Structural studies of the 1 : 1 addition complexes of niobium and tantalum pentachlorides with o-phenylenebis(dimethylarsine)

Abstract

The addition of o-phenylenebis(dimethylarsine), ‘diars.’ in equimolar ratio to the pentachlorides of tantalum and niobium has yielded addition complexes shown by X-ray crystallographic structure determination to have the probable stoicheiometries [TaCl₄(diars)₂]⁺[TaCl₅(OEt)]^–(I), [NbCl₄(diars)₂]⁺₂[NbCl₃O₂]^2–(II), and [NbCl₄-(diars)₂]⁺[NbOCl₄]^–(III). Crystals of (I) are triclinic, space group P. a= 12.983(4), b= 14.484(6), c= 12.359(6)Å, α= 108.04(3), β= 102.17(5), γ= 110.35(5)°, Z= 2, 2 448 observed reflections being refined to R 0.09. Crystals of (II) are monoclinic, space group C2/c or Cc, a= 20.877(4), b= 16.086(3), c= 19.458(2)Å, β= 106.25(1)°, Z= 4, 1 183 observed reflections refined to R 0.08. Crystals of (III) are triclinic, space group Pa= 14.815(3), b= 12.273(2), c= 10.397(2)Å, α= 92.03(1), β= 103.56(2), γ= 110.80(2)°, Z= 2, 2 473 observed reflections refined to R 0.06. In all three, an eight-co-ordinate dodecahedral cation is found; mean distances: Ta–As 2.76₁, Ta–Cl 2.40, Nb–As 2.74₃, and Nb–Cl 2.42₆Å. The structures were determined from diffractometer data [(I) and (III) by the heavy-atom method, (II) by direct methods].