Structural chemistry and magnetic properties of the compounds EuOs4B4 and EuIr4B4 and of the solid solutions (RE)Os4B4-(RE)Ir4B4(RE = Ce, Pr, Sm)

New ternary metal borides, EuOs4B4 and EuIr4B4, have been synthesized from the elements. The compounds were found to crystallize with the structure type of NdCo4B4. Effective paramagnetic moments derived from chi-1vs. T plots over the range 1.8-800 K are in good agreement with theoretical values according to a Hund's rule ground-state 8S/sub 1/2/ for a free Eu2+ ion. Complete solid solution was found for mixed crystals of CeOs4B4-CeIr4B4 (arc melted, quenched, NdCo4B4-type structure) revealing a positive deviation from Vegard's law. Magnetic susceptibilities were determined for the temperature range 1.8-1000 K. At high temperature the magnetic properties are characterized by Van Vleck paramagnetism of closely spaced multiplets due to admixture of the excited term J = 7/2 of the Ce3+F5/2 ground state. At lower temperatures the paramagnetic behavior of cerium changes from that of a practically pure Ce4+ state in CeOs4B4 (μ/sub eff/ = 0.49 μβ) to that of a pronounced Ce3+ state in CeIr4B4 (μ/sub eff/ = 2.21 μβ) presumably due to the larger iridium metal framework and/or the higher electron-to-atom ratio. At very low temperatures, less than or equal to 3.5 K, ferromagnetic ordering was observed for CeIr4B4 and CeIr3Os1B4. For comparison, the magnetic behavior was studied over the range 1.5-300 K of the pseudobinary sections PrOs/sub 4-x/Ir/sub x/B4 and SmOs/sub 4-x/Ir/sub x/B4. Although a slight negative deviation from Vegard's law was observed, there was practically no change from a valence state of Sm3+ for samarium. On the basis of Miedema's model, a thermodynamic calculation for the valence change (Ce/sup III/ → Ce/sup IV/, Eu/sup II/ → Eu/sup III/) has been found to be in good accord with the magnetic behavior observed. 7 figures, 4 tables