Hafnium complexes arsines

Golub et al. have shown that zirconium(IV) and hafnium(IV) form eight-coordinate complexes in solution with NCS" alone or in the presence of DMF 329, 333). The compounds (Et4N)2[M(NCS)8] (M = Zr, Hf) both contain iV -thiocyanato groups, as determined by infrared studies, and are isomorphous 61). Benzyl phenyl arsinic acid has been used as an extractant and, unlike most systems, hafnium complexes are extracted better than zirconium complexes in the presence of NCS" 302). 

Zirconium and hafnium tetrahalides form six-, seven- and eight-coordinate adducts with polydentate phosphine and arsine ligands. The 1 1 adducts [MXt(dppe)] and [MX dpae)] (M = Zr, X = C1 or Br M = Hf, X = C1 dppe = Ph2PCH2CH2PPh2, dpae = Ph2AsCH2CH2AsPh2) have been prepared in benzene media. IR spectra of the [MCLt(dppe)] complexes exhibit four v(M—Cl) modes in the 353-278 cm-1 region, consistent with a six-coordinate octahedral structure.45... 

---