A new mixed-valence iron (Fe(2+)/Fe(3+)) fluoride material with a layered perovskite-related structure has been synthesized and characterized. The material, K4Fe3F12 [K4(Fe(2+))(Fe(3+))2F12], was synthesized using mild hydrothermal conditions. The material exhibits a layered perovskite structure consisting of alternating sheets of apex-linked Fe(2+)F6 and Fe(3+)F6 octahedra; thus, each layer of Fe(2+)F6 centers is sandwiched between two layers of Fe(3+)F6 centers. Magnetization and neutron powder diffraction data show that, upon cooling below 120 K, K4Fe3F12 adopts a magnetically ordered state in which the Fe(3+) and Fe(2+) spins are aligned in an approximately antiparallel manner to each other to yield a pseudoferrimagnetic structure with a net spontaneous moment of 5.41 μB per formula unit at 10 K. Crystal data: K4Fe3F12, trigonal space group R3̅m (No. 166), a = b = 5.7649(9) Å, c = 28.086(9) Å, V = 808.36(3) Å(3), Z = 3, T = 296(2) K.
