KMn3O2(Ge2O7): An S = 2 Magnetic Insulator Featuring Pillared Kagome Lattice.

KMn3O2(Ge2O7) (I) and K0.35Rb0.65Mn3O2 (Ge2O7) (II) are prepared by high-temperature flux-growth methods from mixtures of KO2, Mn2O3, and GeO2 in the molar ratio of 2:3:4, and an excess of KCl or RbCl (silica tube, 800 °C, 3 d, 60% yield for (II)).