HAN Jing LI Ting LI Bing（Department of Chemistry and Chemical Engineering，Ningxia University，Yinchuan 750021，China）

A New Nickel（II）Coordination Compound Constructed by Pyridyl-triazole and Oxybis （Benzoic Acid）:Synthesis，Crystal Structure and the Effect on the Thermal Decomposition of Ammonium Perchlorate①

HAN Jing LI Ting LI Bing②a（Department of Chemistry and Chemical Engineering，Ningxia University，Yinchuan 750021，China）

A new energetic complex，Ni（3，4΄-Hbpt）2（Hoba）2（H2O）2（3，4΄-Hbpt =3-（3-pyridyl）-5-（4΄-pyridyl）-1-H-1，2，4-triazole and H2oba = 4，4΄-oxybis（benzoic acid）），has been synthesized by hydrothermal reaction and characterized by elemental analysis，IR spectroscopy，single-crystal X-ray diffraction，thermogravimetric analyses and X-ray powder diffraction.Single-crystal X-ray diffraction analysis indicates that the complex belongs to the monoclinic system，space group P21/c with a = 10.2357（9），b = 24.594（2），c = 10.4225（9）Å，β = 114.0110（10）°，V = 2396.7（4）Å3，Dc= 1.460 g/cm3，μ = 0.482 mm-1，Mr= 1053.63，F（000）= 1088，Z = 2，the final R = 0.0358 and wR = 0.0973 with I ＞ 2σ（I）.Both3，4΄-Hbpt and H2oba ligands adopt monodentate modes linking one Ni（II）ion to form a 0D motif.Furthermore，the 0D motifs are linked into a3D supramolecular architecture with hydrogen bonds.In addition，the catalytic performance for thermal decomposition of the efficacy of ammonium perchlorate （AP）is explored by differential scanning calorimetry （DSC），which indicates that the complex is a good candidate for a promoter of the thermal decomposition of ammonium perchlorate.

3-（3-pyridyl）-5-（4΄-pyridyl）-1-H-1，2，4-triazole，4，4΄-oxybis（benzoic acid），crystal structure，thermal decomposition，ammonium perchlorate

1　INTRODUCTION

In recent decades，the design and synthesis of compounds based on triazole and its derivatives have been extensively studied as novel functional materials for their potential applications in the areas of absorption，catalysis，optic sensors，and magnetism molecular recognition［1-4］.Due to high nitrogen content，triazole and its derivatives are also widely used as energetic materials［5-8］.As one of the derivatives of triazole，3，5-bis-pyridyl-1-H-1，2，4-triazole （Hbpt）serves as an N，N΄-donor ligand and acts as a bridging ligand，thus mediating exchange coupling.Furthermore，the prototropy and conjugation between the 1H-1，2，4-triazole and pyridyl groups alter the electron density in different sections of the molecules，making the ligand more flexible［9］.Many coordination compounds about Hbpt are extensively studied for their fascinating architectures and potential applications in luminescence，photocatalysisand magnetism［10-12］.However，the potential applications in energetic materials based on Hbpt are rarely reported［13-15］.

Ammonium perchlorate （AP）is the most common oxidizer in composite solid propellants and the thermal decomposition characteristics of AP directly influence the combustion behavior of such solid propellants.The reaction rate and decomposition temperature of the thermal decomposition of AP are closely related to the combustion rate of solid propellants，with lower decomposition temperature resulting in the faster combustion rates［16，17］.

In order to study the effects of compounds containing Hbpt on the thermal decomposition of AP，we choose nickel（II）ion as the coordination center and 4，4΄-oxybis（benzoic acid）（H2oba）as an auxiliary ligand on the basis of the following considerations:（1）the nickel（II）ion shows good catalytic performance for the decomposition of propellants.Besides，this kind of metal ion exhibits good ability to coordinate with many different types of ligands and is more environmentally friendly than toxic heavy metal cations such as lead（II）and mercury（II）［18，19］.（2）There are two carboxyl groups separated by an oxygen atom and two benzene rings，which would reduce the steric interference/hindrance.Moreover，the ligand can improve the oxygen balance of propellant components［20］.In this paper，we report the synthesis and structure of a nickel（II）coordination compound with3，4΄-Hbpt in the presence of oxybis ligand，namely，Ni（3，4΄-Hbpt）2-（Hoba）2（H2O）2，confirmed by single-crystal X-ray diffraction.Furthermore，thermodynamic stability，X-ray powder diffraction and catalytic performance of the title complex in the thermal decompo- sition of AP were explored.

2　EXPERIMENTAL

2.1Materials

Commercially available reagents were used as received without further purification.Elemental analyses （C，H and N）were performed on a Vario EL III analyzer.Infrared spectra were obtained using KBr pellets on a BEQ VZNDX 550 FTIR instrument within the 400～4000 cm-1region.1H NMR spectra were recorded on a Varian Inova 400 instrument using tetramethylsilane （TMS）as an internal standard.Thermal analyses were performed on a NETZSCH STA 449C instrument under an atmosphere of hydrostatic air at a heating rate of 10 ℃min-1.X-ray powder diffraction （XPRD）was received on a Bruker Advance-D8 instrument at room temperature.Differential scanning calorimetry （DSC）experiments were performed on a Perkin-Elmer Pyris 6 DSC thermal analyzer （calibrated using pure indium and zinc as standards）from 50 to 500 ℃.

2.2Synthesis of3，4΄-Hbpt

3，4΄-Hbpt was synthesized according to literature［21］and characterized by IR，EA and NMR.Anal.Calcd.for C12H9N5（%）:C，64.56；H，4.06；N，31.37.Found:C，64.88；H，4.56；N，32.88.m.p:239～241 ℃.IR （cm-1，KBr）:3408（w），3088（m），2623（m），1606（s），1580（s），1447（m），1423（m），1378（m），1362（m），1152（s），1015（m），987（m），832（s），720（m），709（m），528（s）；1H NMR （400 MHz，DMSO-d6，ppm）:6.951～6.980 （1H，d，J = 8.0 Hz），7.508～7.539 （1H，m，J = 4.8 Hz），9.054（1H，s）；10.329 （1H，s，triazole-H）.

2.3Synthesis of Ni（3，4΄-Hbpt）2（Hoba）2（H2O）2

A mixture containing Ni（OAc）2·4H2O （12.4 mg，0.05 mmol），H2oba （12.9 mg，0.05 mmol），3，4΄-Hbpt （11.2 mg，0.05 mmol）and water （6 mL）was sealed in a 15 mL Teflon-lined stainless-steel vessel and heated at 160 ℃ for3 days and then cooled to room temperature at a rate of 5 ℃/h.Green block crystals of compound 1 were collected in a yield of 40% （based on Ni）.Anal.Calcd.for 1 （%）:C，59.28；H，3.64；N，13.29.Found:C，59.05；H，3.01；N，12.57.IR （cm-1，KBr）:3328（m），1686（w），1593（s），1551（s），1423（w），1381（s），1219（s），1175（w），1089（w），879（w），773（w）.

2.4X-ray crystallography

A green crystal of the title complex with approximate dimensions of 0.22mm × 0.19mm × 0.18mm was carried out on a Bruker Smart Apex CCDdiffractometer equipped with graphite-monochromated Mo-Kα radiation （λ = 0.071073 nm）at 293（2）K.The data set was corrected by SADABS program［22］.The structure was solved by direct methods and expanded by difference Fourier techniques with SHELXS-97［23］and refined by full-matrix leastsquares method on F2with SHELXL-97［24］.All nonhydrogen atoms were refined anisortropically.Hydrogen atoms were placed in the geometrically calculated positions.For 1，a total of 11839 reflections were collected in the range of 2.18≤θ≤25.09°，of which 4236 were independent （Rint= 0.0230）.The final R = 0.0358 and wR = 0.0973 for the observed reflections with I ＞ 2σ（I），R = 0.0446 and wR = 0.1008 for all data with （Δρ）max= 0.584 and （Δρ）min= -0.300 e·Å-3.The selected bond lengths and bond angles are listed in Table 1.Hydrogen bonding geometry for the title complex is collected in Table 2.

Table 1.Selected Bond Lengths （Å）and Bond Angles （°）

Table 2.Hydrogen Bond Lengths （Å）and Bond Angles （°）

3　RESULTS AND DISCUSSION

3.1Structural analysis of complex 1

X-ray single-crystal analysis shows that the symmetric unit of 1 consists of one Ni（II）ion，one3，4΄-Hbpt ligand，one deprotonated Hoba-ligand，and one coordinated water molecule.As shown in Fig.1，the Ni（II）is six-coordinated in a distorted octahedral geometry by four oxygen atoms from H2oba and H2O which are in the equatorial positions and two nitrogen atoms of3，4΄-Hbpt which locate at the axial positions.In H2oba，the dihedral angle between two benzene rings is 78.08º.The dihedral angle between3-pyridyl and 4΄-pyridyl in3，4΄-Hbpt is 13.37º.The Ni-N bond length is 2.1310（17）Å，which is in normal range［25，26］.The Ni-O bond distances range from 2.0420（14）to 2.0596（15）Å，which are reduced compared to other Ni-based complexes［27，28］because when carboxyl groups coordinate with Ni（II）ions，the bond lengths are shortened in order to make the complex more stable.In addition，both3，4΄-Hbpt and H2oba ligands adopt monodentate modes，linking one Ni（II）ion to form a 0D motif.Furthermore，the molecular packing is further controlled by intermolecular hydrogen bonds:O（4）-H（4A）…O（5）iii，O（6）-H（6B）…N（1）iiand intramolecular hydrogen bond O（6）-H（6A）…O（1）i（i = -x，-y，-z+1；ii = -x，y+1/2，-z+3/2；iii = -x+1，-y+1，-z+1）.The O（4）-H（4A）…O（5）iiihydrogen-bonding interaction from the H2oba molecules links the structure into a 1D chain.Afterwards，O（6）-H（6A）…O（1）iand O（6）-H（6B）…N（1）iihydrogen-bonding interactions further generate the title complex into a3D supramolecular architecture （Fig.2）.

Fig.1.Coordination environment of the Ni（II）ion with H atoms omitted for clarity （Symmetry code:i = x，-y，-z+1）

Fig.2.Hydrogen bond forming a3D framework

3.2IR analysis of compound 1

The IR spectrum of 1 shows a broad absorption band at3328 cm-1，corresponding to the O-H stretching of coordinated water molecules in the complex.The C=C and C-O absorption bands can be observed at 1593 and 1219 cm-1，respectively.The C-N absorption bands of pyridine can be observed at 1381 cm-1.The νasym（COO-）and νsym（COO-）absorption is evidenced by strong bands at 1686 and 1423 cm-1，which indicate part deprotonation of all carboxylate groups in H2oba.The IR spectrum is in agreement with the crystal structure of compound 1.

3.3Thermal decomposition process of compound 1

Thermogravimetric experiments were conducted to study the thermal stability of the title complex，which is an important parameter for metal-organic framework materials.As shown in Fig.3，the TGA curve suggests the first weight loss of3.45% in the range of 70～203 ℃，corresponding to expulsion of coordinated water molecules （calcd.3.42%）.The main framework remains intact until it is heated to368 ℃，and then releases the3，4΄-Hbpt ligand with an exothermic peak at 410 ℃ （found 41.68%，calcd.42.14%）.After that，the complex loses the other ligand completely in the range of 482～780 ℃ with an exothermic peak at 701 ℃ and converts to NiO with the residual amount of 8.02%，which is in good agreement with the calculated value of 7.12%.The residual sample was characterized by X-ray powder diffraction （XRPD）at room temperature，as shown in Fig.4.It is seen that all diffraction peaks agree well with the standard diffraction data for NiO （JCPDS card file No.47～1049），indicating the metal centre has been oxidized in the heating stage.

Fig.3.TGA curves for the title complex

Fig.4.XPRD patterns of the residual and NiO

3.4Effects on the thermal decomposition of ammonium perchlorate

Ni（3，4΄-Hbpt）2（Hoba）2（H2O）2is explored as a promoter of thermal decomposition of AP，the key component of composite solid propellant.The performance of the compound on the thermal decomposition of AP （compound and AP were mixed at a mass ratio of 1:3）was investigated by DSC measurement with a heating rate of 10 ℃ min-1in N2atmosphere from 100 to 500 ℃ with Al2O3as reference.The total sample mass used was less than 1.0 mg for all runs.Fig.5 shows the DSC curves of both AP and the mixture of AP with the compound.The endothermic peak of AP at 245 ℃ is due to the crystal transformation of AP from orthorhombic to cubic phase.The second and third peaks for pure AP are exothermic，and correspond to the low and high temperature decomposition processes （LTD and HTD），respectively［29，30］.The exothermic peak of LTD process occurs at about 290 ℃ at a heating rate of 10 ℃ min-1，corresponding to the decomposition of AP with the heat of 0.735 kJ g-1；and that for HTD process is at 448 ℃ with the heat of 0.787 kJ g-1.Fig.5 shows the compound has no significant impact on the phase transition of AP，while the two exothermic peaks in AP merge to one with the presence of the title complex and the peak temperature （339 ℃）is lower than the exothermic peak temperature of HTD for pure AP （448 ℃）.The sharp exothermic peak indicates a rapid decomposition process and the decomposition heat increases dramatically to 2.38 kJ g-1.The compound decomposes and releases heat itself，which enhances the total heat of the mixture，as well as the formation of metal at the molecular level on the propellant surface which may contribute toward the catalytic effect［31］.Obviously，AP decomposition is accelerated in the presence of Ni（3，4΄-Hbpt）2（Hoba）2（H2O）2.

Fig.5.DSC curves for AP and AP + compound

4　CONCLUSION

In this paper，we demonstrate a new complex Ni（3，4΄-Hbpt）2（Hoba）2（H2O）2generated from3，4΄-Hbpt and H2oba under coordination-driven assembly.The title complex is a 0D motif，which is linked into a3D supramolecular architecture through hydrogen bonding interaction.The introduction of H2oba greatly influences the coordination modes of3，4΄-Hbpt as well as the final supramolecular structures.Moreover，the effects of the title compound on the thermal decomposition of AP have also been studied.Compound 1 shows good catalytic performance in AP decomposition，which could make it promising energetic additives for AP-based propellants.

REFERENCES

（1）Zhang，J.P.；Zhang，Y.B.；Lin，J.B.；Chen，X.M.Metal azolate frameworks:from crystal engineering to functional materials.Chem.Rev.2012，112，1001-1033.

（2）Pan，M.；Lin，X.M.；Li，G.B.；Su，C.Y.Progress in the study of metal-organic materials applying naphthalene diimides （NDIs）ligands.Coord.Chem.Rev.2011，255，1921-1936.

（3）Kuppler，R.J.；Timmons，D.J.；Fang，Q.R.；Li，J.R.；Makal，T.A.；Young，M.D.；Yuan，D.Q.；Zhao，D.；Zhuang，W.J.；Zhou，H.C.Potential applications of metal-organic frameworks.Coord.Chem.Rev.2009，253，3042-3066.

（4）Ma，L.F.；Wang，L.Y.；Wang，Y.Y.；Batten，S.R.；Wang，J.G.Self-assembly of a series of cobalt（II）coordination polymers constructed from H2tbip and bipyridine-based ligands.Inorg.Chem.2009，48，915-924.

（5）Zhao，F.Q.；Xue，L.；Xing，X.L.；Hu，R.Z.；Zhou，Z.M.；Gao，H.X.；Yi，J.H.；Xu，S.Y.；Pei，Q.Thermochemical properties and thermokinetic behavior of energetic triazole ionic salts.Sci.China.Chem.2011，54，461-474.

（6）Thottempudi，V.；Gao，H.X.；Shreeve，J.M.Trinitromethyl-substituted 5-nitro- or3-azo-1，2，4-triazoles:synthesis，characterization，and energetic properties.J.Am.Chem.Soc.2011，133，6464-6471.

（7）Wei，J.P.；Zhang，D.；Yang，Q.；Chen，S.P.；Gao，S.L.0D Cu（II）and 1D mixed-valence Cu（I）/Cu（II）coordination compounds based on mixed ligands:syntheses，structures and catalytic thermal decomposition for HMX.Inorg.Chem Commun.2013，30，13-16.

（8）Li，S.H.；Wang，Y.；Qi，C.；Zhao，X.X.；Zhang，J.C.；Zhang，S.W.；Pang，S.P.3D energetic metal-organic frameworks:synthesis and properties of high energy materials.Angew.Chem.Int.Ed.2013，52，1-6.

（9）Li，B.；Chen，S.P.；Yang，Q.；Gao，S.L.R-phenyldicarboxyl （R = H，NO2and COOH）modular effect on Ni（II）coordination polymers incorporated with a versatile connector 1H-3-（3-pyridyl）-5-（4-pyridyl）-1，2，4-triazole.Polyhedron 2011，30，1213-1218.

（10）Li，B.；Chen，S.P.；Xie，G.；Yang，Q.；Gao，S.L.Coligand benzenedicarboxylate modulated zinc（II）-3，5-bis （3-pyridyl）-1H-1，2，4-triazole frameworks:synthesis，structure and luminescent property.Struct.Chem.2012，23，417-423.

（11）Huang，F.P.；Zhang，Q.；Yu，Q.；Bian，H.D.；Liang，H.；Yan，S.P.；Liao，D.Z.；Cheng，P.Coordination assemblies of CoII/NiII/ZnII/CdIIwith succinic acid and bent connectors:structural diversity and spin-canted antiferromagnetism.Cryst.Growth.Des.2012，12，1890-1898.

（12）Kan，W.Q.；Liu，B.；Yang，J.；Liu，Y.Y.；Ma，J.F.A series of highly connected metal-organic frameworks based on triangular ligands and d10metals:syntheses，structures，photoluminescence，and photocatalysis.Cryst.Growth.Des.2012，12，2288-2298.

（13）Li，B.；Wei，Q.；Yang，Q.；Chen，S.P；Gao，S.L.Synthesis，crystal structure and thermodynamics of an energetic complex Co（2，3΄-bpt）3·H2O.J.Chem.Eng.Data.2011，56，3043-3046.

（14）Xie，G.；Li，B.；Chen，S.P.；Yang，Q.；Wei，W.；Gao，S.L.Cobalt（II）coordination polymers built on isomeric dipyridyl triazole ligands with pyromellitic acid:synthesis，characterization and their effects on the thermal decomposition of ammonium perchlorate.Sci.Chin.Ser.B 2012，55，443-450.

（15）Li，B.；Shen，D.；Chen，X.Y.；Li，T.；Ren，J.L.；Hu，Q.L.；Liu，W.Y.A new 1-D energetic complex ［Cu（2，3΄-bpt）2·H2O］n:synthesis，structure，and catalytic thermal decomposition for ammonium perchlorate.J.Coord.Chem.2014，67，2028-2038.

（16）Chen，L.J.；Li，L.P.；Li，G.S.Synthesis of CuO nanorods and their catalytic activity in the thermal decomposition of ammonium perchlorate.J.Alloys.Compd.2008，464，532-536.

（17）Ping，C.；Li，F.；Jian，Z.；Wei，J.Preparation of Cu/CNT composite particles and catalytic performance on thermal decomposition of ammonium perchlorate.Prop.Explos.Pyrotech.2006，31，452-455.

（18）Yang，Q.；Chen，S.P.；Xie，G.；Gao，S.L.Synthesis，crystal structure，sensitivity，and effect on thermal decomposition of ammonium perchlorate:an energetic compound Cu（HATZ）（PDA）（H2O）.J.Coord.Chem.2012，65，2584-2592.

（19）Jacobs，P.W.M.；Whitehead，H.M.Decomposition and combustion of ammonium perchlorate.Chem.Rev.1969，69，551-590.

（20）Wang，J.M.；Li，B.；Sun，L.；Li，T.；Zhou，H.L.；Ren，J.L.；Hu，Q.L.Synthesis，structure，thermostability and DFT calculations of a cobalt（II）coordination compound constructed by oxybis（benzoic acid）and pyridyl-triazole.Chin.J.Inorg.Chem.2014，30，683-688.

（21）Browne，E.1，2，4-Triazol-3-ylpyridines.Aust.J.Chem.1975，28，2543-2546.

（22）Sheldrick，G.M.SADABS.Program for Empirical Absorption Correction of Area Detector.University of Gottingen，Germany 1996.

（23）Sheldrick，G.M.SHELXS-97，Program for Crystal Structure Solution.University of Göttingen，Germany 1990.

（24）Sheldrick，G.M.SHELXL-97，Program for Crystal Structure Refinement.University of Göttingen，Germany 1997.

（25）Gao，Z.Q.；Li，H.J.；Gu，J.Z.Syntheses，crystal structures and magnetic properties of Ni（II）and Mn（II）coordination polymers constructed from5-（2΄-ccarboxylphenyl）nicotate and 2，2΄-biimidazole.Chin.J.Struct.Chem.2014，33，434-440.

（26）Mei，C.Z.；Wang，H.R.；Xiong，H.L.；Meng，R.J.；Shen，W.W.；Li，H.H.Hydrothermal synthesis and crystal structure of one3D coordination polymer of nickel（II）achieved from 5-iodo-isophthalic acid ligand.Chin.J.Struct.Chem.2014，33，563-568.

（27）Javier，T.；Carmen，D.；Joan，R.；José，M.；Miguel，M.Synthesis and characterization of ［Cu（Me2oxpn）Ni（NO2）（tmen）］（ClO4）:a single ferrimagnetic dinuclear Cu（II）-Ni（II）complex acting as weak molecule-based magnet.Chem.Commun.2002，3，364-365.

（28）Ou，G.C.；Li，Z.Z.；Zhang，M.；Yuan，X.Y.Chiral resolution of β-dl-phenylalanine using chiral macrocyclic nickel（II）complexes.Chin.J.Struct.Chem.2014，33，707-712.

（29）Lang，A.J.；Vyazovkin，S.Effect of pressure and sample type on decomposition of ammonium perchlorate.Combust.Flame.2006，145，779-790.

（30）Vyazovkin，S.；Wight，C.A.Kinetics of thermal decomposition of cubic ammonium perchlorate.Chem Mater.1999，11，3386-3393.

（31）Kulkarni，P.B.；Reddy，T.S.；Nair，J.K.；Nazare，A.N.；Talawar，M.B.；Mukundan，T.；Asthana，S.N.Studies on salts of3-nitro-1，2，4-triazol-5-one （NTO）and 2，4，6-trinitroanilino benzoic acid （TABA）:potential energetic ballistic modifiers.J.Hazard.Mater.2005，123，54-60.

10.14102/j.cnki.0254-5861.2011-0461

23 July 2014；accepted 18 September 2014 （CCDC 796758）

① Supported by the National Natural Science Foundation of China （No.21263019）

② Corresponding author.E-mail:nxdaxue@126.com （Bing Li）