Synthesis and Stability of Reactive Salts of Dodecafluoro-closo-dodecaborate(2−)

Abstract

The synthesis and characterization of several salts of the B(12)F(12)(2-) anion are reported. The potassium salt was prepared in 72% recrystallized yield by treating K(2)B(12)H(12) with liquid HF at 70 degrees C for 14 h and 20% F(2)/N(2) in liquid HF at 25 degrees C for 72 h. The CPh(3)(+), N(n-Bu)(4)(+), NH(n-C(12)H(25))(3)(+), NH(4)(+), and Li(+) salts were prepared by metathesis reactions. The [NH(n-C(12)H(25))(3)](2)[B(12)F(12)] salt is soluble in aromatic hydrocarbon solvents. The B(12)F(12)(2-) anion is remarkably stable. The salts Li(2)B(12)F(12) and [NH(4)](2)[B(12)F(12)] were stable when heated to 450 and 480 degrees C, respectively. The B(12)F(12)(2-) anion did not react with 98% H(2)SO(4), 70% HNO(3), 3 M KOH, a 10-fold excess of Ce(NH(4))(2)(NO(3))(6) in aqueous solution, or metallic sodium in THF. In addition, B(12)F(12)(2-) did not react with metallic lithium in a mixture of ethylene carbonate and dimethyl carbonate, was not reduced at 0 V versus Li(+/0) in that solvent, and underwent a quasi-reversible oxidation at 4.9 V versus Li(+/0). The structure of [CPh(3)](2)[B(12)F(12)] was determined by single-crystal X-ray diffraction: tetragonal, space group I4(1)/acd, a = 19.102(2), b = 19.102(2), c = 20.535(3) A, V = 7492.2(2) A(3), Z = 8, T = 173(2) K, R(1) = 0.064. The B(12)F(12)(2-) anion weakly interacts with the two symmetry related CPh(3)(+) cations via F.C contacts of 3.087(2) A, which are very close to the 3.17 A sum of van der Waals radii for these two atoms. Taken together, the data suggest that B(12)F(12)(2-) may be useful as a very robust weakly coordinating anion.

Isolating fluorinated carbocations

“…However, unlike structures with fluoroanions, 18,19 there are no close approaches of anion atoms to the carbocationic C atom. With their large size and low charge density, carborane anions tend to yield cation structures in their most ''free'' or intrinsic state.…”

The Structure of (H3O)2B12F12·6H2O – a CCP Lattice of B12F122– Anions Intercalated with a Nonplanar Network of O–H···O Connected O6 Rings

“…Selected interatomic distances and angles are listed in Table 1. The structure of the B 12 F 12 2-anion in this compound is normal, [1,[3][4][5][6] and it is also the most precise structure of any molecular B 12 species, with B-F and B-B esd values of 0.0005-0.0008 Å ( Figure S1). The anions are packed in a cubic close-packed (CCP)-like array, with a network of H 3 O + ions and H 2 O molecules intercalated between the parallel planes of the anions (Figure 1).…”

“…[1][2][3][4][5][6][7] Our hypothesis is that the unique combination of size, shape, high symmetry, thermal stability, and extremely weak Brønsted and Lewis basicity of this anion will lead to unanticipated structures and properties [i.e. unanticipated compared to salts of B 12 H 12 2-, [8][9][10][11] B 12 Cl 12 2-, [12][13][14] B 12 (OH) 12 2-, [15,16] and B 12 (CH 3 ) 12 2- [17] on one hand, and of salts of typical fluoroanions, such as BF 4 -, PF 6 -, Sb 2 F 11 -, SiF 6 2-, and MnF 6 2-, on the other].…”

Kohlenstoff‐Extrusion/Cluster‐Kontraktion: Synthese des fluorierten Cyano‐closo‐undecaborats K2[3‐NC‐closo‐B11F10]

“…[5] Nur vom stabilsten Vertreter der closo-Borate [B 12 H 12 ] 2À sind Salze mit dem entsprechenden perfluorierten Anion [B 12 F 12 ] 2À bekannt. [6,7] Die Chemie der Monocarba-closo-dodecaborate ist Gegenstand intensiver Forschung, da sie für eine Reihe von Anwendungen von Interesse sind. [8,9] Dies ist unter anderem darauf zurückzuführen, dass ihre Eigenschaften durch die Wahl der Substituenten am C-Atom und an den B-Atomen vielseitig variiert werden können.…”