ni–Ow1
Ni–Ow2
Ni–Ow3
0.2080(5)
0.2027(4)
0.2018(5)
0.2080(5)
0.2027(4)
0.2018(5)
0.1270(4)
0.1209(10)
0.1220(4)
0.1366(4)
0.2044(3)
0.0775(4)
0.0530(3)
0.2580(2)
0.0919(15)
0.2771(9)
0.3070(2)
0.2720(3)
0.2980(5)
0.2878(12)
0.2734(14)
0.1360(5)
0.1298(11)
0.1350(5)
0.1337(8)
0.1450(3)
0.1842(15)
0.0833(13)
0.1910(3)
0.0951(7)
0.1959(8)
0.1972(4)
0.2230(3)
0.0825(7)
0.1959(6)
0.2690(2)
0.2807(5)
0.2871(5)
0.0893(5)
0.0926(3)
0.0975(8)
0.0775(4)
0.0893(5)
0.1970(2)
0.09750(8)
ꢀ
Ni–O w1
ꢀ
Ni–O w2
The thermal decomposition process was studied using
a TG technique on a Delta Series TGA7 (Perkin-Elmer,
USA). The conditions of TG were as follows: sample mass
ꢀ
Ni–O w3
O–C1
O2–N4
O3–N4
N1–N2
H1–Ow4
H1–N1
Hw11–Ow1
Hw11–O1
Hw12–Ow1
Ow3–Ow4
Ow1–Ow4
Ow1–O1
Ow1–O1
Ow2–O2
Ow2–N3
N1–C1
◦
−1
ca. 1 mg; heating rate 10 C min ; atmosphere, a flowing
N2/O2 mixture with a ratio of 99%.
All measurements of the enthalpy of solution in deion-
ized water were made using a Calvet microcalorimeter,
type BT215 from SETARAM, France, and operated at
2
98.15 ± 0.005 K. The experimental precision and accuracy
of enthalpies of solution were frequently checked by mea-
suring the enthalpies of solution (ꢀsolH ) of crystalline
KCl (NIST SRM1655) in deionized water at 298.15 K. The
experimental value of ꢀsol
is in excellent agreement with that of ꢀ
1
◦
∞
◦
−1
H
= 17.217 ± 0.053 kJ mol
∞
◦
H
=
sol
∞
−
1
7.234 kJ mol reported in the literature [8].
N2–C2
N3–C1
N3–C2
N4–C2
3
. Results and discussion
Hw12–O1
Hw21–Ow2
Hw21–N3
Hw22–Ow2
Hw22–O2
Hw41–N2
Hw42–Ow1
Hw31–Ow3
Hw31–Ow4
Ow3–O1
Ow4–N1
Ow4–N2
Ow3–Hw32
Ow4–Hw41
Ow4–Hw42
N1–H1
3
.1. Crystal structure
The crystal structure was found to be monoclinic, which
belongs to space group P21/c with crystallographic pa-
rameters of a = 0.9255(2) nm, b = 1.4133(2) nm, c =
◦
3
0
.6465(1) nm, β = 88.42(2) , V = 0.8452 nm , Z = 2,
3
−
−1
Dc = 1.819 g cm , µ = 12.382 cm , F(000) = 480.
The final R = 0.030, wR = 0.036 (unit weight), and
(∆/σ)max = 0.01.
The bond lengths and bond angles are summarized in
Tables 1 and 2. The crystal structure and atom labeling are
shown in Fig. 1.
The analytical results indicate that the formula of the
Hw32–Ow3
Hw32–O1
Hw42–Ow4
molecule is [Ni(H2O) ](NTO)2·2H2O. It is central symmet-
6
rical, and Ni atom is at the symmetrical center. The Ni atom
and six water molecules form an octahedron. Then combin-
ing it with two NTO anions, we can get [Ni(H2O) ](NTO)2.
6
There are two crystallization water molecules in the crystal.
The atoms in NTO anion are almost coplanar. The equa-
tion of the plane is
3.2. Thermal decomposition mechanism of
[Ni(H O) ](NTO) ·2H O
2
2
2
6
The typical TG–DTG curve of [Ni(H2O) ](NTO)2·2H2O
6
−
0.047x + 0.0398y − 0.9981z + 3.6005 = 0
The bond distances of a five-membered ring of NTO an-
is shown in Fig. 2. The DTG curve shows that the thermal
decomposition process of the title compound can be divided
into three stages. The first mass loss is 30.3% between 62.0
ion tend to be equal. The bond lengths of N1–C1, N3–C1,
N3–C2 and N1–N2 are almost equal, while the bond length
of N2–C2 is a little shorter, which is the nearest double bond
in the NTO anions, and that of N4–C2 is a little longer, which
is the longest in the NTO anion. The calculated result indi-
cates that the distance form Ni to the plane of NTO anion
is 0.3299 nm. Thus the distance between two NTO anion
planes is 0.6598 nm.
◦
and 161.5 C, which roughly coincides with the calculated
value (31.3%) of losing eight water molecules from the com-
◦
plex. The IR spectrum of the residue at 170 C shows the
−
1
absorption peak at 3519 cm was absent, which denotes
that the complex has been dehydrated. This process can also
be confirmed by the single crystal structure. The hydrogen
bonds between water molecules and the Ni atom are easy

J. Song et al. / Thermochimica Acta 416 (2004) 39–42
41
Table 2
Bond angles ( )
of each component cannot be determined from the present
experiment and it is impossible to determine the decom-
position change stoichiometrically. The third process is be-
◦
Ow1–Ni–Ow2
Ow1–Ni–Ow3
Ow2–Ni–Ow3
N2–N1–C1
N1–N2–C2
C1–N3–C2
91.2(5)
89.3(7)
90.9(3)
◦
tween 342.0 and 408.0 C. The IR spectrum of the residue at
◦
−1
3
42.0 C shows that a strong absorption peak at 443 cm is
111.0(2)
100.1(5)
102.0(1)
124.0(3)
168.2(3)
135.0(5)
118.0(3)
118.2(7)
124.0(4)
128.0(4)
108.0(5)
119.1(6)
119.0(1)
159.0(2)
170.0(4)
162.1(8)
141.0(1)
122.0(1)
110.0(3)
93.2(5)
assigned to NiO. At the end of this stage, the residue amount
is in good agreement with the calculated amount of 16.2%.
On the basis of the experimental and calculated results, the
O2–N4–O3
Ow4–H1–N1
Ow1–Hw11–O1
O2–N4–C2
O3–N4–C2
O1–C1–N1
O1–C1–N3
N1–C1–N3
N2–C2–N3
N2–C2–N4
Ow1–Hw12–O1
Ow2–Hw21–N3
Ow2–Hw22–O2
Ow2–Hw22–N4
N3–C2–N4
Hw11–Ow1–Hw12
Hw21–Ow2–Hw22
Hw31–Ow3–Hw32
Hw41–Ow4–Hw42
Ow3–Hw31–Ow4
Ow3–Hw32–O1
Ow4–Hw41–N2
Ow1–Hw42–Ow4
thermal decomposition mechanisms of [Ni(H2O) ](NTO)2·
6
2H2O can be expressed as
◦
6
2.0–161.5 C
[Ni(H O) ](NTO) · 2H O −−−−−−→
2
2
6
2
◦
161.5–342.0 C
Ni(NTO)2 −−−−−−−→ Ni(OCN)2
342.0–408.0◦C
+
NiCO3 −−−−−−−→ NiO
3.3. Thermodynamic properties of
[
Ni(H2O) ](NTO)2·2H2O
6
Results for the enthalpy of solution of [Ni(H2O) ](NTO)2·
6
106.5(6)
106.4(8)
167.9(4)
137.3(3)
162.9(3)
144.1(8)
2
H2O in deionized water at 298.15 K are listed in Table 3.
Because [Ni(H2O) ](NTO)2·2H2O is completely ionized
6
in aqueous solution, its ionization can be represented as
◦
ꢀsolH
m
2
[
Ni(H2O) ](NTO)2 · 2H2O −−−→ Ni +(aq, ∞) + 2NTO−
6
(
aq, ∞) + 8H2O(l)
(1)
to be broken. The second process occurs between 161.5 and
◦
3
42.0 C, corresponding to the further decomposition of the
In the above process, the greater values of r were used.
Therefore, the mean of ꢀsol
at infinite dilution.
dehydrated salt. The IR spectrum of the residue shows the
absorption peak of –NO2 has disappeared and the character-
istic absorption peaks of Ni(OCN)2 and NiCO3 have formed
after the decomposition peak appear at 2178, 1203, 1435 and
◦
H
in Table 3 can be considered
m
−1
7
61 cm , respectively. These observations indicate that the
decomposition residue of this stage is a mixture. The amount
Fig. 2. TG–DTG curve of [Ni(H2O)6](NTO)2·2H2O.
Table 3
Enthalpy of solution in water of [Ni(H2O)6](NTO)2·2H2O (cr) at 298.15 K
◦
−1
m (mg)
r
ꢀsolH (kJ mol
)
m
3
3
4
4
4
5
5
7
.870
.900
.100
.340
.860
.240
.700
.093
59502
59044
56164
53058
47381
43945
40399
32465
56.04
56.30
56.01
56.24
56.70
56.35
56.74
56.71
Mean
56.39 ± 0.32
◦
Note: ꢀsolHm denotes the enthalpy of solution in water of [Ni(H2O)6]
NTO)2·2H2O, where m is the mass of Ni(H2O)6](NTO)2·2H2O, and r
the molar ratio n(H2O)/n{[Ni(H2O)6](NTO)2·2H2O}.
(
Fig. 1. Molecular structure of [Ni(H2O)6](NTO)2·2H2O.

4
2
J. Song et al. / Thermochimica Acta 416 (2004) 39–42
◦
By substituting the mean of ꢀsol
H
◦
listed in Table 3
By substituting the above-mentioned data into Eqs. (4)
and (5), the following values are obtained:
m
2+
and the reported values of ꢀ H (Ni , aq, ∞)
=
f
−
m
−
1
◦
m
−
53.97 kJ mol [9]; ꢀ H (NTO , aq, ∞) = −(94.3 ±
f
◦
−1
,
−
1
◦
−1
ꢀH {[Ni(H2O)6](NTO)2·2H2O, cr}=−2832.59 kJ mol
2
.1) kJ mol [10]; and ꢀ H (H2O, l) = −285.83 kJ mol
L
f
m
◦
−1
[
9], into Eq. (2),
ꢀU {[Ni(H O) ](NTO) ·2H O, cr}=−2797.58 kJ mol
L
2
6
2
2
◦
◦
2+
◦
m
−
ꢀ
H
= ꢀ H (Ni , aq, ∞) + 2ꢀ H (NTO , aq, ∞)
sol
m
f
m
f
◦
◦
m
+
8ꢀ H (H2O, aq, ∞) − ꢀ H {[Ni(H2O) ](NTO)2 ·
H2O, cr, 298.15 K}
Acknowledgements
f
m
f
6
2
(2)
The authors gratefully acknowledge the National Science
Foundation of China (grant No. 29971025) for its financial
support.
The following value is obtained:
◦
ꢀ
H {[Ni(H2O) ](NTO)2 · 2H2O, cr} =
f
m
6
−
1
−
(2585.6 ± 4.5) kJ mol
.
References
◦
Setting ꢀH {[Ni(H2O) ](NTO)2 · 2H2O, cr} as the lattice
6
L
◦
enthalpy and ꢀU {[Ni(H2O) ](NTO)2 · 2H2O, cr} as the
[1] K.Y. Lee, L.B. Chapman, M.D. Coburn, J. Energetic Mater. 5 (1987)
27.
6
L
crystal lattice energy
[
[
[
[
[
2] K.Y. Lee, M.M. Stinecipher, Propellants Explosives Pyrotech. 14
(1989) 241.
3] J.R. Song, R.Z. Hu, F.P. Li, Chin. Sci. Bull. 41 (21) (1996) 1806–
Ni2 (g) + 2NTO (g) + 8H2O(g)
+
−
◦
ꢀ
H
L
1
810.
4] J.R. Song, W. Dong, R.Z. Hu, J. Rare Earth 15 (1) (1997) 62–65
in Chinese).
−
−→ [Ni(H2O) ](NTO)2 · 2H2O(cr)
(3)
6
(
5] J.R. Song, R.Z. Hu, B. Kang, F.P. Li, Thermochim. Acta 331 (1999)
49–60.
6] J.R. Song, R.Z. Hu, B. Kang, J. Therm. Anal. Calorimet. 55 (1999)
◦
◦
m
2+
ꢀ
H {[Ni(H2O) ](NTO)2 · 2H2O, cr}=ꢀ H {[Ni(H2O) ]
L
6
f
6
◦
m
·
(NTO)2 · 2H2O, cr, 298.15 K} − ꢀ H (Ni , g)
f
7
97–806.
[7] J.R. Song, Z.X. Chen, H.M. Xiao, R.Z. Hu, Chin. Sci. Bull. 44 (3)
1999) 214–217.
◦
−
◦
m
−
2ꢀ H (NTO , g) − 8ꢀ H (H2O, g)
(4)
f
m
f
(
[
8] R.C. Weast, CRC Handbook of Chemistry and Physics, 70th ed.,
CRC Press, Boca Raton, FL, 1989, p. D-122.
◦
◦
ꢀ
U {[Ni(H2O) ](NTO)2 · 2H2O, cr} = ꢀH {[Ni(H2O) ]
L
6
L
6
[9] R.C. Weast, CRC Handbook of Chemistry and Physics, 63rd ed.,
CRC Press, Boca Raton, FL, 1982, p. D-71, 78.
·
(NTO)2 · 2H2O, cr} − ꢀn RT
(5)
◦
2+
−1
◦
[10] A. Finch, P.J. Gardner, A.J. Head, H.S. Majdi, J. Chem. Thermodyn.
3 (1991) 1169.
11] R.Z. Hu, Z.H. Meng, B. Kang, Thermochim. Acta 275 (1996)
59.
where ꢀ H (Ni , g) = 2930.14 kJ mol
[9], ꢀ H
f
m
f
m
2
−
−1
◦
(
NTO , g) = −374.3 kJ mol
[11], ꢀ H (H2O, g) =
f
m
[
−
1
−1
.
−
241.82 kJ mol [9], ꢀn = −14, RT = 2.5 kJ mol
1