K4Hg2Sn21 crystallizes in the orthorhombic Ama2 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 20-coordinate geometry to one Sn(2), one Sn(5), one Sn(7), one Sn(8), two equivalent Sn(1), two equivalent Sn(10), two equivalent Sn(11), two equivalent Sn(12), two equivalent Sn(3), two equivalent Sn(4), two equivalent Sn(6), and two equivalent Sn(9) atoms. In the second K site, K(2) is bonded in a 2-coordinate geometry to two equivalent Sn(5) and two equivalent Sn(7) atoms. In the third K site, K(3) is bonded in a 6-coordinate geometry to two equivalent Sn(3), two equivalent Sn(4), and two equivalent Sn(6) atoms. In the fourth K site, K(4) is bonded in a 6-coordinate geometry to two equivalent Sn(3), two equivalent Sn(4), and two equivalent Sn(6) atoms. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded to two equivalent Sn(3) and two equivalent Sn(6) atoms to form HgSn4 tetrahedra that share corners with two equivalent Sn(11)KSn4 trigonal bipyramids and corners with two equivalent Sn(12)KSn4 trigonal bipyramids. In the second Hg site, Hg(2) is bonded to one Sn(5), one Sn(8), and two equivalent Sn(4) atoms to form HgSn4 tetrahedra that share corners with two equivalent Sn(11)KSn4 trigonal bipyramids and corners with two equivalent Sn(12)KSn4 trigonal bipyramids. There are thirteen inequivalent Sn sites. In the first Sn site, Sn(1) is bonded in a 5-coordinate geometry to one K(1), one Sn(12), one Sn(13), one Sn(4), and one Sn(9) atom. In the second Sn site, Sn(2) is bonded in a 5-coordinate geometry to one K(1), one Sn(13), one Sn(8), and two equivalent Sn(9) atoms. In the third Sn site, Sn(3) is bonded in a 4-coordinate geometry to one K(1), one K(3), one K(4), one Hg(1), one Sn(11), one Sn(3), and one Sn(9) atom. In the fourth Sn site, Sn(4) is bonded to one K(1), one K(3), one K(4), one Hg(2), one Sn(1), one Sn(10), and one Sn(11) atom to form distorted SnK3Sn3Hg tetrahedra that share  a cornercorner with one Sn(4)K3Sn3Hg tetrahedra,  a cornercorner with one Sn(13)Sn4 tetrahedra, corners with two equivalent Sn(11)KSn4 trigonal bipyramids, corners with two equivalent Sn(12)KSn4 trigonal bipyramids,  an edgeedge with one Sn(12)KSn4 trigonal bipyramid, and  a faceface with one Sn(4)K3Sn3Hg tetrahedra. In the fifth Sn site, Sn(5) is bonded in a 6-coordinate geometry to one K(1), two equivalent K(2), one Hg(2), one Sn(7), and two equivalent Sn(10) atoms. In the sixth Sn site, Sn(6) is bonded in a 6-coordinate geometry to one K(1), one K(3), one K(4), one Hg(1), one Sn(10), one Sn(12), and one Sn(6) atom. In the seventh Sn site, Sn(7) is bonded in a 7-coordinate geometry to one K(1), two equivalent K(2), one Sn(13), one Sn(5), and two equivalent Sn(11) atoms. In the eighth Sn site, Sn(8) is bonded in a 4-coordinate geometry to one K(1), one Hg(2), one Sn(2), and two equivalent Sn(12) atoms. In the ninth Sn site, Sn(9) is bonded in a 5-coordinate geometry to one K(1), one Sn(1), one Sn(2), one Sn(3), and one Sn(9) atom. In the tenth Sn site, Sn(10) is bonded in a 5-coordinate geometry to one K(1), one Sn(10), one Sn(4), one Sn(5), and one Sn(6) atom. In the eleventh Sn site, Sn(11) is bonded to one K(1), one Sn(12), one Sn(3), one Sn(4), and one Sn(7) atom to form distorted SnKSn4 trigonal bipyramids that share  a cornercorner with one Hg(1)Sn4 tetrahedra,  a cornercorner with one Hg(2)Sn4 tetrahedra,  a cornercorner with one Sn(13)Sn4 tetrahedra, corners with two equivalent Sn(4)K3Sn3Hg tetrahedra, corners with two equivalent Sn(12)KSn4 trigonal bipyramids, and  an edgeedge with one Sn(11)KSn4 trigonal bipyramid. In the twelfth Sn site, Sn(12) is bonded to one K(1), one Sn(1), one Sn(11), one Sn(6), and one Sn(8) atom to form distorted SnKSn4 trigonal bipyramids that share  a cornercorner with one Hg(1)Sn4 tetrahedra,  a cornercorner with one Hg(2)Sn4 tetrahedra,  a cornercorner with one Sn(13)Sn4 tetrahedra, corners with two equivalent Sn(4)K3Sn3Hg tetrahedra, corners with two equivalent Sn(11)KSn4 trigonal bipyramids,  an edgeedge with one Sn(4)K3Sn3Hg tetrahedra, and  an edgeedge with one Sn(12)KSn4 trigonal bipyramid. In the thirteenth Sn site, Sn(13) is bonded to one Sn(2), one Sn(7), and two equivalent Sn(1) atoms to form SnSn4 tetrahedra that share corners with two equivalent Sn(4)K3Sn3Hg tetrahedra, corners with two equivalent Sn(11)KSn4 trigonal bipyramids, and corners with two equivalent Sn(12)KSn4 trigonal bipyramids.
K4Hg2Sn21 crystallizes in the orthorhombic Ama2 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 20-coordinate geometry to one Sn(2), one Sn(5), one Sn(7), one Sn(8), two equivalent Sn(1), two equivalent Sn(10), two equivalent Sn(11), two equivalent Sn(12), two equivalent Sn(3), two equivalent Sn(4), two equivalent Sn(6), and two equivalent Sn(9) atoms. The K(1)-Sn(2) bond length is 4.06 Å. The K(1)-Sn(5) bond length is 4.09 Å. The K(1)-Sn(7) bond length is 4.03 Å. The K(1)-Sn(8) bond length is 4.16 Å. Both K(1)-Sn(1) bond lengths are 4.04 Å. Both K(1)-Sn(10) bond lengths are 3.86 Å. Both K(1)-Sn(11) bond lengths are 3.90 Å. Both K(1)-Sn(12) bond lengths are 3.90 Å. Both K(1)-Sn(3) bond lengths are 4.14 Å. Both K(1)-Sn(4) bond lengths are 4.13 Å. Both K(1)-Sn(6) bond lengths are 4.08 Å. Both K(1)-Sn(9) bond lengths are 3.92 Å. In the second K site, K(2) is bonded in a 2-coordinate geometry to two equivalent Sn(5) and two equivalent Sn(7) atoms. Both K(2)-Sn(5) bond lengths are 3.86 Å. Both K(2)-Sn(7) bond lengths are 4.09 Å. In the third K site, K(3) is bonded in a 6-coordinate geometry to two equivalent Sn(3), two equivalent Sn(4), and two equivalent Sn(6) atoms. Both K(3)-Sn(3) bond lengths are 4.07 Å. Both K(3)-Sn(4) bond lengths are 4.18 Å. Both K(3)-Sn(6) bond lengths are 3.84 Å. In the fourth K site, K(4) is bonded in a 6-coordinate geometry to two equivalent Sn(3), two equivalent Sn(4), and two equivalent Sn(6) atoms. Both K(4)-Sn(3) bond lengths are 4.10 Å. Both K(4)-Sn(4) bond lengths are 4.17 Å. Both K(4)-Sn(6) bond lengths are 3.85 Å. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded to two equivalent Sn(3) and two equivalent Sn(6) atoms to form HgSn4 tetrahedra that share corners with two equivalent Sn(11)KSn4 trigonal bipyramids and corners with two equivalent Sn(12)KSn4 trigonal bipyramids. Both Hg(1)-Sn(3) bond lengths are 2.81 Å. Both Hg(1)-Sn(6) bond lengths are 2.82 Å. In the second Hg site, Hg(2) is bonded to one Sn(5), one Sn(8), and two equivalent Sn(4) atoms to form HgSn4 tetrahedra that share corners with two equivalent Sn(11)KSn4 trigonal bipyramids and corners with two equivalent Sn(12)KSn4 trigonal bipyramids. The Hg(2)-Sn(5) bond length is 2.79 Å. The Hg(2)-Sn(8) bond length is 2.79 Å. Both Hg(2)-Sn(4) bond lengths are 2.79 Å. There are thirteen inequivalent Sn sites. In the first Sn site, Sn(1) is bonded in a 5-coordinate geometry to one K(1), one Sn(12), one Sn(13), one Sn(4), and one Sn(9) atom. The Sn(1)-Sn(12) bond length is 2.86 Å. The Sn(1)-Sn(13) bond length is 2.89 Å. The Sn(1)-Sn(4) bond length is 2.90 Å. The Sn(1)-Sn(9) bond length is 2.86 Å. In the second Sn site, Sn(2) is bonded in a 5-coordinate geometry to one K(1), one Sn(13), one Sn(8), and two equivalent Sn(9) atoms. The Sn(2)-Sn(13) bond length is 2.88 Å. The Sn(2)-Sn(8) bond length is 2.89 Å. Both Sn(2)-Sn(9) bond lengths are 2.86 Å. In the third Sn site, Sn(3) is bonded in a 4-coordinate geometry to one K(1), one K(3), one K(4), one Hg(1), one Sn(11), one Sn(3), and one Sn(9) atom. The Sn(3)-Sn(11) bond length is 2.86 Å. The Sn(3)-Sn(3) bond length is 2.89 Å. The Sn(3)-Sn(9) bond length is 2.86 Å. In the fourth Sn site, Sn(4) is bonded to one K(1), one K(3), one K(4), one Hg(2), one Sn(1), one Sn(10), and one Sn(11) atom to form distorted SnK3Sn3Hg tetrahedra that share  a cornercorner with one Sn(4)K3Sn3Hg tetrahedra,  a cornercorner with one Sn(13)Sn4 tetrahedra, corners with two equivalent Sn(11)KSn4 trigonal bipyramids, corners with two equivalent Sn(12)KSn4 trigonal bipyramids,  an edgeedge with one Sn(12)KSn4 trigonal bipyramid, and  a faceface with one Sn(4)K3Sn3Hg tetrahedra. The Sn(4)-Sn(10) bond length is 2.87 Å. The Sn(4)-Sn(11) bond length is 2.87 Å. In the fifth Sn site, Sn(5) is bonded in a 6-coordinate geometry to one K(1), two equivalent K(2), one Hg(2), one Sn(7), and two equivalent Sn(10) atoms. The Sn(5)-Sn(7) bond length is 2.91 Å. Both Sn(5)-Sn(10) bond lengths are 2.87 Å. In the sixth Sn site, Sn(6) is bonded in a 6-coordinate geometry to one K(1), one K(3), one K(4), one Hg(1), one Sn(10), one Sn(12), and one Sn(6) atom. The Sn(6)-Sn(10) bond length is 2.86 Å. The Sn(6)-Sn(12) bond length is 2.87 Å. The Sn(6)-Sn(6) bond length is 2.91 Å. In the seventh Sn site, Sn(7) is bonded in a 7-coordinate geometry to one K(1), two equivalent K(2), one Sn(13), one Sn(5), and two equivalent Sn(11) atoms. The Sn(7)-Sn(13) bond length is 2.89 Å. Both Sn(7)-Sn(11) bond lengths are 2.86 Å. In the eighth Sn site, Sn(8) is bonded in a 4-coordinate geometry to one K(1), one Hg(2), one Sn(2), and two equivalent Sn(12) atoms. Both Sn(8)-Sn(12) bond lengths are 2.87 Å. In the ninth Sn site, Sn(9) is bonded in a 5-coordinate geometry to one K(1), one Sn(1), one Sn(2), one Sn(3), and one Sn(9) atom. The Sn(9)-Sn(9) bond length is 2.83 Å. In the tenth Sn site, Sn(10) is bonded in a 5-coordinate geometry to one K(1), one Sn(10), one Sn(4), one Sn(5), and one Sn(6) atom. The Sn(10)-Sn(10) bond length is 2.89 Å. In the eleventh Sn site, Sn(11) is bonded to one K(1), one Sn(12), one Sn(3), one Sn(4), and one Sn(7) atom to form distorted SnKSn4 trigonal bipyramids that share  a cornercorner with one Hg(1)Sn4 tetrahedra,  a cornercorner with one Hg(2)Sn4 tetrahedra,  a cornercorner with one Sn(13)Sn4 tetrahedra, corners with two equivalent Sn(4)K3Sn3Hg tetrahedra, corners with two equivalent Sn(12)KSn4 trigonal bipyramids, and  an edgeedge with one Sn(11)KSn4 trigonal bipyramid. The Sn(11)-Sn(12) bond length is 2.86 Å. In the twelfth Sn site, Sn(12) is bonded to one K(1), one Sn(1), one Sn(11), one Sn(6), and one Sn(8) atom to form distorted SnKSn4 trigonal bipyramids that share  a cornercorner with one Hg(1)Sn4 tetrahedra,  a cornercorner with one Hg(2)Sn4 tetrahedra,  a cornercorner with one Sn(13)Sn4 tetrahedra, corners with two equivalent Sn(4)K3Sn3Hg tetrahedra, corners with two equivalent Sn(11)KSn4 trigonal bipyramids,  an edgeedge with one Sn(4)K3Sn3Hg tetrahedra, and  an edgeedge with one Sn(12)KSn4 trigonal bipyramid. In the thirteenth Sn site, Sn(13) is bonded to one Sn(2), one Sn(7), and two equivalent Sn(1) atoms to form SnSn4 tetrahedra that share corners with two equivalent Sn(4)K3Sn3Hg tetrahedra, corners with two equivalent Sn(11)KSn4 trigonal bipyramids, and corners with two equivalent Sn(12)KSn4 trigonal bipyramids.