CRYSTAL-STRUCTURES AND MAGNETIC-PROPERTIES OF BA4RU3O10 AND BA5RU3O12

The study of the solid state reactions in air or oxygen of the ternary system Ba-Ru-O shows the existence of the new compounds Ba4Ru3O10 and Ba5Ru3O12. The crystal symmetry of Ba4Ru3O10 is monoclinic (P2(1)/a) with the unit cell constants a = 5.776(1) Angstrom, b = 13.076(1) Angs trom, c = 7.234(2) Angstrom and beta = 113.53(3)degrees. Ba4Ru3O10 is isostructural with Ba4Ir3O10 and the structure consists of trinuclear groups [Ru3O12] of face-sharing octahedra two-dimensionally connected via terminal corners to form [Ru3O10] zig-zag layers. The magnetic pro perties confirm the oxidation state (Ru4+) of ruthenium. Ba5Ru3O12 is isostructural With Ba-5(Ir1.5Ru1.5)O-12 with the cell parameters a = 1 0.862(1) Angstrom, b = 5.893(1) Angstrom and c = 19.790(2) Angstrom (P nma). The crystal structure was refined on the basis of a single cryst al in which part of the ruthenium was replaced by platinum. The struct ure consists of isolated [Ru3O12] trimeric groups separated by barium atoms. Valence bond calculation confirms that the electronic charges a re localized, and the magnetic behaviour is interpreted in terms of an tiferromagnetic isolated trimeric units.