Chinese Journal of Chemistry, 2005, 23, 963—969 Full Paper * E-mail: ztlbit@public.bta.net.cn; Tel. and Fax: 86-10-68913818 Received December 29, 2004; revised and accepted April 15, 2005. Project supported by the National Natural Science Foundation of China (No. 20471008). © 2005 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Synthesis, X-ray Crystal Structure and Thermal Decomposition Character of Semicarbazidium 3,5-Dihydroxy-2,4,6- trinitrophenolate Hemihydrate CHEN, Hong-Yan(陈红艳) ZHANG, Tong-Lai*(张同来) ZHANG, Jian-Guo(张建国) State Key Laboratory of Explosion Science and Technolohy, Beijing Institute of Technology, Beijing 100081, China A new compound, semicarbazidium 3,5-dihydroxy-2,4,6-trinitrophenolate hemihydrate (SCDHTNP•0.5H 2 O), was synthesized by the reaction of the aqueous solutions of semicarbazide with trinitrophloroglucinol. Its structure was determined by single-crystal X-ray diffraction analysis and characterized by elemental analysis, FTIR, DSC and TG-DTG techniques. The crystal is monoclinic with space group P2 1 /n and the empirical formula C 7 H 9 N 6 O 10.50 . The unit cell parameters are: a＝1.3791(3) nm, b＝0.9256(2) nm, c＝2.0468(4) nm, β＝106.93(3)°, V＝2.4995(9) nm 3 , Z＝8, D c ＝1.835 g/cm 3 , M r ＝345.20, F(000)＝1416, s＝0.945, μ(Mo Kα)＝0.174 mm －1 . The final R and wR are 0.0401 and 0.0896. Its structure consists of two semicarbazidium cations, two 3,5-dihydroxy-2,4,6-trinitro- phenolate anions and one crystal water molecule, which are interconnected by electrostatic forces and hydrogen bonds into layer structure, making the title compound very stable. Under a linear heating rate, the thermal decom- position processes of SCDHTNP•0.5H 2 O have one endothermal dehydration stage and two intensive exothermic decomposition stages at 178—241 ℃ to evolve abundant gas products. Keywords semicarbazide, trinitrophloroglucinol, synthesis, crystal structure, thermal analysis Introduction 2,4,6-Trinitro-1,3,5-benzenetriol (trinitrophloroglucinol, TNPG) is a strong acid compound with yellow, needle crystal structure. It is a well-known compound and has been used in chemical industry as an ingredient for making dyes and explosive industry as an ingredient for priming composition, percussion caps and detonator formulations. Its metal salts are also important military and commercial explosives. Some metal salts of the trinitrophloroglucinol are efficient primary explosives and it is of particular interest to investigate the influence of different metals on the structure and the effect this may have on sensitivity and explosive performance. 1-7 Semicarbazide (SCZ) is an important intermediate in organic synthesis. Its molecule has rich nitrogen atom and consists of a hydrazine group, a carbonyl and an amino group, which determine its lively chemical reac- tivity. Furthermore, it is a widely used ligand in coordi- nation compounds and it can be used as a material of nitrogen-rich compounds. 8-11 Till now, few studies on TNPG and SCZ formed salt compounds have been done. A program of research is being conducted into the structural properties of TNPG and its salt. In this paper, the preparation, crystal structure and thermal decompo- sition processes of semicarbazidium 3,5-dihydroxy-2,4, 6-trinitrophenolate hemihydrate (SCDHTNP•0.5H 2 O) were studied, and the relationship between its crystal structure and performance was discussed. Experimental Instruments and materials The elemental analyses were performed on a Carlo Erba 1106 full automatic trace organic element analyzer. IR spectrum was recorded on a Bruker Equinox 55 FTIR spectrometer (KBr pellet) in the range of 400— 4000 cm －1 with the resolution of 4 cm －1 . In the deter- mination of the structure of the single crystal, X-ray intensities were recorded by a Rigaku Raxis-Rapid X-ray single-crystal diffractometer. The DSC experi- ment was carried out on a model Pyris-1 differential scanning calorimeter with a heating rate of 10 ℃/min, and flowing nitrogen gas was used as atmosphere with a flowing rate of 20 mL/min. Sample mass was about 0.5 mg, contained in sealed aluminum pans. The thermal decomposition process of SCDHTNP•0.5H 2 O was stud- ied on a model Pyris-1 thermogravimeter analyzer. About 0.5 mg of sample was held in a platinum pan and a flow of dry oxygen-free nitrogen at 20 mL/min with the heating rate of 10 ℃/min. Trinitrophloroglucinol was prepared by a reported method 12 and crystallized from dilute hydrochloric acid with the purity higher than 99%. Semicarbazide hydro- chloride was refined. Other chemicals were of analytical grade.