Competition between Anion-Deficient Oxide and Oxyhydride Phases during the Topochemical Reduction of LaSrCoRuO 6 .

Binary metal hydrides can act as low-temperature reducing agents for complex oxides in the solid state, facilitating the synthesis of anion-deficient oxide or oxyhydride phases. The reaction of LaSrCoRuO 6 , with CaH 2 in a sealed tube yields the face-centered cubic phase LaSrCoRuO 3.2 H 1.9 . The reaction with LiH under similar conditions converts LaSrCoRuO 6 to a mixture of tetragonal LaSrCoRuO 4.8 H 1.2 and cubic LaSrCoRuO 3.3 H 2.13 . The formation of the LaSrCoRuO x H y oxyhydride phases proceeds directly from the parent oxide, with no evidence for anion-deficient LaSrCoRuO 6- x intermediates, in contrast with many other topochemically synthesized transition-metal oxyhydrides. However, the reaction between LaSrCoRuO 6 and LiH under flowing argon yields a mixture of LaSrCoRuO 5 and the infinite layer phase LaSrCoRuO 4 . The change to all-oxide products when reactions are performed under flowing argon is attributed to the lower hydrogen partial pressure under these conditions. The implications for the reaction mechanism of these topochemical transformations is discussed along with the role of the hydrogen partial pressure in oxyhydride synthesis. Magnetization measurements indicate the LaSrCoRuO x H y phases exhibit local moments on Co and Ru centers, which are coupled antiferromagnetically. In contrast, LaSrCoRuO 4 exhibits ferromagnetic behavior with a Curie temperature above 350 K, which can be rationalized on the basis of superexchange coupling between the Co 1+ and Ru 2+ centers.