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.

Platinum fluorides beyond PtF6?

“…The singlet lies 72.6 kJ mol À1 higher in energy than the triplet ground state. Note that, PtF 6 is experimentally characterised to be regular octahedral (O h symmetry) in the gas-phase [15][16][17] and in the solid state [18]. This small discrepancy between our calculations and the experimental results might be due to a spin-orbit effect (SO) which generates a t 4 3=2 singlet ground-state [18].…”

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

“…However, the most interesting cases involved Re IV metal ions with octahedral geometry in a series of complexes (Fig. 27), which can be categorized as: (i) hexahalorhenates(IV) [119,[139][140][141][142][143][144][145][146] (79), and I (80)) [139], (ii) pentahalorhenates(IV) with one labile coordination site [147,148] such as (NH 2 Me 2 )[Re IV X 5 (DMF)] (where X = Cl (81) and Br (82)) [147], (iii) tetrahalorhenates(IV) with cis-blocking chelating organic ligands [110,[149][150][151][152][153][154][155][156] such as (NBu 4 ) 2 [Re(ox)X 4 ] (where ox = oxalate, X = Cl (83) and Br (84) For a hexa-coordinated 3d 3 ion with ideal O h geometry, significantly high first-order SOC and thus large magnetic anisotropy will be obtained from the triply degenerate ground state (involving d xy , d xz , and d yz orbitals) if Jahn-Teller distortion, which inevitably breaks the degeneracy and minimizes the SOC, is not present. In octahedral complexes, Jahn-Teller distortion splits the lowest lying triply degenerate d orbitals, thereby leading to two sets of orbitals, i.e., d xy and (d xz , d yz ), irrespective of whether the nature of the distortion is compression (where the energy order is d xy < (d xz , d yz )) or elongation (where the energy order is d xy > (d xz , d yz )).…”

Octahedral complexes of the series of actinides hexafluorides AnF6

“…UF 6 , an important part of the nuclear fuel cycle is one of the most frequently studied actinide systems. Single crystal structures of a series of metal hexafluorides (Mo, Tc, Ru, Rh, W, Re, Os, Ir, and Pt) at À140°C were reported by Drews and coworkers [5]. All compounds were shown to crystallize under the same molecular structure exhibiting octahedral symmetry.…”