Ternary arsenides Zr(SixAs1−x)As with PbCl2-type (0 ≤ x ≤ 0.4) and PbFCl-type (x = 0.6) structures

The ternary zirconium silicon arsenides Zr(SixAs1−x)As have been prepared through reaction of the elements at 900 °C. Extensive solubility of Si in the parent binary arsenide ZrAs2 was established in the form of the solid solution Zr(SixAs1−x)As (0 ≤ x ≤ 0.4). Single-crystal X-ray structure determination of the end-member Zr(Si0.39(1)As0.61)As (orthorhombic PbCl2-type, space group Pnma, Z = 4, a = 6.6828(8) Å, b = 3.6377(4) Å, c = 9.1131(11) Å, V = 221.54(4) Å3) revealed that the Si atoms prefer to occupy the interior sites of a four-atom-wide polyanionic ribbon. When the Si composition is increased to x = 0.6, the new ternary arsenide Zr(Si0.57(1)As0.43)As was identified (tetragonal PbFCl-type, space group P4/nmm, Z = 2, a = 3.6539(7) Å, c = 8.2399(15) Å, V = 110.01(4) Å3), in which the Si atoms prefer to occupy the sites of a denser polyanionic square net. Core-line X-ray photoelectron spectra measured on metallic, plate-shaped crystals of Zr(Si0.6As0.4)As support the presence of anionic Si and As atoms. Band structure calculations on idealized ordered models of Zr(Si0.5As0.5)As suggest that a competition between Zr-anion and anion–anion bonding interactions takes place in both structures.