The plastic crystalline A15 phase of dimethylaminoalane, [N(CH₃)₂–AlH₂]₃

Abstract

A plastic crystalline phase of dimethylaminoalane has been discovered at T > 332 K. The phase transitions solid - plastic phase - liquid are fully reversible. The plastic crystalline phase exhibits a cubic unit cell, space group Pm3[combining macron]n, in which the dimethylaminoalane molecules rotate and adopt a structural arrangement reminiscent of the A15 phase.

A Promising Phase Change Material with Record High Ionic Conductivity over a Wide Temperature Range of a Plastic Crystal Phase and Magnetic Thermal Memory Effect

“…The T C is relevant to the interactions between anions and cations; as a result, it is improvable via a rational design of molecule structures of both anion and cation to reduce the interion Coulombic interaction. As depicted in Table , the T C in 1 is slightly higher than the room temperature, while it is worth noting that the Δ T values of the plastic crystal phase spanning ∼123 K (367–490 K)/∼153 K (337–490 K) on heating/cooling are significantly wider than those in the typical ion plastic crystals with single plastic crystal transition, e.g., [Zn­(HPO 4 )­(H 2 PO 4 ) 2 ]­(ImH 2 ) 2 (90 K), [N­(CH 3 ) 2 –AlH 2 ] 3 (36 K), Li­[B­(OCH 2 CH 2 OCH 3 ) 4 ] (63 K), and 3-azabicyclo[3.3.1]­nonane-2,4-dione (55 K) as well as comparable to the Δ T in the plastic crystals, i . e ., [(CH 3 ) 4 N]­[FeBrCl 3 ] and [P 1,2,2,4 ]­[PF 6 ], with multiple plastic crystal transitions wherein the tumbling motion of the cations go through several phases with anisotropic rotations before reaching their state of isotropic tumbling.…”

“…The T C is relevant to the interactions between anions and cations; as a result, it is improvable via a rational design of molecule structures of both anion and cation to reduce the interion Coulombic interaction. As depicted in Table 2, the T C in 1 is slightly higher than the room temperature, while it is worth noting that the ΔT values of the plastic crystal phase spanning ∼123 K (367−490 K)/∼153 K (337−490 K) on heating/cooling are significantly wider than those in the typical ion plastic crystals with single plastic crystal transition, e.g., [Zn(HPO 4 )(H 2 PO 4 ) 2 ](ImH 2 ) 2 (90 K), 36 [N(CH 3 ) 2 −AlH 2 ] 3 (36 K), 42 Li[B(OCH 2 CH 2 OCH 3 ) 4 ] (63 K), 43 As a type of phase change material, the plastic crystal is considered as a kind of thermal energy storage media because the rational phase transition shows larger ΔH values than the general solid-to-solid phase transition materials. The wellknown phase change materials are summarized in Table 3, clearly indicating that, in 1, the ΔH of the plastic crystal phase transition is not only larger than that in most single-component ion plastic crystals listed in Table 2 but also comparable to the values in the famous phase change materials, and 1 shows potential application in thermal energy storage.…”

Polymorphism of dimethylaminoborane N(CH3)2-BH2

“…Different metal hydrides are considered for chemical storage of hydrogen: metal hydrides, complex ISSN 2052-5206 hydrides (e.g. borohydrides and aluminium hydrides), metal imides/amides and amine borane adducts/aminoboranes or aminoalanes (Weidenthaler & Felderhoff, 2011;Ley et al, 2015Ley et al, , 2016Chen et al, 2002;Bernert et al, 2016). Metal hydrides often have low gravimetric hydrogen capacities, whereas complex metal hydrides may suffer from poor reversibility (Ley et al, 2014).…”

“…In the case of six-membered rings, triboratrizanes can finally be dehydrogenated to triboratriazines (aromatic sixmembered rings) (Jaska et al, 2003(Jaska et al, , 2001. Based on recent investigations on alkylaminoalanes, also forming four-or sixmembered rings (Bernert et al, 2016;Ley et al, 2016;Downs et al, 1992), alkylaminoboranes are structurally very interesting. Depending on the reaction conditions, the dehydrocoupling of dimethylamine borane, NH(CH 3 ) 2 -BH 3 , either leads to the dimeric form [N(CH 3 ) 2 -BH 2 ] 2 (Jaska et al, 2001) (CCDC refcode DMABDI01) consisting of a four-membered ring or the trimeric form [N(CH 3 ) 2 -BH 2 ] 3 (Trefonas et al, 1961) consisting of a six-membered ring (see Scheme 1, which also shows the dehydrocoupling of dimethylamine borane adduct to dimethylaminoborane followed by dimerization and trimerization).…”