Lattice effects in the Mössbauer spectra of salts of [Fe4S4(SBut)4]2–. Crystal structures of [NMe4]2[Fe4S4(SBut)4]·HSBut and [N(n-C5H11)4]2[Fe4S4(SBut)4]·HSBut

Abstract

The Mössbauer spectra of salts containing the anions [Fe₄S₄(SBu^t)₄]^2– or [FeX₄]^2–(X = Cl or Br) show relatively invariant isomer shifts, but quadrupole splittings which are cation-dependent, for example varying from 0.84 to 1.32 mm s^–1 for [NR₄]₂[Fe₄S₄(SBu^t)₄]. This observation is rationalized in terms of perturbations exerted by the cations on the field gradient at the iron centres. As aids to this rationalization, the X-ray crystal structures of [NMe₄]₂[Fe₄S₄(SBu^t)₄]·HSBu^t and of [N(n-C₅H₁₁)₄]₂[Fe₄S₄(SBu^t)₄]·HSBu^t were determined.