Low temperature magnetic ordering of a series of structurally characterized chloroferrates

Iron-57 Mössbauer spectroscopic results for a new series of related chloroferrate salts of complex ammonium cations are presented. In particular, spectra of materials based on FeCl₄^–, FeCl₅^2–, FeCl₆^–, [FeCl₅(H₂O)]^2–, and [FeCl₅(CH₃OH)]^2– anions are discussed relative to the systematics of their isomer shifts, coordination numbers, and low temperature 3D critical ordering temperatures. The following specific systems have been studied by Mössbauer spectroscopy and definitively characterized by single-crystal X-ray analysis: [CH₃NH₃⁺]₄[FeCl₆]^3–[Cl^–](A), [Me₂N(-CH₂CH₂)₂NMe₂⁺][FeCl₅^2–] (B), [H₃NCH₂CH₂NH₃²⁺][FeCl₅·H₂O^2–], (C), and [NH₃(CH₂)₆NH₃²⁺]₄[(FeCl₆^3–)(FeCl₄^–)ClCl₄^–] (D). The spectral data for these complexes are considered in the light of results of previous studies for systems such as [K₂FeCl₅·H₂O], [Co(NH₃)₆][FeCl₆], diamethyltriethylenediammoniumpentachloroferrate (E), and the related [FeCl₅·CH₃OH]^2– salt (F). The critical 3D ordering temperatures are 1.45, 6.80, 3.45, and 1.22K forA, B, C, andD, respectively.