Nb21S8 crystallizes in the tetragonal I4/m space group. There are six inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 3-coordinate geometry to one S(2) and two equivalent S(1) atoms. In the second Nb site, Nb(2) is bonded in an L-shaped geometry to two equivalent S(1) atoms. In the third Nb site, Nb(3) is bonded in a 4-coordinate geometry to one S(2) and three equivalent S(1) atoms. In the fourth Nb site, Nb(4) is bonded in a distorted rectangular see-saw-like geometry to four equivalent S(2) atoms. In the fifth Nb site, Nb(5) is bonded in a distorted single-bond geometry to one S(1) atom. In the sixth Nb site, Nb(6) is bonded in a square co-planar geometry to four equivalent S(2) atoms. There are two inequivalent S sites. In the first S site, S(1) is bonded in a 8-coordinate geometry to one Nb(5), two equivalent Nb(1), two equivalent Nb(2), and three equivalent Nb(3) atoms. In the second S site, S(2) is bonded in a 7-coordinate geometry to one Nb(1), one Nb(3), one Nb(6), and four equivalent Nb(4) atoms.
Nb21S8 crystallizes in the tetragonal I4/m space group. There are six inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 3-coordinate geometry to one S(2) and two equivalent S(1) atoms. The Nb(1)-S(2) bond length is 2.49 Å. Both Nb(1)-S(1) bond lengths are 2.60 Å. In the second Nb site, Nb(2) is bonded in an L-shaped geometry to two equivalent S(1) atoms. Both Nb(2)-S(1) bond lengths are 2.50 Å. In the third Nb site, Nb(3) is bonded in a 4-coordinate geometry to one S(2) and three equivalent S(1) atoms. The Nb(3)-S(2) bond length is 2.44 Å. There are two shorter (2.58 Å) and one longer (2.85 Å) Nb(3)-S(1) bond length. In the fourth Nb site, Nb(4) is bonded in a distorted rectangular see-saw-like geometry to four equivalent S(2) atoms. All Nb(4)-S(2) bond lengths are 2.55 Å. In the fifth Nb site, Nb(5) is bonded in a distorted single-bond geometry to one S(1) atom. The Nb(5)-S(1) bond length is 2.66 Å. In the sixth Nb site, Nb(6) is bonded in a square co-planar geometry to four equivalent S(2) atoms. All Nb(6)-S(2) bond lengths are 2.57 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded in a 8-coordinate geometry to one Nb(5), two equivalent Nb(1), two equivalent Nb(2), and three equivalent Nb(3) atoms. In the second S site, S(2) is bonded in a 7-coordinate geometry to one Nb(1), one Nb(3), one Nb(6), and four equivalent Nb(4) atoms.