GdAgSe2 crystallizes in the tetragonal I4_1md space group. Gd(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form GdSe6 octahedra that share corners with four equivalent Gd(1)Se6 octahedra, corners with three equivalent Ag(1)Se5 trigonal bipyramids, edges with four equivalent Gd(1)Se6 octahedra, and edges with six equivalent Ag(1)Se5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 6-8°. Ag(1) is bonded to two equivalent Se(1) and three equivalent Se(2) atoms to form AgSe5 trigonal bipyramids that share corners with three equivalent Gd(1)Se6 octahedra, corners with eight equivalent Ag(1)Se5 trigonal bipyramids, and edges with six equivalent Gd(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 0-79°. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Gd(1) and two equivalent Ag(1) atoms to form SeGd3Ag2 trigonal bipyramids that share corners with three equivalent Se(2)Gd3Ag3 octahedra, corners with eight equivalent Se(1)Gd3Ag2 trigonal bipyramids, and edges with six equivalent Se(2)Gd3Ag3 octahedra. The corner-sharing octahedral tilt angles range from 0-79°. In the second Se site, Se(2) is bonded to three equivalent Gd(1) and three equivalent Ag(1) atoms to form SeGd3Ag3 octahedra that share corners with four equivalent Se(2)Gd3Ag3 octahedra, corners with three equivalent Se(1)Gd3Ag2 trigonal bipyramids, edges with four equivalent Se(2)Gd3Ag3 octahedra, and edges with six equivalent Se(1)Gd3Ag2 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 6-8°.
GdAgSe2 crystallizes in the tetragonal I4_1md space group. Gd(1) is bonded to three equivalent Se(1) and three equivalent Se(2) atoms to form GdSe6 octahedra that share corners with four equivalent Gd(1)Se6 octahedra, corners with three equivalent Ag(1)Se5 trigonal bipyramids, edges with four equivalent Gd(1)Se6 octahedra, and edges with six equivalent Ag(1)Se5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 6-8°. There are two shorter (2.87 Å) and one longer (2.88 Å) Gd(1)-Se(1) bond length. There are two shorter (2.86 Å) and one longer (2.92 Å) Gd(1)-Se(2) bond length. Ag(1) is bonded to two equivalent Se(1) and three equivalent Se(2) atoms to form AgSe5 trigonal bipyramids that share corners with three equivalent Gd(1)Se6 octahedra, corners with eight equivalent Ag(1)Se5 trigonal bipyramids, and edges with six equivalent Gd(1)Se6 octahedra. The corner-sharing octahedral tilt angles range from 0-79°. Both Ag(1)-Se(1) bond lengths are 2.91 Å. All Ag(1)-Se(2) bond lengths are 2.87 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Gd(1) and two equivalent Ag(1) atoms to form SeGd3Ag2 trigonal bipyramids that share corners with three equivalent Se(2)Gd3Ag3 octahedra, corners with eight equivalent Se(1)Gd3Ag2 trigonal bipyramids, and edges with six equivalent Se(2)Gd3Ag3 octahedra. The corner-sharing octahedral tilt angles range from 0-79°. In the second Se site, Se(2) is bonded to three equivalent Gd(1) and three equivalent Ag(1) atoms to form SeGd3Ag3 octahedra that share corners with four equivalent Se(2)Gd3Ag3 octahedra, corners with three equivalent Se(1)Gd3Ag2 trigonal bipyramids, edges with four equivalent Se(2)Gd3Ag3 octahedra, and edges with six equivalent Se(1)Gd3Ag2 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 6-8°.