Sr9CaSi6 crystallizes in the tetragonal I4/m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 5-coordinate geometry to two equivalent Si(1) and three equivalent Si(2) atoms. In the second Sr site, Sr(2) is bonded in a square co-planar geometry to four equivalent Si(2) atoms. Ca(1) is bonded in a square co-planar geometry to four equivalent Si(2) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to eight equivalent Sr(1) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Sr(2), six equivalent Sr(1), one Ca(1), and one Si(2) atom.
Sr9CaSi6 crystallizes in the tetragonal I4/m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 5-coordinate geometry to two equivalent Si(1) and three equivalent Si(2) atoms. There is one shorter (3.40 Å) and one longer (3.44 Å) Sr(1)-Si(1) bond length. There are a spread of Sr(1)-Si(2) bond distances ranging from 3.23-3.29 Å. In the second Sr site, Sr(2) is bonded in a square co-planar geometry to four equivalent Si(2) atoms. All Sr(2)-Si(2) bond lengths are 3.29 Å. Ca(1) is bonded in a square co-planar geometry to four equivalent Si(2) atoms. All Ca(1)-Si(2) bond lengths are 3.22 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 8-coordinate geometry to eight equivalent Sr(1) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to one Sr(2), six equivalent Sr(1), one Ca(1), and one Si(2) atom. The Si(2)-Si(2) bond length is 2.48 Å.