NaCuFeSe2 crystallizes in the trigonal P3m1 space group. Na(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form NaSe6 octahedra that share corners with six equivalent Fe(1)Se4 tetrahedra, corners with six equivalent Cu(1)Se4 tetrahedra, edges with six equivalent Na(1)Se6 octahedra, edges with three equivalent Fe(1)Se4 tetrahedra, and edges with three equivalent Cu(1)Se4 tetrahedra. Fe(1) is bonded to one Se(2) and three equivalent Se(1) atoms to form FeSe4 tetrahedra that share corners with six equivalent Na(1)Se6 octahedra, corners with six equivalent Fe(1)Se4 tetrahedra, edges with three equivalent Na(1)Se6 octahedra, and edges with three equivalent Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 19-51°. Cu(1) is bonded to one Se(1) and three equivalent Se(2) atoms to form distorted CuSe4 tetrahedra that share corners with six equivalent Na(1)Se6 octahedra, corners with six equivalent Cu(1)Se4 tetrahedra, edges with three equivalent Na(1)Se6 octahedra, and edges with three equivalent Fe(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 19-50°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Na(1), three equivalent Fe(1), and one Cu(1) atom to form distorted SeNa3Fe3Cu pentagonal bipyramids that share corners with three equivalent Se(2)Na3FeCu3 pentagonal bipyramids, edges with six equivalent Se(1)Na3Fe3Cu pentagonal bipyramids, and edges with six equivalent Se(2)Na3FeCu3 pentagonal bipyramids. In the second Se site, Se(2) is bonded to three equivalent Na(1), one Fe(1), and three equivalent Cu(1) atoms to form distorted SeNa3FeCu3 pentagonal bipyramids that share corners with three equivalent Se(1)Na3Fe3Cu pentagonal bipyramids, edges with six equivalent Se(1)Na3Fe3Cu pentagonal bipyramids, and edges with six equivalent Se(2)Na3FeCu3 pentagonal bipyramids.
NaCuFeSe2 crystallizes in the trigonal P3m1 space group. Na(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form NaSe6 octahedra that share corners with six equivalent Fe(1)Se4 tetrahedra, corners with six equivalent Cu(1)Se4 tetrahedra, edges with six equivalent Na(1)Se6 octahedra, edges with three equivalent Fe(1)Se4 tetrahedra, and edges with three equivalent Cu(1)Se4 tetrahedra. All Na(1)-Se(1) bond lengths are 3.04 Å. All Na(1)-Se(2) bond lengths are 2.97 Å. Fe(1) is bonded to one Se(2) and three equivalent Se(1) atoms to form FeSe4 tetrahedra that share corners with six equivalent Na(1)Se6 octahedra, corners with six equivalent Fe(1)Se4 tetrahedra, edges with three equivalent Na(1)Se6 octahedra, and edges with three equivalent Cu(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 19-51°. The Fe(1)-Se(2) bond length is 2.46 Å. All Fe(1)-Se(1) bond lengths are 2.50 Å. Cu(1) is bonded to one Se(1) and three equivalent Se(2) atoms to form distorted CuSe4 tetrahedra that share corners with six equivalent Na(1)Se6 octahedra, corners with six equivalent Cu(1)Se4 tetrahedra, edges with three equivalent Na(1)Se6 octahedra, and edges with three equivalent Fe(1)Se4 tetrahedra. The corner-sharing octahedral tilt angles range from 19-50°. The Cu(1)-Se(1) bond length is 2.52 Å. All Cu(1)-Se(2) bond lengths are 2.47 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Na(1), three equivalent Fe(1), and one Cu(1) atom to form distorted SeNa3Fe3Cu pentagonal bipyramids that share corners with three equivalent Se(2)Na3FeCu3 pentagonal bipyramids, edges with six equivalent Se(1)Na3Fe3Cu pentagonal bipyramids, and edges with six equivalent Se(2)Na3FeCu3 pentagonal bipyramids. In the second Se site, Se(2) is bonded to three equivalent Na(1), one Fe(1), and three equivalent Cu(1) atoms to form distorted SeNa3FeCu3 pentagonal bipyramids that share corners with three equivalent Se(1)Na3Fe3Cu pentagonal bipyramids, edges with six equivalent Se(1)Na3Fe3Cu pentagonal bipyramids, and edges with six equivalent Se(2)Na3FeCu3 pentagonal bipyramids.