Synthesis, crystal structure, and properties of the nitridosilicates SrYbSi4N7 and BaYbSi4N7

Pure SrYbSi4N7 and BaYbSi4N7 were obtained by reaction of silicon diimide with metallic strontium/barium and ytterbium. The reactions have been carried out under nitrogen atmosphere in a high-frequency furnace at 1650 degrees C. SrYbSi4N7 (P6(3)mc, a = 598.80(3), c = 974.99(9) pm, Z = 2, R1 = 0.023, wR2 = 0.038) and BaYbSi4N7 (P6(3)mc, a = 603.07(2), c = 981.98(4) pm, Z = 2, R1 = 0.021, wR2 = 0.048) are isotypic and contain M(2+) ions (M = Sr, Ba), Yb3+ ions, as well as a three-dimensional covalent network structure of corner-sharing SiN4 tetrahedra. SrYbSi4N7 and BaYbSi4N7 are the first compounds with one central nitrogen connecting four silicon. These N-[4] bridges significantly extend the spectrum of possible linkages in Si-N network structures.