Can one design Zintl anions? Contributions from the system Sr/Mg/Si to the topic Si2-

Two novel ternary silicides, SrMgSi2 (Pnma, Z = 8, a = 14.374, b = 4.4512, c = 11.398 Angstrom) and Sr11Mg2Si10, (C2/m, Z = 2, a = 19.744, b = 4.754, c = 14.84 Angstrom, beta = 112.47 degrees) have been established in the ternary system Sr/Mg/Si. The compounds are synthezised from the elements under inert conditions. Single crystal structure determinations yield the novel Zintl anions, (1)(infinity)[Si(Si-3)(8-)] a branched chain, and the zig-zag chain piece [Si-8](18-), both of which exhibit significant correlations and differences with respect to the linear chains in (1)(infinity)[Si-] in the binary MSi phases (M = Ca, Sr, Ba) which have been reinvestigated in this context. The variations of the Zintl anions can be traced back mainly to the differences of Mg-Si and Sr-Si interactions. From these findings a functional relationship between Mg content and the formation of endgroup members in Zintl anions of silicon is anticipated.