Fluoride ion donor properties of group 13 trifluorides (MF3, M = Al, Ga, In, Tl) and crystal structures of InF3·3SbF5, TlF3·3SbF5 and TlF3·AsF5·2HF

Abstract

Reactions between strong Lewis acids (i.e. AsF₅, SbF₅) and MF₃ (M = Al, Ga, In, Tl) in anhydrous hydrogen fluoride at ambient temperature proceeded only in three cases, yielding InF₃·3SbF₅, TlF₃·3SbF₅, TlF₃·AsF₅·2HF and TlF₃·AsF₅. Crystal structure of InF₃·3SbF₅ consists from infinite chains of In atoms connected by three SbF₆ units, with two bridging fluorine atoms (F_b) in cis-position. Due to the strong interaction of SbF₆ units with In³⁺, the Sb–F_b bonds are significantly elongated (200.7(4) pm). Such long Sb–F_b bonds have been observed in the crystal structure of SbF₅. The crystal structure of TlF₃·3SbF₅ is built from slabs where thallium atoms are connected by SbF₆ units. The thallium is nine-fold coordinated by fluorine atoms in the shape of a tricapped trigonal prism. In the crystal structure of TlF₃·AsF₅·2HF there are puckered layers, composed of rectangular rings made of Tl and F atoms. The seven-fold coordination around each Tl is completed by three axial fluorine atoms, provided by one HF molecule and two AsF₆ units arranged below and above the puckered layers forming infinite slabs on that way. The second molecule of HF is placed between the slabs. Vibrational spectra of isolated InF₃·3SbF₅, TlF₃·3SbF₅, and TlF₃·AsF₅ are consistent with the presence of highly deformed SbF₆/AsF₆ octahedra.