  The structures of the new compound La1.2Sr2.7IrO7+d and the recently
discovered La1.2Sr2.7RuO7+d have been solved using a combination of X-ray and
neutron diffraction. Both compounds crystallize in the trigonal space group
R-3m and contain isolated MO6 (M=Ru,Ir) octahedra, which are arranged in
well-defined layers. Results of the magnetic susceptibility and XANES
measurements show that the transition metal cations are in a pentavalent state.
While in La1.2Sr2.7RuO7+d an antiferromagnetic interaction between the Ru5+
ions is found, La1.2Sr2.7IrO7+d shows a very small temperature-independent
paramagnetism down to 1.8 K due to the strong spin-orbit coupling
characteristic for the 5d element iridium.
