THE CALCIUM THALLATE CA3TL2O6, 3RD MEMBER OF THE SERIES CANTL2ON+3

A new calcium thallate, Ca3Tl2O6 has been synthesized. It crystallizes in the space group Pbam with a = 11.248(2) Angstrom, b = 16.513(2) An gstrom, and c = 3.3329(3) Angstrom. The ab initio determination of its structure from powder X-ray data shows that it consists of zigzag roc k-salt-type layers [Ca4Tl4O14](infinity) parallel to (010), built up f rom quadruple ribbons of TlO6 octahedra running along c, interconnecte d with single and double ribbons of CaO6 octahedra. Along b, these roc k-salt-type layers share the corners of their octahedra forming tunnel s approximately similar to those observed in CaTi2O4, where calcium io ns are located with a monocapped trigonal prismatic coordination. This oxide represents the third member of the series CanTl2On+3; its relat ionships with the two n = 1 and 2 members CaTl2O4 and Ca2Tl2O5, that c orrespond to a chemical twinning of the rock salt structure, are discu ssed. In fact Ca3Tl2O6 is isostructural with Ca3In2O6. (C) 1995 academ ic Press, Inc.