Water Adducts of the Lewis Superacids: Tris(pentafluoroethyl)gallane and ‐indane

Abstract Lewis superacids (LSA) are defined by a fluoride ion affinity (FIA) that exceeds that of SbF 5 , and are thus characterized as hard according to the HSAB concept. Soft superacidity was defined for compounds exceeding the hydride ion affinity (HIA) of B(C 6 F 5 ) 3 . Herein we report on the synthesis of a Lewis acid being superacidic only on the soft regime: tris(pentafluoroethyl)indane, In(C 2 F 5 ) 3 . It is accessible in the form of its dihydrate [In(C 2 F 5 ) 3 (OH 2 ) 2 ]. An improved synthesis for the gallium analogue [Ga(C 2 F 5 ) 3 (OH 2 ) 2 ] is also reported. Tris(pentafluoroethyl)indane dihydrate, [In(C 2 F 5 ) 3 (OH 2 ) 2 ], was fully characterized by IR and NMR spectroscopy, as well as by single crystal X‐ray diffraction. Due to their stability and convenient accessibility, the hydrates are ideal starting compounds for the chemistry of tris(pentafluoroethyl)gallium and ‐indium compounds, for example hydroxogallates and ‐indates. An attempt to determine its gas‐phase structure and that of the gallium analogue by electron diffraction demonstrates that they lose water ligands upon evaporation. The energetics of these processes were predicted by quantum‐chemical calculations as was the nature of bonding in the free Lewis acids and their mono‐ and dihydrates. Furthermore, the synthesis and structural diversity of hydroxido tris(pentafluoroethyl) gallates and one indate are presented.