The family of iron arsenide superconductors is expanded by the new iron platinum compounds (CaFe1−xPtxAs10)Pt4−yAs8 with novel crystal structures. Layers of FeAs4/4 tetrahedra and of nearly planar PtAs4/2 squares with (As2)4− dumbbells are stacked in different ways, resulting in polytypes with triclinic or tetragonal symmetry. Superconductivity up to 35 K is induced either by Pt doping of the Fe site or by electron transfer from PtAs to FeAs layers.

We report the structural and magnetic phase transitions of triclinic Ca10(FeAs)10(Pt3As8), which is the parent compound of the 1038-type iron-arsenide superconductors. High-resolution x-ray diffraction reveals splitting of the in-plane (a,b) lattice parameters at T(s) ≈ 120 K. Platinum-doping weakens the distortion and shifts the transition temperature to 80 K in Ca10(Fe(1-x)Pt(x)As)10(Pt3As8) with x = 0.03. μSR experiments show the onset of magnetic order near T and a broad magnetic phase transition. The structural transition involves no reduction of the space group symmetry in contrast to the other parent compounds of iron-arsenide superconductors; nevertheless the local fourfold symmetry of the FeAs-layers in Ca10(FeAs)10(Pt3As8) is broken.

The topochemical deintercalation of Na(+) ions from solid NaFeAs at room temperature in THF with iodine yields the superconducting phase Na(1-y)Fe(2-x)As(2) (T(c) ≈ 11 K). This metastable iron arsenide decomposes at 120 °C and is not accessible by high-temperature solid-state synthesis. X-ray powder diffraction confirms the ThCr(2)Si(2)-type structure, but reveals very small coherently scattering domains with a mean composition Na(0.9(2))Fe(1.7(1))As(2). HRTEM investigations show crystalline as well as strongly distorted areas with planar defects. The latter are probably due to sodium loss and disorder which is also detected by (23)Na solid state NMR. The (57)Fe-Mössbauer spectrum of Na(1-y)Fe(2-x)As(2) shows one type of iron atoms in tetrahedral coordination. All results point to one crystallographic phase with very small domains due to fluctuations of the chemical composition. From electronic reasons we suggest the superconducting phase is presumably NaFe(2)As(2) in the ordered fractions of the sample.

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Dinitrogen (N2) ligation is a common and well-characterized structural motif in bioinorganic synthesis. In solid-state chemistry, on the other hand, homonuclear dinitrogen entities as structural building units proved existence only very recently. High-pressure/high-temperature (HP/HT) syntheses have afforded a number of binary diazenides and pernitrides with [N2](2–) and [N2](4–) ions, respectively. Here, we report on the HP/HT synthesis of the first ternary diazenide. Li2Ca3[N2]3 (space group Pmma, no. 51, a = 4.7747(1), b = 13.9792(4), c = 8.0718(4) Å, Z = 4, wRp = 0.08109) was synthesized by controlled thermal decomposition of a stoichiometric mixture of lithium azide and calcium azide in a multianvil device under a pressure of 9 GPa at 1023 K. Powder X-ray diffraction analysis reveals strongly elongated N–N bond lengths of dNN = 1.34(2)–1.35(3) Å exceeding those of previously known, binary diazenides. In fact, the refined N–N distances in Li2Ca3[N2]3 would rather suggest the presence of [N2](3·–) radical ions. Also, characteristic features of the N–N stretching vibration occur at lower wavenumbers (1260–1020 cm(–1)) than in the binary phases, and these assignments are supported by first-principles phonon calculations. Ultimately, the true character of the N2 entity in Li2Ca3[N2]3 is probed by a variety of complementary techniques, including electron diffraction, electron spin resonance spectroscopy (ESR), magnetic and electric conductivity measurements, as well as density-functional theory calculations (DFT). Unequivocally, the title compound is shown to be metallic containing diazenide [N2](2–) units according to the formula (Li(+))2(Ca(2+))3([N2](2–))3·(e(–))2.