Oxide meets silicide – synthesis and single-crystal structure of Ca21SrSi24O2

Abstract

Abstract A few black, rectangular thin plates of Ca21SrSi24O2 were obtained by serendipity in a solid-state reaction of calcium metal, strontium chloride and silicon powder at 1200 K for 2 days designed to produce ‘Ca2SrCl2[Si3]’. The title compound forms next to some CaSi and some remaining educts. Ca21SrSi24O2 crystallizes in the monoclinic space group C2/m (no. 12) with unit cell parameters of a=1895.2(2), b=450.63(5) and c=1397.33(18) pm and β=112.008(7)° (Z=1). The title compound shows planar, eight-membered, kinked Si8 chains with Si–Si distances between 241.4 and 245.0 pm indicating bonding interactions and kinked ‘rope ladders’ connecting the chains with interatomic Si–Si distances in the range 268.1–274.7 pm. Embedded in between these silicon substructures are columns of oxygen centered, apex sharing [(Ca1−x Sr x )6/2O] octahedra and calcium ions.