The low-temperature fluorination of the n = 2 Ruddlesden-Popper phase La2SrCr2O7 yields La2SrCr2O7F2 via a topochemical fluorine insertion reaction. The structure-conserving nature of the fluorination reaction means that the chromium centers of the initial oxide phase retain an octahedral coordination environment in the fluorinated product, resulting in a material containing an extended array of apex-linked Cr(4+)O6 units. Typically materials containing networks of octahedrally coordinated Cr(4+) centers can only be prepared at high pressure; thus, the preparation of La2SrCr2O7F2 demonstrates that low-temperature topochemical reactions offer an alternative synthesis route to materials of this type. Neutron diffraction, magnetization, and μ(+)SR data indicate that La2SrCr2O7F2 undergoes a transition to an antiferromagnetic state below TN ≈ 140 K. The structure-property relations of this phase and other Cr(4+) oxide phases are discussed.

Publisher's copyright statement:This document is the Accepted Manuscript version of a Published Work that appeared in nal form in Inorganic chemistry, copyright c American Chemical Society after peer review and technical editing by the publisher. To access the nal edited and published work see https://doi.org/10.1021/acs.inorgchem.6b01445. Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. IntroductionThe ABO 3 perovskite structure is adopted by complex metal oxide phases with a very wide variety of chemical compositions. Indeed it is possible to incorporate all the transition metals within perovskite frameworks, many of them in a number of different oxidations states. The ubiquity and chemical diversity of perovskite oxide phases primarily arises from the intrinsic thermodynamic stability imparted by the close packed nature of the structure (the framework can be thought of as being derived from a cubic close packed lattice). However, unlike many other structure types derived from close-packed arrangements, the perovskite structure can form thermodynamically stable phases incorporating combinations of A-and B-cations with a large range of radius ratios, due to the mechanical flexibility imparted into perovskite frameworks by the facile collective rotations of the constituent, apex-linked, BO 6 octahedra.In addition to imbuing the perovskite framework with mechanical flexibility, the tilting and twisting distortions of perovskite oxide phases can have a large influence on their physical properties. This can be seen most directly by observing that these facile collective distortions typically lead to changes (tightening) of the B-O-B bond angles between linked BO 6 octahedra, while leaving the internal coordinates of the BO 6 units largely unchanged. As a result the distor-

The financial implications of choosing a particular threshold for clearance of radioactively contaminated land are substantial, particularly when one considers the volume of naturally occurring radioactive material (NORM) created each year by the production and combustion of fossil fuels and the exploitation of industrial minerals. Inevitably, a compromise needs to be reached between the level of environmental protection sought and the finite resources available for remediation. In the case of natural series radionuclides, any anthropogenic input is always superimposed on the inventory already present in the soil; this 'background' inventory is conventionally disregarded when assessing remediation targets. Unfortunately, the term is not well defined and the concept of 'background dose' is open to alternative interpretations. In this paper, we address the issue of natural background from a geochemical rather than from a solely radiological perspective, illustrating this with an example from the china clay industry. We propose a simple procedure for decision making based on activity concentrations of primordial radionuclides and their progeny. Subsequent calculations of dose need to take into account the mineralogical and chemical characteristics of the contamination, which in the case of NORM are invariably reflected in uranium series disequilibrium.

The title compound is prepared by fluorination of La2SrCr2O7 at 310 °C under an O2/F2 gas mixture obtained by heating CuF2 separately at 500 °C under flowing oxygen.