On the Symmetry of the n=1 Ruddlesden-Popper Phase Ca2FeO3Cl

Abstract

Single crystals of Ca2FeO3Cl have been obtained as a by product during single crystal growth experiments of calcium ferrates from a CaCl2 flux. The reddish‐brown optically uni‐axial crystals adopt the tetragonal space group P4/nmm with a = 3.8381(4) Å and c = 13.685(2) Å and Z = 2 formula units per cell. The structure has been determined from a single crystal diffraction data set collected at room conditions and refined to final residual R(|F|) = 0.053 for 163 observed independent reflections with I > 2σ(I). Ca2FeO3Cl belongs to the structure family of the Ruddlesden‐Popper series with n = 1, which is also referred to as the K2NiF4‐type. Main building units are layers of perovskite type corner connected FeO5Cl‐octahedra perpendicular to [001]. The two crystallographically independent calcium ions are located between the octahedral layers and are coordinated by nine ligands each: Ca1 (4×O + 5×Cl) and Ca2 (9×O). Following prior studies Ca2FeO3Cl crystallizes in space group P4. However, the present investigation shows clearly that this assignment is incorrect and that the compound has been described in an unnecessarily low symmetry.

Ca2MnO3X (X = Cl, Br) Oxyhalides with 1-Dimensional Ferromagnetic Chains of Square-Planar S = 2 Mn3+

“…The Ca 2+ cation is too small to be properly accommodated in the A sites of the RP structure without structural distortion. This accounts for the relative paucity of Ca 2 MO 3 Cl phases, which were hereto known only for M = Fe . This factor, combined with the strong Jahn–Teller effect characteristic of high spin Mn 3+ , results in the observed crystal structure of Ca 2 MnO 3 X.…”

“…This is due to the large differences in size and polarizability between the two anionic species (Hume–Rothery rules) . For example, the substitution of chloride for oxide in materials adopting the n = 1 Ruddlesden–Popper (RP) structure type tends to result in oxychloride materials where the Cl – anions replace the apical oxides in an ordered fashion, as shown in the structures of Sr 2 M 3+ O 3 Cl (M = V, Mn, Fe, Co, and Ni) and Ca 2 Fe 3+ O 3 Cl. − Further substitution results in the replacement of the remaining apical oxide as shown by the structures of A 2 Cu 2+ O 2 Cl 2 (A = Ca, Sr) and Sr 2 Co 2+ O 2 Cl 2 . ,, …”

“…There are a large number of known oxyhalide materials with the general formula Sr 2 M 3+ O 3 X (M = V, Mn, Fe, Co, Ni) with structures based on the n = 1 Ruddlesden–Popper (RP) structure type. In these materials, the chloride or bromide anions preferentially occupy the apical sites in an ordered fashion, and they are typically antiferromagnetic insulators due to the 180° M–O–M superexchange interaction within each layer. − …”

“…In these materials, the chloride or bromide anions preferentially occupy the apical sites in an ordered fashion, and they are typically antiferromagnetic insulators due to the 180 ° M-O-M superexchange interaction within each layer. [2][3][4][5][6][7][8][9] This tendency can be overcome by using ions with particular radius or coordination constraints. For example, the A3Fe2O5Cl2 series of phases adopt structures analogous to the n = 2 RP phases with apical chlorides for A = Ca and Sr, while for A = Ba, the structure contains a complex network of corner-sharing FeO4 tetrahedra.…”

Pinalites: Optical Properties and Quantum Magnetism of Heteroanionic A3MO5X2 Compounds

“…Several compounds are known in which one halogen and five oxygen atoms coordinate to a metal atom in a square-pyramidal configuration, similar to CROC. The most diverse compounds are A 2 M 3+ O 3 X, which are analogues of K 2 NiF 4 -type layered perovskites, where A = Sr and Ca, M = Sc, V, Mn, Fe, Co, and Ni, and X = F, Cl, and Br. ,− See ref for oxyfluorides with related layered perovskite structures. The magnetic properties of the materials have also been investigated.…”