Synthesis, formation mechanism, and dehydrogenation properties of the long-sought Mg(NH2BH3)2 compound

Mono- and Bimetalic Amidoboranes

“…11 B NMR spectra of these salts contain a single characteristic signal at ca.´21 ppm (similar to that seen for the parent ammonia borane [18,23,35] On the other hand, the 11 B MAS NMR measurements for the samples in the solid state give one broad peak at about´21 ppm [18,25,29,[38][39][40]43,45]. In Figure 4, we have shown a collection of the 11 B NMR spectra, while, in Table 3, we have listed 11 B NMR chemical shifts and J-coupling constants for various amidoboranes present studied so far.…”

“…On the other hand, several other groups reported for these materials the desorption of hydrogen contaminated with ammonia: α-LiAB [20,25,39,89,90], β-LiAB [20] and NaAB [23,24,87,88,98]. Some amidoborane salts (KAB [25,89], Mg(AB) 2 [29], Al(AB) 3 [35], and LiAl(AB) 4 [35,40]) were reported to desorb pure hydrogen and, currently, there are no contradictory reports. The remaining known amidoborane compounds (RbAB [26], CsAB [26], Sr(AB) 2 [43], Y(AB) 3 [38], LiNa(AB) 2 [39], NaAl(AB) 4 [41], NaMg(AB) 3 [42], Na 2 Mg(AB) 4 [44]) decompose releasing hydrogen contaminated with ammonia, diborane or borazine, all of which are harmful for PEM and alkaline fuel cells.…”

“…Luo et al [29] proposed also an alternative metathetic synthesis of Mg(AB) 2 considering mechanochemical reaction of LiAB and Mg(BH 4 ) 2 according to Equation (14). The product of this reaction is a sticky mixture comprising only Mg(AB) 2 and LiBH 4 .…”

“…All of these approaches were unsuccessful because of the low reactivity of MgH 2 against ammonia borane. Mg(AB) 2 was finally synthesized by Luo et al [29] via a two-step process. The first step involves a 2 h mechanochemical reaction of MgH 2 or metallic magnesium with ammonia borane in molar ratio 1:2, while the second key step consists of aging of the post mill mixture [29].…”

“…Mg(AB) 2 was finally synthesized by Luo et al [29] via a two-step process. The first step involves a 2 h mechanochemical reaction of MgH 2 or metallic magnesium with ammonia borane in molar ratio 1:2, while the second key step consists of aging of the post mill mixture [29]. Synthesis of Mg(AB) 2 can be described overall by Equations (12) and (13).…”