Complexation of Ammonia Boranes with Al³

Area of Science:

• Materials Science
• Inorganic Chemistry
• Hydrogen Storage

Background:

• Ammonia borane (NH₃BH₃, AB) is a promising hydrogen storage material but suffers from exothermic dehydrogenation and poor rehydrogenation.
• Complexation with Al³⁺, as in Al(BH₄)₃·AB, improves dehydrogenation characteristics and enables direct rehydrogenation.

Purpose of the Study:

• To investigate the reactivity of AB derivatives (RNH₂BH₃) with aluminum salts (AlX₃) to expand the range of stable complexes.
• To explore novel aluminum-borane complexes for enhanced hydrogen storage and potential applications in batteries.

Main Methods:

• Synthesis and characterization of novel ammonia borane-aluminum complexes.
• Investigation of dehydrogenation properties and rehydrogenation potential.
• Structural analysis of synthesized compounds, including those with aluminum in both cationic and anionic sites.

Main Results:

• Three new complexes were identified: Al(BH₄)₃·CH₃NH₂BH₃, [Al(CH₃NH₂BH₃)₂Cl₂][AlCl₄], and [Al(NH₂CH₂CH₂NH₂)(BH₄)₂][Al(BH₄)₄].
• The complex Al(BH₄)₃·CH₃NH₂BH₃ exhibits different dehydrogenation properties compared to Al(BH₄)₃·AB.
• Novel structures featuring Al³⁺ in both cationic and anionic components were discovered, relevant for battery electrolytes.

Conclusions:

• The study successfully extended the series of aluminum-borane complexes, enhancing stability and rehydrogenation potential for hydrogen storage.
• The novel complexes with aluminum in cationic and anionic sites are promising for developing new electrolytes for aluminum-based batteries.
• Coordinating multiple ammonia borane units to a single aluminum atom offers a pathway to materials with higher hydrogen content.