A Fresh Look at a Well-Known Solid: Structure, Vibrational Spectra, and Formation Energy of NaNH2

Abstract

Sodium amide (NaNH2) in its α form is a common compound that has recently seen renewed interest, mainly for its potential use as a solid-state hydrogen storage material. In this work, we present a synergic theoretical and experimental characterization of the compound, including novel measured and simulated vibrational spectra (IR and Raman) and X-ray diffraction patterns. We put forward the hypothesis of a low-temperature symmetry breaking of the structure to space group C2/c, while space group Fddd is commonly reported in the literature and experimentally found down to 80 K. Additionally, we report a theoretical estimate of the heat of formation of sodium amide from ammonia to be equal to −12.2 kcal/mol at ambient conditions.