BaNb4(FeO7)2 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 10-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form NbO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one Nb(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-57°. In the second Nb site, Nb(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form NbO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one Nb(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 30-44°. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form FeO6 octahedra that share corners with two equivalent Nb(2)O4 tetrahedra and corners with four equivalent Nb(1)O4 tetrahedra. In the second Fe site, Fe(2) is bonded to two equivalent O(2), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent Nb(1)O4 tetrahedra and corners with four equivalent Nb(2)O4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(2) is bonded in a bent 150 degrees geometry to one Ba(1), one Nb(1), and one Fe(2) atom. In the second O site, O(3) is bonded in a bent 150 degrees geometry to one Nb(1) and one Fe(1) atom. In the third O site, O(4) is bonded in a bent 120 degrees geometry to one Nb(1) and one Nb(2) atom. In the fourth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Nb(2), and one Fe(1) atom. In the fifth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Nb(2), and one Fe(2) atom. In the sixth O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Nb(2), and one Fe(2) atom. In the seventh O site, O(1) is bonded in a 3-coordinate geometry to one Ba(1), one Nb(1), and one Fe(1) atom.
BaNb4(FeO7)2 crystallizes in the monoclinic C2/c space group. Ba(1) is bonded in a 10-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(5), two equivalent O(6), and two equivalent O(7) atoms. Both Ba(1)-O(1) bond lengths are 3.07 Å. Both Ba(1)-O(2) bond lengths are 3.21 Å. Both Ba(1)-O(5) bond lengths are 3.45 Å. Both Ba(1)-O(6) bond lengths are 3.18 Å. Both Ba(1)-O(7) bond lengths are 3.16 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form NbO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one Nb(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-57°. The Nb(1)-O(1) bond length is 1.87 Å. The Nb(1)-O(2) bond length is 1.83 Å. The Nb(1)-O(3) bond length is 1.85 Å. The Nb(1)-O(4) bond length is 1.96 Å. In the second Nb site, Nb(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form NbO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one Nb(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 30-44°. The Nb(2)-O(4) bond length is 1.92 Å. The Nb(2)-O(5) bond length is 1.87 Å. The Nb(2)-O(6) bond length is 1.83 Å. The Nb(2)-O(7) bond length is 1.86 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(5) atoms to form FeO6 octahedra that share corners with two equivalent Nb(2)O4 tetrahedra and corners with four equivalent Nb(1)O4 tetrahedra. Both Fe(1)-O(1) bond lengths are 2.21 Å. Both Fe(1)-O(3) bond lengths are 1.97 Å. Both Fe(1)-O(5) bond lengths are 2.06 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(2), two equivalent O(6), and two equivalent O(7) atoms to form FeO6 octahedra that share corners with two equivalent Nb(1)O4 tetrahedra and corners with four equivalent Nb(2)O4 tetrahedra. Both Fe(2)-O(2) bond lengths are 2.00 Å. Both Fe(2)-O(6) bond lengths are 2.02 Å. Both Fe(2)-O(7) bond lengths are 2.02 Å. There are seven inequivalent O sites. In the first O site, O(2) is bonded in a bent 150 degrees geometry to one Ba(1), one Nb(1), and one Fe(2) atom. In the second O site, O(3) is bonded in a bent 150 degrees geometry to one Nb(1) and one Fe(1) atom. In the third O site, O(4) is bonded in a bent 120 degrees geometry to one Nb(1) and one Nb(2) atom. In the fourth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Nb(2), and one Fe(1) atom. In the fifth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Nb(2), and one Fe(2) atom. In the sixth O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Ba(1), one Nb(2), and one Fe(2) atom. In the seventh O site, O(1) is bonded in a 3-coordinate geometry to one Ba(1), one Nb(1), and one Fe(1) atom.