New Alkaline Earth Aluminum Hydride with One-Dimensional Zigzag Chains of [AlH₆]:  Synthesis and Crystal Structure of BaAlH₅

Abstract

The title hydride and its deuteride were successfully synthesized. The crystal structure of the deuteride was determined by time-of-flight neutron powder diffraction. BaAlD(5) crystallizes with a new orthorhombic structure in space group Pna2(1) (No. 33), cell parameters a = 9.194(1) A, b = 7.0403(9) A, and c = 5.1061(6) A, Z = 4. BaAlH(5) is the first example that contains one-dimensional zigzag chains of [AlH(6)] along the crystallographic c axis.

Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction

“…The average Al-D distances in corner-sharing AlD 6 octahedra in MAlD 5 are consistent with those found in hexa-alanates [3], Sr 2 AlD 7 [14] and Ba 2 AlD 7 [26]. However the D-Al-D angles in the penta-alanates (Table 3) Figure 3 shows the metal cation dependences on the average metal cation-Al and Al-D distances [3,[8][9][10][12][13][14][25][26][27][28][29][30][31][32][33][34][35][36][37] in related alanates (deuterides) with covalent Al-D bonds. The average Al-D distances in corner-sharing AlD6 octahedra in MAlD5 are consistent with those found in hexa-alanates [3], Sr2AlD7 [14] and Ba2AlD7 [26].…”

“…The crystal structure data for MAlD 5 compounds (M: Ca, Sr, Ba) and the average Al-D, M-D and M-Al distances are listed in Table 3 [8,9]. The AlD 6 octahedron chains in MAlD 5 are illustrated in Figure 2.…”

“…Although only EuAlH 5 has been experimentally identified, divalent rare-earth metals with close ionic radius to Ca 2+ , Sr 2+ and Ba 2+ would be speculated to form penta-alanates such as EuAlH 5 . Figure 3 shows the metal cation dependences on the average metal cation-Al and Al-D distances [3,[8][9][10][12][13][14][25][26][27][28][29][30][31][32][33][34][35][36][37] in related alanates (deuterides) with covalent Al-D bonds. The average Al-D distances in corner-sharing AlD 6 octahedra in MAlD 5 are consistent with those found in hexa-alanates [3], Sr 2 AlD 7 [14] and Ba 2 AlD 7 [26].…”

“…Interestingly, alkaline-earth metal tetra-alanates M(AlH 4 ) 2 composed of an alkaline-earth metal (M) and [AlH 4 ] − decompose into MAlH 5 containing corner-sharing AlH 6 octahedron chains [3,[6][7][8][9] after releasing hydrogen from M(AlH 4 ) 2 (Equation (2)). We refer to MAlH 5 as an alkaline-earth metal penta-alanate.…”

“…Therefore, the corner-sharing AlH 6 octahedron chains are a unique feature of alanates composed of alkaline-earth metals. Although the crystal structures of CaAlH 5 [6][7][8] and BaAlH 5 [9] have been experimentally and theoretically identified, the structures of BeAlH 5 , MgAlH 5 and SrAlH 5 have so far not been experimentally proven. BeAlH 5 and MgAlH 5 may be difficult to form due to the small size of Be 2+ and Mg 2+ .…”