Nd3FeGaSe7 crystallizes in the monoclinic P2_1 space group. There are three inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 7-coordinate geometry to one Se(1), one Se(4), one Se(5), one Se(6), one Se(7), and two equivalent Se(2) atoms. In the second Nd site, Nd(2) is bonded in a 7-coordinate geometry to one Se(2), one Se(4), one Se(5), one Se(6), one Se(7), and two equivalent Se(3) atoms. In the third Nd site, Nd(3) is bonded in a 7-coordinate geometry to one Se(3), one Se(4), one Se(5), one Se(6), one Se(7), and two equivalent Se(1) atoms. Fe(1) is bonded to two equivalent Se(5), two equivalent Se(6), and two equivalent Se(7) atoms to form face-sharing FeSe6 octahedra. Ga(1) is bonded in a tetrahedral geometry to one Se(1), one Se(2), one Se(3), and one Se(4) atom. There are seven inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted rectangular see-saw-like geometry to one Nd(1), two equivalent Nd(3), and one Ga(1) atom. In the second Se site, Se(2) is bonded in a distorted rectangular see-saw-like geometry to one Nd(2), two equivalent Nd(1), and one Ga(1) atom. In the third Se site, Se(3) is bonded in a distorted rectangular see-saw-like geometry to one Nd(3), two equivalent Nd(2), and one Ga(1) atom. In the fourth Se site, Se(4) is bonded to one Nd(1), one Nd(2), one Nd(3), and one Ga(1) atom to form corner-sharing SeNd3Ga tetrahedra. In the fifth Se site, Se(5) is bonded to one Nd(1), one Nd(2), one Nd(3), and two equivalent Fe(1) atoms to form distorted SeNd3Fe2 square pyramids that share corners with two equivalent Se(5)Nd3Fe2 square pyramids, corners with three equivalent Se(4)Nd3Ga tetrahedra, edges with two equivalent Se(6)Nd3Fe2 square pyramids, edges with two equivalent Se(7)Nd3Fe2 square pyramids,  a faceface with one Se(6)Nd3Fe2 square pyramid, and  a faceface with one Se(7)Nd3Fe2 square pyramid. In the sixth Se site, Se(6) is bonded to one Nd(1), one Nd(2), one Nd(3), and two equivalent Fe(1) atoms to form distorted SeNd3Fe2 square pyramids that share corners with two equivalent Se(6)Nd3Fe2 square pyramids, corners with three equivalent Se(4)Nd3Ga tetrahedra, edges with two equivalent Se(5)Nd3Fe2 square pyramids, edges with two equivalent Se(7)Nd3Fe2 square pyramids,  a faceface with one Se(5)Nd3Fe2 square pyramid, and  a faceface with one Se(7)Nd3Fe2 square pyramid. In the seventh Se site, Se(7) is bonded to one Nd(1), one Nd(2), one Nd(3), and two equivalent Fe(1) atoms to form distorted SeNd3Fe2 square pyramids that share corners with two equivalent Se(7)Nd3Fe2 square pyramids, corners with three equivalent Se(4)Nd3Ga tetrahedra, edges with two equivalent Se(5)Nd3Fe2 square pyramids, edges with two equivalent Se(6)Nd3Fe2 square pyramids,  a faceface with one Se(5)Nd3Fe2 square pyramid, and  a faceface with one Se(6)Nd3Fe2 square pyramid.
Nd3FeGaSe7 crystallizes in the monoclinic P2_1 space group. There are three inequivalent Nd sites. In the first Nd site, Nd(1) is bonded in a 7-coordinate geometry to one Se(1), one Se(4), one Se(5), one Se(6), one Se(7), and two equivalent Se(2) atoms. The Nd(1)-Se(1) bond length is 3.05 Å. The Nd(1)-Se(4) bond length is 2.97 Å. The Nd(1)-Se(5) bond length is 3.01 Å. The Nd(1)-Se(6) bond length is 3.02 Å. The Nd(1)-Se(7) bond length is 3.03 Å. There is one shorter (3.00 Å) and one longer (3.25 Å) Nd(1)-Se(2) bond length. In the second Nd site, Nd(2) is bonded in a 7-coordinate geometry to one Se(2), one Se(4), one Se(5), one Se(6), one Se(7), and two equivalent Se(3) atoms. The Nd(2)-Se(2) bond length is 3.06 Å. The Nd(2)-Se(4) bond length is 2.98 Å. The Nd(2)-Se(5) bond length is 3.03 Å. The Nd(2)-Se(6) bond length is 2.97 Å. The Nd(2)-Se(7) bond length is 3.01 Å. There is one shorter (3.00 Å) and one longer (3.26 Å) Nd(2)-Se(3) bond length. In the third Nd site, Nd(3) is bonded in a 7-coordinate geometry to one Se(3), one Se(4), one Se(5), one Se(6), one Se(7), and two equivalent Se(1) atoms. The Nd(3)-Se(3) bond length is 3.06 Å. The Nd(3)-Se(4) bond length is 2.97 Å. The Nd(3)-Se(5) bond length is 3.05 Å. The Nd(3)-Se(6) bond length is 3.03 Å. The Nd(3)-Se(7) bond length is 2.98 Å. There is one shorter (3.00 Å) and one longer (3.23 Å) Nd(3)-Se(1) bond length. Fe(1) is bonded to two equivalent Se(5), two equivalent Se(6), and two equivalent Se(7) atoms to form face-sharing FeSe6 octahedra. There is one shorter (2.58 Å) and one longer (2.77 Å) Fe(1)-Se(5) bond length. There is one shorter (2.64 Å) and one longer (2.73 Å) Fe(1)-Se(6) bond length. There is one shorter (2.63 Å) and one longer (2.73 Å) Fe(1)-Se(7) bond length. Ga(1) is bonded in a tetrahedral geometry to one Se(1), one Se(2), one Se(3), and one Se(4) atom. The Ga(1)-Se(1) bond length is 2.44 Å. The Ga(1)-Se(2) bond length is 2.43 Å. The Ga(1)-Se(3) bond length is 2.43 Å. The Ga(1)-Se(4) bond length is 2.41 Å. There are seven inequivalent Se sites. In the first Se site, Se(1) is bonded in a distorted rectangular see-saw-like geometry to one Nd(1), two equivalent Nd(3), and one Ga(1) atom. In the second Se site, Se(2) is bonded in a distorted rectangular see-saw-like geometry to one Nd(2), two equivalent Nd(1), and one Ga(1) atom. In the third Se site, Se(3) is bonded in a distorted rectangular see-saw-like geometry to one Nd(3), two equivalent Nd(2), and one Ga(1) atom. In the fourth Se site, Se(4) is bonded to one Nd(1), one Nd(2), one Nd(3), and one Ga(1) atom to form corner-sharing SeNd3Ga tetrahedra. In the fifth Se site, Se(5) is bonded to one Nd(1), one Nd(2), one Nd(3), and two equivalent Fe(1) atoms to form distorted SeNd3Fe2 square pyramids that share corners with two equivalent Se(5)Nd3Fe2 square pyramids, corners with three equivalent Se(4)Nd3Ga tetrahedra, edges with two equivalent Se(6)Nd3Fe2 square pyramids, edges with two equivalent Se(7)Nd3Fe2 square pyramids,  a faceface with one Se(6)Nd3Fe2 square pyramid, and  a faceface with one Se(7)Nd3Fe2 square pyramid. In the sixth Se site, Se(6) is bonded to one Nd(1), one Nd(2), one Nd(3), and two equivalent Fe(1) atoms to form distorted SeNd3Fe2 square pyramids that share corners with two equivalent Se(6)Nd3Fe2 square pyramids, corners with three equivalent Se(4)Nd3Ga tetrahedra, edges with two equivalent Se(5)Nd3Fe2 square pyramids, edges with two equivalent Se(7)Nd3Fe2 square pyramids,  a faceface with one Se(5)Nd3Fe2 square pyramid, and  a faceface with one Se(7)Nd3Fe2 square pyramid. In the seventh Se site, Se(7) is bonded to one Nd(1), one Nd(2), one Nd(3), and two equivalent Fe(1) atoms to form distorted SeNd3Fe2 square pyramids that share corners with two equivalent Se(7)Nd3Fe2 square pyramids, corners with three equivalent Se(4)Nd3Ga tetrahedra, edges with two equivalent Se(5)Nd3Fe2 square pyramids, edges with two equivalent Se(6)Nd3Fe2 square pyramids,  a faceface with one Se(5)Nd3Fe2 square pyramid, and  a faceface with one Se(6)Nd3Fe2 square pyramid.