Sr2EuNb(CuO4)2 crystallizes in the tetragonal I4/mcm space group. Sr(1) is bonded in a distorted q6 geometry to two equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms. Eu(1) is bonded in a body-centered cubic geometry to eight equivalent O(2) atoms. Nb(1) is bonded to two equivalent O(3) and four equivalent O(1) 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 31°. Cu(1) is bonded to one O(3) and four 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 octahedra are not tilted. There are three inequivalent O sites. In the first O site, O(3) is bonded to four equivalent Sr(1), one Nb(1), and one Cu(1) atom to form distorted OSr4NbCu octahedra that share corners with five equivalent O(3)Sr4NbCu octahedra, corners with eight equivalent O(2)Sr2Eu2Cu2 octahedra, edges with four equivalent O(3)Sr4NbCu octahedra, and faces with four equivalent O(2)Sr2Eu2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 0-54°. In the second O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Sr(1) and two equivalent Nb(1) atoms. In the third O site, O(2) is bonded to two equivalent Sr(1), two equivalent Eu(1), and two equivalent Cu(1) atoms to form distorted OSr2Eu2Cu2 octahedra that share corners with four equivalent O(3)Sr4NbCu octahedra, corners with eight equivalent O(2)Sr2Eu2Cu2 octahedra, edges with three equivalent O(2)Sr2Eu2Cu2 octahedra, faces with two equivalent O(3)Sr4NbCu octahedra, and faces with four equivalent O(2)Sr2Eu2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 0-67°.
Sr2EuNb(CuO4)2 crystallizes in the tetragonal I4/mcm space group. Sr(1) is bonded in a distorted q6 geometry to two equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms. Both Sr(1)-O(1) bond lengths are 2.76 Å. There are two shorter (2.78 Å) and two longer (2.80 Å) Sr(1)-O(2) bond lengths. All Sr(1)-O(3) bond lengths are 2.78 Å. Eu(1) is bonded in a body-centered cubic geometry to eight equivalent O(2) atoms. There are four shorter (2.49 Å) and four longer (2.51 Å) Eu(1)-O(2) bond lengths. Nb(1) is bonded to two equivalent O(3) and four equivalent O(1) 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 31°. Both Nb(1)-O(3) bond lengths are 1.98 Å. All Nb(1)-O(1) bond lengths are 2.02 Å. Cu(1) is bonded to one O(3) and four 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 octahedra are not tilted. The Cu(1)-O(3) bond length is 2.25 Å. All Cu(1)-O(2) bond lengths are 1.95 Å. There are three inequivalent O sites. In the first O site, O(3) is bonded to four equivalent Sr(1), one Nb(1), and one Cu(1) atom to form distorted OSr4NbCu octahedra that share corners with five equivalent O(3)Sr4NbCu octahedra, corners with eight equivalent O(2)Sr2Eu2Cu2 octahedra, edges with four equivalent O(3)Sr4NbCu octahedra, and faces with four equivalent O(2)Sr2Eu2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 0-54°. In the second O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Sr(1) and two equivalent Nb(1) atoms. In the third O site, O(2) is bonded to two equivalent Sr(1), two equivalent Eu(1), and two equivalent Cu(1) atoms to form distorted OSr2Eu2Cu2 octahedra that share corners with four equivalent O(3)Sr4NbCu octahedra, corners with eight equivalent O(2)Sr2Eu2Cu2 octahedra, edges with three equivalent O(2)Sr2Eu2Cu2 octahedra, faces with two equivalent O(3)Sr4NbCu octahedra, and faces with four equivalent O(2)Sr2Eu2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 0-67°.