Facile Solvent-Free Synthesis of Anhydrous Alkali Metal Dodecaborate M₂B₁₂H₁₂(M = Li, Na, K)

Metal dodecaborate, widely regarded as an obstacle of the rehydrogenation of high-density hydrogen storage materials metal borohydrides M(BH 4 ) n, is generally synthesized using liquid-phase process followed by a careful dehydration process. In this study, we propose a new and facile solvent-free synthesis process of dodecaborates using B 10 H 14 with a low melting point of 99.6 °C as a boron source. As a case study, our first challenge focused on the syntheses of anhydrous M 2 B 12 H 12 (M = Li, Na, and K) by heat treatment of starting materials (a) 2MH + 1.2B 10 H 14 or (b) 2MBH 4 + B 10 H 14 at 200–450 °C conditions, which have been proved to be successful for the first time by X-ray diffraction (XRD), Raman, and NMR analysis. Starting materials (b) 2MBH 4 + B 10 H 14 shows better reactivity than that of (a) 2MH + 1.2B 10 H 14, which demonstrates that synthesis of anhydrous M 2 B 12 H 12 by heat treatment of 2MBH 4 + B 10 H 14 is a feasible solvent-free process.