SrNd7Fe8(AsO)8 crystallizes in the tetragonal I4mm space group. Sr(1) is bonded in a 4-coordinate geometry to four equivalent As(1) and four equivalent O(2) atoms. There are three inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 4-coordinate geometry to one As(2), one As(4), two equivalent As(3), two equivalent O(1), and two equivalent O(2) atoms. In the second Nd site, Nd(2) is bonded in a 4-coordinate geometry to four equivalent As(1), two equivalent O(1), and two equivalent O(2) atoms. In the third Nd site, Nd(3) is bonded in a 4-coordinate geometry to four equivalent As(1) and four equivalent O(1) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one As(2), one As(3), and two equivalent As(1) atoms to form a mixture of distorted edge and corner-sharing FeAs4 tetrahedra. In the second Fe site, Fe(2) is bonded to one As(3), one As(4), and two equivalent As(1) atoms to form a mixture of distorted edge and corner-sharing FeAs4 tetrahedra. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 8-coordinate geometry to one Sr(1), one Nd(3), two equivalent Nd(2), two equivalent Fe(1), and two equivalent Fe(2) atoms. In the second As site, As(2) is bonded in a 8-coordinate geometry to four equivalent Nd(1) and four equivalent Fe(1) atoms. In the third As site, As(3) is bonded in a 8-coordinate geometry to four equivalent Nd(1), two equivalent Fe(1), and two equivalent Fe(2) atoms. In the fourth As site, As(4) is bonded in a 8-coordinate geometry to four equivalent Nd(1) and four equivalent Fe(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Nd(2), one Nd(3), and two equivalent Nd(1) atoms to form ONd4 tetrahedra that share corners with two equivalent O(1)Nd4 tetrahedra, corners with two equivalent O(2)SrNd3 tetrahedra, edges with two equivalent O(1)Nd4 tetrahedra, and edges with two equivalent O(2)SrNd3 tetrahedra. In the second O site, O(2) is bonded to one Sr(1), one Nd(2), and two equivalent Nd(1) atoms to form OSrNd3 tetrahedra that share corners with two equivalent O(1)Nd4 tetrahedra, corners with two equivalent O(2)SrNd3 tetrahedra, edges with two equivalent O(1)Nd4 tetrahedra, and edges with two equivalent O(2)SrNd3 tetrahedra.
SrNd7Fe8(AsO)8 crystallizes in the tetragonal I4mm space group. Sr(1) is bonded in a 4-coordinate geometry to four equivalent As(1) and four equivalent O(2) atoms. All Sr(1)-As(1) bond lengths are 3.42 Å. All Sr(1)-O(2) bond lengths are 2.49 Å. There are three inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 4-coordinate geometry to one As(2), one As(4), two equivalent As(3), two equivalent O(1), and two equivalent O(2) atoms. The Nd(1)-As(2) bond length is 3.44 Å. The Nd(1)-As(4) bond length is 3.47 Å. Both Nd(1)-As(3) bond lengths are 3.47 Å. Both Nd(1)-O(1) bond lengths are 2.36 Å. Both Nd(1)-O(2) bond lengths are 2.31 Å. In the second Nd site, Nd(2) is bonded in a 4-coordinate geometry to four equivalent As(1), two equivalent O(1), and two equivalent O(2) atoms. All Nd(2)-As(1) bond lengths are 3.47 Å. Both Nd(2)-O(1) bond lengths are 2.35 Å. Both Nd(2)-O(2) bond lengths are 2.31 Å. In the third Nd site, Nd(3) is bonded in a 4-coordinate geometry to four equivalent As(1) and four equivalent O(1) atoms. All Nd(3)-As(1) bond lengths are 3.45 Å. All Nd(3)-O(1) bond lengths are 2.33 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one As(2), one As(3), and two equivalent As(1) atoms to form a mixture of distorted edge and corner-sharing FeAs4 tetrahedra. The Fe(1)-As(2) bond length is 2.63 Å. The Fe(1)-As(3) bond length is 2.62 Å. Both Fe(1)-As(1) bond lengths are 2.62 Å. In the second Fe site, Fe(2) is bonded to one As(3), one As(4), and two equivalent As(1) atoms to form a mixture of distorted edge and corner-sharing FeAs4 tetrahedra. The Fe(2)-As(3) bond length is 2.63 Å. The Fe(2)-As(4) bond length is 2.63 Å. Both Fe(2)-As(1) bond lengths are 2.62 Å. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 8-coordinate geometry to one Sr(1), one Nd(3), two equivalent Nd(2), two equivalent Fe(1), and two equivalent Fe(2) atoms. In the second As site, As(2) is bonded in a 8-coordinate geometry to four equivalent Nd(1) and four equivalent Fe(1) atoms. In the third As site, As(3) is bonded in a 8-coordinate geometry to four equivalent Nd(1), two equivalent Fe(1), and two equivalent Fe(2) atoms. In the fourth As site, As(4) is bonded in a 8-coordinate geometry to four equivalent Nd(1) and four equivalent Fe(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Nd(2), one Nd(3), and two equivalent Nd(1) atoms to form ONd4 tetrahedra that share corners with two equivalent O(1)Nd4 tetrahedra, corners with two equivalent O(2)SrNd3 tetrahedra, edges with two equivalent O(1)Nd4 tetrahedra, and edges with two equivalent O(2)SrNd3 tetrahedra. In the second O site, O(2) is bonded to one Sr(1), one Nd(2), and two equivalent Nd(1) atoms to form OSrNd3 tetrahedra that share corners with two equivalent O(1)Nd4 tetrahedra, corners with two equivalent O(2)SrNd3 tetrahedra, edges with two equivalent O(1)Nd4 tetrahedra, and edges with two equivalent O(2)SrNd3 tetrahedra.