English

• 0.   Introduction

  In recent years, energetic materials have attracted more and more attention because of their increasing applications in military and civilian applications^[1-3]. The traditional energetic compounds, such as 2, 4, 6-trinitrotoluene (TNT) ^[4], 1, 3, 5-trinitro-1, 3, 5-triazine (RDX)^[5], 1, 3, 5, 7-tetranitro-1, 3, 5, 7tetrazoctane (HMX)^[6], pentaerythritol tetranitrate (PETN) ^[7], 2, 4, 6-triamino-1, 3, 5-trinitrobenzene (TATB) ^[8] and hexanitrohexaazaisowurtzitane (CL-20) ^[9] have good detonation performance. However, in the course of manufacture, transport, and storage of explosives, accidental detonations are easily triggered by stimuli and lead to injury and destruction of property^[10]. Therefore, it is very important to design new energetic materials with good energy properties, good thermal stability, and low sensitivity.

  Nitrogen-rich energetic salts are environmentally friendly high-energy-density materials (HEDMs) that have attracted considerable interest due to the lower vapor pressures, higher heats of formation, and enhanced thermal stabilities^[11]. 1, 2, 4-Triazole has multiple N-coordination sites and relatively small volume, which not only reduces steric hindrance but also increases spatial density. The introduction of oxygen-rich groups on the heterocyclic ring, such as carboxyl and ketone can improve the oxygen balance of the system and increase the coordination modes^[12-13]. Thus, as one derivative of triazole, 3-carboxyl-5-amino-1, 2, 4-triazole (H2atzc) can be considered a good candidate for constructing HEDMs with multiple coordination modes and binding sites^[14].

  Ammonium perchlorate (AP) is a key inorganic oxidizer for rocket technologies which have been widely used as the main component of solid rocket propellant^[15]. The thermal decomposition performance of AP has a great influence on the combustion characteristics of solid propellants^[16]. Most metal oxides and inorganic salts were inert catalysts that do not provide energy and even lose a part of the heat, reducing the performance of the propellant during the combustion process^[17-18]. However, the energetic complexes can provide a diverse structure and greater heat of formation, which may improve combustion performance^[19]. Therefore, the energetic complexes can be applied as an additive to the combustion catalytic of propellants.

  In this work, a new energetic complex [Cd(Hatzc)₂ (H₂O)] (LH1) was designed and synthesized. The topics of energetic properties, thermal stability, safety characteristics, and thermal decomposition effect were studied. What's more, LH1 exhibited a good catalytic effect on the thermal decomposition of AP which has potential application in propellants.

  1.   Experimental

  1.1   Chemicals and methods

  All chemicals of reagent grade were purchased and used without purification. Elemental analyses were performed on a Vario EL Ⅲ analyzer. The FT-IR spectra were recorded on a BEQ VZNDX 550 infrared spectrometer (KBr) from 400 to 4 000 cm^-1. ¹³C NMR spectra were recorded on a Bruker Avance Ⅲ 100 MHz spectrometer. Chemical shifts (in parts per million) were calibrated with dimethyl sulfoxide (DMSO). Differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis were carried out on a TA Instruments NETZSCH STA 449C simultaneous TGA at a heating rate of 10 ℃·min^-1 under hydrostatic air.

  1.2   X-ray crystallography

  The crystal suitable for X-ray diffraction measurements was obtained by slow evaporation of the ethanol solution containing H₂atzc and Cd(CH₃COO)₂·2H₂O at room temperature. The crystal with a size of 0.32 mm× 0.21 mm×0.11 mm was selected for structural determination. The single-crystal X-ray experiment was carried out on a Bruker Smart Apex Ⅱ CCD diffractometer using graphite-monochromatized Mo Kα radiation (λ=0.071 073 nm). The structures were determined by the direct method using SHELXS^[20] and refined by means of full-matrix least-squares procedures on F² with the programs SHELXL-2014^[21]. All non-hydrogen atoms were modified with anisotropic displacement parameters. All H atoms were positioned geometrically and were refined as riding with isotropic displacement parameters. A summary of the crystallography data and structure refinements for LH1 is given in Table 1. The selected bond lengths, bond angles, and hydrogen bonding geometry for complex LH1 are listed in Table 2 and 3.

  CCDC: 2100672.

  Table 1

  

  Table 1.  Crystallographic data and structure refinements for complex LH1

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  Parameter	LH1		Parameter	LH1
  Empirical formula	CdC6H8N8O5		Volume/nm3	1.081 18(14)
  Formula weight	384.6		Z	4
  Crystal system	Monoclinic		Dc/(g·cm-3)	2.363
  Space group	P21/n		μ/mm-1	2.062
  a/nm	0.904 20(7)		F(000)	752
  b/nm	0.901 99(6)		Goodness-of-fit on F2	1.067
  c/nm	1.394 54(11)		Final R indices [I > 2σ(I)]	R1=0.018 5, wR2=0.046 2
  β/(°)	108.083(3)		R indices (all data)	R1=0.021 6, wR2=0.047 8

  Table 2

  

  Table 2.  Selected bond lengths (nm) and angles (°) for complex LH1

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  Cd1—N5	0.224 6(2)	Cd1—N8	0.229 7(2)	Cd1—O6	0.237 4(2)
  Cd1—O1	0.238 12(17)	Cd1—O2a	0.239 83(17)	Cd1—O4	0.244 63(18)
  Cd1—O1a	0.256 61(18)	O2—Cd1b	0.239 83(17)	O1—Cd1b	0.256 61(18)
  N5—Cd1—N8	125.21(8)	N5—Cd1—O6	88.70(8)	N8—Cd1—O6	136.88(8)
  N5—Cd1—O1	72.56(7)	N8—Cd1—O1	88.99(7)	O6—Cd1—O1	75.77(7)
  N5—Cd1—O2a	142.46(7)	N8—Cd1—O2a	83.83(7)	O6—Cd1—O2a	81.40(7)
  O1—Cd1—O2a	137.62(6)	N5—Cd1—O4	89.07(7)	N8—Cd1—O4	70.56(7)
  O6—Cd1—O4	143.35(7)	O1—Cd1—O4	137.52(6)	O2a—Cd1—O4	78.36(6)
  N5—Cd1—O1a	89.54(7)	N8—Cd1—O1a	126.44(7)	O6—Cd1—O1a	72.47(7)
  O1—Cd1—O1a	143.738(12)	O2a—Cd1—O1a	52.93(6)	O4—Cd1—O1a	70.93(6)
  Symmetry codes: a3/2-x, 1/2+y, 1/2-z; b3/2-x, -1/2+y, 1/2-z.

  Table 3

  

  Table 3.  Hydrogen bond parameters for complex LH1

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  D—H…A	d(D—H)/ nm	d(H…A)/ nm	d(D…A)/ nm	∠DHA/(°)
  O6—H6A…O3a	0.075(4)	0.199(4)	0.274 3(3)	175(4)
  O6—H6B…O4b	0.082(4)	0.189(4)	0.269 2(3)	168(4)
  N7—H7…O2c	0.088 00	0.199 0(3)	0.278 1(3)	150
  N9—H9A…O6b	0.088 00	0.247 00	0.325 6(4)	149.00
  N9—H9B…N14c	0.088 00	0.238 00	0.321 4(3)	157.00
  N10—H10…O3d	0.088 00	0.185 0(3)	0.269 3(3)	160(10)
  N11—H11A…O6b	0.088 00	0.226 00	0.310 6(4)	161.00
  N11—H11B…N13d	0.088 00	0.224 00	0.304 0(3)	151.00
  Symmetry codes: a1/2+x, 1/2-y, -1/2+z; b-1/2+x, 3/2-y, 1/2+z; c1/2+x, 3/2-y, 1/2+z; d3/2-x, -1/2+y, 1/2-z.

  1.3   Synthesis of complex LH1

  H₂atzc (2.6 mg, 0.02 mmol) was dissolved in a mixture of NaOH (1 mL, 1 mol·L^-1), C₂H₅OH (5 mL), and water (5 mL), and adjusted to pH 6.0 by adding HCl solution (1.0 mol·L^-1). Then, Cd(CH₃COO)₂·2H₂O (13.0 mg, 0.05 mmol) was dissolved in water (5 mL) at room temperature and the solution was mixed with the solution of H₂atzc. The reaction mixture was stirred for 30 min. It was then allowed to stand at room temperature for three weeks, whereupon colorless block-shaped crystals of LH1 were formed in a 48% yield based on H₂atzc. Anal. Calcd. for CdC₆H₈N₈O₅(%): C, 18.74; H, 2.10; N, 29.14. Found(%): C, 18.85; H, 2.31; N, 28.97. IR (cm^-1, KBr): 3 455s, 3 310s, 1 668s, 1 543w, 1 479m, 1 294s, 678s. ¹³C NMR (100 MHz, DMSO-d₆): δ 139.8, 136.3, 119.6.

  1.4   Sensitivity test

  The mechanical sensitivities (impact (IS) and friction (FS)) of the energetic materials were determined using the standard BAM method^[22]. IS was determined by a Fall Hammer Apparatus. The complex (20 mg) was compacted to a copper cap under the press of 39.2 MPa and was hit by a 2 kg drop hammer, and the calculated value of H50 represents the drop height of 50% initiation probability. FS of LH1 was measured by applying a Julius Peter's machine using a 20 mg sample.

  2.   Results and discussion

  2.1   IR spectrum of LH1

  Fig. 1 shows the FT-IR spectrum of complex LH1. The broad peak with high intensity at 3 455 cm^-1 corresponds to the O—H stretching vibration of the coordinated water molecule^[23-24]. The absorption peaks at 1 543 and 3 310 cm^-1 correspond to δ(N—H) and ν(N—H) of the amino group. The intense absorption band at 1 294 cm^-1 in LH1 corresponds to the C—N stretching vibration. The absorption peaks at 1 668 and 1 479 cm^-1 show symmetric (ν_s(COO^-)) and antisymmetric (ν_as(COO^-)) vibrational absorption peaks of the carboxyl group, respectively, which indicates the oxygen atom in the carboxyl group has been coordinated to the metal ion^[25].

  Figure 1

  

  Figure 1.  FT-IR spectrum of complex LH1

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  2.2   Crystal structure of complex LH1

  Single crystal X-ray diffraction analysis shows that LH1 crystallizes in the monoclinic space group P2₁/n. The lattice unit of compound LH1 consists of one Cd(Ⅱ) ion, two Hatzc^-, and one coordinated water molecule. The Cd(Ⅱ) is seven-coordinated by two N atoms (N5 and N8) from two H₂atzc ligands, four O atoms (O1, O2^a, O4, O1^a) from three H₂atzc ligands, and one O atom (O6) from coordinated water presenting a twisted single-capped trigonal structure (Fig. 2). The Cd—O bond length ranges from 0.237 4(2) to 0.256 61(18) nm and the Cd—N bond length ranges from 0.224 6(2) to 0.229 7(2) nm. As shown in Fig. 3, Hatzc^- ligand adopts a bridging mode linking the adjacent Cd1 and Cd1^a ions to generate a 1D chain. Further, the 1D chains form a 2D pattern through N7— H7…O2^c, N11—H11B…N13^d, and N10—H10…O3^d. Finally, these plains are cross-linked by O6—H6A… O3^a to create a 3D supramolecular network structure (Fig. 4).

  Figure 2

  

  Figure 2.  Coordination environment of LH1: ellipsoid diagram with 50% probability level

  Symmetry code: ^a3/2-x, 1/2+y, 1/2-z

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  Figure 3

  

  Figure 3.  One-dimensional structure diagram of LH1

  Symmetry code: ^a3/2-x, 1/2+y, 1/2-z

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  Figure 4

  

  Figure 4.  Crystal cell frame of complex LH1

  Symmetry codes: ^a 3/2-x, 1/2+y, 1/2-z; ^b-1/2+x, 3/2-y, 1/2+z; ^c 1-x, 1-y, 1-z; ^d-1/2+x, 3/2-y, -1/2+z; ^e 1-x, 1-y, -z; ^f -1+x, y, z; ^g 1/2-x, 1/2+y, 1/2-z

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  2.3   Thermal stability

  To investigate the thermal behavior of LH1, TG-DSC was performed. As shown in Fig. 5, the first weight loss of 4.8% from 140 to 180 ℃ with a loss of a coordination water molecule (Calcd. 4.7%). In a range of 180 to 720 ℃, the complex roughly underwent two weight loss processes, which are mainly the collapse of the main framework with an exothermic peak at 229 ℃ and then releasing all the ligands completely from 229 to 720 ℃. The final product of CdO with a residue mass percentage of 32.7% is in good agreement with the calculated value of 33.3%. There were two main peaks in the DSC curve of LH1. The endothermic peak matched with the dehydration behavior (T_p=164 ℃), while the exothermic peak was at 229 ℃.

  Figure 5

  

  Figure 5.  TG and DSC curves of complex LH1

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  2.4   Energetic properties

  Density functional theory (DFT) was used to compute the energy of detonation (ΔH_det)^[26], which was estimated by using a linear correlation equations (ΔH_det= 1.127ΔE_det+0.046, r=0.968) ^[27]. All the calculations were completed in the Gaussian 09 programs. For LH1, the formation of metal ions was supposed as cadmium oxide. Water, nitrogen, and carbon were assumed to be the final products of the decomposition of the organic part of the framework^[28].

  The detonation reaction for LH1 is described by Eq.1:

  $ {\rm{Cd}}{{\rm{C}}_6}{{\rm{H}}_8}{{\rm{N}}_8}{{\rm{O}}_5} \to {\rm{CdO}} + 4{{\rm{H}}_2}{\rm{O}} + 4{{\rm{N}}_2} + 6{\rm{C}} $

  (1)

  Detonation performance of the related energetic material LH1 here was evaluated by the Empirical Kamlet-Jacob formula, as

  $ D = 1.01{\mathit{\Phi }^{1/2}}\left( {1 + 1.30\rho } \right) $

  (2)

  $ p = 1.558\mathit{\Phi }{\rho ^2} $

  (3)

  $ \mathit{\Phi } = 31.68N{\left( {MQ} \right)^{1/2}} $

  (4)

  where D is detonation velocity (km·s^-1), p is detonation pressure (GPa), Φ is characteristic value of explosive, N is moles of detonation gases per gram of explosive, M is the average molecular weight of the gases, Q is the chemical energy of detonation (kJ·g^-1), and ρ is the density of materials (g·cm^-3).

  As shown in Table 4, the heat of detonation (ΔH_det) of LH1 was calculated as 16.51 kJ·g^-1, which was even much larger than those for the conventional explosives and some energetic complexes. What's more, LH1 had good energetic properties (D=10.4 km·s^-1 and p=55.2 GPa) which make LH1 a promising high -energy solid propellant.

  Table 4

  

  Table 4.  Physicochemical properties of LH1 and relevant energetic materials

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  Compound	ρa/(g·cm-3)	Nb/%	Ωc	Tdecd/℃	ΔHdete/(kJ·g-1)	Df/(km·s-1)	pg/GPa	ISh/J	FSi/N
  LH1	2.363	21.10	-49.92	349	16.51	10.4	55.2	> 40	> 360
  [Co(Hatzc)2(H2O)2]·2H2O[14]	1.866	29.15	-49.85	362	17.18	10.18	46.99	> 40	> 360
  ATRZ-1[28]	1.68	53.35	-58.83	243	15.13	9.2	25.7	22.5	—
  ATRZ-2[28]	2.16	43.76	-49.99	257	5.77	7.8	29.7	30.0	—
  Mn(atzc)2(H2O)2·2H2O[29]	1.853	32.47	-60.26	120	21.05	10.4	48.7	> 40	> 360
  Zn(atzc)2(H2O)[29]	1.998	33.20	-56.87	140	19.15	10.2	48.6	> 40	> 360
  [Zn(Hdtim)(H2O)2]4[30]	2.11	46.12	-63.25	229	14.88	9.6	44.6	> 40	> 360
  [Mn(Hdim)(H2O)2]4[30]	1.97	47.76	-70.96	234	16.51	9.1	38.1	> 40	> 360
  Co(TO)2(DNBA)2(H2O)2[22]	1.68	20.38	-65.18	238	7.23	7.8	26.1	35.7	> 360
  Cu(TZA)(DNBA)[22]	1.94	20.92	-59.74	270	5.77	7.7	27.2	35.0	> 360
  TNT[4]	1.65	18.50	-74.00	244	3.76	7.2	20.5	15.0	353
  RDX[5]	1.81	37.80	-21.60	210	5.81	8.6	33.9	7.5	120
  a Density from X-ray diffraction data; b Nitrogen content; c Oxygen balance; d Onset decomposition temperature; e Heat of detonation; f Detonation velocity; g Detonation pressure; h Impact sensitivity; i Friction sensitivity.

  The sensitivity experiments for LH1 were explored to test the safety of applying energetic materials. The IS was greater than 40 J and the FS exceeded 360 N, which indicates that LH1 was less sensitive to impact and friction. It is probably due to the fact that the tight connection between the nitrogen-rich ligand and metallic nodes constructs a solid and insensitive 3D framework^[31]. Furthermore, the H-bonding interaction between the water molecule and the ligand in LH1 is responsible for the lower friction sensitivity^[2].

  2.5   Effects on thermal decomposition of AP

  To check the effects on the thermal decomposition behavior of AP, complex LH1 was mixed with AP at a mass ratio of 1∶3 to prepare the target sample. The study was investigated by DSC measurements with a heating rate of 10 ℃·min^-1 in nitrogen atmosphere with Al₂O₃ as references. The total sample mass used was about 0.8 mg for all runs.

  Fig. 6 shows the DSC curves of AP and mixtures of AP with LH1. The thermal decomposition of AP possessed three peaks: one endothermic peak and two exothermic peaks. It can be seen that the phase transition (from cubic to orthorhombic system) process of AP reached an endothermic peak at 245 ℃^[32]. The exothermic peaks at 310 and 393 ℃ correspond to the low-temperature decomposition (LTD) process and high-temperature decomposition (HTD) process, respectively. The heat release of the exothermic process was 0.18 and 0.76 kJ·g^-1, respectively^[33].

  Figure 6

  

  Figure 6.  DSC curves for AP and the mixture of AP with LH1 at a heating rate of 15 ℃·min^-1

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  After adding the mixture of AP with LH1, there were no significant impacts on the phase transition of AP, but a noticeable change can be seen in the exothermic phases. The exothermic process at 245-420 ℃ for pure AP became narrow to 322-360 ℃ with the exothermic peaks at 355 ℃, indicating that AP decomposed in a short time with the presence of LH1 at the same heating rate. In addition, the decomposition heat increased dramatically to 1.22 kJ·g^-1 for AP with LH1, significantly higher than the corresponding heat value for pure AP. Obviously, AP was decomposed completely in a shorter time and released much heat in the presence of LH1, which might contribute to the catalytic effects of AP^[19].

  2.6   Non-isothermal kinetics analysis

  Kissinger's method^[34] was employed to determine the apparent activation energy (E_k, kJ·mol^-1) and the preexponential factor (A, s^-1). The Kissinger equation (Eq.5) is as follows:

  $ \ln \frac{\beta }{{T_{\rm{p}}^2}} = \ln \frac{{AR}}{{{E_{\rm{k}}}}}-\frac{{{E_{\rm{k}}}}}{{R{T_{\rm{p}}}}} $

  (5)

  where T_p is the peak temperature (K), R is the gas constant (J·mol^-1·K^-1) and β is the linear heating rate (K·min^-1).

  Non-isothermal kinetic analyses of AP with LH1 were determined by DSC tests. Based on the exothermic peak temperatures measured at four different heating rates of 5, 10, 15, and 20 K·min^-1. The E_a value was calculated as 112.90 kJ·mol^-1 for AP with LH1. Compared with pure AP, the activation energy significantly decreased. Therefore, LH1 provides a certain amount of energy and has a good catalytic effect on AP decomposition (Table 5).

  Table 5

  

  Table 5.  Kinetic parameters of thermal decomposition for AP and AP with LH1

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  Sample	β/(K·min-1)	Tp/K	Ek/(kJ·mol-1)	ln(A/s-1)	Ek/ln(A/s-1)/(kJ·mol-1)
  AP	5	644.1	142.02	9.03	15.73
  	10	666.4
  	15	670.1
  	20	675.3
  AP+LH1	5	600.8	112.90	7.30	15.47
  	10	621.7
  	15	628.3
  	20	636.8

  We compared LH1 with other energetic materials with H₂atzc as ligand, Zn(atzc)₂(H₂O) ^[29] and [Mn(atzc)₂(H₂O)₂]·2H₂O^[29]. Zn(atzc)₂(H₂O) forms a fivecoordination mode showing a distorted tetragonal pyramidal geometry, [Mn(atzc)₂(H₂O)₂]·2H₂O forms a six-coordination mode, displaying a slightly distorted octahedral geometry, while LH1 forms a seven-coordination mode, which displays a twisted single-capped trigonal structure. It can be found that the electronic configuration of the central ion has a strong influence on the structure^[35-36].

  In this essay, the activation energy of pure AP was 142.02 kJ·mol^-1. With the presence of these complexes, the activation energies were changed to 112.90, 156.72, and 187.09 kJ·mol^-1 for AP+LH1, AP+[Mn(atzc)₂(H₂O)₂]·2H₂O, and AP+Zn(atzc)₂(H₂O), respectively. Among the three complexes, complex LH1 exhibited the best catalytic activity for the decomposition of AP.

  From the above, LH1 not only had high detonation velocity, detonation pressure, the energy of detonation, and less sensitivity to the external stimulus, but also had a good catalytic effect on AP. The crucial point in the synthesis of energetic complexes with high energy and low sensitivity is choosing a suitable ligand. The ligand should meet the following requirements. Firstly, the triazole ring of the energetic ligand introduces amino and carboxyl groups, which realizes the feasibility of a single component instead of a multi-component function. Secondly, the energetic ligand could enhance explosive heat and oxygen balance, and decrease sensitivity, which is beneficial for the thermal decomposition of AP. What's more, the presence of coordinated water molecules is beneficial to construct a hydrogen-bonded supramolecular network, which can reduce the sensitivity of the energetic compound LH1.

  3.   Conclusions

  In summary, a new energetic complex [Cd(Hatzc)₂ (H₂O)] (LH1) was synthesized and fully characterized. Compound LH1 possessed promising energetic properties, including low mechanical sensitivities, high detonation pressure, high detonation velocity, and high energy of detonation. DSC experiments reveal that AP was decomposed completely in a shorter time with a large of heat released in the presence of LH1, which indicates that complex LH1 has a good catalytic effect on the thermal decomposition of AP. The present study indicates the probable application of the complex in the solid propellant field. Further investigation is currently underway.

  
  
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  Figure 1  FT-IR spectrum of complex LH1

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  Figure 2  Coordination environment of LH1: ellipsoid diagram with 50% probability level

  Symmetry code: ^a3/2-x, 1/2+y, 1/2-z

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  Figure 3  One-dimensional structure diagram of LH1

  Symmetry code: ^a3/2-x, 1/2+y, 1/2-z

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  Figure 4  Crystal cell frame of complex LH1

  Symmetry codes: ^a 3/2-x, 1/2+y, 1/2-z; ^b-1/2+x, 3/2-y, 1/2+z; ^c 1-x, 1-y, 1-z; ^d-1/2+x, 3/2-y, -1/2+z; ^e 1-x, 1-y, -z; ^f -1+x, y, z; ^g 1/2-x, 1/2+y, 1/2-z

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  Figure 5  TG and DSC curves of complex LH1

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  Figure 6  DSC curves for AP and the mixture of AP with LH1 at a heating rate of 15 ℃·min^-1

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  Table 1.  Crystallographic data and structure refinements for complex LH1

  Parameter	LH1		Parameter	LH1
  Empirical formula	CdC6H8N8O5		Volume/nm3	1.081 18(14)
  Formula weight	384.6		Z	4
  Crystal system	Monoclinic		Dc/(g·cm-3)	2.363
  Space group	P21/n		μ/mm-1	2.062
  a/nm	0.904 20(7)		F(000)	752
  b/nm	0.901 99(6)		Goodness-of-fit on F2	1.067
  c/nm	1.394 54(11)		Final R indices [I > 2σ(I)]	R1=0.018 5, wR2=0.046 2
  β/(°)	108.083(3)		R indices (all data)	R1=0.021 6, wR2=0.047 8

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  Table 2.  Selected bond lengths (nm) and angles (°) for complex LH1

  Cd1—N5	0.224 6(2)	Cd1—N8	0.229 7(2)	Cd1—O6	0.237 4(2)
  Cd1—O1	0.238 12(17)	Cd1—O2a	0.239 83(17)	Cd1—O4	0.244 63(18)
  Cd1—O1a	0.256 61(18)	O2—Cd1b	0.239 83(17)	O1—Cd1b	0.256 61(18)
  N5—Cd1—N8	125.21(8)	N5—Cd1—O6	88.70(8)	N8—Cd1—O6	136.88(8)
  N5—Cd1—O1	72.56(7)	N8—Cd1—O1	88.99(7)	O6—Cd1—O1	75.77(7)
  N5—Cd1—O2a	142.46(7)	N8—Cd1—O2a	83.83(7)	O6—Cd1—O2a	81.40(7)
  O1—Cd1—O2a	137.62(6)	N5—Cd1—O4	89.07(7)	N8—Cd1—O4	70.56(7)
  O6—Cd1—O4	143.35(7)	O1—Cd1—O4	137.52(6)	O2a—Cd1—O4	78.36(6)
  N5—Cd1—O1a	89.54(7)	N8—Cd1—O1a	126.44(7)	O6—Cd1—O1a	72.47(7)
  O1—Cd1—O1a	143.738(12)	O2a—Cd1—O1a	52.93(6)	O4—Cd1—O1a	70.93(6)
  Symmetry codes: a3/2-x, 1/2+y, 1/2-z; b3/2-x, -1/2+y, 1/2-z.

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  Table 3.  Hydrogen bond parameters for complex LH1

  D—H…A	d(D—H)/ nm	d(H…A)/ nm	d(D…A)/ nm	∠DHA/(°)
  O6—H6A…O3a	0.075(4)	0.199(4)	0.274 3(3)	175(4)
  O6—H6B…O4b	0.082(4)	0.189(4)	0.269 2(3)	168(4)
  N7—H7…O2c	0.088 00	0.199 0(3)	0.278 1(3)	150
  N9—H9A…O6b	0.088 00	0.247 00	0.325 6(4)	149.00
  N9—H9B…N14c	0.088 00	0.238 00	0.321 4(3)	157.00
  N10—H10…O3d	0.088 00	0.185 0(3)	0.269 3(3)	160(10)
  N11—H11A…O6b	0.088 00	0.226 00	0.310 6(4)	161.00
  N11—H11B…N13d	0.088 00	0.224 00	0.304 0(3)	151.00
  Symmetry codes: a1/2+x, 1/2-y, -1/2+z; b-1/2+x, 3/2-y, 1/2+z; c1/2+x, 3/2-y, 1/2+z; d3/2-x, -1/2+y, 1/2-z.

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  Table 4.  Physicochemical properties of LH1 and relevant energetic materials

  Compound	ρa/(g·cm-3)	Nb/%	Ωc	Tdecd/℃	ΔHdete/(kJ·g-1)	Df/(km·s-1)	pg/GPa	ISh/J	FSi/N
  LH1	2.363	21.10	-49.92	349	16.51	10.4	55.2	> 40	> 360
  [Co(Hatzc)2(H2O)2]·2H2O[14]	1.866	29.15	-49.85	362	17.18	10.18	46.99	> 40	> 360
  ATRZ-1[28]	1.68	53.35	-58.83	243	15.13	9.2	25.7	22.5	—
  ATRZ-2[28]	2.16	43.76	-49.99	257	5.77	7.8	29.7	30.0	—
  Mn(atzc)2(H2O)2·2H2O[29]	1.853	32.47	-60.26	120	21.05	10.4	48.7	> 40	> 360
  Zn(atzc)2(H2O)[29]	1.998	33.20	-56.87	140	19.15	10.2	48.6	> 40	> 360
  [Zn(Hdtim)(H2O)2]4[30]	2.11	46.12	-63.25	229	14.88	9.6	44.6	> 40	> 360
  [Mn(Hdim)(H2O)2]4[30]	1.97	47.76	-70.96	234	16.51	9.1	38.1	> 40	> 360
  Co(TO)2(DNBA)2(H2O)2[22]	1.68	20.38	-65.18	238	7.23	7.8	26.1	35.7	> 360
  Cu(TZA)(DNBA)[22]	1.94	20.92	-59.74	270	5.77	7.7	27.2	35.0	> 360
  TNT[4]	1.65	18.50	-74.00	244	3.76	7.2	20.5	15.0	353
  RDX[5]	1.81	37.80	-21.60	210	5.81	8.6	33.9	7.5	120
  a Density from X-ray diffraction data; b Nitrogen content; c Oxygen balance; d Onset decomposition temperature; e Heat of detonation; f Detonation velocity; g Detonation pressure; h Impact sensitivity; i Friction sensitivity.

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  Table 5.  Kinetic parameters of thermal decomposition for AP and AP with LH1

  Sample	β/(K·min-1)	Tp/K	Ek/(kJ·mol-1)	ln(A/s-1)	Ek/ln(A/s-1)/(kJ·mol-1)
  AP	5	644.1	142.02	9.03	15.73
  	10	666.4
  	15	670.1
  	20	675.3
  AP+LH1	5	600.8	112.90	7.30	15.47
  	10	621.7
  	15	628.3
  	20	636.8

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