THE CRYSTAL-STRUCTURE OF TLZNPO4 AND TLZN ASO4

Single crystals of the title compounds were obtained by high pressure synthesis in a modified Belt type apparatus. The compounds crystallize in the monoclinic system (space group P2(1)) with a = 8.732(2), b = 5 .468(1), c = 8.841(2)Angstrom, beta = 90.61(2)degrees for TlZnPO4 and a = 8.921(3), b = 5.631(1), c = 8.958(3)Angstrom, beta = 91.03(2)degre es for TlZnAsO4, Z = 4. The structures were refined from diffractomete r data to R = 0.072, R(w) = 0.050 for 3700 (TlZnPO4) and to R = 0.093, R(w) = 0.067 for 3943 (TlZnAsO4) independent absorption corrected ref lections. The compounds are isotypic and belong to the ''stuffed deriv atives'' of the Icmm structure type with a (ZnXO(4))(-) network of alt ernating corner linked ZnO4 and XO(4) tetrahedra (X = P, As) forming c hannels of six-membered rings in the direction of the a axis. These ca vities contain two crystallographically independent Tl cations in an i rregular coordination by eight nearest oxygen atoms.