ChemInform Abstract: Infinitely Adaptive Transition‐Metal Ordering in Ln₂O₂MSe₂‐Type Oxychalcogenides.

Abstract

Infinitely Adaptive Transition-Metal Ordering in Ln 2O2MSe2-Type Oxychalcogenides. -A range of Ln 2O2 Se2 and La2-yCeyO2M 1 Se2 (Ln: La, Ce, M 1 /M 2 : Fe, Zn, Mn, Cd) solid solutions are prepared (60 new compositions) to investigate the effects of systematically changing the relative sizes of [Ln 2O2] 2+ and [MSe2] 2layers on transition metal ordering by powder X-ray and neutron diffraction. Transition metal ordering is determined by the relative sizes of the [Ln 2O2] 2+ and [MSe2] 2layers and can be exquisitely tuned by substitution in either layer. The two extremes of transition metal ordering contain MSe 4/2 tetrahedra that are exclusively edge-sharing (stripe-like) or exclusively corner-sharing (checkerboard-like). Ce 2O2Fe3/4Zn1/4Se2 and Ce 2O2Zn1/6Mn5/6Se2 crystallize in the orthorhombic space group Bmab with Z = 16 and Z = 24, respectively. Ce 2O2Fe1/8Zn7/8Se2 and La2O2Zn1/10Mn9/10Se2 crystallize in the orthorhombic space group Imcb with Z = 20. Ce 2O2CdSe2 crystallizes in the tetragonal space group P4 2/nmc with Z = 2. -(AINSWORTH, C. M.; WANG, C.-H.; JOHNSTON, H. E.; MCCABE, E. E.; TUCKER, M. G.; BRAND, H. E. A.; EVANS*, J. S. O.; Inorg. Chem. 54 (2015) 15, 7230-7238, http://dx.doi.org/10.1021/acs.inorgchem.5b00599 ; Dep. Chem., Univ. Durham, Durham DH1 3LE, UK; Eng.) -W. Pewestorf 41-002 M 1 1-x M 2 x

Structures and Magnetic Ordering in Layered Cr Oxide Arsenides Sr2CrO2Cr2OAs2 and Sr2CrO3CrAs

“…The Cr1 (Cr 2+ ) moment is similar in direction and magnitude to the Cr 2+ moment in the analogous layers in both Ba 2 CrO 2 Cr 2 As 2 and Sr 2 CrO 2 Cr 2 As 2 , 14,15 where the CrO 2 layers are also antiferromagnetic, therefore also supporting the assignment of the Cr1 oxidation state as Cr 2+ . Furthermore, bond valence sums (calculated using bond length data provided by Brese and O'Keefe 39 and where the literature Cr−As bond length used was that for Cr II −As in both cases as a known Cr III −As bond length was not found) corroborate with this assignment as these give Cr1 an oxidation state of +2.090(2) and Cr2 an oxidation state of +2.980 (8). The observed antiferromagnetism, the bond valence sums, and the sizes of the ordered moments are consistent with a lack of mixed valency on the Cr1 and Cr2 sites.…”

3D Transition Metal Ordering and Rietveld Stacking Fault Quantification in the New Oxychalcogenides La2O2Cu2–4xCd2xSe2

“…Our previous work on single-metal layered oxychalcogenides has shown that the combination of a rigid oxide layer and a more flexible chalcogenide layer can lead to structures with remarkable complexity and large superstructures in the ab plane. 14,15 In this work, we have shown that a similar level of complexity can be built into these materials along the stacking direction by using two metals, giving rise to the range of materials from 4Cd/1Cu to 1Cd/4Cu shown schematically in Figure 2. Although we use a conventional description in this − ordering mode which leads to a checkerboard ordering within layers and adjacent layers with Cd positions offset by (1/2, 1/2) in the ab plane such that layers repeat in an ABAB sequence along c. This arrangement would be expected purely on electrostatic grounds and is retained within the Cd blocks of all our materials.…”

“…We have previously described how combining rigid-geometry oxide building blocks with more flexible or adaptive chalcogenide layers can lead to infinitely adaptive structures with remarkable structural complexity (though governed by simple rules) in two dimensions. 14,15 Here we show that this complexity can be extended to three dimensions in a new family of mixed-metal oxychalcogenides. We unravel their crystal chemistry from powder diffraction studies, despite stacking faults leading to nonroutine peak shapes.…”

“…Between these extremes, we can generate compounds with different corner-to edgesharing (C:E) integral ratios such as 5:1 (e.g., (Ce,La)/Mn), 4:1 (e.g., Ce/Zn), 3:1 (e.g., La/Zn) as well as incommensurate intermediate structures. 14,15 As such, we can prepare an infinitely adaptive series with large and complex superstructures in the ab plane.…”

Flux Synthesis, Crystal Structures, and Magnetic Ordering of the Rare-Earth Chromium(II) Oxyselenides RE2CrSe2O2 (RE = La–Nd)

“…These compounds adopt a layered, ZrCuSiAs-related structure with modulated transition-metal selenide layers with a (3 + 1)dimensional structure in the superspace group Cmme(α01/ 2)0s0. 9 Further polymorphs exist with T = Mn and Fe, respectively. To distinguish the polymorphs, we extended the formulas by the Pearson letters.…”