Oxidation of first row transition elements with AsF5 in AsF3 at ambient temperature: Syntheses and structures of M(AsF6)(2)center dot 2AsF(3), M = Fe, Co, Ni

A novel synthetic approach via reactions between pure metals (Cr, Mn, Fe, C o, Ni, Cu) and AsF5 in AsF3 as a solvent has been investigated. AsF5 proved to oxidize these metals to their (+2) oxidation state. In the case of Cr, Mn or Cu the same compounds as those in the superacidic systems MF2-AsF5-aH F (anhydrous hydrogen fluoride) were obtained: CrFAsF6, Mn(AsF6)(2), and Cu FAsF6, respectively. In the case of Fe, Co and Ni a new type of fluoroarsen ates has been isolated: M(AsF6)(2)congruent to 2AsF(3). The latter compound s are isostructural and crystallize in the monoclinic space group P2(1)/n ( no. 14) with Z = 2. Unit cell dimensions of Fe(AsF6)(2)congruent to 2AsF(3) are: a = 733.8(4) pm, b = 1303.0(8) pm, c = 735.4(5) pm, There Exists = 91 .43(7)degrees at 292 K, and for Co(AsF6)(2)congruent to 2AsF(3): a = 725.9( 4) pm, b = 1292.9(7) pm, c = 727.6( 5) pm, There Exists = 91.64(5)degrees a t 288 K. The structure is characterized by layers formed through transcoord inating AsF6 units in the basal plane of the octahedron about the transitio n metal. Both apical positions of this octahedron are occupied by AsF3 mole cules. A main feature of the layers are characteristic rings resulting from the apex-sharing connectivity of AsF6 and MF6 octahedra. As AsF3 molecules of neighbouring layers are localized above and below the center of a parti cular ring, a stacking sequence ABAB... results.