Li4Sr4Nb5FeO20 crystallizes in the monoclinic C2/m space group. Li(1) is bonded in a 4-coordinate geometry to two equivalent O(4) and two equivalent O(7) atoms. Sr(1,2) is bonded to two equivalent O(2); two equivalent O(8); four equivalent O(1,6); and four equivalent O(3,5) atoms to form distorted SrO12 cuboctahedra that share corners with eight equivalent Sr(1,2)O12 cuboctahedra; faces with five equivalent Sr(1,2)O12 cuboctahedra; faces with two equivalent Nb(1)O6 octahedra; faces with two equivalent Nb(2)O6 octahedra; faces with two equivalent Nb(3)O6 octahedra; and faces with two equivalent Fe(1)O6 octahedra. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent O(2) and four equivalent O(1,6) atoms to form NbO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra; corners with four equivalent Fe(1)O6 octahedra; and faces with eight equivalent Sr(1,2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-16°. In the second Nb site, Nb(2) is bonded to one O(2); one O(4); and four equivalent O(3,5) atoms to form NbO6 octahedra that share  a cornercorner with one Nb(1)O6 octahedra; corners with four equivalent Nb(3)O6 octahedra; and faces with four equivalent Sr(1,2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-11°. In the third Nb site, Nb(3) is bonded to one O(7); one O(8); and four equivalent O(3,5) atoms to form NbO6 octahedra that share  a cornercorner with one Fe(1)O6 octahedra; corners with four equivalent Nb(2)O6 octahedra; and faces with four equivalent Sr(1,2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-11°. Fe(1) is bonded to two equivalent O(8) and four equivalent O(1,6) atoms to form FeO6 octahedra that share corners with two equivalent Nb(3)O6 octahedra; corners with four equivalent Nb(1)O6 octahedra; and faces with eight equivalent Sr(1,2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-16°. There are six inequivalent O sites. In the first O site, O(7) is bonded to four equivalent Li(1) and one Nb(3) atom to form distorted OLi4Nb trigonal bipyramids that share  a cornercorner with one O(8)Sr4NbFe octahedra, corners with four equivalent O(4)Li4Nb trigonal bipyramids, edges with two equivalent O(4)Li4Nb trigonal bipyramids, and edges with two equivalent O(7)Li4Nb trigonal bipyramids. The corner-sharing octahedra are not tilted. In the second O site, O(8) is bonded to four equivalent Sr(1,2); one Nb(3); and one Fe(1) atom to form distorted OSr4NbFe octahedra that share corners with five equivalent O(8)Sr4NbFe octahedra,  a cornercorner with one O(7)Li4Nb trigonal bipyramid, and edges with four equivalent O(2)Sr4Nb2 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the third O site, O(1,6) is bonded in a 4-coordinate geometry to four equivalent Sr(1,2); one Nb(1); and one Fe(1) atom. In the fourth O site, O(2) is bonded to four equivalent Sr(1,2); one Nb(1); and one Nb(2) atom to form distorted OSr4Nb2 octahedra that share corners with five equivalent O(2)Sr4Nb2 octahedra,  a cornercorner with one O(4)Li4Nb trigonal bipyramid, and edges with four equivalent O(8)Sr4NbFe octahedra. The corner-sharing octahedra are not tilted. In the fifth O site, O(3,5) is bonded in a distorted linear geometry to two equivalent Sr(1,2); one Nb(2); and one Nb(3) atom. In the sixth O site, O(4) is bonded to four equivalent Li(1) and one Nb(2) atom to form distorted OLi4Nb trigonal bipyramids that share  a cornercorner with one O(2)Sr4Nb2 octahedra, corners with four equivalent O(7)Li4Nb trigonal bipyramids, edges with two equivalent O(4)Li4Nb trigonal bipyramids, and edges with two equivalent O(7)Li4Nb trigonal bipyramids. The corner-sharing octahedra are not tilted.
Li4Sr4Nb5FeO20 crystallizes in the monoclinic C2/m space group. Li(1) is bonded in a 4-coordinate geometry to two equivalent O(4) and two equivalent O(7) atoms. Both Li(1)-O(4) bond lengths are 2.09 Å. Both Li(1)-O(7) bond lengths are 2.07 Å. Sr(1,2) is bonded to two equivalent O(2); two equivalent O(8); four equivalent O(1,6); and four equivalent O(3,5) atoms to form distorted SrO12 cuboctahedra that share corners with eight equivalent Sr(1,2)O12 cuboctahedra; faces with five equivalent Sr(1,2)O12 cuboctahedra; faces with two equivalent Nb(1)O6 octahedra; faces with two equivalent Nb(2)O6 octahedra; faces with two equivalent Nb(3)O6 octahedra; and faces with two equivalent Fe(1)O6 octahedra. Both Sr(1,2)-O(2) bond lengths are 2.84 Å. Both Sr(1,2)-O(8) bond lengths are 2.84 Å. There are two shorter (2.65 Å) and two longer (3.04 Å) Sr(1,2)-O(1,6) bond lengths. There are two shorter (2.79 Å) and two longer (2.80 Å) Sr(1,2)-O(3,5) bond lengths. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent O(2) and four equivalent O(1,6) atoms to form NbO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra; corners with four equivalent Fe(1)O6 octahedra; and faces with eight equivalent Sr(1,2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-16°. Both Nb(1)-O(2) bond lengths are 2.01 Å. All Nb(1)-O(1,6) bond lengths are 2.01 Å. In the second Nb site, Nb(2) is bonded to one O(2); one O(4); and four equivalent O(3,5) atoms to form NbO6 octahedra that share  a cornercorner with one Nb(1)O6 octahedra; corners with four equivalent Nb(3)O6 octahedra; and faces with four equivalent Sr(1,2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-11°. The Nb(2)-O(2) bond length is 2.19 Å. The Nb(2)-O(4) bond length is 1.89 Å. All Nb(2)-O(3,5) bond lengths are 2.01 Å. In the third Nb site, Nb(3) is bonded to one O(7); one O(8); and four equivalent O(3,5) atoms to form NbO6 octahedra that share  a cornercorner with one Fe(1)O6 octahedra; corners with four equivalent Nb(2)O6 octahedra; and faces with four equivalent Sr(1,2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-11°. The Nb(3)-O(7) bond length is 1.92 Å. The Nb(3)-O(8) bond length is 2.08 Å. All Nb(3)-O(3,5) bond lengths are 2.02 Å. Fe(1) is bonded to two equivalent O(8) and four equivalent O(1,6) atoms to form FeO6 octahedra that share corners with two equivalent Nb(3)O6 octahedra; corners with four equivalent Nb(1)O6 octahedra; and faces with eight equivalent Sr(1,2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-16°. Both Fe(1)-O(8) bond lengths are 2.03 Å. All Fe(1)-O(1,6) bond lengths are 2.04 Å. There are six inequivalent O sites. In the first O site, O(7) is bonded to four equivalent Li(1) and one Nb(3) atom to form distorted OLi4Nb trigonal bipyramids that share  a cornercorner with one O(8)Sr4NbFe octahedra, corners with four equivalent O(4)Li4Nb trigonal bipyramids, edges with two equivalent O(4)Li4Nb trigonal bipyramids, and edges with two equivalent O(7)Li4Nb trigonal bipyramids. The corner-sharing octahedra are not tilted. In the second O site, O(8) is bonded to four equivalent Sr(1,2); one Nb(3); and one Fe(1) atom to form distorted OSr4NbFe octahedra that share corners with five equivalent O(8)Sr4NbFe octahedra,  a cornercorner with one O(7)Li4Nb trigonal bipyramid, and edges with four equivalent O(2)Sr4Nb2 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the third O site, O(1,6) is bonded in a 4-coordinate geometry to four equivalent Sr(1,2); one Nb(1); and one Fe(1) atom. In the fourth O site, O(2) is bonded to four equivalent Sr(1,2); one Nb(1); and one Nb(2) atom to form distorted OSr4Nb2 octahedra that share corners with five equivalent O(2)Sr4Nb2 octahedra,  a cornercorner with one O(4)Li4Nb trigonal bipyramid, and edges with four equivalent O(8)Sr4NbFe octahedra. The corner-sharing octahedra are not tilted. In the fifth O site, O(3,5) is bonded in a distorted linear geometry to two equivalent Sr(1,2); one Nb(2); and one Nb(3) atom. In the sixth O site, O(4) is bonded to four equivalent Li(1) and one Nb(2) atom to form distorted OLi4Nb trigonal bipyramids that share  a cornercorner with one O(2)Sr4Nb2 octahedra, corners with four equivalent O(7)Li4Nb trigonal bipyramids, edges with two equivalent O(4)Li4Nb trigonal bipyramids, and edges with two equivalent O(7)Li4Nb trigonal bipyramids. The corner-sharing octahedra are not tilted.