Preparation of Two Quantum‐Chemically Predicted, Isomeric [Br₄F₁₃]^– Anions in the Solid State

Abstract

Two isomeric tridecafluoridotetrabromate(III) anions, [Br4F13]–, both previously predicted by quantum‐chemical calculations, have serendipitously been obtained from the reaction of BrF3 with BaF2. Single crystals of Ba2[Br3F10]2[Br4F13]2 were selected from the reaction mixture at approximately 10 °C. The crystal structure contains two novel, isomeric [Br4F13]– anions besides the known, star‐shaped [Br3F10]– anions. It crystallized in the monoclinic space group P1n1 (No. 7) with a = 8.8519(18), b = 15.217(3), c = 14.628(3) Å, β = 90.34(3)°, V = 1970.4(7) Å3 and Z = 2, mP124 at 100 K. The compound was additionally investigated using quantum‐chemical solid‐state calculations. If however crystals from the above reaction mixture were selected at room temperature, the compound Ba[Br3F10]2·BrF3 was obtained containing disordered BrF3 molecules of crystallization besides [Br3F10]– anions. The [Br4F13]– molecules were no longer present. Ba[Br3F10]2·BrF3 crystallized in the cubic space group Pa3 (No. 205) with a = 12.4903(14) Å, V = 1948.6(7) Å3, Z = 4, cP124, T = 100 K. The much easier to handle latter compound was additionally investigated using powder X‐ray diffraction, as well as IR and Raman spectroscopy.

[(μ3‐F)(BrF5)3]− – An Unprecedented Molecular Fluoridobromate(V) Anion in Cs[Br3F16]

“…Analyzing these tables leads to the conclusion that halogen fluoride ions containing μand μ 3 -bridging F atoms are particularly rare, and most of the known representatives have been obtained only within the last decade. These include the anions [(μ 3 -F)(ClF) 3 ] À , [20] [(μ 3 -F)(ClF 3 ) 3 ] À , [21] [(μ-F)(BrF 3 ) 2 ] À , [22][23][24] [(μ 3 -F)(BrF 3 ) 3 ] À , [24] and the different isomers of the [Br 4 F 13 ] À [25] and [I 3 F 16 ] À anions. [9,26] To the best of our knowledge, only [Br 2 F 5 ] + and [Br 3 F 8 ] + are known on the cationic side, as of yet.…”

“…The only exceptions known so far are the [Br 4 F 13 ] À anions, of which two isomers exist: a branched one that is formally formed by two additional BrF 3 molecules attached each to a different F atom of the [(μ-F)(BrF 3 ) 2 ] À subunit and the second one consists of a [(μ 3 -F)(BrF 3 ) 3 ] À building block with formally one additional BrF 3 molecule attached to one of the outer F atoms. [25] Another exception is the anion in the compound Cs[I 3 F 16 ] in which the coordination number of the I atoms of seven leads to a three-dimensional infinite anionnetwork with μand μ 3 -bridging F atoms. [9] Of all known oligonuclear/polynuclear halogen fluoride ions, [I 3 F 16 ] À was the first to be discovered in form of the compounds AF • 3IF 5 (A = K, Rb, Cs).…”

“…A BrF 3 -moiety is cleaved off from the anion above that temperature resulting in spatially separated BrF 3 molecules of crystallization in the isomeric compound Ba[(μ 3 -F)(BrF 3 ) 3 ] 2 •BrF 3 . [25] The compounds containing trinuclear anions of ClF 3 and ClF, namely Cs[(μ 3 -F)(ClF 3 ) 3 ] and [NMe 4 ][(μ 3 -F)(ClF) 3 ], show even lower thermal stability and thus have to be prepared and handled at temperatures of 0 °C or even lower. [20,21] At elevated temperature, the loss of the respective halogen fluoride and the formation of room temperature stable [ClF 4 ] À or [ClF 2 ] À salts, respectively, has to be expected.…”

“…These halogen fluoride anions all consist of two or three halogen fluoride moieties ClF, X F 3 ( X =Cl, Br), X F 5 ( X =Br, I) forming “oligonuclear” complex ions considering the heavier halogen atoms X as the centers which are μ‐ or μ 3 ‐bridged by a F − anion. The only exceptions known so far are the [Br 4 F 13 ] − anions, of which two isomers exist: a branched one that is formally formed by two additional BrF 3 molecules attached each to a different F atom of the [(μ‐F)(BrF 3 ) 2 ] − subunit and the second one consists of a [(μ 3 ‐F)(BrF 3 ) 3 ] − building block with formally one additional BrF 3 molecule attached to one of the outer F atoms [25] . Another exception is the anion in the compound Cs[I 3 F 16 ] in which the coordination number of the I atoms of seven leads to a three‐dimensional infinite anion‐network with μ‐ and μ 3 ‐bridging F atoms [9] …”

“…In addition, the compound undergoes a phase transition at about 10 °C. A BrF 3 ‐moiety is cleaved off from the anion above that temperature resulting in spatially separated BrF 3 molecules of crystallization in the isomeric compound Ba[(μ 3 ‐F)(BrF 3 ) 3 ] 2 ⋅BrF 3 [25] . The compounds containing trinuclear anions of ClF 3 and ClF, namely Cs[(μ 3 ‐F)(ClF 3 ) 3 ] and [NMe 4 ][(μ 3 ‐F)(ClF) 3 ], show even lower thermal stability and thus have to be prepared and handled at temperatures of 0 °C or even lower [20,21] .…”