Zr2Fe12As7 and Hf2+xFe12−yAs7 with Zr2Fe12P7 type structure: Iron arsenides with layered sections from LiFeAs structure

• We synthesized two new ternary iron arsenides.
• Structure solution indicated relations to iron arsenide superconductors.
• We characterized one title compound with electrical resistivity and magnetization measurements.

The new compound Zr2Fe12As7 was prepared from the elements at 1110 °C. Zr2Fe12As7 crystallizes in the hexagonal Zr2Fe12P7 structure type (space group P6¯, a = 952.10(7) pm, c = 373.24(2) pm, V = 293.01 · 106 pm³, R1 = 0.031, wR2 = 0.077) with one formula unit in the hexagonal unit cell. The structure can be viewed as formed by chemical twinning from slabs occurring in many superconducting alkali, alkaline-earth and rare-earth metal iron pnictides. Zr2Fe12As7 shows Curie-paramagnetism and a metal-like electrical conductivity. The formation and particularly crystal growth of an analogues Hf compound requires higher temperatures of 1350 °C, which additionally provoke partial substitution of Fe by Hf in Hf2+xFe12–yAs7 (x = 1.6(2), y   = 3, space group P6¯, a = 951.1(1) pm, c = 370.39(3) pm, V = 290.17 · 106 pm³, R1 = 0.044, wR2 = 0.097).

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