title: Homoleptic borates and aluminates containing the difluorophosphato ligand - [M(O2PF2)x](y-) - synthesis and characterization.
abstract: Weakly coordinating anions (WCAs) with the difluorophosphato ligand (O2PF2) were the target of this study. Initial experiments were conducted towards the preparation of homoleptic aluminates of the well-studied [Al(OR)4](-)-type. The preparation of the initial target structure Li[Al(O2PF2)4] failed due to the remaining Lewis acidic character of the central aluminum atom. Instead, the formation of Li3[Al(O2PF2)6] and Al(O2PF2)3 was observed with hexacoordinate aluminum atoms and verified by NMR, IR and X-ray crystallography. A possible mechanism towards these compounds was postulated in the solvent induced dismutation of the tetracoordinate Li[Al(O2PF2)4]. A singly charged WCA was realized by the exchange of the central aluminum atom for boron. The [B(O2PF2)4](-) anion was prepared starting from BH3·S(CH3)2 and boron tribromide leading to the protic room temperature Ionic Liquid (IL) [H(S(CH3)2)][B(O2PF2)4] and the neat liquid Brønsted acid H[B(O2PF2)4], respectively, representing a significantly improved synthesis with regard to the first experiments of Dove et al. The basicity of the [B(O2PF2)4](-) anion and its WCA quality were investigated on the basis of the IR-spectroscopic NH-scale and the salt [H(N(Oct)3)][B(O2PF2)4] that places it better than all oxyanions and close to the carboranate based WCAs. A pathway to the solvent free pure Li[B(O2PF2)4] salt was established on a multi-gram scale with excellent purities enabling electrochemical applications (verified by NMR, IR, X-ray crystallography and cyclovoltammetry).
authors.affiliation: Institut für Anorganische und Analytische Chemie and Freiburger Materialforschungszentrum (FMF), Universität Freiburg, Albertstr. 21, 79104 Freiburg, Germany. krossing@uni-freiburg.de.
authors.forename: Christoph
authors.initials: C
authors.lastname: Schulz
authors.forename: Philipp
authors.initials: P
authors.lastname: Eiden
authors.forename: Petra
authors.initials: P
authors.lastname: Klose
authors.forename: Andreas
authors.initials: A
authors.lastname: Ermantraut
authors.forename: Michael
authors.initials: M
authors.lastname: Schmidt
authors.forename: Arnd
authors.initials: A
authors.lastname: Garsuch
authors.forename: Ingo
authors.initials: I
authors.lastname: Krossing