Synthesis and thermal stability of Zr(BH4)4 and Zr(BD4)4 produced by mechanochemical processing

Zirconium tetrahydroborate Zr(BH4)4 and its deuteride compound Zr(BD4)4 were successfully synthesized by mechanochemical reaction between NaBH4 or NaBD4 and ZrCl4, reaching yields of 55% and 46%, respectively. The influence of the synthesis parameters on the yield of Zr(BH4)4 was analyzed. The composition of the ZrCl4:NaBH4 starting mixture and the use of LiBH4 instead of NaBH4 as reactive show a clear effect on the Zr(BH4)4 yield. Instead, milling atmosphere does not affect the amount of the obtained product. FTIR analysis of atmosphere inside of milling vial allows to determine the formation of diborane during milling from Zr(BH4)4 decomposition. Thermal stability of pure Zr(BH4)4 and its deuterated compound was studied by combined gas-phase FTIR and DSC measurements under flowing Ar. We found that Zr(BH4)4/Zr(BD4)4 melt at about 305/303 K, decompose at about 430 K from the gas-phase and show evolution of B2H6/B2D6 under heating.