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Transition-metal oxynitrides with perovskite-type structures are an emerging class of materials with optical, photocatalytic, dielectric and magnetoresistive properties that may be sensitive to oxide-nitride order, but the anion-ordering principles were unclear. Here we report an investigation of the representative compounds SrMO2N (M = Nb, Ta) using neutron and electron diffraction. This revealed a robust 1O/2(O0.5N0.5) partial anion order (up to at least 750 °C in the apparently cubic high-temperature phases) that directs the rotations of MO4N2 octahedra in the room-temperature superstructure. The anion distribution is consistent with local cis-ordering of the two nitrides in each octahedron driven by covalency, which results in disordered zigzag M-N chains in planes within the perovskite lattice. Local structures for the full range of oxynitride perovskites are predicted and a future challenge is to tune properties by controlling the order and dimensionality of the anion chains and networks. [ABSTRACT FROM AUTHOR]

Knowledge of the kinetic and thermodynamic behaviour of aqueous solutions containing two divalent cations and trans-1,2-cyclohexanediaminetetraacetate has been used to design synthetic pathways to ordered bimetallic complexes [ABSTRACT FROM AUTHOR]

Polymetallic solid solutions of the ethylenediaminetetracetic acid (EDTA) and six divalent metal ions exist in the range: MgMnCoZnNiCu(EDTA) · 6HO where α + β + γ + δ + ε + τ=2, 0⩽τ⩽1, 0⩽γ,ε,δ⩽2, 0⩽α, β⩽1. This type of structure is characterized by the presence of two different octahedral carboxylate-bridged coordination sites forming infinite zig-zag chains. Visible and i.r. spectra and t.g.a. analysis show that there is occupational preference for the two coordination sites in the crystalline structure. Due to this preference, and also to the structural features, the heterobimetallic MM′(EDTA) · 6HO compounds constitute a structurally new class of materials which can be described as ordered alternating-heterobimetallic polymeric coordination complexes. [ABSTRACT FROM AUTHOR]