LaPd 2O 4, a Novel Mixed Valent Oxopalladate

A novel ternary oxide of palladium, LaPd 2O 4, has been synthesized by the solid-state reaction of La 2O 3 and PdO, apply high pressure (2 GPa) and KClO 3 as an oxidizing agent. The black crystals of LaPd 2O 4 belong to space group I 4 1/ a of the tetragonal crystal system with four formula units per unit cell which has the dimensions a = 5.9140(5) Å and c = 10.289(1) Å. The crystal structure (determined and refined to a final R value of 2.48% using 392 unique reflections) consists of square planar PdO 4 units which are stacked to form columnar arrangements along [1 0 0] and [0 1 0], respectively. Despite the oxidation state of 2.5, the palladium atoms occupy the same crystallographic site and thus are structurally indistinguishable. Consequently, LaPd 2O 4 has to be classified as mixed valent of type III according to Robin and Day ( Adv. Inorg. Chem. Radiochem. 10, 247 (1967)). Lanthanum is coordinated dodecahedrally by eight oxygen atoms. The structural relationship between LaPd 2O 4 and lanthanum palladates described previously is discussed. The title compound shows temperature-independent paramagnetism down to 5 K.