5-Ferrocenyl-1H-tetrazole-Derived Transition-Metal Complexes: Synthesis, Crystal Structures and Catalytic Effects on the Thermal Decomposition of the Main Components of Solid Propellants

With the aim of developing low-migratory burning-rate (BR) catalysts for solid propellants, a series of transition-metal complexes of 5-ferrocenyl-1H-tetrazole (HFcTz), [Cu-2(bpy)(2)(FcTz)(4)]2C(2)H(5)OH (1), [Pb(phen)(2)(H2O)(3)](FcTz)(2)H2O (3), [Cu(phen)(3)](FcTz)(2)8H(2)O (4), [Mn(phen)(2)(H2O)(2)](FcTz)(2) (5), [Mn(bpy)(H2O)(4)](FcTz)(2) (6), [Ni(phen)(3)](FcTz)(2)9H(2)O (7), and [Co(phen)(3)](FcTz)(2)9H(2)O (8) (bpy = 2,2-bipyridine; phen = 1,10-phenanthroline), were synthesized and structurally characterized. Only a limited number of single crystals of [Pb-2(phen)(4)(CO3)](FcTz)(2)phen9H(2)O (2) were formed so only its crystal structure was analyzed. The complexes show high thermal stability. Cyclic voltammetry investigations suggested that 1 and 3-7 exhibit quasireversible redox systems. Their catalytic effects on the thermal degradation of ammonium perchlorate (AP), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), and 1,2,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) were evaluated by differential scanning calorimetry (DSC) and thermogravimetric (TG) methods. The optimum content of the new compounds in AP, RDX, and HMX was established to be 5, 5, and 2 wt.-%, respectively. They exhibit high catalytic activities in the thermal decomposition of AP and RDX. Among them, 6 was found to be the best ferrocene-based BR catalyst.