Ca _3Sm _3[Si _9N _(17)e] and Ca _3Yb _3[Si _9N _(17)e] nitridosilicates with interpenetrating nets that consist of star-shaped [N ~([4e])(SiN _3) _4e] units and [Si _5N _(16)e] supertetrahedra

摘要

New nitridosilicates Ca _3Sm _3[Si _9N _(17)e] and Ca _3Yb _3[Si _9N _(17)e] were synthesized from the reactions of the pure metals (calcium and samarium/ytterbium) with silicon diimide "Si(NH) _2" in a radio-frequency (rf) furnace at temperatures of up to 1650a °C. These isotypic compounds crystallize in the cubic space group Pbar 43m (no. 215) with lattice parameters a=739.50(3) pm; V=0.4044(1) nm ~3; Z=1; wR _2=0.029 (240 diffraction data, 26 parameters) for Ca _3Sm _3[Si _9N _(17)e] and a=730.20(2) pm; V=0.3893(1) nm ~3; wR _2=0.039 (387 diffraction data, 27 parameters) for Ca _3Yb _3[Si _9N _(17)e]. The new structure type of Ca _3RE _3[Si _9N _(17)e] (RE=Sm, Yb) consists of two independent infinite networks, each of which have an expanded sphalerite (ZnS) topology in which the positions of the Zn and S atoms are replaced by voluminous [N ~([4e])(SiN _3) _4e] units and [Si _5N _(16)e] supertetrahedra, respectively, thereby displaying twofold interpenetration. As well, a structural description of Ca _3Yb _3[Si _9N _(17)e], its thermal stability, and magnetic properties, as well as UV/Vis, IR, and Raman spectra, are presented. Casting the nets: Two independent and identical interpenetrating networks occur in the highly symmetric compounds Ca _3RE _3[Si _9N _(17)e] (RE=Sm, Yb). From a hierarchical point of view, the structure is related to a sphalerite (ZnS) topology (see figure).