NICKEL-(II), NICKEL-(III) AND NICKEL-(IV) COMPLEXES OF 1,2-BIS(DIMETHYL-ARSINO)TETRAFLUOROBENZENE AND X-RAY CRYSTALLOGRAPHIC AND EXTENDED X-RAY ABSORPTION FINE-STRUCTURE STUDIES OF NICKEL-(III) AND NICKEL-(IV) BROMO COMPLEXES

1,2-Bis(dimethylarsino)tetrafluorobenzene, o-C6F4(AsMe2)2, forms high-spin tetragonal nickel(II) complexes [Ni(L-L)2X2] (X = Cl or Br), which remain six-co-ordinate in non-polar solvents, and planar diamagnetic [Ni(L-L)2]\2. Pseudo-octahedral nickel-(III) and -(IV) complexes [Ni(L-L)2X2]n+ are formed on oxidation, and their properties are compared with those of the fluorine-free ligand o-C6H4(AsMe2)2. The X-ray crystal structure of trans-[Ni{o-C6F4(AsMe2)2}2Br2]BF4 has been determined, and revealed a tetragonal cation with Ni-Br 2.543(1) and Ni-As 2.336(1), 2.339(1) angstrom. Nickel and bromine K-edge extended X-ray absorption fine structure data are reported for a variety of complexes of Ni(II), Ni(III) and Ni(IV) with o-C6F4(AsMe2)2, o-C6H4(AsMe2)2 and o-C6H4(PMe2)2, and the results compared with existing data on the chloride analogues.