EuNb8O14 crystallizes in the orthorhombic Pbam space group. Eu(1) is bonded to two equivalent O(3), two equivalent O(5), four equivalent O(1), and four equivalent O(2) atoms to form EuO12 cuboctahedra that share corners with two equivalent Eu(1)O12 cuboctahedra, corners with four equivalent Nb(3)O5 square pyramids, edges with two equivalent Nb(2)O5 square pyramids, edges with four equivalent Nb(3)O5 square pyramids, faces with four equivalent Nb(1)O6 octahedra, and faces with two equivalent Nb(2)O5 square pyramids. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form NbO6 octahedra that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Nb(3)O5 square pyramids, corners with four equivalent Nb(2)O5 square pyramids, edges with two equivalent Nb(3)O5 square pyramids, and faces with two equivalent Eu(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. In the second Nb site, Nb(2) is bonded to one O(5), two equivalent O(1), and two equivalent O(2) atoms to form NbO5 square pyramids that share corners with four equivalent Nb(1)O6 octahedra, corners with six equivalent Nb(3)O5 square pyramids,  an edgeedge with one Eu(1)O12 cuboctahedra, and  a faceface with one Eu(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 4-46°. In the third Nb site, Nb(3) is bonded to one O(1), one O(2), one O(4), one O(5), and one O(6) atom to form NbO5 square pyramids that share  a cornercorner with one Eu(1)O12 cuboctahedra,  a cornercorner with one Nb(1)O6 octahedra, corners with three equivalent Nb(2)O5 square pyramids, corners with three equivalent Nb(3)O5 square pyramids,  an edgeedge with one Eu(1)O12 cuboctahedra,  an edgeedge with one Nb(1)O6 octahedra, and  an edgeedge with one Nb(3)O5 square pyramid. The corner-sharing octahedral tilt angles are 48°. There are six inequivalent O sites. In the first O site, O(3) is bonded in a linear geometry to two equivalent Eu(1) and two equivalent Nb(1) atoms. In the second O site, O(4) is bonded in a distorted T-shaped geometry to one Nb(1) and two equivalent Nb(3) atoms. In the third O site, O(5) is bonded to one Eu(1), one Nb(2), and two equivalent Nb(3) atoms to form distorted corner-sharing OEuNb3 tetrahedra. In the fourth O site, O(6) is bonded in a square co-planar geometry to four equivalent Nb(3) atoms. In the fifth O site, O(1) is bonded in a distorted T-shaped geometry to one Eu(1), one Nb(1), one Nb(2), and one Nb(3) atom. In the sixth O site, O(2) is bonded in a 4-coordinate geometry to one Eu(1), one Nb(1), one Nb(2), and one Nb(3) atom.
EuNb8O14 crystallizes in the orthorhombic Pbam space group. Eu(1) is bonded to two equivalent O(3), two equivalent O(5), four equivalent O(1), and four equivalent O(2) atoms to form EuO12 cuboctahedra that share corners with two equivalent Eu(1)O12 cuboctahedra, corners with four equivalent Nb(3)O5 square pyramids, edges with two equivalent Nb(2)O5 square pyramids, edges with four equivalent Nb(3)O5 square pyramids, faces with four equivalent Nb(1)O6 octahedra, and faces with two equivalent Nb(2)O5 square pyramids. Both Eu(1)-O(3) bond lengths are 3.00 Å. Both Eu(1)-O(5) bond lengths are 2.66 Å. All Eu(1)-O(1) bond lengths are 2.96 Å. All Eu(1)-O(2) bond lengths are 2.78 Å. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(2) atoms to form NbO6 octahedra that share  a cornercorner with one Nb(1)O6 octahedra, corners with two equivalent Nb(3)O5 square pyramids, corners with four equivalent Nb(2)O5 square pyramids, edges with two equivalent Nb(3)O5 square pyramids, and faces with two equivalent Eu(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. The Nb(1)-O(3) bond length is 2.01 Å. The Nb(1)-O(4) bond length is 1.97 Å. Both Nb(1)-O(1) bond lengths are 2.03 Å. Both Nb(1)-O(2) bond lengths are 2.07 Å. In the second Nb site, Nb(2) is bonded to one O(5), two equivalent O(1), and two equivalent O(2) atoms to form NbO5 square pyramids that share corners with four equivalent Nb(1)O6 octahedra, corners with six equivalent Nb(3)O5 square pyramids,  an edgeedge with one Eu(1)O12 cuboctahedra, and  a faceface with one Eu(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 4-46°. The Nb(2)-O(5) bond length is 2.19 Å. Both Nb(2)-O(1) bond lengths are 2.09 Å. Both Nb(2)-O(2) bond lengths are 2.14 Å. In the third Nb site, Nb(3) is bonded to one O(1), one O(2), one O(4), one O(5), and one O(6) atom to form NbO5 square pyramids that share  a cornercorner with one Eu(1)O12 cuboctahedra,  a cornercorner with one Nb(1)O6 octahedra, corners with three equivalent Nb(2)O5 square pyramids, corners with three equivalent Nb(3)O5 square pyramids,  an edgeedge with one Eu(1)O12 cuboctahedra,  an edgeedge with one Nb(1)O6 octahedra, and  an edgeedge with one Nb(3)O5 square pyramid. The corner-sharing octahedral tilt angles are 48°. The Nb(3)-O(1) bond length is 2.15 Å. The Nb(3)-O(2) bond length is 2.11 Å. The Nb(3)-O(4) bond length is 2.19 Å. The Nb(3)-O(5) bond length is 2.05 Å. The Nb(3)-O(6) bond length is 2.15 Å. There are six inequivalent O sites. In the first O site, O(3) is bonded in a linear geometry to two equivalent Eu(1) and two equivalent Nb(1) atoms. In the second O site, O(4) is bonded in a distorted T-shaped geometry to one Nb(1) and two equivalent Nb(3) atoms. In the third O site, O(5) is bonded to one Eu(1), one Nb(2), and two equivalent Nb(3) atoms to form distorted corner-sharing OEuNb3 tetrahedra. In the fourth O site, O(6) is bonded in a square co-planar geometry to four equivalent Nb(3) atoms. In the fifth O site, O(1) is bonded in a distorted T-shaped geometry to one Eu(1), one Nb(1), one Nb(2), and one Nb(3) atom. In the sixth O site, O(2) is bonded in a 4-coordinate geometry to one Eu(1), one Nb(1), one Nb(2), and one Nb(3) atom.