Zinc(II) and Cadmium(II) Complexes of 5-Ferrocenyl-1H-tetrazole: Synthesis, Structures, and Catalytic Effects on Thermal Decomposition of Energetic Compounds

Alkyl-substituted ferrocenes as ferrocene-based burning rate (BR) catalysts in composite solid propellants have high migration tendency and strong volatility during processing and long-time storage of the propellants. For developing low-migratory alternatives, zinc(II) and cadmium(II) complexes, [Zn(phen)(3)](FcTz)(2)center dot 9H(2)O (1), [Cd(phen)(2)(H2O)(2)](FcTz)(2) (3), and [Cd(bpy)(2)(FcTz)(2)]center dot H2O (4) (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline; FcTz = 5-ferrocenyl-1H-tetrazolate), derived from 5-ferrocenyl-1H-tetrazole (HFcTz) were synthesized and structurally characterized. Compound 4 was also studied by density functional theory calculations (DFT). Additionally, a few single-crystals of [Zn(phen)(2)(H2O)(2)](FcTz)(2) (2) suitable for single-crystal X-ray diffraction formed and therefore only its crystal structure was analyzed. The cyclic voltammetry results suggested that 1, 3, and 4 are quasi-reversible redox systems. The TG analysis showed they are of highly thermal stability when their lattice water molecules are not taken into account. Their catalytic performances for thermal decomposition 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 accessed by DSC/TG techniques. Their optimum contents in AP, RDX, and HMX are 5 wt-%, 5 wt-%, and 2 wt-%, respectively. They exhibit highly catalytic activities in thermal degradation of AP and RDX.