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Abstract

Na3OSO5 has been synthesized by solid state reaction of Na2O2 and
osmium powder under a flow of oxygen. Na3OSO5 crystallizes trigonal in
space group P3(1)21 with a = 5.5529(2) angstrom, c = 13.4726(8)
angstrom, V = 359.77(3) angstrom(3), Z = 3, 958 independent
reflections, R-1 = 1,97 %, wR(2) =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 5d(1) system has been
successfully described in the temperature range 50-330 K accounting for
strong spin-orbit coupling, ligand-field potential of D-3h symmetry
(corresponding to the trigonal bipyramidal OSO53- unit), and
cooperative magnetic effects (molecular field parameter lambda(MF)).