Nb2FeSe4 crystallizes in the orthorhombic Cmcm space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 6-coordinate geometry to two equivalent Se(2) and four equivalent Se(1) atoms. In the second Nb site, Nb(2) is bonded in a 7-coordinate geometry to one Fe(2), two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. In the third Nb site, Nb(3) is bonded in a 7-coordinate geometry to one Fe(2), two equivalent Se(3), and four equivalent Se(1) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in an octahedral geometry to two equivalent Se(2) and four equivalent Se(1) atoms. In the second Fe site, Fe(2) is bonded in a 9-coordinate geometry to one Nb(3), two equivalent Nb(2), two equivalent Se(2), and four equivalent Se(1) atoms. There are three inequivalent Se sites. In the first Se site, Se(3) is bonded in a 3-coordinate geometry to one Nb(3) and two equivalent Nb(2) atoms. In the second Se site, Se(1) is bonded in a 5-coordinate geometry to one Nb(1), one Nb(2), one Nb(3), one Fe(1), and one Fe(2) atom. In the third Se site, Se(2) is bonded in a 5-coordinate geometry to one Nb(1), two equivalent Nb(2), one Fe(1), and one Fe(2) atom.
Nb2FeSe4 crystallizes in the orthorhombic Cmcm space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded in a 6-coordinate geometry to two equivalent Se(2) and four equivalent Se(1) atoms. Both Nb(1)-Se(2) bond lengths are 2.65 Å. All Nb(1)-Se(1) bond lengths are 2.65 Å. In the second Nb site, Nb(2) is bonded in a 7-coordinate geometry to one Fe(2), two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. The Nb(2)-Fe(2) bond length is 2.41 Å. Both Nb(2)-Se(1) bond lengths are 2.76 Å. Both Nb(2)-Se(2) bond lengths are 2.76 Å. Both Nb(2)-Se(3) bond lengths are 2.57 Å. In the third Nb site, Nb(3) is bonded in a 7-coordinate geometry to one Fe(2), two equivalent Se(3), and four equivalent Se(1) atoms. The Nb(3)-Fe(2) bond length is 2.41 Å. Both Nb(3)-Se(3) bond lengths are 2.57 Å. All Nb(3)-Se(1) bond lengths are 2.77 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in an octahedral geometry to two equivalent Se(2) and four equivalent Se(1) atoms. Both Fe(1)-Se(2) bond lengths are 2.61 Å. All Fe(1)-Se(1) bond lengths are 2.61 Å. In the second Fe site, Fe(2) is bonded in a 9-coordinate geometry to one Nb(3), two equivalent Nb(2), two equivalent Se(2), and four equivalent Se(1) atoms. Both Fe(2)-Se(2) bond lengths are 2.61 Å. All Fe(2)-Se(1) bond lengths are 2.61 Å. There are three inequivalent Se sites. In the first Se site, Se(3) is bonded in a 3-coordinate geometry to one Nb(3) and two equivalent Nb(2) atoms. In the second Se site, Se(1) is bonded in a 5-coordinate geometry to one Nb(1), one Nb(2), one Nb(3), one Fe(1), and one Fe(2) atom. In the third Se site, Se(2) is bonded in a 5-coordinate geometry to one Nb(1), two equivalent Nb(2), one Fe(1), and one Fe(2) atom.