LAPD2O4, A NOVEL MIXED-VALENT OXOPALLADATE

A novel ternary oxide of palladium, LaPd2O4, has been synthesized by t he solid-state reaction of La2O3 and PdO, apply high pressure (2 GPa) and KClO3 as an oxidizing agent. The black crystals of LaPd2O4 belong to space group I4(1)/a of the tetragonal crystal system with four form ula units per unit cell which has the dimensions a = 5.9140(5) Angstro m and c = 10.289(1) Angstrom. The crystal structure (determined and re fined to a final R value of 2.48% using 392 unique reflections) consis ts of square planar PdO4 units which are stacked to form columnar arra ngements along [1 0 0] and [0 1 0], respectively. Despite the oxidatio n state of 2.5, the palladium atoms occupy the same crystallographic s ite and thus are structurally indistinguishable. Consequently, LaPd2O4 has to be classified as mixed valent of type III according to Robin a nd Day (Adv. Inorg. Chem. Radiochem. 10, 247 (1967)). Lanthanum is coo rdinated dodecahedrally by eight oxygen atoms. The structural relation ship between LaPd2O4 and lanthanum palladates described previously is discussed. The title compound shows temperature-independent paramagnet ism down to 5 K. (C) 1995 Academic Press, Inc.