Syntheses, infrared and Raman spectra of rare earth(III) fluoroarsenates(V)

Rare earth trifluorides (LnF(3)) dissolve in anhydrous hydrogen fluoride (aHF) acidified with AsF5 at room temperature forming stable solutions of solvated rare earth cations Ln(HF)(x)(3+) and AsF6- anions. After the excess of AsF5 and aHF are pumped away at room temperature La(AsF6)(3), LnF(AsF6)(2) with Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Y and Ln(2)F(3) (AsF6)(3) with Ln = Tm, Yb and Lu are isolated, indicating the decreasing stability of Ln(AsF6)(3) and LnF(AsF6)(2) along the series of rare earth metals. This behaviour perfectly reflects the reduced fluorobasicity of rare earth trifluorides along the series. In some selected cases (Ln = La, Nd, Sm and Tm) the isolation of Ln(AsF6)(3) compounds was performed at lower temperatures (263-233 K). The vibrational spectra of all isolated rare earth(III) fluoroarsenates(V) show that deformed AsF6- octahedra are present, indicating a covalent contribution to the fluorine bridges between LnF(3) and AsF5. (C) 1998 Elsevier Science S.A. All rights reserved.