SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF HEXAKIS(CARBONYL)IRON(II) UNDECAFLUORODIANTIMONATE(V), [FE(CO)(6)][SB2F11](2)

Oxidative carbonylation of Fe(CO)(5) in liquid SbF5 and a CO atmospher e, with either AsF5 or Cl-2 as external oxidizing agents, produces [Fe (CO)(6)][Sb2F11](2) in very high yield. The resulting off-white solid material is thermally stable (above 200 degrees C). The homoleptic car bonyl cation [Fe(CO)(6)](2+), the first of its type formed by a 3d-met al, is isostructural with [Ru(CO)(6)](2+) and [Os(CO)(6)](2+) which ar e obtained by reductive carbonylation of M(SO3F)(3), M=Ru or Os. The s tretching force constant of 19.82x10(2) N m(-1) and <(nu)over bar (CO) (av)>, of 2215.5 cm(-1) suggest significantly reduced pi-back-bonding . The single line Fe-57 Mossbauer spectrum at delta=-0.001(6) mm s(-1) relative to alpha-Fe is consistent with a regular octahedral structur e and a (1)A(1g) groundstate for [Fe(CO)(6)](2+). The possible existen ce of [Fe(CO)(6)](3+) formed by oxidation with Cl-2 is discussed.