Structure and bonding of the lithium tetrahydroborate–tetramethylethylenediamine adduct (TMEDA·LiBH4)2, a centrosymmetric dimer containing doubly and triply bridging hydrogen atoms

ARMSTRONG, D R and CLEGG, W and COLQUHOUN, H M and DANIELS, J A and Mulvey, Robert and STEPHENSON, I R and WADE, K (1987) Structure and bonding of the lithium tetrahydroborate–tetramethylethylenediamine adduct (TMEDA·LiBH4)2, a centrosymmetric dimer containing doubly and triply bridging hydrogen atoms. Journal of the Chemical Society, Chemical Communications (8). pp. 630-632. ISSN 0022-4936

Abstract

The title compound, the first alkali metal tetrahydroborate complex to be structurally characterised, has been shown by an X-ray study to be dimeric in the crystal, with each µ2,η3-BH4 group bonding to two metal atoms through one µ2-hydrogen atom apiece and also through one µ3-hydrogen atom; MO calculations at the 6-31G level on unsolvated LiBH4 and the model adducts (H2O)n·LiBH4(n= 1 or 2) and their dimers, with η2- and η3-BH4 geometries, show how their stabilities reflect the number of Li H contacts, whilst illustrating the inadequacies of LiHB and Li2HB 3- and 4-centre bond schemes for such compounds.

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