Iron Stereochemistry in Oxygen-Containing Compounds

摘要

The Voronoi-Dirichlet polyhedra (VDP)and the method of intersecting spheres were used to analyze the coordination of 1598 sorts of Fe atoms in the structure of 985 oxygen-containing compounds.The iron atoms whose oxidation number varies from 1 to 6 can coordinate 2 to 8 oxygen atoms in the crystal structure,giving rise to the FeO_n coordination polyhedra shaped like square antiprisms (n =8),octahedra or trigonal prisms (n =6),square pyramids or trigonal bipyramids (n =5),tetrahedra or squares (n =4),triangles (n =3),or dumbbells (n =2).The effect of the valence state and the coordination number of iron on the VDP parameters was studied.A general linear correlation between the solid angles of the VDP faces corresponding to Fe-O bonds and the corresponding interatomic distances,which vary over a broad range (1.63-2.77 A),was established.It is shown in relation to the A_2Fe_2O_5 oxides (A =Ca,Sr)that VDP characteristics make it possible to reveal essential differences in the crystal structures even for isostructural compounds.The Fe~(IV)O_6 octahedra,unlike isoelectronic Mn~(III)O_6 or Cr~(II)O_6 octahedra,display no Jahn-Teller effect.In was shown in relation to CaFeO_3 that VDP parameters can be used for the quantitative description of the charge disproportionation in the crystal structure.