Structural studies of potassium tetrafluorochromate(III), K[CrF4], and the novel mixed chloride fluoride, dipotassium dichlorohexafluorotrichromate(II), K2[Cr3Cl2F6]

Abstract

The crystal structures of potassium tetrafluorochromate(III), K[CrF₄](1), and dipotassium dichlorohexafluorotrichromate(II), K₂[Cr₃Cl₂F₆](2), are reported. The structure of (1) consists of infinite triangular anionic columns comprising approximately planar Cr₃F₉ units linked above and below by fluoride bridges, the columns being separated by K⁺ ions. Each Cr^III atom is octahedrally co-ordinated by six F atoms. The structure of (2) contains two crystallographically independent Cr^II atoms which have distorted octahedral co-ordination by four equatorial F atoms and two axial Cl atoms. The Cr atoms are linked together by single Cr–F–Cr bridges and also by a novel chloride fluoride double bridge. The structure can also be thought of as comprising two-dimensional CrF₂ sheets, held together by Cl atom bridges. Charge balance is maintained by K⁺ ions. Crystal data for (1) are: a= 15.76(1), b= 7.43(1), c= 18.38(1)Å, Z= 24, orthorhombic, space group Pnma, final R= 0.041 for 1 975 diffractometer data with I_o > 3σ(I_o). Crystal data for (2) are: a= 6.726(1), b= 11.157(5), c= 7.391(3)Å, β= 125.31(4)°, Z= 2, monoclinic, space group P2₁/c, final R= 0.041 for 1 044 diffractometer data with I_o > 2σ(I_o).