Synthesis, X-ray crystal structure and thermal decomposition character of semicarbazidium 3,5-dihydroxy-2,4,6-trinitrophenolate hemihydrate

A new compound, semicarbazidium 3,5-dihydroxy-2,4,6-trinitrophenolate hemihydrate (SCDHTNP•0.5H₂O), 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 P2₁/n and the empirical formula C₇H₉N₆O_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) nm³, Z=8, D_c=1.835 g/cm³, 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- trinitrophenolate 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 decomposition processes of SCDHTNP•0.5H₂O have one endothermal dehydration stage and two intensive exothermic decomposition stages at 178-241°C to evolve abundant gas products.