Sr4Ca(SO4)4 crystallizes in the monoclinic Pm space group. There are four inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 9-coordinate geometry to one O(8), two equivalent O(10), two equivalent O(2), and four equivalent O(12) atoms. In the second Sr site, Sr(2) is bonded in a 7-coordinate geometry to one O(7), two equivalent O(1), and four equivalent O(11) atoms. In the third Sr site, Sr(3) is bonded in a 9-coordinate geometry to one O(6), two equivalent O(12), two equivalent O(4), and four equivalent O(10) atoms. In the fourth Sr site, Sr(4) is bonded to one O(5), two equivalent O(3), and four equivalent O(9) atoms to form distorted SrO7 hexagonal pyramids that share corners with two equivalent Sr(4)O7 hexagonal pyramids,  a cornercorner with one S(4)O4 tetrahedra, corners with two equivalent S(1)O4 tetrahedra, edges with two equivalent Sr(4)O7 hexagonal pyramids, and edges with two equivalent S(1)O4 tetrahedra. Ca(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(11) and two equivalent O(9) atoms. There are four inequivalent S sites. In the first S site, S(1) is bonded to one O(3), one O(8), and two equivalent O(9) atoms to form SO4 tetrahedra that share corners with two equivalent Sr(4)O7 hexagonal pyramids and edges with two equivalent Sr(4)O7 hexagonal pyramids. In the second S site, S(2) is bonded in a tetrahedral geometry to one O(4), one O(7), and two equivalent O(10) atoms. In the third S site, S(3) is bonded in a tetrahedral geometry to one O(1), one O(6), and two equivalent O(11) atoms. In the fourth S site, S(4) is bonded to one O(2), one O(5), and two equivalent O(12) atoms to form SO4 tetrahedra that share  a cornercorner with one Sr(4)O7 hexagonal pyramid. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Sr(2) and one S(3) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Sr(1) and one S(4) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to two equivalent Sr(4) and one S(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to two equivalent Sr(3) and one S(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Sr(4) and one S(4) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Sr(3) and one S(3) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Sr(2) and one S(2) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Sr(1) and one S(1) atom. In the ninth O site, O(9) is bonded in a distorted single-bond geometry to two equivalent Sr(4), one Ca(1), and one S(1) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Sr(1), two equivalent Sr(3), and one S(2) atom. In the eleventh O site, O(11) is bonded in a distorted single-bond geometry to two equivalent Sr(2), one Ca(1), and one S(3) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one Sr(3), two equivalent Sr(1), and one S(4) atom.
Sr4Ca(SO4)4 crystallizes in the monoclinic Pm space group. There are four inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 9-coordinate geometry to one O(8), two equivalent O(10), two equivalent O(2), and four equivalent O(12) atoms. The Sr(1)-O(8) bond length is 2.46 Å. Both Sr(1)-O(10) bond lengths are 2.75 Å. Both Sr(1)-O(2) bond lengths are 2.70 Å. There are two shorter (2.62 Å) and two longer (2.95 Å) Sr(1)-O(12) bond lengths. In the second Sr site, Sr(2) is bonded in a 7-coordinate geometry to one O(7), two equivalent O(1), and four equivalent O(11) atoms. The Sr(2)-O(7) bond length is 2.45 Å. Both Sr(2)-O(1) bond lengths are 2.70 Å. There are two shorter (2.62 Å) and two longer (2.99 Å) Sr(2)-O(11) bond lengths. In the third Sr site, Sr(3) is bonded in a 9-coordinate geometry to one O(6), two equivalent O(12), two equivalent O(4), and four equivalent O(10) atoms. The Sr(3)-O(6) bond length is 2.56 Å. Both Sr(3)-O(12) bond lengths are 2.81 Å. Both Sr(3)-O(4) bond lengths are 2.71 Å. There are two shorter (2.63 Å) and two longer (2.95 Å) Sr(3)-O(10) bond lengths. In the fourth Sr site, Sr(4) is bonded to one O(5), two equivalent O(3), and four equivalent O(9) atoms to form distorted SrO7 hexagonal pyramids that share corners with two equivalent Sr(4)O7 hexagonal pyramids,  a cornercorner with one S(4)O4 tetrahedra, corners with two equivalent S(1)O4 tetrahedra, edges with two equivalent Sr(4)O7 hexagonal pyramids, and edges with two equivalent S(1)O4 tetrahedra. The Sr(4)-O(5) bond length is 2.53 Å. Both Sr(4)-O(3) bond lengths are 2.74 Å. There are two shorter (2.68 Å) and two longer (2.86 Å) Sr(4)-O(9) bond lengths. Ca(1) is bonded in a distorted rectangular see-saw-like geometry to two equivalent O(11) and two equivalent O(9) atoms. Both Ca(1)-O(11) bond lengths are 2.56 Å. Both Ca(1)-O(9) bond lengths are 2.49 Å. There are four inequivalent S sites. In the first S site, S(1) is bonded to one O(3), one O(8), and two equivalent O(9) atoms to form SO4 tetrahedra that share corners with two equivalent Sr(4)O7 hexagonal pyramids and edges with two equivalent Sr(4)O7 hexagonal pyramids. The S(1)-O(3) bond length is 1.48 Å. The S(1)-O(8) bond length is 1.46 Å. Both S(1)-O(9) bond lengths are 1.52 Å. In the second S site, S(2) is bonded in a tetrahedral geometry to one O(4), one O(7), and two equivalent O(10) atoms. The S(2)-O(4) bond length is 1.49 Å. The S(2)-O(7) bond length is 1.47 Å. Both S(2)-O(10) bond lengths are 1.50 Å. In the third S site, S(3) is bonded in a tetrahedral geometry to one O(1), one O(6), and two equivalent O(11) atoms. The S(3)-O(1) bond length is 1.49 Å. The S(3)-O(6) bond length is 1.48 Å. Both S(3)-O(11) bond lengths are 1.51 Å. In the fourth S site, S(4) is bonded to one O(2), one O(5), and two equivalent O(12) atoms to form SO4 tetrahedra that share  a cornercorner with one Sr(4)O7 hexagonal pyramid. The S(4)-O(2) bond length is 1.49 Å. The S(4)-O(5) bond length is 1.47 Å. Both S(4)-O(12) bond lengths are 1.51 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted single-bond geometry to two equivalent Sr(2) and one S(3) atom. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Sr(1) and one S(4) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to two equivalent Sr(4) and one S(1) atom. In the fourth O site, O(4) is bonded in a distorted single-bond geometry to two equivalent Sr(3) and one S(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Sr(4) and one S(4) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Sr(3) and one S(3) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Sr(2) and one S(2) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Sr(1) and one S(1) atom. In the ninth O site, O(9) is bonded in a distorted single-bond geometry to two equivalent Sr(4), one Ca(1), and one S(1) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Sr(1), two equivalent Sr(3), and one S(2) atom. In the eleventh O site, O(11) is bonded in a distorted single-bond geometry to two equivalent Sr(2), one Ca(1), and one S(3) atom. In the twelfth O site, O(12) is bonded in a distorted single-bond geometry to one Sr(3), two equivalent Sr(1), and one S(4) atom.