XeF₂·2CrF₄and XeF₅⁺CrF₅^-:  Syntheses, Crystal Structures, and Some Properties

Abstract

XeF2·2CrF4 was prepared by solvolysis of XeF2·CrF4 in anhydrous hydrogen fluoride (aHF) and subsequent decantation of the majority of dissolved XeF2 in aHF. Remaining XeF2 and a large excess of CrF4 form XeF2·2CrF4 after aHF is removed. Ruby-red single crystals were obtained either by heating the sample in a thermal gradient or by recrystallization in supercritical SF6. The compound crystallizes in the triclinic space group P1̄ with a = 855.1(3) pm, b = 922.1(3) pm, c = 1043.8(3) pm, α = 76.02(2)°, β = 81.36(2)°, γ = 88.08(3)°, and Z = 4 at 293 K. The basic structural unit is formed by four independent Cr atoms, each octahedrally coordinated by six F atoms. Two fluorine ligands are provided by two different XeF2 molecules. The distorted octahedra are connected via common F atoms to form a three-dimensional network. XeF5 +CrF5 - was prepared from XeF6 and CrF4 at room temperature or by the reaction of XeF6 and CrF5 at 333 K. Red single crystals were grown from the solution of XeF5 +CrF5 - in aHF. The compound crystallizes in the orthorhombic space group Pbca with a = 1828.1(13) pm, b = 842.9(7) pm, c = 1852.1(12) pm, and Z =16 at 268 K. The main structural feature is formed by an infinite chain of distorted CrF6 octahedra joined via cis vertexes, while XeF5 + cations compensate the negative charge of each octahedron.

Alkali Metal (Li+–Cs+) Salts with Hexafluorochromate(V), Hexafluorochromate(IV), Pentafluorochromate(IV), and Undecafluorodichromate(IV) Anions

“…The Cr-F-Cr bridge in CsCrF 5 is symmetric and linear (180°), while in RbCrF 5 , it is bent with an angle of 149.4(3)°. It is slightly larger than corresponding angles found in XeF 2 ·CrF 4 (147.3°), [16] XeF 5 CrF 5 (146.0°), [17] and (XeF 5 CrF 5 ) 4 ·XeF 4 (136.6°and 142.3°). [16] There are two crystallographically independent Rb + cations (Rb1 and Rb2) in the crystal structure of RbCrF 5 .…”

“…[14] The presence of infinite [CrF 5 ] n n-chains was previously observed in XeF 2 ·CrF 4 ([CrF 6 ] octahedra share trans vertices, Figure 6a), [16] (XeF 5 CrF 5 ) 4 ·XeF 4 (alternation of cis and trans vertices shared between [CrF 6 ] octahedra, Figure 6b), [16] and XeF 5 CrF 5 ([CrF 6 ] octahedra share cis vertices, Figure 6c). [17] The crystal structure of β-CrF 4 also consists of cis and trans corner-sharing [CrF 6 ] octahedra, which results in a column-type structure (Figure 6f). [13] In α-CrF 4 , columns are formed by [Cr 2 F 10 ] dimers (two [CrF 6 ] octahedra share an edge) that share trans vertices.…”

“…[13] In α-CrF 4 , columns are formed by [Cr 2 F 10 ] dimers (two [CrF 6 ] octahedra share an edge) that share trans vertices. [12] As in [16] and XeF 5 CrF 5 [Cr-F t : 1.69 Å; Cr-F b : 1.90 Å-1.97 Å], [17] which are not involved in further contacts with the Xe species.…”

Atypical Compounds of Gases, which Have Been Called “Noble”

“…9(B). (Cr IV F 4 )(XeF 2 )-known since 1992 92 -and (Cr IV F 4 ) 2 (XeF 2 ) 93 have also been taken into account.…”

Synthesis and Characterisation of [XeF5]3[Ti4F19] Containing a Discrete [Ti4F19]3– Anion

“…In spite of a large number of existing compounds in the XeF 6 /MF 4 (M = transition element) system, [28] reports about the crystal structures of the corresponding [ [29] Ni [30] [31] {the crystal structure of (XeF 5 CrF 5 ) 4 ·XeF 4 was also reported [32] …”