Tm2PbSe4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one Se(2), two equivalent Se(4), and three equivalent Se(1) atoms to form a mixture of edge and corner-sharing TmSe6 octahedra. The corner-sharing octahedral tilt angles range from 48-63°. In the second Tm site, Tm(2) is bonded to one Se(4), two equivalent Se(2), and three equivalent Se(3) atoms to form a mixture of edge and corner-sharing TmSe6 octahedra. The corner-sharing octahedral tilt angles range from 48-63°. Pb(1) is bonded in a 7-coordinate geometry to one Se(4), two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Tm(1) and two equivalent Pb(1) atoms to form distorted SeTm3Pb2 square pyramids that share corners with two equivalent Se(4)Tm3Pb trigonal pyramids, edges with four equivalent Se(1)Tm3Pb2 square pyramids, and edges with three equivalent Se(4)Tm3Pb trigonal pyramids. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Tm(1), two equivalent Tm(2), and two equivalent Pb(1) atoms. In the third Se site, Se(3) is bonded in a 3-coordinate geometry to three equivalent Tm(2) and two equivalent Pb(1) atoms. In the fourth Se site, Se(4) is bonded to one Tm(2), two equivalent Tm(1), and one Pb(1) atom to form distorted SeTm3Pb trigonal pyramids that share corners with two equivalent Se(1)Tm3Pb2 square pyramids, corners with two equivalent Se(4)Tm3Pb trigonal pyramids, and edges with three equivalent Se(1)Tm3Pb2 square pyramids.
Tm2PbSe4 crystallizes in the orthorhombic Pnma space group. There are two inequivalent Tm sites. In the first Tm site, Tm(1) is bonded to one Se(2), two equivalent Se(4), and three equivalent Se(1) atoms to form a mixture of edge and corner-sharing TmSe6 octahedra. The corner-sharing octahedral tilt angles range from 48-63°. The Tm(1)-Se(2) bond length is 2.86 Å. Both Tm(1)-Se(4) bond lengths are 2.78 Å. All Tm(1)-Se(1) bond lengths are 2.85 Å. In the second Tm site, Tm(2) is bonded to one Se(4), two equivalent Se(2), and three equivalent Se(3) atoms to form a mixture of edge and corner-sharing TmSe6 octahedra. The corner-sharing octahedral tilt angles range from 48-63°. The Tm(2)-Se(4) bond length is 2.87 Å. Both Tm(2)-Se(2) bond lengths are 2.92 Å. There is one shorter (2.82 Å) and two longer (2.83 Å) Tm(2)-Se(3) bond lengths. Pb(1) is bonded in a 7-coordinate geometry to one Se(4), two equivalent Se(1), two equivalent Se(2), and two equivalent Se(3) atoms. The Pb(1)-Se(4) bond length is 3.04 Å. Both Pb(1)-Se(1) bond lengths are 3.18 Å. Both Pb(1)-Se(2) bond lengths are 3.20 Å. Both Pb(1)-Se(3) bond lengths are 3.38 Å. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Tm(1) and two equivalent Pb(1) atoms to form distorted SeTm3Pb2 square pyramids that share corners with two equivalent Se(4)Tm3Pb trigonal pyramids, edges with four equivalent Se(1)Tm3Pb2 square pyramids, and edges with three equivalent Se(4)Tm3Pb trigonal pyramids. In the second Se site, Se(2) is bonded in a 5-coordinate geometry to one Tm(1), two equivalent Tm(2), and two equivalent Pb(1) atoms. In the third Se site, Se(3) is bonded in a 3-coordinate geometry to three equivalent Tm(2) and two equivalent Pb(1) atoms. In the fourth Se site, Se(4) is bonded to one Tm(2), two equivalent Tm(1), and one Pb(1) atom to form distorted SeTm3Pb trigonal pyramids that share corners with two equivalent Se(1)Tm3Pb2 square pyramids, corners with two equivalent Se(4)Tm3Pb trigonal pyramids, and edges with three equivalent Se(1)Tm3Pb2 square pyramids.