Synthesis, structure analysis and thermodynamics of [Ni(H 2O)4(TO)2](NO3)2· 2H2O (TO = 1,2,4-triazole-5-one)

Article abstract of DOI:10.1007/s10973-009-0400-1

A novel complex [Ni(H₂O)₄(TO)₂](NO3) 2· 2H₂O (TO = 1,2,4-triazole-5-one) was synthesized and structurally characterized by X-ray crystal diffraction analysis. The decomposition reaction kinetic of the complex was studied using TG-DTG. A multiple heating rate method was utilized to determine the apparent activation energy (E_a) and pre-exponential constant (A) of the former two decomposition stages, and the values are 109.2 kJ mol^-1, 10 ^13.80 s^-1; 108 0 kJ mol^-1, 10^23.23 s^-1, respectively The critical temperature of thermal explosion, the entropy of activation (ΔS^≠), enthalpy of activation (ΔH^≠) and the free energy of activation (ΔG ^≠) of the initial two decomposition stages of the complex were also calculated. The standard enthalpy of formation of the new complex was determined as being-1464.55 ± 1.70 kJ mol^-1 by a rotating-bomb calorimeter. Akademiai Kiado, Budapest, Hungary 2010.

Full text of DOI:10.1007/s10973-009-0400-1

J Therm Anal Calorim (2010) 100:1115–1120
DOI 10.1007/s10973-009-0400-1
Synthesis, structure analysis and thermodynamics
of [Ni(H2O)4(TO)2](NO3)2ꢀ2H2O (TO 5 1,2,4-triazole-5-one)
San-Ping Chen Æ Na Li Æ Qing Wei Æ
Sheng-Li Gao
Received: 14 May 2009 / Accepted: 29 July 2009 / Published online: 28 August 2009
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract
A
novel complex [Ni(H2O)4(TO)2](NO3)2ꢀ
intrigued worldwide interest in the field of energetic
materials based on their high nitrogen composition, high
enthalpies of formation and high densities. Until now, the
syntheses, structures, explosive properties, thermodynami-
cal and thermochemical properties of NTO metal salts have
been extensively studied [4–7], while other metal com-
plexes with simple 1,2,4-triazole derivatives were still in
the stage of syntheses and characterization of their basic
chemical properties [8–10]. Though many scientists have
predicted the potential applications of metal complexes
with TO as burning rate modifiers in the solid propellants
[11–13], the metal complexes have not been extensively
studied. In order to further explore thermodymanic prop-
erties of the transition metal complexes with TO, a new
complex [Ni(H2O)4(TO)2](NO3)2ꢀ2H2O has been synthe-
sized and characterized in this context. A multiple heating
rate method was adopted to calculate the apparent activa-
tion energy (Ea) and pre-exponential constant (A) of the
former two decomposition stages. And the standard
enthalpy of formation of the new complex was determined
by a precise rotating-bomb calorimeter.
2H2O (TO = 1,2,4-triazole-5-one) was synthesized and
structurally characterized by X-ray crystal diffraction
analysis. The decomposition reaction kinetic of the complex
was studied using TG-DTG. A multiple heating rate method
was utilized to determine the apparent activation energy (Ea)
and pre-exponential constant (A) of the former two
decomposition stages, and the values are 109.2 kJ mol-1
,
1013.80 s-1; 108.0 kJ mol-1, 1023.23 s-1, respectively. The
critical temperature of thermal explosion, the entropy of
activation (DS=), enthalpy of activation (DH=) and the free
energy of activation (DG=) of the initial two decomposition
stages of the complex were also calculated. The standard
enthalpy of formation of the new complex was determined
as being -1464.55 1.70 kJ mol-1 by a rotating-bomb
calorimeter.
Keywords 1,2,4-Triazole-5-one ꢀ Nickel complex ꢀ
Thermal analytical kinetic ꢀ Standard enthalpy of formation
Introduction
Since 3-nitro-1,2,4-triazole-5-one (NTO) was first reported
as a explosive agent in 1987 [1], metal complexes of 1,2,4-
triazole derivatives [2, 3] used as ballistic modifiers have
Experimental
Materials
According to the literature method, formic acid (88%,
Xi’an Chemical Co) and semicarbazide hydrochloride
(99%, ACROS) were used to synthesize 1,2,4-triazole-5-
one (TO), and the m.p. is 234.04 °C, which is consistent
with literatures [14, 15]. Ni(NO3)2ꢀ6H2O (AR) was com-
mercially available without further purification.
S.-P. Chen ꢀ N. Li ꢀ Q. Wei ꢀ S.-L. Gao (&)
Key Laboratory of Synthetic and Natural Functional Molecule
Chemistry of Ministry of Education, College of Chemistry &
Materials Science, Northwest University, 710069 Xi’an,
Shaanxi, People’s Republic of China
e-mail: gaoshli@nwu.edu.cn
An appropriate amount of TO (1 mmol, 0.085 g) dis-
solved in water (5 mL) was dropped into an ethanol
S.-P. Chen
e-mail: sanpingchen@126.com
123

1116
S. Chen et al.
solution (15 mL) of nickel nitrate (0.5 mmol, 0.149 g) at
60 °C. After being filtered, the filtrate was left at the room
temperature to obtain the green single crystal for X-ray
measurement. The green precipitates were washed with
anhydrous alcohol for three times and dried at room tem-
perature for further analysis (58% yield based on nickel
nitrate). Anal. calcd. for NiC4H18N8O14: C, 10.42%; H,
3.94%; N, 24.31%; Ni, 12.73%; found: C, 10.15%; H,
crystal data and structure refinement details for the com-
plex are given in Table 1.
Results and discussion
Structure analysis
4.08%; N, 24.79%. IR (KBr, cm-1): t (OH-) 3428 cm-1
t (C–H) 2858 cm-1 (C=O) 1756 cm-1, t (NO3ꢁ) 1386 cm-1
d (NO3ꢁ) 819 cm-1, t (C=N) 1568 cm-1, t (C–N) 1239 cm-1
d (framework of triazolone) 962 cm-1, 746 cm-1, 521 cm-1
,
As shown in Fig. 1, the Ni(II) shows a typical octahedral
central symmetrical geometry, where the Ni(II) coordinates
with four oxygen atoms from coordinated water molecules
in equatorial plane, and two axial nitrogen atoms from two
TO ligands. Selected bond lengths and angles are shown in
Table 2.
,
,
.
Instruments
The hydrogen bonds of the complex have been exam-
ined by PLATON 98, and all the length and angles of
hydrogen bonds fall in the normal range. The formation of
the hydrogen bonds has significant effect on the density,
stability of the complex. It was noteworthy that the for-
mation of hydrogen bonds could decrease the shock sen-
sitivity and increase the structural stability [2, 19, 20ꢁ].
Hydrogen bonds formed with the oxygen atoms of NO3
contribute significantly to construct the three-dimensional
network of the title complꢁex. The electrostatic potential
surface reveals that NO3 has an intrinsic hydrogen
bonding topography in which there are six equivalent
positions representing minimal energy for accepting H?.
C, H, N contents were determined on a Perkin-Elmer 2400
type elemental analyzer, IR spectrum was derived by a
Nicolet 60 SXR FT-IR (Nicolet, USA) spectrometer in the
4000–400 cm-1 regions (KBr pellets). The TG-DTG
experiments were performed with a Netzsch STA 449C
instrument with the heating rates of 5 °C min-1
,
10 °C min-1, 15 °C min-1 and 20 °C min-1 in N2 flowing
of 30 mL min-1 and the sample mass is about 1.5 mg.
The constant-volume combustion energy of the complex
was determined by a precise rotating bomb calorimeter
(RBC-type II). The main experimental procedures were
described previously [16]. The initial temperature was
regulated to 25.0000 0.0005 °C, and the initial oxygen
pressure was 2.5 MPa. The correct value of the heat
exchange was calculated according to Linio–Pyfengdelel–
Wsava formula [17]. The calorimeter was calibrated with
benzoic acid of 99.999% purity. It had an isothermal heat
of combustion at 25 °C of -26434 3 J g-1. The energy
equivalent of calorimeter was determined to be
17936.01 9.08 kJ K-1. The analytical methods of final
products (gas, liquid and solid) were the same as these in
reference [16]. The analytical results of the final products
showed that the combustion reactions were complete. As a
result, either carbon deposits or carbon monoxide formed
during the combustion reactions and the amounts of NOx in
the final gas phase were negligible.
Table 1 Crystallographic data for the complex
Empirical formula
C4H18N8NiO14
Formula weight
460.97
Space group
P - 1
a/nm
0.6636(2)
0.8253(3)
0.9219(5)
109.695(8)
99.645(9)
106.634(6)
0.4355(3)
1
b/nm
c/nm
a/°
b/°
c/°
V/nm
All single crystal X-ray experiments were performed on
a Bruker Smart-1000CCD diffractometer with graphite
Z
Dc/mg m-3
1.758
˚
monochromated MoJa radiation (k = 0.71073 A) using x
F (0 0 0)
Absorption coefficient/mm-1
238
and u scan modes within a range of 2.45 \ h \ 25.09 at
273 K. The crystal size was 0.22 9 0.18 9 0.10 mm. Of
2253 measures reflections, 1,526 observes reflections with
I [ 2r (I) were used in the refinement. The single crystal
structure of complex was solved by direct methods using
SHELXS-97 [18] and all non-H atoms were located using
subsequent Fourier-difference methods. Non-hydrogen
atoms were refined anistropically. The hydrogen atoms of
the organic ligands were generated geometrically. The
1.203
Limiting indices
-7 B h B 7, -9 B k B 9,
-10 B l B 10
Goodness-of-fit on F2
R (int)
0.907
0.0326
R1, wR2 (I [ 2r (I))
R1, wR2 (all data)
Largest diff. peak and hole/e nm-3
0.0506, 0.0989
0.0808, 1069
387, -482
123

Synthesis, structure analysis and thermodynamics
1117
01A
N3A
C2A
C1A
04A
N1A
07A
N2A
02A
03A
06
Ni1
03
02
N4A
06A
05A
05
N4
N2
07
C1
N1
04
N3 C2
01
Fig. 1 Coordination environment of Ni(II) in compound
[Ni(TO)2(H2O)4](NO3)2ꢀ2H2O
Fig. 2 The hydrogen bonds formed with the oxygen atoms of
NO3ꢁ(in order for clarity, the triazole rings coordinated with the
Ni2? in the top of the figure is omitted)
Table 2 Selected bond lengths (nm) and bond angles (8)
Ni(1)–O(2)
Ni(1)–O(3)
Ni(1)–N(2)
N(3)–C(1)
O(1)–C(2)
O(2)1–Ni(1)–O(2) 180.0
O(3)1–Ni(1)–O(3) 180.00(13)
0.2021(3) N(2)–C(1)
0.2052(3) N(2)–N(1)
0.2080(4) N(1)–C(2)
0.1347(5) N(3)–C(2)
0.1236(5)
0.1286(5)
0.1379(5)
0.1346(5)
0.1369(6)
Table 3 Hydrogen bond distance (nm) and angles (°) of the complex
D–HꢀꢀꢀA
d(D–H)
d(HꢀꢀꢀA)
d(DꢀꢀꢀA) \(DHA)
O(2)–H(2A)ꢀꢀꢀO(5)4 0.0876(10) 0.1926(17) 0.2787(5) 167(5)
N(3)–H(3)ꢀꢀꢀO(5)3
0.086
0.194
0.2793(5) 170.1
N(2)–Ni(1)–N(2)1 180.00(18)
O(3)–H(3B)ꢀꢀꢀO(6)8 0.0878(10) 0.1889(14) 0.2760(5) 172(6)
C(1)–N(2)–N(1)
C(1)–N(2)–Ni(1)
N(1)–N(2)–Ni(1)
C(2)–N(1)–N(2)
C(1)–N(3)–C(2)
O(7)–N(4)–O(6)
O(7)–N(4)–O(5)
O(6)–N(4)–O(5)
O(1)–C(2)–N(3)
103.9(3)
131.5(3)
124.6(3)
112.3(3)
108.1(4)
122.4(4)
119.4(4)
118.2(4)
127.9(4)
N(3)–H(3)ꢀꢀꢀO(6)3
N(1)–H(1)ꢀꢀꢀO(7)2
0.086
0.246
0.3108(5) 132.9
0.2801(5) 161.1
0.3109(5) 135(6)
O(2)–Ni(1)–O(3)i
O(2)–Ni(1)–O(3)
O(2)1–Ni(1)–N(2)
O(2)–Ni(1)–N(2)
O(3)i–Ni(1)–N(2)
O(3)–Ni(1)–N(2)
N(2)–C(1)–N(3)
O(1)–C(2)–N(1)
N(1)–C(2)–N(3)
90.18(15)
89.82(15)
89.41(14)
90.59(14)
91.69(14)
88.31(14)
112.3(4)
0.086
0.197
O(3)–H(3A)ꢀꢀꢀO(7)5 0.0877(10) 0.243(5)
O(2)–H(2B)ꢀꢀꢀO(4) 0.0878(10) 0.1817(16) 0.2684(5) 169(6)
O(3)–H(3A)ꢀꢀꢀO(4)6 0.0877(10) 0.249(5)
O(4)–H(4A)ꢀꢀꢀO(1)7 0.0879(10) 0.194(3)
O(4)–H(4B)ꢀꢀꢀO(1)9 0.0877(10) 0.196(2)
0.3152(8) 133(5)
0.2790(6) 162(8)
0.2790(5) 156(5)
Symmetry codes: (1) -x ? 1, -y ? 1, -z, (2) x, y ? 1, z - 1, (3) x,
y ? 1, z, (4) x - 1, y, z - 1, (5) x, y, z - 1, (6) x ? 1, y, z, (7) x - 1,
y - 1, z, (8) -x ? 1, -y, -z ? 1, (9) -x ? 1, -y ? 2, -z ? 1
128.7(4)
103.3(4)
ꢁ
The results indicate that the ideal NO3 would form six
hydrogen bonds with the outside atoms. However, it is
owing to the restriction of steric factors that such ideal
mode is rare [21–23]. In the crystal structure of the title
complex, the hydrogen bonds formed with oxygen atoms of
c
b
0
ꢁ
ꢁ
NO3 express the ideal mode. Oxygen atoms of NO3 as
the acceptor of the bifurcated hydrogen bonds form
hydrogen bond with one oxygen atom and one nitrogen
atoms, which are shown in Fig. 2. Hydrogen bond lengths
and angles are listed in Table 3.
a
As shown in Fig. 3, the triazole rings are parallel with
each other and the distance of the triazole between the
˚
layer are 3.1924, 3.3709 A, respectively. Offset face-to-
face p–p stacking interactions involving triazole ring and
hydrogen bonds construct the three-dimensional network of
the complex [Ni(H2O)4(TO)2](NO3)2ꢀ2H2O.
Fig. 3 Packing arrangement and the hydrogen bonds of
[Ni(TO)2(H2O)4](NO3)2ꢀ2H2O
123

1118
S. Chen et al.
351.90 K (the first step) and 429.65 K (the second step),
respectively.
DSC/mJ
DTG/% min–1
TG/%
472.65mJ
exo
100
90
80
70
60
50
40
30
20
234.92mJ
173°C
Tpi ¼ Tpo þ bbi þ cb2i i ¼ 1 ꢁ 4
where b and c are coefficients.
The corresponding critical temperature of thermal
ð1Þ
0
0
48°C
84.85% (125°C)
40.01% (207°C)
-2
-4
-6
-8
-10
-5
92°C
explosion (Tb) obtained from Eq. 2 taken from [26] is
359.84 and 437.36 K, respectively.
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
-10
-15
EO ꢁ EO2 ꢁ 4EORTpo
16.63% (600°C)
166°C
Tb ¼
ð2Þ
2R
100 200 300 400 500 600 700 800 900 1000
where R is the gas constant (8.314 J mol-1 K-1), EO is the
value of E obtained by Ozawa’s method.
The entropy of activation (DS=), enthalpy of activation
(DH=) and free energy of activation (DG=) are calculated
according to Eqs. 3–6, and the values are listed in Table 5.
T/°C
Fig. 4 DSC, TG-DTG curves of the complex {[Ni(TO)2(H2O)4]
(NO3)2}n with the heating rate 10 °C min-1
Thermogravimetric analysis
kBT
h
¼
R
eDS
ð3Þ
=
A ¼
Typical DSC and TG-DTG curves for the complex with the
heating rates of 10 °C min-1 are shown in Fig. 4.
¼
DH ¼ E ꢁ RT
ð4Þ
ð5Þ
As the TG-DTG has shown, the first endothermic step is
confirmed as the loss of four water molecules, and the lost
amount is 15.15% (cal. 15.62%). The residues are further
decomposed as nickel nitrate [11] at 207 °C and the residue
amount is 40.01% (cal. 39.64%). The final decomposition
product is NiO and the residue amount is 16.73%, which is
in good agreement with the calculated amount of 16.20%.
The decomposition residues are identified by XPRD.
¼
¼
¼
DG ¼ DH ꢁ TDS
where kB is the Boltzmann constant and h the Planck
constant.
As shown in Table 5, the values of DG=, DS=, and
DH= are all positive, indicating that the decomposition
Table 5 The kinetic parameters of the initial two decomposition
process
Thermal analytical kinetics
The first step
The second step
In order to obtain the apparent activation energy (Ea) and
pre-exponential constant (A) of the initial two decomposi-
tion stages of the complex, a multiple heating method is
adopted. From the original data obtained, Kissinger method
[24] and Ozawa’s method [25] are utilized to calculate the
Ea and A. The calculated results are listed in Table 4.
The value (Tpo) of the peak temperature (Tp) corre-
sponding to b ? 0 obtained by Eq. 1 taken from [21] is
T
po/°C)
78.5
132.09
17.21
83.18
129.17
99.92
156.5
209.6
23.23
196.8
206.0
121.4
Ek/kJ mol-1
lg(Ak)/s-1
DS=/J mol-1 K-1
DH=/kJ mol-1
DG=/kJ mol-1
Table 4 The calculated results of apparent activation energy (Ea) and pre-exponential constant (A)
The first step
Kissinger
The second step
Kissinger
Flynn–Wall–Ozawa
131.37
Flynn–Wall–Ozawa
E/kJ mol-1
Lg(A)/s-1
r
132.09
17.21
0.9981
3.716
109.2
209.6
23.23
0.9935
1.318
208.0
206.3
0.9940
0.9983
0.7052
Q (9103)
0.2483
Ea
The heating rate (b) is 5, 10, 15, 20 °C min-1, respectively. The maximum peak temperature (Tp) of the first decomposition process in four
TG-DTG curves are 86, 92, 95, 97 °C, respectively. The maximum peak temperature (Tp) of the second decomposition process in four TG-DTG
curves are 162, 166, 170, 172 °C, respectively. Ea apparent activation energy; A pre-exponential constant; r linear correlation coefficient; Q the
standard mean square deviation
123

Synthesis, structure analysis and thermodynamics
1119
reaction for the title complex is not spontaneous and
readily proceeds at high temperatures.
Conclusions
The single crystal structure of a new complex [Ni(TO)2
(H2O)4](NO3)2ꢀ2(H2O) has been determined by X-ray dif-
fractometer. Hydrogen bonds have significant effect to
construct the three-dimensional net. The kinetic of the
initial two decomposition stages has been investigated by
TG-DTG. The thermal decomposition kinetic study is quite
useful in the evaluation of thermal changes for the title
complex at high temperatures. As an important data to
evaluate the performance of the energetic material, the
standard enthalpy of formation has been determined by a
precise rotating-bomb calorimeter and the standard
enthalpy of formation of the title complex is -1464.55
The standard enthalpy of formation
The constant-volume combustion energy (DcU) of the
complex was determined by six experiments and the
method used was the same as that for calibration of
the calorimeter with benzoic acid. The combustion ener-
gies of the complex were calculated by the formula
WDT ꢁ aG ꢁ 5:983b
DcU ¼
ð6Þ
m
1.70 kJ mol-1
.
where DcU is the constant-volume combustion energy of
the complex, W is the energy equivalent of the RBC-type II
calorimeter (in J K-1), DT the correct value of the tem-
perature rising, a the length of actual Ni-Cr wire consumed
(in cm), G the combustion enthalpy of Ni-Cr wire for
ignition (0.9 J cm-1), 5.983 the formation enthalpy and
solution enthalpy of nitric acid corresponding to 1 mL of
0.1000 mol L-1 solution of NaOH (in J mL-1), b the
volume in mL of consumed 0.1000 mol L-1 solution of
NaOH and m the mass in grams of the sample. The cal-
Supplementary material
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data
Center, CCDC No. 294959. Copies of this information can
be obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: t44-1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
culated result is -6371.01 3.40 J g-1
.
The standard enthalpy of combustion of the complex,
DcHmh ([Ni(TO)2 (H2O)4](NO3)2ꢀ2H2O, s, 298.15 K), was
referred to the combustion enthalpy change of the follow-
ing ideal combustion reaction at 298.15 K and 100 kPa.
Acknowledgements We gratefully acknowledge the financial sup-
port from the National Natural Science Foundation of China (Grant
Nos. 20771089 and 20813100), the National Natural Science Foun-
dation of Shaanxi Province (Grant Nos. 2007B02 and SJ08B09), the
Educational Committee of Shaanxi Province (No. 08JK459) and the
Science and Technology Foundation of the National Defense Key
Laboratory of Propellant and Explosive Combustion of China (Grant
No. 51455010105QT3001).
NiðC2H3N3OÞ2ðH2OÞ ðNO3Þ2 ꢀ 2H2OðsÞ þ 2O2ðgÞ
¼ NiOðsÞ þ 4CO2ð4gÞ þ 4N2ðgÞ þ 9H2OðlÞ
ð7Þ
The standard enthalpy of combustion of the complex was
calculated by the following equations:
DcHmh ¼ DcU þ DnRT
Dn ¼ ngðproductsÞ ꢁ ngðreactantsÞ
ð8Þ
ð9Þ
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,
.
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ÀÂ
Ã
Á
DfHmh NiðH2OÞ4ðTOÞ2 ðNO3Þ2ꢀ2H2O; s; 298:15K
¼4DfHmh ðCO2; g;298:15KÞþ9DfHmh ðH2O; l; 298:15KÞ
þ4DfHmh ðN2; g; 298:15KÞþDfHmh ðNiO; s; 298:15KÞ
ÀÂ
Ã
Á
ꢁDcHmh NiðH2OÞ4ðTOÞ2 ðNO3Þ2ꢀ2H2O; s; 298:15K
when DfHmh (CO2, g,298.15 K) = -393.51 0.13 kJ mol-1
[24], DfHmh (H2O, l, 298.15 K) = -285.83 0.042 kJ mol-1
[27], the result obtained is -1464.55 1.70 kJ mol-1
.
123

1120
S. Chen et al.
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