The Structure of Some Amine Solvates of Magnesium Bis(tetrahydroborate) and DFT Calculations on Solvates of Lithium Tetrahydroborate

Abstract Eight solvates of magnesium bis(tetrahydroborate) have been prepared and characterised by NMR and IR spectroscopy, and five of them also by X‐ray crystallography. Compounds Mg(BH 4 ) 2 ·3NH 2 t Bu and Mg(BH 4 ) 2 ·3pip each have a distorted trigonal‐bipyramidal structure (with the BH 4 group viewed as a simple ligand) while the putative Mg(BH 4 ) 2 ·6py proved to be [Mg(BH 4 ) 2 ·4py] with a pseudooctahedral structure, two py molecules being present as solvent of crystallization. Similarly, Mg(BH 4 ) 2 ·8DMSO contains the cation [Mg(DMSO) 6 ] 2+ in the crystal, and Mg(BH 4 ) 2 ·6NH 2 Bzl has an ionic lattice made up of Mg(NH 2 Bzl) 6 2+ and BH 4 − ions. The BH 4 groups in the molecular compounds are bonded to the Mg centre through double hydrogen bonds. In order to study the bonding in alkali and alkali earth metal tetrahydroborates, DFT calculations were performed for LiBH 4 and its ammonia and dimethyl ether solvates. The minimum‐energy structure for a LiBH 4 molecule has C 3v symmetry; this is not changed when one ammonia molecule is added and is also the result for LiBH 4 ·3NH 3 . Addition of the first NH 3 or Me 2 O molecule contributes more to the stabilisation than a second or a third molecule. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)