Ca16(SiN2)17 crystallizes in the cubic F-43m space group. The structure is three-dimensional. there are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to six N+2.94- atoms to form distorted CaN6 pentagonal pyramids that share corners with four equivalent CaN6 pentagonal pyramids, corners with six SiN4 tetrahedra, and edges with three SiN4 tetrahedra. There are four shorter (2.54 �) and two longer (2.60 �) Ca?N bond lengths. In the second Ca2+ site, Ca2+ is bonded in a body-centered cubic geometry to eight N+2.94- atoms. There are four shorter (2.65 �) and four longer (2.71 �) Ca?N bond lengths. In the third Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to six N+2.94- atoms. There are three shorter (2.26 �) and three longer (2.75 �) Ca?N bond lengths. There are five inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four N+2.94- atoms to form SiN4 tetrahedra that share corners with four SiN4 tetrahedra and edges with three equivalent CaN6 pentagonal pyramids. There is one shorter (1.74 �) and three longer (1.78 �) Si?N bond length. In the second Si4+ site, Si4+ is bonded to four equivalent N+2.94- atoms to form SiN4 tetrahedra that share corners with four equivalent SiN4 tetrahedra and edges with six equivalent CaN6 pentagonal pyramids. All Si?N bond lengths are 1.78 �. In the third Si4+ site, Si4+ is bonded to four N+2.94- atoms to form SiN4 tetrahedra that share corners with three equivalent CaN6 pentagonal pyramids and corners with six SiN4 tetrahedra. There is three shorter (1.74 �) and one longer (1.82 �) Si?N bond length. In the fourth Si4+ site, Si4+ is bonded to four N+2.94- atoms to form SiN4 tetrahedra that share corners with three equivalent CaN6 pentagonal pyramids and corners with three equivalent SiN4 tetrahedra. There is one shorter (1.67 �) and three longer (1.77 �) Si?N bond length. In the fifth Si4+ site, Si4+ is bonded to four N+2.94- atoms to form SiN4 tetrahedra that share corners with three equivalent CaN6 pentagonal pyramids and corners with six SiN4 tetrahedra. There is three shorter (1.72 �) and one longer (1.89 �) Si?N bond length. There are six inequivalent N+2.94- sites. In the first N+2.94- site, N+2.94- is bonded in a distorted rectangular see-saw-like geometry to three equivalent Ca2+ and one Si4+ atom. In the second N+2.94- site, N+2.94- is bonded to three equivalent Ca2+ and two Si4+ atoms to form a mixture of corner and edge-sharing NCa3Si2 trigonal bipyramids. In the third N+2.94- site, N+2.94- is bonded in a 6-coordinate geometry to four Ca2+ and two Si4+ atoms. In the fourth N+2.94- site, N+2.94- is bonded in a tetrahedral geometry to four equivalent Si4+ atoms. In the fifth N+2.94- site, N+2.94- is bonded to four equivalent Si4+ atoms to form corner-sharing NSi4 tetrahedra. In the sixth N+2.94- site, N+2.94- is bonded to three Ca2+ and two Si4+ atoms to form distorted NCa3Si2 trigonal bipyramids that share a cornercorner with one NSi4 tetrahedra, corners with five NCa3Si2 trigonal bipyramids, and edges with four equivalent NCa3Si2 trigonal bipyramids.