BaSrEu4O8 crystallizes in the orthorhombic Pmc2_1 space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), and two equivalent O(8) atoms. Sr(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(6), and two equivalent O(7) atoms. There are four inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to one O(1), one O(3), two equivalent O(4), and two equivalent O(6) atoms to form a mixture of corner and edge-sharing EuO6 octahedra. The corner-sharing octahedral tilt angles range from 52-63°. In the second Eu site, Eu(2) is bonded to one O(2), one O(4), two equivalent O(3), and two equivalent O(5) atoms to form a mixture of corner and edge-sharing EuO6 octahedra. The corner-sharing octahedral tilt angles range from 50-63°. In the third Eu site, Eu(3) is bonded to one O(5), one O(7), two equivalent O(2), and two equivalent O(8) atoms to form a mixture of corner and edge-sharing EuO6 octahedra. The corner-sharing octahedral tilt angles range from 50-63°. In the fourth Eu site, Eu(4) is bonded to one O(6), one O(8), two equivalent O(1), and two equivalent O(7) atoms to form a mixture of corner and edge-sharing EuO6 octahedra. The corner-sharing octahedral tilt angles range from 52-63°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Sr(1), one Eu(1), and two equivalent Eu(4) atoms. In the second O site, O(2) is bonded in a 5-coordinate geometry to two equivalent Ba(1), one Eu(2), and two equivalent Eu(3) atoms. In the third O site, O(3) is bonded to two equivalent Sr(1), one Eu(1), and two equivalent Eu(2) atoms to form OSr2Eu3 square pyramids that share corners with two equivalent O(5)Ba2Eu3 trigonal bipyramids, corners with two equivalent O(7)Sr2Eu3 trigonal bipyramids, edges with two equivalent O(4)Ba2Eu3 square pyramids, edges with two equivalent O(3)Sr2Eu3 square pyramids,  an edgeedge with one O(5)Ba2Eu3 trigonal bipyramid, and  an edgeedge with one O(7)Sr2Eu3 trigonal bipyramid. In the fourth O site, O(4) is bonded to two equivalent Ba(1), one Eu(2), and two equivalent Eu(1) atoms to form OBa2Eu3 square pyramids that share corners with two equivalent O(5)Ba2Eu3 trigonal bipyramids, corners with two equivalent O(8)Ba2Eu3 trigonal bipyramids, edges with two equivalent O(4)Ba2Eu3 square pyramids, edges with two equivalent O(3)Sr2Eu3 square pyramids,  an edgeedge with one O(8)Ba2Eu3 trigonal bipyramid, and edges with two equivalent O(5)Ba2Eu3 trigonal bipyramids. In the fifth O site, O(5) is bonded to two equivalent Ba(1), one Eu(3), and two equivalent Eu(2) atoms to form distorted OBa2Eu3 trigonal bipyramids that share corners with two equivalent O(4)Ba2Eu3 square pyramids, corners with two equivalent O(3)Sr2Eu3 square pyramids,  a cornercorner with one O(7)Sr2Eu3 trigonal bipyramid, corners with two equivalent O(8)Ba2Eu3 trigonal bipyramids, corners with four equivalent O(5)Ba2Eu3 trigonal bipyramids,  an edgeedge with one O(3)Sr2Eu3 square pyramid, edges with two equivalent O(4)Ba2Eu3 square pyramids, and edges with two equivalent O(8)Ba2Eu3 trigonal bipyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to two equivalent Sr(1), one Eu(4), and two equivalent Eu(1) atoms. In the seventh O site, O(7) is bonded to two equivalent Sr(1), one Eu(3), and two equivalent Eu(4) atoms to form distorted OSr2Eu3 trigonal bipyramids that share corners with two equivalent O(3)Sr2Eu3 square pyramids,  a cornercorner with one O(5)Ba2Eu3 trigonal bipyramid,  an edgeedge with one O(3)Sr2Eu3 square pyramid, edges with two equivalent O(8)Ba2Eu3 trigonal bipyramids, and edges with two equivalent O(7)Sr2Eu3 trigonal bipyramids. In the eighth O site, O(8) is bonded to two equivalent Ba(1), one Eu(4), and two equivalent Eu(3) atoms to form distorted OBa2Eu3 trigonal bipyramids that share corners with two equivalent O(4)Ba2Eu3 square pyramids, corners with two equivalent O(5)Ba2Eu3 trigonal bipyramids,  an edgeedge with one O(4)Ba2Eu3 square pyramid, edges with two equivalent O(5)Ba2Eu3 trigonal bipyramids, edges with two equivalent O(8)Ba2Eu3 trigonal bipyramids, and edges with two equivalent O(7)Sr2Eu3 trigonal bipyramids.
BaSrEu4O8 crystallizes in the orthorhombic Pmc2_1 space group. Ba(1) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), and two equivalent O(8) atoms. Both Ba(1)-O(2) bond lengths are 2.91 Å. Both Ba(1)-O(4) bond lengths are 2.81 Å. There is one shorter (2.86 Å) and one longer (3.04 Å) Ba(1)-O(5) bond length. Both Ba(1)-O(8) bond lengths are 2.78 Å. Sr(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(3), two equivalent O(6), and two equivalent O(7) atoms. Both Sr(1)-O(1) bond lengths are 2.83 Å. Both Sr(1)-O(3) bond lengths are 2.67 Å. There is one shorter (2.72 Å) and one longer (3.18 Å) Sr(1)-O(6) bond length. Both Sr(1)-O(7) bond lengths are 2.69 Å. There are four inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to one O(1), one O(3), two equivalent O(4), and two equivalent O(6) atoms to form a mixture of corner and edge-sharing EuO6 octahedra. The corner-sharing octahedral tilt angles range from 52-63°. The Eu(1)-O(1) bond length is 2.35 Å. The Eu(1)-O(3) bond length is 2.41 Å. Both Eu(1)-O(4) bond lengths are 2.45 Å. Both Eu(1)-O(6) bond lengths are 2.31 Å. In the second Eu site, Eu(2) is bonded to one O(2), one O(4), two equivalent O(3), and two equivalent O(5) atoms to form a mixture of corner and edge-sharing EuO6 octahedra. The corner-sharing octahedral tilt angles range from 50-63°. The Eu(2)-O(2) bond length is 2.32 Å. The Eu(2)-O(4) bond length is 2.36 Å. Both Eu(2)-O(3) bond lengths are 2.48 Å. Both Eu(2)-O(5) bond lengths are 2.35 Å. In the third Eu site, Eu(3) is bonded to one O(5), one O(7), two equivalent O(2), and two equivalent O(8) atoms to form a mixture of corner and edge-sharing EuO6 octahedra. The corner-sharing octahedral tilt angles range from 50-63°. The Eu(3)-O(5) bond length is 2.41 Å. The Eu(3)-O(7) bond length is 2.38 Å. Both Eu(3)-O(2) bond lengths are 2.41 Å. Both Eu(3)-O(8) bond lengths are 2.43 Å. In the fourth Eu site, Eu(4) is bonded to one O(6), one O(8), two equivalent O(1), and two equivalent O(7) atoms to form a mixture of corner and edge-sharing EuO6 octahedra. The corner-sharing octahedral tilt angles range from 52-63°. The Eu(4)-O(6) bond length is 2.29 Å. The Eu(4)-O(8) bond length is 2.34 Å. Both Eu(4)-O(1) bond lengths are 2.44 Å. Both Eu(4)-O(7) bond lengths are 2.47 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Sr(1), one Eu(1), and two equivalent Eu(4) atoms. In the second O site, O(2) is bonded in a 5-coordinate geometry to two equivalent Ba(1), one Eu(2), and two equivalent Eu(3) atoms. In the third O site, O(3) is bonded to two equivalent Sr(1), one Eu(1), and two equivalent Eu(2) atoms to form OSr2Eu3 square pyramids that share corners with two equivalent O(5)Ba2Eu3 trigonal bipyramids, corners with two equivalent O(7)Sr2Eu3 trigonal bipyramids, edges with two equivalent O(4)Ba2Eu3 square pyramids, edges with two equivalent O(3)Sr2Eu3 square pyramids,  an edgeedge with one O(5)Ba2Eu3 trigonal bipyramid, and  an edgeedge with one O(7)Sr2Eu3 trigonal bipyramid. In the fourth O site, O(4) is bonded to two equivalent Ba(1), one Eu(2), and two equivalent Eu(1) atoms to form OBa2Eu3 square pyramids that share corners with two equivalent O(5)Ba2Eu3 trigonal bipyramids, corners with two equivalent O(8)Ba2Eu3 trigonal bipyramids, edges with two equivalent O(4)Ba2Eu3 square pyramids, edges with two equivalent O(3)Sr2Eu3 square pyramids,  an edgeedge with one O(8)Ba2Eu3 trigonal bipyramid, and edges with two equivalent O(5)Ba2Eu3 trigonal bipyramids. In the fifth O site, O(5) is bonded to two equivalent Ba(1), one Eu(3), and two equivalent Eu(2) atoms to form distorted OBa2Eu3 trigonal bipyramids that share corners with two equivalent O(4)Ba2Eu3 square pyramids, corners with two equivalent O(3)Sr2Eu3 square pyramids,  a cornercorner with one O(7)Sr2Eu3 trigonal bipyramid, corners with two equivalent O(8)Ba2Eu3 trigonal bipyramids, corners with four equivalent O(5)Ba2Eu3 trigonal bipyramids,  an edgeedge with one O(3)Sr2Eu3 square pyramid, edges with two equivalent O(4)Ba2Eu3 square pyramids, and edges with two equivalent O(8)Ba2Eu3 trigonal bipyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to two equivalent Sr(1), one Eu(4), and two equivalent Eu(1) atoms. In the seventh O site, O(7) is bonded to two equivalent Sr(1), one Eu(3), and two equivalent Eu(4) atoms to form distorted OSr2Eu3 trigonal bipyramids that share corners with two equivalent O(3)Sr2Eu3 square pyramids,  a cornercorner with one O(5)Ba2Eu3 trigonal bipyramid,  an edgeedge with one O(3)Sr2Eu3 square pyramid, edges with two equivalent O(8)Ba2Eu3 trigonal bipyramids, and edges with two equivalent O(7)Sr2Eu3 trigonal bipyramids. In the eighth O site, O(8) is bonded to two equivalent Ba(1), one Eu(4), and two equivalent Eu(3) atoms to form distorted OBa2Eu3 trigonal bipyramids that share corners with two equivalent O(4)Ba2Eu3 square pyramids, corners with two equivalent O(5)Ba2Eu3 trigonal bipyramids,  an edgeedge with one O(4)Ba2Eu3 square pyramid, edges with two equivalent O(5)Ba2Eu3 trigonal bipyramids, edges with two equivalent O(8)Ba2Eu3 trigonal bipyramids, and edges with two equivalent O(7)Sr2Eu3 trigonal bipyramids.