Mössbauer study of the thermal decomposition of dinitrogen tetroxide solvates of iron(III) nitrate

Abstract

The thermal decomposition of the 1·5 N₂O₄ solvate of iron(III) nitrate, [N₄O₆]²⁺2[Fe(NO₃)₄]^–, has been investigated. Four isolable intermediates, [NO]⁺[Fe(NO₃)₄]^–, [NO₂]⁺[Fe(NO₃)₄]^–, [Fe₂O(NO₃)₄], and [FeO(NO₃)], have been characterised, the ultimate product being Fe₂O₃. [Fe₂O(NO₃)₄] and [FeO(NO₃)] both exhibit room temperature Mössbauer effects characteristic of polymeric lattices. The Mössbauer spectra of the complexes M⁺[Fe(NO₃)₄]^–[M = Me₄N, Et_nNH_{4 –n}(n= 1–4), N₄O₆⁺, or NO₂⁺] and M⁺[FeCl₄]^–[M = Et_nNH_{4 –n}(n= 1–4)] all consist of a single resonance with isomeric shifts in the ranges 0·54–0·61 mm s^–1 and 0·30–0·31 mm s^–1, respectively. The two nitrosonium salts, [NO]⁺[FeX₄]^–(X = Cl, NO₃), however, exhibit small quadrupole splittings (Δ= 0·36 mm s^–1, X = Cl; Δ= 0·45 mm s^–1, X = NO₃), which are attributed to the interaction of the highly polarising nitrosonium cation with one of the ligands X.