Synthesis, Crystal Structure and Magnetic Properties of Na3OsO5

Abstract

AbstractNa3OsO5 has been synthesized by solid state reaction of Na2O2 and osmium powder under a flow of oxygen. Na3OsO5 crystallizes trigonal in space group P3121 with a = 5.5529(2) Å, c = 13.4726(8) Å, V = 359.77(3) Å3, Z = 3, 958 independent reflections, R1 = 1,97 %, wR2 = 4.27 %. The crystal structure consists of OsO5 trigonal bipyramids separated by sodium cations, and is isostructural to Na3ReO5. The osmium atoms adopt a packing analogous to ccp, where Na occupies the octahedral and tetrahedral vacancies, so the cation structure is derived from the Li3Bi structure type. Features of the synthesis of Na3OsO5 and related osmates are discussed. Na3OsO5 shows paramagnetic behaviour down to 25 K where it orders antiferromagnetically. Below 7 K a weak ferromagnetic contribution is detected. The paramagnetic region of the 5d1 system has been successfully described in the temperature range 50 – 330 K accounting for strong spin‐orbit coupling, ligand‐field potential of D3h symmetry (corresponding to the trigonal bipyramidal $\rm OsO^{3-}_{5}$ unit), and cooperative magnetic effects (molecular field parameter λMF).