K3AgSn3Se8 crystallizes in the tetragonal P4/nbm space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to four equivalent Se(1) and four equivalent Se(2) atoms. In the second K site, K(2) is bonded in a 8-coordinate geometry to eight equivalent Se(1) atoms. Ag(1) is bonded to four equivalent Se(1) atoms to form distorted AgSe4 tetrahedra that share edges with two equivalent Sn(1)Se4 tetrahedra. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form SnSe4 tetrahedra that share  an edgeedge with one Ag(1)Se4 tetrahedra and  an edgeedge with one Sn(2)Se4 tetrahedra. In the second Sn site, Sn(2) is bonded to four equivalent Se(2) atoms to form edge-sharing SnSe4 tetrahedra. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent K(1), two equivalent K(2), one Ag(1), and one Sn(1) atom. In the second Se site, Se(2) is bonded to two equivalent K(1), one Sn(1), and one Sn(2) atom to form a mixture of edge and corner-sharing SeK2Sn2 trigonal pyramids.
K3AgSn3Se8 crystallizes in the tetragonal P4/nbm space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 8-coordinate geometry to four equivalent Se(1) and four equivalent Se(2) atoms. All K(1)-Se(1) bond lengths are 3.58 Å. All K(1)-Se(2) bond lengths are 3.40 Å. In the second K site, K(2) is bonded in a 8-coordinate geometry to eight equivalent Se(1) atoms. All K(2)-Se(1) bond lengths are 3.59 Å. Ag(1) is bonded to four equivalent Se(1) atoms to form distorted AgSe4 tetrahedra that share edges with two equivalent Sn(1)Se4 tetrahedra. All Ag(1)-Se(1) bond lengths are 2.82 Å. There are two inequivalent Sn sites. In the first Sn site, Sn(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form SnSe4 tetrahedra that share  an edgeedge with one Ag(1)Se4 tetrahedra and  an edgeedge with one Sn(2)Se4 tetrahedra. Both Sn(1)-Se(1) bond lengths are 2.52 Å. Both Sn(1)-Se(2) bond lengths are 2.66 Å. In the second Sn site, Sn(2) is bonded to four equivalent Se(2) atoms to form edge-sharing SnSe4 tetrahedra. All Sn(2)-Se(2) bond lengths are 2.59 Å. There are two inequivalent Se sites. In the first Se site, Se(1) is bonded in a 6-coordinate geometry to two equivalent K(1), two equivalent K(2), one Ag(1), and one Sn(1) atom. In the second Se site, Se(2) is bonded to two equivalent K(1), one Sn(1), and one Sn(2) atom to form a mixture of edge and corner-sharing SeK2Sn2 trigonal pyramids.