Nitrogen-rich 5-(4-pyridyl)tetrazole-2-acetic acid and its alkaline earth metal coordination polymers for potential energetic materials

Article abstract of DOI:10.1016/j.ica.2016.06.015

Tetrazole and its derivatives with rich nitrogen atoms may be potential candidates for energetic materials. Alkaline earth metal coordination compounds based on such ligands are relatively less investigated. Hpytza was prepared from 4-cyanopyridine and sodium azide, ethyl bromoacetate, where Hpytza = 5-(4-pyridyl)tetrazole-2-acetic acid. Hpytza and four alkaline earth metal coordination polymers [Mg(pytza)₂]_n (1), [Ca(pytza)₂(H₂O)₂]_n·3nH₂O (2), [Sr(pytza)₂(H₂O)₂]_n (3) and [Ba(pytza)₂(H₂O)₂]_n·nH₂O (4) were prepared under solvothermal conditions. The thermal behavior of these compounds were characterized by the differential scanning calorimetry (DSC) and thermogravimetric-differential thermogravimetric (TG-DTG) analyses. Furthermore, the critical temperature of thermal explosion and relevant thermal parameters ΔS, ΔH, ΔG of Hpytza and polymers 1-4 were calculated, as well, indicating that these compounds are potential energetic materials.

Full text of DOI:10.1016/j.ica.2016.06.015

Accepted Manuscript
Nitrogen-rich 5-(4-pyridyl)tetrazole-2-acetic acid and its alkaline earth metal
coordination polymers for potential energetic materials
Gao Wen Yang, Yuan Ting Zhang, Qi Wu, Meng Jie Cao, Jiao Wu, Qiu Yan
Yue, Qiao Yun Li
PII:
S0020-1693(16)30325-5
http://dx.doi.org/10.1016/j.ica.2016.06.015
ICA 17106
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
28 March 2016
17 May 2016
6 June 2016
Please cite this article as: G.W. Yang, Y.T. Zhang, Q. Wu, M.J. Cao, J. Wu, Q.Y. Yue, Q.Y. Li, Nitrogen-rich 5-
(4-pyridyl)tetrazole-2-acetic acid and its alkaline earth metal coordination polymers for potential energetic materials,
Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.06.015
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Nitrogen-rich 5-(4-pyridyl)tetrazole-2-acetic acid and its alkaline
earth metal coordination polymers for potential energetic
materials
Gao Wen Yang, Yuan Ting Zhang, Qi Wu, Meng Jie Cao, Jiao Wu, Qiu Yan Yue, Qiao
Yun Li*
*Qiao-Yun Li: Tel: +86-512-52251842; Fax: +86-512-52251842
Email: liqiaoyun61@126.com
Jiangsu Laboratory of Advanced Functional Material, Department of Chemistry and Material
Engineering, Changshu Institute of Technology, Changshu 215500, Jiangsu, P. R. China
Abstract: Tetrazole and its derivatives with rich nitrogen atoms may be potential
candidates for energetic materials. Alkaline earth metal coordination compounds
based on such ligands are relatively less investigated. Hpytza was prepared from
4-cyanopyridine
and
sodium
azide,
ethyl
bromoacetate,
where
Hpytza=5-(4-pyridyl)tetrazole-2-acetic acid. Hpytza and four alkaline earth metal
coordination polymers [Mg(pytza)2]n (1), [Ca(pytza)2(H2O)2]n·3nH2O (2),
[Sr(pytza)2(H2O)2]n (3) and [Ba(pytza)2(H2O)2]n·nH2O (4) were prepared under
solvothermal conditions. The thermal behavior of these compounds were
characterized
by the
differential scanning calorimetry (DSC) and
thermogravimetric-differential thermogravimetric (TG-DTG) analyses. Furthermore,
the critical temperature of thermal explosion and relevant thermal parameters △S, △H,
△G of Hpytza and polymers 1-4 were calculated, as well, indicating that these
compounds are potential energetic materials.
Keywords: Hpytza; alkaline earth metal; luminescence; energetic material; thermal
parameter
1. Introduction
In recent years, the design and exploration of energetic materials has received
1

increasing attention due to not only the energy shortage, but also the conventional
materials are neither high energetic nor environmentally friendly. Typical of energetic
materials, for instance, organic compounds [1], lead salts [2] as well as coordination
compounds [3] have been widely. Recently, tetrazole and its derivatives with high
nitrogen percentage are acknowledged as advanced materials, in the range of
luminescence, magnetism, adsorption materials, etc [4]. Besides, coordination
compounds consisting of metal center and ligands usually show relatively higher
thermal stability, compared with the corresponding ligands. In our previous work, we
reported the synthesis and characterization of 5-[N-acetato(4-pyridyl)]tetrazole and its
alkaline earth metal coordination compounds [5]. To extend our previous work and
explore the relationship of the thermal stability and energetic performance,
5-(4-pyridyl)tetrazole-2-acetato, the isomer of 5-[N-acetato(4-pyridyl)]tetrazole, was
chosen to be reacted with alkaline earth metal salts yielded its four new polymers
[Mg(pytza)2]n (1), [Ca(pytza)2(H2O)2]n·3nH2O (2), [Sr(pytza)2(H2O)2]n (3) and
[Ba(pytza)2(H2O)2]n·nH2O (4). On one hand, the two isomers with abundant nitrogen
and oxygen atoms tend to display various coordination modes, thus leading to
structural variation. On the other hand, the different position of the carboxylate group,
however, may have a fundamental effect on the resulting structures. According to the
latest literature, alkaline earth metal compounds based on tetrazole-carboxylate
ligands are potential energetic materials but rarely investigated [6]. Therefore,
investigations on such compounds will make sense both theoretically and practically.
Furthermore, TGA and DSC tests demonstrate that the four polymers can be taken
advantaged of as potential explosive materials. And the relevant thermal parameters
△S, △H and △G of polymers 1-4 are calculated, as well.
2

Scheme Synthetic strategy for Hpytza and polymers 1-4
2. Results and discussions
2.1 General characterization of polymers 1-4
In this work, one nitrogen rich ligand 5-(4-pyridyl)tetrazole-2-acetic acid and its
alkaline earth metal coordination polymers were prepared. In the IR curve of Hpytza,
the asymmetric vibration of the carboxylate group appears in the usual region
(1730cm-1). Polymers 1-4, however, show the similar peak at the region of 1640 to
1604 cm-1 (1640 cm-1 for 1, 1635 cm-1 for 2, 1604 cm-1 for 3 and 1625 cm-1 for 4),
whose red shift may be explained by the coordination of the carboxylate group to the
metal center (Mg2+, Ca2+, Sr2+, Ba2+). Peaks at 3424 cm-1 for 2, 3428 cm-1 for 3 and
3417 cm-1 for 4, respectively, are ascribed to the O-H vibration of either coordinated
water or guest water molecules. Polymer 1, however, contains neither coordinated nor
guest water molecules, so it does not show a similar peak. The characteristic peaks of
the C=N of both the pyridine and tetrazole rings are at 1562-1386 cm-1 for 1,
1563-1403 cm-1 for 2, 1462-1389 cm-1 for 3 and 1528-1385 cm-1 for 4, respectively,
which may overlap the peaks of the symmetric vibration of the carboxylate group.
2.2 Crystal structure of [Mg(pytza)2]n (1)
3

The X-ray diffraction reveals that polymer 1 crystallizes in monoclinic space group
C2/c. As shown in Fig1a, each Mg(II) ion is in a distorted octahedral coordination
arrangement surrounded by two nitrogen atoms from the tetrazolyl rings and four
oxygen atoms from four carboxylate groups. The Mg-O bond lengths ranging from
2.068 to 2.070Å are in excellent agreement with those of the previously reported
Mg(II) compounds[5, 7a-7e]. So are the Mg-N bond lengths (2.261Å). Each pytza
acts as a tridentate ligand to bridge three Mg(II) centers via one nitrogen atom of the
pyridine ring and the carboxylate group in a µ1,3-COO syn-syn mode. The structure
can be simplified as a (36,416,56) tsi network topology (Fig1b). Compared with
[Mg(H2O)6](a4-ptz)2·2H2O, where a4-ptz=5-[N-acetato(4-pyridyl)]tetrazole, the
isomer of 5-(4-pyridyl)tetrazole-2-acetato, the structure is substantially different since
a4-ptz is uncoordinated to the Mg(II) center, instead, they are held together by
hydrogen bonds. Therefore, the structure transforms a mononuclear to a three
dimensional one. Two non-classic hydrogen bonds exist between the C-H group of
the tetrazolyl ring and the oxygen atom of the carboxylate group [C(6)—H(6A) ···O
(2), O(7)—H(7A) ···O(1)] to stabilize the supramolecular assembly (TableS2, Fig
S1).
Fig1. (a)The coordination environment of Mg2+ in polymer 1. Hydrogen atoms are
omitted for clarity; (b)The 3D structure of polymer 1.
2.3 Crystal structure of [Ca(pytza)2(H2O)2]n·3nH2O (2)
Polymer 2 belongs to monoclinic space group C2/c and the asymmetric unit contains
half of the molecule. As shown in Fig2a, each Ca(II) center is octa-coordinated by
three oxygen atoms from three water molecules and six ones from four carboxylate
groups. The Ca-O bond lengths the range of 2.393 to 2.666Å are in agreement with
4

those of the previously reported Ca(II) compounds[5,7a,7b,7d], so the coordination
arrangement can be described as an irregular square anti-prism. Compared with
[Ca(a4-ptz)2(H2O)2]n·2nH2O whose 1D chain consists of the a4-ptz which acts as a
monodentate ligand via one oxygen atom of the carboxylate group and the bridging
water oxygen atom, there are two kinds of coordination modes of pytza: first, adjacent
two Ca2+ are tetra-bridged by two oxygen atom of two water molecules and four
oxygen atom of two carboxylate groups in a µ1,3-COO syn-syn mode to form a
binuclear unit; then neighboring binuclear units are doubly bridged by the carboxylate
group in a µ1,1,3-COO mode to generate a 1D zigzag chain extending along the b axis
with Ca···Ca distance of 3.8845(15)Å and Ca···Ca···Ca angle of 143.945(31)º
(Fig2b). Adjacent chains are held together by hydrogen bonds to form a 3D network
structure (Table S2, Fig S2).
(a)
(b)
Fig2. (a) The coordination environment of Ca2+ in polymer 2; (b)The 1D chain
structure of polymer 2. Hydrogen atoms are omitted for clarity.
5

2.4 Crystal structure of [Sr(pytza)2(H2O)2]n (3)
The X-ray reveals that the structure of polymer 3 resembles that of polymer 2 except
that it contains neither uncoordinated water molecules. Polymer 3 also displays a 1D
zigzag chain extending along the b axis with Sr···Sr distances of 4.0409 and 4.1825 Å
and Sr···Sr···Sr angle of 143.295º (FigS3). The Sr···Sr distance is larger than that of
Ca···Ca, this can be explained by the fact that the metal radius of Sr2+ is larger than
that of Ba2+. Compared with [Sr(a4-ptz)2(H2O)2]n·2nH2O where a4-ptz adopts a
monodentate mode, pytza acts as a bidentate or tridentate ligand via the carboxylate
group in a µ1,3-COO syn-syn or µ1,1,3-COO mode similar to that of pytza in polymer 2
(FigS4). The Sr-O bond lengths ranging from 2.518 to 2.715Å are in good agreement
with those of the previously reported Sr(II) compounds[5,7b,7c,7e]. Hydrogen bonds
exist between the coordinated water and nitrogen atom as well as uncoordinated water
molecules, by which neighboring 1D chains are held together to form a three
dimensional network (TableS2, FigS5).
2.5 Crystal structure of [Ba(pytza)2(H2O)2]n·nH2O (4)
Polymer 4 crystallizes in monoclinic space group P21. As shown in Fig3, each Ba(II)
center is octa-coordinated by three oxygen atoms from three water molecules, four
oxygen atoms from four carboxylate groups of four pytza ligands and one nitrogen
atom of the pyridyl ring, forming a distorted square antiprism coordination
arrangement. The Ba-O bond lengths ranges from 2.741 to 2.861Å and that of Ba-N is
2.956Å, resembling those of the previously reported Ba(II) compounds[5,7a-7c,7e].
Compared with 1D [Ba4(a4-ptz)8(H2O)8]n·4nH2O, neighboring Ba(II) ions in polymer
4 are doubly bridged by one coordinated water and one oxygen atom of the
carboxylate group in a µ1,1-COO mode to generate a 1D chain with Ba···Ba distance
of 4.1511Å and Ba···Ba···Ba angle of 115.938º. Adjacent 1D chains are bridged by
the tridentate pytza via one nitrogen atom of the pyridyl ring and the carboxylate
group in a µ1,3-COO bridging mode to form a two dimensional layer extending along
the bc plane(Fig4a). The 2D layer can be viewed as a (4,4) grid topology with
6

rhomboidal grids being 12.8688 and 16.4851Å, respectively (Fig4b). Adjacent 2D
layers are held together by hydrogen bonds, leading to the formation of a 3D
supramolecular network (TableS2, FigS6).
Fig3. The coordination environment of Ba2+ in polymer 4. Hydrogen atoms are
omitted for clarity;
Fig4. (a)The 2D layer structure of compound 4; (b) The topology of polymer 4.
Hydrogen atoms are omitted for clarity.
2.6 TG, DTG and DSC of Hpytza and polymers 1-4
To characterize Hpytza and polymers 1-4 in terms of thermal stability, the
thermogravimetric analysis were performed from 30 to 600°C with the heating rate of
10°C·min-1 under nitrogen atmosphere. As shown in Fig5, Hpytza began to
decompose at 255°C and a strong exothermic peak from 262.8 to 268.2°C were
observed. Polymers 1-3 began to decompose at 323, 313 and 297 respectively, leading
to the collapse of the framework (Fig6). An initial mass loss of 8.85% of polymer 4
were observed, which can be ascribed to the removal of both coordinated and
7

uncoordinated water molecules (calculated 9.00%), further mass loss beginning at
266°C are ascribed to the decomposition of the framework structure. Drastic
exothermic peaks from 326.2 to 339.1°C for polymer 1, 316.9 to 317.4 °C for
polymer 2, 298.4 to 316.4 °C for polymer 3, 299.8 to 315.1 °C for polymer 4 were
shown in Fig7, however, one more endothermic peak from of polymer 4 was found.
The comprehensive enthalpy of Hpytza and polymers 1-4 are calculated as -405.1,
-570.1, -565.8, -467.8 and -420.4 J/g, respectively, indicating that these compounds
are potential energetic materials.
Fig5. (a)The TG curves of Hpytza from 30 to 600°C with the heating rate of
10°C·min-1; (b)the DSC curves of polymers 1-4 from 30 to 600°C with the heating
rate of 10°C·min-1.
8

Fig6. The TG curves of polymers 1-4 from 30 to 600°C with the heating rate of
10°C·min-1; (a) for 1; (b) for 2; (c) for 3 and (d) for 4.
Fig7. The DSC curves of polymers 1-4 from 30 to 600°C with the heating rate of
10°C·min-1; (a) for 1; (b) for 2; (c) for 3 and (d) for 4.
2.7 Non-isothermal kinetics of Hpytza and polymers 1-4
Tetrazole and its derivatives are nitrogen-rich compounds that can be used as
potential energetic materials. To evaluate the energetic performance of Hpytza and
polymers 1-4, Kissinger’s method [8] (equation1) and Ozawa’s method [9] (equation2)
were applied to understand the decomposition mechanism and calculate the apparent
activation energy (Ea/kJ·mol-1) and pre-exponential constant (A/s-1).
2
ln(β/Tp )=ln(RA/Ea)-Ea/(RTp)
lgβ+0.4567Ea/(RTp)=C
(1)
(2)
Where Tp stands for the peak temperature (K); R represents the gas constant (8.314
J·mol-1·K-1); β is the linear heating rate (K·min-1); C is a constant. The peak
temperature in the non-isothermal DSC curves are correspondent to the same
conversion degrees at various heating rate.
The peak temperatures of Hpytza and polymers 1-4 with the linear heating rate of 5,
9

10, 15, 20 K·min-1 are listed in Table 1.
Table 1 The peak temperature of Hpytza and polymers 1-4 with different heating rates
Heating rate
5 K·min-1
10 K·min-1
15 K·min-1
20 K·min-1
compound
peak temperature
Hpytza
533
594
584
570
568
541
604
592
578
575
546
609
597
583
582
550
613
600
586
584
1
2
3
4
The apparent activation energy of Hpytza and polymers 1-4 calculated by Ozawa’s
method and Kissinger’s method, the pre-exponential constant lnA and the Arrhenius
equations [lnk=lnA-E/(RT)] are listed in Table 2.
Table 2 The apparent activation energy of Hpytza and polymers 1-4 calculated by
Kissinger’s and Ozawa’s methods and the Arrhenius equations
Compound
Ek (kJ/mol)
190.75
Eo (kJ/mol)
189.94
Arrhenius equation
Hpytza
lnk=42.15-190.34×103/(RT)
lnk=41.75-210.91×103/(RT)
lnk=51.17-251.04×103/(RT)
lnk=45.92-220.80×103/(RT)
lnk=43.68-209.98×103/(RT)
211.32
210.50
1
2
3
4
252.58
249.50
221.68
219.92
210.63
209.32
Eo (kJ·mol-1): the apparent activation energy obtained by Ozawa’s method
Ek (kJ·mol-1): the apparent activation energy obtained by Kissinger’s method
lnA (s-1): the pre-exponential constant in the Arrhenius equation
E (J·mol-1): the average value of Ek and Eo
2.8 Critical temperature of thermal explosion of Hpytza and polymers 1-4
To discuss Hpytza and polymer 1 in terms of thermal safety, the critical temperature
of thermal explosion (Tb) was calculated to obtain the lowest temperature to which a
10

specific charge might be heated without undergoing thermal runaway. The following
equations were used [10].
Tpi=Tp0+bβi +cβi2
(3)
(4)
2
Tbp ={Eo−[Eo −(4EoRTp0)]1/2}/2R
The value of the peak temperatures of Hpytza and polymers 1-4 are 529, 592, 580,
569 and 568 K, respectively, when β→0, where b and c are coefficients. The
corresponding critical temperatures of thermal explosion (Tbp) of Hpytza and
polymers 1-4 obtained from the above equations are 542, 607,
and K,
respectively, where R stands for the gas constant (8.314 J·mol-1·K-1), Eo represents the
apparent activation energy calculated by Ozawa’s method.
2.9 Thermodynamic parameters of Hpytza and polymers 1-4
The thermodynamic parameters of the decomposition of Hpytza and polymers 1-4
△S), enthalpy of
were calculated based on Ea and A. The entropy of activation (
activation (△H), and free energy of activation (△G) corresponding to T = Tp0, Ea=EK,
and A = AK obtained by the following equations [11-12].
A=(kBTe△S/R)/h
△H=Ea−RT
△G=△H−T△S
Where kB is the Boltzmann constant (1.3807×10-23J·K-1), and h is the Plank constant
(6.626×10-34 J·s-1). These thermal parameters are listed in Table 3.
Table 3 Thermal parameters of Hpytza and polymers 1-4
Compound
△S (J·mol-1·K-1)
△H (kJ/mol)
186.40
△G (kJ/mol)
150.07
Hpytza
69.40
96.64
206.48
150.24
1
2
3
4
175.34
247.81
147.24
131.65
217.03
143.47
113.05
205.99
142.96
11

2.10 Discussion of the structure variation and the energetic performance of
polymers 1-4
The work is the extension of our previous publication which reported four alkaline
earth metal coordination compounds derived from 5-[N-acetato(4-pyridyl)]tetrazole
(a4-ptz), the isomer of 5-(4-pyridyl)tetrazole-2-acetato[5]. The different position of
the carboxylate group control the coordination modes of the ligands, thus leading to
structural variation. In [Mg(H2O)6](a4-ptz)2·2H2O, a4-ptz does not coordinated to
Mg2+, instead, it plays the role of balancing the charge. In contrast, pytza acts as a
tridentate bridging ligand via the nitrogen atom of the pyridine ring and the
carboxylate group in a µ1,3-COO syn-syn mode; for [Ca(a4-ptz)2(H2O)2]n·2nH2O,
a4-ptz only acts as a monodentate ligand via the oxygen of the carboxylate group, but
4-pytza adopts both bidentate or tridentate in a µ1,3-COO or µ1,1,3-COO mode to form
a 1D chain. However, the structure of [Ca(a4-ptz)2(H2O)2]n·2nH2O is similar to that of
[Sr(a4-ptz)2(H2O)2]n·2nH2O while [Ca(pytza)2(H2O)2]n·3nH2O also resembles
[Ca(pytza)2(H2O)2]n; last but not least, [Ba4(a4-ptz)8(H2O)8]n·4nH2O is a one
dimensional chain while [Ba(pytza)2(H2O)2]n·nH2O is a two dimensional layer with
(4,4) topology. It is worthwhile to point out that the pyridine-N atoms of pytza
participate in the coordination to Ba2+, however, all the nitrogen atoms of a4-ptz are
uncoordinated.
From the TGA, we can see that the four polymers are more stable than Hpytza, this
can be explained by the coordination of the ligand to the metal center. However,
polymers 1-4 tend to show less stability gradually (decomposition temperature from
323, 313, 297 to 266 °C), which is probably assigned to the larger bond length of the
coordination bonds (Table 4). Polymer 1 contains neither coordinated nor
uncoordinated water molecules, it only shows an exothermic peak. Polymer 2 only
exhibits an endothermic peak since the loss of the uncoordinated water molecules
begins at low temperature, indicating the weak interaction between the guest water
molecules and the one dimensional chain. Polymer 3, however, also shows one
exothermic peak since the hydrogen bonding interactions between the coordinated
water molecules and the pytza ligands are strong and diverse. Polymer 4 shows both
12

exothermic and endothermic peaks because the loss of one uncoordinated water
molecule is an exothermic process while the decomposition of the ligand is an
exothermic one. For Hpytza and polymers 1-4, the apparent activation energy
obtained by Kissinger’s method are similar to those of obtained by Ozawa’s method.
The comprehensive enthalpy of the decomposition process of polymers 1-4 are larger
than Hpytza, which can be explained by the fact that the energy of the coordination
bond is large. The results demonstrates that energetic performance of the coordination
polymers are superior to that of Hpytza.
3.Experimental section
3.1 Synthesis and characterization of 5-(4-pyridyl)tetrazole-2-acetic acid
5-(4-pyridyl) tetrazole (Hpytz) was prepared by [2+3] cycloaddition reactions, by
treating 4-cyanopyridine with NaN3 in toluene in the presence of triethylammonium
chloride. A mixture of ethyl bromoacetate (12.53 g, 0.075 mol), Hpytz (7.35 g, 0.05
mol), and potassium hydroxide (5.61 g, 0.10 mol ) in methanol/ H2O (5:1) was
refluxed 24 hour at 70 °C. After cooling to room temperature, the precipitate was
filtered off, washed with 2×30 mL methanol and dried to give mostly
H(tetrazole)-substituted products 5-(4-pyridyl)tetrazole-2-acetato potassium salt. Then
concentrated
HCl
(12M)
was
added,
forming
the
precipitate
5-(4-pyridyl)tetrazole-2-acetic acid. The precipitate was washed with distilled water
1
and then dried. Yield: 67% based on Hpytz. HNMR (DMSO-d6, δppm):5.81(2H,
-CH2), 8.01(2H,=CH), 8.81(2H,=CH), 11.95(1H, COO-); 13CNMR (DMSO-d6, δppm):
54.39, 78.97, 120.91, 134.55, 151.33, 162.83. Anal. Calcd for C8H7N5O2: C: 46.83, H:
3.44, N: 34.13%; Found: C: 46.65, H: 3.54, N: 34.68%; IR (KBr, cm-1): 3426(m),
1730(s), 1449(m), 1420(m), 1396(m), 1257(s), 906(m), 868(m).
3.2 Synthesis of [Mg(pytza)2]n (1)
Hpytza (0.0205g, 0.1mmol) was dissloved in 1 mL distilled water and the pH value
was adjusted to 5 with KOH (0.2M), then ethanol (5 mL) and Mg(NO3)2·6H2O
13

(0.0256 g, 0.1 mmol) were added. The solution was sealed in a 25 mL telfon stainless
steel and heated at 120°C for 48h. After cooling to room temperature, light yellow
block crystals were obtained. Yield: 45% based on Mg2+. Anal. Calcd for
C16H12MgN10O4: C, 44.42; H, 2.80; N, 32.38%. Found: C, 44.25; H, 2.88; N, 32.33%.
IR (KBr, cm-1): 1687(w), 1640(s), 1562(w), 1458(w), 1429(m), 1386(s), 1299(w),
1220 (w), 1124(w), 1056(w), 1009(w), 823(w), 755(w), 724(m), 685(m).
3.3 Synthesis of [Ca(pytza)2(H2O)2]n·3nH2O (2)
A similar method to that of polymer 1 was adopted to prepare polymer 2 except that
the solvent was changed to a mixture of distilled water (1mL) and ethanol (3mL).
Yield: 40% based on Ca2+. Anal. Calcd for C16H22CaN10O9: C, 35.69; H, 4.12; N,
26.01%. Found: C, 35.25; H, 4.18; N, 26.33%. IR (KBr, cm-1): 3424(m), 1635(s),
1563(w), 1457(w), 1426(s), 1403(s), 1307(w), 1291(w), 1217(w), 1052(w), 1007(w),
826(m), 752(w), 722(m), 677(m).
3.4 Synthesis of [Sr(pytza)2(H2O)2]n (3) and [Ba(pytza)2(H2O)2]n·nH2O(4)
Similar methods to that of polymer 2 were adopted to prepare polymers 3 and 4
except that the solvent was changed to a mixture of distilled water (4mL) and ethanol
(1mL). For 3, yield: 42% based on Sr2+. Anal. Calcd for C16H16SrN10O6: C, 36.12; H,
3.03; N, 26.33%. Found: C, 36.25; H, 3.08; N, 26.52%. IR (KBr, cm-1): 3428(m),
1604(s), 1462(w), 1429(m), 1389(s), 1313(w), 1222(m), 1206 (w), 1013(w), 846(w),
823(m), 729(s), 683(w). For 4, yield: 40% based on Ba2+. Anal. Calcd for
C16H18BaN10O7: C, 32.04; H,3.03; N, 23.36%. Found: C, 32.25; H, 3.12; N, 23.23%.
IR (KBr, cm-1): 3417(m), 1625(s), 1528(w), 1459(w), 1425(m), 1385(s), 1307(m),
1212 (w), 1127(w), 1050(w), 1000(w), 836(m), 752(w), 723(m), 683(w).
3.5 X-Ray crystallography
Single crystal X-ray crystal data were collected on a Rigaku SCX mini CCD
diffractometer equipped with graphite-monochromated Mo-Kα radiation (λ = 0.71073
Å). The intensity data were collected by the ω scan technique and were reduced using
14

the Crystal-Clear program [13], and an absorption correction (multi-scan) was applied.
The reflection data were also corrected for Lorentz and polarization effects. The
structures were solved by direct methods and refined on F2 by full matrix least squares
using SHELXTL [14]. All the non-hydrogen atoms were located from the Fourier
maps, and were refined anisotropically. All H atoms were refined isotropically, with
the isotropic vibration parameters related to the non-H atom to which they were
bonded. Selected bond lengths and angles are listed in Table 4. Crystallographic data
are summarized in Table S1. Hydrogen-bonding parameters are given in Table S2.
Polymers 1-4 are deposited with CCDC number 1426716-1426719.
Table 4. Selected bond distances (Å) and angles (º) for polymers 1-4
[Mg(pytza)2]n (1)
Mg(1)–O(1)
2.070(3)
Mg(1)–O(2)
2.068(3)
Mg(1)–N(5)
2.261(3)
O(1)–Mg (1)–O(1A)
O(1A)–Mg (1)–O(2C)
O(1)–Mg (1)–N(5D)
O(2C)–Mg (1)–N(5D)
N(5D)–Mg (1)–N(5E)
90.35(15)
89.89(9)
O(1)–Mg(1)–O(2C)
O(2C)–Mg (1)–O(2B)
O(1A)–Mg (1)–N(5E)
O(2B)–Mg (1)–N(5D)
179.70(11)
89.87(15)
88.68(10)
91.48(11)
94.99(11)
84.84(11)
174.80(18)
[Ca(pytza)2(H2O)2]n·3nH2O (2)
Ca(1)–O(3B)
2.393(4)
2.426(4)
Ca(1)–O(2)
2.428(4)
2.437(4)
Ca(1)–O(1A)
Ca(1)–O(6)
Ca(1)–O(5)
2.445 (4)
2.561 (4)
Ca(1)–O(4)
2.505(4)
Ca(1)–O(5A)
Ca(1)–O(3)
2.666(4)
79.89(13)
72.10(13)
147.35(13)
74.84(13)
O(3B)–Ca(1)–O(1A)
O(1A)–Ca(1)–O(2)
O(1A)–Ca(1)–O(6)
O(3B)–Ca(1)–O(5)
123.58 (14)
140.45(13)
71.27(14)
85.04(13)
O(3B)–Ca(1)–O(2)
O(3B)–Ca(1)–O(6)
O(2)–Ca(1)–O(6)
O(1A)–Ca(1)–O(5)
15

O(2)–Ca(1)–O(5)
O(3B)–Ca(1)–O(4)
O(2)–Ca(1)–O(4)
O(5)–Ca(1)–O(4)
O(1A)–Ca(1)–O(5A)
O(6A)–Ca(1)–O(5)
O(4A)–Ca(1)–O(5)
O(6A)–Ca(1)–O(5)
O(4A)–Ca(1)–O(5)
O(1A)–Ca(1)–O(3)
O(6)–Ca(1)–O(3)
O(4)–Ca(1)–O(3)
76.50(13)
121.33 (14)
95.79(14)
151.25(13)
75.57(12)
137.59(13)
73.04(13)
137.59 (13)
73.04(13)
136.29(13)
77.40(13)
50.51(12)
O(6)–Ca(1)–O(5)
O(1A)–Ca(1)–O(4)
O(5A)–Ca(1)–O(5)
O(3B)–Ca(1)–O(5A)
O(2A)–Ca(1)–O(5)
O(6)–Ca(1)–O(4)
O(3B)–Ca(1)–O(3)
O(5A)–Ca(1)–O(5)
O(3B)–Ca(1)–O(3)
O(2)–Ca(1)–O(3)
O(5)–Ca(1)–O(3)
O(5A)–Ca(1)–O(3)
116.43(13)
96.38(14)
78.24(13)
150.19(12)
72.34(12)
85.04(14)
71.72(14)
78.24(13)
71.72(14)
78.16(12)
148.14(12)
111.81(12)
[Sr(pytza)2(H2O)2]n (3)
Sr(1)–O(5A)
2.608(2)
Sr(1)–O(3)
2.518(2)
2.542(3)
2.582(3)
2.6718(24)
71.66(8)
79.73(9)
147.11(8)
74.62(8)
74.91(8)
95.31(9)
99.84(9)
73.96(8)
77.39(9)
148.76(7)
Sr(1)–O(3B)
2.715(3)
2.570(3)
2.643(3)
123.34(9)
72.64(9)
138.91(9)
84.12(8)
116.79(8)
121.07(9)
81.97(9)
153.45(8)
136.23(8)
79.42(8)
48.87(8)
Sr(1)–O(2A)
Sr(1)–O(6)
Sr(1)–O(1)
Sr(1)–O(4)
Sr(1)–O(5)
O(3B)–Sr(1)–O(2A)
O(3B)–Sr(1)–O(6)
O(2A)–Sr(1)–O(1)
O(3B)–Sr(1)–O(5A)
O(6)–Sr(1)–O(5A)
O(3B)–Sr(1)–O(4)
O(6)–Sr(1)–O(4)
O(5A)–Sr(1)–O(4)
O(2A)–Sr(1)–O(3)
O(1)–Sr(1)–O(3)
O(4)–Sr(1)–O(3)
O(3B)–Sr(1)–O(6)
O(3B)–Sr(1)–O(1)
O(6)–Sr(1)–O(1)
O(2A)–Sr(1)–O(5A)
O(1)–Sr(1)–O(5A)
O(2A)–Sr(1)–O(4)
O(1)–Sr(1)–O(4)
O(3B)–Sr(1)–O(3)
O(6)–Sr(1)–O(3)
O(5A)–Sr(1)–O(3)
16

[Ba(pytza)2(H2O)2]n·nH2O(4)
Ba(1)–O(1)
2.741(2)
2.807(3)
2.840(3)
2.861(2)
145.27(7)
84.52(7)
74.10(6)
130.10(7)
132.82(4)
67.18(6)
83.19(6)
72.22(7)
74.55(7)
131.36(7)
143.80(7)
131.70(7)
137.92(7)
83.71(6)
Ba(1)–O(6B)
2.7474(19)
2.8278(19)
2.850(2)
2.956(3)
69.39(7)
111.43(6)
63.73(7)
84.45(6)
69.12(7)
133.64(2)
60.38(6)
77.49(8)
77.12(7)
141.83(7)
68.02(7)
137.27(7)
80.06(7)
90.47(8)
Ba(1)–O(4A)
Ba(1)–O(2B)
Ba(1)–O(4)
Ba(1)–O(6)
Ba(1)–O(5)
Ba(1)–N(5C)
O(1)–Ba(1)–O(6B)
O(6B)–Ba(1)–O(4A)
O(6B)–Ba(1)–O(2B)
O(1)–Ba(1)–O(4)
O(4A)–Ba(1)–O(4)
O(1)–Ba(1)–O(6)
O(4A)–Ba(1)–O(6)
O(4)–Ba(1)–O(6)
O(6B)–Ba(1)–O(5)
O(2B)–Ba(1)–O(5)
O(6)–Ba(1)–O(5)
O(6B)–Ba(1)–N(5C)
O(2B)–Ba(1)–N(5C)
O(6)–Ba(1)–N(5C)
O(1)–Ba(1)–O(4A)
O(1)–Ba(1)–O(2B)
O(4A)–Ba(1)–O(2B)
O(6B)–Ba(1)–O(4)
O(2B)–Ba(1)–O(4)
O(6B)–Ba(1)–O(6)
O(2B)–Ba(1)–O(6)
O(1)–Ba(1)–O(5)
O(4A)–Ba(1)–O(5)
O(4)–Ba(1)–O(5)
O(1)–Ba(1)–N(5C)
O(4A)–Ba(1)–N(5C)
O(4)–Ba(1)–N(5C)
O(5)–Ba(1)–N(5C)
Symmetry code: For 1: A:-x,y,0.5-z; B: -x.1-y,-z; C: x,1-y,0.5+z; D: 0.5-x,0.5+y,0.5-z; E: -0.5+x,
0.5+y, z; For 2: A: -x, 1-y, 1-z; B: -x, 2-y, 1-z ; For 3: A: 2-x, 2-y, 1-z; B: 2-x, 1-y, 1-z; For 4:
A: 2-x, -0.5+y, 1-z; B: 2-x, 0.5+y, 1-z; C: 2-x, 0.5+y, -z.
4. Conclusions
In summary, Hpytza and its four alkaline earth metal compounds have been reported
for the first time. It is worthwhile to point out that the position of the carboxylate
group has a substantial effect on the crystal structures of such compounds, compared
with the compounds based on 5-[N-acetato(4-pyridyl)tetrazole]. In addition, the four
polymers show blue light emission at room temperature in the solid state. Our
17

research results show that the energetic performance of the polymers are closely
related to the structures of the polymers and the coordination of the metal ions may
enhance the energetic performance of the such compounds. The four polymers may be
used as potential energetic materials.
Acknowledgment
The authors acknowledge financial support from the Natural Science Foundation of Ji
angsu Province (Grant No. BK2012210), the Natural Science Foundation of the Jiang
su Higher Education Institutions of China
(Grant No.10KJB430001) and the Opening Fund of Jiangsu Key Laboratory of Advan
ced Functional Materials (Grant No.12KFJJ010).
Caption list
Table S1 Selected crystallographic data and structure refinement for polymers 1-4.
Table S2 Hydrogen parameters for polymers 1-4
Fig.S1 The coordination environment of Sr2+ in polymer 3. Hydrogen atoms are
omitted for clarity.
Fig.S2 The The 1D chain structure of polymer 3. Hydrogen atoms are omitted for
clarity.
Fig.S3 The 3D network structure of polymer 2 formed via hydrogen bonds.
Fig.S4 The 3D network structure of polymer 3 formed via hydrogen bonds.
Fig.S5 The 3D network structure of polymer 4 formed via hydrogen bonds.
References
[1](a)Y.H. Joo, H.X. Gao, D.A. Parrish, S.G. Cho, E.M. Goh, J.M. Shreeve, J.
Mater. Chem., 22 (2012) 6123-6130;
(b)L. Liu, Y.Q. Zhang, Z.M. Li, S.J. Zhang, J. Mater. Chem. A., 3 (2015)
14768-14778;
(c)R.H. Wang, Y. Guo, Z. Zeng, B. Twamley, J.M. Shreeve., Chem. Eur. J., 15
(2009) 2625-2634;
(d)T.M. Klapötke, D.G. Piercey, Inorg. Chem., 50 (2011) 2732-2734;
(e) Y.C. Li , C. Qi , S.H. Li, H.J. Zhang, C.H. Sun, Y.Z. Yu, S.P. Pang, J. Am. Chem.
18

Soc., 132 (2010) 12172-12173.
[2]Singh, G.; Prem Felix, S. J. Hazard. Mater., A90, (2002) 1.
[3](a)B.D. Wu, G.T. Zhang, T.L. Zhang, L.Yang, J.G. Zhang, Z.N. Zhou, K.B. Yu,
Chinese J. Struct. Chem., 30 (2011) 431-437;
(b)Z.M. Li, T.L. Zhang, G.T. Zhang, Z.N. Zhou, L. Yang, J.G. Zhang, K.B. Yu, J. Coord.
Chem., 66 (2013) 1276-1286;
[4](a) M. Wriedt, A.A. Yakovenko, G.J. Halder, A.V. Prosvirin, Kim R. MDunbar, H.C.
Zhou, J. Am. Chem. Soc., 135 (2013) 4040-4050;
(b)M. Wriedt, J.P. Sculley, A.A. Yakovenko, Y.G Ma, G. J. Halder, P.B. Balbuena, H.C.
Zhou, Angew. Chem. Int. Ed., 51 (2012) 9804-9808;
(c)Z.M. Li, G.T. Zhang, T.L. Zhang, J.G. Zhang, L. Yang, Z.N. Zhou, S.Y. Qi, K.B. Yu,
F.Q. Zhao, J.H. Yi, S.Y. Xu, H.X. Gao, Acta Chim. Sinica., 69 (2011) 10, 1253-1258;
(d)G.W. Yang, F.F. Zhang, Q. Wu, M.J. Cao, Y. Bai, Q.Y. Li, B. Wei, J.H. Zou, RSC
Adv., 5 (2015) 84439-84445;
(e) D.Y. Chen, J.H. Zou, W.X. Li, B. Xu, Q.Y. Li, G.W. Yang, J. Wang, Y.M. Ding, Y.
Zhang, X.F. Shen, Inorg. Chem. Comm., 40 (2014) 35-38;
(f)M.F. Wu, Z.F. Liu, S.H. Wang, J. Chen, G. Xu, F.K. Zheng, G.C. Guo, J.S. Huang,
CrystEngComm., 13 (2011) 6386;
(g) J.H. Zou, D.L. Zhu, F.F. Li, F.S. Li, H. Wu, Q.Y. Li, G.W. Yang, P. Zhang, Y.X.
Miao, J. Xie, Z. Anorg. Allg. Chem., 640 (2014) 2226-2231;
(h)J.H. Zou, D.Y. Chen, G.W. Yang, Q.Y. Li, J. Yang, L. Shen, RSC Adv., 5 (2015)
27887-27890;
(i)G. Aromi, L.A. Barrios, Ol. Roubeau, P. Gamez, Coord. Chem. Rev., 255 (2011)
485-546;
(j)S.H. Wang, F.K. Zheng, M.J. Zhang, Z.F. Liu, J. Chen, Y. Xiao, A.Q. Wu, G.C. Guo,
J.S. Huang, Inorg. Chem., 52 (2013) 10096-10104;
(k)J. Chen, S.H. Wang, Z.F. Liu, M.F. Wu, Y. Xiao, F.K. Zheng, G.C. Guo, J.S. Huang,
New J. Chem., 38 (2014) 269-276
(l)A. Karmakar, G.M.D.M. Rubio, M.F.C. GuedesdaSilva, S. Hazra, A.J.L. Pombeiro,
Cryst. Growth Des., 15(9) (2015) 4185-4197
19

(m)D.S. Liu, Y. Sui, W.T. Chen, P.Y. Feng, Cryst. Growth Des., 15(8) (2015)
4020-4025.
[5]Y. Zhou, G.W. Yang, Q.Y. Li, K. Liu, G.Q. Gu, Y.S. Ma, R.X. Yuan, Inorg. Chim.
Acta., 362 (2009) 1723-1729.
[6](a)H.S. Huang, Z.M. Li, G.T. Zhang, T.L. Zhang, S.T. Zhang, L. Yang, J.G. Zhang,
Z.N. Zhou, Main Group Chem., 12 (2013) 197-208;
(b) Z.M. Li, T.L. Zhang, L. Yang, Z.N. Zhou, J.G. Zhang, J. Coord. Chem., 65 (2012)
143-155.
[7](a)J. Yang, Q.Y. Li, L. Shen, G.W. Yang, X.Y. Tang, C. Zhai, H.D. Ding, J.N. Jin, W.
Shen, J Chem Crystallogr., 41 (2011) 1483-1489;
(b)G.W. Yang, B.J. Wang, Z.T. Shen, Q.Y. Li, C. Ji, X.F. Shen, M.H. He, J. Coord.
Chem., 65 (2012) 2657-2670;
(c)Q.Y. Li, G.W. Yang, L. Shen, M.H. He, W. Shen, K. Gu, J.N. Jin, Z. Anorg. Allg.
Chem., 638 (2012) 826-831;
(d)B. J. Wang, J. H. Zou, W. X. Li, Z. Wang, B. Xu, S. Li, Y.S. Zhai, D. L. Zhu, Q. Y.
Li, G. W. Yang, J. Organomet. Chem., 749 (2014) 428-432
(e)J.H. Zou, H.J. Cui, B. Xu, D.L. Zhu, Q.Y. Li, G.W. Yang, Y.C. Hua, Inorg. Chim.
Acta., 423 (2014) 430–434
[8]H.E. Kissinger, Anal. Chem., 19 (1957) 1702-1706.
[9](a)T. Ozawa, Bull. Chem. Soc. Jpn., 38(1965), 1881-1886;
(b)J.H. Flynn and L.A. Wall, J Polym Sci, Part B: Polym. Phys., 4 (1966) 323-328.
[10]T.L. Zhang, R.Z. Hu, Y. Xue, F.P. Li, Thermochim Acta., 244 (1994) 171-175.
[11] R.Z. Hu, S.P. Chen, S.L. Gao, F.Q. Zhao, Y. Luo, H.X. Gao, Q.Z. Shi, H.A. Zhao,
P. Yao, J. Li, J. Hazard. Mater., 117 (2005) 103-110.
[12] J.H. Yi, F.Q. Zhao, B.Z. Wang, Q. Liu, C. Zhou, R.Z. Hu, Y.H. Ren, S.Y. Xu, K.Z.
Xu, X.N. Ren, J. Hazard. Mater., 181 (2010) 432-439.
[13] Rigaku CrystalClear. Rigaku Corporation, Tokyo, Japan, (2005).
[14] G.M. Sheldrick, Acta. Cryst. A64 (2008) 112.
20

Nitrogen-rich 5-(4-pyridyl)tetrazole-2-acetic acid and its alkaline
earth metal coordination polymers for high performance
energetic materials
Gao Wen Yang, Yuan Ting Zhang, Qi Wu, Meng Jie Cao, Jiao Wu, Qiu Yan Yue, Qiao
Yun Li*
*Qiao-Yun Li: Tel: +86-512-52251842; Fax: +86-512-52251842
Email: liqiaoyun61@126.com
Jiangsu Laboratory of Advanced Functional Material, Department of Chemistry and
Material Engineering, Changshu Institute of Technology, Changshu 215500, Jiangsu,
P. R. China
5-(4-pyridyl)tetrazole-2-acetic acid and its four alkaline earth metal compounds were
prepared. The structural variation was assigned to not only the isomer, but also the
radius of the metal ion. These coordination compounds are superior to the ligand in
terms of thermal stability and energetic performance.
Corresponding author. Tel.: +86-18762987673; fax: +86-52251842
E-mail address: Qiao Yun Li (liqiaoyun61@126.com)， Jian Hua Zou(zoujh93@126.com)
21