HgCd4Se5 is Lavarevi\'{c}ite-like structured and crystallizes in the trigonal P3m1 space group. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded to one Se(9) and three equivalent Se(5) atoms to form HgSe4 tetrahedra that share corners with three equivalent Cd(4)Se4 tetrahedra, corners with three equivalent Cd(5)Se4 tetrahedra, and corners with six equivalent Hg(1)Se4 tetrahedra. In the second Hg site, Hg(2) is bonded to one Se(10) and three equivalent Se(1) atoms to form HgSe4 tetrahedra that share corners with three equivalent Cd(1)Se4 tetrahedra, corners with three equivalent Cd(5)Se4 tetrahedra, and corners with six equivalent Hg(2)Se4 tetrahedra. There are six inequivalent Cd sites. In the first Cd site, Cd(1) is bonded to one Se(1) and three equivalent Se(6) atoms to form CdSe4 tetrahedra that share corners with three equivalent Hg(2)Se4 tetrahedra, corners with three equivalent Cd(6)Se4 tetrahedra, and corners with six equivalent Cd(1)Se4 tetrahedra. In the second Cd site, Cd(2,3,7) is bonded to four equivalent Se(2,3,7,8) atoms to form corner-sharing CdSe4 tetrahedra. In the third Cd site, Cd(4) is bonded to one Se(4) and three equivalent Se(9) atoms to form CdSe4 tetrahedra that share corners with three equivalent Hg(1)Se4 tetrahedra, corners with three equivalent Cd(8)Se4 tetrahedra, and corners with six equivalent Cd(4)Se4 tetrahedra. In the fourth Cd site, Cd(5) is bonded to one Se(5) and three equivalent Se(10) atoms to form CdSe4 tetrahedra that share corners with three equivalent Hg(1)Se4 tetrahedra, corners with three equivalent Hg(2)Se4 tetrahedra, and corners with six equivalent Cd(5)Se4 tetrahedra. In the fifth Cd site, Cd(6) is bonded to one Se(6) and three equivalent Se(2,3,7,8) atoms to form corner-sharing CdSe4 tetrahedra. In the sixth Cd site, Cd(8) is bonded to one Se(2,3,7,8) and three equivalent Se(4) atoms to form corner-sharing CdSe4 tetrahedra. There are seven inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Hg(2) and one Cd(1) atom to form SeCdHg3 tetrahedra that share corners with three equivalent Se(10)Cd3Hg tetrahedra, corners with three equivalent Se(6)Cd4 tetrahedra, and corners with six equivalent Se(1)CdHg3 tetrahedra. In the second Se site, Se(2,3,7,8) is bonded to one Cd(2,3,7) and three equivalent Cd(6) atoms to form corner-sharing SeCd4 tetrahedra. In the third Se site, Se(4) is bonded to one Cd(4) and three equivalent Cd(8) atoms to form SeCd4 tetrahedra that share corners with three equivalent Se(9)Cd3Hg tetrahedra; corners with three equivalent Se(2,3,7,8)Cd4 tetrahedra; and corners with six equivalent Se(4)Cd4 tetrahedra. In the fourth Se site, Se(5) is bonded to three equivalent Hg(1) and one Cd(5) atom to form SeCdHg3 tetrahedra that share corners with three equivalent Se(10)Cd3Hg tetrahedra, corners with three equivalent Se(9)Cd3Hg tetrahedra, and corners with six equivalent Se(5)CdHg3 tetrahedra. In the fifth Se site, Se(6) is bonded to one Cd(6) and three equivalent Cd(1) atoms to form SeCd4 tetrahedra that share corners with three equivalent Se(2,3,7,8)Cd4 tetrahedra; corners with three equivalent Se(1)CdHg3 tetrahedra; and corners with six equivalent Se(6)Cd4 tetrahedra. In the sixth Se site, Se(9) is bonded to one Hg(1) and three equivalent Cd(4) atoms to form SeCd3Hg tetrahedra that share corners with three equivalent Se(4)Cd4 tetrahedra, corners with three equivalent Se(5)CdHg3 tetrahedra, and corners with six equivalent Se(9)Cd3Hg tetrahedra. In the seventh Se site, Se(10) is bonded to one Hg(2) and three equivalent Cd(5) atoms to form SeCd3Hg tetrahedra that share corners with three equivalent Se(1)CdHg3 tetrahedra, corners with three equivalent Se(5)CdHg3 tetrahedra, and corners with six equivalent Se(10)Cd3Hg tetrahedra.
HgCd4Se5 is Lavarevi\'{c}ite-like structured and crystallizes in the trigonal P3m1 space group. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded to one Se(9) and three equivalent Se(5) atoms to form HgSe4 tetrahedra that share corners with three equivalent Cd(4)Se4 tetrahedra, corners with three equivalent Cd(5)Se4 tetrahedra, and corners with six equivalent Hg(1)Se4 tetrahedra. The Hg(1)-Se(9) bond length is 2.71 Å. All Hg(1)-Se(5) bond lengths are 2.71 Å. In the second Hg site, Hg(2) is bonded to one Se(10) and three equivalent Se(1) atoms to form HgSe4 tetrahedra that share corners with three equivalent Cd(1)Se4 tetrahedra, corners with three equivalent Cd(5)Se4 tetrahedra, and corners with six equivalent Hg(2)Se4 tetrahedra. The Hg(2)-Se(10) bond length is 2.71 Å. All Hg(2)-Se(1) bond lengths are 2.71 Å. There are six inequivalent Cd sites. In the first Cd site, Cd(1) is bonded to one Se(1) and three equivalent Se(6) atoms to form CdSe4 tetrahedra that share corners with three equivalent Hg(2)Se4 tetrahedra, corners with three equivalent Cd(6)Se4 tetrahedra, and corners with six equivalent Cd(1)Se4 tetrahedra. The Cd(1)-Se(1) bond length is 2.69 Å. All Cd(1)-Se(6) bond lengths are 2.70 Å. In the second Cd site, Cd(2,3,7) is bonded to four equivalent Se(2,3,7,8) atoms to form corner-sharing CdSe4 tetrahedra. All Cd(2,3,7)-Se(2,3,7,8) bond lengths are 2.70 Å. In the third Cd site, Cd(4) is bonded to one Se(4) and three equivalent Se(9) atoms to form CdSe4 tetrahedra that share corners with three equivalent Hg(1)Se4 tetrahedra, corners with three equivalent Cd(8)Se4 tetrahedra, and corners with six equivalent Cd(4)Se4 tetrahedra. The Cd(4)-Se(4) bond length is 2.70 Å. All Cd(4)-Se(9) bond lengths are 2.69 Å. In the fourth Cd site, Cd(5) is bonded to one Se(5) and three equivalent Se(10) atoms to form CdSe4 tetrahedra that share corners with three equivalent Hg(1)Se4 tetrahedra, corners with three equivalent Hg(2)Se4 tetrahedra, and corners with six equivalent Cd(5)Se4 tetrahedra. The Cd(5)-Se(5) bond length is 2.69 Å. All Cd(5)-Se(10) bond lengths are 2.69 Å. In the fifth Cd site, Cd(6) is bonded to one Se(6) and three equivalent Se(2,3,7,8) atoms to form corner-sharing CdSe4 tetrahedra. The Cd(6)-Se(6) bond length is 2.70 Å. All Cd(6)-Se(2,3,7,8) bond lengths are 2.70 Å. In the sixth Cd site, Cd(8) is bonded to one Se(2,3,7,8) and three equivalent Se(4) atoms to form corner-sharing CdSe4 tetrahedra. The Cd(8)-Se(2,3,7,8) bond length is 2.70 Å. All Cd(8)-Se(4) bond lengths are 2.70 Å. There are seven inequivalent Se sites. In the first Se site, Se(1) is bonded to three equivalent Hg(2) and one Cd(1) atom to form SeCdHg3 tetrahedra that share corners with three equivalent Se(10)Cd3Hg tetrahedra, corners with three equivalent Se(6)Cd4 tetrahedra, and corners with six equivalent Se(1)CdHg3 tetrahedra. In the second Se site, Se(2,3,7,8) is bonded to one Cd(2,3,7) and three equivalent Cd(6) atoms to form corner-sharing SeCd4 tetrahedra. In the third Se site, Se(4) is bonded to one Cd(4) and three equivalent Cd(8) atoms to form SeCd4 tetrahedra that share corners with three equivalent Se(9)Cd3Hg tetrahedra; corners with three equivalent Se(2,3,7,8)Cd4 tetrahedra; and corners with six equivalent Se(4)Cd4 tetrahedra. In the fourth Se site, Se(5) is bonded to three equivalent Hg(1) and one Cd(5) atom to form SeCdHg3 tetrahedra that share corners with three equivalent Se(10)Cd3Hg tetrahedra, corners with three equivalent Se(9)Cd3Hg tetrahedra, and corners with six equivalent Se(5)CdHg3 tetrahedra. In the fifth Se site, Se(6) is bonded to one Cd(6) and three equivalent Cd(1) atoms to form SeCd4 tetrahedra that share corners with three equivalent Se(2,3,7,8)Cd4 tetrahedra; corners with three equivalent Se(1)CdHg3 tetrahedra; and corners with six equivalent Se(6)Cd4 tetrahedra. In the sixth Se site, Se(9) is bonded to one Hg(1) and three equivalent Cd(4) atoms to form SeCd3Hg tetrahedra that share corners with three equivalent Se(4)Cd4 tetrahedra, corners with three equivalent Se(5)CdHg3 tetrahedra, and corners with six equivalent Se(9)Cd3Hg tetrahedra. In the seventh Se site, Se(10) is bonded to one Hg(2) and three equivalent Cd(5) atoms to form SeCd3Hg tetrahedra that share corners with three equivalent Se(1)CdHg3 tetrahedra, corners with three equivalent Se(5)CdHg3 tetrahedra, and corners with six equivalent Se(10)Cd3Hg tetrahedra.