LaBa2NbCu2O8 crystallizes in the tetragonal I4/mcm space group. Ba(1) is bonded to four equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms to form distorted BaO12 cuboctahedra that share corners with eight equivalent Ba(1)O12 cuboctahedra, faces with five equivalent Ba(1)O12 cuboctahedra, faces with four equivalent Nb(1)O6 octahedra, and faces with four equivalent Cu(1)O5 square pyramids. La(1) is bonded in a body-centered cubic geometry to eight equivalent O(2) atoms. Nb(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra, corners with two equivalent Cu(1)O5 square pyramids, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 13°. Cu(1) is bonded to one O(1) and four equivalent O(2) atoms to form CuO5 square pyramids that share  a cornercorner with one Nb(1)O6 octahedra, corners with four equivalent Cu(1)O5 square pyramids, and faces with four equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. There are three inequivalent O sites. In the first O site, O(3) is bonded in a distorted linear geometry to four equivalent Ba(1) and two equivalent Nb(1) atoms. In the second O site, O(1) is bonded to four equivalent Ba(1), one Nb(1), and one Cu(1) atom to form distorted OBa4NbCu octahedra that share corners with five equivalent O(1)Ba4NbCu octahedra, corners with eight equivalent O(2)Ba2La2Cu2 octahedra, edges with four equivalent O(1)Ba4NbCu octahedra, and faces with four equivalent O(2)Ba2La2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 0-55°. In the third O site, O(2) is bonded to two equivalent Ba(1), two equivalent La(1), and two equivalent Cu(1) atoms to form distorted OBa2La2Cu2 octahedra that share corners with four equivalent O(1)Ba4NbCu octahedra, corners with eight equivalent O(2)Ba2La2Cu2 octahedra, edges with three equivalent O(2)Ba2La2Cu2 octahedra, faces with two equivalent O(1)Ba4NbCu octahedra, and faces with four equivalent O(2)Ba2La2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 0-68°.
LaBa2NbCu2O8 crystallizes in the tetragonal I4/mcm space group. Ba(1) is bonded to four equivalent O(1), four equivalent O(2), and four equivalent O(3) atoms to form distorted BaO12 cuboctahedra that share corners with eight equivalent Ba(1)O12 cuboctahedra, faces with five equivalent Ba(1)O12 cuboctahedra, faces with four equivalent Nb(1)O6 octahedra, and faces with four equivalent Cu(1)O5 square pyramids. All Ba(1)-O(1) bond lengths are 2.86 Å. There are two shorter (2.93 Å) and two longer (2.94 Å) Ba(1)-O(2) bond lengths. There are two shorter (2.97 Å) and two longer (3.26 Å) Ba(1)-O(3) bond lengths. La(1) is bonded in a body-centered cubic geometry to eight equivalent O(2) atoms. There are four shorter (2.54 Å) and four longer (2.55 Å) La(1)-O(2) bond lengths. Nb(1) is bonded to two equivalent O(1) and four equivalent O(3) atoms to form NbO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra, corners with two equivalent Cu(1)O5 square pyramids, and faces with eight equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 13°. Both Nb(1)-O(1) bond lengths are 1.99 Å. All Nb(1)-O(3) bond lengths are 2.02 Å. Cu(1) is bonded to one O(1) and four equivalent O(2) atoms to form CuO5 square pyramids that share  a cornercorner with one Nb(1)O6 octahedra, corners with four equivalent Cu(1)O5 square pyramids, and faces with four equivalent Ba(1)O12 cuboctahedra. The corner-sharing octahedra are not tilted. The Cu(1)-O(1) bond length is 2.35 Å. All Cu(1)-O(2) bond lengths are 2.01 Å. There are three inequivalent O sites. In the first O site, O(3) is bonded in a distorted linear geometry to four equivalent Ba(1) and two equivalent Nb(1) atoms. In the second O site, O(1) is bonded to four equivalent Ba(1), one Nb(1), and one Cu(1) atom to form distorted OBa4NbCu octahedra that share corners with five equivalent O(1)Ba4NbCu octahedra, corners with eight equivalent O(2)Ba2La2Cu2 octahedra, edges with four equivalent O(1)Ba4NbCu octahedra, and faces with four equivalent O(2)Ba2La2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 0-55°. In the third O site, O(2) is bonded to two equivalent Ba(1), two equivalent La(1), and two equivalent Cu(1) atoms to form distorted OBa2La2Cu2 octahedra that share corners with four equivalent O(1)Ba4NbCu octahedra, corners with eight equivalent O(2)Ba2La2Cu2 octahedra, edges with three equivalent O(2)Ba2La2Cu2 octahedra, faces with two equivalent O(1)Ba4NbCu octahedra, and faces with four equivalent O(2)Ba2La2Cu2 octahedra. The corner-sharing octahedral tilt angles range from 0-68°.