Na[Li(NH2BH3)2] – the first mixed-cation amidoborane with unusual crystal structure

Abstract

We describe the successful synthesis of the first mixed-cation (pseudoternary) amidoborane, Na[Li(NH₂BH₃)₂], with theoretical hydrogen capacity of 11.1 wt%. Na[Li(NH₂BH₃)₂] crystallizes triclinic (P) with a = 5.0197(4) Å, b = 7.1203(7) Å, c = 8.9198(9) Å, α = 103.003(6)°, β = 102.200(5)°, γ = 103.575(5)°, and V = 289.98(5) ų (Z = 2), as additionally confirmed by Density Functional Theory calculations. Its crystal structure is topologically different from those of its orthorhombic LiNH₂BH₃ and NaNH₂BH₃ constituents, with distinctly different coordination spheres of Li (3 N atoms and 1 hydride anion) and Na (6 hydride anions). Na[Li(NH₂BH₃)₂], which may be viewed as a product of a Lewis acid (LiNH₂BH₃)/Lewis base (NaNH₂BH₃) reaction, is an important candidate for a novel lightweight hydrogen storage material. The title material decomposes at low temperature (with onset at 75 °C, 6.0% mass loss up to 110 °C, and an additional 3.0% up to 200 °C) while evolving hydrogen contaminated with ammonia.