Impact of Lithium and Potassium Cations on the Mössbauer Spectral and Electrical Properties of Two Mixed-Valence Iron(II/III) Phosphites

Based on the combined corrected chemical analysis, the single-crystal X-ray structural results, and the revised Mössbauer spectral analysis, the best formulation of Li _1.4(1) [Fe _4.4(1) IIFe _0.6(1) ^III (HPO ₃ ) ₆ ]·1.47(3) H ₂ O, 1b , has been obtained; also, from a revised Mössbauer spectral analysis, a revised formulation of K _0.95(5) [Fe _3.95(5 ) ^II Fe _1.05(5) ^III (HPO ₃ ) ₆ ]·0.5 H ₂ O, 2m , has been obtained. The revised analysis of the room-temperature Mössbauer spectral parameters for both compounds is consistent with their crystallographic structures and the different nature and occupancies of the Li ⁺ and K ⁺ crystallographic sites. From a detailed analysis of the impedance spectroscopy measurements of Li _1.43 [Fe _4.43 ^II Fe _0.57 ^III (HPO ₃ ) ₆ ]·1.5 H ₂ O, 1 , between 123 and 189 °C, two processes involving the electric charge response to the ac electric field have been identified. An activation energy for the charge transfer in 1 of 0.91(2) eV or 7340(160) cm ^-1 has been obtained; the charge transfer may involve a correlated hopping of the Li ⁺ ion and an electron between the iron(II) and iron(III) ions.