METAL TETRAHYDRIDOBORATES AND TETRAHYDRIDOBORATO METALATES .18. PREPARATION AND MOLECULAR-STRUCTURES OF TETRAHYDROFURAN, DIETHYLENE DIGLYCOL DIMETHYL ETHER AND 18-CROWN-6 COMPLEXES OF STRONTIUM AND BARIUM TETRAHYDRIDOBORATE

The strontium and barium tetrahydridoborate complexes M(BH4)(2) . 2 diglyme and M(BH4)(2) . 18-crown-6 (M = Sr, Ba) have been prepared from the solvates M(BH4)2 . 2 THF by Ligand displacement. B-11-NMR and IR data reveal strongly polar bonding of the BH4- groups to the metal centers, and X-ray structural analyses of the diglyme and crown ether compounds show molecular units in which the BH4- group is in contact via three H atoms with the metal center. In contrast, M(BH4)2 . 2 THF compounds are chain polymers in the solid state, and each metal center is surrounded by 2 THF molecules in trans position and four BH4- groups each of which forms bridges with two metal centers. Estimations of the effective radius for the BH4- group indicate a high polarity for the M-BH4 interaction.