Complete Series of Alkali-Metal M(BH₃NH₂BH₂NH₂BH₃) Hydrogen-Storage Salts Accessed via\nMetathesis in Organic Solvents

Abstract

We report a new efficient way of\nsynthesizing high-purity hydrogen-rich M­(BH₃NH₂BH₂NH₂BH₃) salts (M = Li, Na, K,\nRb, Cs). The solvent-mediated metathetic synthesis applied here uses\nprecursors containing bulky organic cations and weakly coordinating\nanions. The applicability of this method permits the entire series\nof alkali-metal M­(BH₃NH₂BH₂NH₂BH₃) salts (M = Li, Na, K, Rb, Cs) to be obtained,\nthus enabling their comparative analysis in terms of crystal structures\nand hydrogen-storage properties. A novel polymorphic form of Verkade’s\nbase (C₁₈H₃₉N₄PH)­(BH₃NH₂BH₂NH₂BH₃) precursor was\nalso characterized structurally. For all compounds, we present a comprehensive\nstructural, spectroscopic, and thermogravimetric characterization\n(PXRD, NMR, FTIR, Raman, and TGA/DSC/MS).