THE 1ST OXOFERRATE(I) - ON THE CONSTITUTION OF K3[FEO2] AND K3[NIO2]

Garnet-red single crystals of K3[FeO2] were obtained for the first time by heating intimate mixtures of K6[CdO4] and CdO (molar ratio 1:1.16) in closed Fe-cylinders at 450-degrees-C during 40 d. The same way of preparation via ''reaction with the cylinder surface'' was applied to prepare similarly coloured single crystals of K3[NiO2] (K6CdO4 in closed Ni-cylinders at 500-degrees-C during 49 d). The structure determination by four circle diffractometer data (MoKalphaBAR, K3[FeO2]: 731 out of 731 I(o)(hkl), R = 5.76%, R(w) = 5.33%, K3[NiO2]: 755 out of 755 I(o)(hkl), R = 8.70%, R(w) = 4.25%) confirms the space groups P 4(1)2(1)2 and P 4(3)2(1)2, respectively. K3[FeO2]: a = 604.2(2) pm, c = 1402.7(3) pm, Z = 4 K3[NiO2]: a = 603.6(1) pm, c = 1405.2(2) pm, Z = 4. (powder data, standard deviations in parentheses) Essential feature of the structure are the dumb-bell-like anions [O-M-O]3- (M = Fe, Ni). Their arrangement corresponds to a stuffed derivative of the KrF2-type. Magnetic properties of K3[FeO2] were determined and cover the monovalence of Fe. MAPLE-calculations reveal the strong coincidence of monovalent VIIIb-cations.