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

Abstract

Hydrates of the dihydronium salt of the superweak anion B12F122– have been synthesized and structurally characterized. The structure of (H3O)2B12F12·6H2O consists of a cubic close‐packed (CCP) array of B12F122– anions intercalated with nonplanar, infinite networks of O6 rings composed of H3O+ ions and H2O molecules. Similar to other salts of B12F122–, (H3O)2B12F12·6H2O exhibits rapid structural modification, termed latent porosity, and reversibly desorbswater to form other hydrate phases: (H3O)2B12F12·4H2O,(H3O)2B12F12·2H2O, and (H3O)2B12F12. (H3O)2B12F12·6H2O is another example of the weak coordinating properties of the B12F122– anion.

Myths about the Proton. The Nature of H+ in Condensed Media

“…Per fluor inated CB 11 carborane or B 12 boron cluster anions 34 are less basic than their per chlo rinated counterparts 25,26 so the conjugate acid H(CHB 11 F 11 ) is expected to be stronger than the currently published strongest acid, H(CHB 11 Cl 11 ). The preparation of H(CHB 11 F 11 ) has very recently been achieved in our lab 35 and a demonstration of its superior acidity is seen in the protonation of alkanes.…”

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

“…[236,260] Thes trength of the Brønsted acid is increased as the carborane anion becomes less coordinating and, as ar esult, the strongest neutral acid may be H(HCB 11 F 11 ) [236] closely followed by its chloride-containing relative H(HCB 11 Cl 11 ). [266] Other Neutral Acids:A lthough not as strongly Brønsted acidic as the carborane-based acids,r elated H(WCA) analogues of borate-, aluminate-, and phosphate-based WCAs that feature an EÀObond (where E = B, Al, or P) that can be protonated to give aL ewis acid adduct of the alcohol have also been shown to be strong Brønsted acids that subsequently liberate the corresponding WCA.I nt he case of the borates,the bisoxalatoboric acid (H[BOB]), synthesized form two equivalents of oxalic acid and one equivalent of boric acid, was applied as an initiator for the polymerization of styrene in ar oom-temperature ionic liquid under mild conditions. Thec losely related dianionic closo-dodecaborates have also been shown to form diprotic Brønsted acids of the type H 2 (B 12 X 12 )(where X = Br or Cl) through the use of the analogous bis-silylated carborate anion and HCl.…”

“…[107] Thef luoride-containing analogue H 2 (B 12 F 12 )h as,h owever,o nly been reported as its dihydronium salt (H 3 O) 2 [B 12 F 12 ]. [266] Other Neutral Acids:A lthough not as strongly Brønsted acidic as the carborane-based acids,r elated H(WCA) analogues of borate-, aluminate-, and phosphate-based WCAs that feature an EÀObond (where E = B, Al, or P) that can be protonated to give aL ewis acid adduct of the alcohol have also been shown to be strong Brønsted acids that subsequently liberate the corresponding WCA.I nt he case of the borates,the bisoxalatoboric acid (H[BOB]), synthesized form two equivalents of oxalic acid and one equivalent of boric acid, was applied as an initiator for the polymerization of styrene in ar oom-temperature ionic liquid under mild conditions. [267,268] Ther elated H(P(C 2 O 4 ) 3 )a nd H(P(1,2-O 2 C 6 Cl 4 ) 3 )B rønsted acids are also readily prepared simply from PCl 5 and the corresponding alcohol, and are both strong enough Brønsted acids to protonate diethyl ether.…”

“…Furthermore, both protons of H 2 (B 12 Cl 12 ) were demonstrated to be capable of protonating benzene, thus making its Brønsted acidity comparable with that of the H(HCB 11 Cl 11 ) acid . The fluoride‐containing analogue H 2 (B 12 F 12 ) has, however, only been reported as its dihydronium salt (H 3 O) 2 [B 12 F 12 ] …”

Synthesis and Application of Strong Brønsted Acids Generated from the Lewis Acid Al(ORF)3 and an Alcohol

“…For example, due to acidic cleavage of the B–C bond, H[B(C 6 F 5 ) 4 ] is not suitable for superacid chemistry and the commonly written HBF 4 or HSbF 6 acids only exist in the form H(H 2 O) n + [BF 4 ] − and H(HF) n + [SbF 6 ] − . So far the hypothetical pure H 2 [B 12 F 12 ] superacid has only been isolated as [(H 3 O) 2 ] 2+ [B 12 F 12 ] 2– ·6H 2 O . In a broader sense, the almost perfluorinated neutral radical [HCB 11 (CF 3 ) n F 11– n ] • ( n = 5, 6; only stable at −60 °C) can be mentioned here, which was synthesized by oxidation of the respective anion …”