Role of the Li+node in the Li-BH4substructure of double-cation tetrahydroborates

Abstract

The phase diagram LiBH4–ABH4(A= Rb,Cs) has been screened and revealed ten new compounds LiiAj(BH4)i+j(A= Rb, Cs), withi,jranging between 1 and 3, representing eight new structure types amongst homoleptic borohydrides. An approach based on synchrotron X-ray powder diffraction to solve crystal structures and solid-state first principles calculations to refine atomic positions allows characterizing multi-phase ball-milled samples. The Li-BH4substructure adopts various topologies as a function of the compound's Li content, ranging from one-dimensional isolated chains to three-dimensional networks. It is revealed that the Li+ion has potential as a surprisingly versatile cation participating in framework building with the tetrahydroborate anion BH4as a linker, if the framework is stabilized by large electropositive counter-cations. This utility can be of interest when designing novel hydridic frameworks based on alkaline metals and will be of use when exploring the structural and coordination chemistry of light-metal systems otherwise subject to eutectic melting.