Transition metal pnictide-halides: A class of under-explored compounds

In terms of application, mixed anion compounds have attracted far less attention than mixed cation systems. Interest in the catalytic properties of nitrides has been driven, in part, by their accessibility through new, improved synthesis routes. Although attention in this area extends beyond simple binary systems, to our knowledge, studies have not yet probed the influence of mixed anion compounds. Accordingly, in this review we describe the structures and synthetic routes to transition metal pnictide-halides, which are predominantly nitride-based. It can be anticipated that some of these materials may have interesting catalytic properties, although they have yet to be explored

Modification of the anion sublattice in metal nitrides

The main goal of solid-state chemistry is the synthesis and characterisation of new compounds with technologically exploitable properties. To this aim, one established chemical route is the modification of known inorganic materials, in most cases oxides, via substitution or insertion of cations different from the original makeup. An alternative, and less frequently adopted, approach is the manipulation of the anion sublattice to yield mixed-anion materials. Recent examples of materials with structural and physical properties tunable via both anionic and cationic substitutions are bringing more attention to the potential of this approach as an alternative and/or complementary chemical approach to cationic modifications. Within this review, structural relationships and differences between nitrides and mixed-anion nitrides, such as nitride-halides, nitride-sulfides, nitride-carbides and nitride-borides will be highlighted to set the scenery and the future challenges to a fuller exploitation of the ‘anionic route’ as a strategy towards the design of new materials

Synthesis and characterisation of the quaternary nitride-fluoride Ce2MnN3F2-δ

Ce 2 MnN 3 F 2-δ has been synthesised via low-temperature fluorination of the ternary nitride Ce 2 MnN 3 . To the best of our knowledge, Ce 2 MnN 3 F 2-δ is the first quaternary nitride-fluoride to be reported. The reaction of Ce 2 MnN 3 with 10% F 2 /N 2 at 95-115 °C yields the fluorinated phase Ce 2 MnN 3 F 2-δ , with tetragonal symmetry (P4/nmm a = 3.8554(4) Å and c = 13.088(4) Å based on neutron powder diffraction), accompanied by starting material. Rietveld refinement supports a staged fluorine insertion reaction (into alternate rocksalt layers) to give a product with stoichiometry Ce 2 MnN 3 F 2-δ . A comparison with the formation of Sr 2 TiO 3 F 2 and the isostructural LaSrMnO 4 F indicates that two F - anions are inserted but no F - /N 3- substitution takes place. Magnetic susceptibility measurements show a transition from Pauli paramagnetic behaviour, in Ce 2 MnN 3 , to paramagnetic behaviour upon fluorination. The effective magnetic moment in Ce 2 MnN 3 F 2-δ , μ eff = 5.38 μ B , is consistent with an intermediate value between that of Mn 3+ (4.9 μ B ) and Mn 2+ (5.9 μ B ) supporting the proposed stoichiometry, Ce 2 MnN 3 F 2-δ . © 2009 The Royal Society of Chemistry

Long-range magnetic ordering in Ba2CoS3: A neutron diffraction study

Neutron powder diffraction has been used to determine the magnetic structure of the quasi-one-dimensional compound Ba2CoS3, which contains linear [001] chains of vertex-sharing CoS4 tetrahedra, spaced apart by Ba2+ cations. At 1.5 K the Co2+ cations in the chains are antiferromagnetically ordered with an ordered magnetic moment of 1.97(4) μB per cation aligned along [100]. Each Co2+ cation is ferromagnetically aligned with four cation in neighbouring chains and antiferromagnetically aligned with two others. © 2007 Elsevier Inc. All rights reserved

Investigation of the stability of Co-doped apatite ionic conductors in NH3

Hydrogen powered solid oxide fuel cells (SOFCs) are of enormous interest as devices for the efficient and clean production of electrical energy. However, a number of problems linked to hydrogen production, storage and transportation are slowing down the larger scale use of SOFCs. Identifying alternative fuel sources to act as intermediate during the transition to the full use of hydrogen is, therefore, of importance. One excellent alternative is ammonia, which is produced on a large scale, is relatively cheap and has the infrastructure for storage and transportation already in place. However, considering that SOFCs operate at temperatures higher than 500°C, a potential problem is the interaction of gaseous ammonia with the materials in the cathode, anode and solid electrolyte. In this paper, we extend earlier work on high temperature reactions of apatite electrolytes with NH3 to the transition metal (Co) doped systems, La9.67Si5CoO26 and La10(Si/Ge)5CoO26.5. A combination of PXRD, TGA and XAFS spectroscopy data showed a better structural stability for the silicate systems. Apatite silicates and germanates not containing transition metals tend to substitute nitride anions for their interstitial oxide anions, when reacted with NH3 at high temperature and, consequentially, lower the interstitial oxide content. In La9.67Si5CoO26 and La10(Si/Ge)5CoO26.5 reduction of Co occurs as a competing process, favouring lower levels of nitride-oxide substitution

Time-resolved studies of diffusion via energy dispersive X-ray absorbtion spectroscopy.

The challenges facing the application of X-ray absorption spectroscopy to the study of electrochemically initiated processes in solution are discussed. The results from a feasibility study of the diffusion of Cu2+ from a planar electrode are described. These show that millisecond time resolution can be achieved at a 3rd generation source, but delivery of the full potential of the experiment rests upon the availability of suitable detectors. Keywords: Energy dispersive EXAFS, Electrochemical cell, Diffusion, Copper, Platinu

Stereostructural behaviour of N–N atropisomers:two conglomerate crystallisations and a crystallisation-induced deracemisation

The solid state behaviour of a number of compounds which show hindered rotation around an N–N bond, in some cases leading to axial chirality is described. A diacyl hydrazine, bisanthranoly hydrazine, 1 crystallises in the chiral space group P212121, presenting an example of conglomerate crystallisation. A tetra-acyl hydrazine derived from lactic acid, 2, shows kinetic resolution by crystallisation, as of the two isomers observed in the solution NMR, only one crystallises, again in the space group P212121. Two cyclic acyl hydrazines in the form of biquinazolinones are studied: 2,2′diphenyl-3,3-biquinazolinone, 3 crystallises in the achiral space group Pbca, while 3,3′-dimethyl-2,2′-biquinazoline-4′-thio-4-one, 4 crystallises in the chiral space group P21 giving another example of a conglomerate crystallisation. The single crystal structures of each of the species have been compared to powder XRD data to confirm that the single crystal structures are representative of the bulk material

Using high pressure to prepare polymorphs of the Ba2Co1-xZnxS3(0 ≤ x ≤ 1.0) compounds

In this work, high pressure was used as a tool to induce structural transition and prepare metastable polymorphs of ternary sulfides. Structural transformations under high pressure of compounds belonging to the Ba 2 Co 1-x Zn x S 3 (0 ≤ x ≤ 1.0) series were studied using X-ray diffraction and electron microscopy. All members of the Ba 2 Co 1-x Zn x S 3 series show the Ba 2 CoS 3 -type one-dimensional structure, but, after heating under pressure, the Ba 2 CoS 3 compound (x = 0) separates into BaS and the two-dimensional BaCoS 2-δ (δ ≈ 0), while Ba 2 Co 1-x Zn x S 3 compounds with x ≥ 0.25 maintain their one-dimensional features but rearrange into polymorphs showing the Ba 2 MnS 3 -type structure. All structural transformations can be linked to shortening in interchain metal-metal distances caused by the high pressure, and the role of the zinc in preventing loss of one-dimensionality is discussed. © 2011 American Chemical Society