Tm2Ni21B6 crystallizes in the cubic Fm-3m space group. Tm(1) is bonded to four equivalent Ni(1) and twelve equivalent Ni(2) atoms to form distorted TmNi16 tetrahedra that share edges with six equivalent Tm(1)Ni16 tetrahedra and faces with four equivalent Ni(3)Ni12 cuboctahedra. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one Tm(1) and three equivalent B(1) atoms to form a mixture of distorted corner and edge-sharing NiTmB3 tetrahedra. In the second Ni site, Ni(2) is bonded in a distorted bent 150 degrees geometry to two equivalent Tm(1), one Ni(3), and two equivalent B(1) atoms. In the third Ni site, Ni(3) is bonded to twelve equivalent Ni(2) atoms to form NiNi12 cuboctahedra that share faces with eight equivalent Tm(1)Ni16 tetrahedra. B(1) is bonded in a 8-coordinate geometry to four equivalent Ni(1) and four equivalent Ni(2) atoms.
Tm2Ni21B6 crystallizes in the cubic Fm-3m space group. Tm(1) is bonded to four equivalent Ni(1) and twelve equivalent Ni(2) atoms to form distorted TmNi16 tetrahedra that share edges with six equivalent Tm(1)Ni16 tetrahedra and faces with four equivalent Ni(3)Ni12 cuboctahedra. All Tm(1)-Ni(1) bond lengths are 2.51 Å. All Tm(1)-Ni(2) bond lengths are 2.90 Å. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one Tm(1) and three equivalent B(1) atoms to form a mixture of distorted corner and edge-sharing NiTmB3 tetrahedra. All Ni(1)-B(1) bond lengths are 2.08 Å. In the second Ni site, Ni(2) is bonded in a distorted bent 150 degrees geometry to two equivalent Tm(1), one Ni(3), and two equivalent B(1) atoms. The Ni(2)-Ni(3) bond length is 2.51 Å. Both Ni(2)-B(1) bond lengths are 2.08 Å. In the third Ni site, Ni(3) is bonded to twelve equivalent Ni(2) atoms to form NiNi12 cuboctahedra that share faces with eight equivalent Tm(1)Ni16 tetrahedra. B(1) is bonded in a 8-coordinate geometry to four equivalent Ni(1) and four equivalent Ni(2) atoms.