Syntheses, Structures, and Bonding of NgF2⋅CrOF4, NgF2⋅2CrOF4(Ng=Kr, Xe), and (CrOF4)∞Journal Articles
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AbstractThe noble‐gas difluoride adducts, NgF2⋅CrOF4and NgF2⋅2CrOF4(Ng=Kr and Xe), have been synthesized and structurally characterized at low temperatures by Raman spectroscopy and single‐crystal X‐ray diffraction. The low fluoride ion affinity of CrOF4renders it incapable of inducing fluoride ion transfer from NgF2(Ng=Kr and Xe) to form ion‐paired salts of the [NgF]+cations having either the [CrOF5]−or [Cr2O2F9]−anions. The crystal structures show the NgF2⋅CrOF4adducts are comprised of Ft−Ng−Fb‐ ‐ ‐Cr(O)F4structural units in which NgF2is weakly coordinated to CrOF4by means of a fluorine bridge, Fb, in which Ng−Fbis elongated relative to the terminal Ng−Ftbond. In contrast with XeF2⋅2MOF4(M=Mo or W) and KrF2⋅2MoOF4, in which the Lewis acidic, F4(O)M‐ ‐ ‐Fb‐ ‐ ‐M(O)F3moiety coordinates to Ng through a single M‐ ‐ ‐Fb−Ng bridge, both fluorine ligands of NgF2coordinate to CrOF4molecules to form F4(O)Cr‐ ‐ ‐Fb−Ng−Fb‐ ‐ ‐Cr(O)F4adducts in which both Ng−Fbbonds are only marginally elongated relative to the Ng−F bonds of free NgF2. Quantum‐chemical calculations show that the Cr−Fbbonds of NgF2⋅CrOF4and NgF2⋅2CrOF4are predominantly electrostatic with a small degree of covalent character that accounts for their nonlinear Cr‐ ‐ ‐Fb−Ng bridge angles and staggered O−Cr‐ ‐ ‐Fb−Ng−Ftdihedral angles. The crystal structures and Raman spectra of two CrOF4polymorphs have also been obtained. Both are comprised of fluorine‐bridged chains that arecis‐ andtrans‐fluorine‐bridged with respect to oxygen.
