Study of the Structural, Electronic, and Magnetic Properties of the Barium-rich Iron(IV) Iron(IV) Oxides, Ba₂FeO₄ and Ba₃FeO₅

Crystals of Ba ₂ FeO ₄ and Ba ₃ FeO ₅ , grown from a "self-sealing" KOH-Ba(OH) ₂ flux, have been characterized by single-crystal X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. Ba ₂ FeO ₄ forms nonmerohedral twinned crystals with the monoclinic space group P2 ₁ /n, a = 6.034(2) Å, b = 7.647(2) Å, c = 10.162(3) Å, ß = 92.931(6)°, and Z = 4. Ba ₃ FeO ₅ crystallizes in the orthorhombic space group Pnma, with a = 10.301 (1) Å, b = 8.151 (1) Å, c = 7.611 (1) Å, and Z = 4. While both compounds feature discrete FeO ₄ ^4- tetrahedra, the anion found in Ba ₂ FeO ₄ has shorter Fe-O bonds and is significantly distorted relative to the Ba ₃ FeO ₅ anion. An iron valence of 4+ was confirmed by magnet susceptibility measurements and by the low-temperature isomer shifts of -0.152 and -0.142 mm/s relative to α-iron for Ba2FeO4 and Ba ₂ FeO ₅ , respectively.