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(BH 4 ) 2 · 2 diglyme and M(BH 4 ) 2 · 18‐crown‐6 (M = Sr, Ba) have been prepared from the solvates M(BH 4 ) 2 · 2 THF by ligand displacement. 11 B‐NMR and IR data reveal strongly polar bonding of the BH 4 groups to the metal centers, and X‐ray structural analyses of the diglyme and crown ether compounds show molecular units in which the BH 4 group is in contact via three H atoms with the metal center. In contrast, M(BH 4 ) 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 BH 4 − groups each of which forms bridges with two metal centers. Estimations of the effective radius for the BH 4 group indicate a high polarity for the M‐BH 4 interaction.