Structural, vibrational and thermodynamic studies of pentafluorogermanate salts

Abstract

The crystal structures of two A +GeF 5 − salts (A = XeF 5, ClO 2), coupled with vibrational studies of these and other salts (A = NO 2, SF 3, Bu 4N), show that the anion has at least four different structural forms. In XeF 5 +GeF 5 − the anion consists of infinite chains of trans-bridged GeF 6 octahedra with a GeFGe angle of 141°; ClO 2 +GeF 5 − contains cis-bridged chains with corresponding angles of 143° and 148°. The Raman and infrared spectra confirm earlier studies 1 that GeF 5 − exists as a monomer of D 3h symmetry in Bu 4N +GeF 5 −. In NO 2 +GeF 5 − a polymeric form different from those found in ClO 2 +GeF 5 − and XeF 5 +GeF 5 − must occur. The enthalpies of formation of ClO 2 +GeF 5 − and (SF 3 +) 2GeF 6 2− (the structure of which will be described) were determined from lnK p vs. l/T plots; from lattice energy evaluations of these salts (based upon a Madelung energy obtained by the method 2 of Bertaut) the first and second fluoride ion affinities of GeF 4 have been determined: ΔH(GeF 4(g) + F −(g) = GeF 5 −(g)) = −101, ΔH(GeF 5 −(g) + F −(g) = GeF 6 2−(g)) = +37 kcal mole −1. Similar evaluations led to ΔH(BF 3(g) + F −(g) = BF 4 −(g)) = −91, and ΔH(UF 6(g) + e − = UF 6 −(g)) = −133 kcal mole −1.