MATERIALS WITH LAYERED STRUCTURES - CRYSTAL-STRUCTURE OF ZN1.25IN2.5S3SE2, A NEW POLYTYPE OF ZN2IN2S5 AND THE ISOTYPIC COMPOUNDS CD0.5GA2INS5 AND HG0.8GA1.6IN1.2S5

The crystal structure of Zn//1//. //2//5In//2//. //5S//3Se//2 was determined from single crystal data. The compound crystallizes in the trigonal space group P OVER BAR 3m1-D**3//3//d (No. 164) with Z equals 2. The lattice constants (hexagonal setting) are a equals 3. 927(1) and c equals 31. 83(1) Angstrom. The structure is of a layer type and may be described as a slightly distorted hexagonal closed packing of the anions with two In**3** plus in octahedral voids and all other cations in tetrahedral coordination. The isotypic compounds Cd//0//. //5Ga//2InS//5 and Hg//0//. //8Ga//1//. //6In//1//. //2S//5 have lattice parameters a equals 3. 809(1), c equals 30. 64(1) Angstrom, and a equals 3. 820(1), c equals 30. 929(3) Angstrom, respectively.