La(3)Cu(2)Vo(9): A surprising variation on the YAlO3 structure-type with 2D copper clusters of embedded triangles

La3Cu2VO9 crystallizes in a heretofore unknown superstructural variation of the rare-earth hexagonal structure (P6(3)/mmc) for ABO(3) stoichiometries as characterized by X-ray, neutron and electron diffraction. The alternatin g hexagonal layers of LaO6/3 and (Cu/V)O-3/3 resemble those of YAlO3, excep t that the copper and vanadium order to create an a root 13 x a root 13 x c supercell with P6(3)/m symmetry. The B-cation coordination environments ac commodate copper and vanadium in a two to one molar ratio. The Cu-II lattic e consists of nine atom clusters of triangles in triangles similar to a kag ome lattice. The phase is paramagnetic from 5 to 370 K with three temperatu re regimes that correspond closely to 1/9, 4/9, and 9/9 spins per copper. ( C) 2001 Editions scientifiques et medicales Elsevier SAS. All rights reserv ed.