AZn2(BH4)5 (A = Li, Na) and NaZn(BH4)3: Structural Studies

A combination of in situ synchrotron powder diffraction, energy minimization (DFT), and Raman and infrared spectroscopy confirmed porous interpenetrated 3D-framework structures of recently discovered alkali-metal−zinc borohydrides, AZn 2 (BH 4 ) 5 (A = Li, Na). In the less zinc rich NaZn(BH 4 ) 3 the 3D-framework structural model has been confirmed but with a slightly modified description giving an isolated triangular anion, [Zn(BH 4 ) 3 ] −, rather than a 1D anionic chain, {[Zn(BH 4 ) 3 ] n } n − . Another polymorph of NaZn(BH 4 ) 3, isostructural to a new compound, LiZn(BH 4 ) 3, is proposed by energy minimization. Both compounds, the new NaZn(BH 4 ) 3 polymorph and LiZn(BH 4 ) 3, are, however, not observed experimentally at ambient pressure and in the temperature range of 100−400 K. The alkali-metal−zinc borohydride NaZn(BH 4 ) 3 containing the triangular anion [Zn(BH 4 ) 3 ] − is an equivalent of recently characterized alkali-metal−scandium borohydrides NaSc(BH 4 ) 4 and LiSc(BH 4 ) 4 based on the tetrahedral [Sc(BH 4 ) 4 ] − complex anion.