Solid State Molecular Structures of Transition Metal Hexafluorides

Abstract

Single-crystal structure determinations of all nine transition metal hexafluorides (Mo, Tc, Ru, Rh, W, Re, Os, Ir, and Pt) at -140 degrees C are presented. All compounds crystallize alike and have the same molecular structure. The bond length sequence r(w-F) congruent with r(Re-F) congruent with r(Os-F) < r(Ir-F) < r(Pt-F) is confirmed and paralleled by the sequence r(Mo-F) congruent with r(Tc-F) congruent with r(Ru-F) < r(Rh-F). Within the limits of precision, no systematic deviation from octahedral symmetry can be established. DFT and ab initio calculations predict octahedral structures for MoF6 and RhF6 and tetragonally distorted structures for ReF6 and RuF6. The energy barrier toward octahedral structures is only 2.5 kJ mol(-1) in the two latter cases. Calculated electron affinities are in the sequence MoF6 < TcF6 < RhF6 < RuF6 with a value of 6.98 eV for the latter. O2+RhF6- crystallized in an undisordered manner in P, isostructural to the low-temperature form of O2+AuF6-. RhF6- has a D4h compressed octahedral structure, while AuF6- is essentially octahedral. The absorption spectrum of TcF6 and the 19F and 195NMR spectra of PtF6 are presented.