Nb5B6 crystallizes in the orthorhombic Cmmm space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to four equivalent B(1) and eight equivalent B(3) atoms to form a mixture of edge and face-sharing NbB12 cuboctahedra. In the second Nb site, Nb(2) is bonded in a 7-coordinate geometry to one B(2), two equivalent B(3), and four equivalent B(1) atoms. In the third Nb site, Nb(3) is bonded in a 7-coordinate geometry to one B(1) and six equivalent B(2) atoms. There are three inequivalent B sites. In the first B site, B(1) is bonded in a 9-coordinate geometry to one Nb(3), two equivalent Nb(1), four equivalent Nb(2), and two equivalent B(3) atoms. In the second B site, B(2) is bonded in a 9-coordinate geometry to one Nb(2), six equivalent Nb(3), and two equivalent B(2) atoms. In the third B site, B(3) is bonded in a 9-coordinate geometry to two equivalent Nb(2), four equivalent Nb(1), one B(3), and two equivalent B(1) atoms.
Nb5B6 crystallizes in the orthorhombic Cmmm space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to four equivalent B(1) and eight equivalent B(3) atoms to form a mixture of edge and face-sharing NbB12 cuboctahedra. All Nb(1)-B(1) bond lengths are 2.50 Å. All Nb(1)-B(3) bond lengths are 2.47 Å. In the second Nb site, Nb(2) is bonded in a 7-coordinate geometry to one B(2), two equivalent B(3), and four equivalent B(1) atoms. The Nb(2)-B(2) bond length is 2.59 Å. Both Nb(2)-B(3) bond lengths are 2.38 Å. All Nb(2)-B(1) bond lengths are 2.41 Å. In the third Nb site, Nb(3) is bonded in a 7-coordinate geometry to one B(1) and six equivalent B(2) atoms. The Nb(3)-B(1) bond length is 2.58 Å. There are four shorter (2.42 Å) and two longer (2.44 Å) Nb(3)-B(2) bond lengths. There are three inequivalent B sites. In the first B site, B(1) is bonded in a 9-coordinate geometry to one Nb(3), two equivalent Nb(1), four equivalent Nb(2), and two equivalent B(3) atoms. Both B(1)-B(3) bond lengths are 1.85 Å. In the second B site, B(2) is bonded in a 9-coordinate geometry to one Nb(2), six equivalent Nb(3), and two equivalent B(2) atoms. Both B(2)-B(2) bond lengths are 1.89 Å. In the third B site, B(3) is bonded in a 9-coordinate geometry to two equivalent Nb(2), four equivalent Nb(1), one B(3), and two equivalent B(1) atoms. The B(3)-B(3) bond length is 1.81 Å.