an hydrous H F or SO, at room temperature give adducts of composition M F2-2SbF,. Efforts to prepare similar adducts of the difluorides of Ca, Sr, and Ba led only to non-stoicheiometric compounds. Vibrational spectra and X-ray powder diffraction studies indicate that the Mg, Ni, and Zn compounds and the Fe, Co, and Cu compounds form two distinct isostructural triads. The remaining adducts have structures which differ from each other and from those of the two triads. A single-crystal X-ray study on AgF2*2SbF, has shown that the crystals are triclinic, space group P i , with unit-cell dimensions a = 5.224(1 ), b = 5.467(2), c = 8.779(2) A, a = 75.78(2), p = 89.02(2), y = 65.29(2)", and Z = 1. The Ag2+ ion has square-planar co-ordination with two Ag-F distances, 2.095(5) and 2.1 32(4) 8. Two further F atoms at 2.431 (3) A complete a distorted octahedron.Distorted [SbF,] -octahedra in the structure have four Sb-F distances between 1.830(4) and 1.875(3) A while two others are 1.942(4) and 1.965(4) A.Early vibrational spectroscopic work and ' 9Sn Mossbauer studies suggested the presence of [(SnF),]"' cations in the structures of the 1 : 1 adducts, SnF,-BF,, SnF,*AsF,, and SnF,.SbF,.' The overall accuracy of this interpretation has since been confirmed by a single-crystal X-ray determination on the arsenic compound which showed that it contains the cyclic cation [(SnF)3]3+.2 Another metal(r1) fluoro-cationic species is [Sn2F3]+, found in the SnF,-BF, system,, in 2SnF2-AsF, and 2SnF,-SbF,,4 and in Sn,ClF,.' The possibility that a wide range of cationic and pseudo-cationic species occur in metal difluoride systems is further evidenced by our own vibrational spectroscopic work which has suggested the presence of [MF]', [M2F3]f,6,7 or [(MF),]"+ and our crystallographic work which has confirmed the presence of [(AgF),]"+ in the AgF,*AsF, compound.'In the present paper we report the results of part of a programme designed to probe to what extent such cations appear in the MF2-SbF, system. Results and DiscussionThe adducts MF2*2SbF, (M = Mg, Ni, Zn, Fe, Co, Cu, Cr, Ag, Cd, or Pb) were prepared by the reaction of the appropriate metal difluoride with excess of SbF, at room temperature in anhydrous H F as solvent. All were soluble in H F but were obtained as crystalline solids after removal of volatiles under dynamic vacuum to constant weight (Scheme). MF2 + nSbF5 2 MF2*2SbF5(s0lv.) + ( n -2)SbF,(solv.) -% MF2=2SbF,(cryst.) Scheme. (i) Anhydrous HF solvent at room temperature. (ii) Pump at room temperature t Silver bis(hexafluoroantimonate).

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The adduct UO,F,*AsF, has been prepared as a pale yellow solid b y the reaction of U02F2 with AsF, in anhydrous hydrogen fluoride. The adduct has been identified b y mass balance, chemical analysis, vibrational spectra, X-ray powder diffraction patterns, and thermal analysis.

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I;. 0. Sladky, I). -4. Bulliner, and X. Bartlctt, J . C t m z . SOC.