Barium borohydride chlorides: synthesis, crystal structures and thermal properties

Area of Science:

• Inorganic Chemistry
• Materials Science
• Solid-State Chemistry

Background:

• Barium borohydride chlorides are compounds with potential applications in hydrogen storage and catalysis.
• Understanding their synthesis and formation mechanisms is crucial for optimizing material properties.

Purpose of the Study:

• To synthesize and characterize new barium borohydride chlorides.
• To investigate the mechanisms of their formation and thermal decomposition.
• To explore the influence of alkali metals (Li, Na, K) on the resulting structures.

Main Methods:

• Mechanochemical synthesis and thermal treatment of M BH4-BaCl2 (M = Li, Na, K).
• In situ synchrotron radiation powder X-ray diffraction (SR-PXD) for structural analysis.
• Fourier transform infrared spectroscopy (FT-IR) for chemical bonding.
• Simultaneous thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), mass spectroscopy (MS), and temperature programmed photographic analysis (TPPA) for thermal decomposition studies.

Main Results:

• Two solid solutions of barium borohydride chlorides, o-Ba(BH4)xCl2-x and h-Ba(BH4)xCl2-x, were identified, with varying borohydride content (x).
• LiBH4 showed higher reactivity, leading to hexagonal phases (h-Ba(BH4)xCl2-x) and subsequent transformation to another orthorhombic phase upon heating.
• Na and K borohydrides exhibited lower reactivity, forming simpler orthorhombic phases and solid solutions.

Conclusions:

• Novel barium borohydride chloride compounds were successfully synthesized and characterized.
• The study elucidated distinct reaction pathways and structural transformations dependent on the alkali metal and synthesis conditions.
• The findings provide fundamental insights into the formation and stability of these complex inorganic materials.