High-pressure synthesis and crystal structures of β-MNCl (M = Zr and Hf)

The single crystals of two kinds of metal nitride halides, beta -ZrNCl and beta -HfNCl, have been grown for the first time in the presence of NH4Cl under a high pressure of 3 GPa at 900 degreesC and 1200 degreesC, respectively, Their crystal structures have been refined on the basis of X-ray four-circle diffractometer data. beta -ZrNCl crystallizes in the rhombohedral space group R-3m; 3.6046(4) Angstrom, 27.672(4) Angstrom, and Z = 6; R1/wR2 = 0.0270/0.0751 for 447 observed reflections and 11 variables, For the isostructural compound beta -HfNCl, a = 3.5767(8) Angstrom, c = 27.711(7) Angstrom; 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 c-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 ClAMcNBNCMbClA| ClCMbNANBMaClC|ClBMaNCNAMcClB. This is the first single-crystal study on the layered nitride halides MNX (M = Zr, I-If; X = Cl, Br, I) which recently have gained considerable interest because of the superconductivity caused by alkali metal intercalation. (C) 2001 Academic Press