Facile Solvent-Free Synthesis of Anhydrous Alkali Metal Dodecaborate M_2B_(12)H_(12) (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_2B_(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_2B_(12)H_(12) by heat treatment of 2MBH_4 + B_(10)H_(14) is a feasible solvent-free process.