High-Pressure Synthesis and Crystal Structures of β-MNX (M=Zr, Hf; X=Br, I)

Abstract

The single crystals of four kinds of metal nitride halides, β-MNX (M=Zr, Hf; X=Br, I), were prepared in Pt (or Au) capsules by the reaction of MN or α-MNX powders with NH4X as fluxes under a high pressure of 3–5 GPa at 1000–1100°C. Their crystal structures were determined by single-crystal X-ray diffraction techniques. All four compounds crystallize in a rhombohedral space group R-3m, Z=6 with a=3.6403(6) Å, c=29.270(5) Å for β-ZrNBr, a=3.718(2) Å, c=31.381(9) Å for β-ZrNI, a=3.610(1) Å, c=29.294(6) Å for β-HfNBr, and a=3.689(1) Å, c=31.329(6) Å for β-HfNI. β-ZrNBr is isotypic with SmSI and the others are isotypic with YOF. Both structure variants are composed of structural slabs [X–M–N–N–M–X] (M=Zr, Hf; X=Br, I) stacked together by X…X van der Waals forces, but the ways of the layer stacking sequence are different: XAMcNBNCMbXA∣XCMbNANBMaXC∣XBMaNCNAMcXB∣ in the SmSI-type and XAMbNCNBMcXA∣XCMaNBNAMbXC∣XBMcNANCMaXB∣ in the YOF-type polymorphs.