Affiliation:
1. Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-089 Warsaw, Poland
Abstract
Tetramethylphosphonium borohydride was synthesized via an ion metathesis reaction in a weakly-coordinating aprotic environment. [(CH3)4P]BH4, in contrast to related [(CH3)4N]+ compounds which tend to crystallize in a tetragonal system, adopts the distorted wurtzite structure (P63mc), resembling some salts containing analogous ions of As and Sb. [(CH3)4P]BH4 decomposes thermally in several endo- and exothermic steps above ca. 240 °C. This renders it more stable than [(CH3)4N]BH4, with a lowered temperature of decomposition onset by ca. 20 °C and solely exothermic processes observed. Raman spectra measured at the 0–10 GPa range indicate that a polymorphic transition occurs within 0.53–1.86 GPa, which is further confirmed by the periodic DFT calculations. The latter suggests a phase transition around 0.8 GPa to a high-pressure phase of [(CH3)4N]BH4. The P63mc phase seems to be destabilized under high pressure by relatively closer dihydrogen interactions, including the C–H…H–C contacts.
Subject
General Materials Science
Reference43 articles.
1. Metal Borohydrides and Derivatives—Synthesis, Structure and Properties;Paskevicius;Chem. Soc. Rev.,2017
2. Suárez-Alcántara, K., and García, J.R.T. (2021). Metal Borohydrides beyond Groups i and Ii: A Review. Materials, 14.
3. DOE US (2017). Target Explanation Document: Onboard Hydrogen Storage for Light-Duty Fuel Cell Vehicles. US Drive, 1, 1–29.
4. Synthetic Approaches to Inorganic Borohydrides;Hagemann;Dalt. Trans.,2010
5. Hydrogen Storage Materials: Room-Temperature Wet-Chemistry Approach toward Mixed-Metal Borohydrides;Wegner;Angew. Chem. Int. Ed.,2015