biostudies-literatureUnknown8(1)Albrecht RThe reaction of Fe(NO3)3?9 H2O with KOH under hydroflux conditions at about 200?°C produces red crystals of K2-x Fe4O7-x (OH) x in a quantitative yield. In the crystal structure, edge-sharing [FeO6] octahedra form ?2[ Fe2O6] honeycomb nets. Pillars consisting of pairs of vertex-sharing [FeO4] tetrahedra link the honeycomb layers and form columnar halls in which the potassium ions are located. The trigonal (P 3? 1m) and the hexagonal (P63/mcm) polytypes of K2-x Fe4O7-x (OH) x show oriented intergrowth. The sub-stoichiometric potassium content (x?0.3) is compensated by hydroxide ions. K2-x Fe4O7-x (OH) x is an antiferromagnet above 2?K and its magnetic structure was determined by neutron powder diffraction. Under ambient conditions, K2-x Fe4O7-x (OH) x hydrolyzes and K2CO3???H2O forms gradually on the surface of the K2-x Fe4O7-x (OH) x crystals. Upon annealing at air at about 500?°C, the potassium atoms in the columnar halls start to order into a superstructure. The thermal decomposition of K2-x Fe4O7-x (OH) x proceeds via a topotactic transformation into K1+x' Fe11O17, adopting the rhombohedral ?'' or the hexagonal ?-aluminate-type structure, before ?-Fe2O3 is formed above 950?°C, which then converts into thermodynamically stable ?-Fe2O3.ChemistryOpen74-83https://www.ebi.ac.uk/biostudies/studies/S-EPMC6345222biostudies-literatureOxo-Hydroxoferrate K2-x Fe4O7-x (OH) x : Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures.PMC6345222Hunger JBlock TRuck MPottgen RDoert TSenyshyn AAlbrecht RfalseOxo-Hydroxoferrate K2-x Fe4O7-x (OH) x : Hydroflux Synthesis, Chemical and Thermal Instability, Crystal and Magnetic Structures.The reaction of Fe(NO3)3?9 H2O with KOH under hydroflux conditions at about 200?°C produces red crystals of K2-x Fe4O7-x (OH) x in a quantitative yield. In the crystal structure, edge-sharing [FeO6] octahedra form ?2[ Fe2O6] honeycomb nets. Pillars consisting of pairs of vertex-sharing [FeO4] tetrahedra link the honeycomb layers and form columnar halls in which the potassium ions are located. The trigonal (P 3? 1m) and the hexagonal (P63/mcm) polytypes of K2-x Fe4O7-x (OH) x show oriented intergrowth. The sub-stoichiometric potassium content (x?0.3) is compensated by hydroxide ions. K2-x Fe4O7-x (OH) x is an antiferromagnet above 2?K and its magnetic structure was determined by neutron powder diffraction. Under ambient conditions, K2-x Fe4O7-x (OH) x hydrolyzes and K2CO3???H2O forms gradually on the surface of the K2-x Fe4O7-x (OH) x crystals. Upon annealing at air at about 500?°C, the potassium atoms in the columnar halls start to order into a superstructure. The thermal decomposition of K2-x Fe4O7-x (OH) x proceeds via a topotactic transformation into K1+x' Fe11O17, adopting the rhombohedral ?'' or the hexagonal ?-aluminate-type structure, before ?-Fe2O3 is formed above 950?°C, which then converts into thermodynamically stable ?-Fe2O3.2019-01-01T00:00:00Z2019 Jan2021-02-20T19:51:40Z2019-03-26T22:43:48ZS-EPMC63452223069317010.1002/open.201800229