Leiteite, ZnAs ₂ O ₄ ; a novel type of tetrahedral layer structure with arsenite chains

Leiteite, ZnAs₂O₄, from Tsumeb, Namibia, is monoclinic, a = 4.542(1), b = 5.022(1), c = 17.597(5) Å, β = 90.81(3)°, space group P2₁/c, Z = 2. The crystal structure has been determined by direct methods and refined by the method of least squares to an R factor of 0.048 based on 731 independent reflections measured on an automatic single-crystal X-ray diffractometer. The crystal structure consists of open Zn tetrahedral sheets flanked by single arsenite chains on either side. The composite layers are cross-linked through weak (2.8-3.3 Å) As-O bonds. Leiteite represents a new structure type. The average tetrahedral Zn-O distance is 1.99 Å, and the average As-O distances and O-As-O angles in the two distinct trigonal pyramidal arsenite groups are 1.79 Å, 95.5° for As(l) and 1.78 Å, 95.8° for As(2).