Towards an understanding of the structure and bonding of lithium tetrahydroborate and its amine complexes

A structural and electronic study of lithium tetrahydroborate (LiBH₄) has been carried out in order to understand both its bonding and structural preference. The detailed analysis suggests that both its electronic distribution and hydride character depend on the coordination mode of the [BH₄]^- group to the lithium in each of the calculated structures. We have found that a structure in which the [BH₄]^- acts as a tridentate ligand is preferred. This correlates well with the observed behavior of some complexes of lithium borohydride and aromatic diamines calculated herein. The nature of the coordinating nitrogen also modifies the structure and bonding of LiBH₄, because electronic and ionic effects play important roles in all of the calculated structures. The analysis was performed with the B3LYP functional of density functional theory in conjunction with the 6-311++G(d,p) basis set.