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

Abstract

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 [Cu 2 Cl(OH) 3 ] with space group P 2 1 / m and unit-cell parameters a = 5.6883(5), b = 6.3908(6), c = 5.5248(5) A, β = 90.832(2)°, V = 200.82(3) A 3 . The crystal structure of CuZnCl(OH) 3 , refined to R 1 = 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 Cu 2+ in the highly angle-distorted M1 site by non-Jahn-Teller distorting Zn 2+ . 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 Cu 2 Cl(OH) 3 polymorphs, to the substitution of Zn 2+ for Cu 2+ , even in the presence of large excess of Zn 2+ . 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 Cu M Cl(OH) 3 ( M = Ni 2+ , Co 2+ , Fe 2+ , Mn 2+ , Cd 2+ , and Mg 2+ ) may be synthesized or found in nature.