Hafnium borohydrides

Reid et al. (454) reinvestigated the synthesis of the zirconium and hafnium borohydrides. The reaction of diborane with zirconium tetrachloride dissolved in tetrahydrofuran (THE) does not give a boron-containing product, whereas the reaction of diborane with an ether solution of zirconium tetraethoxide gives the desired metal borohydx ide although it is difficult to separate from the borate ester coproduct. The reaction of Katz (246) was run with potassium fluorozirconate in preference to the sodium salt because the potassium salt reacted more readily,... 

The binary borohydride species Zr( III 11)4 and U(BH4)4 have been investigated by quantum mechanical techniques and, for the zirconium case, also by gas-phase electron diffraction. All confirm that these simple molecules have a staggered conformation of borohydride ligands.15 In a related study, the hafnium analog Hf(BH4)4 has also been analyzed and is essentially isostructural.16 These studies show the molecules to possess tetrahedral symmetry with all of the BH4 ligands triply (i.e., if) bridging. Photoelectron spectra [He(i)] of the half and bent metallocene complexes Zr(7]S-CsHs)(BH4)4, M(7]S-CsHs)2(BH4)2 (M = Zr, Hf), and Ta(7]S-CsHs)2(BH4) have been determined.17... 

Other than the binary hydrides 207), which will not be covered in this review, only a few metal-hydrogen-honded compounds of zirconium and hafnium are presently known, the first being the borohydride M(BH4)4. Although its preparation goes back to the work of Hoekstra and Katz 2i0), it is only recently that structural studies have revealed that metal-hydrogen-boron bridges are involved in the structure. The proton NMR spectrum 263, 582) of a benzene solution shows a quartet... 

Argon gas is used as a carrier gas for reactant vapor. In chloride route, corrosive gas handling and the halogen contamination of the coatings are some issues. Tetra-borohydrides of zirconium and hafnium [Zr(BH) and Hf(BH)J are also reported... 

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