The structure of gillardite, the Ni-analogue of herbertsmithite, from Widgiemooltha, Western Australia

The structure of gillardite, the Ni-analogue [ideally Cu3NiCl2(OH)6] of herbertsmithite [ideally Cu3ZnCl2(OH)6] has been determined at 273(2) K. The crystal used was removed from a sample from the 132N nickel deposit at Widgiemooltha, Western Australia, Australia. Seventeen electron-microprobe analyses gave compositions, based on a total of four cations per formula unit, that ranged from (Cu3.189Ni0.803Co0.002Fe0.006)Cl2(OH)6 to (Cu2.922Ni1.058Co0.020)Cl2(OH)6, with an average result of all analyses of (Cu3.081Ni0.903Co0.012Fe0.004)Cl2(OH)6. The structure was refined using site occupancies indicated by the average composition, although refinement using the ideal composition gave identical results within standard errors. The new species gillardite is trigonal (rhombohedral), space group Rm, with a 6.8364(1), c 13.8459(4) Ã, Z = 3. The oxysalt is isostructural with herbertsmithite, with the two different sites in the paratacamite-type structure being occupied by different cations [paratacamite is Cu4Cl2(OH)6, space group R with a pronounced Rm substructure]. In gillardite, the Cu site is strongly Jahn–Teller-distorted, and the Ni site is regular with respect to Ni–O bond lengths, but with a slight angular distortion from regular octahedral geometry