Tetracyanidoborates with Sterically Demanding Phosphonium Cations – Thermally Resistant lonic Liquids 

Abstract

The reaction of K[B(CN)4] with [Ph4P]Cl, [nBu4P]Br, [nBuPh3P]Br, or [EtPh3P]Cl (Ph = phenyl, nBu = n‐butyl, Et = ethyl) affords [Ph4P][B(CN)4] (1), [nBu4P][B(CN)4] (2), [EtPh3P][B(CN)4] (3), and [nBuPh3P][B(CN)4] (4) in high yields. The structures of the compounds 1–3, which contain the tetrahedral [B(CN)4]– ion, were determined by single‐crystal X‐ray diffraction. 1 crystallizes in the tetragonal space group I\bar{4}2d (no. 122), a = 12.948(2), c = 29.382(6) Å, Z = 8, R1(F)/wR2(F2) = 0.0335/0.0953; 2 and 3 with orthorhombic symmetry; 2: space group Pnna (no. 52), a = 18.2187(6), b = 12.0707(3), c = 11.6704(4) Å, Z = 4, R1(F)/wR2(F2) = 0.0489/0.1532; 3: space group Pnma (no. 62), a = 14.1777(3), b = 13.4214(3), c = 12.3199(2) Å, Z = 4, R1(F)/wR2(F2) = 0.0477/0.1505. The IR, Raman, and NMR spectra as well as thermal data derived from DSC and TGA measurements are reported. Depending on the thermal stability of the phosphonium cation some of the tetracyanidoborates are stable up to ~370 °C with the liquid state having a range of up to 300 K. Such salts could be very useful as weakly coordinating reaction media.

Low Melting Tetracyanidoborate Salts with Alkyl‐, Arylammonium, and Pyridinium Cations: Syntheses, Structures, Properties.

“…The chemical shift of the boron atom ( 11 B) is at −38.27 ppm. These values agree well with those of many other tetracyanidoborate salts . As expected, the chemical shift of the boron atom depends on the electron shielding, which is affected by the chemical surrounding of the nucleus .…”

Synthesis and Structure of Ionic Liquids Containing the ­[Al(OC6H4CN)4]– Anion

“…Interestingly, for [P(Ph) 4 ][Al(O–C 6 H 4 –CN) 4 ] ( 12 ) with the highly symmetric [P(Ph) 4 ] + ion a rather high glass transition point between 15–16 °C was observed, that is 10 or 20 °C higher as it is found for the asymmetric substituted phosphonium salts 11 and 13 . This compares to the melting points of tetracyanoborate salts of [P(Ph) 4 ] + and [PEt(Ph) 3 ] + , that decrease by about 100 °C when asymmetric substituted phosphonium cations are utilized 29. The same trend is found in the tetraphenylborate compounds of [P(Ph) 4 ] + (mp.…”

Rare‐Earth Tetracyanidoborate Salts – Structural Features and Properties Including Luminescence of [RE­(H2O)8][B(CN)4]3·nH2O and [RE­(H2O)7{κ1N‐B(CN)4}][B(CN)4]2 (RE = Y, Tb, Dy, Ho, Er, Tm, Yb, Lu; n ≤ 3)

“…[8] [R 3 By a different method, new tetracyanidoborates can be obtained through metathesis reactions between a halide and potassium tetracyanidoborate. [14] The metathesis reaction works if the starting materials are soluble in the used solvent and the product (or the byproduct) precipitates from the solvent. A third method uses acid-base reactions of the strong tetracyanidoboronic acid, H[B(CN) 4 ]·nH 2 O, which can be obtained from an alkaline tetracyanidoborate through ion exchange.…”