Crystal structure of Ni(NH3)Cl2 and Ni(NH3)Br2

Abstract

Ni(NH3)Cl2 and Ni(NH3)Br2 were prepared by the reaction of Ni(NH3)2X2 with NiX2 at 350°C in a steel autoclave. The crystal structures were determined by X-ray powder diffraction using synchrotron radiation and refined by Rietveld methods. Ni(NH3)Cl2 and Ni(NH3)Br2 are isotypic and crystallize in the space group I2/m with Z = 8 and for Ni(NH3)Cl2: a = 14.8976(3) Å, b = 3.56251(6) Å, c = 13.9229(3) Å, β= 106.301(1)°; Ni(NH3)Br2: a = 15.5764(1) Å, b = 3.74346(3) Å, c = 14.4224(1) Å, β= 105.894(1)°. The crystal structures are built up by two crystallographically distinct but chemically mostly equivalent polymeric octahedra double chains 1∞[NiX3/3X2/2(NH3)] (X = Cl, Br) running along the short b-axis. The octahedra NiX5NH3 share common edges therein. The crystal structures of the ammines Ni(NH3)mX2 with m = 1, 2, 6 can be derived from that of the halides NiX2 (X = Cl, Br) by successive fragmentation of its CdCl2 like layers by NH3.