Synthesis, thermal behavior, and energetic properties of diuronium 1H,1′H-5,5′-bistetrazole-1,1′-diolate salt

Article abstract of DOI:10.1016/j.molstruc.2016.12.009

A new nitrogen-rich energetic salt called diuronium 1H,1′H-5,5′-bistetrazole-1,1′-diolate (DUBTO) was first synthesized by reacting urea with 1H,1′H-5,5′-bistetrazole-1,1′-diolate dihydrate (H₂BTO 2H₂O). The structure of this new energetic salt was fully characterized through single-crystal X-ray diffraction, FT-IR, ¹H NMR, ¹³C NMR, and elemental analysis. DUBTO was crystallized in the monoclinic space group P21/n. The thermal stability was investigated through differential scanning calorimetry (DSC) and thermogravimetric tandem infrared spectrometry. Results showed that DUBTO contained one endothermic process and two exothermic processes. The second exothermic process is mainly intense exothermic decomposition with a mass loss of approximately 69.3% in the temperature range of 523.8–594.6?K. The non-isothermal kinetic parameters of the main exothermic process were calculated based on methods proposed by Kissinger and Ozawa-Doyle. Based on the Kamlet-Jacobs formula, the detonation velocity and detonation pressure of DUBTO were calculated as 8267?m?s^?1 and 29.15?GPa, respectively.

Full text of DOI:10.1016/j.molstruc.2016.12.009

Accepted Manuscript
Synthesis, Thermal Behavior, and Energetic Properties of Diuronium 1H,1′H-5,5′-
bistetrazole-1,1′-diolate Salt
Yu Shang, Bo Jin, Qiangqiang Liu, Rufang Peng, Zhicheng Guo, Qingchun Zhang
PII:
S0022-2860(16)31299-6
10.1016/j.molstruc.2016.12.009
MOLSTR 23207
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
19 September 2016
02 December 2016
02 December 2016
Please cite this article as: Yu Shang, Bo Jin, Qiangqiang Liu, Rufang Peng, Zhicheng Guo,
Qingchun Zhang, Synthesis, Thermal Behavior, and Energetic Properties of Diuronium 1H,1′H-5,5′-
bistetrazole-1,1′-diolate Salt, Journal of Molecular Structure (2016), doi: 10.1016/j.molstruc.
2016.12.009
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ACCEPTED MANUSCRIPT
Highlights



A new energetic salt called diuronium 1H,1′H-5,5′-bistetrazole-1,1′-diolate (DUBTO) was
synthesized successfully and fully characterized.
The results of the non-isothermal kinetic analysis indicated that the Arrhenius equation of the
3
main exothermic process can be expressed as follows: lnk = 46.85 - 218.485 x 10 /RT.
This salt shows excellent impact sensitivities of >40 J and promising detonation velocity and
–
1
detonation pressure of DUBTO were calculated as 8267 m·s and 29.15 GPa, respectively.

ACCEPTED MANUSCRIPT
Synthesis, Thermal Behavior, and Energetic Properties of
Diuronium 1H,1′H-5,5′-bistetrazole-1,1′-diolate Salt
a
a
a
a
b
Yu Shang , Bo Jin , Qiangqiang Liu , Rufang Peng *, Zhicheng Guo , Qingchun
Zhang
a
aState Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University
of Science and Technology, Mianyang 621010, China
bSchool of Nation Defence Science and Technology, Southwest University of Science and Technology, Mianyang
6
21010, China
Abstract. A new nitrogen-rich energetic salt called diuronium 1H,1′H-5,5′-bistetrazole-1,1′-
diolate (DUBTO) was first synthesized by reacting urea with 1H,1′H-5,5′-bistetrazole-1,1′-diolate
dihydrate (H BTO 2H O). The structure of this new energetic salt was fully characterized through
2
2
1
13
single-crystal X-ray diffraction, FT-IR, H NMR, C NMR, and elemental analysis. DUBTO was
crystallized in the monoclinic space group P21/n. The thermal stability was investigated through
differential scanning calorimetry (DSC) and thermogravimetric tandem infrared spectrometry.
Results showed that DUBTO contained one endothermic process and two exothermic processes.
The second exothermic process is mainly intense exothermic decomposition with a mass loss of
approximately 69.3 % in the temperature range of 523.8-594.6 K. The non-isothermal kinetic
parameters of the main exothermic process were calculated based on methods proposed by
Kissinger and Ozawa-Doyle. Based on the Kamlet-Jacobs formula, the detonation velocity and
–
1
detonation pressure of DUBTO were calculated as 8267 m·s and 29.15 GPa, respectively.
Keywords: Diuronium 1H,1′H-5,5′-bistetrazole-1,1′-diolate (DUBTO); N-Oxides; Single crystal;
Thermal properties; Energetic properties
1
. Introduction
Over the past few decades, considerable effort has focused on the development of nitrogen-
rich high-energy-density materials (HEDMs) that exhibit a good balance between sensitivity and
performance in addition to environmental compatibility.[1-9] Nitrogen-rich energetic salts are
among the hottest topics in the field of HEDM.[10] These salts characterized by high energy and
low sensitivity play an important role in energetic materials because of their high heat of
formation (HOF), density, thermal stability, good oxygen balance, and environmentally friendly
properties.[11-14] Considering the requirements of high energy, insensitivity, and stability for
energetic materials, several researchers, including Klapötke,[7, 15-20] Shreeve,[21-27] and
others[28-33], have synthesized many energetic salts through weak intermolecular interactions.
Tetrazole moiety is a promising energetic building block in this research area because it
contains a large number of energetic N–N and C–N bonds, exhibits extensive hydrogen bonding,
and decomposes to produce a high percentage of dinitrogen.[34-36] To improve the energetic
properties of tetrazoles, several recently published studies showed that introduction of N-oxides
yields compounds characterized by higher densityand stability, lower sensitivity, and better
oxygen balance.[8, 37-41] 1H,1’H-5,5’-bitetrazole-1,1’-diol, a typical bitetrazole with N-oxides, is
strongly acidic and bears two protons that can easily form stable oxygen-rich salts with various
nitrogen-rich bases.[42] A series of different 1H,1H-5,5-bitetrazole-1,1-diolates salts were
synthesized and actively studied,[42-47] such as dihydroxylammonium 5,5’-bistetrazole-1,1’-
diolate (TKX-50), which is one of the most promising energetic materials to replace the

Prof. Dr. Bo Jin, jinbo0428@163.com

Prof. Dr. Rufang Peng, rfpeng2006@163.com
a
State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest
University of Science and Technology, Sichuan Mianyang 621010, China

ACCEPTED MANUSCRIPT
commonly used military explosive, RDX (1,3,5-trinitro-1,3,5-triazacyclohexane).[44] Uronium is
an important nitrogen-rich cation used to construct high-performance energetic materials because
of its obvious advantages such as high nitrogen and oxygen percentages, high heat of formation,
and low cost.[48] Similar to hydroxylammonium cation, the oxygen of uronium not only increases
the oxygen balance but also provides the acceptor character of the hydrogen bond. In this study we
present the synthesis and characterization of the new energetic compound DUBTO. Furthermore,
the thermodynamic analysis, energetic properties, and impact sensitivity were performed to obtain
comprehensive data.
2
. Results and Discussion
2
.1 Synthesis
1
H,1′H-5,5′-bistetrazole-1,1′-diolate dihydrate (H BTO·2H O) was synthesized in
2
2
accordance with a previously described procedure.[42] H BTO·2H O was synthesized starting
2
2
from glyoxal, which was treated with hydroxylamine to form glyoxime. Glyoxime was then
chlorinated with Cl gas in ethanol; chloro/azido exchange occurred and yielded diazidoglyoxime,
2
which was cyclized under acidic conditions (HCl gas in diethyl ether) to produce 1. The new
energetic salt was synthesized after 1 was treated with stoichiometric amounts of urea, as shown in
Scheme 1.
Scheme 1. The synthesis of ATHBTO
2
.2 Characterization of DUBTO.
The structure of DUBTO is supported by FT-IR, H NMR, C NMR, and elemental analysis.
1
13
In addition, the crystal structure of DBUTO was measured by X-ray diffraction. Figure 1 shows
−1
the IR spectrum of DUBTO. As shown in Figure 1, the intense broad band at 3447 cm is
-1
attributed to the N–H stretching vibrations of DUBTO, and the peak at 1665 cm corresponds to
the stretching vibrations of C=O.[48] Moreover, the N-oxide of the aromatic tetrazole ring system
-1
shows vibrations at 1384–700 cm [ν(NN), ν(NCN), γ(CN),  aromatic ring], similar to those of
other 1H,1H-5,5-bitetrazole-1,1-diolates salts.[42] Consequently, the infrared spectrum shows
good consistency with the structural features of the compound.

ACCEPTED MANUSCRIPT
Figure 1. IR spectrum of DUBTO
The H NMR and 13C NMR spectra also confirmed the correct structure of DUBTO. In the
1
1
H NMR spectrum, the signal for the amino group of salt occurred as a broad singlet at δ = 6.99
1
3
ppm (s, 4H, NH ).[48] In the C NMR spectrum, the shifts corresponding to the cation and anion
2
in this study are in good agreement with previously recorded shifts for the relevant cation and
1
3
anion.[42, 48] The signals in the C NMR [DMSO-d6] spectrum of salt were found at δ (ppm) =
+
1
60.55 [C=OH ] and 135.22 [CN O].
4
A suitable crystal of DUBTO was obtained by slowly evaporating water at room
temperature, and was then subjected to single crystal X-ray analysis. The X-ray crystallographic
analysis data for DUBTO show that it crystallizes in the monoclinic space group P21/n with a
3
calculated density of 1.695 g/cm (Figure 2) based on two molecules packed in the unit-cell
3
volume of 568.7(2) Å . The selected data and parameters from their X-ray structures are listed in
Table 1. As shown in Figure 2, all of the atoms of BTO anion are almost coplanar, with the largest
#
1
torsion angle of 179.85(16)° in N(2)-N(1)-C(1)-C(1) . With bond lengths of 1.3108(18) to
.3485(18) Å, the distances between the ring atoms of the two tetrazole-oxide rings lie between
the length of formal C-N and N-N single and double bonds (C=N: 1.470 Å, C=N: 1.220 Å; N=N:
.480 Å, N=N: 1.240 Å).[49] Furthermore, the C–C bond connecting the two tetrazole moieties
1
1
#
1
and the N–O bonds are found between a C–C single bond and a C=C double bond (d(C(1)-C(1) )
1.445(3) Å) and between a N–O single bond and a N=O double bond (d(N(1)-O(1)) =
.3272(15) Å), respectively.[42] Selected bond lengths and angles of DUBTO are presented in
=
1
Table 2. This result demonstrates the conjugation of the negative charge throughout the aromatic
rings. Meanwhile, all the torsion angles [i.e., O(1)-N(1)-C(1)-N(4) (-176.79(12)°), O(1)-N(1)-
#
1
C(1)-C(1) (3.0(3)°) ] are close to ±180° and 0°, which illustrates that the atoms of anion are
strictly coplanar. The packing structure of DUBTO viewed along the c axis is built up by
hydrogen bonding. The extensive hydrogen-bonding interactions between cations and anions form
a complex 3D network (Figure 3). Further details are provided in Table 3.
Figure 2. Ball-and-stick molecular structure of DUBTO

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Table 1. Crystal data and structure refinement parameters of DUBTO
Compound
DUBTO
Empirical formula
Formula weight
CCDC number
4 10 12 4
C H N O
290.24
1487783
0.21 x 0.20 x 0.19
Monoclinic
P21/n
3
Crystal size [mm ]
Crystal system
Space group
a [Å]
3.6802(8)
17.688(4)
8.7803(19)
90
b [Å]
c [Å]
α [°]
β [°]
95.758(2)
90
568.7(2)
2
1.695
100(2)
300
γ [°]
3
V [Å ]
Z
-3
ρ
calcd [g·cm ]
T [K]
F(000)
R
Data
int.
0.0214
1011
Restraints
parameters
GOF on F
1
91
1.05
0.0328
0.0859
0.0361
0.0884
[a]
2
[
b]
R
1
(I > 2σ (I))
(I > 2σ (I))
1
(all data)
ωR
R
ωR
2
[c]
2
(all data)
[a]
GOF= Goodness of Fit. [b]
|. [c] ωR
2-F
2)2 )/ω(F
2 2 1/2
R
1
= ∑||F
o
|-|F
c
||/∑|F
o
2
= [(ω (F
o
c
o
) ] .
Figure 3. Ball-and-stick packing diagram of DUBTO viewed down the c axis. Dashed lines indicate hydrogen
bonding
Table 2. Bond Lengths [Å] and angles [°] for DUBTO
bond
Length/Å
bond
Angle/˚
N(1)-O(1)
N(1)-N(2)
N(1)-C(1)
N(2)-N(3)
N(3)-N(4)
N(4)-C(1)
N(6)-C(2)
N(6)-H(6A)
N(6)-H(6B)
1.3272(15)
1.3335(17)
1.3459(18)
1.3108(18)
1.3485(18)
1.3269(19)
1.3137(19)
0.88
O(1)-N(1)-N(2)
O(1)-N(1)-C(1)
N(2)-N(1)-C(1)
N(3)-N(2)-N(1)
N(2)-N(3)-N(4)
C(1)-N(4)-N(3)
C(2)-N(6)-H(6A)
C(2)-N(6)-H(6B)
H(6A)-N(6)-H(6B)
121.51(11)
129.32(11)
109.10(11)
105.96(11)
111.08(12)
105.83(12)
120
120
120
0.88

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N(7)-C(2)
N(7)-H(7A)
N(7)-H(7B)
O(2)-C(2)
O(2)-H(2C)
C(1)-C(1)#1
1.3146(19)
0.88
0.88
1.2895(18)
0.9659
C(2)-N(7)-H(7A)
C(2)-N(7)-H(7B)
H(7A)-N(7)-H(7B)
C(2)-O(2)-H(2C)
N(4)-C(1)-N(1)
N(4)-C(1)-C(1)#1
N(1)-C(1)-C(1)#1
O(2)-C(2)-N(6)
O(2)-C(2)-N(7)
N(6)-C(2)-N(7)
120
120
120
116.6
108.03(12)
127.47(16)
124.51(15)
117.30(13)
121.39(13)
121.31(13)
1.445(3)
Symmetry transformations used to generate equivalent atoms: #1 -x+2,-y+1,-z+3
Table 3. Hydrogen bonds for DUBTO
D-H...A
d(D-H)
d(H...A)
d(D...A)
N(6)-H(6A)...O(1)#1
N(6)-H(6B)...O(2)#2
N(6)-H(6B)...N(2)#3
N(7)-H(7A)...N(4)#4
N(7)-H(7B)...N(3)
0.88
0.88
0.88
0.88
0.88
2.153
2.421
2.523
2.208
2.166
1.511
2.395
2.977
2.949
3.18
2.989
3.031
2.472
3.308
O(2)-H(2C)...O(1)#5
O(2)-H(2C)...N(1)#5
0.966
0.966
Symmetry transformations used to generate equivalent atoms: #1 [x-3/2, -y+3/2, z-1/2]; 2# [x+1/2, -y+3/2, z+1/2];
# [x-1, y, z]; 4# [-x+1, -y+1, -z+2]; 5# [x-1, y, z-1]
3
2
.3 Thermal stability analysis of DUBTO
To investigate the thermal behavior of DUBTO, we analyzed it through differential scanning
calorimetry (DSC) and thermogravimetry–derivative thermogravimetry (TG–DTG), with a linear
heating rate of 10 K/min in flowing high-purity nitrogen. The data curves from these analyses are
shown in Figures 4 and 5. In the DSC curve, three processes occur: one endothermic and two
exothermic. The endothermic process starts at 451.4 K and shows a peak temperature of 460.6 K.
Subsequently, DUBTO becomes unstable and begins to decompose. The first exothermic
decomposition stage is exhibited in the DSC data, and the peak is observed at 465.3 K. The second
exothermic process is a main process with peak temperature of 561.2 K. In addition, TG-DTG
curves showed two main mass loss processes during the decomposition of DUBTO. The first
mass loss occurred at 456.2 K and ended at 479.2 K, accompanied by a mass loss of 10.8 % and a
summit peak located at 466.2 K in the DTG curve. The second stage occurred at 523.8 K and
ended at 594.6 K, along with 69.3 % mass loss and the summit peak in the DTG curve at 562.3 K.
Figure 4. DSC curve of DUBTO

ACCEPTED MANUSCRIPT
Figure 5. TG-DTG curve of DUBTO
To improve our understanding of the thermal decomposition behavior of DUBTO,
thermogravimetric analysis tandem infrared spectrum was used to rapidly identify the constituents
of the thermal decomposition gas. Figure 6 depicts the FT-IR spectra of the thermal
decomposition gas during decomposition at their different temperatures. The figure shows that the
thermal decomposition of DUBTO also exhibits two stages, a characteristic that is consistent with
the TG/DTG results. The first decomposition occurred at approximately 455.2 K. From Figure 6,
−
1
we can deduce that the main decomposition products are H O (3450-3600 cm ) and N O (2192-
2
2
−1
−1
2
330 cm , 748 cm ), which was confirmed by the peak in the corresponding IR spectra.[50] In
the second stage, the main gas products are HN (3456 cm ), N O (2192-2330 cm , 748 cm )
and NO (1786 cm ). When the heating temperature increased to 594.6 K, infrared signals nearly
−1
−1
−1
3
2
−1
disappeared, there by proving that DUBTO was completely decomposed.
Figure 6. FT-IR spectra of gas products of DUBTO during decomposition at individual temperatures.
2
.4 Thermal decomposition Kinetics of DUBTO
The main exothermic process makes a dominant effect on the decomposition of energetic
materials. To explore the decomposition mechanisms of DUBTO and obtain the corresponding
kinetic parameters [the apparent activation energy (E) and the pre-exponential factor (A)], the
Kissinger's method[51] and Ozawa–Doyle's method[52, 53] were employed, depending on the
peak temperatures measured at four different heating rates of 5, 10, 15, 20 K/min (Figure 7). The
Kissinger Equation (1) and Ozawa–Doyle Equation (2) are as follows, respectively:

ACCEPTED MANUSCRIPT
2
ln( /T )  ln(AR / E )  (E / RT )
p
a
a
p
(
1)
2)
lg   C -0.4567E / RT
a
(
-1
where T is the peak temperature (K); A is the pre-exponential factor (s ); E is the apparent
p
a
activation energy (kJ/mol); R is the gas constant (J/mol·K); β is the linear heating rate (K/min) and
C is a constant.
The apparent activation energies E and E , pre-exponential factor A, linear correlation
k
o
coefficients R and R for the complex were calculated by Kissinger’s method and Ozawa–Doyle’s
k
o
method. The results are fairly similar and are shown in Table 4, which are all in the normal range
of kinetic parameters for the thermal decomposition reaction of solid materials. From Table 4, it
can be seen that the exothermic peak T shifts to higher temperatures as the heating rate increases
p
and the linear correlation coefficients are very close to 1, demonstrating that the results are
credible. Using the obtained E (the average of E and E ) and lnA values, the Arrhenius equation
a
k
o
k
3
can be expressed as lnk = 46.85 – 218.485 x 10 /RT for the exothermic process, which can be
applied to estimate the rate constants of the initial thermal decomposition processes of DUBTO.
Figure 7. DSC curves of the main exothermic decomposition of DUBTO at different heating rates
Table 4 Peak temperatures of the exothermic stage at different heating rates and the kinetic parameters
Kissinger 法
Ozawa 法
(kJ/mol) r
o
β(Kmin)
T
p
(K/min)
-1
E
k
(kJ/mol) lnA (s )
r
k
E
o
5
553.6
561.2
565.2
569.8
1
1
2
0
5
0
2
19.43
46.85
0.995
217.54
0.996
2
.5 Energetic properties
The detonation parameters, detonation velocity (D) and detonation pressure (P) are important
parameters of scaling the detonation characteristics of energetic materials. The empirical Kamlet-
Jacobs equations[54] were employed to estimate the values of detonation velocity and detonation
pressure for DUBTO, shown as Equation (3) and (4):
1
/ 2
1
/ 2 1/ 2
D 1.01(NM
Q
)
(11.3)
(
3)
4)
1
/ 2
2
1/ 2
P 1.558 NM
Q
(

ACCEPTED MANUSCRIPT
−1
Where D is the detonation velocity (km·s ), P is the detonation pressure (GPa), N is the
−1
M
explosive detonation that generated gas moles per gram (mol·g ), is the gaseous product of
−
1
−1
the average molecular weight (g·mol ), Q is the explosive detonation chemical energy (kJ·g )
−3
per gram, ρ is the density (g·cm ). The Q value should be calculated first to calculate the D and P
values. Q is also determined by the ΔH of the detonation reactant and product.
f
Figure 8. Born–Haber circle of ionic salt
According to the Born–Haber[55] (m, n, o, and p stand for the factor of C, H , N , O ) energy
2
2
2
cycle (figure 8), the standard heat of formation of a salt can be simplified in equation (5):
H (ionic salt, 298k) = H (anion salt, 298k) + H (cation salt, 298k) - HL
f
f
f
(5)
Where ΔH is the lattice energy of salt and can be predicted by using the formula suggested
L
2
-
by Jenkins et al.[56, 57] The calculated standard enthalpy of formation for the uronium and BTO
were 719.4[48] and 587.7 kJ/mol[42], respectively, as provided in the literature. With the
calculated heats of formation and calculated density, detonation parameters were calculated by the
Kamlet-Jacobs equation. The calculation of the parameters in the Kamlet–Jacobs equation is
shown in Table 5.
Table 5 Calculation of the parameters in the Kamlet–Jacobs equation
M/
g·mol-3)
(
ρ/
(g·cm-3)
-1
ΔH
/(
-1)
kJ·mol
N/(mol·g )
M /
(g·mol-1)
f
2
90.24
1.695
0.0379
22
689.57
−
1
The Q estimated through the ΔH was 1364.41 kJ·g , and the theoretically computed
f
–
1
detonation velocity (D) and detonation pressure (P) were 8267 m·s and 29.15 GPa, respectively.
This exhibits superior detonation performance than that of TNT (6881 m s , 19.50 GPa).[58]
–
1
Sensitivity should be extensively investigated because this parameter is closely linked with
the safety of handling and applying explosives. In this work, the impact sensitivity of the
compound was determined using the fall hammer test with approximately 30 mg samples (10 kg
drop hammer). the impact sensitivity was determined using a BAM Fall hammer apparatus with a
1
0 kg drop weight. The sensitivity was > 40 J, classifying it as impact insensitive energetic
materials. This result indicates that the energetic salt is more insensitive than RDX (7.4 J), HMX
7 J), TNT (15 J).[58]
(
3
Conclusions
A new energetic salt DUBTO was synthesized successfully and fully characterized through
single-crystal X-ray diffraction, multinuclear NMR spectroscopy, IR spectroscopy and elemental
analysis (EA). The thermal stability analysis indicated that a main exothermic process occurred in
the temperature range from 523.8 K to 594.6 K as shown in the DSC curve corresponding to TG-
DTG curves. The results of the non-isothermal kinetic analysis indicated that the Arrhenius
equation of the main exothermic process can be expressed as follows: lnk = 46.85 - 218.485 x
3
1
0 /RT. Moreover, the detonation parameters of DUBTO were calculated by using Kamlet-Jacobs
–
1
equations and the detonation velocity and detonation pressure were calculated as 8267 m·s and
2
9.15 GPa, respectively.
4
Experimental Section

ACCEPTED MANUSCRIPT
4
.1 General: 5,5′-bistetrazole-1,1′-diolate dihydrate was synthesized according to ref.[42]. All
other materials were commercially available and used without further purification. Fourier
transform infrared (FT-IR) spectra was recorded on a Nicolet-5700 FTIR spectrometer by using
−
1
−1
pressed KBr pellets to evaluate the chemical bonding of the samples from 4000 cm to 400 cm .
1
13
H NMR and C NMR spectra were obtained using a JEOL GSX 600 MHz nuclear magnetic
resonance (NMR) spectrometer in a DMSO solution by using tetramethylsilane as an internal
standard. DSC was performed by a Q200 DSC instrument (TA Instruments, United States) in
flowing high-purity nitrogen at a heating rate of 5, 10, 15 and 20 K/min. TGA was performed with
an SDT Q600 TGA instrument (TA Instruments, United States) at a heating rate of 10 K/min in
flowing high-purity nitrogen.
4
.2 X-ray Crystallography: The single crystal of DUBTO was cultured via a slow solvent
3
evaporation method. A colorless prism crystal of dimensions 0.21 x 0.20 x 0.19 mm for DUBTO
was used for single-crystal X-ray diffraction analysis. Data were collected using a three-circle
Bruker platform diffractometer equipped with a graphite monochromator and Mo Kα radiation (λ=
0
1
.71073 Å). An Oxford Cobra low temperature device was used to maintain DUBTO at a constant
00 K during data collection. All calculations were performed using the Crystal Structure
crystallographic software package except for refinement, which was performed using
SHELXL2014. Hydrogen atoms were added theoretically and refined with riding model position
parameters and fixed isotropic thermal parameters. The details of the data collection and
refinement are presented in Table 1.
4
.3 Synthesis of DUBTO: 1H,1′H-5,5′-bistetrazole-1,1′-diolate dihydrate (206 mg, 1 mmol) was
suspended in a few milliliters of water, and urea (120 mg, 2 mmol) was added. The mixture was
briefly heated to reflux and filtered. After cooling to room temperature, the resulting solution was
evaporated slowly at room temperature for two weeks, and the DUBTO precipitated as colorless
-1
prism crystals were obtained, yield 194.3 mg (0.67 mmol, 67 %). IR (KBr) v/cm : 3447 (vs), 2925
1
(
w), 1665 (s), 1384 (w), 1321 (vw) 1178 (w), 1035 (w), 988 (w), 731 (w), 596 (w), 493 (w). H
1
3
NMR (600 MHz, [D ]DMSO, 25 °C) δ/ppm: δ = 6.99. C NMR (150 MHz, [D ]DMSO, 25 °C)
6
6
δ/ppm: 160.55, 135.22. elemental analysis (%) calcd for C H N O (290.24): C, 16.55; H, 3.45;
4
10 12
4
N, 57.93; found: C, 17.31; H, 3.89; N, 57.13.
Acknowledgments
We are grateful for financial support from the National Natural Science Foundation of China
5
(project no.51372211), Open Project of State Key Laboratory Cultivation Base for Nonmetal
Composites and Functional (project no. 14zdfk05) and Southwest University of Science and
Technology Outstanding Youth Fundation (project no. 13zx9107).
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