Tridentate borohydride bridges

The vibrational spectra of the samarium borohydride and borodeuteride complex suggested a tridentate borohydride or borodeuteride bridge. For the smaller Er and... 

The Zr and Hf tetrahydroborates M(BH4)4 are the most volatile compounds of these elements, with boiling points of 123 and 118°C they are also very sensitive to oxidation and hydrolysis. They can be obtained by the reaction of the chlorides with alkali metal borohydrides or of the complex fluorides NaMFs with aluminum borohydride (the fluorides MF4 do not react), followed by distillation from the reaction mixture. According to low-temperature X-ray data, all the borohydride groups are tridentate in both M(BH4)4 complexes, which have Td symmetry. The same is trae for their substituted M(BH3Me)4 derivatives, that is, the metal atom is 12-coordinate. Proton NMR indicates fast exchange of bridging and terminal protons on the NMR timescale in these fluxional molecules see Fluxional Molecule). 

The crystal structure of U(BHtf)if has been examined by single crystal x-ray (4b) and neutron diffraction techniques (4a). Much like the bonding in the well-known boron hydrides (11), this metal borohydride exhibits hydrogen bridge bonds that join the boron atom to the metal. In U(BHt+)i+j there are two tridentate and four... 

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