High-Pressure Synthesis and Crystal Structures of beta-MNCl (M=Zr and Hf)

The single crystals of two kinds of metal nitride halides, -ZrNCl and -HfNCl, have been grown for the first time in the presence of NH4Cl under a high pressure of 3 GPa at 900°C and 1200°C, respectively. Their crystal structures have been refined on the basis of X-ray four-circle diffractometer data. -ZrNCl crystallizes in the rhombohedral space group R-3m; a=3.6046(4) ?, c=27.672(4) ?, and Z=6; R1/wR2=0.0270/0.0751 for 447 observed reflections and 11 variables. For the isostructural compound -HfNCl, a=3.5767(8) ?, c=27.711(7) ?; R1/wR2=0.0372/0.0979 for 454 observed reflections. The compounds are isotypic with SmSI and composed of structural slabs [Cl–M–N–N–M–Cl] (M=Zr, Hf) with close-packed anion layers. Three of those slabs are stacked rhombohedrally in the unit cell along the -axis and held together by Cl...Cl van der Waals interactions. The metal atoms (M) are placed in the octahedral sites between the Cl and N layers, leading to the overall layer sequence of ClAMcNBNCMbClAClCMbNANBMaClCClBMaNCNAMcClB. This is the first single-crystal study on the layered nitride halides MNX (M=Zr, Hf; M=Cl, Br, I) which recently have gained considerable interest because of the superconductivity caused by alkali metal intercalation.