Sr2MnNbO6 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one O(2), one O(4), one O(6), one O(7), one O(9), two equivalent O(3), two equivalent O(8), and three equivalent O(1) atoms to form SrO12 cuboctahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, corners with six equivalent Sr(2)O12 cuboctahedra, faces with two equivalent Sr(2)O12 cuboctahedra, faces with four equivalent Sr(1)O12 cuboctahedra,  a faceface with one Nb(2)O6 octahedra,  a faceface with one Mn(2)O6 octahedra, faces with three equivalent Nb(1)O6 octahedra, and faces with three equivalent Mn(1)O6 octahedra. In the second Sr site, Sr(2) is bonded to one O(1), one O(4), one O(6), one O(7), one O(9), two equivalent O(10), two equivalent O(5), and three equivalent O(2) atoms to form SrO12 cuboctahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, corners with six equivalent Sr(2)O12 cuboctahedra, faces with two equivalent Sr(1)O12 cuboctahedra, faces with four equivalent Sr(2)O12 cuboctahedra,  a faceface with one Nb(1)O6 octahedra,  a faceface with one Mn(1)O6 octahedra, faces with three equivalent Nb(2)O6 octahedra, and faces with three equivalent Mn(2)O6 octahedra. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(3), one O(4), one O(7), one O(8), and two equivalent O(1) atoms to form NbO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with four equivalent Mn(1)O6 octahedra, faces with two equivalent Sr(2)O12 cuboctahedra, and faces with six equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 2-12°. In the second Nb site, Nb(2) is bonded to one O(10), one O(5), one O(6), one O(9), and two equivalent O(2) atoms to form NbO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with four equivalent Mn(2)O6 octahedra, faces with two equivalent Sr(1)O12 cuboctahedra, and faces with six equivalent Sr(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 2-12°. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(3), one O(6), one O(8), one O(9), and two equivalent O(1) atoms to form MnO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra, corners with four equivalent Nb(1)O6 octahedra, faces with two equivalent Sr(2)O12 cuboctahedra, and faces with six equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 2-12°. In the second Mn site, Mn(2) is bonded to one O(10), one O(4), one O(5), one O(7), and two equivalent O(2) atoms to form MnO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, faces with two equivalent Sr(1)O12 cuboctahedra, and faces with six equivalent Sr(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 2-9°. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Sr(2), three equivalent Sr(1), one Nb(1), and one Mn(1) atom. In the second O site, O(2) is bonded in a distorted linear geometry to one Sr(1), three equivalent Sr(2), one Nb(2), and one Mn(2) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to four equivalent Sr(1), one Nb(1), and one Mn(1) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(1), and one Mn(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to four equivalent Sr(2), one Nb(2), and one Mn(2) atom. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(2), and one Mn(1) atom. In the seventh O site, O(7) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(1), and one Mn(2) atom. In the eighth O site, O(8) is bonded in a 2-coordinate geometry to four equivalent Sr(1), one Nb(1), and one Mn(1) atom. In the ninth O site, O(9) is bonded in a 2-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(2), and one Mn(1) atom. In the tenth O site, O(10) is bonded in a 6-coordinate geometry to four equivalent Sr(2), one Nb(2), and one Mn(2) atom.
Sr2MnNbO6 crystallizes in the monoclinic P2_1/m space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded to one O(2), one O(4), one O(6), one O(7), one O(9), two equivalent O(3), two equivalent O(8), and three equivalent O(1) atoms to form SrO12 cuboctahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, corners with six equivalent Sr(2)O12 cuboctahedra, faces with two equivalent Sr(2)O12 cuboctahedra, faces with four equivalent Sr(1)O12 cuboctahedra,  a faceface with one Nb(2)O6 octahedra,  a faceface with one Mn(2)O6 octahedra, faces with three equivalent Nb(1)O6 octahedra, and faces with three equivalent Mn(1)O6 octahedra. The Sr(1)-O(2) bond length is 2.84 Å. The Sr(1)-O(4) bond length is 2.73 Å. The Sr(1)-O(6) bond length is 2.68 Å. The Sr(1)-O(7) bond length is 2.97 Å. The Sr(1)-O(9) bond length is 2.98 Å. There is one shorter (2.71 Å) and one longer (2.97 Å) Sr(1)-O(3) bond length. There is one shorter (2.70 Å) and one longer (3.03 Å) Sr(1)-O(8) bond length. There are a spread of Sr(1)-O(1) bond distances ranging from 2.81-2.96 Å. In the second Sr site, Sr(2) is bonded to one O(1), one O(4), one O(6), one O(7), one O(9), two equivalent O(10), two equivalent O(5), and three equivalent O(2) atoms to form SrO12 cuboctahedra that share corners with six equivalent Sr(1)O12 cuboctahedra, corners with six equivalent Sr(2)O12 cuboctahedra, faces with two equivalent Sr(1)O12 cuboctahedra, faces with four equivalent Sr(2)O12 cuboctahedra,  a faceface with one Nb(1)O6 octahedra,  a faceface with one Mn(1)O6 octahedra, faces with three equivalent Nb(2)O6 octahedra, and faces with three equivalent Mn(2)O6 octahedra. The Sr(2)-O(1) bond length is 2.85 Å. The Sr(2)-O(4) bond length is 2.95 Å. The Sr(2)-O(6) bond length is 3.02 Å. The Sr(2)-O(7) bond length is 2.71 Å. The Sr(2)-O(9) bond length is 2.70 Å. There is one shorter (2.74 Å) and one longer (2.93 Å) Sr(2)-O(10) bond length. There is one shorter (2.74 Å) and one longer (2.99 Å) Sr(2)-O(5) bond length. There are a spread of Sr(2)-O(2) bond distances ranging from 2.81-2.96 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(3), one O(4), one O(7), one O(8), and two equivalent O(1) atoms to form NbO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with four equivalent Mn(1)O6 octahedra, faces with two equivalent Sr(2)O12 cuboctahedra, and faces with six equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 2-12°. The Nb(1)-O(3) bond length is 1.95 Å. The Nb(1)-O(4) bond length is 2.09 Å. The Nb(1)-O(7) bond length is 1.95 Å. The Nb(1)-O(8) bond length is 2.05 Å. Both Nb(1)-O(1) bond lengths are 2.01 Å. In the second Nb site, Nb(2) is bonded to one O(10), one O(5), one O(6), one O(9), and two equivalent O(2) atoms to form NbO6 octahedra that share corners with two equivalent Mn(1)O6 octahedra, corners with four equivalent Mn(2)O6 octahedra, faces with two equivalent Sr(1)O12 cuboctahedra, and faces with six equivalent Sr(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 2-12°. The Nb(2)-O(10) bond length is 1.95 Å. The Nb(2)-O(5) bond length is 2.05 Å. The Nb(2)-O(6) bond length is 1.94 Å. The Nb(2)-O(9) bond length is 2.10 Å. Both Nb(2)-O(2) bond lengths are 2.01 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(3), one O(6), one O(8), one O(9), and two equivalent O(1) atoms to form MnO6 octahedra that share corners with two equivalent Nb(2)O6 octahedra, corners with four equivalent Nb(1)O6 octahedra, faces with two equivalent Sr(2)O12 cuboctahedra, and faces with six equivalent Sr(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 2-12°. The Mn(1)-O(3) bond length is 2.22 Å. The Mn(1)-O(6) bond length is 2.18 Å. The Mn(1)-O(8) bond length is 1.94 Å. The Mn(1)-O(9) bond length is 1.94 Å. Both Mn(1)-O(1) bond lengths are 1.96 Å. In the second Mn site, Mn(2) is bonded to one O(10), one O(4), one O(5), one O(7), and two equivalent O(2) atoms to form MnO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, faces with two equivalent Sr(1)O12 cuboctahedra, and faces with six equivalent Sr(2)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 2-9°. The Mn(2)-O(10) bond length is 2.22 Å. The Mn(2)-O(4) bond length is 1.94 Å. The Mn(2)-O(5) bond length is 1.93 Å. The Mn(2)-O(7) bond length is 2.18 Å. Both Mn(2)-O(2) bond lengths are 1.96 Å. There are ten inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Sr(2), three equivalent Sr(1), one Nb(1), and one Mn(1) atom. In the second O site, O(2) is bonded in a distorted linear geometry to one Sr(1), three equivalent Sr(2), one Nb(2), and one Mn(2) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to four equivalent Sr(1), one Nb(1), and one Mn(1) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(1), and one Mn(2) atom. In the fifth O site, O(5) is bonded in a 2-coordinate geometry to four equivalent Sr(2), one Nb(2), and one Mn(2) atom. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(2), and one Mn(1) atom. In the seventh O site, O(7) is bonded in a 6-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(1), and one Mn(2) atom. In the eighth O site, O(8) is bonded in a 2-coordinate geometry to four equivalent Sr(1), one Nb(1), and one Mn(1) atom. In the ninth O site, O(9) is bonded in a 2-coordinate geometry to two equivalent Sr(1), two equivalent Sr(2), one Nb(2), and one Mn(1) atom. In the tenth O site, O(10) is bonded in a 6-coordinate geometry to four equivalent Sr(2), one Nb(2), and one Mn(2) atom.