Nb3Mn8Si crystallizes in the trigonal P3m1 space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 16-coordinate geometry to one Nb(2), three equivalent Mn(1), three equivalent Mn(3), six equivalent Mn(4), and three equivalent Si(1) atoms. In the second Nb site, Nb(2) is bonded in a 16-coordinate geometry to one Nb(1), three equivalent Nb(3), three equivalent Mn(2), three equivalent Mn(3), and six equivalent Mn(4) atoms. In the third Nb site, Nb(3) is bonded in a 16-coordinate geometry to three equivalent Nb(2), three equivalent Mn(2), three equivalent Mn(4), six equivalent Mn(3), and one Si(1) atom. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to three equivalent Nb(1), three equivalent Mn(3), three equivalent Mn(4), and three equivalent Si(1) atoms to form MnMn6Nb3Si3 cuboctahedra that share corners with six equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, corners with six equivalent Mn(4)Mn6Nb5Si cuboctahedra, edges with six equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, faces with two equivalent Mn(2)Mn6Nb6 cuboctahedra, faces with nine equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, and faces with nine equivalent Mn(4)Mn6Nb5Si cuboctahedra. In the second Mn site, Mn(2) is bonded to three equivalent Nb(2), three equivalent Nb(3), three equivalent Mn(3), and three equivalent Mn(4) atoms to form MnMn6Nb6 cuboctahedra that share corners with six equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, corners with six equivalent Mn(4)Mn6Nb5Si cuboctahedra, edges with six equivalent Mn(2)Mn6Nb6 cuboctahedra, faces with two equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, faces with nine equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, and faces with nine equivalent Mn(4)Mn6Nb5Si cuboctahedra. In the third Mn site, Mn(3) is bonded to one Nb(1), one Nb(2), two equivalent Nb(3), one Mn(1), one Mn(2), four equivalent Mn(3), and two equivalent Si(1) atoms to form MnMn6Nb4Si2 cuboctahedra that share corners with two equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, corners with two equivalent Mn(2)Mn6Nb6 cuboctahedra, corners with four equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, corners with ten equivalent Mn(4)Mn6Nb5Si cuboctahedra, edges with two equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, edges with four equivalent Mn(4)Mn6Nb5Si cuboctahedra, faces with three equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, faces with three equivalent Mn(2)Mn6Nb6 cuboctahedra, faces with four equivalent Mn(4)Mn6Nb5Si cuboctahedra, and faces with eight equivalent Mn(3)Mn6Nb4Si2 cuboctahedra. In the fourth Mn site, Mn(4) is bonded to one Nb(3), two equivalent Nb(1), two equivalent Nb(2), one Mn(1), one Mn(2), four equivalent Mn(4), and one Si(1) atom to form distorted MnMn6Nb5Si cuboctahedra that share corners with two equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, corners with two equivalent Mn(2)Mn6Nb6 cuboctahedra, corners with four equivalent Mn(4)Mn6Nb5Si cuboctahedra, corners with ten equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, edges with two equivalent Mn(4)Mn6Nb5Si cuboctahedra, edges with four equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, faces with three equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, faces with three equivalent Mn(2)Mn6Nb6 cuboctahedra, faces with four equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, and faces with eight equivalent Mn(4)Mn6Nb5Si cuboctahedra. Si(1) is bonded in a 16-coordinate geometry to one Nb(3), three equivalent Nb(1), three equivalent Mn(1), three equivalent Mn(4), and six equivalent Mn(3) atoms.
Nb3Mn8Si crystallizes in the trigonal P3m1 space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 16-coordinate geometry to one Nb(2), three equivalent Mn(1), three equivalent Mn(3), six equivalent Mn(4), and three equivalent Si(1) atoms. The Nb(1)-Nb(2) bond length is 2.95 Å. All Nb(1)-Mn(1) bond lengths are 2.79 Å. All Nb(1)-Mn(3) bond lengths are 2.72 Å. All Nb(1)-Mn(4) bond lengths are 2.81 Å. All Nb(1)-Si(1) bond lengths are 2.90 Å. In the second Nb site, Nb(2) is bonded in a 16-coordinate geometry to one Nb(1), three equivalent Nb(3), three equivalent Mn(2), three equivalent Mn(3), and six equivalent Mn(4) atoms. All Nb(2)-Nb(3) bond lengths are 2.98 Å. All Nb(2)-Mn(2) bond lengths are 2.79 Å. All Nb(2)-Mn(3) bond lengths are 2.83 Å. All Nb(2)-Mn(4) bond lengths are 2.79 Å. In the third Nb site, Nb(3) is bonded in a 16-coordinate geometry to three equivalent Nb(2), three equivalent Mn(2), three equivalent Mn(4), six equivalent Mn(3), and one Si(1) atom. All Nb(3)-Mn(2) bond lengths are 2.84 Å. All Nb(3)-Mn(4) bond lengths are 2.92 Å. All Nb(3)-Mn(3) bond lengths are 2.74 Å. The Nb(3)-Si(1) bond length is 2.79 Å. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to three equivalent Nb(1), three equivalent Mn(3), three equivalent Mn(4), and three equivalent Si(1) atoms to form MnMn6Nb3Si3 cuboctahedra that share corners with six equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, corners with six equivalent Mn(4)Mn6Nb5Si cuboctahedra, edges with six equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, faces with two equivalent Mn(2)Mn6Nb6 cuboctahedra, faces with nine equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, and faces with nine equivalent Mn(4)Mn6Nb5Si cuboctahedra. All Mn(1)-Mn(3) bond lengths are 2.37 Å. All Mn(1)-Mn(4) bond lengths are 2.42 Å. All Mn(1)-Si(1) bond lengths are 2.79 Å. In the second Mn site, Mn(2) is bonded to three equivalent Nb(2), three equivalent Nb(3), three equivalent Mn(3), and three equivalent Mn(4) atoms to form MnMn6Nb6 cuboctahedra that share corners with six equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, corners with six equivalent Mn(4)Mn6Nb5Si cuboctahedra, edges with six equivalent Mn(2)Mn6Nb6 cuboctahedra, faces with two equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, faces with nine equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, and faces with nine equivalent Mn(4)Mn6Nb5Si cuboctahedra. All Mn(2)-Mn(3) bond lengths are 2.49 Å. All Mn(2)-Mn(4) bond lengths are 2.38 Å. In the third Mn site, Mn(3) is bonded to one Nb(1), one Nb(2), two equivalent Nb(3), one Mn(1), one Mn(2), four equivalent Mn(3), and two equivalent Si(1) atoms to form MnMn6Nb4Si2 cuboctahedra that share corners with two equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, corners with two equivalent Mn(2)Mn6Nb6 cuboctahedra, corners with four equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, corners with ten equivalent Mn(4)Mn6Nb5Si cuboctahedra, edges with two equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, edges with four equivalent Mn(4)Mn6Nb5Si cuboctahedra, faces with three equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, faces with three equivalent Mn(2)Mn6Nb6 cuboctahedra, faces with four equivalent Mn(4)Mn6Nb5Si cuboctahedra, and faces with eight equivalent Mn(3)Mn6Nb4Si2 cuboctahedra. There are two shorter (2.32 Å) and two longer (2.44 Å) Mn(3)-Mn(3) bond lengths. Both Mn(3)-Si(1) bond lengths are 2.79 Å. In the fourth Mn site, Mn(4) is bonded to one Nb(3), two equivalent Nb(1), two equivalent Nb(2), one Mn(1), one Mn(2), four equivalent Mn(4), and one Si(1) atom to form distorted MnMn6Nb5Si cuboctahedra that share corners with two equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, corners with two equivalent Mn(2)Mn6Nb6 cuboctahedra, corners with four equivalent Mn(4)Mn6Nb5Si cuboctahedra, corners with ten equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, edges with two equivalent Mn(4)Mn6Nb5Si cuboctahedra, edges with four equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, faces with three equivalent Mn(1)Mn6Nb3Si3 cuboctahedra, faces with three equivalent Mn(2)Mn6Nb6 cuboctahedra, faces with four equivalent Mn(3)Mn6Nb4Si2 cuboctahedra, and faces with eight equivalent Mn(4)Mn6Nb5Si cuboctahedra. There are two shorter (2.28 Å) and two longer (2.48 Å) Mn(4)-Mn(4) bond lengths. The Mn(4)-Si(1) bond length is 2.75 Å. Si(1) is bonded in a 16-coordinate geometry to one Nb(3), three equivalent Nb(1), three equivalent Mn(1), three equivalent Mn(4), and six equivalent Mn(3) atoms.