Ca5(SiN3)2 crystallizes in the monoclinic C2/c space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to two equivalent N(1), two equivalent N(2), and two equivalent N(3) atoms. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to two equivalent N(1), two equivalent N(2), and two equivalent N(3) atoms. In the third Ca site, Ca(3) is bonded to one N(3), two equivalent N(1), and two equivalent N(2) atoms to form distorted CaN5 trigonal bipyramids that share corners with two equivalent Si(1)N4 tetrahedra, corners with two equivalent Ca(3)N5 trigonal bipyramids, edges with two equivalent Si(1)N4 tetrahedra, and  an edgeedge with one Ca(3)N5 trigonal bipyramid. Si(1) is bonded to one N(1), one N(2), and two equivalent N(3) atoms to form SiN4 tetrahedra that share corners with two equivalent Ca(3)N5 trigonal bipyramids,  an edgeedge with one Si(1)N4 tetrahedra, and edges with two equivalent Ca(3)N5 trigonal bipyramids. There are three inequivalent N sites. In the first N site, N(1) is bonded to one Ca(2), two equivalent Ca(1), two equivalent Ca(3), and one Si(1) atom to form a mixture of distorted corner and edge-sharing NCa5Si octahedra. The corner-sharing octahedral tilt angles range from 18-75°. In the second N site, N(2) is bonded to one Ca(2), two equivalent Ca(1), two equivalent Ca(3), and one Si(1) atom to form a mixture of distorted face, corner, and edge-sharing NCa5Si octahedra. The corner-sharing octahedral tilt angles range from 18-75°. In the third N site, N(3) is bonded in a 6-coordinate geometry to one Ca(2), one Ca(3), two equivalent Ca(1), and two equivalent Si(1) atoms.
Ca5(SiN3)2 crystallizes in the monoclinic C2/c space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 6-coordinate geometry to two equivalent N(1), two equivalent N(2), and two equivalent N(3) atoms. There is one shorter (2.57 Å) and one longer (2.83 Å) Ca(1)-N(1) bond length. There is one shorter (2.43 Å) and one longer (2.56 Å) Ca(1)-N(2) bond length. There is one shorter (2.64 Å) and one longer (2.88 Å) Ca(1)-N(3) bond length. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to two equivalent N(1), two equivalent N(2), and two equivalent N(3) atoms. Both Ca(2)-N(1) bond lengths are 2.35 Å. Both Ca(2)-N(2) bond lengths are 2.57 Å. Both Ca(2)-N(3) bond lengths are 2.96 Å. In the third Ca site, Ca(3) is bonded to one N(3), two equivalent N(1), and two equivalent N(2) atoms to form distorted CaN5 trigonal bipyramids that share corners with two equivalent Si(1)N4 tetrahedra, corners with two equivalent Ca(3)N5 trigonal bipyramids, edges with two equivalent Si(1)N4 tetrahedra, and  an edgeedge with one Ca(3)N5 trigonal bipyramid. The Ca(3)-N(3) bond length is 2.48 Å. There is one shorter (2.41 Å) and one longer (2.47 Å) Ca(3)-N(1) bond length. There is one shorter (2.32 Å) and one longer (2.47 Å) Ca(3)-N(2) bond length. Si(1) is bonded to one N(1), one N(2), and two equivalent N(3) atoms to form SiN4 tetrahedra that share corners with two equivalent Ca(3)N5 trigonal bipyramids,  an edgeedge with one Si(1)N4 tetrahedra, and edges with two equivalent Ca(3)N5 trigonal bipyramids. The Si(1)-N(1) bond length is 1.74 Å. The Si(1)-N(2) bond length is 1.71 Å. There is one shorter (1.78 Å) and one longer (1.82 Å) Si(1)-N(3) bond length. There are three inequivalent N sites. In the first N site, N(1) is bonded to one Ca(2), two equivalent Ca(1), two equivalent Ca(3), and one Si(1) atom to form a mixture of distorted corner and edge-sharing NCa5Si octahedra. The corner-sharing octahedral tilt angles range from 18-75°. In the second N site, N(2) is bonded to one Ca(2), two equivalent Ca(1), two equivalent Ca(3), and one Si(1) atom to form a mixture of distorted face, corner, and edge-sharing NCa5Si octahedra. The corner-sharing octahedral tilt angles range from 18-75°. In the third N site, N(3) is bonded in a 6-coordinate geometry to one Ca(2), one Ca(3), two equivalent Ca(1), and two equivalent Si(1) atoms.