Kristallstrukturen und Phasenumwandlungen von Kalium Tetrakis(trifluormethyl)borat, K[B(CF3)4].

Eduard Bernhardt (1)

1 Anorganische Chemie

Below room temperature K[B(CF3)4] was found to be trimorphic according to DSC measurements, single crystal X-ray diffraction and vibrational spectroscopy. In its modification below -65 °C K[B(CF3)4] crystallises in the orthorhombic space group P212121 (Nr. 19) with a = 9.2593(14), b = 9.7527(15), c = 10.2170(16) Å and four formula units in the unit cell. At this temperature the anion exhibit nearly T - symmetry. Between -65 °C and -50 °C K[B(CF3)4] becomes trigonal in the space group P3221 (Nr. 154) / P3121 (Nr. 152) with a = 6.9064(7), c = 17.1509(18) Å, and three formula units per unit cell. In this temperature range the CF3 - groups rotate hindered. At room temperature the salt transforms into a plastic phase in the cubic space group Fm-3m (Nr. 225) with a = 9.9145(28) Å, and four formula units per unit cell, and the anions rotate completely. The unusual properties of K[B(CF3)4] are in part due to the low coordinating ability of the spherical big anions. In comparison to other anions [B(CF3)4]- is very weakly coordinating as demonstrated by the high n(N-H) vibrational frequency (3234 cm-1) of the ion pair (n-C8H17)3N+H···[B(CF3)4]- in CCl4 solution.

Mots clés: Physical Sciences

Eduard Bernhardt. Kristallstrukturen und Phasenumwandlungen von Kalium Tetrakis(trifluormethyl)borat, K[B(CF3)4].. Journal of Inorganic and General Chemistry / Zeitschrift für anorganische und allgemeine Chemie, 2009, 635 (12), pp.2009. ⟨10.1002/zaac.200900144⟩. ⟨hal-00523351⟩