Structural and thermodynamic investigations of Zr(BH₄)₄ and Hf(BH₄)₄ between 280 K and their decomposition temperatures

The borohydrides of zirconium (Zr(BH4)(4)) and hafnium (Hf(BH4)(4)) have been prepared by solid state metatheses. The crystal structures were determined slightly below their melting temperature with in situ cryo crystallisation single crystal XRD. The melting and decomposition process was investigated using differential scanning calorimetry coupled with thermogravimetry and mass spectroscopy. The enthalpies of formation were determined using the decomposition enthalpy, the enthalpy of fusion and the heat capacity measurements in the temperature range from 5 degrees C to 35 degrees C. Standard entropy values of both compounds were obtained by DFT calculations. The determined values were optimised using the CalPhaD method.