Conformationally flexible arsine ligands: Two forms of bis[1,1'-bis(dimethylarsino)ferrocene] dibromonickel(II)

The structure of Ni(fdma)(2)Br-2 (fdma=1,1'-bis(dimethylarsino)ferrocene) is described. Ni(fdma)(2)Br-2 crystallizes in the space group P2(1)/c with a=28.544(4), b=8.989(1), c=19.613(3) Angstrom, beta=106.62(1)degrees and Z=6 and R/wR(2)=0.0439/0.0738 for 4355 (1> 2 sigma(I)) data. The unit cell contains two crystallographically independent but structurally distinct conformers. The geometry of the nickel ion in both conformers is that of a tetragonally-compressed octahedron. In one form the ferrocene moieties of both ligands are parallel while in the other they are approximately at right angles to each other. Both conformers show staggered arrangements of the ferrocenyl rings. The Ni-As bonds are long with an average distance of 2.588(2) Angstrom. In the solid state one of the conformers forms a chain of molecules held together by weak electrostatic Br...H(ferrocenyl) interactions; the Br...H distance is 2.911(4) Angstrom.