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

The single crystals of four kinds of metal nitride halides, -MNX (M=Zr, Hf; X=Br, I), were prepared in Pt (or Au) capsules by the reaction of MN or -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) ?, c=29.270(5) ? for -ZrNBr, a=3.718(2) ?, c=31.381(9) ? for -ZrNI, a=3.610 (1) ?, c=29.294(6) ? for -HfNBr, and a=3.689(1) ?, c=31.329(6) ? for -HfNI. -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: XAMcNBNCMbXAXCMbNANBMaXCXBMaNCNAMcXB in the SmSI-type and XAMbNCNBMcXAXCMaNBNAMbXCXBMcNANCMaXB in the YOF-type polymorphs.