K4Ni3O6 and KNa2Ni2O4, New Quasi One-Dimensional ­Oxonickelates(II, III)†

Two new quasi one-dimensional alkali metal oxonickelates, K4Ni3O6 and KNa2Ni2O4, were obtained by the azide/nitrate route starting from respective stoichiometric mixtures of KN3, KNO3, NaN3, NaNO3, and NiO. According to the X-ray analyses of the crystal structures [K4Ni3O6: C2/m, Z = 2, a = 899, 53(3), b = 610, 24(2), c = 778.75(2) pm, β = 91.665(2)°, R1 = 0.030, wR2 = 0.088; KNa2Ni2O4: P21/n, Z = 4, a = 573.70(2), b = 1072.89(3), c = 844.93(2) pm, β = 102.916(2)°, R1 = 0.038, wR2 = 0.108], the main feature common to both crystal structures are undulating 1∞NiO2 chains consisting of planar, edge-sharing NiO4 squares. The magnetic susceptibilities for both compounds indicate onset of antiferromagnetic ordering at about 5 K. Evaluations of the Curie-Weiss fits result in calculated magnetic moments higher than expected for the respective spin only values, implying some orbital contribution. Below the Neel temperature spin flop or meta-magnetism is observed for both compounds.