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)(BH4)(5) (A = Li, Na). In the less zinc rich NaZn(BH4)(3) the 3D-framework structural model has been confirmed but with a slightly modified description giving an isolated triangular anion, [Zn(BH4)(3)](-), rather than a 1D anionic chain, {[Zn(BH4)(3)](n)}(n-). Another polymorph of NaZn(BH4)(3), isostructural to a new compound, LiZn(BH4)(3), is proposed by energy minimization. Both compounds, the new NaZn(BH4)(3) polymorph and LiZn(BH4)(3), are, however, not observed experimentally at ambient pressure and in the temperature range of 100-400 K. The alkali-metal-zinc borohydride NaZn(BH4)(3) containing the triangular anion [Zn(BH4)(3)](-) is an equivalent of recently characterized alkali-metal-scandium borohydrides NaSc(BH4)(4) and LiSc(BH4)(4) based on the tetrahedral [Sc(BH4)(4)](-) complex anion.