Crystal structures of M2FeO4 (M = K, Rb, Cs)

The crystal structure of K2FeO4, which is isomorphous with β-K2SO4, K2MnO4 and K2CrO4, has been determined in detail. In addition, Rb2FeO4 and Cs2FeO4 are shown to be of the same structural type. Crystals of K2FeO4 are orthorhombic, space group Pnma, a = 7.694(5), b = 5.858(7), c = 10.335(7) with Z = 4. The integrated intensities of 1174 independent reflections were measured with an automated diffractometer and refined to a weighted least-squares residue of 0.046. The average tetrahedral [FeO] bond length, corrected for libration effects, is 1.656(6) Å which is equal within experimental error to values observed for [CrO] and [MnO] tetrahedral bonds.