DOE OSTI2020
Nb4P2S21 crystallizes in the monoclinic C2 space group. The structure is two-dimensional and consists of two Nb4P2S21 sheets oriented in the (1, 0, 0) direction. there are four inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to eight S+1.43- atoms to form NbS8 hexagonal bipyramids that share an edgeedge with one PS4 tetrahedra and faces with two NbS8 hexagonal bipyramids. There are a spread of Nb–S bond distances ranging from 2.49–2.71 Å. In the second Nb5+ site, Nb5+ is bonded to eight S+1.43- atoms to form NbS8 hexagonal bipyramids that share an edgeedge with one PS4 tetrahedra and faces with two NbS8 hexagonal bipyramids. There are a spread of Nb–S bond distances ranging from 2.50–2.71 Å. In the third Nb5+ site, Nb5+ is bonded to eight S+1.43- atoms to form NbS8 hexagonal bipyramids that share an edgeedge with one PS4 tetrahedra and faces with two NbS8 hexagonal bipyramids. There are a spread of Nb–S bond distances ranging from 2.50–2.71 Å. In the fourth Nb5+ site, Nb5+ is bonded to eight S+1.43- atoms to form NbS8 hexagonal bipyramids that share an edgeedge with one PS4 tetrahedra and faces with two NbS8 hexagonal bipyramids. There are a spread of Nb–S bond distances ranging from 2.50–2.71 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four S+1.43- atoms to form PS4 tetrahedra that share edges with two NbS8 hexagonal bipyramids. There are a spread of P–S bond distances ranging from 2.02–2.16 Å. In the second P5+ site, P5+ is bonded to four S+1.43- atoms to form PS4 tetrahedra that share edges with two NbS8 hexagonal bipyramids. There are a spread of P–S bond distances ranging from 2.02–2.17 Å. There are twenty-one inequivalent S+1.43- sites. In the first S+1.43- site, S+1.43- is bonded in a 2-coordinate geometry to two Nb5+ and one S+1.43- atom. The S–S bond length is 2.02 Å. In the second S+1.43- site, S+1.43- is bonded in a 2-coordinate geometry to two Nb5+ and one S+1.43- atom. The S–S bond length is 2.02 Å. In the third S+1.43- site, S+1.43- is bonded in an L-shaped geometry to one Nb5+ and one P5+ atom. In the fourth S+1.43- site, S+1.43- is bonded in an L-shaped geometry to one Nb5+ and one P5+ atom. In the fifth S+1.43- site, S+1.43- is bonded in a 2-coordinate geometry to two Nb5+ and one S+1.43- atom. The S–S bond length is 2.04 Å. In the sixth S+1.43- site, S+1.43- is bonded in a 2-coordinate geometry to two Nb5+ and one S+1.43- atom. The S–S bond length is 2.04 Å. In the seventh S+1.43- site, S+1.43- is bonded in an L-shaped geometry to one Nb5+ and one P5+ atom. In the eighth S+1.43- site, S+1.43- is bonded in an L-shaped geometry to one Nb5+ and one P5+ atom. In the ninth S+1.43- site, S+1.43- is bonded in a 3-coordinate geometry to two Nb5+ and one S+1.43- atom. The S–S bond length is 2.05 Å. In the tenth S+1.43- site, S+1.43- is bonded in a 3-coordinate geometry to two Nb5+ and one S+1.43- atom. The S–S bond length is 2.05 Å. In the eleventh S+1.43- site, S+1.43- is bonded in a 2-coordinate geometry to two Nb5+ and one S+1.43- atom. In the twelfth S+1.43- site, S+1.43- is bonded in a 2-coordinate geometry to two Nb5+ and one S+1.43- atom. In the thirteenth S+1.43- site, S+1.43- is bonded in a 3-coordinate geometry to two Nb5+ and one P5+ atom. In the fourteenth S+1.43- site, S+1.43- is bonded in a 3-coordinate geometry to two Nb5+ and one P5+ atom. In the fifteenth S+1.43- site, S+1.43- is bonded in a distorted water-like geometry to one P5+ and one S+1.43- atom. The S–S bond length is 2.06 Å. In the sixteenth S+1.43- site, S+1.43- is bonded in a distorted water-like geometry to one P5+ and one S+1.43- atom. The S–S bond length is 2.06 Å. In the seventeenth S+1.43- site, S+1.43- is bonded in a 2-coordinate geometry to two Nb5+ and one S+1.43- atom. In the eighteenth S+1.43- site, S+1.43- is bonded in a 2-coordinate geometry to two Nb5+ and one S+1.43- atom. In the nineteenth S+1.43- site, S+1.43- is bonded in a 3-coordinate geometry to two Nb5+ and one S+1.43- atom. In the twentieth S+1.43- site, S+1.43- is bonded in a 3-coordinate geometry to two Nb5+ and one S+1.43- atom. In the twenty-first S+1.43- site, S+1.43- is bonded in a water-like geometry to two S+1.43- atoms.