Sr3CaSi8 crystallizes in the trigonal R32 space group. Sr(1) is bonded in a 8-coordinate geometry to two equivalent Si(1) and six equivalent Si(2) atoms. Ca(1) is bonded in a distorted body-centered cubic geometry to two equivalent Si(1) and six equivalent Si(2) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to three equivalent Sr(1), one Ca(1), and three equivalent Si(2) atoms. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to three equivalent Sr(1), one Ca(1), one Si(1), and two equivalent Si(2) atoms.
Sr3CaSi8 crystallizes in the trigonal R32 space group. Sr(1) is bonded in a 8-coordinate geometry to two equivalent Si(1) and six equivalent Si(2) atoms. Both Sr(1)-Si(1) bond lengths are 3.28 Å. There are a spread of Sr(1)-Si(2) bond distances ranging from 3.22-3.37 Å. Ca(1) is bonded in a distorted body-centered cubic geometry to two equivalent Si(1) and six equivalent Si(2) atoms. Both Ca(1)-Si(1) bond lengths are 3.35 Å. All Ca(1)-Si(2) bond lengths are 3.21 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 7-coordinate geometry to three equivalent Sr(1), one Ca(1), and three equivalent Si(2) atoms. All Si(1)-Si(2) bond lengths are 2.40 Å. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to three equivalent Sr(1), one Ca(1), one Si(1), and two equivalent Si(2) atoms. There is one shorter (2.37 Å) and one longer (2.38 Å) Si(2)-Si(2) bond length.