Crystal structure of a new compound, CuZnCl(OH)3, isostructural with botallackite

Title of Publication: 
Crystal structure of a new compound, CuZnCl(OH)3, isostructural with botallackite
Yang, Hexiong, Barton, Isabel F., Andrade, Marcelo B., and Downs, Robert T.
Publication Info: 
American Mineralogist, Volume 101, pages 986–990, 2016

A new compound, ideally CuZnCl(OH)3, was found on a metallic mining artifact of copper composition at the Rowley mine, Maricopa County, Arizona, U.S.A., and studied with electron microprobe analysis, single-crystal X‑ray diffraction, and Raman spectroscopy. It is isostructural with botallackite [Cu2Cl(OH)3] with space group P21/m and unit-cell parameters a = 5.6883(5), b = 6.3908(6), c = 5.5248(5) Å, β = 90.832(2)°, V = 200.82(3) Å3. The crystal structure of CuZnCl(OH)3, refined to R1 = 0.018, is characterized by brucite-type octahedral sheets made of two distinct and considerably distorted octahedra, M1 and M2, which are coordinated by (5OH + 1Cl) and (4OH + 2Cl), respectively. The octahedral sheets are parallel to (100) and connected by O–H∙∙∙Cl hydrogen bonding. The major structural difference between CuZnCl(OH)3 and botallackite is the complete replacement of Cu2+ in the highly angle-distorted M1 site by non-Jahn-Teller distorting Zn2+. The CuZnCl(OH)3 compound represents the highest Zn content ever documented for the atacamite group of minerals, in conflict with all previous reports that botallackite (like atacamite) is the most resistant, of all copper hydroxylchloride Cu2Cl(OH)3 polymorphs, to the substitution of Zn2+ for Cu2+, even in the presence of large excess of Zn2+. Its discovery, along with the recently described new mineral iyoite, CuMnCl(OH)3, implies that more botallackite-type compounds or minerals with the chemical formula CuMCl(OH)3 (M = Ni2+, Co2+, Fe2+, Mn2+, Cd2+, and Mg2+) may be synthesized or found in nature.

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Figure 1. Backscattered electron image of the CuZnCl(OH)3 crystals.