Structure of the new iron(II) oxalate potassium salt K2Fe[(C2O4)2(H2O)2]·0.18H2O.

The discovery of a new FeII oxalate framework of composition K2Fe[(C2O4)2(H2O)2]·0.18H2O is reported. Its crystal structure was solved by means of single crystal and powder X-ray diffraction. The new organic-inorganic hybrid compound crystallizes in the orthorhombic space group Pca21 with unit-cell parameters: a = 12.0351 (4) Å, b = 15.1265 (5) Å, c = 10.5562 (4) Å. This crystal structure, containing eight chemical formula, consists of a succession of FeO4(H2O)2 octahedra and K+ cations growing along b direction. Magnetization measurements indicate that the title compound is paramagnetic over the investigated temperature range (2-300 K). Both magnetization and 57Fe Mössbauer data indicate that Fe2+ is in a high-spin state.

Correlations between stacked structures and weak itinerant magnetic properties of La2 - x Y x Ni7 compounds.

Hexagonal La2Ni7 and rhombohedral Y2Ni7 are weak itinerant antiferromagnet (wAFM) and ferromagnet (wFM), respectively. To follow the evolution between these two compounds, the crystal structure and magnetic properties of A 2 B 7 intermetallic compounds (A = La, Y, B = Ni) have been investigated combining x-ray powder diffraction and magnetic measurements. The La2-x Y x Ni7 intermetallic compounds with 0 ⩽ x ⩽ 1 crystallize in the hexagonal Ce2Ni7-type structure with Y preferentially located in the [A 2 B 4] units. The compounds with larger Y content (1.2 ⩽ x < 2) crystallize in both hexagonal and rhombohedral (Gd2Co7-type) structures with a substitution of Y for La in both [A 2 B 4] and [AB 5] units. Y2Ni7 crystallizes in the rhombohedral structure only. The average cell volume decreases linearly versus Y content, whereas the c/a ratio presents a minimum at x = 1 due to geometric constrains. The magnetic properties are strongly dependent on the structure type and the Y content. La2Ni7 displays a complex metamagnetic behavior with split AFM peaks. Compounds with x = 0.25 and 0.5 display a wAFM ground state and two metamagnetic transitions, the first one toward an intermediate wAFM state and the second one toward a FM state. T N and the second critical field µ 0 H c2 increase with the Y content, indicating a stabilization of the AFM state. LaYNi7, which is as the boundary between the two structure types, presents a very wFM state at low field and an AFM state as the applied field increases. All the compounds with x > 1, and which contains a rhombohedral phase are wFM with T C = 53(2) K. In addition to the experimental studies, first principles calculations using spin polarization have been performed to interpret the evolution of structural phase stability for 0 ⩽ x ⩽ 2.