Synthesis and Characterization of Eight Compounds of the MU_8Q_(17) Family: ScU_8S_(17), CoU_8S_(17), NiU_8S_(17), TiU_8Se_(17), VU_8Se_(17), CrU_8Se_(17), CoU_8Se_(17), and NiU_8Se_(17)

摘要

The solid-state MU_8Q_(17) compounds ScU_8S_(17), CoU_8S_(17), NiU_8S_(17), TiU_8Se_(17), VU_8Se_(17), CrU_8Se_(17), CoU_8Se_(17), and NiU_8Se_(17) were synthesized from the reactions of the elements at 1173 or 1123 K. These isostructural compounds crystallize in space group C_(2h)~3 - C2/m of the monoclinic system in the CrU_8S_(17) structure type. Xray absorption near-edge structure spectroscopic studies of ScU_8S_(17) indicate that it contains Sc~(3+), and hence charge balance is achieved with a composition that includes U~(3+)as well as U~(4+). The other compounds charge balance with M~(2+) and U~(4+). Magnetic susceptibility measurements on ScU_8S_(17) indicate antiferromagnetic couplings and a highly reduced effective magnetic moment. Ab Initio calculations find the compound to be metallic. Surprisingly, the Sc-S distances are actually longer than all the other M-S interactions, even though the ionic radii of Sc~(3+), low-spin Cr~(2+), and Ni~(2+) are similar.