Sr2NdNbCu2O8 crystallizes in the monoclinic C2/m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 10-coordinate geometry to one O(4), one O(6), two equivalent O(2), two equivalent O(5), and four equivalent O(3) atoms. In the second Sr site, Sr(2) is bonded in a 10-coordinate geometry to one O(4), one O(6), two equivalent O(1), two equivalent O(2), and four equivalent O(3) atoms. Nd(1) is bonded in a body-centered cubic geometry to two equivalent O(4), two equivalent O(6), and four equivalent O(2) atoms. Nb(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra and corners with two equivalent Cu(1)O5 square pyramids. The corner-sharing octahedral tilt angles are 29°. Cu(1) is bonded to one O(3), one O(4), one O(6), and two equivalent O(2) atoms to form CuO5 square pyramids that share  a cornercorner with one Nb(1)O6 octahedra and corners with four equivalent Cu(1)O5 square pyramids. The corner-sharing octahedral tilt angles are 5°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Sr(2) and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded to one Sr(1), one Sr(2), two equivalent Nd(1), and two equivalent Cu(1) atoms to form a mixture of distorted edge, face, and corner-sharing OSr2Nd2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 2-68°. In the third O site, O(3) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(1), and one Cu(1) atom. In the fourth O site, O(4) is bonded to one Sr(1), one Sr(2), two equivalent Nd(1), and two equivalent Cu(1) atoms to form a mixture of distorted edge, face, and corner-sharing OSr2Nd2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 67-68°. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to two equivalent Sr(1) and two equivalent Nb(1) atoms. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to one Sr(1), one Sr(2), two equivalent Nd(1), and two equivalent Cu(1) atoms.
Sr2NdNbCu2O8 crystallizes in the monoclinic C2/m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 10-coordinate geometry to one O(4), one O(6), two equivalent O(2), two equivalent O(5), and four equivalent O(3) atoms. The Sr(1)-O(4) bond length is 2.79 Å. The Sr(1)-O(6) bond length is 2.94 Å. Both Sr(1)-O(2) bond lengths are 2.78 Å. There is one shorter (2.64 Å) and one longer (2.90 Å) Sr(1)-O(5) bond length. There are two shorter (2.77 Å) and two longer (2.82 Å) Sr(1)-O(3) bond lengths. In the second Sr site, Sr(2) is bonded in a 10-coordinate geometry to one O(4), one O(6), two equivalent O(1), two equivalent O(2), and four equivalent O(3) atoms. The Sr(2)-O(4) bond length is 2.79 Å. The Sr(2)-O(6) bond length is 2.75 Å. Both Sr(2)-O(1) bond lengths are 2.78 Å. Both Sr(2)-O(2) bond lengths are 2.86 Å. There are two shorter (2.68 Å) and two longer (2.91 Å) Sr(2)-O(3) bond lengths. Nd(1) is bonded in a body-centered cubic geometry to two equivalent O(4), two equivalent O(6), and four equivalent O(2) atoms. There is one shorter (2.45 Å) and one longer (2.59 Å) Nd(1)-O(4) bond length. There is one shorter (2.44 Å) and one longer (2.50 Å) Nd(1)-O(6) bond length. There are two shorter (2.45 Å) and two longer (2.54 Å) Nd(1)-O(2) bond lengths. Nb(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra and corners with two equivalent Cu(1)O5 square pyramids. The corner-sharing octahedral tilt angles are 29°. Both Nb(1)-O(1) bond lengths are 2.02 Å. Both Nb(1)-O(3) bond lengths are 1.97 Å. Both Nb(1)-O(5) bond lengths are 2.02 Å. Cu(1) is bonded to one O(3), one O(4), one O(6), and two equivalent O(2) atoms to form CuO5 square pyramids that share  a cornercorner with one Nb(1)O6 octahedra and corners with four equivalent Cu(1)O5 square pyramids. The corner-sharing octahedral tilt angles are 5°. The Cu(1)-O(3) bond length is 2.22 Å. The Cu(1)-O(4) bond length is 1.97 Å. The Cu(1)-O(6) bond length is 1.97 Å. Both Cu(1)-O(2) bond lengths are 1.97 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Sr(2) and two equivalent Nb(1) atoms. In the second O site, O(2) is bonded to one Sr(1), one Sr(2), two equivalent Nd(1), and two equivalent Cu(1) atoms to form a mixture of distorted edge, face, and corner-sharing OSr2Nd2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 2-68°. In the third O site, O(3) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(1), and one Cu(1) atom. In the fourth O site, O(4) is bonded to one Sr(1), one Sr(2), two equivalent Nd(1), and two equivalent Cu(1) atoms to form a mixture of distorted edge, face, and corner-sharing OSr2Nd2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 67-68°. In the fifth O site, O(5) is bonded in a 4-coordinate geometry to two equivalent Sr(1) and two equivalent Nb(1) atoms. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to one Sr(1), one Sr(2), two equivalent Nd(1), and two equivalent Cu(1) atoms.