Zirconium tetrahalides compounds

The free energies of formation of corresponding hafnium and zirconium compounds are also nearly equal, so that separation by preferential reaction of one species is difficult, too. Table 7.9 compares the free energies of formation of hafnium and zirconium tetrahalides at 1000 K. 

A few zirconium tetrahalide adducts with urea and its derivatives have been reported. Known compounds include [ZrF4 (Me2N)2CO ],130 [ZrCI4 (H2N)2CO 2]131 and... 

Monocyclopentadienylzirconium trichloride has been prepared from zirconium tetrachloride by reaction with cyclopentadienylmagnesium chloride in toluene/diethyl ether solution 240, 241). Both the chloride and bromide have been prepared from the corresponding tetrahalides and magnesium cyclopentadienide in xylene at 100°-110°C 451), or by continuous recirculation of cyclopentadiene vapor upward through a bed of zirconium trihalide (250°-300°C) resting on a glass sinter. The products were purified by sublimation. Yields were only about 15% compared to the 60-70% obtained from syntheses carried out in solution. The melting points and colors for the monocyclopentadienyl metal trihalides and for other cyclopentadienyl metal halide compounds are tabulated in Table I. 

Compounds of zirconium and hafnium metal tetrahalides with the bidentate ligands ( )4As2C2H4 and ( )4P2C2H4 were prepared 447) by the reaction of the tetrahalide and the ligand in a suspension in benzene. These are presumably species with a coordination number of eight. The infrared absorption frequencies in the 460-250 cm region are tabulated in Table VII. 

Direct reaction of zirconium and hafnium tetrahalides and bromides with excess DMSO under strictly anhydrous conditions yielded products of composition Zr(Hf)Cl4 9DMSO and Zr(Hf)Br4 lODMSO (482). Attempts to recover the tetrahalides by heating only resulted in the production of tarry residues. The S-O-stretching frequency in these compounds was found to be 960 cm" for the nine-solvate and 920 cm for the 10-solvate, which indicates that the DMSO molecules are oxygen bound. 

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