The Crystal Structure of the Potential Ferroelectric Calcium Rhenate(VI, VII) Ca₁₁Re₄O₂₄ and its Relation to the Structure of Sr₁₁Os₄O₂₄

Abstract

The title compound was prepared in well-crystallized form by thermal decomposition of Ca5Re2O12. Its structure was determined from single-crystal X-ray diffractometer data: I41, a = 1107.0(1), c = 1609.3(1) pm, Z = 4, R = 0.056 for 4565 structure factors and 119 variable parameters. The calcium atoms occupy seven different sites with 8, 9, or 10 oxygen neighbors. The two different rhenium atoms are octahedrally coordinated by oxygen atoms with average Re-O distances of 193.1 and 187.7 pm for the six- and seven-valent rhenium atoms, respectively. The compound shows Curie-Weiss behavior with a magnetic moment of μexp = 1.15(±0.10) μB per Re(VI) atom. The structure is closely related to that of Sr11Os4O24 which, however, crystallizes in the space group I2/a. The difference between the two structures arises through the higher coordination numbers of the strontium atoms. It is suggested that at high temperature both compounds crystallize in the common higher symmetry space group I4/a. Since Ca11Re4O24 crystallizes in the pyroelectric class 4 this compound is expected to be ferroelectric.

Preparation and Crystal Structure of Rare Earth Rhenates: the SeriesLn5Re2O12 withLn = Y, Gd-Lu, and the Praseodymium Rhenates Pr3ReO8, Pr3Re2O10, and Pr4Re2O11

“…For the preparation of the compounds Ln 5 Re 2 O 12 stoichiometric mixtures of the rare earth elements and the metaperrhenates Ln(ReO 4 ) 3 were sealed in evacuated silica tubes and annealed for 10 days at 1050°C. The yttrium compound was obtained in the form of a fine powder, the others in the form of dark needles.…”

“…The lattice constants of its C centered monoclinic cell are: a = 778.47(9) pm, b = 773.62(9) pm, c = 706.10(8) pm, b = 114.77(1)°, V = 0.3861 nm 3 .…”

“…In the course of our investigations of alkaline earth and rare earth rhenates and perrhenates we have already reported our results concerning the preparation and crystal structures of the perrhenates Ca 5 Re 2 O 12 and Sr 5 Re 2 O 12 [1], the perrhenate halides Sr 5 (ReO 5 ) 3 X (X = Cl, Br, I) and Ba 5 (ReO 5 ) 3 Cl [2], the reduced rhenate (VI, VII) Ca 11 Re 4 O 24 [3], the series of reduced rhenates(IV) Ln 2 ReO 5 (Ln = Sm, Eu, Gd), the series of rhenates Ln 3 Re 2 O 9 (Ln = Pr, Nd, Sm), where rhenium occurs in the two oxidation states +4 and +5, and the series Ln 4 Re 6 O 19 (Ln = La±Nd), where the rhenium atoms have the fractional oxidation number +4.33 [4].…”

New Insulating Antiferromagnetic Quaternary Iridates MLa10Ir4O24 (M = Sr, Ba)

“…In summary, we report the discovery and characterization of two new quaternary iridates, SrLa 10 Ir 4 O 24 and BaLa 10 Ir 4 O 24 , with the crystal structure similar to Ca 11 Re 4 O 24 31, Sr 11 Re 4 O 24 32 and Ba 11 Os 4 O 24 33 and Sr 9 La 2 Mo 4 O 24 13. By isolating the octahedra and thus eliminating bandwidth and super-exchange as a competing influence on the electronic structure, compounds such as these can provide a platform for testing the detailed nature and range of applicability of the J eff  = ½ description using, for example, resonant inelastic x-ray scattering.…”

“…Apparently this structure type can adjust its M :La ratio to accommodate either the tetravalent Ir or the hexavalent Mo. When only alkaline earth metal is involved and rare earth metal is excluded, the structure type can host transition metal with mixed oxidation states, which has been shown by the synthesis of Ca 11 Re 4 O 24 31 Sr 11 Re 4 O 24 32 and Ba 11 Os 4 O 24 33.…”